WO1999024252A1

WO1999024252A1 - Matrix material containing sheet member for use in making composite laminates

Info

Publication number: WO1999024252A1
Application number: PCT/US1998/024023
Authority: WO
Inventors: Jonas Medney
Original assignee: Compositech Ltd.
Priority date: 1997-11-11
Filing date: 1998-11-10
Publication date: 1999-05-20
Also published as: AU1397299A

Abstract

A composite product and method for preparing a laminate by providing a filamentary structure that has a plurality of filament sections, applying a sheet of matrix material and associating the matrix material with the filamentary structure.

Description

MATRIX MATERIAL CONTAINING SHEET MEMBER FOR USE IN MAKING COMPOSITE LAMINATES

Technical Field The present invention relates to a process for preparing laminates which include a metal foil or temporary or permanent plastic film surface on a composite of a cured matrix material reinforced filamentary structure. These laminates can be processed into composite articles such as printed circuit boards ("PCBs") .

Background Art

It is customary in the art of producing composites of filament reinforced matrix materials to directly apply the matrix material to filaments or fibers before, after or as the filamentary structure is formed. Conventional fiberglass reinforced laminates are often prepared using a woven fabric of fiberglass filaments which is run through a solution or bath of a thermosetting plastic resin, such as an epoxy resin in a solvent solution, in a treater tower that heats the resonated fabric to drive off the solvent and partially cure the resin. The resin/fabric material is then cooled to form a partially cured resin "pre-preg" or "B" stage material. Subsequently, one or more layers of pre-preg material are placed between two outer layers of copper foil or plastic release sheets, and then held between press plates in a suitable mold for curing under heat and pressure conditions, sometimes in a vacuum atmosphere press, to form a laminate. These laminates are typically used in the manufacture of PCBs. While this process is quite successful, it typically requires the use of solvents in the resin to lower the viscosity of the resin and help wet out the filamentary structure. In addition, this process relies on vacuum, pressure and heat to assure that the entire surface of the copper foil is wetted with resin.

U.S. Patent 4,943,334 discloses an improved process for making laminates for PCBs where, e.g., fiberglass or other filaments are wound onto the flat form in layers to provide a filamentary structure over the copper foils, the form and filamentary structure are placed between two plates that act as mold surfaces, resin is introduced onto the filamentary structure, the mold surfaces are closed and placed under vacuum so that the resin can impregnate the filamentary structure, and the resin impregnated filamentary structure is then cured under pressure and/or heat. Often, the mold surfaces each include a copper foil sheet so that both sides of the laminate can be provided with an outer layer of copper foil. While this process is successful, care must be taken when handling the thin copper foils, and also when applying resin to the filamentary structure before closing the mold surfaces to avoid damage to the final product. Thus, there is a need for improvement in this area.

Summary of the Invention

The present invention provides processes which facilitate the handling of foil/resin/glass laminates while also assuring the complete impregnation of the filamentary structure with matrix material and the complete wetting of the copper foil. The invention achieves this result without having to completely saturate the filamentary structure with resin before applying outer layers of plastic film or metal foil and without the use of solvents.

It has now been discovered that, in the case of uniform planar structures in general and flat laminates in particular, it is advantageous to first apply the matrix material, such as a plastic resin, to a sheet member which can then become a permanent or temporary part of the laminate.

In this regard, the present invention relates to a method for preparing a laminate comprising a filamentary structure that is impregnated with a matrix material, which comprises the steps of providing a filamentary structure that has a plurality of filament sections arranged in a desired configuration and interstices between the filament sections, applying matrix material upon a first sheet member in an amount sufficient to fill at least a major amount of the interstices of the filamentary structure; associating the matrix material of the first sheet member with the filamentary structure member by contact therewith to fill the interstices of the filamentary structure with matrix material; and curing the matrix material to form a laminate comprising a composite of the filamentary structure impregnated with cured matrix material and including the first sheet member as an outer surface thereof. In this method, additional matrix material can be applied to a second sheet member so that the filamentary structure is positioned between the first and second matrix material containing sheet members during the association step in order to impregnate all interstices of the filamentary structure with the matrix material. Preferably, the matrix material is applied on the first or second sheet material in the form of a complete film or a series of dots, dashes or lines thereon and in a controlled manner so as to insure that every square inch is provided with essentially the same volume and amount of matrix material.

If desired, the cure of the matrix material can be advanced before placing the sheet member on the filamentary structure. It is preferred to heat the sheet material, matrix material or both to advance the spreading and curing of the matrix material and facilitate the handling and processing of the matrix material impregnated filamentary structures, the articles comprising the same or the resulting laminates.

