CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a Continuation-in-Part of U.S. patent application Ser. No. 11/035,799 filed Jan. 14, 2005 entitled Methods and Structures for the Production of Electrically Treated Items and Electrical Connections, which is a Continuation-in-Part of U.S. patent application Ser. No. 10/776,359 filed Feb. 11, 2004 entitled Methods and Structures for the Production of Electrically Treated Items and Electrical Connections. The entire contents of the above identified applications are incorporated herein by this reference.
BACKGROUND OF THE INVENTION
Polymers are often also referred to as plastics or resins. For the present invention, it is understood that polymers include any of the group of synthetic or natural organic materials that may be shaped or applied when soft and then solidified or hardened. Polymers include thermoplastics and three-dimensional curing materials such as epoxies and thermosets. In addition, certain silicon based materials such as silicones can be considered as polymers or resins. Polymers also include any coating, ink, or paint fabricated using a polymer binder or film forming material.
There a numerous applications where it is desired to impart a metallic property to a polymer. One such property is electrical conductivity. Electrical conductivity may allow for the material to function in many processes requiring conductivity such as electroplating, electrostatic coating, current transport, etc. Techniques have been developed to impart electrical conductivity to a polymer. One way is to add a conductive filler to the polymer matrix. An example of such a filler is particulate silver. A second technique is to apply a metal coating to the surface of the polymer.
One way to apply a metal coating to the surface of a polymer is through simple lamination of a metal foil to a polymeric substrate a process which is well known in the art. A well-established application of this approach is the starting laminate structure for manufacture of many printed circuit boards. This approach can be design limited to essentially two-dimensional surfaces. Furthermore, if it is desired to have selective placement of metal on the final article, the metal foil must be selectively etched.
Another way to apply a metal coating to the surface of a polymer is by physically depositing metal onto a plastic substrate. Physical deposition can be achieved by arc spraying or vacuum deposition processes such as sputtering. These processes are well known in the art.
Yet another way to apply a metal coating to the surface of a polymer is through chemical deposition (for example, electroless plating). Chemical deposition is conventionally achieved by a multi-step process which is well know in the art. The plastic substrate is normally first chemically etched to microscopically roughen the surface. This etching promotes adhesion between the plastic substrate and the subsequently deposited metal. Further steps catalyze the plastic surface in preparation for metal deposition by chemical reduction of metal from solution. Nickel and copper are typical metals employed for “electroless plating”.
The “electroless plating” process employed with conventional plating on plastics comprises many steps involving expensive and harsh chemicals. This increases costs dramatically and involves environmental difficulties. The process is also sensitive to processing variables used to fabricate the plastic substrate, limiting the applications to carefully fabricated parts and designs.
The conventional technology for electroless plating has been extensively documented and discussed in the public and commercial literature. See, for example, Saubestre, Transactions of the Institute of Metal Finishing, 1969, Vol. 47., or Arcilesi et al., Products Finishing, March 1984.
There are a number of limitations associated with conventional vacuum deposition and chemical deposition. One is the relatively thin metallic thickness typically achieved with these techniques. Deposition speed, equipment utilization, deposit integrity and chemical cost often restrict deposits to these relatively small thicknesses. Another limitation is the restricted types of metals that can be applied with these processes.
In many cases it is desired to have increased thickness or variety of the metal deposit. In these cases, a particularly advantageous way to apply metal to a surface is electroplating. Electroplating builds metallic thickness relatively quickly and a wide variety of metals can be electroplated in conventional manner. Regarding plastics however, one will recognize that the surface of the plastic substrate must be conductive in order to permit electroplating. Surfaces of plastic articles can be rendered suitably conductive via a processing such as described above.
In many instances the electroplating process is applied to individual articles arrayed on a positioning rack. The rack is rendered cathodic and all of the articles positioned on the rack are electroplated simultaneously. While the rack may be transported in a sequential fashion through multiple steps it can be considered as a discrete array of parts all processed together as a batch. In this process parts are normally individually positioned to form the array of each individual rack. This often entails manual labor and added cost.
It is a common practice to electroplate metal articles in an essentially continuous fashion. Such processing is often accomplished by unrolling the metal substrate from a spool or roll, passing it through the electroplating sequence, then winding the electroplated material onto a takeup roll. This type of process is often referred to as roll-to-roll or reel-to-reel. Articles such as a metal wire or a metal strip are suitable for such continuous electroplating. With such continuous electroplating handling requirements for the metal articles are reduced and thus the processing cost can be reduced. Furthermore, the continuous electroplating allows for careful control of the manufacturing process (metal thickness etc.) which again results in reduced costs as well as consistent output. To achieve similar benefits it would be desirable to electroplate certain plastic forms in a continuous manner. Continuous electroplating could be particularly suitable for articles produced by certain plastic fabrication processes characterized by a continuous or semi-continuous output. These may include extrusion, thermoforming, printing of inks comprising plastic binders, indexed injection molding etc.
There are a number of reasons of concern regarding the electroplating of plastics in a continuous fashion. One of the primary reasons is the complexity and cost associated with conventional electroplating of plastic. The “electroless plating” process employed with conventional plating on plastics comprises many steps involving expensive and harsh chemicals. This increases costs dramatically and involves environmental difficulties. The process is also very sensitive to processing variables used to fabricate the plastic substrate, limiting the applications to carefully fabricated parts and designs. Furthermore, the multiple process steps are often not conducive to a continuous processing environment. For example, transporting a web or film through multiple baths increases problems associated with cross contamination etc. Yet another problem is that the electroless process tends to be relatively slow in nature.
Another approach to achieve continuous electroplating of polymeric film forms is to first form a very thin layer of metal deposited by vacuum processing such as sputtering. This “metallized” film is then subjected to electroplating to build metal thickness and or characteristic. The result is a structure similar to a metal foil/polymer film lamination but with a possibly different (often thinner) metal layer. The capital equipment required for the electroplating can be very expensive. In addition, unless expensive masking is employed, metal would normally cover the entire film surface and further metal removal processing is required to give the often desired selective metal placement.
In a discussion of the electroplating of thin films the current carrying capacity of the initial thin film is often of concern. The current carrying capacity of a thin film is often reported as a surface resistance in ohms per square. This measurement is made by determining the resistance over a unit length of film having a width of the same unit distance. Ohms per square is not an intrinsic material characteristic because it depends on the thickness of the material. However, it does represent a convenient measurement of relative current carrying capacity for thin films.
A common characteristic of sputtered, vacuum metallized or chemically deposited metallic films is that they possess relatively low current carrying ability. This is a result of the typically relatively thin nature of the metallic film. Sputtering, vacuum metallizing, and chemical deposition are characterized by relatively slow rates of metallic thickness buildup. It is often impractical or uneconomic, or physically difficult to expand the thickness of the metallic film in a significant way. Thus, the metallic films prior to electroplating may often be characterized as having low current carrying ability. This intrinsically leads to problems regarding current transport or conveyance and electrical contacting especially during the initial stages of the electrodeposition process.
For example, it is the current inventor's understanding that a typical thickness for a sputtered copper film intended to be electroplated is approximately 0.25 microns. This would result in a surface resistance of approximately 0.1 ohms per square. It is also the current inventor's understanding that typical metal thicknesses for electroless copper layers prior to electroplating are approximately 0.75 microns. This would result in a surface resistance of approximately 0.03 ohms per square.
It is known that electroplating onto sputtered, or chemically deposited metallic films of these typical thicknesses can be difficult for a number of reasons. One reason is that electroplating current conveyance and management can be sensitive and difficult to control. Burning and breach of cathodic contacts is frequently a problem due to convergence of electroplating current into the reduced area of the contact. This requires special techniques which often increase the capital cost and complexity of the electroplating equipment. For example, during initial stages of electroplating on such films, careful control of current densities, agitation etc. are required. It is one of the objects of the current invention to teach processing and structure which reduces the cost and complexity of electroplating onto films characterized as having a low current carrying capacity including those produced by sputtering, vacuum metallizing, and chemical deposition. For purposes of this specification and claims, a structure having a surface resistance greater than 0.01 ohms per square will be considered as a structure having a low current carrying ability.
A number of attempts have been made to simplify the electroplating of plastics. If successful such efforts could result in significant cost reductions for electroplated plastics and could allow facile continuous electroplating of plastics to be practically employed. Some simplification attempts involve special chemical techniques, other than conventional electroless metal deposition, to produce an electrically conductive film on the surface. Typical examples of the approach are taught by U.S. Pat. No. 3,523,875 to Minklei, U.S. Pat. No. 3,682,786 to Brown et al., and U.S. Pat. No. 3,619,382 to Lupinski. The electrically conductive surface film produced was intended to be electroplated. Multiple performance problems thwarted these attempts.
Other approaches contemplate making the plastic surface itself conductive enough to allow it to be electroplated directly thereby avoiding the “electroless plating” or lamination processes. Efforts have been made to advance systems contemplating metal electrodeposition directly onto the surface of polymers made conductive through incorporating conductive fillers. When considering polymers rendered electrically conductive by loading with electrically conductive fillers, it may be important to distinguish between “microscopic resistivity” and “bulk” or macroscopic resistivity”. “Microscopic resistivity” refers to a characteristic of a polymer/filler mix considered at a relatively small linear dimension of for example 1 micrometer or less. “Bulk” or “macroscopic resistivity” refers to a characteristic determined over larger linear dimensions. To illustrate the difference between “microscopic” and “bulk, macroscopic” resistivities, one can consider a polymer loaded with conductive fibers at a fiber loading of 10 weight percent. Such a material might show a low “bulk, macroscopic” resistivity when the measurement is made over a relatively large distance. However, because of fiber separation (holes) such a composite might not exhibit consistent “microscopic” resistivity. When producing an electrically conductive polymer intended to be electroplated, one should consider “microscopic resistivity” in order to achieve uniform, “hole-free” deposit coverage. Thus, it may be advantageous to consider conductive fillers comprising those that are relatively small, but with loadings sufficient to supply the required conductive contacting. Such fillers include metal powders and flake, metal coated mica or spheres, conductive carbon black and the like.
Efforts to produce electrically conductive polymers suitable for direct electroplating have encountered a number of obstacles. The first is the combination of fabrication difficulty and material property deterioration brought about by the heavy filler loadings often required. A second is the high cost of many conductive fillers employed such as silver flake.
Another obstacle involved in the electroplating of electrically conductive polymers is a consideration of adhesion between the electrodeposited metal and polymeric substrate (metal/polymer adhesion). In some cases such as electroforming, where the electrodeposited metal is eventually removed from the substrate, metal/polymer adhesion may actually be detrimental. However, in most cases sufficient adhesion is required to prevent metal/polymer separation during extended environmental and use cycles.
A number of methods to enhance adhesion have been employed. For example, etching of the surface prior to plating can be considered. Etching can often be achieved by immersion in vigorous solutions such as chromic/sulfuric acid. Alternatively, or in addition, an etchable species can be incorporated into the conductive polymeric compound. The etchable species at exposed surfaces is removed by immersion in an etchant prior to electroplating. Oxidizing surface treatments can also be considered to improve metal/plastic adhesion. These include processes such as flame or plasma treatments or immersion in oxidizing acids.
In the case of conductive polymers containing finely divided metal, one can propose achieving direct metal-to-metal adhesion between electrodeposit and filler. However, here the metal particles are generally encapsulated by the resin binder, often resulting in a resin rich “skin”. To overcome this effect, one could propose methods to remove the “skin”, exposing active metal filler to bond to subsequently electrodeposited metal.
Another approach to impart adhesion between conductive resin substrates and electrodeposits is incorporation of an “adhesion promoter” at the surface of the electrically conductive resin substrate. This approach was taught by Chien et al. in U.S. Pat. No. 4,278,510 where maleic anhydride modified propylene polymers were taught as an adhesion promoter. Luch, in U.S. Pat. No. 3,865,699 taught that certain sulfur bearing chemicals could function to improve adhesion of initially electrodeposited Group VIII metals.
