JPH08283963A - Heat-resistant silver-coated composite and its production - Google Patents

Abstract

PURPOSE: To provide a heat-resistant silver-coated composite excellent in solderability, corrosion resistance and adhesion of a silver coating layer. CONSTITUTION: A silver or silver alloy layer is formed on a substrate with at least the surface having conductivity directly or through a substrate layer consisting of nickel, cobalt or their alloy to constitute a heat-resistant silver- coated composite. The average crystal grain diameter on the inside of the silver or silver alloy layer is controlled to >=3μm and that on the outside to <=2μm. Consequently, the infiltration of oxygen is suppressed at the inside of the silver coating layer, and the corrosion resistance and adhesion are maintained. The solderability of a silicon chip is improved at the outside of the silver coating layer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention has excellent solderability, corrosion resistance, and adhesion of a silver coating layer. For example, the heat-resistant silver-coated composite body is suitable for the production of electronic equipment parts involving high temperature processes such as resin molding. And a manufacturing method thereof.

[0002]

2. Description of the Related Art Silver-coated copper wire is a copper or copper alloy wire coated with a silver or silver alloy layer.
It has both corrosion resistance and solderability of silver, and is widely used as a lead wire of electronic parts and a conductor in electronic equipment. The thickness of the silver or silver alloy coating layer is about 1 to 10 μm in consideration of solderability, corrosion resistance, economy and the like. By the way, in a diode using a silver-coated copper wire as a lead wire, a silver-coated copper wire is cut into a predetermined length, one end thereof is header-processed, a silicon chip is soldered to a header-processed portion, and a resin is applied on it. It is molded and assembled. At the time of resin molding described above, the silver-coated copper wire is exposed to about 20 ° C in the atmosphere at about 20
Left for hours. Further, for the soldering of the silicon chip, a high Pb-Sn high temperature solder having a high melting point is used so that the solder is not melted in the subsequent soldering step with an electronic component or the like. Since this high-temperature solder has a small amount of Sn, the reaction rate with the silver layer is slower than that of the eutectic solder.

[0003] The silver-coated copper wire is heated at the time of soldering a silicon chip, copper is diffused from the copper wire and the appearance is discolored, and the solderability in the subsequent soldering step is significantly deteriorated. Therefore, a silver-coated copper wire in which an underlayer such as nickel is interposed as a diffusion barrier between the copper wire and the silver or silver alloy coating layer to suppress the diffusion of copper from the copper wire has been put into practical use. This underlayer can reduce the thickness of the silver or silver alloy coating layer. However, even if the underlayer is provided in this manner, oxygen in the atmosphere is actively permeated into the silver or silver alloy coating layer by heating during soldering, and the underlayer is oxidized. As a result, the silver or silver alloy coating layer is easily peeled off, the reliability of the lead wire is lowered, and the soldering strength is lowered.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
A method of forming a thick silver coating layer without providing an underlayer, and a method of increasing the average crystal grain size of the silver or silver alloy coating layer to 5 μm or more to suppress the permeation of oxygen through the crystal grain boundaries ( Japanese Patent Publication No. 5-8276) was proposed. However, the former is disadvantageous in terms of cost due to an increase in the amount of silver used, and the latter has a problem that the solderability of the silicon chip deteriorates.

Therefore, the present inventors examined the latter deterioration of solderability, and the reason for this is that the reaction rate between the silver coating layer and the solder becomes slower as the crystal grains become larger, and the reason for this is that The inventors have found that slight stains or defective shapes have an adverse effect on the solderability, and have further researched to complete the present invention. An object of the present invention is to provide a heat-resistant silver-coated composite having excellent solderability, corrosion resistance, and adhesion of a silver or silver alloy coating layer, and a method for producing the same.

