JP2001244394A - Heat dissipating structure of semiconductor package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the heat transfer efficiency between a CPU and a heat sink for CPU heat dissipating structure of personal computer. SOLUTION: Using both of heat conduction grease 10 and heat conduction sheet 6 which is shaped hole style provide heat liberation function that can do with high quality, high heat up CPU package by conduction to heat sink 7 from both side of surface CPU package and basis 3 of CPU package.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat radiation structure for a CPU of a personal computer.

[0002]

2. Description of the Related Art CPU used in mobile personal computers
Is pursuing small, lightweight, thin, and heat-dissipating functions.
It is packaged in a state close to a bare chip. FIG. 4 is a sectional view of a mobile CPU package. In FIG. 4, reference numeral 51 denotes a semiconductor chip, 52 denotes a chip substrate, 53 denotes a bump electrode provided on the semiconductor chip 51, 54 denotes a solder ball, and 55 denotes a sealing resin. The semiconductor chip 51 is made of silicon, and a bump electrode 53 is provided on the back surface. The bump electrodes 53 are connected to the solder balls 54 by conductor circuits (not shown) penetrating the chip substrate 52. The gap between the semiconductor chip 51 and the chip substrate 52 is filled with a sealing resin 55 to protect the bump electrodes 53 from the humidity and temperature of the outside air. The silicon chip surface is exposed on the surface of the semiconductor chip 51, and the semiconductor chip 51
The heat generated inside is improved.

FIG. 5 shows a conventional semiconductor chip 51.
Will be described. In FIG. 5, 56 is a wiring board, 57 is a heat sink, and 58 is heat conductive grease. The solder balls 53 are connected to wiring lands (not shown) provided on the wiring board 56 to form an arithmetic circuit. The heat sink 57 transfers the heat generated by the semiconductor chip 51, and radiates the transferred heat into the air by a cooling means such as a fan 59 that cools the surroundings. Heat transfer between the semiconductor chip 51 and the heat sink 57 is performed via the heat conductive grease 58. The thermally conductive grease 58 is applied to a thickness of 100 μm or less to ensure contact between the semiconductor chip 51 and the heat sink 57 and to reduce thermal resistance. This method has an excellent heat dissipation effect because the thickness of the heat conductive grease 58 can be reduced. However, since the semiconductor chip 51 is sandwiched between the heat sink 57 and the heat sink 57, when the clamping pressure is small, the method may cause vibration. When the holding pressure is large, the contact between the solder ball 53 and the wiring land may be damaged.

A semiconductor chip 51 and a heat sink 5
7A and 7B, a rubber-elastic heat-conductive sheet 60 as shown in FIG. 6A is used, and the elastic sheet 60 is deformed by pressure to improve adhesion and heat conductivity. (FIG. 6B). In this method, since the rubber elastic body is interposed, the stress applied to the semiconductor chip 51 can be made uniform. However, since the thickness of the elastic sheet 60 is increased, there is a disadvantage that heat conduction efficiency is poor.

[0005]

SUMMARY OF THE INVENTION It has been found that the heat dissipation is good and the semiconductor chip is reliably held with the increase in heat generation accompanying the high performance of the semiconductor chip and the miniaturization of the solder ball due to the high density. There is a strong demand for a heat dissipation structure that can be used. Efficient fan systems for heat sinks have been developed to improve heat dissipation, but even with the improved fan system, sufficient heat dissipation is required unless the heat transfer efficiency from the semiconductor chip to the heat sink is increased. Can't get any more. In the structure of FIG. 5, the heat conduction area is limited to the upper area of the semiconductor chip, and in the structure of FIG. 6, the heat conduction area is increased. However, since the heat conduction sheet requires a certain thickness, the heat resistance is large. However, there is a problem that the heat cannot be sufficiently transferred to the heat sink.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the conventional example, and has as its object to provide an efficient heat radiation structure which can cope with a semiconductor chip having high performance and high heat generation.

