US 3802974 A
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Description (OCR text may contain errors)
United States Patent 1191 Emmel METHOD AND APPARATUS FOR INSULATING ELECTRICALLY CONDUCTIVE ELEMENTS  Inventor: Leroy L. Emmel, 1800 Wallace Ave., Costa Mesa, Calif. 92627  Filed: Dec, 1, 1970 [211 Appl. No.: 93,949
52 us. c1 156/55, 156/52, 156/179,
156/282, 156/311, 156/312, 156/498, 156/555,174/117 F,174/117 FF, 161/143  Int. Cl. B321) 5/00, H011) 13/06  Field of Search 156/55, 52, 51, 47, 312, 156/311,282, 179; 174/117 F, 117 FF  7 References Cited UNITED STATES PATENTS 2,361,374 10/1944 Abbott 174/117 FF 3,513,045 5/1970 Emmel 156/55 3/1963 Gore 156/179 X 1 1111 I 3,802,974 1451' Apr.9, 1974 Primary Examiner-George F. Lesmes Assistant E.vanu'ner-Lorraine T. Kendell [57 ABSTRACT A method and apparatus'for insulating a plurality of electrically conductive elements and to produce electrical cable where the method includes heating the unformed insulative material and conductive elements, applying pressureand simultaneously removing heat with a pair of rollers at a relatively low temperature and applying pressure and heat to preselected regions only of the insulative material. The method and apparatus further allow preselected portions of the cable to be unbonded so as to facilitate access to the conductive elements by simply interrupting the application of pressure to the preselected portions. The heat, press and cool and press and bond method may also be accomplished in a step and repeat process using presses to insulative flexible circuits. The above method and apparatus provide more reliable bonding at an accelerated rate of production.
16 Claims, 15 Drawing Figures PATENTEBAPR 91914 SHEEI 1 0F 6 lgl PATENTEDAPR 9 1914 sum 5 OF 6 Ala/011 am/ y 772x01;
A/eakwr/rm Z $4 in V6 WLl Z u m .SHLEI 8 OF 6 I www Q Z M y PATENTEDAPR 9 m4 3 R N BH 1 METHOD AND APPARATUS FOR INSULATING ELECTRICALLY CQNDUCTIVE ELEMENTS BACKGROUND or THE INvENTIoN a more economical manner, for facilitating exposure of the electrically conductive elements to allow electrical contact to be made, and for bonding flexible electrical circuits.
2. Description of the Prior Art Electrical cable is simply a plurality of electrically conductive elements aligned parallel one another in a predetermined spacing encapsulated (except for the ends of the cable) with synthetic resin electrical insulative material. Physically, the cable appears as a thin flexible strip of synthetic resin having small embedded metallic wires.
Efforts -to make electrical cable less expensively, quicker, and more reliable have spawn many methods and apparatus exemplified by the prior art, One such method,sometirnes referred to as the hot-roll method, comprises locating two grooved rollers closely adjacent one another, heating the rollers to a temperature to cause fusion of the synthetic resin insulative material used and passing a plurality of conductive elements sandwiched between insulative strips to achieve a bonded electrical cable. Another method, such as exemplified by US. Pat. No. 3,082,292 to R. W. Gore, comprises moving the sandwich of electrical wire and insulator between two grooved rollers and then passing the formed but unbonded cable to an oven to achieve bonding. Yet, another method as exemplified by US. Pat. No. 3,531,045 to L. L. Emmel et al., commonly referred to as the chill-roll process comprises passing the layered electrically conductive elements and insulative material through a heating device to heat the entire un bonded cable to well over the temperature necessary for bonding and then passing the cable through two grooved rollers which are at a temperature below that of bonding.
Each of the prior art processes provided an unreliable bond; that is, fusion of the abutting surfaces of the insulative material could not be reliably accomplished without causing substantial difficulties with other portions of the cable. For example, some of the methods required heating to a substantiallyhigher temperature than necessary to cause fusion to compensate for heat loss before maximum pressure is brought-to bear to cause bonding; this excessive heat frequently oxidized for use, the insulative material tends to recede from the conductive elements leaving the ends of the conductive elements undesirably exposed. A further problem with overheating occurs after pressure has been released; if the cable is still above fusion temperature, there is a tendency for the insulative material to deform to its original flat shape and unbond. One solution to the latter problem is to use more adhesive material to retard undesirable deformation. However, this results in a cable which is substantially thicker than need be and which concurrently increases material expenses.
