CROSS REFERENCE TO RELATED APPLICATIONS
FIELD OF THE INVENTION
This applications claims benefit of U.S. Provisional Application Serial Nos. 60/203,289, 60/204,099, 60/204,109 and 60/204,110, filed May 11, 2000, May 15, 2000, May 15, 2000 and May 15, 2000 respectively.
The present invention relates to a system, i.e. a process and apparatus for separating (cutting) brittle materials using laser micro-crack propagation (ZERO WIDTH CUTTING TECHNOLOGY, OWCT«).
The cutting of glass has been done for centuries. The techniques developed many years ago are still in use today and remain fundamentally unchanged. The method generally consists of scribing a line, conforming to the shape desired, onto the surface to be cut with a material that is much harder than the glass itself, and then breaking the glass along the scribe line. The scribing material is typically made from diamond or zirconia.
The scribing action chips away the surface of the glass and creates tiny fragments of glass from the glass surface leaving a small groove in the wake of the scribe. This groove creates a localized area of high stress in the glass. Because of this stress, the glass tends to fracture along this line when it is stressed beyond its strength threshold. Thus, to break a piece of glass, one first scribes it and then “bends” it until it breaks. The problem with this method is that the break line is somewhat unpredictable because when the scribe chips away the glass and the glass particles flake away, it does so in an unpredictable and irregular geometry. The best way to control the break line predictability is to make the scribe line as narrow and as deep as possible. There are, however, certain practical limitations as to just how narrow and deep the scribe line can be made. Some of these limitations are: scribe point diameter, scribe point geometry, scribing pressure, homogeneity of the glass substrate material and the velocity of the scribing.
The practical limits of a diamond point, for present day industrial diamond scribes, is in the range of 0.0015″ (0.00381 cm) radius. Smaller size points can be made but increased wear factors and higher degrees of point fragility make their use infeasible or impractical. The larger point sizes, though more robust, create larger glass flake sizes and correspondingly, a larger stressed area and a shallower groove. This condition induces an unpredictable and more irregular break line.
The scribe point geometry also influences the break line qualities. As points wear they become faceted, i.e., flat spots are worn on the spherical diamond tip. These facets change the pressures applied to the glass as they mark it. This change in pressure (force) causes variations in the degree of scribing action that is applied to the glass, which in turn affects the uniformity of the notch and therefore the stress field created and thereby influences break characteristics, edge quality, etc. These characteristics, although specifically described for a “pointed” scribe are similar, if not identical, for scribing “wheels” that are used in some industrial glass scribing machines.
Scribing pressure variations are not easily controllable, even with machine automation, because of the “amorphous” nature of the glass, surface irregularities, hardness, non-uniformities, and variations in the actual (microscopic) point of contact between the scribe point and the glass surface.
Homogeneity of the glass material is critical to a clean conventional mechanical break because, unless the scribing stresses are created evenly and in a symmetrical pattern around the scribe line, the glass will not fracture predictably. This will cause poor edge geometry and cut accuracy.
Poor edge geometry results in fragile edges. Fragile edges limit the ability to safely handle the glass and restrict the use of certain processing steps and equipment. When a fragile edge is stressed (and there is no predictable stress threshold), it can cause the glass to develop microscopic errant cracks, which will grow larger with time. It is not possible to reliably predict how long the cracks will take to sufficiently weaken the glass and induce failure. Thermal cycling and exposure to vibration accelerate crack formation and propagation, but not at a predictable rate or along a predictable path. Each glass part has its own individual set of variables. This presents the worst of all possible scenarios, dealing with an unpredictable randomized failure mode.
Changes in the scribing velocity, caused by variations of the glass surface (hills and valleys) will vary the effective applied scribing pressure, causing variations in the depth and width of the scribed line. This, then, impacts the repeatability and predictability of the glass break path and, therefore, the edge geometry, quality, fragility and accuracy.
Another disadvantage of mechanical scribing is that it creates volumes of tiny glass particles. Unless these particles are collected (adding more equipment and expense to the operation) they may find their way into the air and eventually onto a work surface, or more critically, a device surface. These tiny glass flakes are both abrasive and contaminating and may not be cleaned or controlled by conventional low cost means.
Mechanical scribing has been the only practical method of glass cutting for centuries and it has also been the method for starting (initiating) a break at/on the edge of a glass substrate. Edge scribing, or notching, although common, is not the most reliable method of starting a break because of the above stated reasons. Edge starts, or “Cut Initiation Defect”, implemented by mechanical scribing has the same unpredictability and irregularity as does the general mechanical scribing method due to the same influences and limiting characteristics of the glass and the scribing implement.
Recently lasers have been adapted to cut glass by thermally ablating through the glass material. This method can work, but has several undesirable characteristics.
First, in thermal ablative laser cutting, the glass is burned away or evaporated by the heat generated by the laser's beam. The material is severed, one part from the other. This process actually consumes material requiring dimensional parameters to be adjusted for cut losses (kerf).
Second, the cut-edge of the glass is a melted edge. Melted edges have an unpredictable and irregular geometry. This necessitates post-cut edge processing such as grinding to the required geometry with a diamond or zirconia abrasive wheel. Such processing is costly in both time and materials and, because of vibration caused by the grinding process, additional shear stresses may be imparted to the glass, further increasing the risk of fracture or errant micro-crack formation.
Third, heat induced stress, set up by the laser's thermal ablation (or evaporation) of the glass, in the heat affected zone at the margins of the cut creates uncontrolled residual thermal stress which will create fragility on the edges which greatly increases the propensity for edge damage. This randomized stress may further complicate the cutting process when these parts must be re-cut as part of another processing cycle or put through an edge finishing operation.