The filamentary structure is advantageously provided by winding the filament sections on a mandrel or flat form having front and rear faces to provide a filamentary structure on each face of the flat form. Then, two first sheet members can be provided with applied matrix material, and the matrix material containing first sheet members can be associated with the filamentary structures on the front and rear faces of the form so that a laminate can be produced on each face of the flat form. Preferably, one or both faces of the flat form can include a second sheet member prior to winding of the filament sections thereon in order to provide the second sheet material as an outer layer of the laminate. Advantageously, single or double-sided adhesive tape can be used to secure the second sheet material to the flat form before the filament sections are would thereon. The tape may be applied in partial or continuous strips, as desired.

The filament sections may be wound on the flat form in layers, with at least one layer being wound at a 90° angle to at least one other layer. When each face of the flat form is provided with a second sheet member, each laminate includes first and second sheet members as outer layers. In a preferred embodiment, each second sheet member includes a backing plate, and, after winding of the filament sections to form a filamentary structure on each second sheet member, each filamentary structure is contacted with a first sheet member that contains matrix material thereon. This procedure forms first and second articles, each comprising the filamentary structure impregnated with uncured matrix material between the first and second sheet members. These articles can be assemblies including the flat form placed in a press, and the matrix material of the articles is cured, optionally while applying a vacuum and heat, to form the laminates. Essentially any number of articles limited only by the capacity of the press can be placed and arranged therein before curing the matrix material.

The first or second sheet members may be the same or different and are typically a plastic film or a metal foil. When the sheet member is a metal foil, the surface of the foil that is to contact the filamentary structure can be treated to render it more receptive to receive and retain the matrix material thereon. Alternatively, the filament sections can be treated with a binder that has an affinity for the matrix material to facilitate filling of the interstices of the filamentary structure by the matrix material. Also, the matrix material may be heated to facilitate filling of the interstices of the filamentary structure, while one or more of heat, pressure or vacuum can be used to assist in the curing of the matrix material.

If desired, a portion of the matrix material can be applied directly upon the filamentary structure prior to contacting the filamentary structure with the matrix material containing first sheet member. Advantageously, the first sheet member can be supported with a backing plate to facilitate handling of the first sheet member and contact with the filamentary structure. In this method, a number of articles can be produced, with each article including first and second plates that include copper foil thereon and a matrix material impregnated filamentary structure therebetween. Also, a multiple article structure containing a desired number of articles can be produced by adding additional matrix material and foil containing plates to the filamentary structure and then winding additional filaments sections thereon. To cure the matrix material, one or a number of single or multiple article structures can be placed in a press, with the number of articles or structures being limited only by the capacity of the press.

Another embodiment of the invention relates to an article comprising a backing plate having first and second faces and mechanical properties sufficient to facilitate transport and handling of the backing plate; a sheet member having first and second faces, with the first face contacting a face of the backing plate; and uncured matrix material applied at least to portions of the second face of the sheet member.

The sheet material and backing plate are preferably rectangular with the sheet material having a greater area than that of the backing plate. This enables the edges of the sheet member to extend beyond and be taped to or crimped around at least two edges of the backing plate so that matrix material cannot flow between the sheet member and backing plate on those edges.

As above, the matrix material may be present in the form of a complete film or a series of dots, dashes or lines on the sheet member. The sheet member is preferably a plastic film or a metal foil, while the backing plate is preferably a metal sheet having sufficient strength to support and protect the sheet member during transport and handling.

Brief Description of the Drawings

Preferred features of the invention can be reviewed in the following detailed description read in conjunction with the appended drawing figures, wherein: Figure 1 is a front view of a copper foil/backing plate article that contains matrix material on the foil;

Figure 2 is a side view of the article of Figure 1;

Figure 3 is a front view of a flat form or mandrel that contains a sheet attached thereto by tape with a wound filamentary structure thereon;

Figure 4 is a front view of a mandrel that contains a sheet attached thereto by two-sided tape and also with a wound filamentary structure thereon;

Figure 5 is a side view of a sandwich of two articles according to Figure 1 surrounding the flat form of Figure 3;

Figure 6 is a side view of an article having narrowed edge portions along the entire perimeter on both the front and back surfaces of the plate;

Figure 7 is a side view of a press device for contacting and curing a "sandwich" of multiply wound filament/resin structures for forming laminates; and

Figure 8 is a side view of a press device into which four separate books of resin impregnated filamentary structures between outer plates are placed for curing.

Detailed Description of the Preferred Embodiments

In the following description, the preferred method for preparing the filamentary structure would be the same as that disclosed in U.S. Patent 4,943,334, the content of which is expressly incorporated herein by reference thereto.

