JP4807302B2 - Heat dissipation component - Google Patents

Description

  The present invention relates to a heat dissipation component used for heat diffusion and heat dissipation from a heat source of an electronic device.

  In electronic devices that are small in size and high in performance, LSIs, power amplifiers, and the like serve as heat sources, and various heat dissipating parts are used to efficiently diffuse and dissipate heat generated from these.

  Especially for thin electronic devices such as mobile phones, the main thermal conductivity is 100 to 1000 W / (m · K) in the surface direction even when the thickness is small, and graphite is the most suitable for heat diffusion and heat dissipation. A graphite sheet as a component is used.

For example, Patent Document 1 is known as prior art document information relating to the invention of the present application.
JP 2005-159318 A

  Such a graphite sheet is soft, and in order to prevent damage and cracking of the graphite sheet due to mechanical impact or the like, a heat radiating component in which the front and back surfaces of the graphite sheet are covered with a cover layer separate from the graphite sheet is used.

  The cover layer used here is as thin as possible so as not to hinder heat transfer.

  However, when a heat dissipation component such as that described above is used in a thin electronic device such as a mobile phone, a case or operation button of a mobile phone, for example, on the opposite side of a heat source such as an LSI or power amplifier across the heat dissipation component A local hot part called a heat spot may be formed on the side. Since such a heat spot causes discomfort when the human body touches the case or the operation button, it is necessary to alleviate the heat spot.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a heat dissipation component that can alleviate a heat spot induced by local heat generation of an LSI or a power amplifier.

  In order to achieve this object, the heat dissipating component of the present invention includes a first cover layer that covers one main surface of a graphite sheet mainly composed of graphite, and a second cover layer that covers the other main surface. The heat dissipation component has a thermal resistance of the second cover layer larger than that of the first cover layer.

  In the heat dissipation component of the present invention, the thermal resistance of the second cover layer covering the other main surface is larger than the thermal resistance of the first cover layer covering one main surface of the graphite sheet, and the first heat resistance is low. The heat spot corresponding to the heat source can be alleviated by using the cover layer facing the heat generation source and the second cover layer having a large thermal resistance facing the case where the human body touches and using it as a heat dissipation component. It has the effect of being able to.

  Hereinafter, a heat dissipation component of the present invention will be described with reference to an embodiment and drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view of a heat dissipation component 4 according to Embodiment 1 of the present invention. One main surface of a graphite sheet 1 mainly composed of graphite is a first cover layer 2 and the other main surface is a second cover. The cover layer 3 covers the structure.

  The first cover layer 2 and the second cover layer 3 have a larger area than the graphite sheet 1, and the side surface of the graphite sheet 1 is either or both of the first cover layer 2 and the second cover layer 3. It has a covered configuration.

  Here, on the first cover layer 2 and the second cover layer 3, an adhesive layer (not shown) having a thickness of several μm is formed on one side (graphite sheet 1 side). While being joined to the sheet 1, the first and second cover layers 2 and 3 are joined together.

  In FIG. 1, the dimension in the thickness direction is schematically enlarged for explanation.

  FIG. 2 is a cross-sectional view of the operation unit 11 of the mobile phone using the heat dissipating component 4 shown in FIG. 1, and 12 is an operation button. A board 13 and a battery 17 on which various electronic components are mounted are disposed inside the operation unit 11, and a power amplifier 14 and an LSI 15 that also serve as a heat source are mounted on the board 13. 1 is disposed on the inner surface of the case 16 so as to face the power amplifier 14 and the LSI 15, and heat generated from the power amplifier 14 and the LSI 15 is dissipated into the outside air through the case 16. .

  In FIG. 2, the heat dissipation component 4 is illustrated as being mounted apart from the power amplifier 14 and the LSI 15, but the heat dissipation component 4 is brought into contact with the power amplifier 14 and the LSI 15 as the mobile device becomes thinner in recent years. In some cases, it can be attached.

  In the case of the first embodiment, the heat dissipation component 4 is attached so that the second cover layer 3 faces the case 16 and the first cover layer 2 comes to the side facing the power amplifier 14 and the LSI 15. ing.

  In the first embodiment, the graphite sheet 1 of the heat radiating component 4 was obtained by thermally decomposing an organic film mainly composed of polyimide at a temperature of 2500 ° C. to 3000 ° C. in a neutral atmosphere or a reducing atmosphere. A pyrolytic graphite sheet was used.

