JP4691067B2 - Thermally conductive sheet - Google Patents

Description

  The present invention relates to a heat conductive sheet used for connecting, for example, an electronic / electrical component that is mounted on various electronic / electrical devices and requires a cooling heat sink.

  In recent years, the problem of cooling semiconductor elements mounted on various electronic / electrical devices represented by computers and the like has attracted attention as an important issue. As a cooling method for a semiconductor element or the like that needs to be cooled, a fan is attached to a device housing on which the device is mounted, and the air inside the device housing is cooled, or a cooling device ( A method of cooling by attaching a heat sink) is typical.

  When a heat sink is attached to a semiconductor element or the like to be cooled (hereinafter referred to as a component to be cooled), sufficient cooling performance cannot be obtained if the thermal connectivity between the component to be cooled and the heat sink is low. Usually, simply contacting a heat sink to a component to be cooled often has a contact resistance at the contact portion that is too large to achieve sufficient cooling. If the component to be cooled and the heat sink are joined by soldering or the like, they can be connected with a low thermal resistance, but there is a problem of thermal consistency due to the difference in thermal expansion coefficient between the component to be cooled and the heat sink. Often occurs.

  Specifically, aluminum materials with excellent thermal conductivity are often used as heat sinks, but semiconductor elements that are parts to be cooled often have a much lower coefficient of thermal expansion than that. And the thermal integrity at the joint between the component to be cooled. If it becomes so, problems, such as generation | occurrence | production of the curvature by the big difference of a thermal expansion coefficient, and generation | occurrence | production of peeling in a junction part will arise.

  In order to eliminate the above-mentioned problem of thermal compatibility at the joint between the heat sink and the component to be cooled, it is effective to sandwich a molded product such as a rubber sheet between the component to be cooled and the heat sink. There have been proposed various heat conductive sheets as the molded article (for example, see Patent Document 1).

JP 2001-168246 A

  However, in recent years, since the amount of heat generated by semiconductor elements has increased, it is necessary to improve the heat transfer performance of the above-described heat conductive sheet. For this purpose, there is a means for increasing the heat conductivity of the heat conductive sheet. When the thermal conductivity is increased, there is a drawback that the thermal conductive sheet becomes hard, and this means has a limit. In addition, a sheet that is relatively soft and thin is desired as the heat conductive sheet. However, when the thickness of the heat conductive sheet is reduced, there is a problem that the sheet is easily torn or stretched and the handleability is deteriorated. Therefore, there is a thin film heat conductive sheet with good handleability. It has been demanded. Furthermore, there is also a heat conductive sheet having a plastic film bonded to the surface. However, this heat conductive sheet has a drawback that the plastic film can be partially wrinkled only by light bending and the appearance is deteriorated.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a heat conductive sheet that is thin and has good strength, elasticity, flexibility, and handleability.

  As a result of intensive studies to solve the above-described problems, the present inventors have found that when a thin plastic film is bonded to the surface of a thin and soft heat conductive layer so as to have an appropriate surface roughness, it is good. A thin-film heat conductive sheet having strength, elasticity, flexibility and handleability can be obtained, and a plastic film is applied to the surface of the heat conductive layer so as to have a surface roughness with an appropriate thickness as described above. It has been found that the combined heat conductive sheet can be pressure-bonded with less stress because it has a small contact area with the heat sink when it is pressure-bonded to the heat sink.

This invention is made | formed based on the knowledge mentioned above, and provides the heat conductive sheet shown to following (1)-(6).
(1) Thermal conductivity, characterized in that a plastic film having a thickness of 5 to 12 μm is laminated on the surface of the thermal conductive layer with a texture so that the surface roughness is 36 to 148 μm in Rz. Sheet.
(2) The heat conductive sheet according to (1), wherein the plastic film is a polyester film.
(3) The heat conductive sheet according to (1) or (2), wherein the heat conductive layer is formed of a non-crosslinked mixture.
(4) The heat conductive sheet according to (3), wherein the non-crosslinked admixture contains acrylic rubber and / or a thermoplastic elastomer as a main component.
(5) The thermal conductive sheet according to (4), wherein the thermoplastic elastomer is a styrene elastomer.
(6) The heat conductive sheet according to any one of (1) to (5), wherein the heat conductivity of the heat conductive layer is 1.5 W / mk or more.

  The heat conductive sheet of the present invention is a thin film and has excellent heat conductivity, strength, elasticity, flexibility, and handleability, and is suitable for applications such as joining a component to be cooled such as a semiconductor element and a heat sink. Can be used for

  Hereinafter, the present invention will be described in more detail. There is no limitation on the material of the heat conductive layer in the heat conductive sheet of the present invention, but a non-cross-linked admixture in which a non-cross-linked polymer such as rubber or thermoplastic elastomer is used as a base resin and a heat-conductive filler is blended with the base resin. It can be used suitably. The heat conduction layer preferably has a heat conductivity of 1.5 W / mk or more, particularly 1.7 W / mk or more. The heat conductive layer is suitably formed in a sheet shape having a thickness of 0.3 to 1.0 mm. Furthermore, the heat conductive sheet of the present invention preferably has a heat-resistant temperature of 100 ° C. or higher and does not cause fluidization at a normal temperature to 80 ° C., which is a general temperature range related to electronic components.