Because of these unpredictable characteristics, the mechanical scribe and break method of glass cutting is still preferred to thermal ablation laser cutting and is used in most applications.
In U.S. Pat. No. 5,609,284 (Kondratenko), a technique is disclosed that enables the scribing and splitting of glass with no debris, cutting waste, or kerf loss. This laser based, glass (or other brittle material) cutting system, called ZERO WIDTH CUTTING TECHNOLOGY, OWCT«, does not rely on burning or melting the glass in order to cut it. Rather, the system, which relies on the thermo-physical properties of glass, uses a laser, in a controlled manner, to heat the area of interest of the glass to a specific temperature and then stress a certain part of that heated area of the glass with a cooling jet. (The term “glass” is used here for conventional convenience, however, it includes all brittle materials, ceramics, metal-glasses, etc. that are susceptible to the process.) Consistent with this process, high tensile stresses are developed from the heated surface penetrating into the body of the glass, induced by the precise laser heating (or other appropriate energy transfer method) and immediate controlled cooling with a water/cool air mist or other fluid medium. These stresses overcome the molecular binding forces within the glass and result in the creation of a micro-crack having a width on the angstrom level, and exhibiting little, or no, measurable separation between the cleaved surfaces across the cut line, except for the broken intermolecular bonds. The micro-crack, which is of a controlled size (height), propagates from the top surface (where the heat energy is applied) down into, and through, the body of the glass and linearly, in a plane normal to the surface of the glass, following the heat/chill path created by the translation of the laser beam/cooling jet over the glass surface. While the result of this process is roughly analogous to a conventional mechanical scribing process, ZERO WIDTH CUTTING TECHNOLOGY, OWCT« cuts result in no kerf loss, perfectly square and straight edges, lack of residual mechanical and thermal stress, and extreme cut geometry precision and regularity. The cut material will, therefore, hold together, and workpieces defined by a closed geometry cut will be retained by the base plate from which they are cut because there is no actual clearance space for the material to separate.
After a micro-crack has been induced by ZERO WIDTH CUTTING TECHNOLOGY, OWCT« in the glass, the glass may be separated by several conventional methods. As was mentioned above, a bending moment is applied to the glass, one vector being applied to either side of the micro-crack on the “top” surface of the material, and a pivotal vector being applied in the opposite direction, on the opposite “bottom” surface, and immediately under the ZERO WIDTH CUTTING TECHNOLOGY, OWCT« “scribed line” (micro-crack). Upon application of the bending moment, the glass can be cleanly split along the propagated micro-crack.
- SUMMARY OF THE INVENTION
Typically, prior to application of the laser beam/chill jet “scribing” process, a lead crack, or “Cut Initiation Defect”, is induced to aid in the initial formation of the ZERO WIDTH CUTTING TECHNOLOGY, OWCT« micro-crack. This “defect” is necessary, on conventionally “scribed and broken” edges, where a laser ZERO WIDTH CUTTING TECHNOLOGY, OWCT« cut will be started, to assure that the ZERO WIDTH CUTTING TECHNOLOGY, OWCT« micro-crack will start from the exact desired location, and not an errant weak point left by conventional “scribe and break” residual stresses. The placement of a “Cut Initiation Defect” on the edge of a ZERO WIDTH CUTTING TECHNOLOGY, OWCT« surface is imperative for successful laser scribing, because any previously laser scribed edge is 5 to 10 times stronger than a conventionally “scribed and broken” edge due to the lack of residual stress in the severed surfaces. The lead crack, or “Cut Initiation Defect”, may be initiated using a conventional mechanical scribe or by laser ablation or laser induced stress flaking of the glass along its edge.
According to one aspect, the invention herein embodies the heating of the outer perimeter of a base plate, to release a captive workpiece, of brittle material which contains therein a workpiece defined by a laser micro-crack cut line. The heating causes the base plate material to expand away from the micro-crack cut line, therein expanding the interstice between the base plate and the captive workpiece, releasing the workpiece defined by the micro-crack cut line.
According to a second aspect, the invention herein employs a gas emitting tape. This tape is designed such that the adhesive, or other component of the tape, when heated slightly, out-gasses a gaseous material such as nitrogen or some other gas. The formation of gas under a micro-crack cut line applies a vectored force against the glass (brittle material) along the line of the micro-crack, but opposite its location and below its extent on the opposing surface. This force vector acts as the pivotal vector in the breaking couple, which completes the propagation of the micro-crack through the thickness of the material and completely separating the brittle material along the micro-crack scribe (cut) line.
According to a third aspect, the invention herein employs ultrasonic energy to cause breakage of a brittle material along a micro-crack scribe line.
According to a fourth aspect, the invention herein employs the application of high pressure gas or fluid along a micro-crack cut line, therein forcing the material on either side of the cut line apart.
BRIEF DESCRIPTION OF THE DRAWINGS
According to a fifth aspect, the invention herein embodies the use of two beams of laser energy to create a laser beam incident composite footprint, which efficiently creates stress vectors required to split brittle materials via the controlled expansion of the base material. Additionally, the use of two beams allows for fine control of the laser energy parameters, as well as propagation characteristics of the resulting micro-crack. Consistent with this aspect of the invention, it is possible to change the beam energy profile without recalibrating the system, maintain the highest possible level of intermolecular stress on/in the brittle material without special lasers, laser controls, or power sources, and easily reset the energy footprint of the system according to physical and mechanical characteristics of variant brittle materials.
