Pressure compensator, in particular a press pad for equipping hydraulic single-stage and multi-stage hot and cold presses

Abstract

A press pad for use in hydraulic single- or multi-stage hot and cold presses for producing printed circuit boards, high pressure laminates or similar plates, comprising two outer layers, arranged on opposite sides of the press pad, each consisting of a sheet of heat-resistant, preferably thermoplastic, polymer with a very low coefficient of friction, an intermediate layer, arranged between the outer layers, consisting of a textile sheet structure made of fibers, and two bonding layers, arranged respectively between the intermediate layer and each outer layer, consisting of a fluoroelastomer, preferably a fluororubber, in which at least a majority of the fibers of the textile sheet structure of the intermediate layer, preferably all of the fibers, consist of a material with a negative coefficient of linear thermal expansion in order to increase the number of press cycles and to prevent wear during the pressing process. Furthermore, a method for producing the press pad is disclosed.

Description

[Technical field]

[0001] The present invention relates to a press pad for use in hydraulic single or multi-stage hot and cold presses for producing printed circuit boards, high pressure laminates or similar boards, comprising: - two outer layers arranged on opposite sides of the press pad, each consisting of a sheet of a heat-resistant, preferably thermoplastic, polymer having a very low coefficient of friction; - an intermediate layer arranged between the outer layers and consisting of a textile sheet made of fibers; - two bonding layers each disposed between the intermediate layer and each of the outer layers, each of which is made of a fluoroelastomer, preferably a fluororubber; The present invention relates to a press pad comprising:

[0002] The present invention further provides a method for making a press pad for use in hydraulic single or multi-stage hot and cold presses for making printed circuit boards, high pressure laminates or similar boards, the press pad comprising: - two outer layers arranged on opposite sides of the press pad, each consisting of a sheet of a heat-resistant, preferably thermoplastic, polymer having a very low coefficient of friction; - an intermediate layer arranged between the outer layers and consisting of a textile sheet made of fibers; - two bonding layers each disposed between the intermediate layer and each of the outer layers, each of which is made of a fluoroelastomer, preferably a fluororubber; Equipped with At least the majority of the fibers of the textile sheet structure of the intermediate layer, preferably all of the fibers, are made of a material having a negative coefficient of linear thermal expansion; It concerns the method.

[0003] By fluoroelastomer (or synonymously herein "fluorinated elastomer") is meant within the scope of the present invention, in addition to fluororubbers, other groups of fluorinated elastomers, such as perfluororubbers (FFKM), tetrafluoroethylene / propylene rubbers (FEPM) or fluorinated silicone rubbers (FVMQ), the latter of which tend to be less suitable for testing with the press pad according to the invention.

[0004] Background technology The press pads of the type mentioned at the outset are used in various hydraulic single- and multi-stage hot and cold presses and serve to distribute and transmit the pressing pressure as uniformly as possible over the entire surface of the product to be produced, which may be a printed circuit board for producing electronic circuits, a high-pressure laminate (HPL) made of multiple layers of paper impregnated with melamine and phenolic resins or similar plates. The requirements imposed on such press pads, also called pressure compensators, are, on the one hand, a heat conductivity as high as possible, uniformly over the entire surface, in order to keep the process times during the heating and cooling steps short, and, on the other hand, a high elasticity or high resilience in order to return as far as possible to the starting state after removal of the pressing pressure at the end of the pressing cycle over as many pressing cycles as possible. The latter requirement can also be regarded as a small so-called "compression deformation residue". Furthermore, the press pads are tasked with the task of having the lowest possible static and dynamic friction, i.e., a low coefficient of static and dynamic friction, in particular against the metallic hot platen in the press. Particularly when producing printed circuit boards, high demands are placed on the press pads used, since such products are produced under very high press pressures, long press times and high press temperatures. On the one hand, the printed circuit boards must have very low thickness deviations, and on the other hand, no particle-like impurities must be generated or attached to the printed circuit boards during the production process, since this would significantly increase the risk of defects in the printed electronic circuits subsequently produced from the printed circuit boards during further processing of the printed circuit boards. In this context, low coefficients of static and dynamic friction are important, since if the press pad and the press plate or press platen are attached to each other, significant wear phenomena can occur on the surface of the press pad during expansion and contraction processes due to temperature changes in the press pad.

