JP2007324334A - Heat-conductive grease and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a heat conductive grease which can maintain proper heat conducting performance for a long time, has proper viscosity, facilitates handling, and contributes to improvement in productivity. <P>SOLUTION: The heat conductive grease 20 has characteristics of: (1) the upper limit value of thermal resistance being 0.05°C/W at pressurization, applying a load of 2×10<SP>5</SP>Pa or higher between an IC chip 14 and a heat sink 15; (2) the viscosity at normal temperature is within a range of 100 Pa s or higher and 300 Pa s or lower; and (3) the value specified by thickness/area is 0.6/m or smaller, when it is placed between the IC chip 14 and the heat sink 15. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermally conductive grease used by being filled between a heating element and a heat radiating member. Furthermore, the present invention relates to an electronic device in which, for example, a heat generating CPU and a heat sink are thermally connected by a heat conductive grease.

  For example, an electronic device such as a portable computer includes a heat sink that emits heat generated by the CPU. In order to increase the heat dissipation performance of the CPU, it is necessary to efficiently transfer the heat of the CPU to the heat sink by suppressing the thermal resistance of the heat conduction path from the CPU to the heat sink.

  For this reason, in a conventional electronic device, a thermal conductive grease is filled between the CPU and the heat sink, and the CPU and the heat sink are thermally connected via the thermal conductive grease.

  The thermally conductive grease is applied to the surface of the CPU by a dispenser, for example, and after this application, the heat sink is overlaid on the CPU to fill the space between the CPU and the heat sink. Further, since the heat sink is fixed on the printed wiring board on which the CPU is mounted, the heat conductive grease is appropriately pressed between the CPU and the heat sink.

By the way, as a means for increasing the thermal conductivity from the CPU to the heat sink, it is known to increase the intrinsic thermal conductivity of the thermal conductive grease or to keep the thermal resistance of the thermal conductive grease small. As an example of the thermally conductive grease having the smallest thermal resistance at the present stage, for example, X23-7804B of Shin-Etsu Chemical Co., Ltd. is listed, and the thermal resistance value is 0.05 ° C./W (for example, Patent Document 1).
JP 2003-176414 A

  However, the thermal conductive grease having the lowest thermal resistance and the highest thermal characteristics at the present stage has a viscosity as high as 400 Pa · s at room temperature. For this reason, the heat conductive grease has a high viscosity and is difficult to handle. In particular, when the heat conductive grease is applied to the CPU, an automatic applicator such as a dispenser cannot be used.

  Therefore, there is a problem that it becomes an obstacle to performing an efficient application work of the heat conductive grease and is not suitable for mass production.

  An object of the present invention is to obtain a heat conductive grease that can maintain good heat conduction performance over a long period of time and that can be easily handled with an appropriate viscosity and contributes to an improvement in productivity.

  Another object of the present invention is to obtain an electronic device that can efficiently transmit heat of a heating element to a heat radiating member over a long period of time, and that makes it easy to handle thermally conductive grease, thereby improving productivity. .

In order to achieve the above object, a thermally conductive grease according to one embodiment of the present invention includes:
(1) The upper limit value of the thermal resistance when a pressure of 2 × 10 ⁵ Pa or more is applied between the heating element and the heat dissipation member is 0.05 ° C./W,
(2) The viscosity at normal temperature is in the range of 100 Pa · s to 300 Pa · s,
(3) The value defined by the thickness / area when filled between the heating element and the heat radiating member is 0.6 / m or less.

In order to achieve the above object, an electronic apparatus according to one aspect of the present invention provides:
A casing, a heating element housed in the casing, a heat radiating member that releases heat of the heating element, a space between the heat generating element and the heat radiating member, and the heat generating element and the heat radiating member And thermally conductive grease for thermal connection.
The above thermal conductive grease
(1) The upper limit value of the thermal resistance when pressurized by applying a load of 2 × 10 ⁵ Pa or more between the heating element and the heat radiating member is 0.05 ° C./W,
(2) The viscosity at normal temperature is in the range of 100 Pa · s to 300 Pa · s,
(3) The value defined by the thickness / area when filled between the heating element and the heat radiating member is 0.6 / m or less.

  According to the present invention, it is possible to prevent an increase in thermal resistance with the passage of time, and it is possible to favorably maintain the thermal conductivity performance of the thermal grease. In addition, handling of the thermal conductive grease becomes easy, and workability when applying the thermal conductive grease can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings applied to a portable computer.

  FIG. 1 discloses a portable computer 1 which is an example of an electronic apparatus. The portable computer 1 includes a main unit 2 and a display unit 3. The main unit 2 has a flat first housing 4, and a keyboard 5 is disposed on the upper surface of the first housing 4.

  The display unit 3 includes a flat second housing 6 and a liquid crystal display panel 7. The liquid crystal display panel 7 has a screen 7 a and is accommodated in the second housing 6. The screen 7 a is exposed to the outside of the portable computer 1 through an opening 8 opened in the front surface of the second housing 6.