Specifically, the filamentary structure is prepared by winding filament sections about a flat form. The filaments are wound in layers which are typically arranged at right angles and in mirror image relation about a symmetry plane. Alternately, it is possible to prepare filamentary structures by winding filament sections around a frame or in a loom or other filament arranging device. Although fiberglass filaments are preferred, any of the types of filaments disclosed in the '334 patent could be used. Other steps for preparing a filamentary structure that does not contain resin are generally known in the art and any could be suitable for use in the present invention depending upon the final laminate to be prepared. If desired, woven fabrics of such filaments can be used as the filamentary structures. When laminates for use as PCBs are intended, the methods disclosed in the '334 patent for forming the filamentary structures are preferred. A sheet member is then selected. Again, depending upon the final product, a metal foil, plastic film or other sheet material can be used as this member. The sheet member becomes an outer surface of the laminate. A metal foil such as copper is preferably used to form this surface when it is to later be etched to form circuit patterns, while a plastic film is typically used as a release film to enable the laminate to be easily removed from the mandrel. In some instances, the plastic film can remain as the outer surface of the laminate. Generally, the sheet member is not sufficiently thick or rigid to support its weight and the weight of the matrix material that is to be applied, so that it is placed on a backing plate, i.e., a metal or plastic sheet having a greater thickness than the foil or film. Typical sheet members of metal foils have a weight of about 0.5 to 4 ounces per square foot, while the metal or plastic backing plates typically have a thickness of between about 0.01 and 0.125 inch. One preferred arrangement includes the use of 1 ounce per square foot copper foil on a backing plate of an aluminum sheet that is 0.050" to 0.062" thick. Depending upon how it is to be used in the laminate, the sheet member is selected to have certain properties or is treated to impart the desired properties. For example, when copper foil is utilized, it is helpful to treat the surface of the foil that is to receive the matrix material with a chemical treatment such as zinc chromate to enhance the ability of the matrix material to bond to the copper foil. This enables the foil to be securely bonded to the composite so that it can be further processed such as by etching to provide printed circuits that are securely adhered to the composite.

Alternatively, a plastic film can be used as a removable or remaining outer surface of the laminate. In this embodiment, depending upon the desired result, the plastic film is selected to be sufficiently incompatible or compatible with the matrix material so that it will not strongly or very strongly, respectively, bond thereto. Thereafter, the film can be removed from the laminate or left on the laminate after the matrix cures.

Depending upon the desired final product, the laminate can be provided with one or two outer surfaces of foil or film. For example, two copper foils allow circuits to be provided on each side of the laminate. One of ordinary skill in the art can select the desired materials for the sheet members as well as the appropriate properties or treatments for the selected sheet members to achieve the desired construction of the laminate. After the appropriate selection and/or treatment of the surface of the sheet member, the matrix material is then applied thereto. The matrix material is generally applied as a liquid having a viscosity of between about 100,000 and 300,000 cps, and typically 200,000 cps at ambient temperature. These high viscosities are useful in enabling the matrix material to remain in place on the surface of the sheet member. The matrix material is applied to the sheet member with conventional equipment which is capable of depositing very accurately calculated and controlled volumes upon each square inch of the sheet member. The high viscosity of the matrix material helps maintain that accuracy during subsequent handling of the sheet member. The viscosity can be varied through the use of conventional fillers or additives, and this is within the general knowledge of the skilled artisan. A lower viscosity matrix material can be used when the sheet member is applied to the filamentary structure in the horizontal position, or when the filamentary structure is relatively tight, or when relatively lower pressures are used to hold the sheet member and filamentary structure together during cure. The lower viscosity material can more easily penetrate into the interstices of the filamentary structure, but is also more likely to be displaced from the sheet member. Preferably, solvents are not used to dilute the matrix material or to reduce its viscosity.

The matrix material can also be heated to facilitate application to the sheet member or filling of the filamentary structure. Typically, the matrix material would be a plastic resin, such as an epoxy resin, but other conventional thermosetting or thermoplastic resins are suitable. The skilled artisan can best select the desired balance between filamentary structure arrangement and matrix material type, viscosity and curing conditions to the desired properties and obtain an essentially void free laminates.

The matrix material can be placed uniformly onto the sheet member, or can be applied only onto selected portions or desired areas. As noted above, a complete film of matrix material or the application of dots, dashes, stripes, zig-zag lines, or other shapes or configurations can be used. Stripes or lines are preferred since they can be aligned with the filament sections of the filamentary structure. The amount of matrix material that is applied is that which is sufficient to fill the interstices of the filamentary structure while wetting out substantially the entire surface of the sheet member so that it can be securely adhered to the filamentary structure. Generally, the sheet member has a greater perimeter and area than that of the filamentary structure, to allow for trimming after curing, with the laminates being cut out from within the perimeter and area of the filamentary structure.