[0007]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention provides a heat conductive sheet having elasticity around a semiconductor chip, the upper surface of the semiconductor chip, the side surface of the semiconductor chip, and the surface of the semiconductor substrate. It is configured so that heat in three directions can be efficiently conducted to the heat sink, and the pressure applied to the semiconductor chip is also shared by the heat conductive sheet so that excessive pressure is not applied to the upper surface of the semiconductor chip. is there.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a wiring board on which a semiconductor chip is mounted, an elastic heat conductor surrounding the periphery of the semiconductor chip, and a coating on an upper surface of the semiconductor chip. Heat conductive grease, a heat sink opposed to the heat conductive grease, and a spring means provided between the heat sink and the wiring board, the upper surface of the semiconductor chip, the semiconductor Since heat in three directions on the side surface of the chip and the surface of the semiconductor substrate can be efficiently conducted to the heat sink, the heat dissipation is excellent.

According to a second aspect of the present invention, in the first aspect, the thickness of the heat conductor is larger than the height of the back of the semiconductor chip. Since heat conduction to the semiconductor chip can be ensured and the pressure applied to the semiconductor chip can be shared by the heat conductor, heat dissipation is good and reliability is high.

According to a third aspect of the present invention, in the second aspect, a spring means is provided between the wiring board and the heat sink with reference to a boss provided on the bottom surface of the housing of the wiring board. The spring pressure is stable, so that an optimal pressure can be set, and the heat radiation efficiency is good.

An embodiment of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is a perspective view showing a heat dissipation structure of the present invention, FIG. 2 is a sectional view, and FIG. 3 is an enlarged sectional view of a main part of a spring means.

1 and 2, 1 is a semiconductor package, 2 is a semiconductor chip, 3 is a chip substrate, 4 is a wiring board, 5 is a sealing resin, 6 is a heat conductive sheet, 7 is a heat sink, 8 is a fan, 9 is a solder ball, 10 is a thermally conductive grease, and 11 is a bottom surface of the housing of the mobile personal computer in which the wiring board 4 is built.

The structures of the semiconductor package 1 and the wiring board 4 are the same as those described in the conventional example. Since the semiconductor package 1 is mounted on the wiring board 4 by a conventional method, the description will not be repeated. .

The heat sink 7 has a built-in fan 8, and the fan 8 in FIG. 2, for example, sucks warm air near the housing bottom surface 11 and discharges it to the outside of the housing (arrows indicate the flow of air). Shown).

Pressure is applied to the semiconductor package 1 by a spring means provided between the heat sink 7 and the wiring board 4 to increase the thermal conductivity between the semiconductor package 1 and the heat sink 7. An example of the structure of the spring means according to the first embodiment will be described with reference to FIG.

In FIG. 3, 20 is a boss provided on the bottom surface 11 of the housing, 21 is a screw hole provided on the boss 20, 22 is a through hole provided on the heat sink 7, 23 is a screw, 24 is a coil spring, and 25 is a spring. Stop bosses 26 are stupid holes provided on the wiring board 4. The screw hole 21, the hole 26, and the hole 22 are aligned, and the wiring board 4 and the heat sink 7 are overlapped. The screw 23 loaded with the coil spring 24 is inserted into the hole 22, and the wiring board 4 and the heat sink 7 are fixed on the boss 20 by screwing. As shown in FIG. 2, since the semiconductor package 1 is sandwiched between the wiring board 4 and the heat sink 7, the semiconductor package 1 is pressed by a spring 24.

When the semiconductor package 1 is mounted on the wiring board 4, the surface height of the semiconductor chip 2 has a mounting height variation (about 0.5 mm) due to a variation in the melting of the solder bumps 9. The wiring board 4 is fixed to the bottom surface 11 of the housing by completely screwing the screw 23. However, even in the case of the semiconductor package 1 in which the mounting variation is the largest, there is a gap between the spring stopper boss 25 and the wiring board 4. It is designed to have a gap. With this configuration, the semiconductor package 1 is held between the heat sink 7 and the wiring board 4 with a predetermined range of pressing force.