  In this case, as the base resin, a resin mainly composed of one or both of acrylic rubber and thermoplastic elastomer can be preferably used, thereby obtaining an advantage that no siloxane is generated from the heat conductive sheet. it can. That is, when silicone rubber is used as the material of the heat conductive layer, the silicone rubber may adversely affect the electrical contact portion due to the generation of siloxane (inhibit conductivity). Or, when a thermoplastic elastomer is used, the above disadvantages do not occur.

  The thermoplastic elastomer is preferably a styrene elastomer such as SBS (styrene / butadiene block copolymer), SIS (styrene / isoprene block copolymer), SEBS (hydrogenated SBS), or SEPS (hydrogenated SIS). .

  Examples of the thermally conductive filler include aluminum oxide, aluminum hydroxide, magnesium oxide, magnesium hydroxide, boron nitride, aluminum nitride, and zinc oxide powder.

  Although the compounding quantity of each component in the non-crosslinked blend mentioned above can be determined as appropriate, the proportion of the heat conductive filler is usually 200 to 700 parts by weight, particularly 300 to 500 parts by weight, with respect to 100 parts by weight of the base resin. It is suitable to mix with. Moreover, components other than the base resin and the heat conductive filler can be appropriately blended with the non-crosslinked admixture.

Although there is no limitation in the material of the plastic film in the heat conductive sheet of this invention, what consists of polyethylene, a polypropylene, polyester, a polyimide, etc. can be mentioned. The thickness of the plastic film is suitably 5 to 12 μm.

The heat conductive sheet of the present invention can be produced, for example, by forming a sheet of a heat conductive layer by an extrusion method or the like, and pressing a plastic film on the sheet of the heat conductive layer with a surface roll or the like. A wrinkle can be formed on a plastic film by a wrinkle roll or the like. Examples of the shape of the texture include, for example, a plastic film 10 illustrated in FIG. 1A in which a large number of continuous or non-continuous substantially wavy textured textures 12 are arranged substantially in parallel, and the plastic illustrated in FIG. Examples of the film 14 include a grid-like shape in which a large number of vertical line marks 16 and horizontal line marks 18 are arranged so as to be orthogonal. The plastic film is preferably formed to have a surface roughness (Rz) of 36 to 148 μm .

  In the present invention, the plastic film may be laminated only on one side of the heat conductive layer, or may be laminated on both sides, but when laminated on both sides, the thermal resistance of the heat conductive sheet increases, so only on one side. Lamination is preferred.

  EXAMPLES Hereinafter, although an Example shows this invention more concretely, this invention is not limited to the following Example.

In this example, the material of the heat conductive layer sheet was as follows.
(No. 1): A mixture in which acrylic rubber is used as a base resin, and a heat conductive filler (aluminum oxide, aluminum hydroxide, the same applies hereinafter) is mixed therewith. Thermal conductivity 2.8 W / mk, hardness 60 (measured with Type C (Asker C type) according to JIS K 7312, the same applies hereinafter).
(No. 2): A styrene-based thermoplastic elastomer as a base and a heat conductive filler mixed therewith. Thermal conductivity 1.8 W / mk, hardness 40.
(No. 3): A styrene-based thermoplastic elastomer as a base and a heat conductive filler mixed therewith. Thermal conductivity 1.2 W / mk, hardness 40.

In this example, the material of the plastic film was as follows.
(No. 1): A commercially available polyester film (manufactured by Teijin DuPont Films, Inc., product name Teijin Tetron Film)
(No. 2): Commercially available polyimide film (manufactured by Toray DuPont Co., Ltd., product name Kapton).

  The above-described heat conductive layer sheet and plastic film are superposed in the combinations shown in Table 1, and these are inserted together between the embossing roll and the flat roll to perform pressure bonding / rolling forming, thereby allowing Examples 1 to 8 The heat conductive sheets of Comparative Examples 3 to 5 and 7 were produced. In Example 9, a heat conductive sheet was produced by press molding. In Comparative Examples 1 and 2, a plastic film was not used, and heat conduction was performed only with the sheet of the heat conductive layer without performing crimping / rolling molding or press molding. In Comparative Example 6, a heat conductive sheet was produced by inserting a sheet of a heat conductive layer and a plastic film superimposed between a pair of flat rolls and performing crimping and rolling. .