An additional major obstacle confronting development of electrically conductive polymeric resin compositions capable of being directly electroplated is the initial “bridge” of electrodeposit on the surface of the electrically conductive resin. In electrodeposition, the substrate to be plated is often made cathodic through a pressure contact to a metal contact tip, itself under cathodic potential. However, if the contact resistance is excessive or the substrate is insufficiently conductive, the electrodeposit current favors the metal contact and the electrodeposit may have difficulty bridging to the substrate. The “bridging” problem extends to substrates having low surface current carrying capacity such as vacuum metallized or electrolessly plated films. In some cases, “burning ” or actual “deplating” of very thin metal deposits can be experienced during the initial moments of “bridge” formation.
Moreover, a further problem is encountered even if specialized racking successfully achieves electrodeposit bridging to the substrate. Many of the electrically conductive polymeric resins have resistivities far higher than those of typical metal substrates. Also in many cases, such as the electroplating of conductive ink patterns or thin metal films, the conductive material may be relatively thin. The initial conductive substrate can be relatively limited in the amount of electrodeposition current which it alone can convey. In these cases the initial conductive substrate may not cover almost instantly with electrodeposit as is typical with thicker metallic substrates. Rather the electrodeposit coverage may result from lateral growth over the surface, with a significant portion of the electrodeposition current, including that associated with the lateral electrodeposit growth, passing through the previously electrodeposited metal. This restricts the size and “growth length” of the substrate conductive pattern, increases plating costs, and can also result in large non-uniformities in electrodeposit integrity and thickness over the pattern.
Rates of this lateral growth likely depend on the ability of the substrate to convey current. Thus, the thickness and resistivity of the initial conductive substrate can be defining factors in the ability to achieve satisfactory electrodeposit coverage rates. When dealing with continuously electroplated patterns, long narrow metal traces are often desired, deposited on relatively thin initial conductive substrates such as printed inks. These factors of course work against achieving the desired result.
This coverage rate problem likely can be characterized by a continuum, being dependent on many factors such as the nature of the initially electrodeposited metal, applied voltage, electroplating bath chemistry, the nature of the polymeric binder and the resistivity of the electrically conductive polymeric substrate. As a “rule of thumb”, the instant inventor estimates that coverage rate problems would demand attention if the resistivity of the conductive polymeric substrate rose above about 0.001 ohm-cm. Alternatively, electrical current carrying capacity of thin films is often reported as a surface resistivity in “ohms per square”. Using this measure, the inventor estimates that coverage rate issues may demand attention should the surface resistivity rise above about 0.01 ohms per square.
Beset with the problems of achieving adhesion and satisfactory electrodeposit coverage rates, investigators have attempted to produce directly electroplateable polymers by heavily loading polymers with relatively small conductive filler particles. Fillers include finely divided metal powders and flake, conductive metal oxides and intrinsically conductive polymers. Heavy loadings may be sufficient to reduce both microscopic and macroscopic resistivity to levels where the coverage rate phenomenon may be manageable. However, attempts to make an acceptable directly electroplateable resin using the relatively small fillers alone encounter a number of barriers. First, the fine conductive fillers can be relatively expensive. The loadings required to achieve the particle-to-particle proximity to achieve acceptable conductivity increases the cost of the polymer/filler blend dramatically. The fine fillers may bring further problems. They tend to cause deterioration of the mechanical properties and processing characteristics of many resins. This significantly limits options in resin selection. All polymer processing is best achieved by formulating resins with processing characteristics specifically tailored to the specific process (injection molding, extrusion, blow molding, printing, etc.). A required heavy loading of filler severely restricts ability to manipulate processing properties in this way. A further problem is that metal fillers can be abrasive to processing machinery and may require specialized screws, barrels, and the like. Finally, despite being electrically conductive, a polymer filled with conductive particles still offers no mechanism to produce adhesion of an electrodeposit since the particles may be essentially encapsulated by the resin binder, often resulting in a non-conductive or non-binding resin-rich “skin”.
For the above reasons, fine conductive particle containing plastics have not been widely used as bulk substrates for directly electroplateable articles. Rather, they have found applications in production of conductive adhesives, pastes, and inks. Recent activity has been reported wherein polymer inks heavily loaded with silver particles have been proposed as a “seed layer” upon which subsequent electrodeposition of metal is achieved. However, high material costs, application complexity, electrodeposit growth rate issues and adhesion remain with these approaches. In addition, it has been reported that these films are typically deposited at a thickness of approximately 3 microns resulting in a surface resistance of approximately 0.15 ohms per square. Such low current carrying capacity films likely would experience the electroplating problems being addressed by the processes and structure of the current invention.
The least expensive (and least conductive) of the readily available conductive fillers for plastics are carbon blacks. Typically the resistivity of a conductive polymer is not reduced below approximately 1 ohm-cm using carbon black alone. Thus in a thin film form at a thickness of 5 microns a surface resistivity would typically be approximately 2,000 ohms per square. Attempts have been made to produce electrically conductive polymers based on carbon black loading intended to be subsequently electroplated. Examples of this approach are the teachings of U.S. Pat. Nos. 4,038,042, 3,865,699, and 4,278,510 to Adelman, Luch, and Chien et al. respectively.
Adelman taught incorporation of conductive carbon black into a polymeric matrix to achieve electrical conductivity required for electroplating. The substrate was pre-etched in chromic/sulfuric acid to achieve adhesion of the subsequently electroplated metal. However, the rates of electrodeposit coverage reported by Adelman may be insufficient for many applications.
Luch in U.S. Pat. No. 3,865,699 and Chien et al. in U.S. Pat. No. 4,278,510 also chose carbon black as a filler to provide an electrically conductive surface for the polymeric compounds to be electroplated. The Luch U.S. Pat. No. 3,865,699 and the Chien U.S. Pat. No. 4,278,510 are hereby incorporated in their entirety by this reference. However, these inventors further taught inclusion of an electrodeposit coverage or growth rate accelerator to overcome the galvanic bridging and lateral electrodeposit growth rate problems described above. An electrodeposit coverage rate accelerator is an additive functioning to increase the electrodeposition coverage rate over and above any affect it may have on the conductivity of an electrically conductive polymer. In the embodiments, examples and teachings of U.S. Pat. Nos. 3,865,699 and 4,278,510, it was shown that certain sulfur bearing materials, including elemental sulfur, can function as electrodeposit coverage or growth rate accelerators to overcome those problems associated with electrically conductive polymeric substrates having relatively high resistivity.
In addition to elemental sulfur, sulfur in the form of sulfur donors such as sulfur chloride, 2-mercapto-benzothiazole, N-cyclohexyle-2-benzothiaozole sulfonomide, dibutyl xanthogen disulfide, and tetramethyl thiuram disulfide or combinations of these and sulfur were identified. Those skilled in the art will recognize that these sulfur donors are the materials which have been used or have been proposed for use as vulcanizing agents or accelerators. Since the polymer-based compositions taught by Luch and Chien et al. could be electroplated directly they could be accurately defined as directly electroplateable resins (DER). These DER materials can be generally described as electrically conductive polymers characterized by having an electrically conductive surface with the inclusion of an electrodeposit coverage rate accelerator. In the following, the acronym “DER” will be used to designate a directly electroplateable resin as defined in this specification.
Specifically for the present invention, directly electroplateable resins, (DER), are characterized by the following features.
- (a) presence of an electrically conductive polymer characterized by having an electrically conductive surface;
- (b) presence of an electrodeposit coverage rate accelerator;
- (c) presence of the electrically conductive polymer characterized by having an electrically conductive surface and the electrodeposit coverage rate accelerator in the directly electroplateable composition in cooperative amounts required to achieve direct coverage of the composition with an electrodeposited metal or metal-based alloy.
In his patents, Luch specifically identified elastomers such as natural rubber, polychloroprene, butyl rubber, chlorinated butyl rubber, polybutadiene rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber etc. as suitable for the matrix polymer of a directly electroplateable resin. Other polymers identified by Luch as useful included polyvinyls, polyolefins, polystyrenes, polyamides, polyesters and polyurethanes.
In his patents, Luch identified carbon black as a means to render a polymer and its surface electrically conductive. As is known in the art, other conductive fillers can be used to impart conductivity to a polymer. These include metallic flakes or powders such as those comprising nickel or silver. Other fillers such as metal coated minerals and certain metal oxides may also suffice. Furthermore, one might expect that compositions comprising intrinsically conductive polymers may be suitable.
Regarding electrodeposit coverage rate accelerators, both Luch and Chien et al. in the above discussed U.S. patents demonstrated that sulfur and other sulfur bearing materials such as sulfur donors and accelerators served this purpose when using an initial Group VIII “strike” layer. One might expect that other elements of Group 6A nonmetals, such as oxygen, selenium and tellurium, could function in a way similar to sulfur. In addition, other combinations of electrodeposited metals and nonmetal coverage rate accelerators may be identified. Finally, the electrodeposit coverage rate accelerator may not necessarily be a discrete material entity. For example, the coverage rate accelerator may consist of a functional species appended to the polymeric binder chain or a species adsorbed onto the surface of the conductive filler. It is important to recognize that such an electrodeposit coverage rate accelerator can be extremely important in order to achieve direct electrodeposition in a practical way onto polymeric substrates having low conductivity or very thin electrically conductive polymeric substrates having restricted current carrying ability.
Despite the multiple attempts identified above to dramatically simplify the plastics plating process, the current inventor is not aware of any such attempt having achieved recognizable commercial success.
In order to eliminate ambiguity in terminology, for the present invention the following definitions are supplied:
“Metal-based” refers to a material or structure having at least one metallic property and comprising one or more components at least one of which is a metal or metal-containing alloy.
“Alloy” refers to a substance composed of two or more intimately mixed materials.
“Group VIII metal-based” refers to a substance containing by weight 50% to 100% metal from Group VIII of the Periodic Table of Elements.
“Electroplateable material” refers to a material that exhibits a surface that can be exposed to an electroplating process to cause the surface to cover with electrodeposited material.
OBJECTS OF THE INVENTION
An object of the invention is to provide novel methods of facile continuous manufacture of electrochemically or electrophysically treated items.
A further object of the invention is to expand permissible options for the continuous production of electroplated items.
A further object of the invention is to expand options for the electrochemical or electrophysical treatment of objects in a continuous fashion.
A further object of the invention is to teach novel and facile methods for achieving electrical connections via electrodeposition.
A further object of the invention is to teach processing and structure which reduces the cost and complexity of electroplating onto films characterized as having a low current carrying capacity.
SUMMARY OF THE INVENTION
The current invention involves production of electrochemically or electrophysically treated objects. In many cases the production can be characterized as continuous. In many embodiments the electrochemical treatments comprise electrodeposition. In many embodiments the electrodeposition involves electroplating onto substrates whose initial current carrying capacity is relatively limited. In many embodiments the production involves the electroplating of electrically conductive polymers. In many embodiments the electrically conductive polymer comprises a directly electroplateable resin.
BRIEF DESCRIPTION OF THE DRAWINGS
The various factors and details of the structures and manufacturing methods of the present invention are hereinafter more fully set forth with reference to the accompanying drawings wherein:
FIG. 1 is a top plan view of an object used to understand the continuous processing nature of the disclosed invention.
FIG. 2 is a perspective view of a processing tank useful in describing the continuous processing of the invention.
FIG. 3 is a top plan view of an object processed according to the teachings of the current invention.
FIG. 4 is a sectional view taken substantially from the perspective of lines 4-4 of FIG. 3.
FIG. 5 is a view similar to FIG. 4 following an additional processing step according to the invention.
FIG. 6 is top plan view of an embodiment according to the current invention.
FIG. 7 is a sectional view taken substantially from the perspective of lines 7-7 of FIG. 6.