Another major difficulty facing the electrical cable industry and its customers is quickly, economically and reliably exposing the electrically conductive elements of a bonded cable to allow electrical contact to be made. Present methods include grinding away the insulative' material in order to expose the conductive elements; this frequently causes damage to the conductive elements since it is difficult to accurately control the grinder. Another method includes the application of heat to the insulative material to allow its separation from the conductive elements; this causes deformation of the cable, oxidizes the conductive elements and enhances the chance of cable delamination. Neither of the above methods are suited for fully automatic operation since both methods disturb the positioning of the conductive elements which is critical for automatic connection to another electrical element such as an electrical connector having multiple electrical contact positions. For example, a three inch wide cable may easily contain sixty electrically conductive wires in alignment, each wire parallel to the others. Position tolerances are i0.0005 inches. Grinding, heating or cutting through insulation which may be 0;0O5 inches is exceedingly delicate and difficult.
Still another problem faces the flexible circuit industry. A flexible circuit may be defined as a specifically designed layer of electrically conductive material bonded between two layers of insulative material. Insuring a reliable bond between the two insulative layers and achieving this bond in a relatively short time span has always eluded solution.
- SUMMARY F THE INVENTION A solution to all of the mentioned problems is accomplished by the present invention which provides a 1 method for insulating an element comprising the steps the electrically conductive elements thereby making future electrical contact difficult. Excessive heat creates the generation of excessive amounts of gas causing gas bubbles in the cablejStill another problem related to internal stresses formed in the insulative material during the insulative materials manufacture. When heated, the areas, representing overly stressed and'normally stressed regions, expand at different rates causing wrinkles in the insulative cover. Removing wrinkles re quires critical machine adjustments and excessive machine tension applied to the insulative material during the cable-making process. Upon cutting such a cable of providing an element'positioned between layers of insulative material; moving the element and the insulative material relative a first pressure station; selectively applying pressure to form the insulative material about the element; moving the formed insulated materialand the'element relative a second pressure station; and se lectively applying pressure and sufficient heat to the insulative material to bond the layers. The invention further includes a method for simultaneouslyinsulating a plurality of elements including the-bonding of layers of insulative material about the plurality of elements with heat and pressure and for facilitating exposure of the elements at predetermined locations wherein the improvement comprises interrupting the application of pressure to predetermined locations of the insulative material. I
In addition to the methods, the invention includes the apparatus for accomplishing the methods; that is, apparatusv for manufacturing cable as well as apparatus for manufacturing flexible electrical circuits.
It is a general aim of the presentinvention to provide a a methodand apparatus for achieving a superior bonding of insulative material'about' an interior element. Other aspects of the presentinvention include bonding electrically insulative material about an electrically conductive element, the provision of a method and apparatus for reducing the heat requiredto achieve necessary bonding, for reducing the stress induced in the electrically insulative material, for eliminating the need to finely adjust the apparatus in response to excessive stresses in the insulative material, and for cooling the bonded material quickly so as to provide a permanent form. I 1 A corollary aim of the'present invention is to provide a'method and apparatus for increasing the'speed of cable manufacture in one embodiment and in another embodiment to increase the speed of flexible circuit Another object of the present inventionis to provide Yet, a further aspect of the present invention is to provide a reliable and inexpensive manner for bonding flexible circuits.
Other objects and advantages of the invention will appear from the following description taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of a method and an apparatus for simultaneously insulating a aligned elements to produce a cable.
' FIG. 2 is an enlarged partly modified diagrammatic I view. of a portion of the embodiment shown in FIG. 1.
- FIG. 4 is an enlarged diagrammatic elevational view taken within the'circle 4-4 of FIG. 2; FIG. 5 is an enlarged elevational sectional view taken along line '55 of FIG. 2.
plurality of e FIG. 6 is an enlarged diagrammatic elevational view taken within the circle 6-6 of FIG. 2. FIG. 7 is a graph illustrating the temperature of the insulative material of a prior art process.
FIG. 8 is a graph illustrating the temperature of the insulative material of another prior art process.
FIG. 9 is a graph illustrating the temperature of the insulativematerial of the present inventive method.
FIG. 10 is an enlarged-diagrammatic view of a portion of the view shown in FIG. 1 illustrating the forming and bonding rollers in a disengaging position.
FIG. 11 is an elevational sectionalview of the unformed and unbonded cable taken along line l1"l1 of FIG. 10.
FIG. 12 is a diagrammatic perspective view illustrat-' line 14' 14 of FIG. 13.