  The display unit 3 is supported on the rear end portion of the first housing 4 via a hinge (not shown). For this reason, the display unit 3 rotates between a closed position lying on the main unit 2 so as to cover the keyboard 5 from above and an open position standing up from the main unit 2 so as to expose the keyboard 5 and the screen 7a. It is possible to move.

  As shown in FIG. 2, the first housing 4 accommodates a printed wiring board 10. A CPU socket 11 is mounted on the upper surface of the printed wiring board 10. The CPU socket 11 supports the CPU 12. The CPU 12 is an example of a heating element and is housed in the first housing 4.

  As schematically shown in FIG. 3, the CPU 12 includes a base substrate 13 and an IC chip 14. The base substrate 13 is supported by the CPU socket 11 via a plurality of pins (not shown). The IC chip 14 is mounted on the central portion of the upper surface of the base substrate 13. The IC chip 14 generates a large amount of heat during operation, for example, as the processing speed increases and the number of functions increases, and active heat dissipation is required to maintain a stable operation.

  A metal heat sink 15 as a heat radiating member is attached to the upper surface of the printed wiring board 10. The heat sink 15 is, for example, a square plate shape that is slightly larger than the CPU 12, and leg portions 16 positioned at the four corner portions are fixed to the printed wiring board 10 via screws 17.

  The heat sink 15 has a flat heat receiving surface 18 and a plurality of heat radiating fins 19. The heat receiving surface 18 covers the CPU 12 from above, and its central portion faces the IC chip 14. The radiating fins 19 are located on the opposite side of the heat receiving surface 18 and protrude from the heat sink 15.

  As shown in FIG. 3, a thermally conductive grease 20 is filled between the surface of the IC chip 14 that generates heat and the heat receiving surface 18 of the heat sink 15. The thermal conductive grease 20 is applied between the surface of the IC chip 14 and the heat receiving surface 18 by, for example, applying it to the surface of the IC chip 14 and then fixing the heat sink 15 to the upper surface of the printed wiring board 10. As a result, the IC chip 14 and the heat sink 15 are thermally connected via the thermally conductive grease 20.

  The thermally conductive grease 20 is mainly composed of a thermally conductive base material having electrical insulation and a thermally conductive filler. As the base material, for example, silicone oil can be used. The thermal conductivity of silicone oil is generally 0.2 or less.

  As the thermally conductive filler, for example, metal oxide such as aluminum oxide or ceramic particles can be used. The thermally conductive filler is blended at a predetermined ratio with respect to the base material, and generally the limit of the blending ratio of the thermally conductive filler is 95%.

According to the present embodiment, the thermally conductive grease 20 receives a load of 2 × 10 ⁵ or more when filled between the surface of the IC chip 14 and the heat receiving surface 18 of the heat sink 15. By adding this load to the thermally conductive grease 20, the upper limit value of the thermal resistance of the thermally conductive grease 20 is regulated to 0.05 ° C./W, which is the highest performance at the present time.

  Furthermore, it is desirable that the heat conductive grease 20 has a viscosity at room temperature within a range of 100 to 300 Pa · s. When the viscosity of the heat conductive grease 20 is less than 100 Pa · s, for example, when the IC chip 14 is erected vertically immediately after the heat conductive grease 20 is applied to the IC chip 14, the heat conductive grease 20 exerts the influence of gravity. As a result, it hangs down and cannot stop on the IC chip 14.

  When the viscosity of the thermal conductive grease 20 exceeds 300 Pa · s, the thermal conductive grease 20 becomes more viscous and difficult to apply on the IC chip 14. In other words, the thermal conductive grease 20 has a high viscosity and becomes difficult to handle when applied to the IC chip 14, and cannot be applied using an automatic application machine such as a dispenser.

  For this reason, for example, when the filling rate of the thermally conductive filler is fixed, a low-viscosity silicone oil with a high thermal conductivity is used as the substrate, or the filling rate of the thermally conductive filler is set to the viscosity of the substrate. The viscosity of the heat conductive grease 20 is adjusted within the above range by appropriately changing the balance.

  On the other hand, since the thermal resistance of the thermal conductive grease 20 is proportional to the thickness of the thermal conductive grease 20 filled between the IC chip 14 and the heat sink 15, the thinner the thermal conductive grease 20, the smaller the thermal resistance. Heat conduction performance is improved.

  When the heat conductive grease 20 is filled between the IC chip 14 and the heat sink 15, the shape of the heat conductive grease 20 can be expressed by a value obtained by dividing the thickness of the heat conductive grease 20 by the area. The thickness / area of the thermal conductive grease 20 can be obtained by the thermal resistance x thermal conductivity of the thermal conductive grease 20.

  The following Maxwell's formula is known as a typical theoretical formula for obtaining the thermal conductivity when a base material and a thermally conductive filler are blended.

Thermal conductivity after blending = (1 + 2 × filler filling rate) / (1-filler filling rate) × base material thermal conductivity Here, the thermal conductivity of silicone oil, which is a general base material, is 0.2 or less. And the limit of the filling rate of the thermally conductive filler is 95%. When this thermal conductivity value and the filling rate value are applied to the above Maxwell equation, the thermal conductivity after blending is 12 It becomes as follows.

