Cushion material

Abstract

This invention relates to a cushion material for hot pressing, comprising at least one perfluoroelastomer sheet and at least two fabric sheets, in which the cushion material is useful for high temperature pressure condition.

Description

TITLE OF THE INVENTIONCUSHION MATERIALFIELD

[0001] This invention relates to a cushion material comprising perfluoro elastomer sheet and fabric, which is useful as a hot-press cushioning material used under high- temperature press condition.BACKGROUND

[0002] A laminated board such as a printed circuit board or IC carrier board is manufactured by a hot-pressing process. During the hot-pressing process, a cushion material is put between a layered materials to be laminated and a hot platen, to ensure uniform laminate of the layered materials.

[0003] Cushion materials of elastomer sheet laminated with fabric are known, for example, JPU48031033B, JP5204429B and WO2003537381A. As an elastomer for cushion materials, common elastomers such as ethylene propylene diene rubber (EPDM), silicone rubber and fluoroelastomer are used. Heat-resistance for those elastomers have been limited, for example, up to 230 degrees C for fluoroelastomer.

[0004] Recently, because of a requirement of higher semiconductor properties and electronic properties, PTFE resin and / or liquid crystal polymer (LCP) have been used to materials of a printed circuit board. The temperature of hot-press process for such material is around 300 degrees C, it is much higher than the heat-resistance of traditional elastomers. Therefore, instead of elastomers, glass fiber fabric, aramid fiber fabric, stainless fiber fabric, and kraft paper are used as a cushion material for such high-temperature press condition, as disclosed in JP6790297B and JP2019161206A.

[0005] In addition, in the manufacturing process for mounting power semiconductors on insulating substrate, the press temperature is also around 300 degrees C. Silicone elastomer is used as cushion material for the application, however, due to lack of the heat-resistance of silicone to 300 degrees C, the silicone elastomer cannot be used repeatedly thus need to change after each press.

[0006] In the market, there are no elastomer cushioning materials that can be used repeatedly at such higher temperature (300 degrees C) with excellent cushioning ability.SUMMARY

[0007] Cushion material formed from perfluoro elastomer sheet and fabric sheets having higher heat-resistance can resolve the problem.

[0008] Therefore, the invention is directed to a cushion material for hot pressing comprising at least two fabric sheets and at least one perfluoroelastomer sheet, thefabric sheets are located to both upper side and lower side of the perfluoroelastomer sheet, in which the perfluoroelastomer sheet is formed from a perfluoroelastomer composition comprising:(A) a perfluoroelastomer comprising copolymerized units of:(i) one or more unsaturated perfluorinated olefins;(ii) one or more perfluorovinyl ether selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and a mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl) ether;(iii) one or more cure site monomers selected from the group consisting of bromine atoms, iodine atoms and nitrile group;(B) one or more curing agent, and(C) optionally one or more filler.

[0009] The invention further directed to a hot pressing equipment used for manufacturing of a printed circuit board comprising PTFE resin and / or liquid crystal polymer, in which the hot pressing equipment comprises a cushion materials disclosed above.

[0010] The invention further directed to a hot pressing equipment used for manufacturing process for mounting power semiconductors on insulating substrate, in which the hot pressing equipment comprises a cushion materials of claim 1.