The amount of matrix material to be applied is typically on the order of about 2 to 10% and typically about 3 to 5%, by volume greater than the calculated amount needed to fill the interstices of the filamentary structure. In some circumstances, it may be beneficial to apply some of the matrix material to the filamentary structure before it is contacted by the matrix material of the sheet member. This may be useful for filamentary structures having greater thicknesses, greater filaments per area, or multiple layers of filament sets. The application of the additional matrix material can be achieved by spraying, brushing, squeegee or other conventional means. To eliminate voids, dirt or other discontinuities in the final laminate, the matrix material can be applied to the sheet member in a clean environment, such as a clean room that circulates filtered air. This avoids introducing particulate matter onto the sheet member, which matter would cause voids or defects in the final laminate or PCB products.

In the most preferred embodiment, the sheet member is a copper foil that is unwound from a coil and held horizontally. The matrix material is an epoxy resin that is held in a reservoir and directed to a nozzle that is movable above the surface of the copper foil and which oscillates back and forth while dispensing the resin onto the foil. A gear pump is utilized to dispense the resin, with a computer being used to control the amount of resin dispensed, the speed of movement of nozzle and the operation of the gear pump so that a precise, uniform, calculated volume of resin can be applied to each square inch of foil.

Any of a wide variety of liquid, settable matrix materials can be utilized. Any thermosetting or even thermoplastic resin should be suitable. Preferably, epoxy resins having the appropriate viscosity and physical properties are used. The '334 patent discloses suitable epoxy resin compositions that can be used in this invention. After the matrix material is applied to the sheet member, contact can be made with the filamentary structure. As noted above, the contacting step can be conducted in the horizontal or vertical position. Other positions can be used but these may complicate arrangement of the curing equipment that is utilized in subsequent processing.

A number of techniques can be used to facilitate impregnation of the filamentary structure and wet out of the sheet member. The filament sections of the filamentary structure can be treated with a suitable binder or surfacing material that has an affinity for the matrix material. This treatment can be conducted prior to or after the formation of the filamentary structure. Typically, silanes or other conventionally used compounds can be applied in this treatment. Certain filament suppliers have the capability to apply such compounds to the filaments during manufacture, so that a separate treatment in the laminate manufacturing facility is not required.

After the filamentary structure and matrix material containing sheet member are contacted, heat, pressure and/or vacuum can be used either simultaneous, separately or in any combination to facilitate wet out and impregnation of the filamentary structure by the matrix material. The specific conditions will vary depending upon the desired final product and the type and viscosity of the matrix material that is used. The *334 patent can be consulted for typical curing conditions for preferred combinations.

As solvents do not have to be included in the matrix material, significant improvements are provided by the invention. There is no concern of environmental damage due to release of such solvents, nor is there any need for equipment to collect or destroy such solvents. Furthermore, there will be no residual solvent in the laminate which can be a cause of voids or other defects. Also, the use of high viscosity matrix materials makes it easier to incorporate filler materials therein, thus providing greater versatility in the possible properties of the matrix materials, the resulting laminates and the final PCB products.

The laminates that are produced are of consistently high quality and improved over conventionally produced laminates. Providing the sheet member with matrix material assures that the portion of the laminate beneath the sheet member will be formed of cured matrix material and will not include unwet reinforcement knuckles or other matrix material, depleted spots or other non-uniform areas. As solvent is not used, the potential for defects in the composite is also reduced. As the matrix material is typically applied just before forming the laminate, there is no need to maintain an expensive inventory of resin-impregnated fabrics with appropriate environmental controls as is required, e.g., with treater towers. The control of the disposition of the matrix material is much more accurate so that less matrix material is used and the costs of producing the laminate are reduced. Capital costs for matrix material application equipment are likewise reduced. Although the preceding discussion explains the application of the matrix material to one sheet member, it is understood that it is also possible to apply a portion of the required matrix material to two sheet members and form a sandwich of the filamentary structure between these sheet members. The resultant laminate will have two outer surfaces of, e.g., metal foil, plastic film, or one of each. Some of the total amount of matrix material can be applied to one sheet member with the balance applied to the other. Those of ordinary skill in the art can determine by routine testing the relative amounts of matrix that should be applied to each sheet member. While equal amounts can be applied to each sheet member, the relative amounts will generally vary between 20 and 80% on one sheet member with the balance on the other. When a flat form is used for the preparation of symmetrical filamentary structures, no matrix material is generally applied to the form or to any sheet member which is applied to the form before the filament sections are wound or placed thereon. For these embodiments, the matrix material is only applied to the two outer first sheet members, so that, after placement in the mold and curing, two symmetrical laminates are formed. As a copper foil or plastic release film is applied to the form before winding of the filament sections, the resulting laminates can be easily separated from the form in the same manner disclosed in the '334 patent.

