JPS62276703A - Formation of gold film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a method suitable for forming a gold coating on a ceramic package housing a semiconductor integrated circuit element.

[Conventional technology]

One of the packaging methods for accommodating semiconductor integrated circuit devices is a method using a ceramic (mainly alumina) substrate, in which a recess is provided to accommodate the device, and the flat bottom of the recess is It is common to apply a gold coating to bond elements. Conventionally, to form a gold film on such a depression, a gold paste consisting of gold powder, glass powder, and an organic vehicle is diluted with an organic solvent and dropped, and then
Heat to ~200°C to make the dripping paste rich and spread throughout, and evaporate the solvent and dry.
This is done by firing at a temperature of 00°C. However, with this method, if gold powder adheres to the sidewalls of the recess or if the peripheral edges of the fired film become smeared, there are doubts about the reliability of the adhesive strength, and stains on the glass cause problems in bonding the elements. In order to solve this problem, attempts have been made to make the particle sizes of gold powder and glass powder the same, and to use glass powder with as high a specific gravity as possible, but the problem has not yet been completely solved.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for forming a gold film that can completely eliminate adhesion of gold powder to the side wall, scratches on the peripheral edge of the gold film, and glass stains on the surface of the gold film.

[Means for solving problems]

In order to achieve this objective, the present inventor discovered that the above-mentioned problems are caused by various factors (surface tension of the paste, sedimentation of each powder in the paste, or rise due to convection) during the drying process of the gold paste. We predicted that the above-mentioned drawbacks could be overcome if we did so, and as a result of various experiments, we arrived at the present invention. That is, the method for forming a gold film of the present invention consists of 60-96% by weight of gold powder with an average particle size of 0.1-10 μm, 2-20% by weight of glass powder with an average particle size of 1-25 μm, and 2-20% by weight of an organic binder. It is characterized in that a molded thin piece of the mixture is placed on a ceramic substrate and fired at a temperature above the softening point of the glass powder and below the melting point of gold.

The gold powder used in the present invention has an average particle size of 0.1 to 10 μm. This is because if it is less than 0.1 μm, the bulk becomes too large and a dense gold film cannot be obtained, and if it exceeds 10 μm, the surface of the gold film becomes too rough and it becomes difficult to bond the elements. The content of gold powder needs to be 60 to 96% by weight. This is because if the gold powder content is less than 60% by weight, there will be too much glass powder and/or binder, and if there is too much glass powder, the glass will stand out on the surface of the gold coating, and if there is too much binder, a dense film will not be obtained. . On the other hand, the content of gold powder is 96
If the weight percentage is exceeded, the amount of glass powder and/or binder becomes too small, the molded flakes become brittle, and the adhesion between the gold coating and the substrate also decreases.

Any glass powder may be used as long as it has a softening point of 430 to 600' and a coefficient of thermal expansion of 40 x 10-' to 100 x IO-7/°C. For example, lead borosilicate glass powder may be used. , the average particle size must be 1 to 25 μm. If it is less than 1 μm, the glass will soften before the binder burns or volatilizes, causing foaming on the gold coating surface, and if it exceeds 25 μm, large pinholes will remain in the gold coating, which is undesirable. The content of this glass powder needs to be 2 to 20% by weight.

If it is less than 2% by weight, there is too little glass and sufficient adhesive strength cannot be obtained, and if it exceeds 20% by weight, the glass will stand out on the surface of the gold coating, making it impossible to bond the elements.

In the present invention, a binder is used to enable molding in a state in which the gold powder and glass powder are uniformly mixed. Although various known materials can be used as such a binder, ceramic When placed on a substrate and fired, it needs to disappear almost completely, and for this reason, the binder needs to be organic. It is desirable that this precipitate binder burns or volatilizes at a temperature below 500°C.

This is because if this temperature is too high, the glass powder will soften first and pinholes will occur on the surface of the gold coating due to foaming. Examples of organic binders that satisfy the above conditions include ethyl cellulose and methyl methacrylate. The content of the organic binder needs to be 2 to 20% by weight. 2
If the amount of binder is less than 20% by weight, the strength of the molded flakes will be low and the pieces will easily break during handling, and if it exceeds 20% by weight, the amount of gas generated during firing will be large and a dense gold coating will be formed. Because you can't get it.

To obtain molded flakes by mixing the above gold powder, glass powder, and organic binder, the mixture may be molded using a mold, or if the organic binder can be dissolved in a suitable solvent, the mixture may be mixed with this solvent. A method in which the paste is formed into a paste, which is thinly applied to the desired dimensions on a flat board by screen printing, and then peeled off from the substrate after drying, or a method in which the paste is formed into a sheet and, after drying, is punched out in the desired dimensions. ,
Men's methods such as these can also be adopted.

The formed thin piece thus obtained is placed in a recess of a ceramic substrate and fired at a temperature above the softening point of the glass powder used and below the melting point of gold. This is because at temperatures below the softening point of the glass powder, the gold coating will not fuse to the ceramic substrate, and at temperatures above the melting point of gold, the gold will melt and will not form a uniform coating. A preferred firing temperature is 700 to 950°C, and such firing can be performed in exactly the same manner as a conventional method using gold paste.

〔Example〕

Gold powder, glass powder, and organic binder are mixed in various proportions, and a small amount of organic solvent is added to this to form a paste.
Spread the paste on a glass plate in a size of 5 squares x 2.5 cranes.
After screen printing to a thickness of 0 μm and drying by heating at 150° C. for 10 minutes, the dried film was peeled from the glass plate to obtain a shaped thin piece. The flakes were approximately 20 μm thick. The formed flakes were fired in a belt-type firing furnace with a recess of 6.4 mm x 3.3 ms and a black aluminum plate with the same settings. After observing the periphery of the fired film for scratches and stains on the glass, a silicon chip was bonded to the gold coating using a Gui bonder, and the bonding strength was measured. The results are shown in Table 1. In Table 1, regarding stains on glass, if no stains were observed at all, it was marked O, if the area of the stain was 1710 or less, it was marked Δ, and if it was larger than that, it was marked X. Furthermore, no scratches were observed in this example, and naturally, no gold powder was observed to adhere to the side walls of the recesses. Bonding force and chipping property are determined by pushing the silicon chip from the side and peeling it off. If the chip peels off at the interface between the chip and the gold metallized layer, the chipping property is poor, marked with an X, and the area of this interface peeling is 10
Less than % is marked Δ, and no interfacial peeling is observed at all, marked ○. If peeling occurs between the substrate and the pressure is less than 5 kg, the bonding force is poor, and marked X. Cases where there was peeling or chip cracking due to pressure were marked with an ○ mark.

From the results in Table 1, it can be seen that 55% by weight of gold powder is too small and causes problems in chip attachment, and conversely, 98% by weight is too large and the bonding force is insufficient, and 0.5 μm of glass powder It can be seen that if it is too small, stains appear on the glass and the chipability deteriorates, and 29 μm is too large.

〔Effect of the invention〕

According to the present invention, it is possible to form a gold coating in the necessary size on the necessary part, and the thickness of the gold coating can be reduced. Further, according to the present invention, as described above, it is possible to form a gold coating of only the required size, which results in the saving of expensive gold.

Claims (1)

[Claims] 60-96% by weight of gold powder with an average particle size of 0.1-10 μm,
A molded thin piece of a mixture consisting of 2 to 20% by weight of glass powder with an average particle size of 1 to 25 μm and 2 to 20% by weight of an organic binder is placed on a ceramic substrate, and the temperature is above the softening point of the glass powder and below the melting point of gold. A method for forming a gold film, characterized by firing at a temperature of .