[0011] The invention further directed to a method for making a cushion material for hot pressing, comprising the steps of:(1) preparing at least one perfluoroelastomer sheet formed from a composition comprising:(A) a perfluoroelastomer comprising copolymerized units of:(i) one or more unsaturated perfluorinated olefins;(ii) one or more perfluorovinyl ether selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and a mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl) ether; and(iii) one or more cure site monomers selected from the group consisting of bromine atoms, iodine atoms and nitrile group;(B) one or more cure site agent, and(C) optionally one or more filler,(2) applying the perfluoroelastomer sheet between two fabric sheets,(3) hot pressing the layered sheets, to adhere the fabric sheets and perfluoroelastomer sheet, then(4) further heating the hot pressed layerd sheet to form cross-linkage of the perfluoroel astomer .BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Fig. l is a chart for thickness retention rate for Examples 1 to 3 and Comparative Examples 1 to 4.Fig. 2 is compressive stress curve of test sample for Example 1.Fig. 3 is compressive stress curve of test sample for Example 2.Fig. 4 is compressive stress curve of test sample for Comparative Example 1.Fig. 5 is compressive stress curve of test sample for Comparative Example 2.Fig. 6 is compressive stress curve of test sample for Comparative Example 3.Fig. 7 is compressive stress curve of test sample for Comparative Example 4.Fig. 8 is compressive stress curve of test sample for Example 3.Fig. 9A is surface appearance (a photo) of test sample for Example 1, before compression test.Fig. 9B is surface appearance of test sample for Example 1, after compression test.DETAILED DESCRIPTION

[0013] AbbreviationsThe claims and description herein are to be interpreted using the abbreviations and definitions set forth below.“h”, “hrs” refers to hours.“%” refers to the term percent.“wt %” refers to weight percent.“°C” refers to degree Celsius.“mole %” refers to mole percent.“parts” refers to parts by weight.“phr” refers to parts per hundred parts of fluoroelastomer (rubber); one of skill in the art uses and recognizes this term of measurement. For example, 3 parts of a component per 100 parts fluoroelastomer is written as 3 phr. In these compounds, processes, and articles described herein, phr is based on 100 parts of fluoroelastomer.“g” refers to grams.

[0014] Cushion material(I) Perfluoro elastomer sheetPerfluoro elastomer layer is a cured perfluoro elastomer and is formed from a composition comprising (A) perfluoroelastomer comprising copolymerized units of:(i) unsaturated perfluorinated olefins, (ii) unsaturated perfluorinated olefin typically perfluorovinyl ether and (iii) cure site monomers, (B) curing agent and optionally (C) filler and (D) other ingredients.

[0015] (A) PerfluoroelastomerPerfluoroelastomers described herein may comprise at least the following three copolymerized units: (i) one or more unsaturated perfluorinated olefins; (ii) one or more unsaturated perfluorinated olefin co-monomers different than unsaturated perfluorinated olefin (i) and are selected from the group consisting of perfluorovinyl ethers, unsaturated perfluorinated olefins and mixtures of perfluorovinyl ethers and unsaturated perfluorinated olefins; and (iii) one or more cure site monomers selected from the group consisting of nitrile-containing fluorinated olefins, nitrile-containing fluorinated vinyl ethers, or a mixture of these.

[0016] Alternatively, perfluoroelastomers may comprise at least the following three copolymerized monomer units: (i) about 25 to 74.9 mole percent of one or more unsaturated perfluorinated olefins; (ii) about 25 to 74.9 mole percent of one or more unsaturated perfluorinated olefin co-monomers different than unsaturated perfluorinated olefin (i) and are selected from the group consisting of perfluorovinyl ethers, unsaturated perfluorinated olefins, and mixtures of perfluorovinyl ethers and unsaturated perfluorinated olefins; and (iii) about 0.1 to 10 mole percent of one or more cure site monomers selected from the group consisting of nitrile-containing fluorinated olefins, nitrile-containing fluorinated vinyl ethers, or a mixture of these, wherein the mole percent of each of (i), (ii), and (iii) is based on the total mole percent of (i), (ii), and (iii) in perfluoroelastomer .

[0017] Perfluoroelastomers described herein may contain any of a variety of end groups as a result of the use of varying initiators or chain transfer agents during polymerization. Non-limiting examples of end groups include sulfonate, sulfonic acid, carboxylate, carboxylic acid, carboxamide, difluoromethyl groups, trifluorovinyl groups, or perfluorinated alkyl groups.

[0018] (i) Unsaturated Perfluorinated OlefinsExamples of unsaturated perfluorinated olefins include tetrafluoroethylene (C2F4), hexafluoropropylene and combinations of these. The concentration of unsaturated perfluorinated olefin (i) may range from 25 and 74.9 mole percent of the total moles of monomer units in perfluoroelastomer.

