JPS59178754A - Heat dissipating member for heat generator - Google Patents

Abstract

PURPOSE:To reduce the thermal stress generated in a semiconductor element by decreasing the thermal resistance by a method wherein junction is performed by interposing an intermediate member made of porosity of good thermal conductivity between said element generating heat and a heat dissipator, when said dissipator is adhered to said element. CONSTITUTION:When the semiconductor element 4 is adhered to the lower surface of a disk 2 surrounding a copper stud 1, the intermediate member made of a porous member 3 such as copper is interposed between the disk 2 and the element 4. This porous member 3 is fabricated by the compression sintering by a copper powder metallurgical method and is made to have a deisred rate of vacancy. Thereafter, the lower surface of the outer periphery of the disk 2 is brazed to a ceramic body 6 surrounding the element 4, and the terminals provided to the element 4 are connected to lead wires 8 by means of fine wires 5. Next, while the outer end of the lead wire 8 is led out, a ceramic body 9 serving as the bottom is fixed to the ceramic body 6 with sealing glass 7, thus sealing the element 4.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a heat sink that is thermally bonded to a heat generating body such as a semiconductor element, and in particular reduces the thermal stress generated in the heat generating body such as a semiconductor element, and The purpose is to prevent destruction, and it is used in semiconductor products such as LSIs, ICs, and diodes.

[Background of the invention]

In conventional heat generating elements such as LSIs, ICs, and diodes, in order to prevent the elements from breaking due to thermal stress, the heat dissipating member is made of a material with good thermal conductivity such as copper and a molybdenum plate or a tungsten plate. It is constructed by joining an intermediate member having a low coefficient of expansion, and the element is joined to the intermediate member having a low coefficient of expansion of the heat dissipating member. In this way, by inserting the molybdenum plate as an intermediate member in the heat dissipation member, matching between the semiconductor element with low expansion and the copper member with high thermal expansion can be achieved. However, when an intermediate member with a low expansion coefficient such as a molybdenum plate is used as a heat dissipation member, there are disadvantages such as the high thermal resistance of this member, which hinders heat dissipation, and the fact that molybdenum plates are expensive. .

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat dissipation member for a heat generating body that reduces thermal stress occurring in a heat generating body such as a semiconductor element and has low thermal resistance.

[Summary of the Invention] Heat dissipation, characteristics, and strength are contradictory to each other at the joints of heating elements such as semiconductor elements. If a member having a low expansion coefficient, such as a molybdenum plate, is used as part of the heat dissipating member, heat dissipation will be poor, but stress generated in the element will be reduced. still,
If a member having a low expansion coefficient, such as a molybdenum plate, is not used as part of the heat dissipation member, heat dissipation will be improved, but large stress will be generated in the element. As a result of considering a situation in which this low thermal expansion member was removed and stress was reduced, it was found that the conductive member bonded to the element should be made softer. In order to implement this, the present invention makes at least the element bonding surface side of the thermally conductive member a porous body, so that the heat dissipating member has low thermal resistance and low stress.

[Embodiments of the invention]

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the heat radiating element for a heating element of the present invention will be described with reference to FIGS. 1 and 2.

A member with good thermal conductivity, such as a copper stud 1, is soldered with silver to a disc 2, which is brazed to a ceramic body 6, and a porous member 3, such as copper, as an intermediate member with good thermal conductivity. is forming.

A semiconductor element 4 is bonded to the inner surface of the porous member 3 using a gold-silicon eutectic alloy, and a terminal of the semiconductor element 4 is connected to an external Kovar lead wire 8 via a lead wire 5. The ceramic body 6 and the sealing ceramic body 9 are bonded and sealed by a low melting point glass 7.