Exemplary embodiments of the invention are set forth in the following description and shown in the drawings, wherein like numerals depict like parts, and wherein:
FIG. 1 illustrates a plan view of a locked workpiece;
FIG. 2 illustrates a locked workpiece in side view;
FIG. 3 illustrates, in side elevation, a locked workpiece having drafted side;
FIG. 4 illustrates, in plan view, a locked workpiece containing a locked scrap piece;
FIG. 5a illustrates brittle substrate adhered to an out-gassing tape;
FIG. 5b is of a brittle substrate and out-gassing tape enlarged for detail;
FIG. 6 illustrates the out-gassing tape employed to separate a workpiece from a brittle substrate;
FIG. 7 is a perspective view of an exemplary ultrasonic breakout system utilizing an ultrasonic horn;
FIG. 8 is a perspective view of an exemplary ultrasonic breakout system using energized fluid;
FIGS. 9a and 9 b are perspective views and FIG. 9c, an enlarged cross-sectional and plan view of a brittle substrate containing a micro-crack cut line;
FIG. 10 is a perspective view of the brittle substrate illustrated in FIGS. 9a-9 c following separation;
FIG. 11 is a perspective view of an exemplary apparatus for separating a brittle substrate consistent with the fourth aspect of the present invention.
FIG. 12 schematically depicts an exemplary apparatus for dual beam cutting of brittle materials;
FIGS. 13a-13 b illustrate an exemplary method of variable beam alignment;
FIGS. 14a-14 d depict variable energy footprint profiles achievable consistent with the present invention; and
DETAILED DESCRIPTION OF THE INVENTION
First Aspect of the Invention
FIGS. 15a-15 e graphically compare beam footprint profile to beam profile energy distribution and net energy distribution.
Referring to FIGS. 1 through 4, a first aspect of the present invention is illustrated in which a workpiece defined by a micro-crack cut line may be separated from a base plate material through the application of a temperature differential across the micro-crack cut line. In an exemplary embodiment illustrated in FIGS. 1 through 3, the principles of the present invention may advantageously be used to free a locked workpiece 12 from a base plate 10. The “locked” workpiece 12 results from a closed, or partially closed, geometry micro-crack cut line 14, which defines the workpiece in the base plate 10. The base plate 10 is a brittle material which may be, but is not limited to, mineral glass, vitreous silica, metal glasses, crystalline material, and ceramics. Preferably, the micro-crack cut line 14, defining the workpiece 12, is formed using ZERO WIDTH CUTTING TECHNOLOGY, OWCT«.
The locked workpiece may be released from the base plate 10 by heating the base plate 10 outside of the perimeter of the cut line 14. Heating the base plate 10 in this manner causes the base plate 10 to heat up faster than the locked workpiece 12, resulting in the expansion of the base plate 10. This expansion of the base plate 10 results in a broadening of the separation of the intermolecular split of the micro-crack 14. With sufficient separation of the micro-crack, the VanDer Waals and/or any electrostatic retaining forces between the base plate 10 and the workpiece 12 will be overcome, therein allowing the release of the workpiece 12 from the base plate 10. It should be understood at this point, that the magnitude of the temperature differential required to separate the workpiece 12 from the base plate 10, will vary according to a number of parameters. Exemplary controlling parameters include the relative size of the workpiece, the thickness of the brittle material, the composition of the brittle material, and therein the thermal, chemical, and mechanical properties.
FIG. 3 illustrates an alternate embodiment of a locked workpiece 12 defined by a drafted micro-crack cut line 14, wherein the perimeter of the cut line 14 on one surface 16 of the base plate 10, in the exemplary case the top surface, is offset outside the perimeter of the cut line 14 on the opposed surface 18. The temperature differential breaking of the drafted workpiece 12 is preferably effectuated by heating the surface 16 of the base plate 10 corresponding to the larger workpiece face 13.
The heating of the base plate 10 may be accomplished using a laser or other energy beam. When the brittle material of base plate 10 is glass, a 10.6 micron CO2 laser preferably is used due to its extremely efficient thermal effects on glass. A CO2 laser at this wavelength does not penetrate deeply into glass, thereby producing heat propagation from the laser incident footprint at the surface of the glass into the body of the base plate 10. This characteristic allows the propagation of the heat through the glass material to be controlled without the need to maintain extremely critical focal parameters. A higher frequency laser, such as a Nd:YAG laser, may be used; however, great control must be exercised over the focal point to prevent localized excess heat generation inside of the base plate 10. Internal heat generation, as caused by improper focal control and/or uncontrolled thermal penetration, may result in the formation of a stress plane parallel to the surface of the base plate and, possibly, uncontrolled or undesired splitting of the material.
In addition to the use of a laser, alternate methods of heating the base plate 10 may be employed to achieve temperature differential separation along a micro-crack cut line 14. Exemplary alternate heating methods may include, but are not limited to, radiant heating using quartz or infrared heating elements, heated gas jets, flame heating, etc. It is critical, however, when employing such alternate heating methods, that the application of heat be highly controllable with respect to the location of heating, the rate of heating, the intensity of heating, and the duration of heating. Regardless of the method of heating employed, the above described principles must be adhered to, specifically the heating must be sufficient to produce a sufficient temperature differential across, and thereby a widening of, the microcrack 14 without producing damaging stress planes within the base plate 10. Additionally, the end use of the workpiece 12 must be kept in mind with regards to the introduction of surface distortion or imperfection; change in character of the material, e.g., by annealing; and/or introduction of contaminants.
