JP2003198167A - Thermal conductive composition, thermal conductive sheet, bonding method of heater and heat dissipator, and bonding structure of heater and heat dissipator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal conductive composition exhibiting excellent versatility because of low dependence of thermal conduction efficiency on the use conditions and bonding a heater and a heat dissipator with high thermal conduction efficiency while exhibiting excellent shape follow up performance to a rough surface by pressing. <P>SOLUTION: The thermal conductive composition being interposed between a heater and a heat dissipator contains at least one kind of thermoplastic resin, a capsule encapsulating a liquid substance, and thermal conductive fine particles. The capsule comprises a capsule material forming a shell, and the encapsulated liquid substance which leaks when the capsule is applied with a pressure exceeding the withstanding pressure thereof. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in versatility because it has little dependence of heat conduction efficiency on usage conditions. The present invention relates to a heat conductive composition capable of bonding with high heat conduction efficiency, a heat conductive sheet, a method for bonding a heating element and a radiator, and a bonding structure for a heating element and a radiator.

[0002]

2. Description of the Related Art Conventionally, a sheet (hereinafter also referred to as a heat conductive sheet) using a heat conductive composition has been used for transmitting heat generated by a heat generating element such as an electric / electronic component to a heat radiator and dissipating the heat. It is used by being interposed between the heating element and the radiator. However, the surfaces of the heat generating element and the heat radiating element are often not smooth, and the heat conductive sheet is often unable to adhere to each other to obtain a sufficient contact area. Therefore, there is a problem in that even if a heat conductive sheet is used between the heat generating element and the heat radiating element, the heat conduction efficiency is poor and a sufficient heat radiating effect cannot be obtained.
In order to increase the heat conduction efficiency, it is necessary to improve the adhesion of the heat conductive sheet to the heat generator and the heat radiator.

As a technique for improving the adhesion to the heating element and the radiator, US Pat. No. 5,950,
No. 066 discloses a heat conductive composition obtained by adding heat conductive fine particles to a resin having a melting point of about 30 to 90 ° C. Similarly, US Pat. No. 6,054,198 discloses a heat conductive composition which is liquefied by a phase transition. These heat-conductive compositions are intended to be melted by heat from a heating element and to fill the boundary surface between the heating element and the heat-dissipating element to improve the adhesion and obtain a high heat-dissipating effect. .

However, the above-mentioned thermally conductive composition is
At temperatures below the melting point, such as the melting point and phase transition temperature, the adhesiveness does not improve and the heat dissipation effect cannot be exhibited.Therefore, heat depending on the usage conditions such as the heat generation amount of the heating element, the heat radiation capacity of the heating element, and the surrounding environment of the heating element. It is necessary to change the design of the conductive composition, and there is a problem of poor versatility. In addition, since the above-mentioned thermally conductive composition requires a certain time to melt and fill the boundary surface, the temperature of the heating element such as an electronic component rises before a sufficient heat radiation effect is exhibited. There is also a problem in that the heating element may be overloaded and a load may be applied to the heating element.

[0005]

In view of the above situation, the present invention is excellent in versatility because it has little dependency of heat conduction efficiency on use conditions, and exhibits excellent shape following ability on rough surfaces by crimping. And a heat conductive composition capable of bonding a heat generating element and a heat radiating element with high heat conduction efficiency, a heat conductive sheet, a method of bonding the heat generating element and the heat radiating element, and a bonding of the heat generating element and the heat radiating element It is intended to provide a structure.

[0006]

The present invention relates to a heat conductive composition used by being interposed between a heat generating element and a heat radiating element, which comprises a thermoplastic resin, a capsule containing a liquid substance and a heat conductive material. Containing fine particles, the capsule,
It is composed of an encapsulant forming an outer shell and the liquid substance encapsulated in the encapsulant, and the liquid substance in the capsule is heat-conductive composition by being subjected to a pressure exceeding the pressure resistance of the capsule. It is a thermally conductive composition that leaks to the outside. The present invention is described in detail below.

The heat conductive composition of the present invention is used by being interposed between a heat generating body and a heat radiating body. The heating element is not particularly limited, and examples thereof include electric / electronic parts. The radiator is not particularly limited, and examples thereof include radiators such as heat sinks and heat pipes, electric cooling devices such as Peltier elements, and cooling devices that circulate a cooling medium such as cooling water.