FIG. 8 is a sectional view taken substantially from the perspective of lines 8-8 of FIG. 6.
FIG. 9 is a view similar to FIG. 7 following the step of exposing the FIG. 7 structure to an electroplating process.
FIG. 10 is a view similar to FIG. 8 following the step of exposing the FIG. 8 structure to an electroplating process.
FIG. 11 is a sectional view of the FIG. 9 structure taken substantially from the perspective of lines 11-11 of FIG. 9.
FIG. 12 depicts one form of process by which the electroplating of FIGS. 9 through 11 is achieved in a continuous fashion.
FIG. 13 is a top plan view depicting an additional optional processing step for the article produced in the FIG. 12 process.
FIG. 14 is a schematic drawing of one form of electroplating process according to the invention.
FIG. 15 is a top plan view of an embodiment according to the current invention.
FIG. 16 is a top plan view showing the embodiment of FIG. 15 undergoing a processing step according to the current invention.
FIG. 17 is a schematic depiction of an electroplating process according to the invention.
FIG. 18 is a top plan view of an embodiment according to the current invention.
FIG. 19 is a top plan view showing the embodiment of FIG. 18 undergoing a processing step according to the current invention.
FIG. 20 is a schematic view of another electroplating process according to the current invention.
FIG. 21 is a sectional view taken substantially from the perspective of lines 21-21 of FIG. 20.
FIG. 22 is a top plan view taken substantially from the perspective of lines 22-22 of FIG. 21.
FIG. 23 is a sectional view taken substantially from the perspective of lines 23-23 of FIG. 20.
FIG. 24 is a top plan view taken substantially from the perspective of lines 24-24 of FIG. 23.
FIG. 25 is a sectional view taken substantially from the perspective of lines 25-25 of FIG. 20.
FIG. 26 is a top plan view taken substantially from the perspective of lines 26-26 of FIG. 25.
FIG. 27 is a schematic view of another electroplating process according to the current invention.
FIG. 28 is a sectional view taken substantially from the perspective of lines 28-28 of FIG. 27.
FIG. 29 is a top plan view taken substantially from the perspective of lines 29-29 of FIG. 28.
FIG. 30 is a sectional view taken substantially from the perspective of lines 30-30 of FIG. 27.
FIG. 31 is a top plan view taken substantially from the perspective of lines 31-31 of FIG. 30.
FIG. 32 is a sectional view taken substantially from the perspective of lines 32-32 of FIG. 27.
FIG. 33 is a top plan view taken substantially from the perspective of lines 33-33 of FIG. 32.
FIG. 34 a sectional view taken substantially from the perspective of lines 34-34 of FIG. 27.
FIG. 35 a top plan view taken substantially from the perspective of lines 35-35 of FIG. 34.
FIG. 36 is a top plan view of an embodiment according to the current invention.
FIG. 37 is a bottom plan view of the FIG. 36 embodiment.
FIG. 38 is a schematic depiction of another electroplating process useful in the current invention.
FIG. 39 is a schematic depiction of another electroplating process useful in the current invention.
FIG. 40 is a schematic end view of a component used in the process of FIG. 39.
FIG. 41 is a schematic side view of a component used in the process of FIG. 39.
FIG. 42 is a top plan view of an article useful in the current invention.
FIG. 43 is a sectional view taken substantially from the perspective of lines 43-43 of FIG. 42.
FIG. 44 is a top plan view of a structural arrangement utilizing the article embodied in FIG. 42.
FIG. 45 is a sectional view taken substantially from the perspective of lines 45-45 of FIG. 44.
FIG. 46 is a sectional view taken substantially from the perspective of lines 46-46 of FIG. 47.
FIG. 47 is a top plan view similar to that of FIG. 44 following an additional processing step.
FIG. 48 is a sectional view similar to that of FIG. 46 following an additional processing step.
FIG. 49 is a sectional view illustrating a potential failure mode for the article embodied in FIG. 48.
FIG. 50 is a sectional view similar to FIG. 46 suggesting structure to avoid the failure depicted in FIG. 49.
FIG. 51 is a top plan view similar to FIG. 42 but showing a modification to the embodiment of FIG. 42.
FIG. 52 is a top plan view similar to FIG. 42 but showing a modification to the embodiment of FIG. 42.
FIG. 53 is a top plan view similar to FIG. 42 but showing a modification to the embodiment of FIG. 42.
FIG. 54 is a top plan view similar to FIG. 47 but utilizing the article embodied in FIG. 52.
DESCRIPTION OF PREFERRED EMBODIMENTS
Many applications of the current invention will employ a generally planar or sheet-like structure having thickness much smaller than its length or width. This sheet-like structure may also have a length far greater than its width, in which case it is commonly referred to as a “web”. Because of its extensive length, a web can be conveyed through one or more processing steps in a way that can be described as “continuous”. “Continuous” web processing is well known in the paper and packaging industries. It is often accomplished by supplying web material from a feed roll to the process steps and retrieving the web onto a takeup roll following processing (roll-to-roll or reel-to-reel processing).
Web processing of metal forms is known in the electrochemical art. For example, “continuous” anodizing or electroplating of metal sheet or strip is practiced. In these cases the metal dimensions are as described above characterizing a “web”. Use of web processing for electrochemical processing polymeric materials is more difficult, at least in part because of the insulating characteristics of most polymers. Nevertheless, the instant inventor has recognized that web processing can be practiced with many advantages in the electrochemical or electrophysical processing of polymers.
A first advantage is that an insulating web can serve as a permanent or temporary positioning or support structure for articles intended for electrochemical processing. Electrochemical processes are normally immersion processes. Electrochemical baths are often heavily agitated. Many forms would not be self-supporting in such an environment. Forms of thin metal foil or conductive polymer ink patterns are examples. Conductive inks or paints such as particulate metal filled inks or paints can be considered for electrochemical treatment when supported on a web. Another advantage is many electrochemical and electrophysical processes may require certain positioning or placement among the items to be treated. Size or structural constraints might prevent certain items from being adequately positioned using a classic batch electrical processing rack. Positioning of such items onto a conveyance web could facilitate such processing and reduce labor burden in racking.
Another advantage of web processing using polymeric based webs is that the web can remain as a permanent support for the treated items or can be removed, in which latter case it would serve as a temporary or surrogate support during processing. As a permanent support, the web may serve as a base for packaging material options such as pressure sensitive or hot melt adhesive layers, overlaminates, printing, etc.
Another advantage of web processing is that often it can be accomplished in an essentially continuous operation thereby achieving the advantages of continuous processing.
Another advantage of web processing is that the web can comprise many different materials, surface characteristics and forms. For example, the web can constitute a nonporous film or may be a fabric. Relatively inexpensive substrates such as coated paper can be employed when such laminate materials can tolerate exposure to the electrochemical process. Combinations of such differences over the expansive surface of the web can be achieved. Indeed, as will be shown, the web itself can comprise materials such as conductive polymers or even metal fibers which will allow the web itself to undergo electrochemical processing.
Because the surface area of web being processed at any one time in an individual electrochemical operation can be relatively expansive and moving, it may be inconvenient to bring an electrical characteristic such as current or voltage to a myriad of different points simultaneously using discrete individual contacts. Thus another characteristic of web processing is that it allows the desired electrical characteristic (current, voltage, etc.) to be conveyed to a large number of points over an expansive surface using simplified buss structures, as will become clear in the discussion of embodiments to follow. Because the items being electrochemically treated may have complex structure, it may be difficult to specify a direction of electrical flow at any one point on the surface of an item being treated. However, often web processing will be characterized as having a conductive path, or buss, intended to convey the electrical characteristic (current, voltage etc.) between a source of electrical characteristic contacting the conductive path and a remote structure intended to be exposed to the electrical process. For example, a buss used for electroplating is a conductive path extending from a source of electrical potential to a point proximal or contacting a surface intended to be electroplated. The buss often extends in a direction parallel to the length direction of the web (sometimes referred to as “machine direction”). However, this is not necessarily the case. A buss is intended to convey the appropriate electrical characteristic and may extend in a direction angular to the “machine direction”. A buss can constitute a portion of the final electrotreated article or can be separate, in which case it may be removed following electrotreatment. A buss may comprise structure in the form of extending arms or fingers to electrically connect remote points to a main buss artery. In typical practice a buss may supply electrical communication between one or more items or structures and the source of the electrical characteristic. Thus in many cases the buss may electrically connect multiple structures undergoing treatment. However, this is not necessarily the case. As will be seen, buss structural concepts can be used to effectively promote treatment of the entire web itself or to form a convenient surface to facilitate a sliding contact.
In many cases it is desirable to have a buss exhibiting relatively high current carrying capacity. This allows the buss to transport necessary current without experiencing significant variations in voltage. This consideration leads one in the direction of using very conductive materials such as copper of a form having adequate cross section perpendicular to current flow. However, maintaining positioning and contact of such forms with structure to be electroplated can be complicated and expensive.
As will be taught herein, in many cases it would be advantageous to form portions of a buss structure from electrically conductive resins positioned on the web prior to electrochemical processing. This takes advantage of the ease of application, adhesive characteristics, and flexibility of conductive resins. In these cases a subsequent electrodeposition of metal over the surface of the initial buss structure may augment the current carrying ability of the buss structure. However, in many situations the buss would be severed and discarded following the electroplating and therefore the cost of the electrically conductive polymer used to define the buss structure can be a significant factor. The electrically conductive polymeric materials chosen to define the buss structure may need to be inexpensive and thin, factors which may lead to reductions in initial current carrying capacity of the buss structure.
The following specification discussion, taken along with the descriptive figures, will reveal and teach structural, process, and material improvements related to the continuous electroplating of material forms having limited current carrying ability prior to electroplating. In many cases the eminently suitable characteristics of electrically conductive polymers in the production of continuously electroplated articles will become clear. In many embodiments, an electrically conductive polymer formulated as a directly electroplateable resin (DER) is particularly suitable.
As pointed out above in this specification, attempts to dramatically simplify the process of electroplating on plastics have met with commercial difficulties. Nevertheless, the current inventor has persisted in personal efforts to overcome certain performance deficiencies associated with electroplating onto material structures having low current carrying ability, conductive plastics and DER's. Along with these efforts has come a recognition of unique and eminently suitable applications for electrically conductive polymers and often more specifically the DER technology for continuous electroplating. Some examples of these unique applications for continuously electroplated items include electrical circuits, electrical traces, circuit boards, antennas, capacitors, induction heaters, connectors, switches, resistors, inductors, batteries, fuel cells, coils, signal lines, power lines, radiation reflectors, coolers, diodes, transistors, piezoelectric elements, photovoltaic cells, emi shields, biosensors and sensors.
Regarding the DER technology, a first recognition is that the “microscopic” material resistivity generally is not reduced below about 1 ohm-cm. by using conductive carbon black alone. This is several orders of magnitude larger than typical metal resistivities. Other well known finely divided conductive fillers (such as metal flake or powder, metal coated minerals, graphite, or other forms of conductive carbon) can be considered in DER applications requiring lower “microscopic” resistivity. In these cases the more highly conductive fillers can be considered to augment or even replace the conductive carbon black.
Moreover, the “bulk, macroscopic” resistivity of conductive carbon black filled polymers can be further reduced by augmenting the carbon black filler with additional highly conductive, high aspect ratio fillers such as metal containing fibers. This can be an important consideration in the success of certain applications such as achieving higher current carrying capacity for a buss. Furthermore, one should realize that incorporation of non-conductive fillers may increase the “bulk, macroscopic” resistivity of conductive polymers loaded with finely divided conductive fillers without significantly altering the “microscopic resistivity” of the conductive polymer. This is an important recognition regarding DER's in that electrodeposit coverage speed depends on the presence of an electrodeposit coverage rate accelerator and on the “microscopic resistivity” and less so on the “macroscopic resistivity” of the DER formulation. Thus, large additional loadings of functional non-conductive fillers can be tolerated in DER formulations without undue sacrifice in electrodeposit coverage rates or adhesion. These additional non-conductive loadings do not greatly affect the “microscopic resistivity” associated with the polymer/conductive filler/electrodeposit coverage rate accelerator “matrix” since the non-conductive filler is essentially encapsulated by “matrix” material. Conventional “electroless” plating technology does not permit this compositional flexibility.
