JP2002093960A - Multi-chip module cooling structure and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a cooling structure of a multi-chip module having high heat conduction efficiency. SOLUTION: The cooling structure of the multi-chip module is:
A multi-chip module 10 including a substrate 2 and a plurality of semiconductor devices 1 mounted on the substrate 2, and a plurality of heat conductors 3 provided on the upper surface of each of the plurality of semiconductor devices 1
A heat dissipating member 20 thermally coupled to the upper portions of the plurality of heat conductors 3 and movably attached thereto;
It includes a plurality of low melting point metal members 4 provided between each of the heat conductors 3 and the heat radiation member 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling structure of a multi-chip module and a method of manufacturing the same, and more particularly, to a cooling structure of a multi-chip module having high heat conduction efficiency and a method of manufacturing the same.

[0002]

2. Description of the Related Art A plurality of large scale integrated circuits (Large Scale)
In a multi-chip module in which an integrated circuit (LSI) is mounted on one substrate, the amount of heat generated by the LSI increases as the degree of integration of the LSI increases. LSI
If the calorific value of itself increases, increasing the heat radiation area of the heat sink or increasing the heat transfer coefficient has no effect.
It is necessary to improve the efficiency of the heat conduction part from the heat sink to the heat sink.

On the other hand, the thickness of each of the LSIs mounted on the multi-chip module has manufacturing variations,
Even when the SI is mounted on the substrate, there is a variation in mounting, so that there is a problem that the LSI warps or tilts.
In each LSI, the variation in the height direction alone is 2
It reaches as large as 00 to 300 micrometers. Generally, the cooling structure of a multi-chip module includes a plurality of LSIs.
Cooling is performed by contacting two heat sinks, but due to this variation, a gap is generated between each LSI and HS. In order to fill this gap, high thermal conductivity
It is important to improve the cooling performance.

[0004]

A technique for filling the above-mentioned gap by using a thermally conductive rubber sheet is disclosed in Japanese Patent Laid-Open No. 2-1964.
53. However, since the thermal conductivity of rubber materials is two orders of magnitude lower than that of metals, LS with high calorific value
When used for I, there is a problem because heat does not conduct.

Japanese Patent Application Laid-Open No. 11-135691 discloses that each LSI
A low melting point metal, aluminum nitride, and heat conductive grease are provided between the heat sink and the heat sink. However, even with this method, there is no guarantee that the thickness of the grease portion can be reduced, and as a result, a problem arises because the thermal resistance of the grease portion increases.

As a workaround for this technique, Japanese Patent Laid-Open No. 2000-3
In 1360, the grease is removed, and the LSI and the heat sink are fixed with a fixed solder. However, this structure has a problem in that thermal expansion due to heat generation of the LSI cannot be absorbed and excessive thermal stress acts on the LSI.

Accordingly, an object of the present invention is to provide a cooling structure for a multi-chip module having high heat conduction efficiency.

[0008] Another object of the present invention is to generate L
An object of the present invention is to provide a cooling structure for a multi-chip module that does not apply excessive pressure to the LSI even if the SI thermally expands.

Another object of the present invention is to provide a cooling structure of a multi-chip module which does not require a change of a heat radiating member even if the thickness of an LSI changes, the warpage of a substrate or the dimensional tolerance of mechanical parts varies. Is to do.

[0010]

According to the present invention, there is provided a cooling structure for a multi-chip module, comprising: a multi-chip module including a substrate and a plurality of semiconductor devices mounted on the substrate; A plurality of heat conductors provided on an upper surface of each of the plurality of semiconductor devices; a heat dissipating member thermally coupled to the upper portions of the plurality of heat conductors and movably attached to the plurality of heat conductors; And a plurality of low melting point metal members provided between each of the above and the heat radiation member.

In another cooling structure for a multi-chip module according to the present invention, the heat radiating member has a plurality of concave portions provided at positions corresponding to the plurality of semiconductor devices, respectively, Each of the members is embedded in each of the plurality of recesses.