The heat conductive composition of the present invention contains a thermoplastic resin, a capsule containing a liquid substance, and heat conductive fine particles. The thermoplastic resin is not particularly limited, but it is preferable to use a resin having adhesiveness. Specifically, for example, acrylic resin, methacrylic resin, styrene-block copolymers such as styrene-butadiene-styrene block copolymer and styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate resin, butadiene Resin, isobutylene resin,
Olefin resin, urethane resin, epoxy resin,
Examples thereof include vinyl acetate resins, styrene resins, butyral resins, poval resins, silicone resins, and modified resins thereof. The above thermoplastic resins may be used alone or in combination of two or more.

The capsule containing the liquid substance is composed of an encapsulating material forming an outer shell and the liquid substance contained in the encapsulating material. The heat conductive composition of the present invention comprises the capsule. The liquid substance in the capsule leaks out of the heat-conductive composition by receiving a pressure exceeding the pressure resistance of. The heat conductive composition is generally used by being fixed between a heat generating body and a heat radiating body on a mounting board by being crimped by a method such as fixing with a clip or screwing. The composition has a pressure exceeding the pressure resistance of the capsule at the time of pressure bonding and leaks the liquid substance from the capsule containing the liquid substance to fill the interface between the heat generating element and the heat radiating element with the heat generating element and the heat radiating element. Establish a bond with.

The above-mentioned encapsulation material is not particularly limited as long as it can be destroyed by receiving a pressure exceeding the pressure resistance of the encapsulation. For example, (meth) acrylic resin, acrylonitrile resin, vinylidene chloride resin, melamine formaldehyde, etc. There is something like.

The pressure resistance of the capsule can be adjusted by changing the glass transition point, the degree of cross-linking, etc. of the capsule material. For example, in order to obtain a hard and brittle capsule material, it is preferably uncrosslinked. The pressure resistance of the capsule is the minimum pressure required to break the capsule. The preferable lower limit of pressure resistance of the capsule is 1 N / cm ² , and the upper limit thereof is 2000 N / cm ² .
cm ² . When it is less than 1 N / cm ² , the encapsulant may unintentionally be broken when the heat conductive sheet made of the heat conductive composition of the present invention is wound or during transportation, and the handleability is improved. Is reduced. If it exceeds 2000 N / cm ² , the pressure when destroying the encapsulant may damage the heating elements such as electronic components. A more preferable lower limit of the pressure is 3 N / cm ² and an upper limit thereof is 1000 N / cm ² .

As the liquid substance, a substance having a plasticizing effect on the thermoplastic resin or a substance having poor compatibility with the thermoplastic resin can be used, but the boiling point thereof is 100 ° C. or more. Preferably there is. 100 ° C
If it is less than the above value, it is volatilized by the heat from the heating element, causing voids in the obtained heat conductive sheet to deteriorate the heat conduction efficiency, or causing contact failure when used for heat dissipation of electronic parts. Sometimes. It is more preferably 150 ° C. or higher.

The liquid substance having the plasticizing effect is not particularly limited, and examples thereof include phthalic acid ester, trimellitic acid ester, aliphatic dibasic acid ester phosphoric acid ester, ricinoleic acid ester, polyester / epoxidized ester, acetic acid. Common plasticizers such as esters may be mentioned.

The liquid substance having poor compatibility with the above-mentioned thermoplastic resin is not particularly limited, since its compatibility is changed depending on the combination with the above-mentioned thermoplastic resin. For example, mineral oil hydrocarbons, animal and plant hydrocarbons, liquid paraffin, Examples include silicone oil, squalane, animal and plant oils, the above plasticizers, and the like.

The particle size of the capsule is not particularly limited, but when the heat conductive composition of the present invention is formed into a sheet and used as a heat conductive sheet, it is usually about half the sheet thickness.

The preferred lower limit of the content of the capsule in 100 parts by weight of the thermoplastic resin is 1 part by weight, and the upper limit is 100 parts by weight. If it is less than 1 part by weight, the effect on the heat conduction efficiency may not be sufficiently exhibited. If it exceeds 100 parts by weight, the physical properties of the resin such as tackiness may be adversely affected.

The heat conductive composition of the present invention contains heat conductive fine particles for the purpose of improving heat conductivity. The heat conductive fine particles are not particularly limited, and examples thereof include ceramic heat conductive fine particles of boron nitride, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, zinc oxide, etc .; metal powders of aluminum, copper, silver, etc. Etc. Of these, boron nitride, silicon carbide, aluminum nitride, aluminum, copper, and silver are preferable because they have high thermal conductivity and excellent thermal conductivity can be obtained with a small filling amount.