[0019] (ii) Unsaturated Fluorinated Olefin Co-MonomersUnsaturated perfluorinated olefin co-monomer (ii), which is different than unsaturated perfluorinated olefin (i), is selected from the group consisting of perfluorovinyl ethers, unsaturated perfluorinated olefins, and mixtures of perfluorovinyl ethers and unsaturated perfluorinated olefins.

[0020] Examples of perfluorovinyl ethers used to prepare perfluoroelastomer include, perfluoro(alkyl vinyl) ethers (PAVE), perfluoro(alkoxy vinyl) ethers, and mixtures of perfluoro(alkyl vinyl) ethers (PAVE) and perfluoro(alkoxy vinyl) ethers. Suitable perfluorinated(alkyl vinyl) ethers which may be used to prepare the compounds described herein include those shown in formulas (II) to (VI):

[0021] CF2=CFO(RfO)n(Rf"O)mRf (II)

[0022] wherein Rf and Rr are different linear or branched perfluoroalkylene groups of 2-6 carbon atoms, m and n are independently 0-10, and Rf is a perfluoroalkyl group of 1-6 carbon atoms.

[0023] Additional examples of perfluoro(alkyl vinyl) ethers includes compositions of formula (III):

[0024] CF2=CFO(CF2CFXO)nRf (III),

[0025] wherein X is F or CF3, n is 0-5, and Rf is a perfluoroalkyl group of 1-6 carbon atoms. Alternatively, n is 0 or 1 and Rf contains 1-3 carbon atoms. Examples of such perfluorinated (alkyl vinyl) ethers include perfluoro(methyl vinyl) ether and perfluoro(propyl vinyl) ether.

[0026] Other perfluoro(alkyl vinyl) ether monomers for the preparation of fluoroelastomer include monomers of formulas (IV), (V), and (VI):

[0027] CF2=CFO[(CF2)mCF2CFZO]nRf (IV),

[0028] wherein Rf is a perfluoroalkyl group having 1-6 carbon atoms, m=0 or 1, n=0-5, and Z=F or CF3;

[0029] CF2=CFO[(CF2CFCF3O)n(CF2CF2CF2O)m(CF2)p]CxF2x+i(V),

[0030] wherein m and n=l-10, p=0-3, and x=l-5. Specific embodiments of this class include monomers where n=0-l, m=0-l, and x=l and

[0031] CF2=CFOCF2CF(CF3)O(CF2O)mCnF2n+i(VI),

[0032] wherein n=l-5, m=l-3, and where, alternatively, n=l.

[0033] Examples of perfluoro(alkyl vinyl) ethers include perfluoro methyl vinyl ether, perfluoropropyl vinyl ether, and perfluoroethyl vinyl ether. Examples of perfluoro(alkoxy vinyl) ethers include perfluoromethoxy vinyl ether, perfluoropropoxy vinyl ether, and perfluoroethoxy vinyl ether.

[0034] Examples of unsaturated perfluorinated olefins include tetrafluoroethylene (C2F4); hexafluoropropylene; and combinations of these. Mixtures of perfluorovinyl ethers and unsaturated perfluorinated olefins may also be used.

[0035] The concentration of unsaturated perfluorinated olefin co-monomer in fluoroelastomer ranges from 25 to 74.9 mole percent, alternatively from 30to 65 mole percent, alternatively from 45 to 55 mole percent, based on the total mole percent of monomer units in perfluoroelastomer.

