JPH10219199A - Silicone rubber sheet for thermal contact bonding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sheet which is used for thermal contact bonding and excellent in surface releasability, and scarcely contaminates surrounding equipment parts, an adherend, etc., by subjecting a sheet obtained by dusting scaly powder on the surface of a silicone rubber sheet to water washing to remove excess powder. SOLUTION: A sheet obtained by dusting talc and/or mica preferably having a mean particle diameter of 0.5-30μm on the surface of a silicone rubber sheet is washed with water to remove excess powder. The silicone rubber sheet comprises one obtained by blending an organopolysiloxane, a filler and a curing agent, forming the blend into sheet and curing the sheet and has a thickness of 0.1-10mm. It is used for thermal contact bonding and particularly used in electrically and mechanically connecting an electrode connected to a panel to a lead electrode of a flexible printed circuit board through an anisotropically conductive adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention is excellent in surface releasability,
Silicone rubber sheet for thermocompression bonding that does not easily contaminate surrounding device parts and objects to be compressed.Especially, an electrode connected to a liquid crystal panel and a lead electrode of a flexible printed circuit board are electrically connected via an anisotropic conductive adhesive. TECHNICAL FIELD The present invention relates to a silicone rubber sheet for thermocompression bonding used when connecting mechanically and mechanically.

[0002]

2. Description of the Related Art In recent years, portable computers, word processors,
Liquid crystal panels are increasingly used as displays for video cameras, navigation systems, portable televisions, and the like. In manufacturing this liquid crystal panel, an electrode connected to the liquid crystal panel and a driving LSI for driving the liquid crystal are used.
Is electrically and mechanically connected to a lead electrode of a flexible printed circuit board (FPC) on which is mounted by using an anisotropic conductive adhesive.

[0003] In this case, a sheet for thermocompression bonding is used between the pressing tool and the FPC to transfer heat from the pressing tool to the anisotropic conductive adhesive and to apply uniform pressure. As the thermocompression bonding sheet, a fluororesin film such as polytetrafluoroethylene (PTFE) may be used, but a silicone rubber sheet having low elasticity, flexibility, and good heat conductivity in order to apply pressure evenly. It has become common to use. However, since the silicone rubber sheet is more adhesive than the fluororesin film on the sheet surface, the silicone rubber sheet adheres to the pressure sheet or FPC in close contact with the sheet, significantly reducing the workability of the pressure bonding step and forcing the sheet. When peeling off, fine scratches may be formed and durability may be deteriorated.

As the silicone rubber sheet for thermocompression bonding, for example, a silicone rubber compounded with boron nitride and a conductive substance and reinforced with a glass cloth (Japanese Patent Laid-Open No. 5-1 / 1993)
No. 98344), silicone rubber mixed with boron nitride and a conductive material, reinforced with glass cloth to impart antistatic properties (Japanese Patent Application Laid-Open No. 6-36853), and silicone rubber made of ceramic, metal, etc. A compound containing a heat conductive substance (JP-A-6-289352), a compound containing silicone rubber and carbon black having a volatile content of 0.5% or less excluding water to improve heat resistance (JP-A-6-289352). No. 7-11010) and the like. However, these do not improve the tackiness of the sheet surface.

Therefore, the present inventors have developed a composite for heat-compression bonding which has no stickiness on the sheet surface and excellent strength by forming a composite of a sheet in which carbon black is mixed with silicone rubber and a heat-resistant resin film. A silicone rubber composite sheet has been proposed (JP-A-8-174765). However, in this sheet, since the silicone rubber is bonded to the heat-resistant resin film, the flexibility is lower than that of the rubber alone. This tendency is particularly enhanced when heat-resistant resin films are provided on both sides of the sheet. For this reason, it becomes difficult to apply pressure uniformly at the time of pressurization, and it is necessary to increase the pressing force. However, this pressing force has a limit in relation to the strength of the object to be pressed.

Therefore, when a silicone rubber having a low hardness is used, the flexibility is improved. However, it is necessary to reduce the filling amount of carbon in order to reduce the hardness of the rubber. Deteriorate. In addition, in order to reduce the adhesiveness of the rubber surface, a method of dusting powder such as talc or mica is known, but in this case, there is a problem that the powder easily falls off and contaminates the surroundings. In addition, when the powdered sheet is used, the powder gradually adheres to the pressing tool, so that uniform pressing cannot be performed. Therefore, it is necessary to perform periodic cleaning. In addition, after attaching the FPC, the liquid crystal panel is cleaned. Since it is difficult to do so, a device that does not contaminate the process is required.