The purity of the above heat conductive fine particles is 95.
It is preferably at least wt%. If it is less than 95% by weight, the thermal conductivity is lowered, and in order to compensate for it, the addition amount must be further increased, and the flexibility of the thermally conductive composition of the present invention is impaired. More preferably, it is 97% by weight or more.

The preferable average particle size of the heat conductive fine particles is 100 μm or less. When it exceeds 100 μm, the smoothness of the surface of the obtained heat conductive sheet becomes low, the heat conductive sheet and the heat radiating body cannot be sufficiently adhered, and it becomes difficult to obtain high heat conductive efficiency. A more preferable average particle diameter has a lower limit of 0.3 μm and an upper limit of 50 μm.

The thermoplastic resin 1 of the heat conductive fine particles
The preferable lower limit of the content is 00 parts by weight, and the upper limit thereof is 500 parts by weight. If it is less than 10 parts by weight, the effect on the thermal conductivity may not be sufficiently exhibited. If it exceeds 500 parts by weight, the strength of the heat conductive composition of the present invention may be significantly reduced and the shape retention may be impaired. A more preferable lower limit of the content is 15 parts by weight and an upper limit thereof is 400 parts by weight.

If necessary, additives such as tackifying resins, fillers, thickeners, pigments and antioxidants are added to the heat conductive composition of the present invention as long as the heat conductivity is not significantly impaired. May be.

The heat conductive composition of the present invention leaks the liquid substance in the capsule when subjected to a pressure exceeding the pressure resistance of the capsule. As a result, the leaked liquid substance is filled even at the interface with the non-smooth heat-generating body or the heat-dissipating body, which is difficult to be tightly adhered to and joined, so that the liquid substance can be joined with high adhesion.
Therefore, the heat conductive composition of the present invention can bond the heat generating element and the heat radiating element with high heat conduction efficiency by means of pressurization, regardless of usage conditions.

The heat conductive composition of the present invention can be molded and processed into a heat conductive sheet. A heat conductive sheet using the heat conductive composition of the present invention is also one aspect of the present invention. In the present specification, the sheet includes a film and a tape. The method for obtaining the heat conductive sheet of the present invention is not particularly limited, and examples thereof include a solvent casting method, a UV polymerization method, and a sheet molding method such as hot melt coating. In the solvent casting method, for example, a mixture is prepared by dispersing or dissolving a thermoplastic resin, a capsule containing a liquid substance, thermally conductive fine particles, and optionally a tackifier and other additives in a solvent such as toluene. Then, this is applied onto the surface of a support such as a release liner and cured to form a sheet made of the heat conductive composition of the present invention. At this time, if the surface of the sheet is covered with a release-treated film having a release force different from that of a support such as a release liner, the handleability is further improved.

The preferable lower limit of the thickness of the heat conductive sheet of the present invention is 10 μm, and the upper limit thereof is 200 μm. If it is less than 10 μm, sufficient adhesion may not be obtained, and the heat transfer efficiency may decrease. If it exceeds 200 μm, the heat conduction efficiency may be lowered and the cost becomes high. A more preferable lower limit is 30 μm and an upper limit is 150 μm.

As described above, the heat conductive composition of the present invention is used by being interposed between the heat generating element and the heat radiating element. The heat conductive composition or the heat conductive sheet of the present invention is interposed between the heating element and the heat radiating element, and the liquid substance in the capsule is pressurized by applying a pressure exceeding the pressure resistance of the capsule. A method of joining the heat generating element and the heat radiating element, which leaks out to the outside or the heat conductive sheet to fill the interface between the heat generating element and the heat radiating element, is also one aspect of the present invention.

The heat conductive composition or the heat conductive sheet of the present invention is interposed between the heat generating element and the heat radiating element, and the liquid substance in the capsule containing the liquid substance is outside the heat conductive composition or the above. The joint structure between the heat generating element and the heat radiating body, which is leaked out of the heat conductive sheet and filled with the liquid substance at the interface between the heat generating element and the heat radiating body, is also one aspect of the present invention.

By using the heat conductive composition, the heat conductive sheet, the method of joining the heating element and the heat radiating body, and the joining structure of the heating element and the heat radiating body of the present invention, In the joining, the dependence of the heat conduction efficiency on the use condition is small, and when the pressure bonding is performed, the shape conformability to the rough surface is exerted and the heat generating element and the heat radiating element can be joined with high heat conduction efficiency.