[0005] In the manufacture of printed circuit boards, epoxies, polyamides, polyethylene terephthalate and polyethylene naphthalate are typically used as substrate materials, especially due to their positive physical and chemical properties. The substrates most frequently used in the manufacture of printed circuit boards remain glass fiber reinforced (fiberglass) epoxy resins to which copper foil is bonded on one or both sides. Due to their solid structure and durability, such epoxy resin composite structures reinforced with fiberglass provide outstanding mechanical strength. Otherwise, the epoxy resin impregnation provides a good electrical insulator and a flame-retardant material. The latter property is becoming more and more important, since the use of certain electronic components in printed electronic circuits tends to increase temperatures.

[0006] Printed circuit boards are typically the most important items of electronic components and circuits that carry out energy, signal and data transmission from a source to a desired target location. The two main functions of a printed circuit board are, on the one hand, the stable fixing of electronic components and, on the other hand, the conductive connection between the various components in the printed circuit board. In this case, the current flow between the individual electronic components arranged on the same printed circuit board is made possible by conductor paths, tracks or signal paths. These are formed by etching from copper sheets that form a surface layer on an intermediate layer made of a non-conductive substrate (fiberglass epoxy resin). A printed circuit board must maintain high performance during its life to avoid transmission delays or incorrect data transmission.

[0007] A known simple configuration of such a printed circuit board is the so-called single-sided printed circuit board, which has conductor tracks formed from a copper foil cladding on only one side. In cases of increased complexity, the printed circuit board is copper-clad on both sides. If this is not sufficient, the possibility exists for so-called multi-layered multi-layered printed circuit boards. In this case, several thin epoxy resin plates with all the cladded printed circuit boards are appropriately bonded to the prepreg. In the case of very complex circuits, such a multi-layered printed circuit board may consist of up to 50 layers of alternating epoxy resin plates and copper foils.

[0008] During the production process, such printed circuit boards or their "semi-finished products" are assembled into several pressing packages and passed into hot and cold presses between pressing platens, which are mostly made of stainless steel with smooth surfaces. In order to compensate for thickness variations in the pressing equipment, the pressing pads mentioned at the beginning are inserted between the pressing platens and the hot platens of the pressing machine. The individual press stages typically have hot platens, which can be used for heating and cooling by passing thermo oil through them. Under high pressure and temperature, the resin used in the pressing object first melts, bonding the conductor tracks, for example to the epoxy resin interlayer, and then hardens to form the finished printed circuit board. Depending on the required condensation and polymerization time, the initially performed heating process is then interrupted by cooling while maintaining the pressure.

[0009] Prior art press pads for press installations for producing the aforementioned high-pressure laminates are still very often formed today by press pads made of paper materials, for example wool felt paper or soda kraft paper.Furthermore, plastic pads in the form of textile surfaces made of synthetic fibers or plate- or layer-shaped plastic materials are often used without an integrated textile surface in the form of a woven, warp-knitted, weft-knitted or nonwoven fabric.

[0010] From the US Pat. No. 4,461,800, a press pad for a molding press is known. The known press pad comprises a laminated core. The core comprises at least one hard cushion layer. The cushion layer is arranged between two rigid plates. The plates have a high thermal conductivity. Furthermore, the known press pad comprises two soft cushion layers, including a porous elastic layer. The soft cushion layers are glued to each of the surfaces of the laminated core. Furthermore, the aforementioned hard cushion layer comprises at least one porous elastic sheet impregnated with a binder. The aforementioned press pad has a complex structure and has a relatively short lifespan.

[0011] EP 1 084 821 A describes a press pad comprising a layer of felt-like padding material with first and second surfaces located opposite each other and a core part formed on the first surface of the padding material. The core part has a first surface in contact with the first surface of the padding material and an opposite second surface. The layer of felt-like padding material further comprises a matrix fabric woven from a thread material and a nonwoven fiber layer which is needle-punched. The core part further comprises an elastic material, a spongy rubber material or a thermoplastic elastomer, which contains hollow spaces distributed in the form of closed closed cells.

[0012] Furthermore, EP 1978528 A1 discloses a press pad for producing printed circuit boards. The press pad may have, as layers, a fabric, paper, film or sheet-like structure combined with at least one further layer of fluoroelastomer. Preferably, the fluoroelastomer comprises a fluororubber component of a polyol vulcanization system, a vulcanizing agent, a vulcanization accelerator and an acid acceptor.