For the porous member 3, porous sintered copper formed by compression sintering using a copper powder metallurgy method is used, for example. The porosity of the sintered copper is adjusted to a predetermined ratio by adjusting the pressure. In order to form sintered copper with uniform porosity, it is important to strictly control the pressure distribution and sintering temperature. When porous sintered copper is used as the heat sink, the sintered copper and the semiconductor element 4 are bonded by gold plating on the surface of the sintered copper, and the semiconductor element 4 is bonded using gold-silicon eutectic. In this case, if the porous copper surface is extremely uneven and gold plating is difficult, it is necessary to crush only the very thin layer on the surface to eliminate the porosity before plating, or to remove only the very thin skin layer on the surface during sintering. can be used by lowering the porosity to near zero to make it easier to plate the sintered heat sink. Next, examples of the thermal conductivity and yield stress of porous copper formed by powder metallurgy are shown. The porosity of the three types of porous copper that was formed was 0.5%, 13%, and 30%.

The thermal conductivity of these porous coppers with porosity of 0, 13, and 30q6, respectively, measured by the laser flattening method is 400K.
cat/m, h, C,280Kca7/m, h,
C.

It was 150Kc3t/m, h, c. - Power porosity 0
%.

The yield stress of 13% and 30% porous copper is 300MPa
.

It was 124MP, 42MP. Also, the longitudinal elastic modulus is 135000M, P, , 1010O500,,35
It was 000MP.

The thermal conductivity of the molybdenum plate, measured by the same method as for porous copper above, is 140 K CatAn, h
, t:'. To replace a molybdenum plate with porous copper, the thermal conductivity of the molybdenum plate is 140K CaL/m,
h, porous copper having a higher thermal conductivity than C can be employed. For example, porous copper with a porosity of 30 cm is 10 KCa.
-/% m, h, and C are superior to the thermal conductivity of molybdenum plates. The smaller the porosity, the better the heat transfer properties. on the other hand,
In terms of strength, the yield stress of molybdenum plate is 530M, P,
, the longitudinal elastic modulus is 35000M,P, so by comparing the product of the magnitude of thermal expansion and the longitudinal elastic modulus or yield stress,
The smaller this product is, the more the stress applied to the semiconductor element by the heat sink is relaxed. Here, the coefficient of linear expansion of porous steel is related to the porosity (17X10-'t?').

The molybdenum plate is 4.9X10-6r'. Therefore, it is necessary to reduce the strength by a linear expansion coefficient ratio of 4.9/17 x 1/3.5. That is, any porous steel with a longitudinal elasticity value of sintered copper may be used, and porous steel with a porosity of 13 or more is suitable. The above example is an example of an implementation method from one aspect regarding thermal conductivity and strength, but in detail, stress distribution due to thermal expansion difference, temperature distribution due to difference in heat dissipation structure, bonding material, thickness of porous member, etc. Various ranges of porosity can be adopted, and the range is from 8 to 50 inches.

Next, another example of the heat sink of the present invention will be explained with reference to FIG.

This example has a structure in which the copper studs and the intermediate member in the examples shown in FIGS. 1 and 2 are replaced with only one porous member.

In FIG. 3, the heat radiator is a porous member 10 made of only porous steel and brazed to a circular plate 6 which is brazed to a ceramic plate 6. In FIG. A semiconductor element 4 is bonded to the inner surface of the porous member 10 using a gold-licon eutectic alloy. The terminals of this semiconductor element 4 are connected to external Kovar lead wires 8 via lead wires 5.

Furthermore, the ceramic plate 6 and the sealing ceramic plate 9 are
They are bonded and sealed by low melting point glass 7. With this configuration, there is no need for an intermediate member having a low elongation that forms part of the heat radiating body, and the structure and processing become easy, and further miniaturization can be achieved. Generally, in a structure in which flat plates of different materials are stacked, the thermal resistance R in the plate thickness direction is determined by the value (R-Σ-) that is the sum of the ratio of thermal conductivity (λ) to plate thickness t. For example, if λ is a conventional structure, the molybdenum plate thickness is 0.8 m, =
1.75xl O-' (m2.h, C/Kcat
). When this stacked structure is made of porous copper material with a porosity of 13%, the plate thickness at which the thermal resistance becomes equal is 几=
-Yo80, t=4.9 sm. In other words, in order to replace the combined thickness of the molybdenum plate and copper plate, which is 5.8 mm, with sintered copper with a porosity of 13 mm, it is necessary to reduce the thickness to 4.9 mm from the viewpoint of heat dissipation. be. Such use is effective when pure copper with zero porosity is thin.