[0036] (iii) Cure Site MonomersPerfluoroelastomer (A) further comprises copolymerized units of one or more cure site monomers comprising at least one nitrile substituent group. Alternatively, the cure site monomers are selected from the group consisting of nitrile-containing fluorinated olefins and nitrile-containing fluorinated vinyl ethers (iii). The amount of such cure site monomers is, generally, from 0.1 to 10 mole percent, alternatively between 0.3 and 1.5 mole percent, based on the total mole percent of polymerizable monomer units used to prepare fluoroelastomer. Although more than one type of cure site monomer may be present, cure site monomers comprise at least one nitrile substituent group. Useful nitrile-containing cure site monomers include those of formulae (VII)-(XI):

[0037] CF2=CF-O(CF2)n-CN (VII)

[0038] wherein n=2-12, alternatively 2-6;

[0039] CF2=CF-O[CF2-CFCF3-O]n-CF2-CFCF3-CN (VIII),

[0040] wherein n=0-4, alternatively 0-2;

[0041] CF2=CF-[OCF2CFCF3]x-O-(CF2)n-CN (IX),

[0042] wherein x=l-2, and n=l-4; and

[0043] CF2=CF-O-(CF2)n-O-CF(CF3)CN (X),

[0044] wherein n=2-4.

[0045] Monomers of formula (IX) are used as cure site monomers. Especially, cure site monomers include perfluorinated polyethers having a nitrile group and a trifluorovinyl ether group. Alternatively, cure site monomer is perfluoro(8-cyano-5-methyl-3,6-dioxa- 1 -octene) (8-CNVE) and represented by formula (XI):

[0046] CF2=CFOCF2CF(CF3)OCF2CF2CN (XI)

[0047] B) Curing AgentsThe compound comprises at least one curing agent (B). The perfluoroelastomers employed in the compounds of the present invention are capable of undergoing crosslinking reactions with any of the known curatives for perfluoroelastomers such as, but not limited to, polyhydroxy compounds such as the combination of organic peroxides and polyfunctional coagents (U.S. Pat. Nos. 4,214,060; 4,983,680), organotin (U.S. Pat. No. 5,789,489), bis(aminophenols) such as diaminobisphenol AF (U.S. Pat. No. 6,211,319 Bl), aromatic tetraamines such as 3,3'-diaminobenzidene, 2,2-bis[3- amino-4-(N-phenylamino)phenyl] hexafluoropropane, and ammonia generating compounds such as urea and other compounds disclosed in U.S. Pat. No. 6,281,296 and WO 01 / 27194.

[0048] One curing agent that may be employed is an ammonia generating compound, which decompose to produce ammonia at curing temperatures. Examples of suchammonia generating compounds include, dicyandiamide, aldehyde ammonia condensation products, including acetaldehyde ammonia; and other compounds, such as hexamethylenetetramine; carbamates, for example t-butyl carbamate, benzyl carbamate, and HCF2CF2CH(CH3)OCONH2; urea; urea hydrochloride; thiourea; amides, such as phthalamide; metal ammine complexes, such as tetraamine copper (II) sulfate hydrate; ammonia-Lewis acid adducts; carboxamides, such as oxamic acid; biuret; unsubstituted amidines, such as formamidine, formamidine hydrochloride, and formamidine acetate. Typically, such ammonia generating compounds decompose and generate ammonia between 40 to 330 degrees C, alternatively between 90 to 220 degrees C.The amount of curing agent will necessarily depend on the degree of crosslinking as well as the type and concentration of reactive moieties, but one example of the level of the curing agent should be about 0.1 to 7 parts compound per 100 parts perfluoroelastomer, alternatively about 1 to 5 parts compound per 100 parts perfluoroelastomer.

[0049] C) FillersThe compounds described herein may additionally comprise filler. Various kind of fillers can be used, and both organic and inorganic filler can be used.

[0050] Examples of such filler include, carbon black, glass fiber, metal oxide such as almina (AI2O3) or titanium oxide (TiCE), anhydrous silica such as acidic silica or fumed silica. Examples of titanium dioxide include Ti-Pure™ R-101 available from Chemours and Pigment White 6. Examples of barium sulfate include Blanc Fixe available from Solvay Chemicals, and Huberbrite® available from Huber Engineering Materials. Examples of such silicas include anhydrous silica available from Degussa Aktiengesellschaft (Frankfurt, Germany) under the Aerosil® trademark. A particularly useful type is Aerosil® 200 silica. Other suitable silicas include Reolosil® silicas, available from Tokuyama KK (Tokyo, Japan), for example Reolosil® QS13, Reolosil® QS102, and Reolosil® QS30. Silica amounts range from 1 to 25 phr, alternatively, no more than 1 to 7 phr.

