JP2001177017A - Electronics cooling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To connect a package consisting of a porous material and a heat sink with each other at a low contact heat resistance in the case where there are large undurations on the contact surface of the package to the heat sink. SOLUTION: A sheet formed by coating a compound 71 on a base material 70 having barrier properties to the component of oil is installed on the side of a package and a heat conductive grease is made to interpose between the sheet and the heat sink to connect the package with the heat sink.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat connecting structure between a heat generating element and a heat sink used in an electronic apparatus such as a computer.

[0002]

2. Description of the Related Art In an electronic apparatus such as a computer, a heat sink is attached to a heating element in order to cool a heating element such as a semiconductor which generates a large amount of heat. When the heating element and the heat sink are brought into contact with each other, a large contact thermal resistance generally occurs due to roughness and undulation on each surface. For this reason, a thermally conductive grease is interposed between the two, or a thermally conductive flexible rubber sheet or the like is interposed. The former example is found, for example, in JP-A-64-12561, and the latter example is found in JP-A-2-196453. There is also a sheet in which a sheet in which a heat-meltable compound is applied to a base material such as aluminum is sandwiched so that the compound is melted to absorb the roughness and undulation on the surface.

[0003]

A semiconductor element used for an electronic device such as a computer is subject to mechanical restrictions.
Often packaged in a case such as ceramic. In this case, the ceramic needs to be a material having high thermal conductivity, but depending on the material, the ceramic has a porous shape. If the contact surface between the package made of a porous material and the heat sink has a large undulation, the contact thermal resistance can be reduced by using a thermally conductive grease as in the conventional example. However, there is a problem that the liquid (oil) component in the grease enters the package.

On the other hand, in the case of a heat conductive flexible rubber sheet or a sheet coated with a compound, it is necessary to increase the thickness of the rubber sheet or the compound in order to absorb a large undulation, and it is difficult to reduce the thermal resistance. (Because these are generally lower in thermal conductivity than the thermally conductive grease).

[0005] In order to solve these problems, an object of the present invention is to provide a case where a contact surface between a package made of a porous material and a heat sink has a large undulation.
An object of the present invention is to provide a structure capable of connecting a package and a heat sink with low contact thermal resistance.

[0006]

Means for Solving the Problems To achieve the above object, a heat conductive medium layer having a fluidity having a different thickness on each surface of a sheet-like substrate impermeable to liquid (oil) components. (At least one of which is impervious to the package), and the layer of the heat-conducting medium that is impervious to the package is placed on the package side. Connected. At this time, the thermal conductivity of the thicker thermal conductive medium is made higher than that of the other thermal conductive medium.

That is, since the heat conduction medium has fluidity,
Even if there is a large undulation on the contact surface between the package and the heat sink, it can enter the gap formed between the two. On the other hand, the sheet-like substrate can be deformed following the undulating surface of the package due to the pressure of the heat transfer medium. Therefore, the gap created due to the undulation at the contact surface between the package and the heat sink is filled with the thicker heat conduction medium even when the heat conduction medium is used together with the sheet-like base material.

On the other hand, the gap formed between the package and the sheet-like base material due to the surface roughness of the package is filled with the thinner heat conductive medium. At this time, in particular, the heat dissipation performance is improved by increasing the thermal conductivity of the thicker heat conductive medium. Therefore, even when the contact surface between the package and the heat sink has a large undulation, the connection between the package and the heat sink can be made with a small contact thermal resistance.

Further, since the sheet-like base material has a barrier property against the oil component, the oil component contained in the heat conduction medium (thicker layer) does not reach the package surface.
(The heat conductive medium on the package side is impervious to the package.) That is, even if the material of the package is porous, the oil component in the heat conductive medium does not enter the package. Absent.

[0010]

Embodiments of the present invention will be described below. 1 and 2 show an embodiment of the electronic device of the present invention. FIG.
3 is a cross-sectional view of a portion where the packaged high-heat generating element 4 (for example, a CPU of a computer) is mounted on the wiring board 9. The heating element 4 is mounted on the wiring expansion board 5 and is sealed by a cap of the package 3. The heating element 4 and the cap of the package 3 are made of Ag.
The heat generated by the heating element 4 is bonded to the cap of the package 3 with a small thermal resistance and is radiated by the heat sink 1 attached to the cap of the package 3.

The cap of the package 3 is desirably made of ceramic having high thermal conductivity, and AlSi or the like is used. The package is attached to the wiring board 9 via the socket 6, and an electrical connection is made. The package 3 and the fin base 2 of the fin 1 are connected to each other via a heat conductive member 7 in which a heat conductive medium and a sheet-shaped base material are combined.

