JPS59116357A - Metal having low melting point - Google Patents

Abstract

PURPOSE:To obtain an alloy having a low m.p., a low expansion coefft. during solidification and superior heat conductivity by alloying Ga with In and Sn in a specified ratio. CONSTITUTION:Each semiconductor chip 2 is attached to a substrate 4 ith solder 3, and a heat conductor 1 made of liq. metal is interposed between the chip 2 and a cover 5 so as to release heat generated in the chip 2 during operation. An alloy having a composition consisting of, by weight, <60% Ga, 25-50% In and 18-40% Sn or further contg. <2% Zn and <0.4% Bi or <0.5% Pb and <0.4% Cd is used as the heat conductor 1. The alloy has 9-10 deg.C low m.p. and undergoes little change in the volume at the melting starting temp. and during solidification, so no load is placed on the chip 2 and the solder 3 by expansion during solidification.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a semiconductor cooling device, and particularly to a heat conductive medium (low melting point metal) used when cooling a semiconductor chip mounted on a wiring board. .

[Prior art]

The first semiconductor cooling device using a liquid metal thermal conductor
As shown in the figure, a semiconductor chip 2 is mounted on a substrate 4 via a solder 3, a liquid metal thermal conductor 1 is interposed between the semiconductor chip 2 and a cover 5, and the surface of the cover 5 is A device has been proposed in which the semiconductor chip 2 is configured to be cooled by a cooling body, and the heat generated during operation of the semiconductor chip 2 is absorbed by the liquid metal thermal conductor 1.

There are two to three types of metals or alloys that can be used as the liquid metal heat conductor and are in a liquid state at around room temperature, and a typical one is mercury. However, this mercury has a melting point of 140C and a vapor pressure of 1.3X10-
It has the disadvantage of being difficult to handle because it is as high as 3 Hg (20 tons?).

Therefore, metals that have a higher melting point than mercury but have the possibility of becoming liquid at around room temperature include galliwaum and cedium, and the melting point of these metals is about 30C.

However, cesium has a high vapor pressure and is difficult to handle, and there are many problems because there is no basic data.

On the other hand, gallium has a melting point of 30t? Moreover, the vapor pressure is extremely low (10''wnHg), making it easy to handle.

Although basic research on gallium is not sufficient, various properties have been clarified due to the existence of a considerable amount of data.The currently known gallium alloy with the lowest melting point has a composition of gallium (Ga2). 62%, indium (In): 22%, tin (Sn): 16%, and its melting point is approximately 11 tl'.

However, pure gallium (100%) is a typical metal that exhibits volumetric expansion during solidification, and the amount of expansion is approximately 3%, so this gallium is used as the heat transfer medium 1 of the cooling device.
When used as a chip, the load increases due to expansion during solidification.
and solder 3, so the chip 2 inch thick solder 3
may have a significant negative impact on. Therefore, it is desirable that the heat transfer medium 1 has a melting point as low as possible and a small amount of expansion upon solidification.

[Purpose of the invention]

The present invention provides a liquid metal thermal conductive medium that satisfies the above requirements;
That is, the object is to provide a low melting point metal that has a low melting point and a small amount of expansion during solidification.

[Summary of the invention]

In order to achieve the above object, the present invention has a weight ratio of gallium (Qa): 60% or less, indium (In): 25 to 5%.
0%, tin (Sn): 18 to 40%, and the remainder consisting of impurities.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail.

The amount of shrinkage during solidification of additional elements added during the production of gallium alloys is as shown in Table 1 below (described in the Metal Data Book).

Table 1 It is thought that when the content of the above gallium (Ga) is reduced, the amount of expansion during solidification is reduced. However, in order to lower the melting point of a gallium alloy, it is necessary to have a potassium content above a certain level, or it is necessary to add indium and tin, such as in a ternary alloy of gallium-indium-tin.

In order to achieve the above objective in the ternary alloy of gallium-indium-tin, which is the basis for practical use, it is necessary to reduce the gallium content and supplement this reduced amount of potassium with indium and tin. Furthermore, by adding elements that lower the melting point such as bismuth and zinc, it is possible to further reduce the melting start temperature and the amount of expansion during solidification.

Based on the results of various studies and experiments based on the above-mentioned concept, the present invention has a composition in which gallium is 60% or less, indium is 25 to 50%, tin is 18 to 40%, and the remainder is impurities. Or, in addition to the above ingredients, zinc: 2% or less and bismuth 20.4% or less are added, or in addition to the latter component, lead: 0.5% or less, cadmium. = 0.4% or less of the component composition.

To explain the reason for limiting the composition of each component as described above, gallium (Ga) is a metal that expands during solidification as shown in Table 1, so the amount of expansion during solidification of the product of the present invention is to be reduced. Therefore, it is preferably 60% or less. The content of indium (In) and tin (Sn) was set to be in the range of 25 to 50% and 18 to 40%, respectively.
This is because if it is outside this range, the amount of solid phase increases during cooling, which is undesirable.

Zinc and bismuth are particularly effective elements for lowering the melting point of the ternary alloy of gallium-indium-tin, but even if the former zinc is added in an amount of 2% or more, it will crystallize at room temperature and the amount of solid solution will decrease. The limit is around 2%, and as shown in Table 1, the latter bismuth is a metal that expands during solidification like gallium, so in order to reduce the amount of expansion during solidification of the product of the present invention, it should be set at 0. It is preferably 5% or less.

Sample A1 made of pure gallium and sample shop 3 of the product of the present invention
The component composition, melting start temperature, and volume change rate during solidification of 4 to 4 are as shown in Table 2 below.

As is clear from the table above, samples A3 to A5 of the products of the present invention
The melting start temperature is 8 to 10C1, and the volume change rate during solidification is 1.2% or less, and the melting start temperature is significantly lower than that of pure gallium of sample A1, and the volume change rate is reduced to less than half. do. Furthermore, it is clear that the melting start temperature and volume change rate are even smaller when compared with known sample A2.

〔Effect of the invention〕

As explained above, according to the present invention, the melting start temperature is reduced to 1
Since the temperature can be kept at 0'C or less and the amount of volumetric expansion during condensation can be reduced, it is possible to obtain a thermally conductive medium (cooling medium) that hardly applies stress to the semiconductor chip even if it solidifies.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a semiconductor cooling device. No. 1 [12 Nippon Co., Ltd., 1 Horiyamashita, Hadano City Inside Tachi Seisakusho Kanagawa Factory

Claims (1)

[Claims] 1. Component composition in terms of weight ratio: Galiwam (Ga): 60% or less, Indium (In): z5 to 50%, Tin (Sn) =
A low melting point metal characterized by comprising 18 to 40% and the remainder consisting of impurities. 2. Zinc (Zn): 2% or less by weight, bismouth (
13i): The low melting point metal according to claim 1, wherein 0.4% or less of the metal is added. 3. Lead (Pb): 0.5% or less, cadmium (by weight)
Cd): The low melting point metal according to claim 2, characterized in that 0.4% or less is added.