Further, another cooling structure of the multi-chip module according to the present invention is characterized in that each of the plurality of low-melting-point metals is filled between the corresponding recess and the upper surface of the semiconductor device. I do.

In another cooling structure of the multi-chip module according to the present invention, the low melting point metal includes a solder.

Further, another cooling structure of the multi-chip module according to the present invention is characterized in that the heat radiating member moves according to a variation in mounting height and inclination of the plurality of semiconductor devices.

In another cooling structure for a multi-chip module according to the present invention, the heat radiating member moves in accordance with thermal expansion of the plurality of semiconductor devices.

Further, another cooling structure of the multi-chip module according to the present invention includes: a plurality of springs for pressing the heat radiating member against respective upper surfaces of the plurality of semiconductor devices according to heights and angles of the plurality of semiconductor devices; A plurality of screws for attaching each of the plurality of springs to the substrate.

According to the method of manufacturing a cooling structure of a multi-chip module of the present invention, a first step of providing a low melting point metal in each of a plurality of recesses provided on a lower surface of a heat radiating member; The lower surface is attached via a tape member, and the upper surface of each of the plurality of semiconductor devices provided on the multi-chip module is brought into contact with the low melting point metal provided on each of the plurality of recesses via the tape member. A second step of applying heat to the low melting point metal of the heat dissipating member to melt the low melting point metal, and a fourth step of lowering the temperature of the low melting point metal to solidify it. A fifth step of removing the heat radiating member and the tape member from the multi-chip module; and a step of removing each of the plurality of semiconductor devices on the multi-chip module. Comprising a sixth step of forming a heat conductive member on the surface, and a seventh step of attaching the lower surface of the heat radiating member and the multi-chip module.

According to another aspect of the present invention, there is provided a method of manufacturing a cooling structure for a multi-chip module, comprising the steps of:
The multi-chip module and the lower surface of the heat dissipation member are attached via an elastic member.

Further, in the method for manufacturing a cooling structure for a multi-chip module according to another aspect of the present invention, in the seventh step, the multi-chip module and the lower surface of the heat radiating member are attached via an elastic member. I do.

According to another aspect of the present invention, there is provided a method of manufacturing a cooling structure for a multi-chip module, comprising the steps of:
The amount of the low-melting-point metal is set according to a variation in height or a slope of the corresponding semiconductor device.

Further, in the method of manufacturing a cooling structure for a multi-chip module according to another aspect of the present invention, the low melting point metal includes solder, and the low melting point metal is supplied by a solder sheet in the first step. And

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a cooling structure for a multichip module and a method of manufacturing the same according to the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, a cooling structure of a multi-chip module according to the present invention includes a multi-chip module 10.
, A heat conductor 3, a low melting point metal 4, a flange 5, a heat radiating member 20, a spring 7, and a screw 8.

The multi-chip module 10 includes a substrate 2 and a plurality of LSIs 1 mounted on the upper surface of the substrate 2. The plurality of LSIs 1 mounted on the substrate 2 have different height dimensions, tilt angles, and warpage amounts. This is due to variations in the thickness of the silicon wafer of each of the plurality of LSIs 1, manufacturing variations in the mounting of the substrate, warpage of the substrate 2 itself, and the like.

The heat conductor 3 is provided on the upper surface of each of the plurality of LSIs 1. The thermal conductor 3 reduces the contact thermal resistance between the solids of the LSI 1 and the low melting point metal 4. Thermal conductor 3 includes silicone grease or a compound. When microscopically observing the heat-dissipating surface and the heat-sink base surface of a solid LSI, fine irregularities are present. Heat is transferred only at the portions where the fine irregularities are in contact. The thermal resistance of this portion is called contact thermal resistance, and a large thermal loss occurs. Therefore, a fluid heat conductor 3 such as grease or a compound is filled to fill the gaps of the unevenness. However, the thermal conductivity of the resin material constituting the thermal conductor 3 is inferior to that of metal by two orders of magnitude, so that the thinner the thickness of the thermal conductor 3, the better the cooling performance.