The matrix material containing sheet member can also be used to apply the matrix material to conventional woven filament structures in place of the prepregs produced by treater towers. These towers are inherently dirty, with dirt and other contaminants being introduced when the woven fiberglass is run through the resin/solvent solution. In another embodiment of the present invention, the matrix material containing sheet member can be applied onto a woven filament structure which is placed on a support member, with or without a film or foil thereon. Also, two sheet members, one or both of which contain matrix material, can be sandwiched about the woven filamentary structure. This procedure would minimize the introduction of dirt or other contaminants into the resulting laminate in addition to avoiding the use of solvents.

Referring now to the drawings, Figure 1 illustrates an article 10 according to the invention, in the form of a copper foil 15 which is supported by an aluminum backing plate 20 having lug members 25 to facilitate handling and transport of the article 10. Uncured epoxy resin is applied to the surface of the foil in the form of parallel lines 30. The lines typically about 0.3" wide and are spaced by about the same distance. The figure exaggerates the spacing between the lines for clarity in illustrating the invention, but one of ordinary skill in the art would know or could determine by routine testing the amount of resin that should be applied to the surface of the foil 15 in order to fill the interstices of the filamentary structure. Typically, an excess of resin of about 2-5% greater than the exact amount needed is applied to assure that all interstices are filled. This amount can vary depending upon the type of resin and filler.

Figure 2 illustrates that the foil 15 is secured to the backing plate 20 by adhesive tape 35, which, in the most preferred embodiment, holds the foil flat, excludes particulates from surface between foil and plate, and seals the edges of the plate so that any resin which is inadvertently displaced to the rear surface of the foil is prevented from entering the space between the foil and backing plate, where it would adhere the two together during the curing step and interfere with the separation of the resultant foil-surfaced laminate from the backing plate.

Figure 3 illustrates a flat form or mandrel 50 which has been provided with a sheet member 55, and a filamentary structure 60 wound thereon. The filamentary structure has two layers, the first of which is provided by winding filaments around the mandrel. Then, the mandrel is rotated 90° and the second layer is providing by winding filaments around the rotated mandrel. Additional layers can be provided by rotating the mandrel and continuing to wind filaments there around. The '334 patent includes further details on this preferred method for forming the filamentary structure.

The mandrel 50 of Figure 3 also includes a second sheet member on its rear side. The winding of filament thus provides the same structure on both sides of the mandrel. Any of wide variety of materials can be used for the sheet members depending upon their desired end use. For example, a film of plastic or other non-adherent film material can be used when it is desired to enable the final laminate to be separated and removed from the mandrel. These films are preferably treated so that they do not securely bond to the resin and thus can easily be removed after the laminate is cured. Typically, however, a plastic film or metal foil is used which is bonded to the filamentary structure by the matrix material to form an outer surface of the laminate. A metal foil such as copper is preferred for use as the film so that circuit patterns can eventually be provided on the surface of the laminate according to well known subsequent processing techniques.

To secure the film 55 to the mandrel 50, adhesive tape 65 can be applied at the corners of the film 55, as shown in Figure 3. Alternatively, as shown in Figure 4, two sided adhesive tape 75 can be placed between the backing plate and foil around the perimeter of the backing plate to join the two together. When two sided tape is utilized, it is preferred to use a tape that provides adhesives of different bond strengths on each side. The stronger bond strength adhesive contacts the foil, while the lower bond strength adhesive contacts the backing plate. This facilitates removal of the foil from the backing plate so that the laminate can be trimmed and then subjected to final processing. Generally, the trimming operation removes the portions of the foil that contain the tape, thus avoiding a separate step for removal of tape or tape residue from the foil, backing plate, or final product.

When copper foil is used as sheet member 55, adhesive tape 65 or 75 can be applied along the entire periphery of the foil to prevent migration of dust particles or resin behind the foil. Also, when foil is applied to the mandrel, it is preferred to wind at least three layers of filaments, with the second layer being wound at a 90° angle to the others and including about twice the amount of filaments as the first and third layers so that the strength of the filaments in each direction is approximately the same. Thus, the final laminate is symmetrical regardless of the initial orientation of the laminate.

