JPS60248803A - Production of silver powder - Google Patents

Abstract

PURPOSE:To obtain silver powder for a conductive adhesive agent having a low concn. of residual ion and the narrow width of a grain size distribution in a method for adding a reducing agent to an aq. silver salt soln. and precipitating silver powder by using the specific aq. silver salt soln. CONSTITUTION:The reducing agent is added to the aq. ammonical silver nitrate soln. directly or after adding water soluble nitrate thereto to precipitate silver powder. The silver powder is thus obtd. The aq. ammonical silver nitrate soln. refers to the soln. prepd. by adding about >=30pts.wt. 30% ammonia water by 100pts.wt. silver nitrate to silver nitrate soln. The precipitated silver powder has the small width of the grain size distribution and has good reproducibility thereof even if the silver salt is reduced by hydrazine according to the above-mentioned method. Harmful residual ions are not contained in the precipitated silver powder if caustic alkali is not used and therefore a rinsing stage, etc. which are post-stage are made simpler.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing silver powder with high purity and low residual ion concentration.

In recent years, silver thread conductive adhesives have come into widespread use as conductive materials for integrated circuits such as IC-USI. The silver powder used in this adhesive is fine and has a small particle size.
In addition, high purity quality characteristics are required, with residual ionic substances such as halogen elements and alkali metals being 5 oppm or less, which are easily ionized and harmful to integrated circuits.
The present invention relates to a method for producing silver powder used in a conductive adhesive for integrated circuits.

[Conventional technology]

A common method for producing silver powder used in conductive adhesives is a chemical reduction substitution precipitation method. This method is a method in which a reducing agent is added to an aqueous silver salt solution to precipitate silver powder, and the reducing agent used here is mainly caustic alkali.

The silver powder obtained in this way contains more than 100 ppm of caustic alkali as residual ions, so
It is not desirable to apply it to integrated circuits. Further, when caustic alkali is not used as a reducing agent, for example when reduction is performed with hydrazine, the particle size distribution of the precipitated silver powder is large and is not reproducible.

[Problems to be solved by the present invention]

The present inventors have made efforts to improve the drawbacks of the above-mentioned conventional techniques, and to develop a method for producing silver powder with a low residual ion concentration of 50 ppm or less, which is harmful to semiconductors, and a high-quality silver powder with less variation in powder properties. As a result of research, the present invention was completed.

[Means for solving problems]

The present invention is a method for producing silver powder, characterized in that silver powder is precipitated by adding a reducing agent directly or after adding a water-soluble nitrate to an ammoniacal silver nitrate aqueous solution.

The ammoniacal silver nitrate aqueous solution referred to in the present invention refers to silver nitrate 1
00 parts by weight, 30 parts by weight or more of 30% ammonia water (9 parts by weight or more as ammonia, the same applies hereinafter) is added to an aqueous silver nitrate solution.

By using this ammoniacal silver nitrate aqueous solution, even when reduced with hydrazine, which has been a problem in the past, the particle size distribution I11 of the precipitated silver powder is small and the reproducibility is good. Furthermore, when caustic alkali is not used, the precipitated silver powder does not contain harmful residual ions, so the post-process water washing step etc. is simplified.

In the present invention, high purity silver powder can be obtained without adding water-soluble nitrate, but it is better to add water-soluble nitrate to narrow the particle size distribution [11] and to control the particle size.

The water-soluble nitrate used here is copper nitrate or zinc nitrate.
The amount of additive d is preferably in the range of 0.5 parts by weight to 10 parts by weight based on 100 parts by weight of silver nitrate in the ammoniacal silver nitrate aqueous solution. The reason for this is that if it is less than 0.5 parts by weight, the above effect will be small, and if it is more than 10 parts by weight, the effect of particle size adjustment will be saturated, and even if more is added, the effect will not be increased. This is because not only is it not possible, but on the contrary, residual impurities increase, making it impossible to obtain highly pure silver powder.

As the reducing agent used in the present invention, aldehydes such as formalin and hydrazine can be used, but it is preferable to use hydrazine in terms of reduction efficiency.

〔Example〕

Examples of the present invention will be described below.