The heat dissipating member 20 includes a heat sink base 6.
And a heat radiating section 9.

The heat sink base 6 is made of a metal having good heat transfer, and is made of, for example, aluminum or copper.
The heat radiating portion 9 is made of a metal having good heat transfer, and is formed of, for example, aluminum or copper. The heat sink base portion 6 and the heat radiating portion 9 are connected via a heat radiating sheet 10. The heat radiation sheet 10 is a flexible rubber sheet or the like. Since the contact between the heat sink base portion 6 and the heat radiating portion 9 is a solid-to-solid contact, the surface is uneven and has a contact thermal resistance. The heat dissipation sheet eliminates contact thermal resistance.

The heat sink base 6 has a plurality of recesses. The plurality of recesses are formed on the lower surface of the heat sink base 6. Each of the plurality of recesses is provided at a position facing each of the plurality of LSIs.

A plurality of low melting point metals 4 are fixed to the heat sink base 6 in order to accurately transfer the mounting shape of each LSI described above. The lower surface of each low melting point metal 4 is in contact with the corresponding upper surface of the LSI 1 via the heat conductor 3. Specifically, the low melting point metal 4 is embedded in each of the plurality of recesses of the heat sink base 6. The low melting point metal 4 includes a low melting point solder.

In the present embodiment, the term “transfer” refers to forming a plane in which the height or inclination of the lower surface of the low-melting metal 4 is the same or substantially the same as the upper surface of the LSI 1 according to the height or inclination of the corresponding LSI 1. What you do. That is, when the heat radiating member 20 is attached to the multi-chip module 10, the lower surface of each of the plurality of low melting point metals 4 and the upper surface of the corresponding LSI 1 are in intimate contact with each other.

The heat sink base 6 is constantly pressed toward the LSI 1 by a plurality of springs 7. The spring 7 is mounted on a flange 5 provided on the periphery of the substrate 2 with a support upright and screws 8. The spring 7 is connected to the 4
It is preferable to use a plurality of them in a corner or the like. This is because the base 6 can be moved more flexibly. The spring force of the spring 7 is determined by the weight of the heat sink, the load resistance of the LSI, and the like. The spring 7 having a low spring constant is selected. This is because there is little load fluctuation even when following the dimensional change of the LSI 1 and it is advantageous. Specifically, the spring constant of the plurality of springs 7 is 100 g / mm or less. That is, the springs 7 are set so as to move by 1 mm and generate a force of about 100 grams or less.

A heat radiator 9 is mounted on the upper surface of the heat sink base 6. The heat dissipating portion 9 is provided with fins as shown in FIG. 1 and dissipates heat to the surrounding air, or dissipates heat to liquid such as water or CFC substitute, and its structure is freely selected. Further, although the case where the fin 9 and the heat sink base 6 are joined by the heat radiating sheet 10 is shown in the drawing, the fin 9 and the heat sink base may be integrated.

Thermal conduction is the transfer of heat within a substance. Therefore, if a substance having a large thermal conductivity is used and the length of the path in the heat transfer direction is shortened, the cooling capacity can be increased.
However, as described above, the heat conducting member 3 to be filled between the LSI 1 and the heat sink base portion 6 does not improve the heat radiation property by mixing a filler such as ceramic alumina or aluminum nitride with silicone oil as a heat conducting medium. However, its thermal conductivity is still 2 compared to metal
The order is inferior. Therefore, how to keep the thickness of the heat conducting member small is a key to determining the cooling performance. In the cooling structure of the present invention, since the mounting shape such as the warpage or inclination of the LSI is directly transferred to the low melting point metal, the thickness of the heat conducting member can be made uniform and thin over the entire heat dissipation surface of the LSI.