Yet another recognition regarding the DER technology is its ability to employ polymer resins and formulations generally chosen in recognition of the fabrication process envisioned and the intended end use requirements. Thus DER's can be produced in material forms that are often suitable for continuous electroplating. In order to provide clarity, examples of some such fabrication processes are presented immediately below in subparagraphs 1 through 6.
- (1) Should it be desired to electroplate an ink, paint, coating, or paste which may be printed or formed on a substrate, a good film forming polymer, for example a soluble resin such as an elastomer, can be chosen to fabricate a DER ink (paint, coating, paste etc.). The DER ink composition can be tailored for a specific process such flexographic printing, rotary silk screening, gravure printing, flow coating, spraying etc. Furthermore, additives can be employed to improve the adhesion of the DER ink to various substrates. One example would be tackifiers.
- (2) Should it be desired to electroplate a fabric, a DER ink can be used to coat all or a portion of the fabric intended to be electroplated. Furthermore, since DER's can be fabricated out of the thermoplastic materials commonly used to create fabrics, the fabric itself could completely or partially comprise a DER. This would eliminate the need to coat the fabric.
- (3) Should one desire to electroplate a thermoformed article or structure, DER's would represent an eminently suitable material choice. DER's can be easily formulated using olefinic materials which are often a preferred material for the thermoforming process. Furthermore, DER's can be easily and inexpensively extruded into the sheet like structure necessary for the thermoforming process.
- (4) Should one desire to electroplate an extruded article or structure, for example a sheet or film, DER's can be formulated to possess the necessary melt strength advantageous for the extrusion process.
- (5) Should one desire to injection mold an article or structure having thin walls, broad surface areas etc. a DER composition comprising a high flow polymer can be chosen.
- (6) Should one desire to vary adhesion between an electrodeposited DER structure supported by a substrate the DER material can be formulated to supply the required adhesive characteristics to the substrate. For example, the polymer chosen to fabricate a DER ink can be chosen to cooperate with an “ink adhesion promoting” surface treatment such as a material primer or corona treatment. In this regard, it has been observed that it may be advantageous to limit such adhesion promoting treatments to a single side of the substrate. Treatment of both sides of the substrate in a roll to roll process may adversely affect the surface of the DER material and may lead to deterioration in plateability. For example, it has been observed that primers on both sides of a roll of PET film have adversely affected plateability of DER inks printed on the PET. It is believed that this is due to primer being transferred to the surface of the DER ink when the PET is rolled up.
All polymer fabrication processes require specific resin processing characteristics for success. The ability to “custom formulate” DER's to comply with these changing processing and end use requirements while still allowing facile, quality electroplating is a significant factor in the continuous electroplating teachings of the current invention. Conventional plastic electroplating technology does not permit great flexibility to “custom formulate”.
Another important recognition regarding the suitability of DER's for continuous electroplating is the simplicity of the electroplating process. Unlike many conventional electroplated plastics, DER's do not require a significant number of process steps during the manufacturing process. This allows for simplified manufacturing and improved process control. It also reduces the risk of cross contamination such as solution dragout from one process bath being transported to another process bath. The simplified manufacturing process will also result in reduced manufacturing costs.
Yet another recognition of the benefit of DER's for continuous electroplating is the ability they offer to selectively electroplate an article or structure. As will be shown in later embodiments, it is often desired to continuously electroplate a polymer or polymer-based structure in a selective manner. DER's are eminently suitable for such continuous yet selective electroplating.
Yet another recognition of the benefit of DER's for continuous electroplating is their ability to withstand the pre-treatments often required to prepare other materials for plating. For example, were a DER to be combined with a metal, the DER material would be resistant to many of the pre-treatments such as cleaning which may be necessary to electroplate the metal.
Yet another recognition of the benefit of DER's for continuous electroplating is that the desired plated structure often requires the plating of long and/or broad surface areas. As discussed previously, the coverage rate accelerators included in DER formulations allow for such extended surfaces to be covered in a relatively rapid manner thus allowing one to consider the use of continuous electroplating of conductive polymers.
These and other attributes of DER's in the production of continuously and sequentially electroplated articles will become clear through the following remaining specification, accompanying figures and claims.
Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. In some of the drawings, like reference numerals designate identical or corresponding parts throughout several embodiments and an additional letter designation is characteristic of a particular embodiment.
Referring to FIG. 1, there is shown in top plan view an article useful in teaching the current invention. Article 10 shown in FIG. 1 has a width W-1 and a length L-1. Article 10 is intended to be exposed to an electroplating process. It will be noted that many of the embodiments of the current invention will be described in conjunction with the electroplating or electrodeposition process. However, one skilled in the art will readily realize that many of the teachings apply to additional electrochemical or electrophysical processing such as anodizing, electroetching, electrocleaning, electrostatic spraying etc. and that the scope of the invention may cover such additional processing despite the embodiments being specifically described in conjunction with electroplating or electrodeposition. Furthermore, electrodeposition can envision depositing a wide variety of materials. These can vary from conductive (such as a metal) to semi-conductive to even non-conductive (such as an electrodeposited paint coating). In the embodiments of this specification electrodeposition will normally refer to a process of depositing a conductive material. Of course one skilled in the art will readily recognize the suitability of any particular embodiment regarding deposition of other materials.
Article 10 has a surface 11 at least a portion of which is to be exposed to an electrochemical process such as electroplating. It may be desirable for example, to coat the entire Article 10 surface 11 with an electrodeposit. Alternatively, Article 10 could constitute a supporting substrate for a surface pattern intended to be electroplated. For the teachings of this invention, an article may be described as having structural characteristics such as planar, film, web-like, sheet-like, etc.
FIG. 2 is a perspective view of an electrochemical bath such as an electroplating bath generally designated by numeral 12. Bath 12 has sidewalls 13 and bottom 15. Bath 12 also has width W-2, length L-2, and height H-2. As may often be the case for convenience, practicality, performance or simple dimensional constraints, the entirety of Article 10 can't be exposed to the electroplating process represented in bath 12 simultaneously. In such cases, simultaneous plating of all portions of Article 10 intended to be plated is prevented. Thus, Article 10 must be electroplated in a sequential or continuous manner whereby at any one time a first portion of Article 10 will be exposed to the plating process, while a second portion remains unexposed to the plating process.
For purposes of this instant specification and claims, continuous or sequential electroplating will be construed as a process wherein at least a first portion of an article is exposed to an electroplating process while at least a second portion of the article remains unexposed to that electroplating process. In order to provide clarity, examples of processing which can be considered within the scope of the definition of continuous or sequential electroplating are presented immediately below in subparagraphs 1 through 3.
- (1) Classic roll-to-roll (sometimes referred to as reel-to-reel) electroplating of metal wire or strip. Here, a first portion of the article, now plated, is exiting the bath while a second portion of the article is being plated while yet a third unplated portion of the article is entering the plating process.
- (2) A roll-to-roll web process wherein an article is continuously processed by passing the article such as a film or web sequentially or continuously through a plating bath.
- (3) A process wherein either the entirety or a portion of the article can be immersed in the plating bath but the article is exposed to or removed from the electroplating process gradually, continuously, or sequentially during the plating cycle. Such a process might be envisioned for example in a case where a gradient of electrodeposit thickness is desired over a distance. Alternatively, in the case of a DER where there is an identifiable growth rate of initial electrodeposit over the surface, such sequential removal could be used to promote uniformity of deposit thickness over an expansive surface.
Referring now to FIG. 3, there is shown a top plan view of an article generally designated by numeral 14, having length L-3 and width W-3. In many cases, length L-3 would be considerably greater than width W-3. In addition, length L-3 is often considerably greater than a maximum dimension of an electroplating bath through which it is intended to be processed.
Referring now to FIG. 4, article 14 is shown to have thickness Z-3. Z-3 is often much smaller than either W-3 or L-3 such that article 14 can generally be characterized as a web or film. Such a web or film can be produced by many processes as is know in the art. Examples may include blown film or roll casting techniques, fabric processing techniques and extrusion. It is seen in FIG. 4 that in this embodiment article 14 comprises a laminate of layers 17 and 19. At least a portion of the surface of layer 19 is receptive to electrochemical processing. One such process would be electroplating wherein material may comprise a DER or a thin metal film. Layer 17 shown can be for example an insulating support layer chosen for any number of functional reasons. One will realize that layer 17 may be omitted depending on the desired result of the subsequent electrochemical process.
The embodiment of FIG. 5 shows the FIG. 4 sectional structure following the process step of exposing the FIG. 4 sectional structure to an electroplating process. In FIG. 5, electrodeposit 20 covers the electroplateable surface of material 19. In this and in other embodiments of the present invention the electrodeposit is understood to be either a single layer or multiple layers of material as is understood in the electroplating art. In most embodiments the electrodeposit will be metal-based and conductive. Various combinations of materials may be considered. For example, in certain applications it may be advantageous to employ metals which exhibit reduced internal stress, in which case sulfamate nickel may be appropriate. It is also the case that in certain applications iron may be a preferred choice of metal. Iron is relatively inexpensive and non-toxic. Furthermore, iron may provide benefits related to recycling due to the possibility of magnetic separation. In other cases electrodeposit 20 may comprise copper, taking advantage of copper's relatively high conductivity. In the FIG. 5 embodiment and in following embodiments of this specification numeral 20 will be referred to as an electrodeposit. However, it will also be understood that numeral 20 may designate material comprising one or more layers and may include layers such as an anodized layer, electrostatically coated layer, chemical conversion layer, etc.
In FIG. 5, layer 17 is composed of insulating material so that bottom surface 21 is not coated with electrodeposit. Should it be desired to coat all surfaces of an article such as article 14 with electrodeposit one will understand that insulating layer 17 could be eliminated or replaced with another material capable of being plated, or layer 17 could be sandwiched between top and bottom layers of electroplateable material.
In some cases, it may be desirable to electrodeposit material in a way to achieve thru web conductivity of the final article. Such was described in application Ser. No. 11/305,799 herein incorporated in its entirety by reference.
Another specific embodiment of a film or web structure according to the invention is identified generally by the article designated by numeral 22 of FIG. 6. FIG. 6 is a top plan view of article 22. Further clarification of the structural aspects of article 22 can be seen by reference to FIG. 7, a sectional view taken substantially from the perspective of lines 7-7 of FIG. 6 and FIG. 8, a sectional view taken substantially from the perspective of lines 8-8 of FIG. 6. Article 22 is characterized by having length L-6 and width W-6. It is contemplated that length L-6 is greater than width W-6 such that article 22 can be processed in an essentially continuous fashion such as the electroplating processes shown in FIGS. 14, 17, 20, 38, and 39 to be presented and taught later in this specification. Article 22 comprises insulating web substrate 24 upon which structural patterns 26 have been selectively positioned. Insulating substrate 24 serves as a support web for the structural patterns 26. Selective structural patterns 26 may comprise any number of electroplateable materials. For example, patterns of electroplateable objects formed of thin chemically or physically deposited metal, electroplateable polymeric materials such as electrically conductive polymers and DER's can be considered.