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 In a separable flask equipped with a cooling tube, a thermometer and a stirrer, 99.5 parts by weight of 2-ethylhexyl acrylate (manufactured by Mitsubishi Chemical Co., Ltd.) and 2-hydroxyethyl methacrylate (manufactured by Osaka Organic Industry Co., Ltd.) ) 0.5 parts by weight, 0.2 parts by weight of n-dodecanethiol and 90 parts by weight of ethyl acetate were added, and the temperature was raised to a temperature at which reflux occurred under a nitrogen gas atmosphere, and the temperature was maintained for 20 minutes. Then, a solution prepared by dissolving 0.2 parts by weight of benzoyl peroxide in 5 parts by weight of ethyl acetate was added dropwise and reacted for 4 hours, and then a solution of 0.1 parts by weight of benzoyl peroxide dissolved in 5 parts by weight of ethyl acetate was added. The mixture was added dropwise and the reaction was continued for 3 hours. Then, 100 parts by weight of ethanol was stirred and mixed to obtain a copolymer solution. The weight average molecular weight of the obtained copolymer was measured by gel permeation chromatography in terms of styrene and found to be 150,000.

Boron nitride (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: 100 parts by weight of solid content of the obtained copolymer solution)
Grade SGP, scale shape, particle size 18 μm, purity 9
9.8%, aspect ratio = 32 μm / 1.5 μm) 10
A capsule that mixes 0 parts by weight until it becomes homogeneous and further encapsulates a liquid substance (Matsumoto Yushi-Seiyaku Co., Ltd., trade name: Microsphere SQ, outer shell material: polymethylmethacrylate, inclusion substance: squalane, ratio of inclusion substance : 80% by weight) 1
0 part by weight was added to obtain a dispersion of the heat conductive composition.

The obtained dispersion of the heat conductive composition was applied to the surface of a polyethylene terephthalate film having a thickness of 50 μm which had been subjected to a mold release treatment so that the dried thickness would be 100 μm, and then set at 80 ° C. Dry in a dryer for 10 minutes,
A heat conductive sheet was obtained.

Example 2 Boron nitride (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: grade SGP, scale shape, particle diameter 18 μm, per 100 parts by weight of solid content of the copolymer solution prepared in Example 1), Purity 99.8%, aspect ratio = 32μ
(M / 1.5 μm) 200 parts by weight are mixed until uniform and further encapsulate a liquid substance (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., trade name: Microsphere SQ, outer shell material: polymethylmethacrylate, inclusion substance A heat conductive sheet was obtained in the same manner as in Example 1 except that 30 parts by weight of squalane and the inclusion substance ratio: 80% by weight) were added to obtain a dispersion liquid of the heat conductive composition.

Example 3 To 100 parts by weight of the solid content of the copolymer solution prepared in Example 1, 300 parts by weight of aluminum nitride (manufactured by Tokuyama Corporation, trade name: Grade F) was mixed until uniform. In addition, a capsule containing a liquid substance (Matsumoto Yushi-Seiyaku Co., Ltd., trade name: Microsphere E
P-28, outer shell material: formalin polycondensation resin, inclusion material: bisphenol A type epoxy, inclusion material ratio: 80
%) Was added to obtain a thermally conductive composition dispersion, and a thermally conductive sheet was obtained in the same manner as in Example 1.

(Comparative Example 1) Boron nitride (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: grade SGP, scale shape, particle diameter 18 μm, relative to 100 parts by weight of solid content of the copolymer solution prepared in Example 1) Purity 99.8%, aspect ratio = 32μ
m / 1.5 μm) 100 parts by weight was added, and a heat conductive sheet was obtained in the same manner as in Example 1 except that a dispersion liquid of the heat conductive composition was obtained without adding a capsule containing a liquid substance. It was

(Comparative Example 2) 20 parts by weight of cetyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd., melting point: about 50 ° C.) and boron nitride (electrical) were added to 80 parts by weight of the solid content of the copolymer solution prepared in Example 1. Chemical Industry Co., Ltd., trade name: Grade SGP, scale shape, particle size 18 μm, purity 99.8%, aspect ratio = 32 μm / 1.5 μm) Add 200 parts by weight, and add a capsule containing a liquid substance. A heat conductive sheet was obtained in the same manner as in Example 1 except that a dispersion of the heat conductive composition was obtained.