Further, according to the present invention, since the fluid resin is applied with an extremely thin thickness and the heat radiation member 20 is floating with respect to the LSI 1, the difference in thermal expansion can be absorbed.

Next, a method of manufacturing the cooling structure of the multichip module according to the present invention will be described.

Referring to FIG. 2, a flange 5 with a stay attached around the multichip module 10 is assembled. The plurality of LSIs 1 are warped or tilted with respect to the substrate due to manufacturing or mounting variations. A concave portion or a concave portion is formed in the heat sink base portion 6 at a position facing each LSI. The low melting point metal 4 is filled in the concave portions and the concave portions. The amount of the low melting point metal 4 is filled with an optimum amount obtained by calculating the volume variation of the LSI 1. For this reason, it is advantageous to use it in the form of a solder sheet or the like.

In this state, the surface of the multi-chip module 10 on which the LSI 1 is provided and the heat sink base 6
Is brought into contact with the lower surface of the cooling structure in the same manner as in the final form of the cooling structure. More specifically, the multichip module 10 and the heat sink base 6 are assembled by tightening the screws 8 to the columns of the flange 5 via the springs 7. At this time, LS
In order to prevent the fusion of I1 and low melting point metal 4, a heat-resistant tape such as an interfacial deactivator or Teflon (registered trademark) is interposed on the surface of LSI1. The spring force of the spring 7 is determined by the withstand load of the LSI 1, but it is advantageous to select a spring having a small spring constant because the load variation is small.

In FIG. 3, the multi-chip module 1
Heat is applied to the low melting point metal 4 of 0. Specifically, in a state where the multi-chip module 10 and the heat sink base 6 are assembled, the multi-chip module 10 is left in a constant temperature environment such as a thermostat. The temperature of the atmosphere is set near the melting point of the low melting point metal 4. The melting point of the low melting point metal 4 is adjusted by the composition of the components so as to be lower than the heat resistant temperature of the substrate 2 and the components mounted on the substrate 2.

The ambient temperature is lowered from the temperature at which the low melting point metal 4 is melted, and the low melting point metal 4 is solidified again. Thereby, the shape of the LSI 1 is transferred to the low melting point metal 4. That is, the lower surface of each of the plurality of low melting point metals 4 is formed to have an inclination corresponding to the warpage of the substrate or the inclination of the opposed LSI. When the low melting point metal 4 is solidified, a cooling method and a cooling rate are adjusted so that the low melting point metal 4 does not cause shrinkage or voids.

Referring to FIG. 4, the heat sink base 6 and the heat-resistant tape are removed from the multi-chip module 10. As for the low melting point metal 4, the shape of the warp or inclination of each LSI 1 is transferred as it is.

After removing the interfacial deactivator and heat-resistant tape applied to the surface of the LSI 1, a heat conductive member 3 such as grease or a compound is applied to the upper surface of each of the plurality of LSIs 1 on the multi-chip module 10.

Next, the multichip module 10 and the lower surface of the heat sink base 6 are attached. At this time, the heat conductive member 3 on the LSI 1 and the corresponding low melting point metal 4 of the heat sink base 6 come into contact with each other. As a result, the cooling structure of the multi-chip module shown in FIG. 1 is obtained.

In the above embodiment, the heat radiating member 20 is divided into the heat sink base portion 6 and the heat radiating portion 9, but the heat radiating member 20 may be an integral structure.

In the present embodiment, the low-melting point metal 4 such as solder is used for shape transfer, but a resin filled with a metal filler to increase the thermal conductivity may be used.

[0045]

As described above, according to the present invention, the cooling performance can be improved in a multichip module in which the heat generation of each LSI is large. This is because the shape of the warpage or tilt of each LSI mounted on the board can be directly transferred to the base surface of the heat sink using a low-melting metal, so that the thickness of heat conductive members such as grease and compounds is minimized. This is because it can be made as small as possible.

In the present invention, since a fluid heat conducting member is used, a difference in thermal expansion due to heat generation can be absorbed. Therefore, no excessive load is applied to the LSI.