[0006]

According to the first aspect of the present invention,
In a heat-resistant silver-coated composite in which a silver or silver alloy layer is formed on a base material having at least a surface of conductivity, directly or via an underlayer made of nickel, cobalt, or an alloy thereof, the silver or The heat-resistant silver-coated composite is characterized in that the average crystal grain size on the inside of the silver alloy layer is 3 μm or more and the average crystal grain size on the outside is 2 μm or less.

In the present invention, tough pitch copper (TPC), Cu-0.1 and
wt% Ag alloy, Cu-0.15 wt% Sn alloy, Al, Al alloy or other conductive metal material, or iron-based or nickel-based metal material, or conductive metal such as copper on ceramics or plastic A clad or plated composite material or the like is applied. The shape of the base material is, for example, a round wire for a lead wire, a square wire, a plate material for a circuit conductor (printed circuit, etc.), a strip material,
It is a foil material or the like. An electroplating method is usually applied to form a silver or silver alloy layer (hereinafter abbreviated as a silver coating layer) on the substrate. The thickness is about 0.5 to 5.0 μm. Ag-0.1 to 5 wt% Sn alloy, Ag
-0.1 to 5 wt% Sb alloy, Ag-0.1 to 10 wt% In alloy, etc. are applied. Between the base material and the silver coating layer, if necessary,
An underlayer made of nickel, cobalt or an alloy thereof is interposed. Since this underlayer suppresses the diffusion of copper from the base material, the thickness of the silver coating layer can be reduced.

In the present invention, the reason why the average crystal grain size inside the silver coating layer is limited to 3 μm or more is that if the average grain size is less than 3 μm, the number of crystal grain boundaries in the silver coating layer increases, and oxygen propagates through the grain boundaries and silver is coated with silver. This is because it penetrates into the layer in a large amount and oxidizes the base material or the underlayer. The average grain size inside the silver coating is 7μ
m or more is preferable. The reason for limiting the average crystal grain size on the outside of the silver coating layer to 2 μm or less is that when the average crystal grain size exceeds 2 μm, the reaction rate between the silver coating layer and the solder becomes slow, and the surface of the silver coating layer becomes dirty. This is because the defective shape affects the solderability. That is, in the present invention, the average crystal grain size on the outside of the silver coating layer is made finer to 2 μm or less to accelerate the reaction rate with the solder, so that the influence of dirt on the surface does not affect the solderability. Of. The average grain size on the outside of the silver coating layer is preferably 0.5 μm or less.

According to a second aspect of the present invention, the silver or silver alloy layer a is formed on a substrate having at least a surface of conductivity, directly or through an underlayer made of nickel, cobalt, or an alloy thereof. In that order, the step of performing heat treatment at a temperature of 300 ° C. or higher in a non-oxidizing gas atmosphere, and the step of forming a silver or silver alloy layer b again on the silver or silver alloy layer after the heat treatment in this order. The method according to claim 1, wherein
It is a method for producing the heat-resistant silver-coated composite described.

In the present invention, for example, the steps of silver layer a plating → heat treatment → silver layer b plating are performed on a copper wire or a copper wire having an underlayer formed on the surface thereof. Here, the silver layer a refers to the inside of the silver coating layer, and the silver layer b refers to the outside. The silver layer a is recrystallized in the heat treatment step, and the crystal grains become larger than 3 μm. The heat treatment is performed in a non-oxidizing gas atmosphere such as nitrogen or argon. The reason why the heat treatment temperature is limited to 300 ° C. or higher is that the silver layer a is recrystallized below 300 ° C., but the average crystal grain size is small below 3 μm and oxygen permeation cannot be sufficiently suppressed. When the heat treatment temperature is higher than 800 ° C, components such as copper wires may diffuse into the silver coating layer violently and the appearance of the silver coating layer may be discolored. Therefore, the heat treatment temperature is preferably 800 ° C or lower. If the heat treatment time is less than 5 seconds, an average crystal grain size of 3 μm or more may not be obtained, so that the heat treatment time is preferably 5 seconds or more. The reason for limiting the average crystal grain size of the silver layer b plated on the silver layer a after the heat treatment to 2 μm or less is that the reaction rate with the solder becomes slow when the average grain size exceeds 2 μm.
This is because the silver layer surface is affected by dirt and the like and solderability is reduced. An average crystal grain size of 2 μm or less can be obtained by ordinary silver plating. By using the strike plating bath, the average crystal grain size can be 1 μm or less.