, 4 FIG. 15 is an enlarged diagrammatic view of a multilayer circuit between etched rnold plates.
DESCRIPTION OF THE PREFERRED i EMBODIMENTS While the'present invention is susceptible of various modifications and alternative constructions,illustrative embodiments are shown in the drawings and will herein be describedi'n detail. It should be understood, however, that it is not the intention tolimit the invention 'to the particular forms disclosed; but, on the contrary, the intention is to cover all modifications,equivalents and alternative constructions falling within the spirit and scope of the invention as expressed in' the appended claims.
The product for which the present method and apparatus are directed may be generally described as a plurality of aligned'electrically conductive elements insulated with a suitable synthetic resin material to'provide a compact, flexible cable. Thisel'ectrical cable has wide usage in compact systems; the cable, or harness as it is often referredto, acts to provide electrical paths between such components as printed circuit boards and provides a compact and light-weight element compatible with small components toform a very compact system. a j
Referring to FIG. l,'a number of electrically conductive elements 10 are brought together andaligned one from another by being passed around idler rollers or drums 12, 14, l61and 20. It is preferable that the rollers 14 and 20 have grooves 'or recesses located in their outer surfaces inorder to provide alignment guides for the conductive elements. The rollers are located so as to provide with drive rollers 30 and 31 a constant tension on the conductive elements which enhances alignment. Two oppositely disposed supply spools 22 and 24 are provided to supply an upper layer 26 of insulative material and a lower layer 28 of insulative material, respectively, so as to sandwich the conductive elements.
The .insulative materials are commonly referred to as webs. The lower layer 28'passes between a driveroller 23 and an idler roller 25 which are in pressure contact while theupper layer 26 passes betweena drive roller 27 and an idler roller 29 which are in pressure contact. Toinsure tension on the upper and lower layers of the insulative material,'the velocity of rotation of the drive rollers 23 and 27 is somewhat less than the velocity of rotation of the drive rollers -30 and 31 Tension is easily adjusted by simply altering the relationship of the rotational velocity of the drive rollers 23 and 27 and the rotational velocity of the drive rollers 30 and 31. All of the elements mentioned thus far are suitably attached to a frame 32 (which is illustrated in diagrammaticoutline form" using phantom lines) as are storage spools 33, 34, and 35. 1' A major disadvantage of all prior art methods and apparatus has been the reliability of the'bonding'of the insulative layers for encapsulating the conductive elements. Often, for. example, a cable is formed where the two layers of insulativematerial are brought together and-apparently attached only to become delaminated 7 upon handling. In accordancewith one of the impor-' tant aspects of the present invention, a cable is formed -in-whic h the two layers of insulative material are completely bonded so as to entrap the conductive elements to provide a flexible cable which is permanently formed. Referring once again to FIG. 1, the aligned conductive elements are passed through a heater 36 which is connected to the frame-32. The conductive elements having the upper layer 26 of insulative material and the lower layer 28 of insulative material in alignment then move througha second heating station by being passed through a heater 38 which .is attached to the frame 32. Each of the heaters are at a temperature to warm the conductive elements and the insulative material so as to increase the plasticity of the insulative material; nevertheless, the temperature is below that which would cause the insulative material to bond. During this time the plurality of conductive elements are in a parallel alignment relative one another as well as in planar alignment and are aligned relative the two layers of insulative material. The heaters 36 and 38 may comprise planar infra-red radiant heaters.
It is reiterated that the deficiencies in the prior art generally center about the supply of heat to the cable and proper timing-of the application of pressure. Thus, in the hot-roll process, either the heat is insufficient to cause bonding because forming and bonding were performed simultaneously or too much heat was supplied so that the cable departed the location of pressure application excessively heated thereby allowing the deformation of the cable to its original condition. With other processes, excessive heat application caused excessive generation of gas which frequently formed undesirable gas pockets within the bonded cable. Further, the excessive application of heat causes the conductive elements to form an oxidation coating which requires removal before a reliable electrical connection can be made between the cable and another part of the system in which it is employed. Still another problem is that the insulative material is frequently received with high 50 each connected to a heat source and control unit 49.
Referring to FIGS. 3 and 5, the outer surfaces of the rollers are shown in more detail. For example, the roller 44 includes an outer surface having alternate ridges, such as ridges 64, 66 and 68, and recesses such as recesses 70 and 72; in a like manner, the roller 46 has an outer surface having ridges 74, 76 and 78 with alternate recesses 80 and 82. The roller 48-has an outer surface having alternate ridges 64a, 66a and 68a and" recesses 70a and 72a; the roller 50 corresponds to the roller 48 with ridges 74a, 76a, 78a and recesses 80a and 820.
