JPH1112753A - Electroless gold plating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroless gold plating method good in liq. stability even when continuously used. SOLUTION: A neutral electroless gold plating soln. consisting of the gold sulfite or chloroaurate as a gold ion source, the sulfite and thiosulfate as a gold complexing agent, the borate as a buffer, the urea-based compd. as a reducing agent, the phenyl compd. as a reduction promoter and a pH regulator is used for continuous plating in this method. In this case, an alkaline soln. consisting of a gold salt or aurate, a sulfite and a thiosulfate and an acidic soln. consisting of a urea compd. and a phenyl compd. as the reduction poromoter are replenished during plating, and the solns. are continuously filtered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electroless gold plating method.

[0002]

2. Description of the Related Art Among conventional electroless gold plating solutions, an electroless gold plating solution which does not contain cyan and performs plating with a neutral or weak alkali is known, for example, from Japanese Patent Application Laid-Open No. 3-104877. Further, when gold plating is performed frequently and gold ions are consumed and the amount of gold ions is reduced, plating cannot be performed. Therefore, it is necessary to supply an amount corresponding to the reduction in the amount of gold ions. Usually, a solution containing gold ions is added to the plating solution.
As a solution for replenishing such gold ions, an alkaline solution composed of a gold salt, a sulfite and a thiosulfate is used.
Further, since the reducing agent and the reduction accelerator are consumed by the plating reaction, the acidic solution composed of the urea compound as the reducing agent and the phenyl compound as the reduction accelerator is also replenished.

[0003]

Since the pH of the electroless gold plating solution as described above is around neutral, the phenyl compound as a reduction accelerator gradually self-decomposes, and the product is contained in the plating solution. Therefore, there is a problem that the decomposition of the liquid proceeds while repeating a bad environment in which the gold ions are suspended in the liquid as fine metal particles and then ionized again by a substitution reaction with the gold ions.

When the plating solution is used continuously, the above-described replenishment of gold ions, a reducing agent and a reduction accelerator, that is, an addition of an alkaline solution and an acidic solution,
The phenyl compound self-decomposes by the alkaline solution,
Since the gold complex composed of the sulfite and the thiosulfate is decomposed by the acidic solution, the gold complex is suspended in the liquid as fine metal particles, and has the same problem as described above.

Accordingly, an object of the present invention is to provide an electroless gold plating method having good solution stability even when used continuously.

[0006]

According to the electroless gold plating method of the present invention, gold sulfite or chloroaurate is used as a source of gold ions, sulfite or thiosulfate is used as a gold complexing agent.
A method of performing a continuous plating process using a neutral electroless gold plating solution comprising borochloric acid as a buffer, a urea compound as a reducing agent, a phenyl compound as a reduction promoter, and a pH adjuster, wherein gold salt or gold acid is used. The plating is performed while replenishing an alkaline solution composed of a salt, a sulfite and a thiosulfate, and an acidic solution composed of a urea compound and a phenyl compound, and continuously performing a filtration treatment.

As a source of the gold ion of the present invention, gold sulfite or chloroaurate is used.
Sodium chloroaurate or potassium chloroaurate can be used for sodium gold sulfite, potassium gold sulfite, and chloroaurate. The gold concentration was 5.0 × 10 as gold ions.
^-3 mol / l to 5.0 × 10 ⁻² mol / l is preferable, and the gold ion concentration is 5.0 × 10 ⁻³ mol / l.
If it is less than 5, the gold deposition rate is remarkably slow, 5.0 × 10 ^-2 mo
If it exceeds l / l, the plating characteristics do not change and it is not economical.

As the gold complexing agent, a sulfite and a thiosulfate are preferably used. As the sulfite, sodium sulfite or potassium sulfite is preferably used, and the concentration of the sulfite is 0.08 mol / l to It is preferable to use it in the range of 1.20 mol / l. The concentration of sulfite is 0.08mol / l
If less than 1, the plating solution becomes unstable and the solution is decomposed, and
If it exceeds 0 mol / l, the plating solution is not completely dissolved and the plating solution becomes cloudy. As the thiosulfate, sodium thiosulfate or potassium thiosulfate is preferably used, and the concentration of the thiosulfate is preferably in the range of 0.01 mol / l to 0.60 mol / l. Thiosulfate concentration of 0.01mol / l
If it is less than 0.1%, the plating solution becomes unstable, the solution is decomposed, and the plating solution becomes less than 0.1%.
If it exceeds 60 mol / l, it does not completely dissolve and the plating solution becomes cloudy.

As the buffer, borate is used, and sodium tetraborate or potassium tetraborate is preferably used. The concentration of borate is 0.02 mol / l to 0.20 m 2.
It is preferably used in the range of ol / l. If the concentration of borate is less than 0.02 mol / l, the effect as a buffer is weak, the pH of the plating solution tends to fluctuate, and 0.20 mol / l
If it exceeds l, it does not completely dissolve and the plating solution becomes cloudy.