[0007]

SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide a silicone rubber sheet for thermocompression bonding which is excellent in surface releasability and is less likely to contaminate peripheral device parts, objects to be compressed and the like. is there. A second object of the present invention is to provide a silicone rubber sheet for thermocompression bonding, which is flexible and can be pressed uniformly at a low pressure and excellent in workability and durability.

[0008]

SUMMARY OF THE INVENTION The above objects of the present invention are attained by washing a sheet obtained by pulverizing scaly powder on the surface of a silicone rubber sheet with water to remove excess powder. This is achieved by a silicone rubber sheet for thermocompression bonding. Silicone rubber sheet used in the present invention,
It is obtained by blending an organopolysiloxane, a filler and a curing agent, forming the mixture into a sheet, and then curing.

The organopolysiloxane used for the silicone rubber for forming the silicone rubber sheet of the present invention is:
The average degree of polymerization is 200 or more, and the average composition formula R _n SiO
It is preferably represented by _{(4-n) / 2} (n is an integer of 1.95 to 2.05). R in the formula represents a substituted or unsubstituted monovalent hydrocarbon group. Specific examples of R include an alkyl group such as a methyl group, an ethyl group and a propyl group, a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group,
Examples include an alkenyl group such as a vinyl group and an allyl group, an aryl group such as a phenyl group and a tolyl group, and a halogenated hydrocarbon group in which these hydrogen atoms are partially substituted with a chlorine atom, a fluorine atom, or the like.

In the present invention, it is preferable that the main chain of the organopolysiloxane is composed of dimethylsiloxane units, or that the main chain of the organopolysiloxane is introduced with a vinyl group, a phenyl group, a trifluoropropyl group or the like. Further, those in which the molecular chain ends are blocked with a triorganosilyl group or a hydroxyl group are preferred, and examples of the triorganosilyl group include a trimethylsilyl group, a dimethylvinylsilyl group, and a trivinylsilyl group. The degree of polymerization used in the present invention is 20 as described above.
0 or more, and the viscosity at 25 ° C. is 3
Those having a value of 00cs or more are preferred. When the polymerization degree is 200 or less, there is a disadvantage that the mechanical strength after curing is inferior and becomes brittle.

As the filler, carbon black having a volatile content of 0.5% by weight or less excluding moisture is used when heat resistance is prioritized, and good thermal conductive filler is used when heat conductivity is prioritized. Is mainly used. Volatile content excluding water is 0.
Carbon black of 5% or less improves the heat resistance of the silicone rubber sheet, improves the thermal conductivity and mechanical strength, and imparts antistatic properties due to conductivity.

Carbon black is classified into furnace black, channel black, thermal black, acetylene black and the like according to the production method. Carbon black having a volatile content of 0.5% or less used in the present invention includes: Acetylene black and JP-A-1-272
Preferred is conductive carbon black disclosed in US Pat. The method for measuring volatile matter is JIS K 6221.
It is described in "Test Methods for Carbon Black for Rubber". Specifically, a prescribed amount of carbon black is placed in a crucible, and the loss of volatilization after heating at 950 ° C. for 7 minutes is measured.

The amount of the carbon black is 20 to 150 parts by weight based on 100 parts by weight of the organopolysiloxane.
It is preferably used in an amount of from 40 to 100 parts by weight. If the amount is less than 20 parts by weight, the thermal conductivity becomes insufficient, and if it exceeds 150 parts by weight, the compounding becomes difficult and the moldability becomes extremely poor.

The good thermal conductive filler used in the present invention includes inorganic powders such as aluminum oxide, boron nitride, aluminum nitride, aluminum hydroxide, magnesium oxide, zinc oxide, quartz and graphite, or silver, nickel and copper. And metal powder such as iron. The compounding amount is 50 parts by weight based on 100 parts by weight of the organopolysiloxane.
It is preferably used in the range of 1 to 1,200 parts by weight, particularly 100 to 1,000 parts by weight. When the amount is less than 50 parts by weight, the thermal conductivity becomes insufficient. When the amount exceeds 1,200 parts by weight, the moldability deteriorates, the mechanical strength after curing is lowered, and the rubber becomes less flexible. Further, carbon black and a good thermal conductive filler may be used in combination.