Example 1゜Silver nitrate aqueous solution ('AgNO3100g/HzO300m
Add 30 g of a 30% ammonia aqueous solution to l) to obtain an ammoniacal silver nitrate aqueous solution. Hydrazine hydrate is then added to form a white precipitate. At this time, hydrazine hydrate is added until all the roots of the ammoniacal silver nitrate aqueous solution are formed as precipitates. The obtained precipitate was thoroughly washed with water by decantation, filtered, and then dried at low temperature. The powder thus obtained is a silver powder with an average particle size of 1.5 μm, a particle size distribution of 1 μm, and a residual ion concentration (hereinafter simply referred to as residual ion concentration) of 20 ppm including water-soluble alkaline substances and halogen substances. there were.

When a paste obtained by uniformly kneading 80 parts by weight of the silver powder obtained as described above and 20 parts by weight of the epoxy resin adhesive is cured at 150°C for 30 minutes, the specific resistance I
A conductive adhesive having characteristics of 10-'Ω-cm and adhesive strength of 50 kg/cnj was obtained.

Example 2゜Silver nitrate aqueous solution (ΔgNto3100g/1Iz0300
ml) was added with 40 g of 30% ammonia aqueous solution to make an ammoniacal silver nitrate aqueous solution.
・611zOO, 5g) was added. Hydrazine hydrate was then added to form a white precipitate. The precipitate thus obtained was filtered and washed with water in the same manner as in Example 1. The powder thus obtained had an average particle size of 1. Opm, 1.5 μm in particle size distribution, residual ion concentration 30 p p
m'0) was silver powder. Which silver powder was made into a paste had the same characteristics as Example 1.

Example 3゜Silver nitrate aqueous solution (8gNo3100g/Hz0300m
40g of 30% ammonia aqueous solution was added to l) to make an ammoniacal silver nitrate aqueous solution and zinc nitrate (Zn(NO+) z
・Add 611z010g). Hydrazine hydrate was then added to form a gray-yellow precipitate. The precipitate thus obtained was filtered and washed with water in the same manner as in Example 1. The powder thus obtained was a silver powder with an average particle diameter of 0.2 μm, a particle size distribution width of 0.2 μm, and a residual ion concentration of 50 ppm. A paste obtained from this silver powder had properties equivalent to those of Example 1.

Example 4゜Silver nitrate aqueous solution (8 gN (h 100g/HzO300m
40 g of a 30% ammonia aqueous solution was added to l), and 5 g each of copper nitrate and zinc nitrate were added to make an ammoniacal silver nitrate aqueous solution.

Next, hydrazine hydrate was added to form a gray precipitate. The precipitate thus obtained was filtered and washed with water in the same manner as in Example 1. The powder thus obtained has an average particle size of 0
．． The silver powder had a particle size distribution width of 0.08 μm, a particle size distribution width of 0.05 μm, and a residual ion concentration of 50 ppm.

The cured product made by turning this silver powder into a paste has a specific resistance of 5
x io-'Ω-cm and adhesive force of 50 kg/cn+.

Comparative example Silver nitrate aqueous solution (f1gN03100g/IIz0300
ml), and then add a caustic soda aqueous solution (NaO8100g/IILO200ml).
is added to form a white precipitate. The precipitate thus obtained was filtered and washed with water in the same manner as in Example 1. The powder thus obtained was a silver powder with a particle size of 1.0 μm and a residual ion concentration of 200 ppm.

〔Effect of the invention〕

Since the silver powder obtained by the present invention is a high purity silver powder with few residual ions, it is suitable as a raw material for conductive adhesives used in semiconductors.

patent applicant Fukuda Metal Foil and Powder Industry Co., Ltd.

Claims (4)

[Claims] (1) A method for producing silver powder, which comprises adding a reducing agent directly or after adding a water-soluble nitrate to an ammoniacal silver nitrate aqueous solution to precipitate silver powder. (2) The method for producing silver powder according to claim 1, wherein the water-soluble nitrate is one or both of copper nitrate and zinc nitrate. (3) The method for producing silver powder according to any one of claims 1 to 2, wherein the reducing agent is hyacin. (4) Any one of claims 1 to 3, characterized in that the amount of water-soluble nitrate added is 0.5 to 10 parts by weight per 100 parts by weight of silver nitrate in the ammoniacal silver nitrate aqueous solution. The method for producing silver powder described in .