As one of normal skill in the art will understand, in order for the patterns 26 to be electroplated, there has to be electrical communication between structural patterns 26 and a source of cathodic potential or contact. In the FIG. 6 embodiment, electrical buss structure 27 serves to provide electrical communication between the structural patterns 26 and the source of cathodic potential or contact. Electrical buss structure 27 includes buss artery 28 extending along the length of article 22 and fingers 30 joining artery 28 with structural patterns 26. Buss structure 27 may comprise electroplateable material. However, it may also comprise any material capable of transporting the necessary current to allow for electroplating, such as a coated metal wire or strip. FIG. 7 shows article 22 has a thickness Z-6. In many cases, thickness Z-6 is considerably smaller than width W-6 or length L-6 so that Article 22 can be characterized as being generally planar or sheet-like in structure. It is seen in FIGS. 6 and 7 that the sectional view in FIG. 7 is taken through structural patterns 26, finger 30 and buss artery 28. In the FIG. 7 embodiment, structural patterns 26, fingers 30, and buss artery 28 are all formed from the same electroplateable material and are thus shown as continuous in section. This is not necessarily the case. Materials used for structural patterns 26, buss artery 28, and fingers 30 do not necessarily need to be the same. Also structural patterns 26, buss artery 28, and fingers 30 can be formed at different times and by different processing. Furthermore, 26, 28 and 30 are shown to have simple rectangular cross sections. This presentation is appropriate to simplify the teachings of the present invention. However, one will recognize that more complex structure can be used. The purpose and use of these buss structures will be discussed further in subsequent embodiments of electroplating processes.
FIG. 9 is a view similar to FIG. 7 following the step of exposing the FIG. 7 structure to an electroplating process. Electrodeposit 20 a now coats the originally exposed surfaces of the electroplateable materials supported by insulating substrate 24. In the FIG. 9 embodiment electrodeposit 20 a can include multiple layers.
FIG. 10 is a view similar to FIG. 8 following the step of exposing the FIG. 8 structure to an electroplating process. As with FIG. 9, FIG. 10 shows electrodeposit 20 a coating the originally exposed surface of electroplateable materials supported by insulating substrate 24.
FIG. 11 is a sectional view of the FIG. 9 structure taken from the perspective of lines 11-11 of FIG. 9.
FIG. 12 depicts one form of process by which the electroplating of FIGS. 9 through 11 is achieved in a continuous fashion. FIG. 12 depicts a roll-to-roll process. Substrate structure as depicted in FIGS. 7 and 8 is unwound from feed roll 33 and travels in the direction of arrow 34 to electroplating process 36. Upon exiting electroplating process 36, the structure has now been transformed to that as indicated in FIGS. 9 through 11. FIG. 11 is of course a magnified view of this exit structure. The exit structure is then rewound onto takeup roll 38. Suitable electroplating processes 36 will be taught later in this specification.
FIG. 13 indicates an optional step in the continuous processing of the web following the electroplating process 36. It is shown in FIG. 13 that buss artery 28 and optionally a portion or all of fingers 30 are removed by slitting along length L-6 leaving individual selectively electroplated structural patterns 26 on the remainder of insulating support 24. Since materials forming buss structure 27 (artery 28 and fingers 30) may often be discarded it may be desirable that they comprise materials and amounts that are relatively inexpensive.
FIG. 14 is an embodiment of one form of electroplating bath and process as identified 36 in FIG. 12 useful in the current invention. In this embodiment of an electrochemical process according to the invention, a web of structure similar to that embodied in FIGS. 6 through 8 will be used for illustrative purposes. Thus article 22 a comprises a series of repetitive structures joined through buss fingers 30 a to connecting buss artery 28 a. It should be recognized that the processing concepts and teachings extend to other structures as well, such as that embodied in FIGS. 3 through 5. In FIG. 14 it is seen that article 22 a having a film or web like structure is transported through an electroplating process generally designated as 36 a in the direction as indicated by arrows 34 a. Article 22 a enters electroplating process 36 a at entry point 50 and exits at exit point 52. Rollers 54 serve to transport the web through electroplating process 36 a as shown. Electroplating process 36 a utilizes anodes 56 as indicated by the positive polarity shown. Cathodic contact in this embodiment is made at two points. The first cathodic contact 58 is immersed under the level of the electroplating solution 60. The second cathodic contact 62 is positioned on article 22 a following its exit from the electroplating bath. One will appreciate that multiple contacts 58 and 62 may be used to advantage especially in light of the “sliding” or moveable nature of these contacts and the current transport requirements of electroplating process 36 a as discussed more fully below.
In FIG. 14 contact 62 if used alone (absent contact 58) may prove incapable of adequately transporting the necessary electroplating current associated with electroplating process 36 a. Contact 62 may be separated by a relatively extended distance from areas of active electrodeposition. Thus excessive resistive heating losses may occur during the transport of electroplating current from contact 62 thereby disrupting the integrity and effectiveness of the contact. In addition a detrimental voltage difference over the electroplating surface may result. The extent of this problem will depend on a number of factors including line speed, the surface being actively electroplated, and linear distance from the contact to the electrodeposit growth surface.
Thus in the FIG. 14 process an additional contact 58 immersed under the level of the plating solution may prove very beneficial. The function of contact 58 is to convey current associated with the electrodeposition of article 22 a. Since contact 58 is immersed in the plating solution, it may be easier to maintain temperature control and the integrity of the contact. It will be understood that contact 58 can be used alone or in conjunction with contact 62.
Considering now the processing of article 22 a through electroplating process 36 a of FIG. 14, it will be appreciated that cathodic electroplating current may be required to traverse a considerable distance in the length direction L-6 from contact such as identified by 58 or 62. Should the conductive material originally defining buss structure 27 (buss artery 28 a and fingers 30 a ) of article 22 a (i.e. prior to the electroplating process) be highly conductive such as a relatively thick metal or metal-based material, this distance of current transport may not be significant. In this case the resistance to current transport may be slight, perhaps to the point where the potential is essentially constant throughout the length of buss artery 28 a actively transporting current. However, should the conductive material originally defining buss artery 28 a be less conductive than typical metals, or be very thin, the buss may be characterized as having low current carrying capability prior to electroplating. This situation can occur should the materials used to define buss artery 28 a be of higher conductivity but of reduced cross sectional area perpendicular to the current flow, or alternatively if the materials forming initial buss artery 28 a are chosen from relatively resistive materials. Absent sufficient metal electrodeposit, the original unplated buss may not be capable by itself of adequately conveying electroplating current without unacceptably large potential differences along length L-6. In this case the conductive electrodeposited metal may be required to convey much, if not most, of the cathodic electroplating current along buss artery 28 a to contacts 58 and 62. In this case, a distinct “growth front” of electrodeposited metal may be established on the original buss 28 a upstream (opposite direction of web travel) of the initial cathodic source in contact with the electroplated metal coating the buss. This “growth front” progresses laterally over the surface of the buss in a direction away from the initial cathodic source/electroplated buss contact.
Thus, when electroplating a continuous “buss” defined by material or structure of low current carrying capacity (such as many DER formulations or thin conductive buss traces) cathodic contact is often best achieved by contacting to previously electrodeposited metal. In this way the conductive electrodeposited metal increases in thickness and robustness during the travel time between the initial metal deposit and the initial cathodic contact, and reliable ohmic contact is achieved between the cathodic contact and metal electrodeposit.
The ability for the conductive electrodeposit to effectively convey the required cathodic electroplating current depends on its cross sectional area as well as the conductivity of the electrodeposited metal employed. The conductive electrodeposit thickness at any particular point in the FIG. 14 process depends on at least current density, efficiency and elapsed time under electroplating. Thus in a process such as depicted in FIG. 14 the conductive electrodeposit thickness may be very thin to non-existent shortly after entry into the solution at point 50 of FIG. 14 and thickest at the exit point 52. Because of this gradient in conductive electrodeposit thickness, it is possible to experience a significant difference in potential between the plating surfaces immediately adjacent to a contact such as 58 and those remote from the contact, especially in the upstream (opposite of web travel) direction where the conductive electrodeposit may become progressively thinner. This effect can be particularly significant when using electroplateable materials or structure of relatively low current carrying ability to initially define buss 27 a of article 22 a. Again, this is a result of the inability of a low current carrying ability material initially defining buss 27 a to contribute significantly to current transport.
Many electrically conductive resins, including many DER formulations, can be characterized as materials of low current carrying ability wherein conductive electrodeposit coverage is achieved by lateral electrodeposit growth over the surface with the conductive electrodeposit carrying a large portion of the electroplating current to/from the cathodic contact. This situation could also exist even for relatively higher conductivity materials, such as a particulate metal filled polymer or very thin vacuum metallized or electrolessly deposited metal, should the current be required to traverse an extended distance through a restricted cross section. It is currently believed that the speed of this lateral electrodeposit growth is at least partially dependent on the driving potential difference between the solution and the initial conductive surface at the advancing electrodeposits lateral growth front. Typically the higher the driving potential difference, the more rapid the rate of lateral growth. It will be appreciated that in a process such as depicted in FIG. 14, the more rapid the rate of lateral conductive electrodeposit growth upstream (opposite the web travel direction) over buss artery 28 a away from the initial cathodic contact, the more rapidly the web can be conveyed through the bath. The rate of lateral growth would not normally be exceeded by the linear web speed. Thus it is informative and helpful to consider ways in which the electrodeposits lateral growth rate can be maintained at acceptable levels especially with respect to achieving coverage of the current carrying buss.
The lateral electrodeposit growth situation is illustrated in more detail in the embodiments of FIGS. 15 and 16. FIG. 15 is a top plan view of an article generally designated as 22 b. Article 22 b is similar to article 22 of the FIG. 6 embodiment. Article 22 b comprises web substrate 24 b. Web substrate 24 b normally will be characterized as having length L-15 and width W-15. The thickness of web material 24 b is normally much less than either W-15 or L-15. In addition, L-15 can be considerably greater than W-15 so that web substrate 24 b can be considered “continuous” in the direction L-15 and is capable of being processed in a continuous fashion. Electroplateable material 19 b is positioned in structural patterns 26 b similar to that shown in FIGS. 6 through 8 on web material 24 b. Included is a buss structure 27 b. As with the embodiment of FIGS. 6 through 8, material forming the buss structure 27 b need not be the same as that forming structural patterns 26 b. Buss structure 27 b has a width indicated by “B” and extends continuously in the direction L-15 as shown. In the FIG. 15 embodiment material forming buss structure 27 b and structural patterns 26 b can comprise any number of electroplateable materials. These include very thin chemically or vacuum deposited metals, particulate metal-filled resinous inks and DER formulations as defined herein. The materials can be applied by appropriate methods. As pointed out earlier, the formulation and fabrication flexibility of DER's often make them a preferred choice of material in these applications. DER's can be applied by thermoplastic processes and printing processes. For example, a DER buss portion 28 b can be formed by such methods as co-extrusion, printing or laminating at the same time that the substrate web film is produced.
FIG. 16 illustrates the situation which may exist while passing article 22 b through one form of electroplating process such as that shown in FIG. 14. The situation depicted in FIG. 16 may arise when using materials or forms of buss structure 27 b that can be characterized as having low current carrying capacity. In FIG. 16 a cathodic contact 58 b is positioned to continuously contact buss artery portion 28 b as article 22 b is continuously moved past cathodic contact 58 b. Article 22 b is moved in the direction indicated by arrow 70. Electrodeposit has covered those surface areas of buss structure 27 b and structures 26 b as indicated by numeral 20 b. This situation ensures good cathodic contact at contact 58 b. Surface areas of buss structure 27 b and structures 26 b remaining uncovered with electrodeposit are indicated by numeral 74. The electrodeposit growth front on the buss 27 b is indicated by numeral 76 and the electrodeposit growth front on the structural patterns 26 b is indicated by numeral 78. The electrodeposit growth front 76 on buss structure 27 b travels over the buss artery 28 b in a direction opposite the web travel direction 70. For reasons discussed below, a voltage drop indicated by “delta V” in FIG. 16 exists between the buss growth front 76 and the cathodic contact 58 b.