To ensure a reliably bonded and permanently formed cable, the unformed cable is bonded in a two-step operation. First, the unformed cable moves between the rollers 44 and 46 of the forming station 42, FIGS. 2 and 4 and then between the rollers 48 and 50 of the bonding station 42, FIGS. 2 and 6. Returning once again to FIG. 3, the forming station rollers'44'and 46 use'the conductive elements, as exemplified by the conductive elements 10a and 10b, as mandrels around which the two layers of insulative material 26 and 28 are cold formed. Prior to entering the forming rollers 44 and 46, the unformed cable was heated by the heater 38 to a temperature to increase its plasticity but below the temperature at which the insulative material fuses.
stress areas formed during its own manufacture. When heated, the high stress regions have a different rate of expansion than adjacent regions which causes excessive wrinkles at locations along the insulative material. Thus, it becomes necessary to critically tune the apparatus forming the cableby aligning to a high degree of precision the shafts for the supply spools and the rollers and increasing the tension on the preformed cable. When the cable is formed and severed for application, the increased tension used during manufacturing causes the insulative material to constrict once the tension is relieved so as to expose, undesirably, the conductive elements at the point of severance. Wrinkles also leave'air pockets and folds in the final cable causing thecable to be rejected. Finally, the above difficulties require the speed of processing the cable through the apparatus to be relatively slow, thereby increasing manufacturing time and expense.
In accordance with an important aim of the present invention, a method and apparatus is provided which reduces the amount of heat necessary to cause bonding, reduces stress in the insulative material,-eliminates the need 'for fine adjustment of the machine, increases the speed of production and substantially increases the reliability of the bond achieved. I
To ensure proper and reliable bonding, the unformed cable 39 of the present invention is moved through a forming station and abonding station 42. The forming station 40 includes two adjacent rollers 44 and 46, or nips as they are frequently referred to, each connected to a heat removal and control unit 45. The bonding station 42 includes two adjacent rollers 48 and When the unformed cable passes between the rollers 44 and 46, which applies pressure selectively to the regions of the insulative-material between the locations of the aligned conductive elements, that is the ridges of the rollers aligned between the conductive element 10- cations, there is a .stretching of the insulative layers in the region where they pass over a conductive element while in the regions between the placement of the conductive element there is a squeezing of the insulative material causing it to cold flow about the conductive elements. It is important to note that prior to the forming station, the unformed cable was at an elevated temperature to increase its plasticity; the forming rollers 44 and 46, however, are at a lower temperature so as to cool the cable before it is moved to the bonding station. When pressure is applied by the forming rollers there is a desired cold flow of the insulative material about the conductive elements causing the insulative material to form in the desired manner; at the same time, there is a heat transfer (see FIGS. 3 and 4) from the unformed cable to the rollers causing the insulative material to cooland stabilize 'in the formed configuration. Thus, upon passing beyond the forming rollers 44 and 46, the cable which will be referred to as formed cable 39a, FIG. 1, appears visually to be finished bonded cable; however, as noted'in FIG. 3, abutting surfaces 92 and 94 of the upper and lower layers of insulative material, respectively, are still clearly distinguishable.
It is to be understood that the heating step accomplished by the heater 38 may be dispensed with when using some insulative materials which are readily formed at room temperature; however, with the more popular insulative materials, it is contemplated that a heating step is desirable. The heating step not only increases the plasticity of the insulative material, but also serves to relieve any residual stresses present from the insulative materials manufacturing process. I
In accordance with another important aspect of the present invention, the relatively cool formed cable is heated to bonding temperature at preselected locations only so as to minimize the total amount of heat transferred 'to' the cable. Thus,
all the disdvantages in the prior art dueto excessive heating have been obviated. The bonding rollers are identical to the forming rollers, except that the bonding rollers are at a temperature at or slightly above that needed to bond the insulative material. Because only the ridges of the rollers such as ridges 64a, 66a, 68a, 74a, 76a and 78a, FIG. 5, come into contact with the insulative material (the recesses may be 0.005 to 0.010 inches fromthe insulative material) the 'heat of bonding is essentially transmitted through the ridges to'the insulative material in the location where contact is made. For purposes of'illustration, the locations are designated 91, 93 and 95. The transfer of heat is diagrammatically illustrated by wavy arrows. Any gas pockets remaining after the forming station are closed at the. bonding station. The combination of heat sufficient to cause bonding and pressure assuresa complete bonding of the two layers of insulative materialso that the abutting surfaces of the formed cable are no longer distinguishable. Y
lt is important, of course, that the formed cable be raisedto the bonding temperature by the time maximum pressure is applied to the cable. Referring to FIG'. 6',it is seen that because of the radial dimension of the rollers, there is contact between the insulative material and the rollers prior to the time that full pressure is applied; full pressure is applied to the insulative material at'a location which is coincident with a line representing the shortest distance between the centers of the rol- I lers 48 and 50 and depicted in FIG. 6 by the letters P and thev'ertical arrows (see also FIG. '4). Since the thickness of the insulative material ranges from 0.002
' perature. To accomplish rapid cooling, the formed ,ca-
ble, asfme ntion'ed, is cooled by the forming rollers 44 and 4610 arelatively low temperature. The cable is heated by-the bonding rollers only in the locations 91, 93 and 95, FIG. 5, establishing a substantial tempera- I ture gradient over the width of the cable causing a'heat flow from the highly heated regions to the cooler region's which are occupied by and immediately adjacent the conductive elements. Since good electrically conductive elements are generally also excellent heat con-.