[0051] Additional types of fillers include micropowders or fluoroadditives. Micropowders are ordinarily partially crystalline polymers. Micropowders include finely divided, easily dispersed plastic fluoropolymers that are solid at the highest temperature utilized in fabrication and curing of the compounds described herein. The term “solid” refers to a plastic fluoropolymer that has a crystalline melting temperature above the processing temperature(s) of the compounds described herein.

[0052] Micropowders that can be used in these compounds include, but are not limited to, micropowders based on the group of polymers known as tetrafluoroethylene (TFE) polymers. This group includes polytetrafluoroethylene (PTFE) and copolymers of TFE.

[0053] D) other ingredientsAdditives such as stabilizers, plasticizers, lubricants, and processing aids typically utilized in compounding can be incorporated into the compounds described herein,provided they have adequate stability for the intended service conditions. In particular, low temperature performance can be enhanced by incorporation of perfluoropoly ethers.

[0054] copolymerizable modifying monomer such that the micropowders do not melt or soften during processing of fluoroelastomer A that comprise the micropowders. The modifying monomer may be, for example, hexafluoropropylene (HFP), perfluoro(propyl vinyl) ether (PPVE), perfluorobutyl ethylene, chlorotrifluoroethylene, or another monomer that introduces side groups into the polymer molecule.

[0055] Tetrafluoroethylene polymers used as additives in these compounds include copolymers of TFE having sufficient concentrations of copolymerized units of one or more monomers to reduce the melting point below that of PTFE. Such copolymers generally have melt viscosity in the range of 0.5-60* 103Pa s, but viscosities outside this range are also known. Perfluoroolefms and perfluoro(alkyl vinyl) ethers are preferred comonomers. Hexafluoropropylene and perfluoro(propyl vinyl) ether are most preferred. Examples of TFE copolymers include TFE / hexafluoropropylene copolymer and TFE / perfluoro(propyl vinyl)ether copolymers, provided they satisfy constraints on melting temperature with respect to perfluoroelastomer processing temperature. These copolymers can be utilized in powder form as isolated from the polymerization medium, if particle size is acceptable, or they can be ground to suitable particle size starting with stock of larger dimensions.

[0056] The amount of such other ingredients in these compounds ranges from about 0.01 to 100 phr and alternatively about 0.1 to 50 phr.

[0057] The compounds described herein may be prepared by mixing until homogeneous perfluoroelastomer (A), curing agent(s) (B), and optionally fillers (C) and any other ingrediednts (D), to form perfluoro elastomer sheet. Rubber compounding procedures such as a two roll rubber mill, an internal mixer, for example, a Banbury internal mixer, or in an extruder can be used to mixing the compounds. Then the compounds can be formed into sheets, using calender roll or any other equipments.

[0058] (II) Fabric sheet(s)The cushion material of the invention comprises fabric sheets. Any known fabric can be used as long as it’s heat resistance is over 300 degrees C. Examples of such fabric include; Meta-aramid fiber fabric, para-aramid fiber fabric, glass fiber fabric, carbon fiber fabric, ceramic fiber fabric, poly-benzobisoxazole fiber fabric and metal fiber fabric. Meta-aramids fiber fabric and glass fiber fabric are preferably used.

[0059] Both woven fabric and non-woven fabric can be used. For woven fabric, any types of fabric can be used, such as Plain weave, twill weave and satin weave. Also multiple weave fabric can be used.

[0060] The thickness of fabric is, exemplary from 0.01 to 5mm, alternatively from 0.1 to 2 mm, alternatively from 0.2 to 1 mm.