The dimensions of the semiconductor chip 2 are 0.85 m in height.
m, a width of 11.5 mm and a depth of 9.2 mm, but the periphery is covered with the sealing resin 5 and adhered to the chip substrate 3, so that the semiconductor chip 2 is not a perfect cube.

The heat conductive sheet 6 has an opening, and the semiconductor chip 2 is accommodated in the opening. The outer periphery of the opening has the same area as the chip substrate 3. The heat conductive sheet 6 is a silicon-based resin, and heat conductive sheets having different heat conductivity, hardness, thickness, and the like are commercially available. The heat conductive grease 10 is also commercially available for heat dissipation, and different materials such as heat conductivity and viscosity can be obtained.

A method of assembling the semiconductor package 1 having the above-described structure and a heat radiation function will be described.

A heat conductive sheet 6 is mounted around the semiconductor package 1 mounted on the wiring board 4. Next, the heat conductive grease 10 is thinly applied to the head of the semiconductor chip 2, the screw holes 21, the holes 26, and the holes 22 are aligned, and the wiring board 4 and the heat sink 7 are overlapped. When the screw 23 loaded with the coil spring 24 is inserted into the hole 22 and the wiring board 4 and the heat sink 7 are fixed on the boss 20 by screwing, the heat dissipation structure of FIG. 2 is obtained. The load applied to the semiconductor package 1 is 0.8 kg to
It is in the range of 1.4 kg.

The heat dissipation structure of the semiconductor package according to the first embodiment has the following features. (1) The heat conduction path from the semiconductor package 1 to the heat sink 7 is formed from the head of the semiconductor chip 2 to the heat conductive grease 10.
Through the heat conductive sheet 6 from the side of the semiconductor chip 2, from the chip substrate 3 to the heat conductive sheet 6
There are three routes that go through. (2) The load applied to the semiconductor package 1 is made uniform by the spring 24 and the load is applied to the package substrate 3.
Since the semiconductor chip 2 is subjected to the entire area, the semiconductor chip 2 is hardly mechanically damaged.

Next, the results of measuring the internal temperature of the semiconductor chip 2 by supplying electricity to the semiconductor package heat dissipation structure are shown in Table 1.

[0025]

[Table 1] Table 1 shows measured data of temperature rise when a semiconductor package (CPU) is removed from a commercially available mobile personal computer and a thermal package is attached instead. The structure of the thermal package has the dimensions and thermal characteristics of CP
It is made to resemble U and has a built-in resistor inside.
By applying a direct current, the same temperature measurement result as when using the CPU package is obtained.

The thermally conductive grease used in Table 1 is:
G765 (Shin-Etsu Chemical Co., Ltd., thermal conductivity 2.8 W / mK). Two types of heat conductive sheets were used. In Table 1, what is described as the heat conductive sheet 1 is the trade name Sarcon GR-i (Fuji Polymer Industries, thermal conductivity 5.6 W / mK), and what is described as the heat conductive sheet 2 is the trade name FSB-A. (Electrochemical industry, thermal conductivity 8.0 W / mK). The thickness of the thermally conductive grease existing in the gap between the heat sink and the thermal package is 100 μm or less. The CPU surface temperature is the temperature of the sensor near the surface built in the thermal package.

The measurement is performed using a mobile personal computer.
The liquid crystal panel was opened on the office desk at room temperature, and the fan rotation speed was set to a predetermined value. The experiment was started from a calorific value of 10.2 W, and the saturation temperature was measured. When the temperature rise was saturated, the calorific value was sequentially increased, and the saturation temperature for each calorific value was measured.

In Table 1, the second column from the left, “only application of grease” refers to the case where a heat conductive sheet is not used, and is a measurement result in the prior art. The third to fifth columns from the left show the heat dissipation structure of the first embodiment, and the third column shows that t = 0.
7 mm heat conductive sheet 1, the fourth column is t = 0.9m
The fifth column shows the case where the thermal conductive sheet 1 of t = 0.9 mm is used. Numerical values in the third to fifth columns of Table 1 indicate the saturation temperature according to the conventional technique and the first embodiment.
Is the difference from the saturation temperature.

