JPS59162295A - Stainless steel product provided with solderability - Google Patents

Abstract

PURPOSE:To provide solderability to a stainless steel product by directly forming very thin plating of Au, Ag, Pd or an alloy thereof on the steel product by such an extent of deposition that a color tone between the color tone of stainless steel and that of said metal or alloy is assumed. CONSTITUTION:Very thin plating of Au, Ag, Pd or an alloy thereof such as Pd- Ni, Au-Ag, Au-Pd or Au-Cu is directly formed on a stainless steel product made of SUS-304, SUS-316, SUS-430 or the like by such an extent of deposition that a color tone between the color tone of stainless steel and that of said metal or alloy is assumed. Thus, solderability is provided to the stainless steel product which is difficult to solder.

Description

DETAILED DESCRIPTION OF THE INVENTION Stainless steel is difficult to solder due to the presence of a strong passivation film on its surface, and conventionally it has been considered impossible to solder it directly.

However, if the passivation film on the stainless steel surface is removed with hydrofluoric acid or a mixed acid of hydrofluoric acid and nitric acid, and then soldered immediately after,
Although it can barely be soldered, it has not been put into practical use because there is residual hydrofluoric acid that corrodes the solder area or its surroundings.

In addition, stainless steel strips have been made that are pretreated with a mixed acid of hydrofluoric acid and nitric acid, then copper plated on the stainless steel surface, and then tin or solder plated on top to give it solderability. According to this method, the process is complicated, the production cost is high, and oxides are generated on the surface due to aging, resulting in a material surface that inhibits solderability.

Another method to impart solderability to stainless steel was to apply Ni plating to the punching material for electronic parts, but the solderability deteriorated dramatically due to changes in Ni over time.
It was almost unusable.

The inventor of this invention has conducted extensive research on applying gold plating directly to stainless steel to impart solderability, and after a long period of trial and error, he has developed a special surface treatment method and the use of extremely thin gold, silver, and baladium after that treatment. We have experimentally discovered that directly plating stainless steel with alloys, etc. is the best way to impart solderability.

According to the method of this invention, the amount of plating metal deposited is extremely small, and even though precious metals are used, the cost is lower than that of thick solder plating, and gold in particular has excellent corrosion resistance. , we have developed a solderable stainless steel product that does not change over time and does not form surface oxides, so it has excellent reliability in soldering work.

Stainless steel is called a stainless steel because it is alloyed with iron and Cr, and a passivation film is formed on its surface.

This invention makes it possible to easily solder to stainless steel by plating and covering the surface of Cr, which generates a passivation film, with gold or other metal, making it impossible to generate a passivation film again. This is an invention.

First, only the passivation film on the stainless steel surface is removed by a special pretreatment method shown in the example, and immediately after that, gold or other metal is plated. (Hereinafter, the type of metal to be plated will be explained using gold as an example.) (The thickness of the gold plating used in this invention is OO5μ or less.
．． It is preferably within 0.001μ. ) Cr on stainless steel surface
Through this pretreatment, the passivation film on the surface of the atoms is completely removed and the atoms become highly active, but the Cr surface is selectively plated with gold, and the gold surrounds the Cr atoms. It will be covered.

Therefore, the activation of Cr is suppressed by gold and cannot react with iron, making it impossible to regenerate the passivation film unique to stainless steel.

This phenomenon was verified by the experiment described below. That is, 5 US
-450 (Cr-'18% Fe-80% others) stainless steel hoop material was plated with very thin gold by the method of the present invention, and then sent to a salt spray machine to produce J l5-Z.
As a result of a corrosion resistance test conducted according to the 2571 standard, this sample started to develop red rust after 6 hours, and the entire surface was covered with red rust after 12 hours.

This rusting rate is an early rusting phenomenon that is the same rate as iron.
The alloying effect of Cr contained in 5US-450 in stainless steel, that is, the ability to generate a passivation film, has been lost, and the surface of the Cr in the alloy has been selectively plated with gold, so the iron content has been lost. It was found that only one of the vessels had been exposed to an atmosphere of salt spray.

On the other hand, the unplated material 5VS-4'50 did not rust even after 240 hours in the salt spray test due to the presence of a strong passivation film.