The fin 1 is fixed by screws 8 together with the socket 6 and the back plate 10 provided on the back side of the wiring board 9. At this time, the fin 1 is always pressed against the package 3 by using the spring 11.

FIG. 2 is an enlarged view of a connection portion between the fin base 2 and the package 3. A heat conductive grease 72 as a heat transfer medium is provided between the fin base 2 and the package 3.
A sheet on which a compound 71 is applied as a heat transfer medium is interposed on a base material 70. The base material 70 is, for example, an Al foil having a barrier property against an oil component. A sheet (the side on which the compound 71 is applied) is placed on the package 3 side, and a thermally conductive grease 72 is interposed between the sheet and the fin base 2.

The thermal conductive grease 72 is obtained by mixing a filler (fine particles of ceramic or the like having high thermal conductivity) into Si oil. Compound 71 applied to sheet
Is applied to at least the surface that comes into contact with the package 3 (or may be applied to both surfaces). The compound 71 is, for example, a wax that melts at about 50 ° C., and the thickness is desirably as thin as the surface roughness existing on the surface of the package 3 can absorb (about 10 to 20 μm in thickness).

The thickness of the grease 72 is set such that the size of the gap caused by the undulation (generated by the undulation between the fin base 2 and the package 3) can be absorbed. Therefore, it is larger than the thickness of the compound 71 layer and several tens of μm.
m or more. Since the heat conductive grease 72 is more fluid than the compound 71, even if there is a gap caused by undulation on the contact surface between the package 3 and the fin base 2, it can enter the gap formed between the two.

On the other hand, the sheet on which the compound 71 is applied can be deformed following the undulating surface of the package 3 by the pressure of the grease 72. On the other hand, the gap formed between the package and the sheet due to the surface roughness of the package 3 is caused by the compound 71 applied to the sheet being melted due to the rise in the package surface temperature accompanying the operation of the heating element, resulting in minute irregularities. It is filled by going in. Note that the gap created due to the surface roughness of the fin base 2 is filled with the heat conductive grease 72.

Accordingly, the heat conductive grease and the Al foil base material 70
Even if the sheets made of fins are used at the same time, the gap generated between the package 3 and the fin base 2 is filled, and the two are thermally connected with a small contact thermal resistance. That is,
Large gaps caused by undulations are absorbed by grease having a large layer thickness and large thermal conductivity, while small gaps caused by surface roughness are absorbed by a compound layer having a small layer thickness,
Since the compound layer can be made thin, it is not necessary to select a compound layer having a particularly large thermal conductivity.

Further, since the base material 70 of the sheet has a barrier property against the oil component, the oil component contained in the heat conductive grease 72 does not reach the surface of the package 3.
That is, even if the material of the package 3 is porous, such as AlSi, the oil component in the grease does not enter the package. It goes without saying that the compound is impervious to the package material.

Next, a method of applying the thermal conductive grease 72 will be described with reference to FIG. FIG. 3 shows a simplified package mounting structure similar to that of FIG. Since the thermal conductive grease 72 has fluidity, it can fill gaps following irregularities on the contact surface. However, particularly when the contact surface is large, air may remain and the contact thermal resistance may increase.

Therefore, the thermally conductive grease 72 is potted in a substantially circular region at the center of the contact surface, and the fin base 2 is pressed so that the grease 72 spreads uniformly from the center toward the periphery. Thereby, the fin base 2
Air does not remain between the substrate and the base material 70. Excess grease protruding from the periphery of the contact surface is absorbed by, for example, a grease reservoir (a groove provided along the periphery of the contact surface) 73 provided at an end of the contact surface of the fin base 2.

FIG. 4 shows another embodiment of the present invention. The package mounting structure may be the same structure as that of FIG. 1 or a structure without using a socket. In this embodiment, a base material 70 such as an Al foil having a barrier property against oil is attached to the fin base connecting portion on the surface of the package (porous material) by an adhesive 7.
4 attached. The base material 70 is adhered following the undulating surface of the package 3. Adhesive 7
4 is desirably large in thermal conductivity, preferably as thin as possible.

The compound described in FIGS. 1 and 2 may be used. A thermally conductive grease 72 is interposed between the package 3 to which the base material 70 is bonded and the fin base 2. The thermal conductive grease 72 is applied in a manner similar to that described with reference to FIG.
No air remains between the fin base 2 and the base material 70 of the sheet.