Next, an example other than the one in which the porous member constituting the heat sink is formed by sintering only copper powder as shown in FIG. 3 will be described. By increasing the porosity only on the semiconductor element bonding surface side of the heat sink and lowering the porosity in other parts, it is possible to reduce thermal stress due to the difference in thermal expansion with the semiconductor element and improve thermal conductivity at the same time. . A heat sink having such a structure can be created by placing copper powder on a copper material and sintering it.

In addition, a heat dissipation body made by mixing copper powder with a material with a low expansion coefficient such as molybdenum powder, kunksten powder, or graphite powder and sintering it is used only near the joint surface (or the entire surface) between the sintered body and the semiconductor element. As a result, it is possible to provide a heat dissipating body with excellent heat dissipation properties and with a low thermal stress generated in the semiconductor element. - It is also possible to use a copper sintered body made of two or more materials in which pores are formed by mixing a material with better thermal conductivity. 5 for copper powder
When creating a sintered body containing % graphite, thermal conductivity and strength comparable to those estimated by calculation were obtained.

In each of the above embodiments, the element is directly bonded to a heat sink made of a material with a good thermal conductivity without intervening an intermediate member with a low expansion coefficient such as molybdenum, so heat conduction is improved and the element has a low expansion coefficient. Material costs are saved by eliminating the need for intermediate parts. In particular, materials with a low expansion coefficient such as molybdenum are expensive materials, and saving material costs is a significant effect. Further, since the intermediate member is generally made by punching or sintering and both sides of the plate are not parallel and are not curved, when the one-piece element and the copper heat sink are joined together, the thin-walled element is joined in a curved manner. Eliminating the intermediate member with a low coefficient of expansion simplifies the structure of the joint portion of the element, and has the effect of eliminating bending caused by the intermediate member such as molybdenum. Further, intermediate members such as molybdenum have fixed thermal and mechanical properties, and when an intermediate member such as molybdenum is introduced, the stress generated in silicon in semiconductor components made of elements, intermediate members, and copper is uniquely determined. However, when using sintered porous steel,
By changing the porosity, thermal conductivity, yield, tensile strength, etc. can be controlled depending on the purpose.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reduce thermal stress occurring in an element and at the same time obtain a heat sink with low thermal resistance.

[Brief explanation of the drawing]

FIG. 1 is a plan view illustrating an embodiment of the heat sink of the present invention;
FIG. 2 is a sectional view taken along the line AA in FIG. 1, and FIG. 3 is a sectional view illustrating another embodiment of the heat sink of the present invention. DESCRIPTION OF SYMBOLS 1... Copper stud, 3... Porous tube member, 4... Semiconductor element, 6... Ceramic body, 7... Sealing glass, 8... Lead wire, 9... Ceramic body , 10...
・Porous member. χ 1 Figure 2 Darkness 3 Figure

Claims (1)

[Claims] 1. Thermal connection with the heating element and absorption of the heat of the heating element. In a heat dissipating member for a heat generating element in which a heat dissipating body made of a heat conductive member for dissipating heat is visible, a porous portion having a predetermined porosity is formed at least on a side surface of the heat dissipating body to which the heat generating body is bonded. A heat dissipating member for a heating element characterized by the following. 2. The heat dissipating member for a heat generating body according to claim 1, wherein the heat dissipating body is made of a porous member, and the heat generating body is joined to the heat dissipating body. 3. A heat dissipating member for a heat generating body according to claim 1, characterized in that a porous member is bonded to one surface of the heat dissipating body, and a heat generating body is bonded to this porous member. 4. The heat dissipating member for a heat generating element according to claim 2, wherein the porosity of the heat dissipating body on the side where the heat dissipating element is joined is made larger than that of other parts by '4c%. 5. The heat radiation for a heating element according to any one of claims 1 to 3, wherein the porous portion is porous copper formed by sintering copper powder. Element. 6. Any one of claims 1 to 3, wherein the porous portion is porous copper formed by partially sintering copper powder and low expansion material powder. A heat dissipating member for a heating element according to. 7. Any one of claims 1 to 7, characterized in that the porosity of the porous portion is selected to be 8 to 50 cm.
A heat dissipating member for a heating element as described in 2.