Before placing the sheet members on the mandrel, the surface of the mandrel is cleaned to remove dirt or other contaminants. Polished surfaces are preferred so that films or foils on the outer surfaces of the laminate are maintained sufficiently smooth to be useful as the outer surfaces of a printed circuit board. As explained above, the same filamentary structure is provided on each side of the mandrel. After the filamentary structure is wound, two articles 10 as shown in Figure 1 are applied to each side of the mandrel with the resin bearing side of the foil in contact with the filamentary structure. The assembly is then placed in a press under sufficient pressure to cause the resin to fully wet out and impregnate the filamentary structure and fill all interstices.

Preferably, the mandrel 50 and/or the backing plates 20 can be heated to facilitate this operation. Typically, the backing plate is heated while the heating of the mandrel is optional. Typical curing conditions include the use of pressures of 0.5 to 10 psi at temperatures of about 150°C or above for 0.5 to 20 minutes. A pressure of about 1-2 psi while heating at a temperature of about 150 to 240°C for 3 to 4 minutes is generally sufficient. The application of the heat and pressure lowers the viscosity of the matrix material and helps it wet out the filamentary structure. The matrix material spreads uniformly and ends up very close to if not identically in its final position in the resulting laminate.

Optionally, vacuum can be applied to assist in the spreading of the matrix material and the removal of air from the filamentary structure. Thereafter, the filaments are cut around the edges of the mandrel to eliminate tension on the filament sections and ensure that a warp free laminate will be formed after the curing step. Although the matrix material will typically be partially cured at this point in the process, it will not be completely cured in this operation. Instead, the partially cured laminates are then forwarded to a high pressure curing operation for final cure.

Advantageously, a backing plate 20 can be used to hold the metal foil on the mandrel. Then, after the filaments are cut, two "books" or "sandwiches" are obtained, each having outer backing plates and a layer of foil, an epoxy resin impregnated filamentary structure and a plastic film therebetween. These books are typically removed from the mandrel, then stacked in a press, placed under a pressure of 10 to 200 psi, subjected to a vacuum and heated to a temperature of 230 to 260°F for 15 to 60 minutes to fully cure the resin and form the laminates. Depending upon the size and number of platens of the press, from 2 up to as many as 10 to 200 to 500 books or more can be stacked and cured simultaneously. Surprisingly, it has been found that the resulting laminates are void free, dimensionally stable and show no evidence of filament splaying. As no tension is present in the filaments as the laminate fully cures, no stress is introduced that can cause buckling of the finally cured laminate.

Figure 5 illustrates the stacking of the books, along with another feature of the invention. The backing plates 20 used in this embodiment have a narrower edge perimeter 70 on at least two sides of the plates. This enables the copper foil 15 to be bent or crimped around the edge perimeter to hold the foil flat to the backing plate 20 and fully prevent the epoxy resin from spreading around the back of the foil and between the foil and the backing plate 20. This avoids the use of adhesive tape described above in the embodiment of Figure 2.

Figure 6 illustrates an alternative embodiment of the narrower edge perimeter backing plate 40 of the invention, where both the front and back surfaces of the plate have narrower edges 45A, 45B. In this embodiment, the foil 15 is bent over both narrower edges to be secured to the plate. If desired, two foils 15 can be applied, one to each face of the plate 40, with the perimeters of the foils being bent or crimped around the narrower edges 45A, 45B to secure each foil to the plate 40. In this way, the use of adhesive tape is avoided. Alternatively, single or double-sided tape can be used to secure the foil to the front and back surfaces of the plate along the narrower edges 45A, 45B, with the tape being applied continuously or intermittently.

After the laminates are cured, the foil edges are un- crimped or the adhesive tape is removed so that the laminates can be separated from the backing plates. The edges of the laminates are trimmed and the laminates are cut to the desired size. As laminates of typically 3' x 4' or larger size are desired, the mandrels and backing plates are made a few inches wider to provide additional area which can be trimmed to produced slightly larger size laminates which can be produced before cutting to the final size.

Although Figure 5 illustrates one way of stacking two books, it is also suitable to reverse the position of the books in the stack. One of ordinary skill in the art can best select the optimum way to stack the books in any particular press. If desired, the books do not have to be removed from the mandrel prior to stacking in the press. In another embodiment of the invention, the number of separate books to be placed in the press can be reduced by conducting additional windings of filaments onto additional articles placed on the mandrel. In a first step, after a copper foil is placed on both sides of the mandrel 50, filaments are wound thereon as described above in the detailed description of Figure 3. Instead of using two articles 20 as shown in Figure 1, any number of additional flat forms or plates can be used, with each one being provided with a copper foil on each side. Although, conceptually, additional mandrels 50 can be used instead of plates, the mandrels generally have a greater thickness that is not necessary for strength purposes and which instead reduces the number of additional articles that can be placed in the press due to this grater thickness. Thus, a thinner plate is preferred for use as the additional articles.