As can be seen from this phenomenon, when very small amounts of gold or other metals are plated on stainless steel, the surface of Cr is selectively plated, suppressing the activation of Cr and preventing the regeneration of the passivation film. When soldering to this surface, it became possible to easily and firmly solder gold on Cr existing in a dotted or mesh pattern and Fe or Fe--Ni alloy without a passivation film.

Regarding the solderability of gold plating, F. GordOn Fosler of Bell Laboratories, USA, found that if more than 4% gold gets into the solder during soldering, the solder becomes brittle and its mechanical strength decreases. , and when the total concentration is more than 20%,
It has been announced that this will definitely lead to a decrease in strength.

This refers exclusively to the solderability of gold plating on copper alloys, as soldering to stainless steel has hardly been attempted in the past. It has been pointed out that it reduces

Stainless steel hoop material or wire material, which can be mass-produced, is inexpensive, and has excellent solderability that does not change over time, has been considered difficult to manufacture due to conventional technology, but with the ultra-thin plating method of the present invention, it has been difficult to manufacture. , which made this production possible and demonstrated superior solderability in terms of material, corroborated the above announcement that thick gold plating has a negative effect on solderability, and as a result of various experiments, it was found that ultra-thin gold plating is superior to stainless steel. I discovered that plating is the best method for soldering.

Moreover, ultra-thin gold plating on stainless steel maintains solderability for a long time because the gold does not diffuse into the stainless steel, but if gold is plated on a copper alloy as in this invention, instead of thick gold plating, the gold will not diffuse into the stainless steel. Even if extremely thin gold plating is applied, the gold will diffuse into the copper alloy and disappear from the surface in a short period of time, losing its effect.

In addition, in order to test whether the φ stainless steel products obtained by this invention will generate a passivation film again and inhibit solderability, we will conduct a passivation film formation process that is commonly performed in the stainless steel industry. We tried the nitric acid immersion method.

This method is a method that quickly forms a passivation film in order to prevent rust from forming when stainless steel is exposed by cutting.

That is, a sample of the 5t-Ts-404 hoop material obtained by the present invention was immersed in a 15V% solution of nitric acid (68%) for 20 minutes, washed with water, dried, and then subjected to a flux-free solderability test using a soldering bath. It was found that the solderability was as good as before dipping in nitric acid, and the passivation film did not regenerate even with this forced method, indicating that Cr activation was completely suppressed.

Example 1 A stainless steel hoop material made of SUS-104 with a thickness of 0.2 ttrm, a width of 40 (rolled), and a length of 800 m was directly coated with ultra-thin gold plating through the following process. Process A commercially available alkaline degreasing solution was heated to 70% in a stainless steel tank.
The stainless steel strip is heated to ~80°C, and the stainless steel strip is sequentially passed through this tank for primary degreasing, and then heated to 40~60°C.
DC electrolytic degreasing was carried out in an alkaline bath by applying a voltage of 100 volts, with the stainless steel plate as the anode and the stainless steel hoop as the cathode.

■Chemical polishing process The stainless steel hoop material is then polished using hydrochloric acid (35% solution).
20 volumes of sulfuric acid (85% solution), 10 volumes of citric acid (powder), 1 volume of acetic acid (90% candy solution), and 5 volumes of nitric acid (68% solution), polyethylene glycol. 0.2% by weight of nonionic or amphoteric surfactants such as alkyl ethers and polyethylene glycol fatty acid esters, and amine corrosion inhibitors (
For example, Lion Armor's Armohipoo 28) o,
Oxides and impurities on the surface of the stainless steel hoop were removed by passing it through a bath containing 1% by weight while irradiating it with 600 watts of ultrasonic waves.

■Electrolytic activation process Phosphoric acid (85% solution) 10% by volume, sulfuric acid (85% solution) 10% by weight, citric acid (powder) 5% by weight
, 1% by weight of acetic acid (90% solution), 0.2% by weight of a nonionic or amphoteric surfactant as above and 0% of a corrosion inhibitor.
A bath to which 1% by weight was added was heated to 60°C, a (=) current was passed through the stainless steel hoop material, and a (+) current was passed through the titanium platinum plated plate, set at 4 volts, and passed through the bath. The surface of the hoop material was activated.

