JPH03153879A - Substitution type electroless tin or solder plating method - Google Patents

Abstract

PURPOSE:To form a plating layer having a large film thickness in a short period of time by pretreating the surface of Cu or Cu alloy with an aq. soln. contg. a specific oxidizing agent at the time of subjecting the surface to substitution type electroless tin plating or substitution type electroless solder plating in order to improve anti-rust property and solderability. CONSTITUTION:The material of the Cu or Cu alloy to be subjected to the electroless plating of Sn or solder is first degreased and cleaned in accordance with the conventional practices. The Cu or Cu alloy material is immersed into an aq. soln. of pH1 to 13 contg. at least one kind of the oxidizing agents consisting of peroxides, such as H2O2, Na2O2 and K2O2, salts of peroxy-acid, such as Na2S2O8, (NH4)2S2O8 or org. nitro compd., such as sodium m- nitrobenzene sulfonate at 0.01 to 2.0mol/l concn. and is thereby surface treated. The electroless Sn plating layer and solder layer having >=1mum thickness are formed in an extremely short period of time by using the substitution type electroless tin plating liquid essentially consisting of a stannous salt and thiourea or the substitution type electroless solder plating liquid consisting of the compsn. further added with a lead salt.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a displacement type electroless tin or solder plating method.

In recent years, surface mounting has been applied to printed wiring boards, requiring a solder plating layer or a tin plating layer, but with the increase in the number of independent circuit boards and the fine patterning of wiring circuits, electroplating can no longer be used. The number of cases in which electroless tin plating or electroless solder plating is applied is increasing.

When the purpose of rust prevention or soldering of copper or copper alloy is to improve properties, the film thickness of tin plating or solder plating should be at least 0.5
The thickness is required to be 1 μm or more, and in practice, it is preferably 1 μm or more.

Conventionally, substitution type electroless tin or solder plating baths have been used, such as tin plating baths containing stannous salts and thiourea as main components, and solder plating baths containing stannous salts, lead salts, and thiourea as main components. There are known plating baths and autocatalytic plating baths in which a reducing agent such as hydrazine or hypophosphorous acid is added to these displacement plating baths.

In autocatalytic plating baths, it is usually necessary to reduce the concentration of each component in the bath in order to prevent rapid metal precipitation, so-called bath decomposition. For this reason, the deposition rate of the plating film is slow,
It is not possible to obtain a plating film thickness of 1 μm or more in a short period of about 3 to 5 minutes. Furthermore, when plating is carried out for a long time to obtain a plated film with a high film thickness, there are problems such as the plating depositing on unnecessary parts, and especially in the case of pattern plating, the plating depositing outside the pattern.

On the other hand, in displacement-type plating baths, plating does not precipitate on unnecessary areas, but the tin or solder deposited by displacement stops when the entire surface of the copper or copper alloy material is covered. There is a problem that a plating film thickness of about 0.2 to 0.5 μm or more cannot be obtained.

Means for Solving the Problems The present inventor has conducted extensive research in order to solve the above-mentioned problems. As a result, when forming a plating film on a workpiece made of copper or copper alloy using a displacement plating bath, it is necessary to oxidize the surface of the workpiece in advance using an aqueous solution containing an oxidizing agent. discovered that a thick plating film can be formed in a short period of time by displacement plating.

That is, the present invention is characterized in that after the copper or copper alloy to be plated is treated with an oxidizing agent-containing aqueous solution having a pH of 1 to 13, displacement type electroless tin plating or displacement type electroless solder plating is performed. This invention relates to a substitution type electroless tin or solder plating method.

Generally, the metal precipitation reaction in a displacement plating bath can be expressed as shown in the following equation.

Local cathode reaction A6→A”+ne- (dissolution reaction)
Local anodic reaction B"+ne-→B" (precipitation reaction)
Here, A is the raw metal and B″+ is the metal ion in the bath.

That is, electrons released when the raw metal is dissolved in the plating bath due to the local cathode reaction move to metal ions in the plating bath as shown in the local anode reaction, and a plating film is deposited. Therefore, the ease with which the raw metal can be dissolved greatly affects the substitution reaction.