The expansion of the micro-crack cut line 14, and therefore the release of workpiece 12, is dependent, among other parameters, upon the magnitude of the temperature differential across the micro-crack cut line 14. It may, therefore, be readily appreciated that the release of the workpiece 12 from the base plate 10 may be facilitated, and/or accelerated, by reducing the temperature of the workpiece 12 relative to the base plate 10, thereby increasing the temperature differential across the micro-crack cut line 14 for a given base plate 10 temperature. Furthermore, the reduction in temperature, or chilling, of the locked workpiece 12, results in the workpiece 12 contracting away from the base material 10, further broadening the intermolecular split at the micro-crack cut line 14. Consistent with these concepts, by chilling the workpiece 12 in conjunction with heating of the base plate 10, the required temperature differential and resultant broadening or separation of the micro-crack cut line 14 may be achieved at a lower base plate 10 temperature.
Alternately, temperature differential across the micro-crack cut line 14 may be created to facilitate separation of the workpiece 12 from the base plate 10 solely by chilling the workpiece 12, i.e., without heating the base plate 10. The ability to separate the workpiece 12 from the base plate 10 at a reduced temperature yields several benefits. First, because it is not necessary to heat the base plate 10 to as high of a temperature, an economic benefit is realized from the decreased energy input requirement. The lower temperature of the base plate 10 also reduces the risk of damaging the workpiece 12, or the base plate 10, through unwanted localized annealing, or the introduction of internal stresses or cracks. Finally, chilling the workpiece 12 may also create a situation in which less laser beam control is required during the heating process because a more diffuse heating process may be utilized.
Chilling the workpiece 12 consistent with the above described principles may be achieved through a variety of methods. A first exemplary chilling method may comprise the application of a chilled gas or other fluid medium to the surface of the workpiece 12. Exemplary chilled fluids may comprise chilled air, dry liquid nitrogen, gasified liquid nitrogen, carbon dioxide or fluidized carbon dioxide “snow”. A second exemplary method of chilling the workpiece 12 may comprise the application of a low boiling substance to the surface of the workpiece 12. Upon contact with the surface of the workpiece 12, the low boiling substance vaporizes, thereby providing evaporative cooling of the workpiece 12. Consistent with a third alternate method, the workpiece 12 may be chilled using a thermoelectric and/or thermo-mechanical apparatus, by means such as conductive cooling. Appropriate cooling apparatuses may include a standard compressor and coil unit or a Peltier cooler.
The incorporation of a chilling process into the temperature differential separation of a workpiece 12 from a base plate 10 may be especially useful when releasing workpieces containing locked scrap 20. Referring to FIG. 4, an exemplary workpiece 12 is illustrated locked in a base plate 12 by a closed geometry micro-crack cut line 14. The locked workpiece 12 is further illustrated containing a scrap (or plug) 20 that is locked in the workpiece by a second closed geometry micro-crack cut line 22, disposed inside the first. By carefully coordinating a heating operation consistent with the present invention applied to the base plate 10, and further a chilling operation consistent with the present invention applied to the scrap 20, the workpiece 12 may be simultaneously separated from both the base plate 10 and the scrap 20 in a single unified operation. Accordingly, a multi-tiered temperature differential is established, such that the heating of the base plate 10 broadens the intermolecular split of micro-crack at 14, while the chilling of the scrap 12 causes the scrap 20 to contract away from the workpiece 12, therein broadening and separating the micro-crack at 22. While the above description pertains to a unified operation, it should be understood that within the context of the present invention, the sequential release of the workpiece 12 from the base plate 10, and the release of the scrap 20 from the workpiece 12, is similarly contemplated. Furthermore, it is herein contemplated that both a heating and a chilling operation may be carried out for each of the sequential steps.
- Second Aspect of the Invention
While the description above has been made in the context of freeing a locked workpiece, it will be readily apparent that the principles of the present invention are equally applicable to non-locked workpieces. Similarly, it will be appreciated that the invention described hereinabove is equally suitable for use with brittle materials that have been scribed or cut by methods other than with ZERO WIDTH CUTTING TECHNOLOGY, OWCT« or similar, including brittle materials that have been scribed using common mechanical scribing techniques.
Consistent with the second aspect of the present invention, a workpiece defined by a micro-crack cut line may be separated from a base plate of brittle material using a gas releasing tape. Referring to FIGS. 5a and 5 b, a brittle substrate 200 is illustrated comprising a micro-crack 202 disposed within the body of the brittle substrate 200. The micro-crack 202 delineates the desired cut path for separation of the brittle substrate 200 into a workpiece and a base plate. Adhered to the bottom surface 204 of the brittle substrate 200 is a gassing tape 206. The brittle substrate 200, with the gassing tape 206, is further retained to a vacuum table 208, therein supporting and immobilizing the brittle substrate 200 during a cutting operation. The incorporation of the gassing tape 206 between the brittle material 200 and vacuum table 208 provides two notable benefits. First, the gassing tape 206 holds the brittle substrate 200 firmly, including retaining any small pieces cut from the brittle substrate 200. Second, the gassing tape 206 provides additional material, in the form of the bulk of the gassing tape 206, thereby allowing the brittle substrate to be held gently, but tightly, during the vacuum process by distributing the stress of the vacuum more uniformly over the brittle substrate 200, acting as a stress normalizer. This last aspect is especially important when cutting small pieces or extremely delicate, i.e., thin, brittle substrates which would have a tendency to deform immediately over the vacuum holes, therein influencing the geometry of the brittle substrate 200, and its scribing characteristics. The process consistent with the present invention is preferably carried out with the brittle substrate 200 retained in the above-described manner.