The curing agent used in the present invention can be appropriately selected from those conventionally known and commonly used for curing silicone rubber. For example, in the case of a radical reaction, di-t-butyl peroxide, 2,5
Organic peroxides such as -dimethyl-2,5-di (t-butylperoxy) hexane, dicumyl peroxide, and the like, in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the organopolysiloxane. Part.

When the organopolysiloxane has two or more alkenyl groups, the addition of an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms in one molecule and a platinum group metal-based catalyst. Reaction hardeners are exemplified. The amount of the organohydrogenpolysiloxane is preferably such that the molar ratio of the hydrogen atom bonded to the silicon atom to the alkenyl group of the organopolysiloxane (≡Si—H / alkenyl group) is 0.5 to 5; The content of the metal catalyst is preferably 1 to 1,000 ppm based on the organopolysiloxane.

When the organopolysiloxane contains two or more silanol groups, a condensation reaction of an organosilicon compound having two or more hydrolyzable groups such as an alkoxy group, an acetoxy group, a ketoxime group, a propenoxy group, etc. Curing agents. In the present invention, it is preferable to use an organic peroxide or an addition reaction curing agent from the viewpoint of ease of molding.

In addition, if necessary, reinforcing silica fillers such as hydrophilic silica and hydrophobic silica, fillers such as clay, calcium carbonate, diatomaceous earth and titanium dioxide, low molecular weight siloxane esters, and organic compounds having silanol groups By adding a dispersing agent such as a silicon compound, a silane coupling agent, an adhesion imparting agent such as a titanium coupling agent, a platinum group metal-based catalyst for imparting flame retardancy, and tetrafluoropolyethylene particles for increasing the green strength of a rubber compound. Is also good.

The method of compounding the silicone rubber compound for producing the silicone rubber sheet of the present invention is as follows. The above components are kneaded using a mixer such as a two-roller, kneader, Banbury mixer, or planetary mixer. Although good, it is generally preferred that only the curing agent be added immediately before use.

As a method of forming a silicone rubber sheet, a method of hot-press curing a silicone rubber compound containing all components up to a curing agent in a mold, or processing into a predetermined shape with a calender or an extruder, A thermosetting method, a liquid silicone rubber compound or a silicone rubber compound dissolved in a solvent such as toluene and liquefied is mixed with polyethylene terephthalate (PE).
T) or the like, and a method of coating the film on a film, drying the solvent, and then heat-curing.

The thickness of the silicone rubber sheet thus formed is preferably in the range of 0.1 to 10 mm. When the thickness is 0.1 mm or less, the pressure cannot be applied sufficiently because the pressure-sensitive member cannot follow the pressure-bonded body sufficiently. On the other hand, when the thickness is 10 mm or more, the heat transmission becomes poor, which is not preferable. It is necessary that the shape of the powder that reduces the tackiness by powdering on the surface of the silicone rubber sheet is scale-like. Powder having a shape other than scaly has poor elongation when applied to a sheet, and tends to cause uneven coating. In addition, the scale-like powder adhered after washing with water has a large adhesion area with the sheet surface, and thus is less likely to fall off during the pressure bonding step.

As the scaly powder, talc, mica, hexagonal boron nitride and the like can be used. As is well known, talc is composed of hydrous magnesium silicate and contains some impurities such as iron oxide. Mica, on the other hand, is a crushed mica of natural origin, with aluminum, potassium,
It is a silicate compound such as magnesium. In addition, there are graphite and dihydrated molybdenum as scaly powders, but since they are black, there is a drawback that dirt is conspicuous.

The average particle size of the flaky powder is 0.5 to 30 μm.
It is preferably in the range of m. When the particle diameter is 0.5 μm or less, the particles are likely to aggregate, and if the particles adhere to a sheet, the smoothness is deteriorated, so that uniform pressing cannot be performed. Particle size is 30
A similar problem occurs when the thickness exceeds μm. The scaly powder may be used alone or as a mixture, but it is particularly preferable to use talc and / or mica.

The method of powdering the surface of the silicone rubber sheet is as follows: 1) a method in which the powder is contained in a gauze, a sponge, a brush or the like and mechanically rubbed. 3) Dispersing the powder in water and passing a sheet through it. Also, as a method of washing excess powder attached to the sheet with water,
1) A method of mechanically rubbing in water with a gauze, a sponge, a brush, or the like, 2) A method of spraying water on a sheet like a shower, 3) A method of ultrasonic cleaning in water, and the like. Finally, it is dried to obtain a form usable as a silicone rubber sheet for thermocompression bonding. The resulting sheet has an extremely thin layer with powder adhering to the surface, so it has good releasability from pressure tools and objects to be pressed, and has the advantage that the powder does not easily fall off and does not pollute the surroundings. There is.