As a reducing agent, a urea compound is used,
It is preferable to use thiourea, methylthiourea, or dimethylthiourea.
It is preferable to use in the range of 2.6 × 10 ⁻³ mol / l to 7.0 × 10 ⁻² mol / l. When the concentration of the urea compound is 2.6
If it is less than × 10 ⁻³ mol / l, the gold deposition rate is extremely slow,
When it exceeds 7.0 × 10 ^-2 mol / l, the plating solution becomes unstable and the solution is decomposed.

As the reduction accelerator, a phenyl compound is preferably used, and hydroquinone, methylhydroquinone, catechol, pyrogallol, aminophenol, phenylenediamine or the like is preferably used. The concentration of the phenyl compound is 5.0 × 10 ^{− 4} mol / l to 3.0 × 10
It is preferred to use in the range of ^-2 mol / l. When the phenyl compound concentration is less than 5.0 × 10 ⁻⁴ mol / l, the gold deposition rate is extremely slow, and when the concentration exceeds 3.0 × 10 ⁻² mol / l,
The plating solution becomes unstable and the solution decomposes.

In an alkaline solution comprising a gold salt or a gold salt and a sulfite and a thiosulfate, gold ions are
As a sulfite or chloroaurate, or a complexing agent for gold, a sulfite and a thiosulfate, and a hydroxide for adjusting pH are used. For gold sulfite, use sodium gold sulfite or potassium potassium sulfite, and for chloroaurate, use sodium chloroaurate or potassium chloroaurate. The concentration of gold is 2.5 × 10 ^-2 mol as gold ions. It is preferably used in the range of / l to 2.5 × 10 ^-1 mol / l. Gold ion concentration 2.5 ×
If it is less than 10 ^-2 mol / l, the replenishment efficiency is low and it is not economical. If the gold ion concentration exceeds 2.5 × 10 ⁻¹ mol / l, the replenisher becomes unstable and the solution is decomposed.

As the sulfite, sodium sulfite or potassium sulfite is preferably used, and the concentration of the sulfite is preferably in the range of 0.08 mol / l to 0.12 mol / l. The concentration of sulfite is 0.08mol / l
If the amount is less than the above, the amount becomes insufficient for gold ions, the plating solution becomes unstable, and the solution is decomposed. On the other hand, if it exceeds 0.12 mol / l, gold ions become insufficient and the gold deposition rate becomes extremely slow. As the thiosulfate, sodium thiosulfate or potassium thiosulfate is preferably used, and the concentration of the thiosulfate is preferably 0.01 mol / l to 0.60 mol / l. If the thiosulfate concentration is less than 0.01 mol / l, it becomes insufficient for gold ions, so that the plating solution becomes unstable and the solution is decomposed. On the other hand, if it exceeds 0.60 mol / l, gold ions become insufficient and the gold deposition rate becomes extremely slow.

As the hydroxide, it is preferable to use sodium hydroxide and potassium hydroxide, and it is preferable to use the hydroxide at a pH of 9 to 13. pH 9
If the pH is lower than 13 or the pH exceeds 13, the replenisher becomes unstable and the liquid decomposes.

The replenisher containing the reducing agent, the reduction accelerator and the acid is
A urea compound is used as a reducing agent, a phenyl compound is used as a reduction accelerator, and an inorganic acid is used as an acid.

As the urea compound, thiourea, methylthiourea or dimethylthiourea is preferably used, and the concentration of the urea compound is from 2.6 × 10 ⁻² mol / l to
It is preferable to use in the range of 2.6 mol / l. If the concentration of the urea compound is less than 2.6 × 10 ⁻² mol / l, the replenishing efficiency is low and it is not economical. If it exceeds 2.6 mol / l, when the temperature of the plating solution falls to 15 ° C. or lower, recrystallization occurs and it is difficult to control the storage of the plating solution.

As the phenyl compound, hydroquinone,
It is preferable to use methylhydroquinone, catechol, pyrogallol, aminophenol, phenylenediamine and the like, and the concentration of the phenyl compound is 1.0 × 10 ⁻³ mo.
It is preferably used in the range of l / l to 1.0 mol / l.
If the phenyl compound concentration is less than 1.0 × 10 ⁻³ mol / l, the replenishment efficiency is low and it is not economical. If it exceeds 1.0 mol / l, when the temperature of the plating solution falls to 15 ° C. or lower, it recrystallizes and it is difficult to control the storage of the plating solution.

As the inorganic acid, hydrochloric acid or sulfuric acid is preferably used, and the inorganic acid is preferably used at a pH of 1 to 4. When the pH is less than 1, the liquid characteristics are not changed, but the effect is not changed, and it is not economical. If the pH exceeds 4, the replenisher becomes unstable and the solution decomposes.