ductive elements, there'isa rapid dissipation of the heat by conduction through the conductive elements as well as dissipation of heat throughthe immediate environment by the .usual convection process; thus, very rapid. cooling is affected immediately upon leaving the high temperature bonding rollers so that the bond and the formation of the cable is permanent. 'By way of example, it is'contemplated that the locations 91, 93 and 95 v selectedlocations only.
'duction per unit of time. It is to be appreciated that the vantages of excessive gas, oxidationof the conductive elements and redeforination after removal'of the bonding pressure. To emphasize the differences between the priorart and the present invention, reference is made to FIGS.
.7, 8 and 9 illustrating a heating curve for the insulative material during three manufacturing processes.
The hot-roll process, FIG. 7, shows by the curve 200 the insulative material is heated above the bonding temperature at the hot roller station 202 and has a very slow heat dissipation rate as exemplified by the curve portion 204. If the temperature is above bonding after leaving the rollers, deformation is-likely to occur. The
chill-roll process, FIG. 8, shows the curve 206 substan? tially above the bonding temperature line 208 so as .to allow forming and bonding in the cool roller station 210. The disadvantages of excessive heating have already been mentioned. The'present method, FIG. 9, shows the curve 212 well below the bonding temperature line 214 during forming at the cool roller station 216 and only slightly above the line 214 at the bonding station 218. It is to be noted that in the hot and chill-' roll processes, the insulative material is heated along its entire'width above the bonding temperature, while in the present method, only a relatively small portion of the cable is heated to bonding temperature. Hence, there is a very rapid drop in temperature after passing the bonding station 218. Therefore, not only does the concept of forming and bonding at two separate stations providea superior result, but in more detail the superior results are achieved by'forming about the conductive element so as to use them as mandrels and then, cooling prior to bonding followed by bonding at By wayof example,
ethylene-propylene (FEP) has been found to be a suit-. able synthetic resin insulative material with the FEP havinga temperature of fusion of about 530 F. As mentioned, the material is produced in thicknesses for the purpose of forming cable between 0.002 to 0.010 inches. It is contemplated that the heater 38 will heat the unformed cable to a temperature of about 450 F to cause desired plasticity of the TFE while the rollers 44'and 46 are maintained at a temperature of about 100 F. Thus, the formed cable will be at some temperature close to that of the rollers 44 and 46.The bonding rollers 48 and 50 are maintained at a temperature of about 550 F so as to provide sufficient heat for fusion will occupy approximately 30 percent of the width of the cable so that only 30 percent of the cable receives heat sufficient for bonding. Because of the low total amount of heat applied for bonding and because of the' forming step, there is less insulative layer distortion and no conductive element position shifts. Hence, a wider cable may be processed achieving a greater proof the FEP coatings. The process proceeds at about 40' feet per minute. By way of comparison, the FEP coated TFE is a milky blue color at 530 F, tan at room temperature and transparent at 640 F. In the chill-rollv process described hereinabove, it"was necessary to heat the material to the transparent condition in order to achieve a suitable bond. It is understood that TFE will not fuse to itself if its temperature is increased; thus, a coating of FEP is necessary to achieve bonding. l-low- Teflon. polytetrafluoroethylene (TFE) material coated 'with fluorin'ated I 9 ever, if FEP alone is used as the insulative material, heating to about 530 F will cause fusion andthus bonding when pressure is applied.