[0061] Examples of commercially available aramid fiber fabric include, Nomex NX-2232, NX-2239 and NX-2245 Meta-aramid fiber fabric available from TEIKOKU SEN-I Co., Ltd..: CO1200, CO1500, CO1600, CO1700, CO1910, CO2016, CO3501, C03500, CO3942, CO5261, CO5252 from TEIJIN FRONTIER CO., LTD.. Examples of commercially available grass fiber fabric include, KS4010, S4155 and KS4325 available from Nitto Boseki Co., Ltd; NGC330, NGC450, NGC850, NGC1000 and NGC2000 available from Nihon Glass Fiber Industrial Co., Ltd.; TOMBO No.8400, TOMBO No. 8400H and TOMBO No.8400R available from Nichias Corporation; TR7610N, TR9010N and TRI 6 ION available from Maeda glass Co., Ltd.; and CGC- 850, CGC-1000, CGC-1200 and CGC-2000 available from Chubu Kogyo Co. Ltd.;

[0062] (III) Process for preparing the cushion materialTwo fabric sheets are located each platy surface of perfluoro elastomer sheet, then hot- pressed the layered sheets, for example, under 1 to 100 tons, at 120 to 250 degrees C, for 5 to 30 minutes. The pressure, temperature and time are vary and sufficient to adhere the fabric sheets and perfluoro elastomer sheet. During the hot-pressed step, a part of cross-linkage can be generated. Additional heating (post cure) can be conducted using oven, for example, from 180 to 350 degrees C, alternatively from 250 to 310 degrees C, for 4 to 30 hours in air or nitrogen condition, to ensure forming cross-linkage of the curing agent with cure site monomer(s).

[0063] The cushion material of the invention can be single-layered or multi-layered.‘ Single-lay erd’ means the cushion material comprises one perfluoro elastomer sheet and two fabric sheets, i.e. one perfluoro elastomer sheet is sandwiched by two fabric sheets. ‘Multi-lay erd’ means the cushion material comprise at least two perfluoro elastomer sheets, and each of these perfluoro elastomer sheets is sandwiched by fabric sheets, i.e. two or more perfluoro elastomer sheets and fabric sheets are stacked alternately (one by one).

[0064] The obtained cushion material can be used under higher temperature than those of the traditional cushion materials. Therefore, the cushion material is useful for a hot- pressing equipment for a printed circuit board comprising PTFE resin and / or liquid crystal polymer (LCP). The temperature of hot-press process for such material is around 300 degrees C, much higher than the heat-resistance of traditional elastomers.

[0065] Also, the cushion material is useful for a hot-pressing equipment in the manufacturing process for mounting power semiconductors on insulating substrate. The cushion material of the invention can be repeatedly used for such hot-pressing process because of its higher heat-resistance.EXAMPLES

[0066] MaterialsFFKM sheet: Perfluoroelastomer compound, comprising tetrafluoroethylene (TFE), perfluoro(methyl vinyl) ether (PMVE), nitrile-containing cure-site monomer, carbon black and curing agent, was mixed by two roll rubber mill and were formed into a sheet (300mm square, 0.55-0.60mm thickness) by calender roll.Aramid sheet: Nomex® fiber Fabric NX-2245 from TEIKOKU SEN-I CO., LTD. (Plain weave, 0.37 thickness, 45 threads / inch density and 20 / 2 cotton count.))Glass fiber sheet: KS4325 from Nitto Boseki Co., Ltd. (Twill weave, 0.85 thickness, 48 threads / inch density.))FKM Sheet 1 : Fluoroelastomer compound, SOLVAY Tecnoflon® FOR 5351 / U grade (comprising 72 wt.% units of polymer with curing agent, 2 wt.% units of magnesium oxide, 4 wt.% units of calcium hydroxide and 22 wt.% units of carbon black) was mixed by two roll rubber mill and formed into a sheet (125mm square, 0.5mm thickness) by press equipment.FKM Sheet 2 (Commercial FKM / fabric material): Commercially available cushion material product, KINYO-Board R225 from Kinyosha.