One copper foil on each additional plate is provided with resin as described above with respect to articles 20, and the additional plates are applied to each side of the mandrel that has been provided with the filamentary structures. The resin bearing foil side of each additional mandrel is placed in contact with a filamentary structure. Thereafter, additional filamentary structures are wound onto the exposed copper foil surfaces of the additional mandrels. After these additional filamentary structures are wound onto the additional mandrels, the copper foils of two articles 20 as in Figure 1 can be provided with resin and applied as described above, or two additional mandrels that have been provided with copper foil on each side can be used if additional winding of filamentary structures is desired. This enables multiple filamentary structures to be wound and then provided with resin to form a book or sandwich of multiple mandrels and uncured filament/resin structures which can be cured into laminate products.

Instead of additional plates or mandrels, it is possible to utilize a copper-aluminum-copper ("CAC") article such as laminate 30 of U.S. patent 5,153,050 when additional laminates are desired. To the extent necessary, that patent is expressly incorporated herein by reference thereto. One advantage of the CAC article compared to the copper foil containing plate is that the CAC article is even thinner so that the overall thickness of the multiple article and uncured filament/resin structures would be less, thus enabling more of such articles and structures to be cured to laminates at one time in the press.

This is illustrated in Figure 7, where a mandrel 50 according to Figures 3 or 4, after being provided with a foil sheet and then being wound on each side with filamentary structures, is used as the core or center of the sandwich. A copper surface of a first CAC article 80 is provided with resin as described above and is then placed on one of the filamentary structures 60, and the copper surface of another CAC article 85 is also provided with resin as described above and is then placed on the other filamentary structure 60. The CAC articles are then provided with filamentary structures 90, 95 on their opposite copper faces. These steps can be repeated as often as necessary. For simplification, only two additional CAC articles 100, 105, wound with filamentary structures 110, 115 are shown in Figure 7.

Figure 8 illustrates another embodiment where four books 130, 135, 140 145, each made of two articles 20 with a resin impregnated filamentary structure 60 therebetween, are stacked and placed in the press for curing of the resin to form the laminates. As noted above, any number of books can be stacked and arranged in the press depending upon the thickness of the books and the capacity of the press. Again, the books can be individually prepared and stacked or can be prepared by adding additional plates and continuing the winding of filaments to form multiple laminate books. After the desired number of articles are wound with filaments, the final outermost sides of the book or sandwich are provided by applying resin to the copper foil of articles 20 as described above and by then placing them on each filamentary structure 110, 115. If desired, a copper-aluminum article that does not have the narrower edges of article 20 can instead be used with the copper side being provided with resin and used to contact the filamentary structure. The final book or sandwich is placed between two mold surfaces 120, 125, pressure is applied, the tension in the filament sections is reduced and the laminates are cured. Tension can be reduced by simply cutting the filament sections around the edges of the laminates. When plates are used instead of CAC articles, adjustable edges can be provided on those mandrels for reducing filament tension as shown in Figures 8 and 8A of the '334 patent.

While the invention has been described in terms of its preferred embodiments, it is recognized that one or ordinary skill in the art would be taught to also make certain modifications and enhancements and these are contemplated as being within the true spirit and scope of the invention that is defined by the following claims.

Claims

THE CLAIMSWhat is claimed is:

1. A method for preparing a laminate comprising a filamentary structure that is impregnated with a matrix material, which comprises the steps of: providing a filamentary structure that has a plurality of filament sections arranged in a desired configuration and interstices between the filament sections; applying matrix material upon a first sheet member in an amount sufficient to fill at least a major amount of the interstices of the filamentary structure; associating the matrix material of the first sheet member with the filamentary structure member by contact therewith to fill the interstices of the filamentary structure with matrix material; and curing the matrix material to form a laminate comprising a composite of the filamentary structure impregnated with cured matrix material and including the first sheet member as an outer surface thereof.

2. The method of claim 1 which further comprises applying additional matrix material to a second sheet member so that the filamentary structure is positioned between the first and second matrix material containing sheet members during the associating step in order to impregnate all interstices of the filamentary structure with the matrix material .

3. The method of claim 1 which f rther comprises applying the matrix material on the first sheet material, in the form of a film or a series of dots, dashes or lines thereon.

4. The method of claim 1 which further comprises advancing the cure of the matrix material before placing the sheet member on the filamentary structure.