The silicone rubber sheet of the present invention is excellent in heat resistance, thermal conductivity, strength and workability, and has elasticity as silicone rubber, so that it can be used for forming a laminate or a flexible printed board with a press molding machine. Sheets used to transfer heat to and apply pressure evenly,
Thermo-compression bonding used when connecting the electrodes connected to the liquid crystal display and the lead electrodes of the FPC on which the drive LSI is mounted by an electric-mechanical connection by interposing an anisotropic conductive adhesive Effective as a sheet.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The silicone rubber sheet for thermocompression bonding of the present invention is obtained by appropriately scaly powdering flake-like powder on the surface of a silicone rubber sheet produced by a known method, washing with water, and washing with water. It can be easily obtained by removing the powder.

[0027]

The effects of the present invention are listed below. 1) The surface of the sheet has releasability, and the sheet does not adhere to the pressing tool or the object to be pressed. As a result, the workability of the pressure bonding step is improved, and the durability of the sheet itself is improved. 2) Since the extra powder on the sheet surface is removed, the surroundings are hardly contaminated. This is an important characteristic particularly when used for connecting a liquid crystal panel. 3) The sheet is flexible and can be pressed uniformly at low pressure. 4) Since the sheet slightly moves without contact during pressurization, uniform pressure can be applied without air entrapment during pressure bonding.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. Embodiment 1 FIG. 99.85 mol% of dimethylsiloxane units
Methylvinylpolysiloxane unit having an average degree of polymerization of 8,000 consisting of 0.15 mol% of methylvinylsiloxane units
00 parts by weight, 0.10% of volatile matter with an average particle size of 40 nm
50 parts by weight of acetylene black and reinforcing silica
5 parts by weight of Aerosil R-972 (trade name, manufactured by Degussa) were blended with two rolls, kneaded and homogenized.

The obtained silicone rubber compound 10
0.1 part by weight of an isopropyl alcohol solution of chloroplatinic acid (amount of platinum 2% by weight) with respect to 0 part by weight, and 0.05 of acetylenic alcohol (3-methyl-1-butyl-3-ol) as a reaction inhibitor 1 part by weight and 1.2 parts by weight of methyl hydrogen polysiloxane represented by the following formula 1 were added and kneaded well with a two-roll mill to prepare a curable silicone rubber compound.

Embedded image

The obtained silicone rubber compound is
Using a calendering machine, the mixture was fractionated to a thickness of 0.30 mm, and then a 100 μm-thick polyethylene terephthalate (P
ET) The image was transferred onto a film and cured in a heating furnace at 160 ° C. for 5 minutes. Next, the silicone rubber sheet is
The sheet was peeled off from the ET film, and talc powder having an average particle diameter of 13 μm was rubbed on the sheet using a gauze and applied evenly. After further heat treatment at 200 ° C. for 4 hours in a dryer,
The sheet was washed while being rubbed with a sponge in running water to remove excess powder and dried to prepare a silicone rubber sheet for thermocompression bonding.

Embodiment 2 FIG. 9 dimethylsiloxane units
9.85 mol% of methyl vinyl siloxane unit 0.15
100 parts by weight of methylvinylpolysiloxane having an average degree of polymerization of 8,000 and 400 parts by weight of aluminum oxide powder (alumina AL-45: trade name, manufactured by Showa Denko KK) as a good thermal conductive filler. Surface area 200m
² / g and a silica fine powder Aerosil 200 (trade name manufactured by Nippon Aerosil Co.) 30 parts by weight, and α is represented by the following formula 2, .omega.-dihydroxy methylpolysiloxane 5
Parts by weight using a kneader,
Heat treated at 2 ° C. for 2 hours.

Embedded image

After cooling, 100 parts by weight of the obtained silicone rubber compound was mixed with an organic peroxide C-2 as a curing agent.
1.5 parts by weight (manufactured by Shin-Etsu Chemical Co., Ltd.) were added and mixed with two rolls, and then the thickness was 0.3
After being separated into 0 mm, it was transferred onto a 100 μm PET film and cured in a heating furnace at 160 ° C. for 5 minutes.

Next, the silicone rubber sheet thus obtained was peeled off from the PET film, and the average particle size was 2
The mica powder of 0 μm was rubbed on the sheet using gauze and applied without unevenness. The sheet was further heat-treated at 200 ° C. for 4 hours in a drier, washed with a sponge in running water to remove excess powder, and dried to prepare a silicone rubber sheet for thermocompression bonding.