Usually, in such a displacement plating method, the workpiece is degreased and treated with acid, and then the workpiece is immersed in a displacement plating bath to deposit the metal. Since metal precipitation stops when the entire surface of the treated object is coated, the plating film thickness should be 0.2 to 0.5μ.
The limit is about m.

On the other hand, according to the present invention, after cleaning the workpiece by degreasing or the like, the workpiece is immersed in an oxidizing agent-containing aqueous solution, and then immersed in a displacement plating bath.
A displacement plating film with a thickness of about 1 μm or more can be formed in a short time. The reason why the method of the present invention enables displacement plating with a high film thickness in a short time is as follows.
By immersing a copper or copper alloy material in an oxidizing agent-containing aqueous solution, oxides are formed on the surface of the copper or copper alloy. Such oxides tend to undergo electron transfer, and the material metal is not easily immersed in the displacement plating bath. This is believed to be because melting becomes easier, and as a result, tin or solder becomes easier to precipitate.

The object to be treated to which the method of the present invention is applied is copper or a copper alloy such as brass, and its shape is not particularly limited.

In the method of the present invention, first, the copper or copper alloy material is subjected to a cleaning treatment such as degreasing according to a conventional method.

This material is then treated with an aqueous solution containing an oxidizing agent.

Examples of oxidizing agents include peroxides such as hydrogen peroxide, sodium peroxide, potassium peroxide, calcium peroxide, ammonium peroxide, diethyl peroxide, and cyclohexene peroxide; sodium persulfate, ammonium persulfate, and perboric acid. Beroxo salts such as sodium, ammonium perborate, sodium beloxophosphate, sodium beloxocarbonate, sodium peroxotungstate, potassium peroxonitrate; sodium m-nitrobenzenesulfonate, sodium p-nitrobenzenesulfonate;
Organic nitro compounds such as sodium m-nitrotoluenesulfonate, nitroanilic acid, sodium 0-nitrobenzoate, sodium m-nitrophthalate, sodium nitronaphthalenesulfonate, and sodium nitropropionate can be used.

In the present invention, at least one of the above-mentioned oxidizing agents may be used, but two or more types may be used in combination. The concentration of the oxidizing agent in the oxidizing agent-containing aqueous solution is 0.01 to 2
．． Although the effect is recognized in the range of about 0moN/N,
It is preferably 0.1 to 1.0 moN/l. If the concentration of the oxidizing agent is too low, the time required to oxidize the copper-based material becomes undesirable. Moreover, if the oxidizing agent concentration becomes high, there is no problem in terms of performance, but the production cost increases. The oxidizing agent-containing aqueous solution can be used at a pH of 1 to 13, but preferably at a pH of 2 to 9. If the pH is too low, the copper or copper alloy material will be etched, making the plating appearance rough and uneven, which is not preferable. Furthermore, if the pH is too high, the oxidizing agent will undergo severe self-decomposition, resulting in high costs, which is not preferable.

Treatment with an oxidizing agent-containing aqueous solution is usually performed by immersing the object to be treated in the aqueous solution.

The temperature of the aqueous solution is suitably from room temperature to about 80°C, and preferably from about 30 to 50°C from the viewpoint of workability. The processing time is
Usually, the time may be about 3 to 10 minutes.