  Further, polyethylene terephthalate (hereinafter referred to as PET film) having a thickness of 25 μm was used as the first cover layer 2, and a polystyrene film having a thickness of 25 μm was used as the second cover layer 3.

  About the measurement of the thermal resistance of these organic films, it can measure simply, for example using the resin material thermal resistance measuring apparatus by Hitachi, Ltd. etc.

  Using such a measuring apparatus, the thermal resistance was measured using a sample having the same shape and the same thickness of 25 mm in thickness, 5 mm in length, and 5 mm in width with respect to the PET film and the polystyrene film.

  As a result, the thermal resistance of the PET film was 3.5 ° C./W, and the thermal resistance of the polystyrene film was 9.0 ° C./W.

  Next, the effect of reducing the heat spot when using the heat dissipating component of the first embodiment will be described in detail.

  First, as shown in FIG. 2, the first cover layer 2 is opposed to the power amplifier 14 and the LSI 15 that are heat sources, and the second cover is placed on the opposite side of the mobile phone case 16 as shown in FIG. The layers 3 were mounted so that they face each other.

  Next, in the state which operated the mobile telephone at room temperature 25 degreeC, the presence or absence and the temperature of the heat spot of the outer surface of case 16 were observed using infrared thermography.

  As a comparative example, a conventional heat dissipating part in which the front and back surfaces of the graphite sheet 1 are covered with the same PET film (thermal resistance 3.5 ° C./W) having a thickness of 25 μm is mounted in a mobile phone in the same manner as described above, and the same as above. Then, the presence or absence of a heat spot and its temperature were observed.

  As a result of observation by infrared thermography, when the conventional heat dissipating part of the comparative example is used, a heat spot corresponding to local heat generation of the power amplifier 14 is observed on the surface of the case 16, and the temperature is about 55 ° C. It was.

  In contrast, according to the first embodiment, the graphite sheet 1 is used as the first cover layer 2 as a PET film (thermal resistance 3.5 ° C./W), and the second cover layer 3 is used as a polystyrene film (thermal resistance 9.0). When the heat-radiating component 4 covered with two kinds of organic films (° C./W) is made to face the case 16 side with the second cover layer 3 of the polystyrene film, the temperature of the heat spot on the surface of the case 16 is The temperature decreased to about 30 ° C., and the heat spot was relaxed.

  As another example of the first embodiment, a polystyrene film (thermal resistance: 9.0 ° C./W) having a thickness of 25 μm is used as the second cover layer 3, and a polyamide film having a thickness of 25 μm is used as the first cover layer 2 ( Using a product name Reny 1022F manufactured by Mitsubishi Engineering Plastics Co., Ltd., with a thermal resistance of 2.0 ° C./W), the heat dissipating component 4 covering the graphite sheet 1 is mounted in the mobile phone in the same manner as described above. Existence and temperature were measured.

  In this case, the temperature of the heat spot on the surface of the case 16 was 27 ° C., and the heat spot was relaxed as described above.

  Here, as a material constituting the case 16 of a small portable electronic device such as a mobile phone, a plastic having a low thermal conductivity is usually used. Therefore, the heat spot of the power amplifier 14 immediately appears on the surface of the case 16. is not.

  However, such a plastic case 16 having a low thermal conductivity is slow in moving and diffusing heat in the surface direction as in the thickness direction, so that it takes time, but the power amplifier 14 is placed on the surface of the case 16 after a while. A heat spot is formed by the heat generation.

  However, in the heat radiating component 4 of the first embodiment, the heat of the power amplifier 14 can be diffused in the plane direction by the graphite sheet 1 having a large thermal conductivity in the plane direction, and the second is provided on the side facing the case 16. The cover layer 3 is made to have a higher thermal resistance than the first cover layer 2 provided on the side facing the heat source such as the power amplifier 14, so that an excellent effect that the generation of heat spots can be suppressed. Can be obtained.

  Here, as the graphite sheet 1 has a higher ability to efficiently diffuse the heat transmitted from the power amplifier 14 in the plane direction, it becomes more advantageous for the relaxation of the heat spot. Therefore, the thermal conductivity is about 100 W / (m · K). It is preferable to use as the graphite sheet 1 a pyrolytic graphite sheet having a thermal conductivity as large as 600 to 1000 W / (m · K) rather than the expanded graphite sheet.