Comparative Examples 1 to 3. The silicone rubber sheet of Example 1 which does not powder talc powder (Comparative Example 1), the silicone rubber sheet of Example 2 which does not powder mica powder (Comparative Example 2), and the silicone rubber sheet of Example 1 Then, a product which was not washed with water after the talc powder was ground (Comparative Example 3) was produced.

Comparative Example 4 A primer C (manufactured by Shin-Etsu Chemical Co., Ltd.) was applied to an aromatic polyimide film (Kapton: trade name, manufactured by Toray Dupont Co., Ltd.) having a thickness of 12 μm, and then dried at room temperature for 30 minutes.

The curable silicone rubber compound prepared in Example 1 was applied to a thickness of 0.3 using a calender molding machine.
After dispensing into 0 mm, it was transferred onto a 100 μm PET film, and the Kapton film coated with a primer was pressed from above the sheet, and passed through a heating furnace at 160 ° C. for 5 minutes to cure the silicone rubber compound. I let it. Next, the PET film was peeled off and dried in a dryer for 200 hours.
Heat treatment was performed at 4 ° C. for 4 hours to prepare a silicone rubber composite sheet for thermocompression bonding.

Crimping Test Under the silicone rubber sheet for thermocompression bonding prepared in Examples 1 and 2 and Comparative Examples 1 to 4, a 30 μm thick Teflon (manufactured by Dupont Japan, Limited) film, and then a 25 μm pitch The two FPCs with copper electrodes sandwiched between the 22 μm-thick anisotropic conductive adhesive (aligning the upper and lower copper electrodes) were placed, and then placed on the crimping machine,
Pressing was performed for 20 seconds with a pressing tool of 340 ° C. at a pressing pressure of 40 kgf / cm ² . This pressure bonding was repeated, and the number of times the sheet was in close contact with the pressing tool and the number of times until the anisotropic conductive adhesive could not be cured by heating under a uniform pressure were measured. This number was confirmed by the conduction of the copper electrodes of the upper and lower FPCs.

In the case of the silicone rubber composite sheet for thermocompression bonding of Comparative Example 4, the measurement was performed with the Kapton film side facing the pressing tool. In addition, since the thickness of the film is increased and the heat transmission is deteriorated, the pressing time is extended to 25 seconds. As is evident from the results in Table 1, in the case of Comparative Examples 1 and 2, the sheet comes into close contact with the pressing tool every time it is pressed, so that the workability is poor and the pressing step time is long. Further, the sheet itself is easily damaged, so that the durability is reduced.

[0039]

[Table 1] In the case of Examples 1 and 2 and Comparative Example 3, since the pressurizing tool becomes gradually contaminated by continuous use, cleaning is required. However, in the case of Examples 1 and 2, the cleaning can be performed before the work because cleaning of the pressurizing tool is performed once / two days, whereas in the case of Comparative Example 3, it is performed twice / one. Cleaning is required every day, and each time the crimping machine must be cooled, which is very troublesome.

In Example 1 and Comparative Example 4, a crimping test was performed under exactly the same conditions except that the pressing force of the pressing tool was reduced to 30 kgf / cm ² . The conduction of the copper electrode of the FPC was good, but in the case of Comparative Example 4, some conduction failure occurred.
In the case of the silicone rubber composite sheet for thermocompression bonding of Comparative Example 4, there is no problem with the adhesion to the pressure tool and the contamination of the pressure tool, but the compression time is extended as compared with the present invention (Example). , The pressing pressure had to be increased.

Claims (5)

[Claims] 1. A silicone rubber sheet for thermocompression bonding, wherein a sheet obtained by pulverizing scaly powder on the surface of a silicone rubber sheet is washed with water to remove excess powder. 2. The powder used for powdering has an average particle size of 0.5-3.
The silicone rubber sheet for thermocompression bonding according to claim 1, which is talc and / or mica having a thickness of 0 µm. 3. The silicone rubber sheet for thermocompression bonding according to claim 1, wherein the silicone rubber sheet contains carbon black having a volatile content other than water of 0.5% by weight or less. 4. The silicone rubber sheet for thermocompression bonding according to claim 1, wherein the silicone rubber sheet contains a good thermal conductive filler. 5. The silicone rubber sheet has a thickness of 0.1 to 1
The thermally conductive silicone rubber sheet according to any one of claims 1 to 4, which is 0 mm.