[0013] Furthermore, from EP 0 842 764 A1, a press pad made of textile yarns is known, which exhibits an extended service life under high mechanical loads. The textile yarns consist of flame-retardant melamine resin fibers.

[0014] Furthermore, EP 0 493 630 discloses a press pad which consists of an asbestos-free material and is intended for use in a high-pressure single-stage press for producing high-pressure laminates.

[0015] Furthermore, from DE 103 37 403 A1 a press pad is known which has a fabric which at least partially comprises threads made of heat-resistant polymer material, the particularity being that the threads which comprise the polymer material contain a gas content of at least 1%.

[0016] Furthermore, EP 1 386 723 discloses a press pad having a fabric with warp and / or weft threads which each have alternating thread types with different elasticity in the direction transverse to the thread axis.

[0017] Another press pad for high pressure applications is evident from EP 0 488 071 A1. This press pad has a pressure of 400 N / cm 2 ~1200N / cm 2 Suitable for press pressure and temperatures of 160℃~200℃.

[0018] Finally, German Utility Model No. 20011432 also discloses a press pad made of asbestos-free material for a high-pressure multi-stage press or a high-pressure single-stage short-cycle press, respectively, for producing high-pressure laminates. The known press pad comprises a textile fabric which comprises yarns made of aromatic polyamide and metal yarns. In particular, the fabric is provided, at least on one surface only, with a coating made of a heat-resistant and pressure-resistant polymeric material. This coating covers the fabric over its entire surface in the form of a continuous layer.

[0019] All of the press pads mentioned above are only inadequately able to meet the high demands that must be imposed when used in high-pressure press installations for producing high-pressure laminates, namely a long service life, very good recovery properties, uniform pressure compensation and a very low coefficient of friction.

[0020] assignment The problem underlying the present invention is to propose a press pad for use in single- or multi-stage hot and cold presses, which better meets the aforementioned requirements when producing high-pressure laminates.

[0021] solution Starting from the press pad of the initially mentioned form, the above-mentioned object is achieved according to the invention in that at least the majority of the fibers, preferably all of the fibers, of the textile sheet structure of the intermediate layer consist of a material with a negative coefficient of linear thermal expansion (coefficient of linear thermal expansion), the coefficient of linear expansion relating to the expansion in the longitudinal direction of the fibers.

[0022] Since the fibers forming the textile sheet of the intermediate layer are entirely or at least largely made of a material with a negative coefficient of linear thermal expansion, unlike the properties of known press pads of the construction type referred to in this specification, during the pressing process, i.e. when the temperature rises inside the press installation, no expansion occurs, but on the contrary, shortening of the fibers occurs. Even if the heat-resistant material of the outer layer of the press pad according to the invention and / or one or more materials of the bonding layer, i.e. fluoroelastomer, preferably fluororubber, have a positive coefficient of linear thermal expansion, the use of a material with a negative coefficient of linear thermal expansion for the textile sheet of the intermediate layer nevertheless has a surprisingly very positive effect, since the total expansion of the press pad is significantly reduced compared to the prior art. Since the fibers of the textile sheet of the intermediate layer typically have a significantly higher modulus of elasticity than the fluoroelastomer, preferably fluororubber material, of the bonding layer surrounding the intermediate layer, the intermediate layer shortening in length forces both bonding layers, which have, so to speak, rubber-elastic properties, to contract, creating greater compressive stresses in the bonding layers. This would occur even if the material of the tie layer were to undergo a lengthwise expansion during temperature rise without cooperating with the shrinking intermediate layer. The same applies to both outer layers made of heat-resistant polymers, albeit somewhat weakened, because they are unable to fully follow the expansion effects also inherently imposed due to the good adhesive properties of the tie layer made of fluoroelastomer, preferably fluororubber.

[0023] Due to the fibers with a negative coefficient of linear thermal expansion which are processed in the intermediate layer in the form of a textile surface structure according to the invention, the expansion of the press pad can therefore be reduced in an unpredictable manner overall, i.e. also in the region of its outer layer. This is therefore extremely important, since in practice, the particularly high linear expansion of known press pads, despite the coefficient of friction of the material of the outer layer, which has already been deliberately selected to be very small in the prior art, can lead to undesirable relative movements between the outer layer and the press or hot platen which contacts this outer layer, and thus to wear of the pad material, i.e. of the material of the outer layer, and thus to the formation of very undesirable impurities inside the press or the printed circuit produced by the press. As already mentioned above, contamination of the printed circuit board in the region of the subsequent processing of the printed circuit board to form the printed circuit can lead to malfunctions in the printed circuit.