(Evaluation) The thermal resistances of the heat conductive sheets produced in the respective examples and comparative examples were measured.
The thermal resistance is obtained by measuring the heat transfer characteristics between the two systems. The smaller the thermal resistance, the quicker the transfer of heat from the heating element to the radiator, and It means that it has a high heat dissipation effect. The apparatus shown in FIG. 1 was used for the measurement of the thermal resistance. That is, a heat conductive composition layer obtained by removing a polyethylene terephthalate film which is a support from an adhesive sheet is laminated on an aluminum cooler 1 which is a heat radiator, and a heater 3 which is a heat generator is further laminated thereon. Were laminated. In addition, cooler 1
Has a structure in which water at 23 ° C. is supplied and circulated from the constant temperature water tank 6, and the surface area of the heater 3 is 3 cm × 3 cm.
= 9 cm ² , and the surface roughness was Ra 1.2 μm. The heater 3 is pressed from above the presser plate 5 through the support plate 4 with a predetermined pressure to form a joint structure of a heating element and a radiator.
10 minutes after the power was turned on, the temperature T1 of the heater 3 and the temperature T2 near the sheet contact surface of the cooler 1 were measured. It should be noted that the measurement was performed by setting the amount of electric power supplied to the heater 3 to 30 W, 50
It changed to W and 100W, and implemented it, respectively. Thermal resistance is
It was determined by the following formula (1). Thermal resistance (° C / W) = (T1-T2) / (amount of power supplied to heater 3) (1) The results are shown in Table 1.

[0037]

[Table 1]

As shown in Table 1, the thermal conductive sheets produced in Examples 1 to 3 had a small thermal resistance in each temperature region regardless of the temperature T1 of the heater 3. On the other hand, since the heat conductive sheet produced in Comparative Example 1 did not include the capsule enclosing the liquid substance, the adhesion with the cooler 1 and the heater 3 was poor, and the heat resistance was large in each temperature range. Moreover, since the heat conductive sheet produced in Comparative Example 2 contained cetyl alcohol that melts at around 50 ° C., Examples 1 to 3 were performed at a temperature higher than 50 ° C.
Although it showed a thermal resistance equivalent to that of the heat conductive sheet produced in, but since it did not include a capsule enclosing a liquid substance,
In the temperature range of 50 ° C. or lower, the adhesion with the cooler 1 and the heater 3 was poor and the thermal resistance was large.

[0039]

EFFECTS OF THE INVENTION According to the present invention, the heat conduction efficiency is less dependent on the operating conditions, so that it is excellent in versatility. It is possible to provide a heat conductive composition capable of bonding with a high heat conduction efficiency, a heat conductive sheet, a method for bonding a heating element and a radiator, and a bonding structure for a heating element and a radiator.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a measuring device used for evaluation of an example of the present invention.

[Explanation of symbols]

1 cooler 2 Thermal conductive sheet 3 heater 4 Support plate 5 restraints 6 constant temperature water tank

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shunji Tawarashi             Sekisui Chemical Co., Ltd.             Industry Co., Ltd. (72) Inventor Jun Hasegawa             Sekisui Chemical Co., Ltd.             Industry Co., Ltd. F term (reference) 5E322 DB06 DB08 DC01 FA01 FA05                 5F036 AA01 BA23 BB21

Claims (4)

[Claims] 1. A heat conductive composition which is used by being interposed between a heat generating body and a heat radiating body, and which contains a thermoplastic resin, a capsule containing a liquid substance and heat conductive fine particles. The capsule is composed of an encapsulant forming an outer shell and the liquid substance encapsulated in the encapsulant, and the liquid substance in the capsule is exposed to a pressure exceeding the pressure resistance of the capsule. A thermally conductive composition which is characterized by leaking out of the thermally conductive composition. 2. A heat conductive sheet comprising the heat conductive composition according to claim 1. 3. The heat conductive composition according to claim 1 or the heat conductive sheet according to claim 2 is interposed between a heat generating body and a heat radiating body, and pressure is applied at a pressure exceeding the pressure resistance of the capsule. A heat generating element and a heat radiating body, characterized in that the liquid substance in the capsule is leaked out of the heat conductive composition or the heat conductive sheet to fill the interface between the heat generating body and the heat radiating body with the liquid substance. How to join with. 4. The heat conductive composition according to claim 1 or the heat conductive sheet according to claim 2 is interposed between a heat generating body and a heat radiating body, and the liquid substance in a capsule containing the liquid substance is A joint structure between a heat generating element and a heat radiating body, wherein the liquid substance is leaked to the outside of the heat conductive composition or the heat conductive sheet and the liquid substance is filled in the interface between the heat generating element and the heat radiating body. .