In the present invention, after the silver or silver alloy layer a is formed, it is possible to carry out processing, and then heat treatment and formation of the silver layer b are carried out successively. Here, an appropriate amount of strain is applied to the silver layer a by processing, and the crystal grains of the silver layer a are further coarsened by the next heat treatment to improve the oxygen permeation suppression effect of the silver layer a. If the reduction rate of processing is less than 5%, the strain will be insufficient and the effect of coarsening the crystal grains will not be sufficient, and if it exceeds 98%, the strain will be too large and the crystal grains will become finer by heat treatment. Come to do. Therefore, it is preferable that the surface-reduction processing rate in processing is 5 to 98%.

According to the third aspect of the present invention, the silver or silver alloy layer a is formed directly on the substrate having at least the surface of conductivity or through the underlayer made of nickel, cobalt or an alloy thereof. Step, heat treatment in a non-oxidizing gas atmosphere at a temperature of 300 ° C. or higher, processing at a surface-reduction processing rate of 30% or lower, and silver or silver alloy layer on the processed silver or silver alloy layer again. The method for producing a heat-resistant silver-coated composite body according to claim 1, wherein the steps of forming the silver alloy layer b are performed in this order.

The steps of the present invention are carried out in the order of silver layer a formation → heat treatment → processing → silver layer b formation. That is, it is the same as the method according to claim 2, except that processing is performed after the heat treatment. The silver layer a was recrystallized by heat treatment and had an average crystal grain size of 3 μm.
It becomes larger than m, the structure is densified in the next processing, and the strength is increased. The reason why the surface-reduction processing rate of the processing is limited to 30% or less is that when the surface-reduction processing rate exceeds 30%, the average crystal grain size of the silver layer a becomes less than 3 μm and the oxygen permeation suppression effect is sufficiently obtained. This is because it will not be possible.

In the present invention, after forming the silver layer a, it is possible to carry out processing and then heat treatment. According to this method, the silver layer a has a coarse crystal grain size, a fine grain size, and a high strength. For the same reason as above, the reduction rate of processing is preferably 5 to 98%, and the reduction rate of processing is
30% or less.

It is also possible to subject the heat-resistant silver-coated composite produced by the invention described in claim 2 or 3 to processing (processing) with a surface-reduction processing rate of 30% or less. By this processing, the silver layer a and the silver layer b become dense and have high strength. The reason why the surface-reduction processing rate is 30% or less is the same as that described above.

[0016]

EXAMPLE The heat-resistant silver-coated composite of the present invention was produced by the eight production steps shown in Table 1. 0.8 to 1.0 mmφ for base material
The tough pitch copper wire of was used. Ag or Ag for the silver coating layer
-Sb alloy was used. The electroplating of the silver coating layer was performed under the following conditions. [Ni base layer] Bath composition: 400 g of nickel sulfamate
/ Liter, nickel chloride 30g / liter, boric acid 30g / liter.
Bath temperature: 50 ° C. Current density: 10 A / dm ² . [Ag layer] Bath composition: silver cyanide 50 g / liter, potassium cyanide 60 g / liter, potassium carbonate 30 g / liter. Bath temperature: 30
° C. Current density: 2 A / dm ² . [Ag alloy layer] Bath composition: Silver cyanide 50 g / liter, potassium cyanide 60 g / liter, antimony potassium tartrate 2.5 g
/ Liter, potassium carbonate 30 g / liter. Bath temperature: 30 ° C. Current density: 2 A / dm ² .