The forming station and bonding station rollers are of identical design so as to be interchangeablejeach has removable sleeves to provide the desired groove profile. The rollers may be made of aluminum with stainless steel sleeves and with a small core for the insertion of a resistance rod heater. It is to be understood that only one roller of each pair may be'grooved, i.e'., have alternating ridges and recesses depending upon the-insulative material used. Further, there may be a temperample, it may be necessary for only the roller 48 to be at or .above bonding temperature to cause reliable bonding. Whether or not both rollers need have the same temperature may depend upon the velocity of the process and the insulative material used. It is to be understood further that the conductive elements may be round or generally rectangular in cross section or any other convenient shape without detracting from the invention herein.
- apply to electrically insulative, thermally insulative or force (impact) insulative for example.
The bonded cable 39b proceeds to a'cooler 100' which may be a roller at a low temperature before proceeding to a slitter 102 which may be provided to cut the bonded cable along a direction parallel to the longitudinal axis of the conductive elements to form whatever width cable is desired. Referring to FIG. 2, a modified apparatus is illustrated in phantom line including a conveyor belt 140 to support a cable which is weak in tensile strength. The belt carries the tensile load. Such a fragile cable is one with relatively small conductive elements which may have the insulative material formed and bonded by grooved upper rollers only. I
'In accordance with another important aspect of the present invention, provision is made for facilitating exposure of the conductive elements to allow an electrical connection to be made withthe cable. As mentioned hereinabove; various methods exist for exposing the conductive elements of a bonded cable. The present invention contemplates passing preselected portions of the unform ed cable 39 through the forming sure and/or heat. This is accomplished by mounting the rollers 44, 46, 48 and 50 to links 110, 112, 114 and 116, FIG. 10, respectively, which in turn are pivotally mounted about shafts 118, 120, .122 and 124, respec-;
tively. Thus, the rollers are movable from the position shown in FIGS. 1 and 2 to the position shown in FIG. 10. Movement of .the rollers from one position to another can be accomplished manually orv by a motor snd timing mechanism 126. The way in which bonding is prevented may be accomplished by any one of the following: pivoting the bonding rollers 48-and 50 so as to prevent actual bonding; pivoting the forming rollers 44 and 46 so as to prevent-an optimum bond; or preferably operating the forming station rollers and the bonding station rollers in sequence so that the preselected porature differential between each roller of a pair; for ex- -and/or bonding stations without the application of pres-' tion is neither formed nor bonded. When working in sequence, one pair of rollers is always closed to insure alignment of the conductive elements. Referring to FIG. ll, the insulative layers 26 and 28 remain in a sandwich about the conductive elements 10a, 10b, 10c, 10d and 102 without bonding and formation taking place.
Referring now to FIG. 12, exposure of the conductive elements 10a, 10b, 10d and 10e is easily accomplished by cutting through the layers 26 and 28 of the insulative material in that region which has not been bonded. It has been found that the unbonded regions, perhaps several inches in length, will balloon outwardly so that cutting and removing of the insulative material is easilyaccomplished without damaging or misaligning the conductive elements. The insulative material may be folded back from the cut to form flaps 130, 132, 1134 and 136 or the flaps may be suitably cut away. Another major advantage of the present method and apparatus is that accomplishing the preparation of the cable'to allow easy exposure of the conductive elements does not require stopping the cable manufacturing apparatus nor in any other way disrupting the process.
In accordance with yet another important aspect of the present invention, provision is made for substantially increasing the rate of production of flexible electrical circuits and for providing a reliable bond between various layers of insulative material. A flexible circuit is somewhat analogous to electrical cable in that the flexible circuit generally comprises a substrate layer or film of insulative material bonded or laminated to a layer or film of electrically conductive material. The conductive material is covered with a second layer or film of insulative material; it is to be understood that .an alternating pattern of mutiple conductive layers and insulative layers may be formed. The process of making a flexible circuit includes attaching the substrate layer of insulative material and the conductive layer in a suitable fashion followed by the removal, selectively, of conductive material to provide a preselected circuit designed. The removal process often is accomplished by chemical etching and is well known in the industry. After the circuit has been formed by the conductive material, the cover layer of insulative material is then attached. It is the attachment of the cover layer of insulative material which is causing problems by requiring an excessive amount of equipment time to accomplish and by not achieving a reliable result.