[0024] In the press pad according to the invention, even if a (slight) expansion does eventually occur on the outer surface as a result of the temperature rise during the pressing process, despite the negative coefficient of linear thermal expansion of the fibers of the middle layer, this expansion is mitigated as well as possible by the use of a material with a very low coefficient of friction for the outer layer, because due to this low coefficient of friction, typical adhesion in the sense of bonding of the outer layer material to the press platen or hot platen is avoided. In the case of such bonding, subsequent forced peeling is likely to cause damage to the press pad in the form of tearing or peeling pieces, which in turn results in the above-mentioned contamination phenomena and thus the above-mentioned quality losses in the produced printed circuit boards.

[0025] By extremely low coefficient of friction of the polymeric material of the outer layer, within the scope of this application, is meant a coefficient of friction of less than 0.06, preferably less than 0.05, and more preferably less than 0.04.

[0026] The fibres within the scope of the invention disclosed herein may be filaments, i.e. monofilaments or multifilaments, e.g. (twisted) multifilaments, which are then processed by classical textile processing methods (weaving, weft knitting, warp knitting, nonwoven fabric production) to form a textile surface. The fibres according to the present application may be staple fibres or endless fibres, e.g. spun fibres, which are processed to form a nonwoven material and then to form the textile surface of the intermediate layer.

[0027] The term "heat resistant polymer" of the outer layer within the scope of this application should be understood to mean heat resistant up to at least 240°C, preferably at least 260°C, and even more preferably up to 300°C.

[0028] Preferably, the fibers of the textile sheet of the intermediate layer comprise para-aramid and / or meta-aramid and / or carbon and / or glass, preferably consisting exclusively of one of the aforementioned materials or of a fiber mixture consisting of several of the aforementioned materials. In addition to a negative coefficient of linear thermal expansion, the aforementioned fibers also have a high tensile strength, which is necessary to ensure the required stabilizing function of the intermediate layer.

[0029] According to the invention it is further specified that the intermediate layer comprises a woven and / or warp knitted and / or weft knitted and / or nonwoven material and / or a felt material, preferably a needle punched felt.

[0030] According to a particularly preferred embodiment of the press pad according to the present application, the textile sheet structure of the intermediate layer is preferably provided, on both opposing sides, with needle-punched short fibres over its surface, preferably made of the same material as the textile sheet structure or of a material different from the fibres of the textile sheet structure. The needle-punched short fibres, which extend predominantly in a direction perpendicular to one or the opposing surface, achieve, in addition to the tensile stress stabilisation, an additional padding effect due to the perpendicular orientation of the short fibres.

[0031] In a further configuration of the invention, it is specified that the outer layer sheet is made of polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy polymer (PFA), tetrafluoroethylene hexafluoropropylene copolymer (FEP) or polychlorotrifluorotriethylene (PCTFE). All of the aforementioned materials are distinguished by their high heat resistance and low coefficient of friction.

[0032] In order to achieve a strong and durable bond of the outer layer to the bonding layer, the surface of the sheet of the outer layer facing the bonding layer may be prepared for adhesion promotion, preferably over the entire surface, i.e. etched with liquid ammonia or subjected to treatment with a sodium naphthalene solution or plasma treatment, in particular chemically etched or preferably subjected to ionization treatment with low-pressure plasma.

[0033] The fluoroelastomer, preferably the fluororubber polymer (which is initially provided partially crosslinked), according to the invention is - Copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) or - Terpolymer of vinylidene fluoride (VDF), hexafluoropropylene (HFP) and tetrafluoroethylene (TFE) or - Polymers consisting of vinylidene fluoride (VDF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE) or - Polymers consisting of vinylidene fluoride (VDF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), perfluoromethyl vinyl ether (PMVE) and ethene For the crosslinking of the (initially partially crosslinked) fluoroelastomer, preferably fluororubber polymer components, crosslinking with peroxides, diamines or bisphenols is basically considered. Of these three crosslinking mechanisms, crosslinking with diamines is the oldest. In this case, blocked diamines are used as crosslinking agents, in particular to achieve good adhesion between the elastomer and, for example, metals. The second crosslinking form is the bisphenol mechanism, also called the dihydroxy mechanism. Crosslinking with bisphenols shows better resistance to hydrolysis and higher temperatures and an improvement in terms of the so-called compression deformation residue. Furthermore, fluororubbers can also be crosslinked with peroxides (triazine method) by free radicals. Tests with silicone elastomers (as an alternative to fluororubbers) have shown significantly shorter service periods and less good stability and dimensional stability.