After treatment with an oxidizing agent-containing aqueous solution, displacement tin or solder plating is performed. As the plating bath, any known displacement type electroless tin plating bath or displacement type electroless solder plating bath can be used. Examples of such displacement type electroless plating baths include inorganic stannous salts such as stannous sulfate, stannous chloride, stannous borofluoride, and stannous methanesulfonic acid.
stannous alkanolsulfonic acids such as tin, stannous acetate,
Approximately 10 to 80 g/4 of a tin compound such as an organic acid tin salt such as tin hydroxyacetate, a mineral acid such as hydrochloric acid, sulfuric acid, or borohydrofluoric acid, acetic acid, 10 to 150 g of acids such as organic acids such as phenolsulfonic acid
It contains about 30 to 300 g/R of a sulfur compound such as thiourea or its derivatives, and if necessary, 10 to 100 g/R of a chelating agent such as tartaric acid, citric acid, or malic acid as a deposited film improver. A displacement-type electroless tin plating bath containing about 0.2 to 5 g of a nonionic surfactant such as polyethylene glycol nonylphenyl ether and about Q, and to such a tin plating bath, lead chloride,
Substitution type with the addition of lead compounds such as inorganic marine salts such as lead nitrate and lead borofluoride, and organic acid lead such as lead acetate, lead sulfamate, lead citrate, and lead methanesulfonate at approximately 5 to 50 g/47. It can refer to electroless solder plating baths, etc.

Conditions for displacement plating can be according to conventional methods. Usually, the object to be treated is immersed in a plating bath until a plating film of the desired thickness is deposited. Plating may be performed for about 1 to 30 minutes.

Effects of the Invention According to the method of the present invention, it is possible to form a thick tin plating film or a solder plating film in a short time, and it is also possible to form a highly accurate plating pattern.

Example Hereinafter, the present invention will be explained in more detail by showing examples.

Example 1 A 5×10 cm copper plate was immersed in a 50 g/l aqueous solution of an alkaline degreaser (trademark, A-clean A220, Okuno Pharmaceutical Co., Ltd.) at 60° C. for 5 minutes to degrease the copper plate. Then, after washing with water, 50°C 35% hydrogen peroxide solution 50-/f
After being immersed in I aqueous solution for 5 minutes, it was washed with water and displacement plating was performed.

As a plating bath, a displacement type tin plating bath containing 30 g/fl of stannous chloride, 100 g/N of thiourea, 50 mt'/R of hydrochloric acid, and 1 g/47 of a nonionic surfactant was used.

By immersing in a 50°C bath for 2 minutes, the film thickness was reduced to 1.
A tin plating film of 1 μm was formed.

In addition, in place of the above-mentioned displacement type tin plating bath, stannous chloride 20g/I), lead chloride 15g/j7, hydrochloric acid 50-/Ω,
Thiourea 80g/Ω and nonionic surfactant 1g/ρ
2 under the same conditions using a displacement type solder plating bath containing
When displacement plating was performed for a minute, a solder plating film with a film thickness of 1.3 μm was formed.

Both the tin plating film and the solder plating film described above were dense and had good adhesion to the copper plate.

Comparative Example 1 Instead of immersion treatment in hydrogen peroxide aqueous solution, 98% sulfuric acid 1
Displacement tin plating and displacement solder plating were performed in the same manner as in Example 1, except that the sample was immersed in a 00ml/Q aqueous solution at 25° C. for 2 minutes. As a result, the film thickness of the tin plating film was 0.1 μm, and the film thickness of the solder plating film was 0.3 μm, and only a very thin plating film was formed.

Example 2 In place of the hydrogen peroxide aqueous solution used in Example 1, the following
Substitution tin plating or substitution solder plating was performed under the same conditions as in Example 1 using the oxidizing agent-containing aqueous solution shown in the table. The pa of the oxidizing agent-containing aqueous solution was adjusted with sulfuric acid or sodium hydroxide. For comparison, displacement plating was also performed in the case where the same treatment was performed using an aqueous solution containing no oxidizing agent and only adjusting the pHg, instead of the treatment with an oxidizing agent-containing aqueous solution.

Table 1 shows the thickness and appearance of the formed plating film.

Claims (2)

[Claims] (1) Substitution characterized by treating the copper or copper alloy to be plated with an oxidizing agent-containing aqueous solution having a pH of 1 to 13, and then performing displacement type electroless tin plating or displacement type electroless solder plating. Type electroless tin or solder plating method. (2) The plating according to claim 1, wherein the oxidizing agent-containing aqueous solution contains 0.01 to 2.0 mol/l of at least one oxidizing agent selected from peroxides, peroxo acid salts, and organic nitro compounds. Method.