From Table 1, the following is clear. (1) The saturation temperature can be reduced by 0.5 to 1.2 ° C. as compared with the conventional heat dissipation structure. (2) When a heat conductive sheet having a high heat conductivity is used, the heat radiation effect is large. (3) The heat radiation effect differs depending on the thickness of the heat conductive sheet.
It is preferable that the semiconductor chip is slightly thicker than the height of the semiconductor chip. The height of the semiconductor chip 2 of the first embodiment is 0.8
Although the thickness is 5 mm, even in the case of a heat conductive sheet having a thickness of 0.7 mm, the height is raised by the sealing resin 5, and the heat conductive sheet is considered to be taller around the semiconductor chip 2. (4) Although the temperature difference between the conventional saturation temperature and the saturation temperature of the present invention becomes smaller as the calorific value increases, this is a phenomenon because the cooling capacity of the heat sink has reached its limit. If the number of rotations is increased by increasing the number of rotations, it is considered that the difference in the heat radiation effect between the conventional and the present invention becomes more remarkable.

In Table 1, when compared with the conventional example, at most 1.
A heat radiation effect of 2 ° C. was obtained. The heat dissipation effect of 1.2 ° C. is the same level of effect as increasing the rotation speed of the fan by about 200 rpm in the heat dissipation structure of the conventional example. That is, the heat dissipation structure of the present invention can reduce the fan rotation speed, thereby reducing the noise of the fan (estimated to be about 1.5 dB) and reducing the drive voltage of the fan (about 0.25).
V is estimated), the power consumption is reduced, and the battery driving time can be extended.

Although the heat conductive sheet of the first embodiment has a uniform thickness, the pressing force can be made uniform by chamfering the lower portion of the heat conductive sheet by the thickness of the sealing resin. And good results can be obtained.

The load applied to the semiconductor package is
When a load is applied to the heat conductive sheet, the proper load is such that the upper surface of the heat conductive sheet is substantially at the surface height of the semiconductor chip.

Although the embodiment has been described with respect to a mobile CPU as a semiconductor package, it goes without saying that the present invention is also effective for a metal package, a resin mold package, and the like.

Although the coil spring has been described as the spring means, similar results can be obtained by using another spring or an elastic body instead of the coil spring.

[0035]

According to the present invention, the heat transfer efficiency between the semiconductor package and the heat sink can be improved,
A heat dissipation structure corresponding to a semiconductor package with high performance and high heat generation can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a heat dissipation structure of a semiconductor package according to a first embodiment.

FIG. 2 is a sectional view of a heat dissipation structure of the semiconductor package according to the first embodiment;

FIG. 3 is an enlarged sectional view showing a main part of a spring means of the heat radiation structure according to the first embodiment.

FIG. 4 is a cross-sectional view illustrating an example of the structure of a semiconductor package.

FIG. 5 is a sectional view showing an example of a heat dissipation structure in a conventional semiconductor package.

FIG. 6 is a cross-sectional view showing another example of a heat dissipation structure in a conventional semiconductor package. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor package 2, 51 Semiconductor chip 4, 56 Wiring board 6, 60 Thermal conductive sheet 7, 57 Heat sink 10, 58 Thermal conductive grease

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H05K 7/20 H05K 7/20 D

Claims (3)

[Claims] A wiring board on which a semiconductor chip is mounted; an elastic heat conductor surrounding the semiconductor chip;
Heat dissipation of a semiconductor package, comprising: heat conductive grease applied to an upper surface of a semiconductor chip; a heat sink facing the heat conductive grease; and a spring means provided between the heat sink and the wiring board. Construction. 2. The heat dissipation structure of a semiconductor package according to claim 1, wherein the thickness of the heat conductor is greater than the height of the semiconductor chip. 3. The heat dissipation structure for a semiconductor package according to claim 2, wherein a spring means is provided between the wiring board and the heat sink with reference to a boss provided on the bottom surface of the housing of the wiring board.