■Gold plating process Citric acid 1209/13. Sodium citric acid 1209/l
, a current density of 10 A/Dm2 in a plating bath containing 50 g/l of nickel sulfamate and 8 g/l of potassium gold cyanide.
At a plating solution temperature of 35°C in the range of ~Roni/Dd, (-) current was applied to the stainless steel hoop material, and (+) current was applied to the titanium/platinum plated plate.
) Gold plating was carried out by passing an electric current for 6 seconds.

As a result, a gold plating layer with a thickness of OO1μ was formed on both sides of the stainless steel hoop material, and the stainless steel hoop material of the present invention was obtained.

Note that the thickness of the gold plating layer, 001 μm, is not an actual measurement value, but an average value obtained by dividing the amount of gold deposited by the area, and when visually observed, the color tone is intermediate between the color tone of stainless steel alone and the color tone of the entire stainless steel. It is showing.

Example 2 A bobbin-wound SUS-3160 stainless steel wire with a wire diameter of 0.04 mm was subjected to the same process as in Example 1, and was continuously and directly plated with extremely thin gold.

Example 6 5US-430 thickness 0.1 ttan, width 50mm,
A 1.000 m long stainless steel 7-plate was continuously and directly plated with ultra-thin silver through the following process.

■Alkaline electrolytic degreasing process A commercially available alkaline degreasing solution was heated in a stainless steel tank for 70 min.
The stainless steel hoop material is heated to ~80°C and sequentially passed through this tank for primary degreasing, and then heated to 40~60°C.
DC electrolytic degreasing was carried out in an alkaline bath at 0.degree. C., with the stainless steel plate as the anode and the stainless steel hoop material as the cathode, by applying a voltage of 100 volts.

■Electrolytic activation process: Apply (+) current to the titanium-platinum plated plate in a solution of 20% nitric acid (68% concentration), 6% hydrofluoric acid (55% concentration), and the balance water, using a stainless steel hoop. A (-) current was passed through the material at a current density of 10 A/Dm2 to continuously activate the surface.

(2) Alkali neutralization step Potassium cyanide (powder) was passed through a solution containing 5 parts by weight to perform alkali neutralization.

■Silver strike plating process Set the liquid temperature to 25°C in a plating solution containing 6 parts by weight of silver cyanide, 15 parts by weight of copper cyanide, and 60 parts by weight of potassium cyanide. A (+) current was applied to the plate, and strike plating was applied continuously for 5 seconds at a current density of 5 A/Dm2.

Example 4 SUS-304 thickness 01, width 20, length 1.00
A 0 m stainless steel hoop material was continuously and directly plated with palladium-nickel alloy through the following process.

■Alkaline electrolytic degreasing process The procedure was carried out in the same manner as in Example 1.

■Chemical polishing process The same procedure as in Example 1 was carried out.

■Electrolytic activation process The procedure was carried out in the same manner as in Example 1.

■Palladium-nickel alloy plating process Sulfamic acid 8%, Pd metal content 20g/7, Ni metal content 10jj
/II neutral solution, current density 08A/Dm2~06A
/Dm2 at a plating solution temperature of 30°C, a (-) current is applied to the stainless steel hoop material, and a (+) current is applied to the titanium-platinum plated plate.
) Pd-Ni alloy plating was carried out for 7 seconds by applying an electric current.As a result, approximately 001μ of Pd-Ni was plated on the stainless steel surface.
Ni alloy plating was applied to obtain the stainless steel hoop material of the present invention.

The thickness of the plating layer, 001μ, is not an actual measurement value, but an average value obtained by dividing the amount of Pd-Ni alloy deposited by the area, and when visually observed, the color tone of stainless steel alone and Pd
Example 5 A hard spring wire with a wire diameter of 01 and SUS=6.51 was continuously heated through the same process as in Example 1. A thin gold plating was applied.

Example 6 Ultra-thin gold plating with a width of 12 mm was applied directly to the center of a die-cut lead frame of SUS-:504 with a thickness of 0.2'5 yn+n, a width of 24 wn, and a length of 700 m through the following process. Ta.

■Masking process Masking is performed by pressing with silicone rubber so that there is a non-plated area of 6 m from both ends in the width direction.

■Alkaline electrolytic degreasing process The same procedure as in Example 1 was carried out.