[0067] Analytical methodsCompression Test:1. Test sample was set in tensile tester with compression jig (SHIMADZU CORPORATION Autograph AGS-5KNG) .2. Test sample was compressed with Imm / min speed at room temperature until 3.5Mpa surface pressure. After reaching at 3.5Mpa surface pressure, compression was released with Imm / min speed until OMPa surface pressure.3. Test sample and tensile tester were heated to targeted temperature and continued heating for 1 hour.4. Test sample was compressed with Imm / min speed at targeted temperature until 3.5Mpa surface pressure, then kept at 3.5 Mpa for 40minutes.5. Compression was released with Imm / min speed until OMpa surface pressure.6. After 5minutes, the above processes 4 and 5 were repeated, and the sample was compressed totally 5 cycles.7. The sample was removed from tensile tester and kept it at room temperature for 30min. Then the thickness of the sample was measured.8. The tensile tester was cooled to room temperature.9. From 1. to 8. processes were repeated, and the sample was compressed totally 20 cycles.

[0068] Thickness changeThickness of test samples before, and after 5, 10, 15 and 20 cycles compression were measured. Thickness retention rate is also calcurated.

[0069] Dimension changeDimensions of test samples, both vertical and width directions were measured before and after 20 cycles compression test. Dimension increase rate (%) was also calculated to check dimension change after compression test.

[0070] Surface pressure changeSurface pressure with compressing at room temperature was measured during compression test. Slope value from 1.5Mpa to 3.5Mpa, before and after 20 cycles compression were calculated.

[0071] Examples 1 and 2FFKM sheet were cut to 125 mm square, and aramid sheets were cut to 150 mm square. Three aramid sheets and two FFKM sheets are stacked alternately. Then, the layered sheets were heated at 170 degrees C for 7 minutes using press equipment (PAN STONE HYDRAULIC INDUS.CO., LTD Model: P-V-250-APCD) at 40 ton, then heated at 305 degrees C for 10 hours in oven. Test sample was cut into 30 mm square, to prepare FFKM cushion material test sample. The thickness of the test sample was 2.04 to 2.05mm.The compression test was conducted at 280 degrees C for Example 1, 300 degrees C for Example 2.

[0072] Comparative Examples 1 and 2FKM sheet 1 were cut to 125mm square, and aramid sheets were cut to 150mm square. Three aramid sheets and two FKM sheets are stacked alternately. Then, the layered sheets were heated at 170 degrees C for 10 minutes using press equipment (PAN STONE HYDRAULIC INDUS. CO., LTD Model: P-V-250-A-PCD, at 40ton, then heated at 250 degrees C for 8 hours in oven. Test sample was cut into 30 mm square, to prepare FKM cushion material test sample. The thickness of the test sample was 2.02 mm. The compression test of test sample was conducted at 280 degrees C for Comparative Example 1, at 300 degrees C for Comparative Example 2.

[0073] Comparative Examples 3 and 4FKM sheet 2 was cut into 30mm square to prepare FKM cushion material test sample. The thickness of the FKM sheet 2 was 2.30 mm. The compression test of test sample was conducted at 280 degrees C for Comparative Example 3, at 300 degrees C for Comparative Example 4.

[0074] Compression test Result :Surface appearance (photo) of Example 1 test sample are shown in Fig.s 9A and 9B.Dimension change is shown in Table 1, while the thickness change is shown in Table 2.

[0075] Table 1

[0076] Table 2

[0077] FFKM sheet hardly expands the dimensions and keeps original shape and dimensions. On the other hand, FKM sheets (FKM sheet 1 and FKM sheet 2) expand the dimensions and changed the shape, especially at 300 degrees C. Thickness change of FFKM sheet is 85 % or more after 20 cycles compression test. On the other hand, thickness of FKM sheets decreases after compression test and the thickness change ofFKM sheets is less than 85 %. Therefore, FFKM sheet keeps good thickness retention rate compared to FKM sheets.