As shown in FIG. 16, the cathodic contact is best made to previously electrodeposited metal along the moving buss of the continuous web. Thus, the lateral growth speed of electrodeposit away from the contact in a direction opposite the web travel direction determines the speed at which the web can be conveyed through the continuous electroplating process. If the lateral electrodeposit growth speed is insufficient, the electroplated portion of the buss will be conveyed past the cathodic contact and the cathodic contact may be rendered essentially ineffective. Thus, a general “rule-of-thumb” is that the faster the lateral growth of electrodeposit over the buss, the faster the web can be processed.
An important parameter determining the lateral growth of electrodeposit over the surface of a buss 27 b is the voltage at the electrodeposit growth front. This parameter is not only dependent on the overall applied voltage to the cell, but also on the voltage drop between the cathodic contact and the growth front. When electroplating a continuous buss artery 28 b extending in a continuous web direction, the voltage drop from the cathodic contact to the growth front can be an important consideration. In practice, one prefers to have some measurable “lead length” between the contact and growth front to ensure that electrodeposited metal is present at contact 58 b despite minor process disruptions which may occur. Such a “lead length” is illustrated in FIG. 16 as dimension 80 corresponding to the distance over which “delta V” occurs. (Typically, this “lead length” may be greater than 2 inches). However, the voltage drop over this “lead length” may be considerable, since the electrodeposited metal on the buss artery 28 b is still very thin in this area and thus incapable of conducting large currents without associated voltage drop. Also, material forming the original buss structure 27 b may be of very low current carrying capacity. In addition, the current emanating from the electroplating structures 26 b extending from the buss over this “lead length” further contributes to voltage drop.
A first way to maintain an acceptably high rate of the electrodeposit lateral growth is to simply increase the overall rectified potential applied to the bath. This will tend to raise the growth front potential, but is counteracted to some extent by the increased IR drop from the growth front to the initial cathodic contact due to the inevitable increased current densities on surfaces already plated between the growth front and cathodic contact. This method may also be restricted in that current densities in those portions where the voltage drop is less of a factor (for example downstream from the initial contact) may be caused to exceed desirable values leading to undesired electrodeposit thickness for the overall process or burning at contact 58 b.
Another way to achieve an acceptably high rate of electrodeposit lateral growth is compositional modification to increase coverage rates. This can take the form of additives to increase current carrying capacity and/or in the case of DER's variation in the amounts and nature of the growth rate accelerators. For example, it has been observed that DER inks comprising a weight percentage of 4% sulfur will typically cover more rapidly than a DER ink comprising a weight percentage of 2% sulfur. In this regard one will recognize that the material defining the buss structure 27 b need not be the same as the material defining the selective patterns 26 b.
Yet another way to achieve an acceptably high rate of electrodeposit lateral growth is to the increase the thickness of the electroplateable material. For example, multiple printing operations can be employed to increase the buss thickness. Also, the buss structure may be formed through a process operation different than that used to form the structural patterns intended for electroplating. For example, while the structural patterns may be formed with flexographic printing techniques, the buss or portions of the buss may be formed with a roller, extrusion etc. One will thus recognize that it may be advantageous to process a web whereby the composition and/or thickness of the buss material is chosen to have higher current carrying capacity than that of the selective patterns.
Another way to achieve an acceptably high rate of electrodeposit lateral growth is to reduce the distance between the initial cathodic contact and the growth front. This decreases the distance over which current must be conveyed thereby reducing potential loss. One can institute feedback control wherein the “lead length” is closely integrated with the web speed so that the “lead length” is always maintained within a certain (normally shortened) distance. In this way the IR drop associated with electroplating on previously electrodeposited surfaces can be closely maintained and minimized. A potential problem with this approach is that cathodic contact will be occurring to a very thin electrodeposit and special precautions may be required to avoid burning and scraping and possible bipolar effects leading to actual deplating of the thin electrodeposit. In order to maintain acceptable manufacturing tolerances regarding the linear growth front speed and to achieve an acceptable thickness of electrodeposit at contact point 58 b the linear distance between the growth front and contact 58 b may be typically of the magnitude of greater than 2 inches.
Yet another method to achieve acceptably high driving potential at the growth front is demonstrated in FIG. 17. In this embodiment electroplating process 36 c is intended to accomplish simply an initial electrodeposit “strike” over the surfaces of buss structure 27 c and possibly portions of structures 26 c such as those embodied in article 22 b of FIG. 15. As is known in the art, an electroplating strike bath is not necessarily intended to deposit the thickness of electrodeposit required for the final article but is intended instead to simply cover the article. In this particular case contact 58 c is made very close to the exit point 52 c of article 22 c. The web length immersed in the bath between entry point 50 c and exit point 52 c is adjusted such that the residence time is sufficient to allow electrodeposition of buss structure 27 c and desired portions of structures 26 c without requiring that electrodeposit thickness be increased excessively in process 36 c. Thus the amount of current transport required of buss artery 28 c to contact 58 c is manageable and the potential drop between contact 58 c and the electrodeposit growth front is lower. The combination of strike process 36 c and subsequent process 36 a such as shown in FIG. 14 accomplishes two beneficial results. First, contacting of the buss and current management may be made easier by separating the processes associated with the initial strike from that employed to increase thickness of the electrodeposit. It has been found that use of a strike bath such as depicted in FIG. 17 enables significant increases in achievable processing rates due to the ability to increase electrodeposit coverage rates of the current carrying buss. Using the strike bath, the plating potential can be increased while still avoiding burning from excess electroplating current. As explained above, this allows for increased electrodeposition coverage rates. Second, using a “strike” bath in combination with a subsequent “buildup” bath allows the strike electrodeposit to be different from the subsequent electrodeposit which may constitute a large portion of the electrodeposited material. For example, the strike deposit may be nickel while the subsequent electrodeposit could comprise copper.
One will recognize that while the embodiments above of article 22 a, 22 b, and 22 c involve the plating of a buss and selective patterns, the teachings and principles could also be applied to plating other structures in a continuous manner such as an entire web or film.
Yet another way to accelerate electrodeposit coverage of a material structure having low initial current carrying capacity is to position a conductive trace proximal or in contact with the structure. The conductive trace possesses a higher current carrying capacity than that of the material structure. In this way a conductive “parallel path” is supplied to transport electroplating current from those areas between the cathodic contact and the growth front on the material structure which consequently minimizes associated voltage drop along this length.
One such approach is embodied in FIGS. 18 and 19. FIG. 18 is a plan view of an article generally designated as 22 d. In many respects, article 22 d is similar to articles 22, 22 a, 22 b, 22 c of FIGS. 6, 14, 15, and 17 respectively. Similar features among the various embodiments will be designated in FIGS. 18 and 19 by numerals used in those previous embodiments followed by a letter designation indicating the particular embodiment of FIGS. 18 and 19. FIG. 18 shows a first portion of buss artery 28 d formed by a conductive wire (or cable, strand or trace) 90 embedded or otherwise positioned in contact with a second buss portion 91. Second buss portion 91 initially has low current carrying ability. Thus first buss portion 90 and second bus portion 91 combine to define buss artery 28 d. Prior to electroplating, second buss portion 91 has low current carrying capability, being thin and/or comprising material of relatively high intrinsic resistivity. Here the conductive wire 90 is used to minimize the voltage drop over the electroplated portion removed from the cathodic contact. This effect is illustrated in FIG. 19. FIG. 19 shows the situation arising when passing the article 22 d through an electroplating process such as depicted in FIG. 14. However, in the FIG. 19 embodiment the augmentation of the overall buss current carrying ability by the conductive wire 90 (partially shown in phantom in FIG. 19) allows the “lead length” 80 d of the FIG. 19 embodiment to be considerably greater than the “lead length” 80 of the FIG. 16 embodiment. In addition, the conductive wire extends forward into a region of the buss artery 28 d not yet fully covered with electrodeposit, causing electroplating to be initiated in these forward region. This forward region is designated by numeral 92 in FIG. 19. Thus, the requirement that the electrodeposit growth front actually traverse the full length of buss artery 28 d in the web “machine direction” (FIG. 16) is changed to the situation that the growth front needs to travel only a distance associated with the width of the buss artery 28 d in order for complete buss artery coverage (FIG. 19). Of course, once a particular portion of the buss is covered, it starts to build metal electrodeposit thickness such that the electrodeposit assumes an ever increasing role in current transport to the cathodic contact. This approach allows the web to be conveyed through the electroplating process at considerably greater speed than that permitted by having the lateral growth solely directed in the direction opposite the direction of web transport.
Augmenting the current carrying ability of the buss artery 28 d by extending a highly conductive material contacting the buss can be accomplished using numerous process design techniques. One such process is embodied in FIG. 20 wherein a continuous metal wire, cable or strip 90 e positioned in contact with the buss as indicated in FIGS. 18 and 19. In the embodiment of FIG. 20 a web of structure similar to that of FIGS. 6 through 8 and 15 will be used for illustrative purposes. This structure consists of the web including structures 26 e connected by buss structure 27 e.
In describing some of the processes in the present specification, the web embodiment similar to that presented in FIGS. 6 through 8 and 15 will be employed. It will be recognized that the features of the invention extend to other web forms such as that of FIGS. 3 through 5 wherein an entire surface of the web is to electroplated. In addition, it will be understood that the processing embodiments of the present specification extend to all material and structure defined herein as having low current carrying capacity, including metallic films as previously identified. In FIG. 20, there is depicted an electroplating process designated as 36 e. Electroplating process 36 e has solution level 60 e and anode 56 e. Partially or completely immersed below the electroplating solution level 60 e is support drum 86. It is understood that drum 86 represents one of a number of transport mechanisms which could be considered to convey an article through an electroplating process as will be known in the art. For example, drum 86 can be replaced by rollers defining a geometry other than circular. In this embodiment drum 86 is partially immersed in electroplating solution and normally comprises insulating material. In this embodiment, web article 22 e is passed into the bath at entry point 50 e, travels through the electroplating process supported by and around drum 86 and exits the electroplating process at 52 e. A conductive wire or strip 90 e is caused to pass through the bath around the drum to contribute to the overall current carrying ability of combination or aggregate buss 27 e. Wire or strip 90 e is at cathodic potential relative to anode 56 e. Following the electroplating process 36 e, wire or strip 90 e may be removed and optionally transported through a deplating or stripping process depicted as 92. Alternately, wire or strip 90 may be conveyed with the web to additional processing.
FIG. 21 is a sectional view taken substantially from the perspective of lines 21-21 of FIG. 20. FIG. 22 is a top plan view taken substantially from the perspective of lines 22-22 of FIG. 21. It is seen from FIGS. 21 and 22 that, prior to entry into electroplating process 36 e, article 22 e consists of patterned structures 26 e supported on insulating support web 24 e. In this embodiment, patterned structures 26 e comprise electroplateable material. Conductive fingers 30 e join patterned structures 26 e to buss artery 28 e. The initial buss portion 27 e comprising fingers 30 e and artery 28 e is of low current carrying capacity.
FIG. 23 is a sectional view taken substantially from the perspective of lines 23-23 of FIG. 20. FIG. 24 is a top plan view taken substantially from the perspective of lines 24-24 of FIG. 23. It is seen in FIGS. 23 and 24 that wire, cable or strip 90 e overlays and extends in contact along the length of buss artery 28 e. Drum 86 further supports article 22 e.
FIG. 25 is a sectional view taken substantially from the perspective of lines 25-25 of FIG. 20. FIG. 26 is a top plan view taken substantially from the perspective of lines 26-26 of FIG. 25. It is seen from FIGS. 25 and 26 that conductive wire or strip 90 e overlaps and contacts initial buss artery 28 e to supply cathodic potential and convey electroplating current. At this point the buss structure comprises the material originally forming fingers 30 e, buss artery 28 e, wire or strip 90 e and the corresponding surface electrodeposit 20 e. Electrodeposit 20 e now coats much of the originally exposed electroplateable surfaces of patterned structures 26 e, fingers 30 e, buss artery 28 e and wire or strip 90 e.