One prior art method used to bond the cover layer of insulative material to the remainder of the circuit is to sandwich the material in a press, heat the press so as to apply the proper bonding temperature and pressure and then cool the entire press so as to allow the circuit to solidify. After the cooled circuit is removed, the entire press must then be reheated forthe next cycle.
Presently, if the insulative material is FEP such a cycle may-take upwards of 25.minutes.
Referring now to FIGS. 13, 14 and 15, the concept of the method described hereinabove with regard to the manufacture of electrical cable is adaptable to the manufacture of flexible circuits. The new method would comprise placing a layer of insulative material and a formed circuit pattern bonded to a substrate on t a conveyor belt 200 having small pegs 202 for locating the various stations of the process; that istthe 'belt moves from station to'station with stops at each station "fora predetermined period of time. First, the flexible "circuit is'positioned within a heater 210 for increasing theplasticity of the insulative material much in the 'sa'me fashion as the'heater 380i FIG. ll increases-the plasticity of the insulative material of the cable. Se-
The temperature of the press 212isbelow thatof the unformed circuit. When the press is closed, the insulative material is cold formed about the conductive mate- .tola' bonding station, which includes a bonding-press 2 18 having an upper platen"219 ,"up'per etched mold plate22l), lower platen 221 and lowe'retched mold plate 222. The press is at a temperature above .that of bonding of the insulative material. The press is closed to applythe pressureand heat-sufficient to cause bonding in-a fashionanalogous to the operationof the bondcondly, the heated flexible circuit is moved'to a forming station comprisinga press 212 having-an upper platen 213 and a lower platen 214. An etched moldplate 2151s" attached to the upper platen while an etched mold'plate' 216 is attached to the lower platen.
mg rollers 48 and 50 of FIG. 1.- The flexible circuit; is y then moved to a trimming station which includes still another press.223" having specially formed heads 224 and 225 to trim'the flexible circuit in the desired fashion. The-flexible circuit 'which has been trimmed is moved-beyond thetrimming station to allow its removalfrom} the conveyor belt. Hence, a rapid but reli 'ablebond .is achieved'betweenthe insulative-layers of the flexible circuit. j I Y Referring now'toFIG. 14, .there is shown in morede- .tail'a crosss'ec tion of the forming station press 212. The
flexible circuit-232 is positioned on-the conveyor belt 200 located" bytwo oppositely disposed series of pins 202, and is comprised of asubstrate layer 234 to which is bonded a layer of conductive material 2 36.'A cover layer ofinsulative material240 is'sandwi'ched between the: conductive'material and the conveyor belt. The
cuit is'cold formed while at the same time'being cooled. At the bonding station at least the lower platen 221 is a heated to a temperature slightly to cause-bonding.
above that necessary- Referring now to FIG. 15, a multilayer flexible circuit is illustrated between an upper mold plate 250 and a lower mold plate 252, both of which are etched to have ridges such asjthe ridge 254 ofthe upper plate and ridge2 56 ,of the lower plate. The circuit includes three layers of insulative material, a bottom layer 258, amid dle layer 260 and an upper'layer'262. Located to each side of the middle layer 26.0 are two metallic electrically conductive elements 264 and 266. As shown,
the middle layer 260 at the region designated 270. The
etched mold plates 250 and 252 are designed -to have properly dimensioned and "located ridges aligned with the regions-268,270fonce again it is appreciated-that the process of heating to relieve stresses,cold forming to provide coldflowof the material and to facilitate heat conduction'afte'r the bonding stage, followed by selective heating to the temperature of bonding is accomplished easily and quickly. As with the cable method, the electrically conductive layers 264 and 266 act as heat conducting path to cool the circuit-as soon as bonding has been accomplished'to lower the temperature. and prevent deformation.
1. A- method forinsulating an'element comprising the steps of: I
providin gan elementpositioned between layers of insulative material;
ement positioned therebetween relative a first pressure station} 1' v I selectively; applying pressure to form'said layers of insulative material about said element substantially maintaining ,a-distinguishable and separable inter face between'said layers; v I moving said formed insulative material and said ele-' ment relative a secondpressure station; and: 1 selectivelyapplying pressure and sufficient-heat substantially simultaneously to said formed insulative material. to bond said layers; r
2. A method as claimed in claim 1,-further includingv ".'the step of: 1 t
heating said layers of insulative material with said element positioned therebetween prior to said step of .selectivelyapplying pressureat said first pressure station to facilitate formation of said insulative ma terial but insufficient to cause bonding ofsaid inslu .lative materi ali and a 3 wher ein said 'step of selectively z'said fi r's't'pressure station includes cooling said in;
sulative materialand element. 1
. 3. A method as claimed in claim a mmafii said [elementis an1emcai y i conductive element I.