[0034] With regard to the method described at the beginning for producing a press pad for use in hydraulic single- or multi-stage hot and cold presses, the underlying problem is solved by feeding a fluororubber material in a pre-crosslinked state between one of the two outer layers and the intermediate layer, respectively, and distributing it there evenly over the entire surface, and transferring the fluororubber material to a final crosslinked state in the multilayer composite thus formed under pressure over the entire surface and at elevated temperature, thereby permanently adhering the multilayer composite to the press pad.

[0035] In this production form, a multilayer composite is first produced using a fluororubber material that is only pre-crosslinked and therefore not final crosslinked, which already has sufficient cohesion for subsequent handling. To obtain a multilayer composite that can be used as a high-pressure press pad with a lasting and extremely tight bond between the individual layers, the precursor multilayer composite is then final crosslinked under elevated pressure and temperature.

[0036] For this final crosslinking step, the temperature is typically 130°C to 160°C and the pressure is typically 0.5 N / mm 2 ~1.0N / mm 2 (Dr. Espe, please add typical values ​​here). To produce a press pad from a multilayer composite that is initially only held together by a precrosslinked fluorinated rubber, preferably fluororubber, different known types of installations can be used. For example, a simple press installation can be used in which the press pad is stationary during the pressing steps. One variant is an endless belt installation with a cooling device through which the press pad runs during the final crosslinking step. In this installation, the pressing time is controlled via the belt speed. Another possibility is the use of a roll coating installation, also called the "Auma lamination installation". In this installation, a circulating steel belt is guided over a partially heatable drum and the pressing pressure is adjusted via the pressing force of the steel belt on the drum.

[0037] The invention will be explained in more detail below on the basis of an embodiment of a press pad shown in the drawings. [Brief description of the drawings]

[0038] [Figure 1] FIG. 2 is a partial cross-sectional view of a press pad. [Diagram 2] FIG. 2 is a partial enlarged view of the intermediate layer of the press pad shown in FIG. 1.

[0039] Working Example The press pad 1 has a symmetrical structure with respect to a mid-plane 2 and comprises an intermediate layer 3, bonding layers 4 arranged on both sides of said intermediate layer, and two outer layers 5 forming the outer surfaces of the press pad 1.

[0040] The intermediate layer comprises a textile sheet 6. This textile sheet 6 consists of a single- or multi-ply woven fabric 7 and para-aramid staple fibers 8 which are needle-punched and entangled on both sides of the fabric 7. The longitudinal direction of the staple fibers runs perpendicular to the surface of the fabric 7. Overall, the composite of the fabric 7 and the needle-punched staple fibers 8 forms a so-called needle-punched felt.

[0041] Both outer layers 5 are PTFE sheets each having a thickness of about 200 μm. PTFE is a heat-resistant material with high abrasion resistance and an extremely low coefficient of friction. The surface of each outer layer 5 facing the intermediate layer 3 is chemically etched with an etchant, specifically ammonia.

[0042] The formation of a multilayer composite in which the individual layers are very tightly attached or bonded to one another is achieved by using initially only partially or pre-crosslinked fluororubber, for example consisting of the monomers vinylidene fluoride and hexafluoropropylene. The bonding layer 4 formed from this fluororubber has a thickness of about 800 μm. The partially crosslinked fluororubber is modified by a coupling agent so that it has particularly good adhesive properties. The fluororubber is thus in contact on the one hand with the etched surface of the outer layer 5 and on the other hand with the needle-punched intertwined short fibers 8 of the textile surface 6 of the intermediate layer 3. Due to the initially relatively low consistency of the pre-crosslinked fluororubber, it is forced deep into the areas between the short fibers 8 of the textile surface 6. The composite is thus particularly tight and at the same time durable.

[0043] In the illustrated example, the multi-layer composite as described above is subjected to pressure (0.5 N / mm ) in a roll calendering apparatus for the purpose of final crosslinking of the fluororubber. 2 ) and temperature (150°C) for final crosslinking.