The gassing tape is a special adhesive tape, known in the semi-conductor art, which may be present either as a single or double sided adhesive tape. When the tape 206 is heated slightly, it out-gasses a gaseous material such as nitrogen, carbon dioxide, etc. Alternately, the gassing tape 206 may be configured such that the out-gassing of the tape 206 is activated by exposure to radiation of a specific wavelength(s), for example infrared or ultraviolet. The tape's coating is so produced that the gasifying coating is “narrowly” sensitive to radiation. That is to say; the coating only out-gasses in the immediate area which is exposed to the reactive radiation “heat and/or heating”. Heating a narrow band or track on the tape will not result in the entire tape out-gassing, but only the specific area that is heated. This characteristic of the tape's coating gives it the ability to selectively stress the glass (brittle material) in the proper vector, at the same time the micro-crack is created by the laser beam/chill jet combination, thus separating the material “simultaneously” with the scribing operation.
Tapes of this variety are known in the art for such purposes as holding small parts together for processing. When the tape is caused to out-gas, the resulting evolved gas pushes or lifts adhered semiconductor parts, or other material, from the surface of the tape, thereby releasing it from the tape or producing a semi-released condition. As best illustrated in FIG. 5b, exemplary single-sided gassing tape 206 consistent with the present invention comprises a gassing adhesive 210 and a backing material 212, which may comprise, for example, a paper or polymeric backing material.
In addition to securing the brittle substrate 200 and normalizing stresses resulting from the vacuum table 208, the gassing tape may be employed to provide complete fracture, and/or separation, of the brittle substrate 200 during the cutting process. As illustrated in FIG. 6, when the brittle substrate 200 is traced with a laser to induce a micro-crack 202, the laser power may be controlled to provide sufficient heat transfer to the gassing adhesive 210 to produce the out-gassing thermal reaction in the tape 206. Alternately, when the out-gassing reaction is activated by radiation of a specified wavelength, the micro-crack 202 may be produced as a separate operation without producing out-gassing. The out-gassing reaction, and therefore the material separation, may be induced at a later time.
When the out-gassing reaction occurs, the majority of the gas generation takes place immediately underneath the footprint of the laser beam and symmetrically balanced between each side of the linear axis of the path of the laser beam, i.e., the evolving gas 214 builds under the micro-crack scribe line 202 that the laser beam creates when it scribes the brittle substrate 200. The generated gas 214 produces a line of highly localized pressure along the micro-crack scribe line 202. The pressure of the generated gas 214 under the micro-crack scribe line, and the adhesive force between the tape 206 and the brittle substrate 200 adjacent to the micro-crack scribe line, results in a force couple having the same effect as a mechanical bending couple about the micro-crack scribe line. As illustrated in FIG. 6, the resultant couple causes the brittle substrate 200 to break along the micro-crack scribe line 202, exactly following the laser path. However, as opposed to a normal breaking operation, because the adhesive character of the tape 206, aside from the out-gassed line under the micro-crack 202, remains intact, neither the brittle substrate 200 nor the cut piece move. The substrate, therefore, is completely broken and fully separated, but is still attached in the exact same orientation as prior to the cutting operation. This allows for the processing of very small pieces of brittle substrate 200, for example 4 mm by 4 mm squares and smaller.
Utilizing the method according to the second aspect of the present invention, many of the problems of handling high density dicing of brittle materials in the subcentimeter range, present in conventional cutting processes, may be overcome. According to conventional cutting methods, when a thin substrate is cut through the full thickness of the substrate, the resultant pieces may “float around,” thereby damaging themselves and/or interfere with subsequent cutting processes unless a sintered metal vacuum table, or a vacuum table having one vacuum hole per cut piece, is employed. However, even with such specialized vacuum tables, the substrate may deform, rendering high tolerance cutting nearly impossible. As previously described, the backing 212 of the tape 206 will aid in normalizing the stresses produced by the vacuum table 208, therein minimizing distortion of the substrate 200, and the adhesive character of the tape 206 will maintain cut pieces in position preventing edge damage. Subsequent to the cutting process, either the tape 206 or the brittle substrate 200 may be gently heated producing out-gassing to release the cut product, either in bulk or selectively. Alternately, because the adhesive 210 is pressure sensitive, the tape 206, with the substrate adhered thereto, may be gently rolled over a square edge or a pin grid to lift the cut pieces off of the tape 206 without damage.
- Third Aspect of the Invention
Furthermore, in addition to the above described benefits and characteristics, the incorporation of gassing tape 206 may be beneficially employed for use with high-speed cutting operations. Highly polished glass materials exhibit low coefficients of friction, and therefore, during high-speed cutting operations, the high rates of acceleration and deceleration of the cutting bed may result in sliding of the brittle substrate 200 on the cutting bed. Mounting the brittle substrate 200 on the tape 206 not only increases interface coefficient with the vacuum table 208, but the backing 212 of the tape 206 allows for a stronger bond than between the rigid polished substrate 200 and the surface of the vacuum table 208. In addition, the application of the tape 206 to the brittle substrate 200 protects the surface of the glass from any damage that may occur at the substrate/vacuum table interface.