  Since the upper limit value of the thermal resistance of the thermal conductive grease 20 is defined as 0.05 ° C./W as described above, each value of thermal resistance and thermal conductivity is expressed as thermal resistance × thermal conductivity. When applied to the theoretical formula, the value representing the shape of the thermally conductive grease 20 determined by the thickness / area is 0.6 / m or less.

  Therefore, in order to keep the thermal resistance of the thermal conductive grease 20 small, the value representing the shape of the thermal conductive grease 20 when filled between the IC chip 14 and the heat sink 15 is 0.6 / m or less. Is desirable.

  The thermally conductive grease 20 filled between the IC chip 14 and the heat sink 15 is used for the printed wiring board 10 and other circuits mounted on the printed wiring board 10 during the manufacture of the portable computer 1 or during maintenance and inspection by the user. There is a possibility of adhering to the part.

For this reason, it is desirable that the volume resistivity of the heat conductive grease 20 be 1 × 10 ¹⁰ Ω · cm or more in consideration of preventing occurrence of a short circuit accident or defective insulation.

According to such an embodiment of the present invention, when the thermal conductive grease 20 is pressurized with a load of 2 × 10 ⁵ Pa or more, the upper limit value of the thermal resistance of the thermal conductive grease 20 is set to 0.05 ° C. / W. Thereby, even if the heat conductive grease 20 is subjected to thermal stress for a long period of time, an increase in thermal resistance due to the thermal stress can be prevented.

  Therefore, the original heat conduction performance of the heat conductive grease 20 can be maintained for a long time. As a result, the heat dissipation performance of the CPU 12 is stabilized, and the reliability of the portable computer 1 is improved.

  Moreover, although the thermal resistance of the thermal conductive grease 20 is suppressed to a low level, the viscosity of the thermal conductive grease 20 can be kept appropriate. For this reason, the thermally conductive grease 20 does not flow out around the IC chip 14 and stops reliably between the IC chip 14 and the heat sink 15.

  At the same time, since the heat conductive grease 20 can be easily handled, the heat conductive grease 20 can be applied to the IC chip 14 using an automatic application machine such as a dispenser. As a result, there is an advantage that the application work of the heat conductive grease 20 can be performed efficiently and contributes to the improvement of the productivity of the portable computer 1.

  It should be noted that the present invention is not limited to the above-described embodiment, and can be implemented with various modifications without departing from the spirit of the invention.

  For example, the heating element is not limited to the CPU, and may be other circuit components that generate heat, such as a multichip module.

1 is a perspective view of a portable computer according to an embodiment of the present invention. 1 is a cross-sectional view of a portable computer according to an embodiment of the present invention. Sectional drawing which shows the state which connected thermally between CPU and a heat sink with heat conductive grease in embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 4 ... Housing | casing (1st housing | casing), 12 ... Heat generating body (CPU), 15 ... Heat-radiating member (heat sink), 20 ... Thermally conductive grease.

Claims (7)

Thermally conductive grease filled between the heating element and the heat dissipation member,
(1) The upper limit value of the thermal resistance when pressurized by applying a load of 2 × 10 ⁵ Pa or more between the heating element and the heat radiating member is 0.05 ° C./W,
(2) The viscosity at normal temperature is in the range of 100 Pa · s to 300 Pa · s,
(3) The value defined by the thickness / area when filled between the heating element and the heat dissipation member is 0.6 / m or less.
Thermally conductive grease characterized by 2. The heat conductive grease according to claim 1, wherein the volume resistivity is 1 × 10 ¹⁰ Ω · cm or more. A heat conductive grease containing a heat conductive base material and a heat conductive filler,
(1) The upper limit value of the thermal resistance when a pressure of 2 × 10 ⁵ Pa or more is applied is 0.05 ° C./W,
(2) The viscosity at normal temperature is in the range of 100 Pa · s to 300 Pa · s,
(3) The value specified by the thickness / area at the time of mounting is 0.6 / m or less,
(4) Volume resistivity is 1 × 10 ¹⁰ Ω · cm or more,
Thermally conductive grease characterized by   4. The thermal conductive grease according to claim 3, wherein when the blending ratio of the filler is fixed, the viscosity of the thermal conductive grease is regulated within the above range by lowering the viscosity of the base material. . A housing,
A heating element housed in the housing;
A heat radiating member that releases heat of the heating element;
A heat conductive grease that is filled between the heat generating element and the heat radiating member, and thermally connects the heat generating element and the heat radiating member;
The above thermal conductive grease
(1) The upper limit value of the thermal resistance when pressurized by applying a load of 2 × 10 ⁵ Pa or more between the heating element and the heat radiating member is 0.05 ° C./W,
(2) The viscosity at normal temperature is in the range of 100 Pa · s to 300 Pa · s,
(3) An electronic device characterized in that a value defined by a thickness / area when filled between the heating element and the heat dissipation member is 0.6 / m or less. 6. The electronic device according to claim 5, wherein the thermally conductive grease has a volume resistivity of 1 × 10 ¹⁰ Ω · cm or more.   7. The electronic device according to claim 5, wherein the thermally conductive grease is applied to the heating element.

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