  Further, in order to efficiently transmit heat from a heat source such as the power amplifier 14 to the graphite sheet 1, it is preferable that the first cover layer 2 on the heat source side has a smaller thermal resistance, and the case 16 on the side opposite to the heat source is applied to the case 16. The second cover layer 3 in the facing direction is more advantageous for relaxing the heat spot as the thermal resistance is larger.

  The heat resistance of the first cover layer 2 is preferably 4 ° C./W or less, because it can efficiently absorb heat from the heat source, and more preferably 2 ° C./W or less.

  When the thermal resistance of the second cover layer 3 is less than 5 ° C./W, the effect of mitigating the heat spot decreases, and conversely, when the thermal resistance increases to exceed 30 ° C./W, the case 16 As a result, it becomes difficult for heat to be transmitted, and as a result, heat dissipation to the outside air through the case 16 is hindered, heat radiation to the outside of the device cannot be performed, and inconvenience that the heat is trapped inside the operation unit 11 may occur.

  Therefore, the thermal resistance of the second cover layer 3 is preferably about 5 to 30 ° C./W.

  In terms of the ratio of thermal resistance, the ratio of the thermal resistance of the first cover layer 2 to the thermal resistance of the second cover layer 3 is preferably about 1: 2 to 1:10.

  This is because when the thermal resistance ratio is smaller than 1: 2, the effect of mitigating the heat spot is reduced, and when the thermal resistance ratio is larger than 1:10, the thermal resistance of the second cover layer 3 is increased. This is because it becomes difficult to dissipate heat to the outside air through the case 16 or the like.

(Embodiment 2)
The second embodiment is different from the first embodiment in that a metal foil such as an aluminum foil or a copper foil is used instead of the PET film as the first cover layer 2 covering the pair of main surfaces of the graphite sheet 1. is there.

  With respect to this aluminum foil, when the thermal resistance was measured with a sample having a thickness of 25 μm, a length of 5 mm, and a width of 5 mm, as in Embodiment 1, it was 0.1 ° C./W.

  With the heat dissipating component of the second embodiment, the heat spot on the case 16 was observed using infrared thermography under the condition of the ambient temperature of 25 ° C. with the mobile phone operated as in the first embodiment. .

  As a result, in this heat dissipation component using aluminum foil as the first cover layer 2, the heat spot temperature was 26 ° C., which is slightly higher than room temperature, and the heat spot was almost eliminated.

  This is because the thermal diffusion effect of the aluminum foil and the graphite sheet 1 is synergized by using an aluminum foil as the first cover layer 2 whose thermal resistance is much lower than that of the organic film (that is, high thermal conductivity). As a result, it is considered that the temperature of the heat spot was lowered.

  In Embodiment 2, the aluminum foil is used as the metal foil, but the same effect can be obtained even when a copper foil or a tin foil is used.

(Embodiment 3)
The third embodiment is different from the first embodiment in that the second cover layer 3 covering one main surface of the graphite sheet 1 is made of a base material such as a PET film such as a double-sided tape instead of a PET film. It is a point using the adhesive material layer which formed the adhesive material on both surfaces.

  As the adhesive layer, a 20 μm PET film serving as a base material on which an adhesive mainly composed of 2.5 μm vinyl acetate or the like was formed was used.

  About this adhesive material layer, when thickness was 25 micrometers similarly to Embodiment 1, and the thermal resistance was measured with the sample whose length is 5 mm and width is 5 mm, it was 5.0 degreeC / W.

  With respect to the heat dissipating part of the third embodiment, the heat spot on the case 16 was observed using infrared thermography under the condition of the ambient temperature of 25 ° C. with the cellular phone operated as in the first embodiment. .

  As a result, in the heat radiating component 4 using the adhesive layer as the second cover layer 3, the heat spot temperature is 35 ° C., which is effective in reducing the heat spot as in the first and second embodiments. It could be confirmed.

  The heat dissipating component of the third embodiment also has an effect that the second cover layer 3 is formed of an adhesive material layer, so that it can be easily attached to a device.

(Embodiment 4)
The fourth embodiment is different from the first embodiment in that a PET film of the same material is used for the first cover layer 2 and the second cover layer 3, and the thickness of the PET film used as the second cover layer 3 is different. The heat resistance of the second cover layer 3 is increased by making it thicker than the thickness of the PET film used as the first cover layer 2.