As illustrated in FIG. 7, a system according to the third aspect of the present invention employs ultrasonic energy to separate a workpiece from a base plate of brittle material. This system advantageously may be employed both for extracting locked workpieces from a base plate of brittle material, or for effecting complete separation of non-locked workpieces from a base plate of brittle material. In FIG. 7, an apparatus for ultrasonic breakout is shown generally 300, comprising a base plate 302 of brittle material containing a workpiece 304 defined by a micro-crack cut line 306. The brittle material may be, but is not limited to, mineral glass, vitreous silica, metal glasses, crystalline material, and ceramic, and the micro-crack cut line 306 is preferably formed in accordance with ZERO WIDTH CUTTING TECHNOLOGY, OWCT«. The exemplary apparatus 300, consistent with the present invention, further comprises an ultrasonic horn 308, which is coupled to an ultrasonic generator 301, through a cable 315, and a transducer 310. The ultrasonic horn 308 is configured so that the horn face 312 exactly matches the workpiece 304 in geometry and contour. Horn materials can be of steel, aluminum or other material appropriate for the excitation frequency required for the material to be separated. When metallic materials are used for the horns, a flexible “rubber” or polymer seal 316 is needed between the horn and the workpiece to prevent the horn from damaging the material's surface, and to provide efficient coupling of the ultrasound energy to the workpiece. In order to provide for efficient energy coupling, the horn must completely surround the micro-crack in static release applications. The horn can follow behind the laser beam/chill jet track, but must cover both sides of the micro-crack transversely in dynamic separation applications. The breakout, i.e., the removal of the workpiece 304 from the base plate 302, is carried out with the horn 308 mechanically coupled to the workpiece 304, such as by physical contact between the ultrasonic horn 308 and its seal 316, and the workpiece 304. The ultrasonic generator 301 is energized, and ultrasonic pulses transmitted from the ultrasonic generator 301 are transmitted through the cable 315 to the transducer 310, and then to the ultrasonic horn 308, thereby exciting the workpiece 304 with ultrasonic vibrations. The ultrasonic excitation of the workpiece 304 occurs as a high frequency, very low amplitude oscillation/translation of the workpiece 304 within the base plate 302. The vibration of the horn 308 may act coplanar with the workpiece 304, i.e., side to side, or alternately may act perpendicular to the workpiece 304, i.e., up and down. Still alternately, the vibration of the horn may be multidirectional.
The workpiece 304 may then be extracted from the base plate 302 by applying a force normal to the surface of the workpiece 304. The normal force applied to the ultrasonically energized workpiece 304 may be provided according to a number of methods. The extraction of the workpiece 304 may be effected by a perpendicular motion of the horn 308, whereby the horn “pushes” the workpiece 304 through the base plate 302. Alternately, the energized workpiece 304 may be drawn through the base plate 302 by applying a vacuum to the side of the workpiece 304 opposite the horn 308. According to yet another method, the workpiece 304 may be extracted from the base plate 302 by applying a hydraulic or pneumatic pressure to either side of the workpiece 304. In a further alternate embodiment, a fluid may be used to apply hydraulic/pneumatic pressure to either side of the workpiece, for example from a gas jet disposed in the face 312 of the horn 308. Similarly, the ultrasonic horn 308 may comprise one, or several, vacuum ports in the horn face 312, such that vacuum force may be applied to the energized workpiece 304 enabling the workpiece 304 to be drawn from the base plate 302.
As an alternative to employing an ultrasonic horn for energizing the workpiece 304, a fluid medium may be ultrasonically energized and caused to impinge the workpiece 304. In a first exemplary embodiment illustrated in FIG. 8, a stream of gas, such as air, nitrogen, carbon dioxide, etc., is directed from a supply 320 and passed through a transducer 322 coupled to an ultrasonic generator 324. The ultrasonic generator 324, working through the transducer 322, energizes the stream of gas in ultrasonic pulses. The ultrasonically energized stream of gas is ducted through a nozzle 326 directed to impinge a workpiece 304 delineated in a base plate 302 of brittle material by a micro-crack cut line 306. Consistent with this embodiment, the energized gas stream may be used to serve the dual purposes of ultrasonically energizing the workpiece 304 and applying an extracting force on the workpiece 304. It will be apparent to one skilled in the art that, consistent with the above described principles, many fluids, including non-gaseous fluids such as water and other liquids, may be used to practice the present invention.
- Fourth Aspect of the Invention
The system consistent with this aspect of the present invention also allows the introduction of multiple control parameters, for example, ultrasonic frequency, ultrasonic energy, the ultrasonic energy footprint provided by the horn, etc., as well as mechanical, but zero displacement, force generated to push the workpiece through the base plate. Additionally, the speed at which the workpiece is pushed through the base plate may be regulated. The introduction of such control parameters allow very fine manipulation of the workpiece, reducing unacceptable levels of damage, or cycle time reduction, as might result when working with extremely small parts or sensitive surface coatings.
According to a fourth aspect of the invention, a system is provided employing a pressurized fluid for separating a brittle substrate along a micro-crack cut line. As illustrated in FIGS. 9a-9 c and FIG. 10, a brittle substrate 402, which may be, but is not limited to, mineral glass, vitreous silica, metal glass, ceramic, or crystalline material, comprises a micro-crack cut line 404 along which separation is desired. A nozzle 406 for dispensing a pressurized fluid is positioned above, and directed at, the micro-crack cut line. Separation of the brittle substrate 402 is achieved by forcing the pressurized fluid or gaseous fluid into and along the micro-crack 404, whereby the dynamic force produces a localized stress sufficient to propagate the micro-crack through the body of the brittle substrate 402 and fully separate the brittle substrate 402 along the micro-crack line 404. The nozzle should be placed such that the jet of fluid is directed into the micro-crack and between its edges. It can be at an oblique angle to the plane of the glass, but coincident with the scribe line. Given that the laser beam/chill jet is fixed (and in the first quadrant) and the workpiece is moving right to left under the laser beam, and that the separation nozzle is to the right of the chill jet (the chill jet being to the right of the laser beam), if the scribe line is in the X axis and the depth of the scribe is in the Z axis, then the nozzle can be at any appropriate angle between 0 and 90 degrees (1st quadrant) and 0 degrees (normal) in Y and displaced whatever distance is necessary from the micro-crack in Z. The Z axis displacement will be influenced by the nozzle's exit hole geometry, the spray pressure, fluid medium, etc.