■Chemical polishing process The same procedure as in Example 1 was carried out.

■Electrolytic activation process The same procedure as in Example 1 was carried out.

■Gold plating process The same procedure as in Example 1 was carried out.

The physical and chemical performance tests of the stainless steel product according to the present invention were conducted as follows. The base grain was scratched with a cutter and a peeling test was performed using adhesive tape, but no peeling of the gold was observed.

◎Bending test The above sample was bent 180 degrees and a peeling test was performed using adhesive tape, but the gold did not peel off.Furthermore, the test was repeated by repeatedly bending the sample to break it, but the gold peeled off on the broken surface. It was acknowledged that there was no such thing.

■Chemical performance◎High temperature and high humidity test 5O8-3r6-L hoop material with ultra-thin gold plating according to this invention is MIL-8TI)-2
After testing for 7 days in an atmosphere of 98% humidity and 65°C, which is the standard for D2D-106C, a solderability test was conducted, and good solderability was obtained without any deterioration in solderability.

◎Thermal Shock Test A 5US-604 wire with a wire diameter of 0.2 m+n coated with ultra-thin gold plating according to this invention was heated at 185 degrees.
After repeating the cycle of C-30 minutes and -15C-3O minutes five times, good solderability was obtained, similar to the sample before the test.

The solderability of the stainless steel products obtained by the above method was tested using the following method.

■ Method using solder test A sample of 5Us-304 coated with ultra-thin gold plating was set in this test machine, and the "wetting" phenomenon of the solder was electrically detected. It was found that the solderability of the solder to phosphor bronze was superior to that of phosphor bronze tested under the same conditions.

■Test using a solder bath Melt tin 6:lead 40 solder in a solder bath, set the temperature to 2'50℃, and apply ultra-thin gold plating to 5O8-4 according to this invention.
50,5US-504,5US-416,5US-63
The surfaces of each product in No. 1 were cleaned with trichloroethane and soldered without flux at dipping times of 6 seconds and 5 seconds, and all exhibited good solderability, with a solder paste rating of 95 or higher. ” was acknowledged.

■Test using an electric soldering iron Use a commercially available electric soldering iron to solder wire (tin 6: lead 4).
Hoop material of 5O8-304, which was plated with ultra-thin gold, and S-316L-O0, which was also plated with ultra-thin gold.
, 2 mm (D wire), and found that the joint had excellent solderability, and that there was no problem with soldering stainless steel having a different composition.

■A sample of 5US-304 hoop material plated with ultra-thin silver according to the present invention and a 5US-430 hoop material of ultra-thin gold plating were soldered with resin-cored solder wire using an electric soldering iron, but good solder was obtained. I got sex.

■Tensile strength test Two ultra-thin gold-plated 5O8-304 hoops are soldered with a tin 6:lead 4 solder, and the tensile strength is +2.
6.2-4,5 Kq/- for iron at 00G
1 to 9/mA, but at +100°C it was 14 to 2.6 mA compared to 13 to 2-4 Kg/rruM for iron.
It exhibited a tensile strength of K9/-, which was superior to iron.

■Au, Ag, Pd for stainless steel hoop material
.

Pd-Ni, Au-Ag, Au-'Pd
XAu-Cu was plated extremely thinly, and after being left for two weeks, these products were soldered alone or two or three of these products were soldered together, but Au had the best solderability, and Ag, Au -
Ag, Au-Cu, Au-PdXPd.

It was found that the solderability deteriorates in the order of Pd-Ni.0 As explained above, the stainless steel product of this invention has the outstanding corrosion resistance of stainless steel, and has superior springiness, creep properties, and properties compared to copper alloys. It has excellent strength and is inexpensive, and by adding solderability, which was the biggest drawback, it can be applied to a wide range of industrial fields.

That is, it can be used for parts that require soldering, such as connectors, sockets, switches, terminals, battery holders, springs, and facsimile thin wires, and is an extremely significant invention from an industrial perspective.

Claims (1)

[Claims] An extremely thin layer of gold, silver, or palladium or an alloy thereof is directly plated onto a stainless steel product, and the amount of the metal or alloy to be plated depends on the color of the stainless steel and the amount of the metal or is a stainless steel product with solderability characterized by exhibiting a color tone intermediate to that of the alloy.