[0078] Slope value from 1.5 Mpa to 3.5 Mpa is shown in Table 3. Compressive stress curve for each test sample is shown in Fig.s 1 to 7 respectively.

[0079] Table 3

[0080] Due to mechanical factors and variations in each sample shape, the data at the initial compression stage is expected to vary widely. The data that has been compressed to a certain extent (ex. over 1.5Mpa) is considered to be highly reliable, then slope value is calculated the range between 1.5Mpa and 3.5MPa.

[0081] FFKM sheet hardly changes slope value from 1.5Mpa to 3.5MPa, on the other hand, FKM sheet increased slope value. It means that FKM sheet hardens and loses cushion ability under 280 and 300 degrees C.

[0082] Example 3Glass fiber sheets were used instead of aramid sheets of Example 2. The same procedure of Example 2 was conducted, i.e. three glass fiber sheets and two FFKM sheets are stacked alternately, then the layered sheets were pressed at 170 degrees C for 7 minutes at 40 ton, then heated at 305 degrees C for 10 hours in oven. Press equipment PAN STONE HYDRAULIC INDUS.CO., LTD Model: P-V-250-APCD was used. The thickness of the test sample was 3.78 to 3.88mm.The compression test was conducted at 300 degrees C.

[0083] Table 4Same as Examples 1-2, surface pressure was measured during compression test, and slope value was calculated. The result is shown in Table 5.

[0084] Table 5

Claims

CLAIMSWhat is claimed is:

1. A cushion material for hot pressing comprising at least two fabric sheets and at least one perfluoroelastomer sheet, the fabric sheets are located to both upper side and lower side of the perfluoroelastomer sheet, in which the perfluoroelastomer sheet is formed from a perfluoroelastomer composition comprising:(A) a perfluoroelastomer comprising copolymerized units of:(i) one or more unsaturated perfluorinated olefins;(ii) one or more perfluorovinyl ether selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and a mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl) ether;(iii) one or more cure site monomers selected from the group consisting of bromine atoms, iodine atoms and nitrile group;(B) one or more curing agent, and(C) optionally one or more filler.

2. The cushion material for hot pressing of claim 1, wherein the fabric sheet is aramid fiber sheet or glass filer sheet.

3. The cushion material for hot pressing of claim 1, wherein the cushion material comprises at least three fabric sheets and at least two perfluoroelastomer sheets, in which the fabric sheets and the perfluoroelastomer sheets are stacked alternately.

4. The cushion material for hot pressing of Claim 1, wherein the thickness of the cushion material is from 0.5 to 10.0 mm.

5. The cushion material for hot pressing of claim 1, when a thickness of the cushion material for hot pressing is defined as To, and the thickness of the cushion material after 20 cycles of compression test under 3.5 MPa compression for 40 minutes at 300 degrees C is defined as T20, T20 / T0 is larger than 0.85.

6. A hot pressing equipment used for manufacturing of a printed circuit board comprising PTFE resin and / or liquid crystal polymer, in which the hot pressing equipment comprises a cushion materials of claim 1.

7. A hot pressing equipment used for manufacturing process for mounting power semiconductors on insulating substrate, in which the hot pressing equipment comprises a cushion materials of claim 1.

8. A method for making a cushion material for hot pressing, comprising the steps of:(1) preparing at least one perfluoroelastomer sheet formed from a composition comprising:(A) a perfluoroelastomer comprising copolymerized units of:(i) one or more unsaturated perfluorinated olefins;(ii) one or more perfluorovinyl ether selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and a mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl) ether; and(iii) one or more cure site monomers selected from the group consisting of bromine atoms, iodine atoms and nitrile group;(B) one or more cure site agent, and(C) optionally one or more filler,(2) applying the perfluoroelastomer sheet between two fabric sheets,(3) hot pressing the layered sheets, to adhere the fabric sheets and perfluoroelastomer sheet, then(4) further heating the hot pressed layerd sheet to form cross-linkage of the perfluoroel astomer .

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