In an exemplary embodiment consistent with the present invention, the micro-crack 404 is formed by controlled localized heating of the brittle substrate 402 using a laser and subsequent cooling of the brittle substrate 402 by a fluid cooling medium dispensed from a chill jet nozzle 406. The chill jet 406, utilized in the cutting process to effect the cooling of the brittle substrate, can be configured to additionally comprise a high pressure regulator for supplying compressed air in the range of 60-120 psi during the separation process. Preferably, the chill jet 406 is configured to selectively provide either the cooling medium and the high pressure air corresponding to the phase of the operation, i.e., cutting or separation phase. Utilizing the chill jet 406 for dispensing the high pressure air stream provides the added benefit that the chill jet nozzle 406 is articulated, enabling translation of the jet 406, and therein also the compressed air stream, along the path of the micro-crack 404. This characteristic eliminates the need for a second articulation apparatus. However, the high pressure air stream used for achieving separation of the brittle substrate 402 need not be as precisely focused as the stream of cooling medium used during the cutting operation, but rather only generally sprayed over the surface of the micro-crack cut line 404. With properly coordinated air pressure and angle of attack, e.g. about 30 to 60 degrees, preferably about 45 degrees, sufficient mechanical stress will be induced to propagate the micro crack 404 through the body of the brittle substrate 402 and separate the material.
In addition, when the brittle substrate 402 is held by vacuum on a vacuum table, the vacuum will permit enough slippage to allow the material to physically separate by several microns when the compressed air leaks underneath the brittle substrate 402. The full body separation induced by the pressurized air stream can separate the brittle substrate 402 far enough so that it is possible to visually inspect, and verify, that the separation has occurred properly before the cut workpieces are removed from the cutting apparatus. This verification may be achieved, for example, with automatic image recognition, as well as surface raster scanning phenomena. This degree of separation, and the verification facilitated thereby, are not available with current techniques which provide a separation of only a few angstroms.
- Fifth Aspect of the Invention
In an alternate embodiment consistent with the present invention, the stream of pressurized gas may be modified to incorporate the use of ultrasonic excitation of the gas stream, as shown in FIG. 11. Consistent with this embodiment, an ultrasonic generator 420 may be coupled to a transducer 422 capable of exciting a fluid medium stream in ultrasonic pulses. From the transducer 422, the stream of gas is dispensed through a nozzle 424 directed at a micro-crack cut line 404. When the gas stream is excited in this manner the pressure of the gas jet may be reduced, thereby decreasing the potential damage to thin or coated materials. Additionally, the ultrasonically excited gas stream may allow for an increase in the separation speed, thereby allowing higher cutting speeds and greater throughput.
The fifth aspect of the invention herein relates to a system of applying a plurality of separate or overlapped geometric energy fields to a brittle material to develop surface tension and internal stresses, which create a micro-crack through the body, thus causing partial body or full body internal separation of the material. This method can be accomplished in several ways by using several different kinds of hardware configurations, via the application of multiple laser energy footprints, i.e., energy fields, on a brittle material, modulated at different energy levels.
The exemplary embodiment of the invention described below embodies the use of two beams of laser energy for splitting brittle materials including, but not limited to, mineral glass, metal glasses, vitreous silica, crystalline materials, and ceramics. However, it should be understood that a single laser may be used in order to develop the dual beam system of the present invention. When a single laser is employed, the laser beam may be split into two beams that may be manipulated separately. However, the advantage of using two independent lasers is that one has total independent control over the power output, beam profile, energy distribution, and pulse characteristics of each laser beam and therefore, total control over the energy footprint of the laser energy beam pattern impinging upon the target brittle substrate. It should further be understood that multiple lasers, or multiple beams, may be used to lay down multiple overlapping or non-overlapping footprints of laser energy on the target substrate in order to create high intermolecular stresses, and therein result in a micro-crack fissure which may be propagated in a controlled manner through the material.
Referring to FIGS. 12 and 13a through 13 b, an exemplary apparatus is generally shown 500 comprising two laser sources 502 and 504. Each of the two laser sources 502 and 504 project a laser beam 506 and 508, wherein the central axis of the laser beams 506 and 508 are substantially parallel. The two laser beams 506 and 508 are directed through identical, but “mirror image”, optical paths using reflecting, zero phase shift mirrors 507 and 509. The two beams 506 and 508 are then directed to a target brittle substrate 510 by a movable prismatic, or “V” mirror (with zero phase shift) 512, such that the paths of the laser beams 506 and 508 are generally parallel. According to this configuration, the prismatic or V mirror 512 may be moved “in” and “out” along the objective axes of the laser beams 506 and 508, varying the incident footprint spacing of the two beams 506 and 508 on the brittle substrate 510 from a near completely overlapping configuration to a spaced apart configuration. When each of the independent beams 506 and 508 is configured to have an elliptical profile, the variable combination of the energy footprints, resulting in a composite footprint, may range from a single ellipse, comprising the two discrete but superimposed beams, to two completely separated, parallel ellipses, as illustrated in FIGS. 14a through 14 d.