As a method of performing continuous filtration, one turn is made when a volume corresponding to the volume of the liquid in the tank is filtered, and one turn is performed.
It is preferable to use a filter having a capacity of 26 to 26 turns / h, and if it is less than 1 turn / h, the plating solution is decomposed because the rate of increasing the fine gold particles is higher than the collecting speed of the fine gold particles by filtration. On the other hand, if it exceeds 26 turns / h, a good gold plating film cannot be obtained because the circulation speed of the solution is too high.

The electroless gold plating method of the present invention has a liquid temperature of 50
It can be used at a temperature of from 95C to 95C. If the solution temperature is lower than 50 ° C., the deposition rate of gold is extremely slow. If the temperature exceeds 95 ° C., the plating solution becomes unstable and the solution is decomposed. According to the electroless gold plating method of the present invention, a gold film of 0.4 to 4 μm is obtained per hour when gold is plated after plating 3 μm of nickel and 0.05 μm of substituted gold on copper. In addition, gold 2.5
When 2.5 g of gold is consumed in one g / l of the electroless gold plating solution of 1 g / l, the plating solution does not become unstable even when continuous plating is performed for 20 turns, and good results are obtained.

[0021]

【Example】

EXAMPLE A copper-clad laminate of 15 cm × 15 cm was used as a material to be plated, and the material to be plated was degreased, soft-etched, and pickled, and a substituted palladium catalyst for electroless nickel plating, SA-100.
(Manufactured by Hitachi Chemical Co., Ltd., trade name) at 25 ° C. for 2 minutes, washed with water, and electroless nickel plating solution NIPS-1
℃ 80 (manufactured by Hitachi Chemical Co., Ltd.) at 80 ℃
It was immersed for 5 minutes to form a 3 μm-thick nickel film on copper. Next, it was immersed in a replacement gold plating solution HGS-100 (trade name, manufactured by Hitachi Chemical Co., Ltd.) at 80 ° C. for 10 minutes,
A substituted gold film having a thickness of 0.05 μm was formed on the nickel film. The material to be plated was immersed in 5 L of an electroless gold plating solution having the composition shown in Table 1 at 70 ° C., and plating was performed continuously, and the stability of the plating solution was examined. At this time, one turn was performed when all 5 L of the liquid in the tank was filtered.
Turn / h filtration was performed. Gold and other components were replenished with the replenisher shown in Table 2 to obtain a gold concentration of 2.
In a 5 g / l electroless gold plating solution, the time when 2.5 g of gold was consumed was regarded as one turn, and 200 ml of replenisher A and 60 ml of replenisher B were replenished for 2.5 g of gold replenishment. As a result of processing up to 20 turns, the solution did not decompose and could be used stably.

COMPARATIVE EXAMPLE After forming a substituted gold film in the same manner as in the example, immersion was carried out in an electroless gold plating solution having the composition shown in Table 1 at 70 ° C. and 5 L, plating was continuously performed, and stability of the plating solution was obtained. Was examined. Also,
Gold and other components were replenished with the replenishers shown in Table 2 in the same manner as in the examples. However, no filtration treatment was performed. As a result, gold particles were generated in the liquid after the 0.2-turn treatment, and the liquid was decomposed after 0.4 turns.

[0023]

[Table 1]

[0024]

[Table 2]

As described above, according to the electroless gold plating method of the present invention, gold sulfite or chloroaurate as a source of gold ions, sulfite or thiosulfate as a complexing agent for gold, borate as a buffer, In a method for continuously treating a non-cyanide-containing neutral electroless gold plating solution containing a urea-based compound as a reducing agent, a phenyl compound as a reduction accelerator, and a pH adjuster,
By performing the continuous filtration treatment from 1 turn / h to 26 turns / h, the liquid stability of 20 turns or more can be maintained.

[0026]

As described above, according to the present invention, it is possible to provide an electroless gold plating method having good solution stability even when used continuously.

Claims (2)

[Claims] 1. Sources of gold ions are gold sulfite or chloroaurate, gold complexing agents are sulfites and thiosulfates, buffering agents are boric acid, reducing agents are urea compounds, reduction promoters. A continuous plating process using a neutral electroless gold plating solution comprising a phenyl compound and a pH adjuster, comprising: a gold salt or an alkaline solution comprising a gold salt and a sulfite and a thiosulfate; An electroless gold plating method comprising performing plating while replenishing an acidic solution comprising a compound and a phenyl compound, and continuously performing a filtration treatment. 2. The method according to claim 1, wherein the filtration is performed by a filter having a capacity of 1 to 26 turns / h, wherein one turn is a time when a volume corresponding to the volume of the liquid in the tank is filtered. 2. The electroless gold plating method according to 1.