  As the sivolol, one having a surface roughness (Rz) of 90 μm was used. Further, the surface roughness of the plastic film surface of the molded product was adjusted by adjusting the roll temperature and the line speed at the time of crimping and rolling. The roll temperature was adjusted in the range from room temperature to 80 ° C. The higher the roll temperature, the greater the surface roughness of the plastic film surface. The line speed was adjusted in the range of 1 m to 2 m per minute. The higher the line speed, the smaller the surface roughness of the plastic film surface. In this roll pressure bonding / rolling system, a large number of continuous or non-continuous substantially wavy lines were arranged on the surface of the plastic film substantially in parallel with the flow direction of the plastic film (see FIG. 1A). Further, in Example 9, a number of vertical and horizontal lines were provided on the surface of the plastic film by press molding so as to go straight in a grid pattern (see FIG. 1B).

The following methods examined the presence or absence (appearance) of wrinkles due to bending of the thermal conductive sheets of Examples and Comparative Examples, handling (testing whether deformation or tearing occurred), and thermal resistance.
(Presence or absence of generation of wrinkles due to bending): The inner and outer folds at R10 of the thermally conductive sheet cut to 150 × 200 mm were repeated 10 times.
(Handability): A heat conductive sheet cut to 40 × 40 mm is attached to an aluminum plate, a load of 100 g / cm ² is applied to the heat conductive sheet at room temperature for 5 minutes, and then the heat conductive sheet is peeled off and visually observed. Observations were made, and those with no deformation or tearing were marked with ◯, and those with certain were marked with ×.
(Thermal resistance): A heat conductive sheet having approximately the same area is sandwiched between two aluminum plates of 10 mm × 32.5 mm × 32.5 mm, and the thickness of the heat conductive sheet is accurately compressed by 0.02 mm. A sample to which an aluminum plate was fixed was prepared, and a heater was connected to the upper part via a heat conductive grease, and a heat sink was thermally connected to the lower part via a heat conductive grease. Here, heat of 12 W is applied to the heater, the temperature of the upper aluminum plate and the lower aluminum plate is measured with a thermocouple, the temperature after 10 minutes is recorded, the temperature difference ΔT is obtained, and the heat is calculated according to the following equation: Resistance was calculated. The practical value of the thermal resistance is 1.0 ° C./W or less.
Thermal resistance (° C / W) = ΔT (° C) / 12 (W)
Table 1 shows materials, molding conditions, and test results of Examples and Comparative Examples.

  Table 1 shows the following. In Example 1, the heat resistance is limited because the thickness of the heat conductive sheet is relatively 1 mm. Examples 2 to 5 are suitable examples, and the thermal resistance is relatively small. In Example 6, the thickness of the plastic film is relatively thick, and the thermal resistance is large, but it is in a usable range. Example 7 is an example in which the material of the plastic film is polyimide, which is preferable. Example 8 is an example in which the surface roughness of the plastic film is reduced, and the thermal resistance is low. Example 9 is an example in which molding is formed by pressing to provide vertical and horizontal uniform textures. Although the heat resistance is slightly higher than that of the textured lines having substantially wavy lines on the same conditions, it can be used. Comparative Examples 1 and 2 are examples of a thermally conductive sheet not reinforced with a plastic film. In a handling test, Comparative Example 1 was broken, and Comparative Example 2 was greatly deformed and inferior in strength. Comparative Examples 3 and 4 are examples in which the surface roughness of the plastic film is large, and the thermal resistance is large and inferior in this respect. Comparative Example 5 is inferior in this respect because the plastic film is thick and the thermal resistance is excessive. In Comparative Example 6, flat rolls were used as the rolls at the time of pressure bonding / rolling and the surface of the plastic film was flattened, so that large wrinkles were generated by bending and the appearance was inferior. Comparative Example 7 is an example using a heat conductive layer having a low thermal conductivity, and the thermal resistance is too large and inferior in this respect.

(A), (b) is an enlarged view which shows an example of the surface of the plastic film of the heat conductive sheet which concerns on this invention, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Plastic film 12 Substantially wavy line texture 14 Plastic film 16 Vertical line texture 18 Horizontal line texture

Claims (6)

A heat conductive sheet, characterized in that a plastic film having a thickness of 5 to 12 μm is laminated on the surface of the heat conductive layer with a texture so that the surface roughness is 36 to 148 μm in Rz.   The thermally conductive sheet according to claim 1, wherein the plastic film is a polyester film.   The thermally conductive sheet according to claim 1, wherein the thermally conductive layer is formed of a non-crosslinked mixture.   The thermally conductive sheet according to claim 3, wherein the non-crosslinked admixture contains acrylic rubber and / or a thermoplastic elastomer as a main component.   The thermally conductive sheet according to claim 4, wherein the thermoplastic elastomer is a styrene elastomer.   The heat conductive sheet according to any one of claims 1 to 5, wherein the heat conductivity of the heat conductive layer is 1.5 W / mk or more.

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