  That is, a PET film having a thickness of 25 μm (thermal resistance: 3.5 ° C./W) is used as the first cover layer 2, and a PET film having a thickness of 50 μm (thermal resistance: 7.0 ° C./W) or as the second cover layer 3 With respect to the heat dissipating component 4 using a 75 μm PET film (thermal resistance 10.5 ° C./W), an infrared thermography was used under the condition of an ambient temperature of 25 ° C. in a state where the mobile phone was operated as in the first embodiment. The heat spot was observed.

  As a result, when a 50 μm thick PET film was used as the second cover layer 3, a slight heat spot was observed, and the temperature of the heat spot was 32 ° C.

  When a 75 μm thick PET film was used as the second cover layer 3, the heat spot was further relaxed, and the heat spot temperature was 31 ° C.

  As described above, the heat spot can also be alleviated by making the thickness of the second cover layer 3 thicker than that of the first cover layer 2.

  In the fourth embodiment, films having the same material and different thicknesses may be used. Therefore, it is easy to obtain materials and an organic film with low cost can be used.

  The value of the thermal resistance is obtained by measuring the thermal resistance of a PET film having a length of 5 mm, a width of 5 mm, and a thickness of 25, 50, and 75 μm in the same manner as in the first embodiment.

  In general, it is said that the discomfort caused by the heat spot appears prominently when the temperature of the heat spot is 40 ° C. (that is, the difference from the ambient temperature is 15 ° C.) or more, as shown in the first to fourth embodiments. It can be seen that by using the heat dissipating component 4 of each embodiment, a great effect can be obtained in suppressing the heat spot.

  Although the heat spots generated by the power amplifier 14 have been described in the above first to fourth embodiments, the heat spots can be similarly mitigated also in the case of the LSI 15 that generates a large amount of heat.

  FIG. 2 shows an example in which the heat dissipation component 4 is attached to the inside of the case 16 of the operation unit 11. However, the present invention is not limited to this, depending on the arrangement of the power amplifier 14 and the LSI 15 serving as a heat source. You may attach to the inner side of the operation button 12, and you may attach to both the inner side of the case 16 and the inner side of the operation button 12.

  Further, Embodiment 1 shows a case where organic films of different materials are used for the first cover layer 2 and the second cover layer 3, and Embodiment 4 uses organic films of the same material and different thicknesses. However, the thermal resistance of the second cover layer 3 may be increased by using different materials and thicknesses for the first cover layer 2 and the second cover layer 3.

  There are not many kinds of combinations of materials that are easy to obtain and easy to use and have different thermal resistances. However, by changing the material and thickness of the first cover layer 2 and the second cover layer 3 as described above, The difference in thermal resistance between the first cover layer 2 and the second cover layer 3 can be further optimally controlled, and the heat spot can be alleviated more effectively.

  Moreover, although the thing similar to a plastic film was mainly used as an organic film, it is not limited to this, It consists of another organic film, for example, the film which consists of silicon rubber, the film which consists of urethane rubber, or fluororubber A film having a large thermal resistance such as a film may be used as the second cover layer 3.

  A heat dissipation component according to the present invention includes a first cover layer that covers one main surface of a graphite sheet containing graphite as a main component, and a second cover layer that covers the other main surface. The heat radiation component is characterized in that the thermal resistance of the second cover layer is larger than that of the layer, and the heat spot corresponding to the heat source can be mitigated. This is useful for heat dissipation parts.

Sectional drawing of the thermal radiation component in Embodiment 1 of this invention Sectional drawing of the operation part of the mobile telephone in Embodiment 1 of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Graphite sheet 2 1st cover layer 3 2nd cover layer 4 Thermal radiation component 11 Operation part 12 Operation button 13 Board | substrate 14 Power amplifier 15 LSI
16 Case 17 Battery

Claims (2)

A graphite sheet mainly composed of graphite, and a first cover layer covering the one main surface of the graphite sheet, and a second cover layer covering the other main surface of the graphite sheet, the first The cover layer is made of an organic film, the second cover layer is made of an adhesive layer, and the heat resistance of the second cover layer is larger than that of the first cover layer. . A graphite sheet containing graphite as a main component; a first cover layer covering one main surface of the graphite sheet; and a second cover layer covering the other main surface of the graphite sheet; The heat dissipation component is characterized in that the cover layer has a thickness greater than that of the first cover layer, and the thermal resistance of the second cover layer is greater than that of the first cover layer.

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