Further, according to the present invention, since the heat sink base has a floating structure,
Even if the thickness of I changes, the warpage of the substrate or the dimensional tolerance of the mechanical parts varies, it can be handled without adjustment without changing the heat sink base part.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a method of manufacturing a cooling structure for a multi-chip module according to the present invention.

FIG. 3 is a view illustrating a method of manufacturing a cooling structure of a multi-chip module according to the present invention.

FIG. 4 is a diagram illustrating a method of manufacturing a cooling structure for a multi-chip module according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 LSI 2 Substrate 3 Heat conductor 3 4 Low melting point metal 4 5 Flange 5 6 Heat sink base part 7 Spring 8 Screw 9 Heat radiating part 10 Multi chip module 20 Heat radiating member 30 Sales server 100 Network

Claims (12)

[Claims] A multi-chip module including a substrate and a plurality of semiconductor devices mounted on the substrate; a plurality of thermal conductors provided on an upper surface of each of the plurality of semiconductor devices; A heat dissipating member thermally coupled to the upper portion of the heat conductor and movably attached thereto; and a plurality of low melting point metal members provided between each of the heat conductors and the heat dissipating member. A cooling structure for a multi-chip module, characterized in that: 2. The heat dissipating member has a plurality of recesses provided at positions corresponding to the plurality of semiconductor devices, respectively, and each of the plurality of low melting point metal members is embedded in each of the plurality of recesses. The cooling structure for a multi-chip module according to claim 1, wherein: 3. The cooling structure for a multi-chip module according to claim 2, wherein each of the plurality of low-melting-point metals is filled between the corresponding recess and an upper surface of the semiconductor device. 4. The cooling structure for a multi-chip module according to claim 1, wherein said low melting point metal includes solder. 5. The cooling structure for a multi-chip module according to claim 1, wherein said heat radiating member moves in accordance with a variation in mounting height and inclination of said plurality of semiconductor devices. 6. The cooling structure for a multi-chip module according to claim 1, wherein said heat radiating member moves in accordance with thermal expansion of said plurality of semiconductor devices. 7. A plurality of springs for pressing the heat radiating member onto respective upper surfaces of the plurality of semiconductor devices according to heights and angles of the plurality of semiconductor devices; and a plurality of springs for attaching each of the plurality of springs to the substrate. The cooling structure for a multi-chip module according to claim 1, further comprising a screw. 8. A multi-chip, comprising: a first step of providing a low melting point metal in each of a plurality of recesses provided on a lower surface of a heat radiating member; and attaching a multi-chip module and a lower surface of the heat radiating member via a tape member. A second step of bringing the respective upper surfaces of the plurality of semiconductor devices provided on the module into contact with the low-melting point metal provided in each of the plurality of recesses via the tape member; A third step of applying heat to the low-melting-point metal to melt the low-melting-point metal; a fourth step of lowering the temperature of the low-melting-point metal to solidify; and the heat dissipation member and the tape from the multi-chip module. A fifth step of removing a member, a sixth step of forming a heat conducting member on an upper surface of each of the plurality of semiconductor devices on the multi-chip module, A method for manufacturing a cooling structure for a multi-chip module, comprising: a seventh step of attaching a chip module and a lower surface of the heat dissipation member. 9. The method according to claim 8, wherein in the second step, the multi-chip module and the lower surface of the heat radiating member are attached via an elastic member. 10. The method according to claim 8, wherein in the seventh step, the multi-chip module and the lower surface of the heat radiating member are attached via an elastic member. 11. The multi-chip according to claim 8, wherein in the first step, the amount of the low-melting-point metal is set according to a variation in height or a slope of the corresponding semiconductor device. Manufacturing method of module cooling structure. 12. The method for manufacturing a cooling structure for a multi-chip module according to claim 8, wherein said low melting point metal includes solder, and said low melting point metal is supplied by a solder sheet in said first step. .