Upon exiting the bath, the structure originally defining buss portion 27 e may be capable of adequately conveying associated electroplating currents since it is now coated with conductive electrodeposit. The composite web indicated as 110 in FIG. 20 and now having attached electrodeposit 20 e can be separated from wire or strip 90 e. The composite web 110 is then conveyed as appropriate, such as through additional electroplating processing. Wire or strip 90 e is optionally conveyed through a “deplating or strip process” 92 to remove electrodeposit and recycled back to the bath. In this way wire or strip 90 e acts as a component of the buss supplying an auxiliary path to augment electrical connection between the individual patterned structures 26 e to the source of cathodic potential during the electroplating process 36 e.
Another web embodiment made possible using the electroplating process concept of FIG. 20 is shown in FIGS. 27-35. In FIG. 27, web article 22 g is passed into the bath at entry point 50 g, travels through the electroplating process supported by and around drum 86 g and exits the electroplating process at 52 g. A conductive wire or strip 90 g is caused to pass through the bath around the drum to participate as a component of a composite buss 27 g as shown more clearly in FIGS. 28-33.
FIG. 28 is a sectional view taken substantially from the perspective of lines 28-28 of FIG. 27. FIG. 29 is a top plan view taken substantially from the perspective of lines 29-29 of FIG. 28. It is seen from FIGS. 28 and 29 that, prior too entry into electroplating process 36 g, article 22 g consists of patterned structures 26 g supported on insulating web 24 g. Patterned structures 26 g comprise electroplateable material. Conductive fingers 30 g comprising conductive material extend from patterned structures 26 g. In contrast to the embodiments presented in FIGS. 20-26, patterned structures 26 g of the FIGS. 28 and 29 embodiments are not connected at this point. Fingers 30 g can conveniently comprise a material such as a conductive polymeric ink. Alternately, fingers 30 g may comprise a thin layer of chemically or physically deposited metal. Fingers 30 g and patterned structures 26 g need not be composed of the same material. In addition, fingers 30 g and patterned structures 26 g can comprise multiple layers.
FIG. 30 is a sectional view taken substantially from the perspective of lines 30-30 of FIG. 27. FIG. 31 is a top plan view taken substantially from the perspective of lines 31-31 of FIG. 30. These views, taken just prior to entry into the electroplating bath, show that wire 90 g has been positioned to overlap and contact the fingers 30 g extending from patterned structures 26 g. In this way a combination or composite buss 27 g comprising wire 90 g and conductive fingers 30 g is created to enable conveyance of electroplating current from patterned structures 26 g along the length of article 22 g to a cathodic contact such as contacts 58 g shown in FIG. 27.
FIG. 32 is a sectional view taken substantially from the perspective of lines 32-32 of FIG. 27. FIG. 33 is a top plan view taken substantially from the perspective of lines 33-33 of FIG. 32. Electroplated material 20 g now coats the originally exposed surfaces of combination buss structure 27 g (wire 90 g plus fingers 30 g) and patterned structures 26 g.
After exiting the electroplating process 36 g, wire 90 g may be separated from contact with the web and fingers 30 g as shown in the embodiment of FIGS. 34 and 35. Alternatively, the wire may be transported along with the web to additional electrochemical or electrophysical processing.
Yet another structural web article 22 h suitable for processing via a process embodiment similar to that depicted in FIGS. 20 and 27 is shown in FIGS. 36 and 37. FIG. 36 is a view taken at a point similar to that of FIGS. 23 and 30 Oust prior to entry into an electroplating bath). The top plan view of FIG. 36 shows wire or cable 90 h overlapping traces of material forming a coil pattern 98. The coil pattern is formed of a material having low current carrying ability. FIG. 37 is a bottom plan view of the FIG. 36 structure. In FIG. 37 wire or cable 90 h and coil pattern 98 is shown in phantom. FIG. 37 also shows extensions 100 and 102 positioned on the bottom side of web article 22 h. Extension 100 and 102 are electrically joined to the remaining coil pattern positioned on the opposite side through hole vias 104. One will understand that subjecting web article 22 h to processing such as taught in FIGS. 20 and 27 will quickly result in electrodeposit forming over the coil pattern on the top side of web article 22 h. Subsequent processing whereby the backside of web article 22 h is exposed to electroplating solution will further result in electrodeposition of extensions 100 and 102 through the holes 104. Following this initial electrodeposit coverage, wire 90 h may be separated from web article 22 h or may be transported along with web article 22 h to additional processing as in prior embodiments.
Yet another option to achieve rapid processing rates through increasing web speed would be to avoid the situation wherein the electroplating current is required to be transported primarily in the length direction of the web. Such a situation can be achieved by causing the web to be supported vertically in the electroplating bath (i.e. the width dimension is caused to have a vertical component). Cathodic contacting is made through a series of “clips” positioned proximal the upper edge of the web. Each of these “clips” would be responsible for current associated with a limited surface area of the web, approximately the distance between “clips” times the web width. Such a process has been utilized commercially to electroplate complete web surfaces having an initial thin coating of sputtered or chemically deposited metal. When electroplating patterned structures however, it is often difficult, expensive or inconvenient to generate the initial electroplateable patterns on the expansive web using chemical or physical metal deposition techniques. In addition, since the patterned structures can be relatively small in comparison to the web width, it is often desired to position multiple patterned structures across the width dimension. Electrical connecting of these multiple structures requires a buss structure extending in the web width direction. One will realize that the use of a conductive wire as shown in FIGS. 20 and 27 would be a convenient way to achieve contacting to this buss structure extending in the web width direction. This is similar to the contacting of the finger buss portions 30 shown in previous embodiments. Since the buss is normally discarded following processing, the relatively inexpensive DER ink compositions are eminently suitable as material to define such a buss for this form of processing.
Another option which increases the current carrying capacity of an initially low current carrying capacity buss, is to apply a distinct trace of highly conductive ink along the length and in contact with the initial buss structure. This approach was taught in application Ser. No. 11/035,799 herein incorporated in entirety by reference. This approach has an advantage in that the highly conductive ink augments the current carrying capacity of the buss structure not only during initial electrodeposit coverage but throughout possible subsequent electrochemical processing which may be desired.
The following solid ingredients were weighed out:
1. 33 grams of Kraton (Kraton 1450—Kraton Polymers)
2. 16.5 grams of carbon black (Vulcan XC-72—Cabot Corporation)
3. 0.5 grams of elemental sulfur
These solid ingredients were mixed and dissolved in approximately 10 ounces of a xylene solvent. This produced a fluid ink/coating formulation which, after drying, consisted of:
2. Carbon Black=33%
A length of PET film was coated with this ink/coating solution in the form of a 1 inch wide buss stripe pattern. The stripe pattern was allowed to dry and then was immersed as a cathode in a standard Watts nickel plating bath similar to that depicted in FIG. 17. The PET film was pulled through the bath at a rate of approximately 3 inches per minute. The stripe pattern covered quickly with nickel electrodeposit. At an applied contact potential of 3 volts, the electrodeposit growth front maintained its position approximately 6 inches upstream from the emergence point of the film from the plating bath.
A piece of PET sheet 4 mil thick was cut into a sheet of linear dimensions 13 inch by 8.5 inch. This sheet was then wrapped around a polyethylene pipe having a 4 inch diameter. A DER strip, 1 inch wide was applied as a simulated buss on the exterior of the PET sheet extending circumferentially around the pipe. A length of copper wire, 0.019 inch in diameter was then wrapped around the pipe overlaying and in contact with the DER buss. The pipe/PET/DER buss/copper wire assembly was immersed in a standard Watts nickel electroplating bath and the copper wire was made cathodic at 3 volts overall potential relative to the anode. It was observed that the buss completely covered with nickel electrodeposit in 15 seconds. This shows that very rapid coverage of extended lengths of buss can be achieved with this approach. The approach therefore allows linear web process speeds to be greatly increased.
One intent of the electroplating processes and embodiments of FIGS. 17-37 is to achieve rapid electrodeposit coverage of a buss structure initially characterized as having low current carrying ability. As noted, such embodiments may be appropriate for buss structures comprising very thin metal deposits, conductive polymeric inks and relatively resistive materials such as carbon filled polymers. Processes such as those embodied in FIGS. 17-37 can be used to accomplish electrodeposit coverage and perhaps some degree of electrodeposit thickening over the surfaces of buss structure 27 and appended structures as noted. Indeed, while the embodiments used to teach the processing of FIGS. 17-37 shows repeating patterned structures one skilled in the art will recognize that the process principles apply to electroplating the entire surface of a web should electroplateable material form that entire surface, since the physical principals employed are similar. However, one notes that after a sufficient period of processing time, the electrodeposit coating the buss will have thickened sufficiently so that it may function adequately in subsequent processing without special considerations relating to initial electrodeposit coverage. In this case the subsequent processing may be of more conventional and perhaps simpler design wherein the electroplated buss is expected to function as a structure of higher current carrying ability.
Additional electrodeposit thickening or variations in electrodeposited material on the patterned structures may be achieved in subsequent electroplating processes similar to that originally presented in the FIG. 14 embodiment. With many electroplating processes, electrodeposit typically thickens at a rate about 1 micron per minute. Many, if not most, applications require multiple microns of thickness. Naturally, increasing the web speed increases the amount of web length being processed at a particular instant since a certain residence time will be required in the electroplating process to build the required thickness over the surface of the appended structures. Furthermore, the electroplating of the appended structures may place considerable current carrying requirements on the buss. If one considers accomplishing a specific thickening in a single electroplating bath, a problem may arise regarding the length of web required in that bath and the amount of current conveyance expected of the buss. This is especially the case where the appended structures have large surface area, or in the particular case wherein the entire web surface is to be electroplated as in the embodiment of FIGS. 3-5. In the cases of extended lengths of web undergoing processing in a single electroplating cell, considerable demands can be placed on the cathodic contacts. If the cathodic contacts are positioned outside the plating cell (for example at entry and exit) the amount of current conveyance expected of the buss and the contacts may become excessive at extended lengths of web being processed simultaneously in a single cell. One possibility is positioning of appropriately spaced “under bath” contacts as depicted as 58 in FIG. 14. However, such contacts may be design limited and difficult to maintain due to their depth of immersion in the plating solution.
An alternative arrangement to accomplishing electrodeposit thickening while allowing increased web processing speed is presented in FIGS. 38 through 41. In FIG. 38, web article 22 i is passed through electroplating “strike” process 36 i similar to that taught above in conjunction with FIG. 20. Web article 22 i is similar to web articles 22, 22 a, 22 b, 22 c, 22 d, and 22 e of previous embodiments, having a buss comprising an artery extending in the length direction of the web combined with fingers extending to patterned structures. The buss (artery plus fingers) comprises, at least in part, material structures initially characterized as having low current carrying capacity. A difference between the process embodiment of FIG. 38 and that of FIG. 20 is that in the FIG. 38 embodiment the web is “turned over” or “flipped” during its travel through electroplating process 36 i. This results in the buss structure and appended structural patterns facing upward in subsequent processing, resulting in processing advantages as will be shown. The web exiting electroplating process 36 i of FIG. 38 will have all or a portion of its buss, and often a portion of its appended structure, coated with electrodeposit. Electrodeposit coverage rates in a electroplating process 36 i such as that embodied in FIG. 38 can increased, as previously taught. The web exiting electroplating process 36 i is designated as 110 i in FIG. 38. Web article 110 i is then fed through one or more individual cells, designated as 112, 114, 116, and 118 in FIG. 39. Further details of these cells are presented in FIGS. 40 and 41. FIG. 40 presents an end view of individual electrochemical cells such as those designated 112 and 114 in FIG. 39 while FIG. 41 presents a side view. It is seen in FIG. 39 that cathodic contacts 58i are made to the electroplated buss at both the entry and exit of the individual electrochemical cells in this embodiment. Thus, the contacts are exterior the cells. In this embodiment, the web is transported substantially horizontally into and out of the bath through slots 120 in the sides of the bath. In this embodiment the bath level is continuously maintained by pumping solution from a sump, such as designated 122 in FIGS. 40 and 41, via pump 124 back into the individual cells. An overflow arrangement 126 directs overflowing solution back to sumps such as 122. Slots 120 need not make a seal with the web article 110 i since flow through the slots 120 is also directed to sump 122. It has been found that flow out of the slots and into the region of the contacts actually is helpful in cooling the contacts and also continuing the electrodeposition process in the region between the individual cells. This reduces the risk of metal passivation during the transport between cells. The advantages of such “flooding” are made possible by the fact that the electroplateable material faces upward on the web. Anode 130 is positioned above web article 110 i. This allows for easy replenishment of anode material. In addition, the upward facing electroplated structure permits rapid, straightforward optical or electrical scanning for process control and quality control procedures, very critical to high volume, minimum labor production. Finally, sparger tubes 180, shown in phantom in FIGS. 40 and 41, serve two purposes. First, they prevent the web article from floating. Secondly, directing solution from pump 124 to these tubes produces vigorous mechanical agitation on the electroplating surface to permit increased deposition speeds.