[0044] During tests with the press pad 1 as described above, excellent properties could be seen. When the press pad 1 was used in a press installation for producing multi-layer printed circuit boards, a significantly higher number of possible press cycles was shown in comparison with the known press pad. After the end of the tests, the dimensional stability of the press pad 1 was almost completely given. Even after extremely long periods of use, a sufficiently high residual recovery could still be seen after removal of the pressing pressure. The surface of the outer layer 5 consisting of a PTFE sheet showed no changes in terms of wear or damage. [Explanation of symbols]

[0045] 1 Press Pad 2 intermediate plane 3. Middle tier 4 Bonding layer 5 Outer layer 6. Textile Sheet Structures 7 Textiles 8 Staple Fiber

Claims

1. 1. A press pad for use in hydraulic single or multi-stage hot and cold presses for producing printed circuit boards, high pressure laminates or similar plate-like articles, comprising: - two outer layers arranged on opposite sides of the press pad, each consisting of a sheet of heat-resistant, preferably thermoplastic, polymer with a very low coefficient of friction; - intermediate layers arranged between the outer layers and consisting of textile sheets made of fibers; two bonding layers, each of which is arranged between said intermediate layer and each of said outer layers, and which are made of fluorinated rubber, preferably fluororubber; A press pad comprising: A press pad characterized in that at least the majority of the fibers, preferably all of the fibers of the textile sheet structure of the intermediate layer, consist of a material with a negative coefficient of linear thermal expansion.

2. 2. The press pad according to claim 1, wherein the fibers of the textile sheet structure of the intermediate layer consist of para-aramid and / or meta-aramid and / or carbon and / or glass, preferably consisting exclusively of one of the aforementioned materials or of a fiber mixture consisting of several of the aforementioned materials.

3. 3. Press pad according to claim 1 or 2, characterized in that the intermediate layer comprises a woven and / or warp knitted and / or weft knitted and / or nonwoven material and / or felt material, preferably a needle-punched felt.

4. 3. A press pad according to claim 1 or 2, characterized in that the textile sheet structure of the intermediate layer, preferably on both opposing sides, comprises needle-punched entangled staple fibres over its surface, preferably made of the same material as the textile sheet structure or of a material different from the fibres of the textile sheet structure.

5. 3. The press pad according to claim 1 or 2, characterized in that the sheets of the outer layer consist of polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy polymer (PFA), tetrafluoroethylene hexafluoropropylene copolymer (FEP) or polychlorotrifluorotriethylene (PCTFE).

6. 3. Press pad according to claim 1 or 2, characterized in that the surface of the sheet of the outer layer facing the bonding layer is preferably prepared over the entire surface for adhesion enhancement, in particular by chemical etching or by ionization treatment, preferably by low-pressure plasma.

7. The (partially crosslinked) fluororubber polymer copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) or - terpolymers of vinylidene fluoride (VDF), hexafluoropropylene (HFP) and tetrafluoroethylene (TFE) or polymers consisting of vinylidene fluoride (VDF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE) or - Polymers consisting of vinylidene fluoride (VDF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), perfluoromethyl vinyl ether (PMVE) and ethene 3. The press pad according to claim 1, wherein the press pad comprises:

8. 3. A press pad according to claim 1 or 2, characterized in that the (partially crosslinked) fluororubber polymer component is crosslinked with peroxides, diamines or bisphenols.

9. 1. A method for fabricating a press pad for use in hydraulic single or multi-stage hot and cold presses for fabricating printed circuit boards, high pressure laminates or similar boards, said press pad comprising: - two outer layers arranged on opposite sides of the press pad, each consisting of a sheet of heat-resistant, preferably thermoplastic, polymer with a very low coefficient of friction; - intermediate layers arranged between the outer layers and consisting of textile sheets made of fibers; two bonding layers, each of which is arranged between said intermediate layer and each of said outer layers, and which are made of fluorinated rubber, preferably fluororubber; Equipped with at least the majority of the fibres of the textile sheet of the intermediate layer, preferably all fibres, consist of a material with a negative coefficient of linear thermal expansion; In the method, 1. A method for forming a press pad, comprising: supplying a fluoroelastomer, preferably a fluororubber material, in a pre-crosslinked state between one of said outer layers and said intermediate layer, respectively, and distributing it uniformly over the entire surface thereof; and, in the multilayer composite thus formed, bringing said fluorinated rubber, preferably said fluororubber material, to a final crosslinked state under pressure over the entire surface and at an elevated temperature, thereby permanently bonding said multilayer composite together to form said press pad.

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