While the exemplary apparatus 500 has been described in terms of two separate lasers 502 and 504 projecting two separate laser beams 506 and 508 which directed from a V mirror 512 to impinge the target substrate 510 along parallel axes, it should be understood that, consistent with the present invention, alternate configurations are contemplated to achieve the dual beam pattern. In a first alternate embodiment, the separate beams 506 and 508 may be projected to the target substrate 510 from separate aiming mirrors, rather than a common V mirror 512. Consistent with a further alternate embodiment, a common V mirror 512 may be employed, but rather than moving the V mirror 512 in and out to vary the incident pattern, the V-angle of the mirror may be manipulated to control the degree of overlap of the beams. Consideration must be made, however, for the fact that the power distribution of a beam having an oblique angle of attack relative to the target substrate will vary from the power distribution in a laser footprint having a perpendicular angle of attack.
The energy distribution in the laser beams may be configured to generally follow a Gaussian distribution pattern through the cross section of the axis of the beam, as illustrated for a single beam in FIG. 15a. In the case of ZERO WIDTH CUTTING TECHNOLOGY, OWCT«, the laser beam geometry may be an elongated ellipse or “knife edge” or variant thereof. The long axis of the beam is parallel to, and usually coincident with, the “scribe line”. Therefore, the energy density within the beam footprint on the target substrate will similarly be distributed in a Gaussian pattern about the major axis of the ellipse normal to the central axis of the beam, i.e., about the axis of approach of the beam. As seen in FIG. 15a, this Gaussian distribution, in an elliptical beam, exhibits a concentration of energy in the center of the beam and a depletion, i.e., falling off, of energy to each side of the beam moving away from the major axis. According to the Gaussian function, the energy intensity distribution in the beam(s) (in overlapping or partially overlapping beams), are accumulative as a function of the lateral positional displacement of one beam from the other. Therefore, the peak of the Gaussian net energy distribution curve, i.e., the energy density distribution of the composite footprint of two completely superimposed beams of identical power, is twice that of a single beam, as illustrated in FIG. 15b.
Referring to FIGS. 15a through 15 e, there is illustrated the relationship between the individual beam footprints, the individual beam energy distributions, and the power distribution of the composite footprint. When the two superimposed beams are separated laterally, that is the major axes are separated while maintaining the minor axes in alignment, the Gaussian peaks of each of the beams' individual energy distribution curve is displaced one away from the other and the concentration of the energy distribution of the two beams is split. This has the effect of changing the energy distribution on the brittle substrate target surface. The resultant change of the energy distribution, due to this manipulation, is related to the distance that the major axis of each elliptical beam is displaced, one from the other. Assuming a baseline reference of two completely overlapping elliptical beams having coaxial major axes aligned with the desired cut line, as illustrated in FIG. 15b, the further apart the beams are moved one from another, the lower the power concentration along the center of the composite footprint, i.e., the cut line, as seen in the progression from FIGS. 15b to FIG. 15e. Consistent with the accumulative characteristic of the beam energy, as the two beams are moved out of alignment, the energy distribution applied to the surface of the brittle substrate takes on a tri-modal profile. The separation of the two beams, and the resultant power profile, allows the composite power footprint laid down on a given material to be controlled with extreme precision. This composite power footprint generates the internal intermolecular stresses, which separate the material along the intermolecular boundaries.
With conventional micro-crack generation, the laser beam is focused such that the power footprint on the surface of the brittle substrate puts the proper amount of thermal energy on the surface of the brittle substrate and stresses it through expansion. When the gas or liquid chill jet is applied to the surface of the brittle substrate, the surface immediately contracts. This thermal differential creates stress vectors, which penetrate the brittle material and separate it to a typical maximum of approximately 80% of its full body thickness. By contrast, the invention herein permits one to “straddle” the cut line by developing a composite energy distribution, such as tri-modal power profile, or a “head and shoulders” profile. This distribution creates three varying thermal gradient zones.
While three separate laser beams may be used to produce the three zones, two lasers, having accumulative energy distribution profiles, advantageously may be employed to create the “head and shoulders” effect exhibiting a composite overlap of power in the Gaussian peak distribution point at the head and lower power fields to either side, separated by a specific distance that is a function of the overlap of the beams, as shown in FIGS. 15b through 15 e. The separation, or combination, of these beams results in an accumulative energy distribution profile that when taken into account, in terms of power applied to a specific area on the target, can place the desired amount of power at that point on the target, plus a specific concentration of power on each side. This then creates additional expansion on the surface of the brittle substrate on each side of the primary expansion. This additional expansion, on each side of the primary node, further stresses the primary node and causes it to split faster, i.e., or at a lower overall power level, and in some cases without the auxiliary chill jet being applied. This method is capable of creating much higher internal tensile forces in the brittle material, and may be used to fully separate materials such as glass, and accomplish full body separation of some materials 0.7 mm and below in thickness.
While the above description of the invention has been made with reference to energy beams having a Gaussian energy distribution, it should be understood that this is not required to achieve the benefits of the present invention. Alternate energy distributions may be employed to achieve the same general effect. For example, two laser beams having a uniform energy distribution, i.e., energy distributions in which the energy level is uniform across the width of the beam and footprint, may be employed to produce a stepped “head and shoulders” energy distribution pattern. It should further be appreciated that, similarly, various other energy distribution patterns may be employed to achieve energy distribution patterns analogous to the “head and shoulders” patterns, or other advantageous energy distribution patterns.
It is also possible, herein, to develop full body separation of brittle materials of 0.7 mm and above. The additional forces created by the overlaps of the beams may be manipulated through beam spacing (separation) into the optimum level or optimum geometric placement for the most advantageous heat distribution, which causes the optimum expansion for a specific type of brittle material being processed. Thus, the method herein may be applied to many different types of brittle materials and, therefore, provides flexibility with this method that obviates the limitations of the prior art.