One of the major advantages to a multiple cell arrangement such as that depicted in FIG. 39 is the ability to effectively manage electroplating current at specific points in the electroplating process. The individual cell arrangement allows one to adjust current density and voltage at various stages in the process. This is equivalent to subdividing a large plating bath into small discrete highly controllable sections. This allows for electroplating current densities to be varied in a controllable fashion during the various stages of processing. It will be realized that the length of the cell, designated approximately by L-41, can be chosen so the amount of electroplating current being transported along the electroplated buss to contacts 58 i is not excessive. In other words, the amount of electroplating surface in an individual cell is matched to the current carrying ability of the buss at that point in the process along with the ability of the contacts 58 i to transfer the current. In addition, since the web is transported horizontally, the height H-41 of the cell can be relatively small. The cell width, indicated as W-40 in FIG. 40, is determined in large measure by the width of web article 110 i. Finally, since the web is transported through the array of small cells in a substantially linear, horizontal fashion, web transport concerns are reduced.
In FIG. 39, there is shown an initial array of cells 112 all having the same solution and draining into a common sump 122. One will realize that the impressed potential and current density can vary among the cells. This initial array of cells 112 is followed by rinse 114 draining into sump 134. This is followed by a second array of plating cells 116 draining into sump 136. Cells 1 16/sump 136 often are similar to cells 112/sump 122 in the FIG. 39 embodiment. However, one will recognize that the electrodeposit applied by cells 112 can be different than the electrodeposit associated with cells 116. For example, cells 112 can be depositing nickel while cells 116 may be depositing copper. Finally, rinse 118 drains into sump 138.
One realizes that using the arrangement of FIG. 39, increased residence time (at constant web speed) is achieved by simply adding additional cells. Alternately, should the “buss coverage process” allow, increased web travel speed, maintaining the same residence time, can be accomplished by adding additional cells. Thus, by simple addition of cells the capacity of the process can be made readily scaleable.
It is to be noted that the process of using multiple individual cells to accomplish electrodeposition has significant advantages for web processing. In the FIG. 39 process embodiment, the multiple cell arrangement is taught as a portion of a hybrid process in conjunction with an initial coverage process 36 i embodied in FIG. 38. This particular combination is not required to achieve benefits of the multiple cell arrangement. Other initial “strike” or “coverage” processes, techniques structure and material selections as taught herein to achieve initial electrodeposit coverage of an initially low current carrying capacity buss structure may be satisfactory. Indeed, one may also consider using one or more electrochemical cells such as that embodied in FIGS. 40 and 41 to achieve initial electrodeposit coverage.
The benefits of using multiple individual electroplating cells to electrochemically process a web in a substantially horizontal fashion extend to web articles which may be characterized as having current carrying capacities greater than the low current carrying materials and structures as defined earlier in this specification. For example, this process arrangement can have significant advantages when processing a wide range of web articles including those wherein the electrodeposit extends over a major or complete portion of the web.
Turning now to FIG. 42, there is shown in top plan view of an electrical article, identified as 150, useful in the practice of aspects of the instant invention. FIG. 43 is a sectional view taken substantially from the perspective of lines 43-43 of FIG. 42. In FIGS. 42 and 43 there is depicted an electrical device 152. Electrical device 152 can comprise any number of items such as a microchip, conductor, capacitor, etc. Extending from the electrical device 152 are conductive lead structures 154. Leads 154 comprise conductive material and at least a portion of the exposed surface of the leads is conductive. The purpose of the leads is to facilitate electrical joining of device 152 to additional components such as a circuit trace, antenna, etc. Device 152 and leads 154 are positioned on substrate 156 which is typically an electrical insulator. In the embodiment shown, the substrate 156 is of rectangular structure having edge portions 158. Of course alternate structures or shapes for substrate 156 can be considered. In certain markets such as RFID communications device 152 can comprise a microchip and article 150 is often referred to as a strap.
FIGS. 44 and 45 depict one possible positioning arrangement for article 150 in conjunction with additional components. FIG. 44 is a top plan view of this positioning arrangement, generally identified as 160. FIG. 45 is a sectional view taken substantially from the perspective of lines 45-45 of FIG. 44. In the embodiment of FIGS. 44 and 45, article 150 is shown to be positioned on a flexible insulating substrate 162. Adhesion of electrical article 150 to substrate 162 may conveniently be achieved by conventional adhesion techniques, such as the use of an adhesive (not shown in FIG. 45). Additionally in this embodiment trace patterns 164, also positioned on flexible insulating substrate 162 extend to a point proximal article 150. It will be understood that article 150 could reside on or be in direct contact with at least a portion of trace patterns 164. While trace patterns 164 are shown as a single layer, it is understood that they may be formed from multiple layers. A portion of the top exposed surface of trace patterns 164 is receptive to being coated with a metal deposit. In preferred embodiments, at least a portion of the top exposed surface of trace patterns 164 is receptive to receiving an electrodeposited metal.
FIGS. 46 and 47 show the positioning arrangement following an additional processing step. The arrangement is designated as 166 in FIGS. 46 and 47 to reflect this additional step. FIG. 47 is a top plan view of arrangement 166 while FIG. 46 is a sectional view taken substantially from the perspective of lines 46-46 of FIG. 47. In FIGS. 46 and 47, it is seen that additional material 168 has been positioned bridging from at least a portion of the top exposed surface of leads 154 to at least a portion of the top exposed surface of trace patterns 164. At least a portion of the top exposed surface of material 168 is receptive to being coated with a metal deposit. In preferred embodiments, at least a portion of the top exposed surface of material 168 is receptive to receiving an electrodeposited metal. One will understand in light of this embodiment and the teachings to follow, that it may be advantageous for material 168 to comprise a DER. In the embodiment of FIGS. 46 and 47, a portion of the surface of leads 154 remains uncovered with material 168. However, this is not necessarily the case, as will be explained by the teachings to follow.
FIG. 48 is a sectional view similar to FIG. 46 of the arrangement shown in FIGS. 46 and 47 after an additional processing step. The arrangement is designated as 170 in FIG. 48 to reflect this additional step. Arrangement 170 now includes a metal deposit 172 extending over the originally exposed surface of trace patterns 164, over the originally exposed surface of material 168, and onto the originally exposed surface of leads 154. This metal deposit 172 forms a highly conductive connection between leads 154 (thus device 152) and the trace patterns 164. In addition, the trace patterns 164 now have enhanced current carrying ability. In preferred embodiments, metal deposit 172 is achieved by electrodeposition of metal. One will understand that should material 168 be itself highly conductive, such as for example a highly conductive silver filled ink, the entire surface of the lead could be coated with material 168. In this case the metal deposit would not actually be in direct contact with the lead 154, but a highly conductive connection would still be achieved.
One problem that can be encountered with the electrical connections as illustrated in FIG. 48 is encountered due the flexibility of substrate 162. This flexibility allows easy bending. While this may be a significant advantage in many cases, it also permits high stress levels to build at certain points such as indicated by arrow 174 in FIG. 48 when the arrangement is flexed or bent.
The high bending stress level at the region indicated by arrow 174 in FIG. 48 may result in cracking of a relatively non-ductile metal deposit 172 as is depicted in FIG. 49 thereby leading to a breach in the highly conductive connection. This situation would naturally be aggravated should substrate 156 be relatively rigid in comparison to flexible substrate 162. In this case a sharp, crease-like bend is promoted in substrate 162 as depicted in FIG. 49. This is indeed the case in many instances. Substrate 156 is often chosen to be relatively thick may comprise rigid materials such as epoxies and polyimides. One reason for these material choices is the use of classic high temperature electrical joining techniques such as soldering and conductive epoxies.
A number of techniques can be used to alleviate the stress concentration problem depicted in FIGS. 48 and 49. A first technique is to choose materials and forms for bridge material 168 intended to soften the “step-like” profile of the eventual metal deposit depicted in FIG. 48. One such technique is illustrated in FIG. 50 which shows bridge material 168 j applied as a thicker mass of significantly softened contour. Such a thickened mass of gentle contour can be achieved by application of a bridge material 168 j formulated as a high solids fluid, such as a thermoplastic melt. Another technique would be to choose bridge material 168 to be very soft and conformable such as a foam or soft elastomer. Yet another option to avoid the possible stress fracture depicted in FIG. 49 is to include a fibrous filler in the bridge material 168. Such inclusion would increase the tensile modulus of the bridge material thereby spreading out stress levels. Should the fibrous material be conductive such as metal fibers, sufficient conductivity may be retained across the connection even if there is a breach in the metal deposit's continuity. As noted earlier, a wide variety of material properties and forms are available using DER technology, making DER's particularly suitable as a bridge material to counteract these stress effects.
Yet another option to counteract the stress concentration problem is to use a thin, flexible material for substrate 156, such as a PET film. Such a conformable substrate would resist the stress concentration depicted in FIG. 49. It is noted that the metal deposition processing involved in making the connections taught here, and specifically electroplating, are relatively low temperature processes. Thus, using thinner, less rigid materials for substrate 156 is entirely feasible.
Yet another option to counteract the stress concentration effect depicted in FIGS. 48 and 49 is embodied in FIGS. 51 through 54. In these embodiments the form of the substrate portion 156 of the electrical article 150 is changed by modifying the stress sensitive edge portions 158 of substrate 156.
In FIGS. 51-53 the geometry of substrate 156 has been modified to help reduce the stress concentration depicted in FIG. 49. In the embodiments of FIGS. 51 and 53 edge portions 158 k and 158 m are shown as structurally triangular and arcuate respectively. In FIG. 52, substrate 156L includes extensions 176 of edge portions 158L on opposite ends of edge portions 158L. In these cases the ends of the edge portions extend further than the central region of the edge portions to effectively increase bending radius and prevent sharp, crease-like bending of the flexible substrate surface over which the eventual metal deposit traverses.
For example, FIG. 54 is a top plan view similar to FIG. 47 showing electrical article 150L mounted on a flexible substrate 162L. In FIG. 54, bridge material 168L extends from at least a portion of trace patterns 164L to at least a portion of electrical leads 154L in a fashion similar to that arrangement depicted in FIGS. 46 and 47. However, in the FIG. 54 embodiment, the extensions 176 at the ends of the edge portions 158L also adhere to the substrate 162L. One will understand that when bending occurs, the adhesion of these extensions will prevent a sharp, crease-like bending of flexible substrate 162L in regions adjacent the edge portions 158L crossed by the bridge material 168L and ultimately the deposited metal.
Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications, alternatives and equivalents may be included without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications, alternatives and equivalents are considered to be within the purview and scope of the invention and following claims.