and said insulative material isan electrically insulative materialiand I furtherincluding heating said element prior to the 1 step of providing an element positioned between 1 layers of insulative material. 4. A'method as claimed in claim 1, wherein:
' said element comprises-a plurality of elongated parallel aligned,electrically conductive elements. 5. A method as claimedin claim 4, wherein said'step of selectively applying pressure and sufficient heat substantially simultaneously includes applying pressure and sufficient heat substantially simultaneously topredetermined regions only of said insulativematerial.
there are gaps betweenthe conductive elements which ideally shbuldbe enclosed with ansi'nsulative' material to' prevent possible short ,circuiting. This is accom-,
- plished by forming and then bonding the upper layer 262'to themiddle layer 260 at a region-designated 268 while at the same time bonding the lower layer 258 to 6. A method as claimed in claim 5, wherein saidstep of applying pressure and sufficient heat comprises applying said pressure and said heat substantially simultaneously to the insulative material between said parallel aligned conductive elements. 6 I Y 7. A method as tate formation of said insulative material at said moving said layers ofinsulative material with said el-" applying pressure at claimed in claim 6, including the step first pressure station but insufficient to cause bonding of said insulative material; and
wherein the step of selectively applying pressure at said first pressure station includes simultaneously cooling said insulative material and conductive elements to facilitate heat dissipation from said insulative material after moving away from said second station.
8. A method as claimed in claim 7, wherein;
said insulative material are elongated strips;
said first pressure station comprises two rollers atleast one of which. having an outer surface comprising alternating recesses and ridges;
said second pressure stationcomprises two rollers at least one of which having an outer surface comprising alternating recesses and ridges; and
the heat transfer occasioned by said heating and said cooling at-said second and first pressure stations, respectively, includes transmitting heat through said ridges of said rollers to and from said insulative material, respectively.
9. A method isclaimed in claim 1, wherein said element comprises a predesigned electrically conductive layer bonded to a layer of insulative material.
' 10. A method as claimed in claim 9, wherein said step of selectively applying pressure and sufficient heat includes applying sufficient heat to predetermined re,- gions only of said insulative material.
11. A method as claimed in claim 10, including the step of:
heating prior to said first pressure station said insulative material and said conductive layer to facilitate formation of said insulative material at said first pressure station, but insufficient to cause bonding of said insulative material; and
wherein the step of selectively applying pressure at said first pressure station includes simultaneously cooling said insulative material and said conductive layer to facilitate heat dissipation from said insulative material after moving away from said second station.
12. A method for simultaneously insulating a plurality of electrically conductive elements to form electrical cable including heating and applying pressure to insulative material wherein the improvement'comprises the sequence of steps of:
heating the conductive elements and the insulative material to facilitate forming of said insulative material butinsufficient to cause bonding of said insulative material;
. 14 applying pressure to said .insulative material to form said insulative material about said conductive elements and simultaneously cooling said insulative material and-said conductive elements; and applying pressure and sufficient heat substantially simultaneously to bond said insulative material about said conductive elements.
13. A method as claimed in claim 12, wherein the second pressure application step includes applying pressure and heat to a preselected portion of said insulative material only. i
14. A method for simultaneously insulating a plurality of elements including the step of forming layers of insulative material about said plurality of elements substantially maintaining a distinguishable and separable interface between said layers and the step of bonding said layers of insulative material about said plurality of elements with the substantially simultaneous application of heat and pressure and for facilitating the removal of said insulative material for said elements at predetermined locations wherein the improvement comprisesinterrupting the application of heat and pressure to the predetermined locations of the insulative material to prevent bonding.
15. A method as claimed in claim 14, wherein the sequence of steps comprise:
heating said elements and said insulative material; applying pressure to and removing heat from said insulative material to form said material about said elements maintaining a distinguishable and separable interface between said layers of material;
applying pressure and heating substantially simultaneously to said insulative material to bond said material; and
interrupting the substantially simultaneous application of pressure and heat to said insulative material at predetermined locations to prevent bonding and to facilitate the insulative material to be cut and spaced from the elements.
16. A method as claimed in claim 15, further including the step of interrupting said step of application of pressure and removal of heat in time sequence with said step of interrupting the substantially simultaneous application of pressure and heat so that said predetermined region is not exposed to either of the steps of applying pressure to and removing heat'from said insulative material and applying pressure and heat substantially simultaneouslyvto said insulative material.