According to this embodiment, the package 3 and the base 7
The gap created due to the surface roughness of the package 3 occurring between 0 is filled with the adhesive 74. On the other hand, the gap generated due to the undulation of the contact surface between the fin base 2 and the package 3 can be absorbed by the thermally conductive grease.
Further, since the base material 70 has a barrier property against the oil component, the oil component contained in the heat conductive grease 72 does not reach the surface of the package 3. That is, even if the material of the package 3 is porous like AlSi or the like,
The oil component in the grease does not enter the package.

FIG. 5 shows another embodiment of the present invention. In the present embodiment, between the fin base 2 and the package 3, a material in which a thermally conductive grease 72 is sealed in a bag-shaped base material 70 (having a barrier property against oil) is sandwiched. . The compound is applied to the outer surface of the base material 70. The fin 1 and the package 3 may be fixed by a spring using a spring as shown in FIG. 1 so that the fin 1 is always pressed against the package 3 (not shown). Thermal grease 70 sealed in a bag
When the fin base 2 and the package 3 are pressed against each other, pressure is applied to the fin base 2 and the package 3.
Deforms following the undulation of the surface.

On the other hand, the minute gap caused by the surface roughness of the contact surface between the fin base 2 and the package 3 is filled by the compound 71. The compound 71 is the same as in the embodiment described with reference to FIGS. According to the present embodiment, the gap generated due to the undulation and surface roughness of the contact surface is filled to keep the contact thermal resistance small, and the heat conductive grease 72 is held in the bag, so that the handleability is improved. There is a feature that is excellent.

FIG. 6 shows an example in which the present invention is applied to a multichip module. In the multi-chip module, a plurality of packages 13 in which heating elements are sealed are mounted on a wiring board 14 having pins 14 for electric signals, and a cap 12 is provided.
Is sealed by. A heat dissipation structure such as a heat sink is connected to the surface of the cap 12. In addition, cap 1
2 itself may be a heat sink. Package 13
A heat conductive grease 72, a base material 70 having a barrier property against oil, and a compound 71 applied to the base material are interposed between the cap and the cap 12.

In consideration of workability and treatment of excess grease (excess grease does not flow to the package side), the base material 70 on which the compound 71 is applied is a single sheet that can simultaneously connect all the packages. The thermal conductive grease 72 is applied to the mounting position of the package 13 on a one-to-one basis. The functions of the base material 70 coated with the compound 71 and the heat conductive grease 72 are the same as those described above. In particular, in the present embodiment, the swell of the surface of the package 13 and the inner surface of the cap 12 as well as the height variation between the packages 13 are absorbed, and all the packages 13 and the cap 12 are connected with a small thermal resistance.

[0028]

Since the present invention is configured as described above, it has the following effects.

The gap formed due to the undulation at the contact surface between the package and the heat sink and the gap formed due to the surface roughness of the package generated between the package and the substrate are filled with the heat transfer medium, and the small contact heat is generated. The resistance allows the connection between the package and the heat sink, and even if the material of the package is porous, the oil component contained in the heat conduction medium does not enter the package.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electronic apparatus cooling apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a contact surface of FIG. 1;

FIG. 3 is a cross-sectional view of a case where the heat conduction grease according to the first embodiment is applied to an electronic device cooling device.

FIG. 4 is a cross-sectional view of a case where a heat conductive grease according to a second embodiment of the present invention is applied to an electronic device cooling device.

FIG. 5 is a sectional view showing the vicinity of a fin base and a package according to a third embodiment of the present invention.

FIG. 6 is a sectional view showing the vicinity of a fin base and a package according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 fin, 2 fin base, 3 package, 4…
Heating element, 5: enlarged board, 9: wiring board, 7: heat conductive member, 70: base material, 71: compound, 72: heat conductive grease.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahiro Oguro 1st Horiyamashita, Hadano-shi, Kanagawa Prefecture In-house Enterprise Server Division, Hitachi, Ltd. (72) Inventor Takayuki Uda 1st Horiyamashita, Hadano-shi, Kanagawa Japan, Inc. F-term (reference) 5F036 AA01 BB21 BC03

Claims (1)

[Claims] An electronic device for cooling a heating element by connecting a heat sink to a package containing the heating element mounted on a wiring board, wherein heat conducting medium layers having different thicknesses are formed on both surfaces of a base material. An electronic equipment cooling device, wherein the constituted heat conducting member is interposed between a package and a heat sink.