With respect to each of the obtained silver-coated copper wires, the solder wetting time, the solder wettability, and the adhesion of the silver coating layer were examined under the following conditions. The results are shown in Tables 2 and 3 together with the production conditions.
Shown in [Solder wetting time] A 95% Pb-Sn solder bath heated to 350 ° C was dipped at a speed of 2 mm / sec. To a depth of 2 mm and kept for 10 sec. The results were evaluated at zero cross time. [Solder wettability] After heating the silver-coated copper wire in the atmosphere at 230 ℃ for 10 hours, dip it in the eutectic solder bath kept at 270 ℃ for 5 seconds and measure the solder adhesion area. It was expressed as a ratio (%) to the area. [Adhesion of silver coating layer] With a gauge length of 50 mm, 35 in the positive direction
The degree of peeling of the silver coating layer was observed after twisting 30 times and then 30 times in the opposite direction.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

As is clear from Tables 2 and 3, the products of Examples of the present invention (Examples 1 to 13) have a large average crystal grain size of 3 μm or more on the inside of the silver (silver or silver alloy) coating layer. Penetration was suppressed, and as a result, the solder wetted area was expanded and solderability was improved. There was also no peeling of the silver coating layer. Further, since the average crystal grain size on the outside of the silver coating layer is as small as 2 μm or less, the solder wetting time is shortened, and the influence of dirt on the surface of the silver coating layer is reduced. On the other hand, in Comparative Examples 14 and 15, which are Comparative Example products, the solder wetting area was reduced and the silver coating layer was peeled off in the twist test. This is because the silver coating layer has a small average crystal grain size and a large amount of oxygen permeates to oxidize the surface of the copper wire. Comparative Example 16 is
Since the average crystal grain size of the silver layer was large, the solder wettability and the adhesion of the silver coating layer were good, but the solder wetting time became longer and the solderability could be adversely affected by surface stains, etc. found.

A diode for resin molding was assembled using each of the silver-coated copper wires, and the solderability of the silicon chip was examined. As a result, it was confirmed that the products of the present invention all exhibited good solderability and had excellent corrosion resistance without discoloration in appearance. On the other hand, in the comparative example product, the soldering strength of the silicon chip was low and discoloration occurred.

[0023]

As described above, the silver-coated composite of the present invention is excellent in solderability, corrosion resistance, and adhesion of the silver coating layer, and is used for manufacturing electronic equipment parts involving high temperature steps such as resin molding. It is extremely useful for

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Claims (3)

[Claims] 1. A heat-resistant silver-coated composite in which a silver or silver alloy layer is formed on a substrate having at least a surface of conductivity, directly or through an underlayer made of nickel, cobalt, or an alloy thereof. 2. The heat-resistant silver-coated composite according to, wherein the average crystal grain size inside the silver or silver alloy layer is 3 μm or more and the average crystal grain size outside is 2 μm or less. 2. A step of forming silver or a silver alloy layer a directly or at least through an underlayer made of nickel, cobalt, or an alloy thereof on a substrate having at least a surface of conductivity, a non-oxidizing property. The method is characterized in that a step of performing heat treatment at a temperature of 300 ° C. or higher in a gas atmosphere, and a step of forming a silver or silver alloy layer b again on the silver or silver alloy layer after the heat treatment are performed in this order. The method for producing a heat-resistant silver-coated composite according to claim 1. 3. A step of forming a silver or silver alloy layer a directly or at least through an underlayer made of nickel, cobalt, or an alloy thereof on a base material having at least a surface of conductivity, a non-oxidizing property. A step of heat-treating at a temperature of 300 ° C. or higher in a gas atmosphere, a step of processing at a surface-reduction rate of 30% or less, and a silver or silver alloy layer b is formed again on the silver or silver alloy layer after the processing. The method for producing a heat-resistant silver-coated composite according to claim 1, wherein the steps are performed in this order.