5. The method of claim 1 wherein the filamentary structure is provided by winding the filament sections on a flat form having front and rear faces to provide a filamentary structure on each face of the flat form, and which further comprises providing two first sheet members with applied matrix material, and associating the matrix material containing first sheet members with the filamentary structures on the front and rear faces of the form so that a laminate can be produced on each face of the flat form.

6. The method of claim 5 wherein at least one face of the flat form includes a second sheet member prior to winding of the filament sections thereon in order to provide the second sheet material as an outer layer of the laminate.

7. The method of claim 6 which further comprises securing the second sheet member to the flat form utilizing single or double sided adhesive tape prior to the winding of the filament sections thereon.

8. The method of claim 7 wherein the adhesive tape is a double-sided adhesive tape that has different strength adhesives on each side so that one side of the tape can provide a stronger bond than the other side.

9. The method of claim 5 wherein the filament sections are wound on the flat form in layers, with at least one layer being wound at an angle to at least one other layer, and wherein each face of the flat form is provided with a second sheet member so that each laminate includes first and second sheet members as outer layers.

10. The method of claim 9 wherein each second sheet member includes a backing plate, and, after winding of the filament sections to form a filamentary structure on each second sheet member, each filamentary structure is contacted with a first sheet member that contains matrix material thereon, to form first and second articles, each comprising the filamentary structure impregnated with uncured matrix material between the first and second sheet members, with the first sheet members providing outermost surfaces.

11. The method of claim 10 which further comprises cutting the filament sections about the edges of the flat form, removing the first and second articles from the flat form, placing the articles in a press, and curing the matrix material of the articles, optionally while applying a vacuum and heat, to form the laminates.

12. The method of claim 11 which further comprises placing and arranging a desired number of articles in the press before curing the matrix material.

13. The method of claim 10 which further comprises providing each outermost surface of the first sheet members with a third sheet member, winding filament sections on the third sheet members to provide a filamentary structure thereon, contacting each filamentary structure with another first sheet member that contains matrix material thereon to form additional articles comprising a filamentary structure impregnated with uncured matrix material between sheet members and optionally repeating these steps until a multiple article structure containing a desired number of articles is produced.

14. The method of claim 13 which further comprises placing the multiple article structure in a press, reducing the tension in the filament sections of each article, and curing the matrix material of the articles, optionally while applying a vacuum and heat, to form the laminates.

15. The method of claim 14 which further comprises placing and arranging a desired number of multiple article structures in the press before curing the matrix material.

16. The method of claim 14 which further comprises selecting the any of the first, second or third sheet members to be the same or different and to be one of a plastic film or a metal foil.

17. The method of claim 16 wherein at least one of the sheet members is a metal foil and which further comprises treating a surface of the foil to render it more receptive to receive and retain the matrix material thereon.

18. The method of claim 1 which further comprises forming the filamentary structure of one or more layers of woven filaments.

19. The method of claim 1 which further comprises treating the filament sections with a binder that has an affinity for the matrix material to facilitate filling of the interstices of the filamentary structure by the matrix material.

20. The method of claim 1 which further comprises utilizing one or more of heat, pressure or vacuum to assist in the curing of the matrix material.

21. The method of claim 1 which further comprises heating the matrix material to facilitate filling of the interstices of the filamentary structure by the matrix material.

22. The method of claim 21 wherein the matrix material is heated under pressure to partially cure the matrix material after it has filled the interstices of the filamentary structure.

23. The method of claim 22 which further comprises applying one or more of heat, pressure or vacuum in a secondary operation to completely cure the partially cured matrix material.

24. The method of claim 1 which further comprises applying a portion of the matrix material directly upon the filamentary structure prior to contacting the filamentary structure with the matrix material containing first sheet member.

25. The method of claim 1 which further comprises supporting the first sheet member with a backing plate to facilitate handling of the first sheet member and contact of the matrix material with the filamentary structure.

26. An article comprising: a backing plate having first and second faces and mechanical properties sufficient to facilitate transport and handling thereof; a sheet member having first and second faces, with the first face contacting a face of the backing plate; and uncured matrix material applied at least to portions of the second face of the sheet member.

27. The article of claim 26 wherein the sheet member and backing plate are rectangular and the sheet member has a greater area than that of the backing plate.

28. The article of claim 27 wherein the sheet member has edges that extend beyond and are crimped around at least two edges of the backing plate so that matrix material cannot flow between the sheet member and backing plate on those edges.

29. The article of claim 26 wherein the matrix material is present in the form of a film or a series of dots, dashes or lines on the sheet member.

30. The article of claim 26 wherein the sheet member is a plastic film or a metal foil and the backing plate is a metal sheet having sufficient strength to support and protect the sheet member during transport and handling.