JP3331289B2 - Electroless gold plating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless gold plating method for electrolessly plating gold on a metal surface.

[0002]

2. Description of the Related Art Conventionally, electroless plating deposits metal ions in a plating bath without using an external power supply, so that it is possible to perform plating on electrically independent portions and complex shapes.
It is suitable as functional plating because it can easily automate plating work.

When performing thick electroless gold plating, first, substitution-type electroless gold plating is performed, and then reduction-type electroless gold plating is performed.
-20471). Recently, metal patterns to be electrolessly gold-plated have become complicated and delicate, and the pattern intervals required for plating have become extremely narrow (for example, about 50 to 500 μm).

[0004]

Therefore, when electroless gold plating is performed on such a finely spaced metal pattern, gold spread tends to occur between the patterns, and adjacent patterns may be electrically connected. .

The present invention pays attention to such a conventional technique, and provides an electroless gold plating method in which gold spread does not occur between patterns even with finely spaced patterns.

[0006]

In order to achieve the above object, the present invention provides a method for cleaning a material to be plated with a cyanide-containing solution after substitutional electroless gold plating, and thereafter reducing the electroless gold. The plating is performed.

[0007]

DETAILED DESCRIPTION OF THE INVENTION Generally, a substitution type electroless gold plating bath
Is KAu (CN)_TwoBased on pH 3-8, temperature
It is used in the range of 70 to 90 ° C. At this time, K in the bath
Au (CN) _TwoIs decomposed into AuCN. this
AuCN is formed outside the specified metal pattern
May be done. Normal pattern formed in predetermined pattern
The deposit is completely metallic gold (Au), but the above AuCN
Not completely metal. And this AuCN is gold
At the core of this process,
Electrolytic gold plating reacts and gold spread grows between patterns
Will do. This creates gold spread between patterns
It is a mechanism to do.

Accordingly, the inventor has considered a method of removing AuCN generated during substitutional electroless gold plating. Specifically, after performing the substitution type electroless gold plating, the material to be plated was washed with a cyanide-containing solution. Since AuCN generated in an incomplete state is dissolved in a cyanide-containing solution, AuCN can be easily removed by washing the material to be plated after the substitutional electroless gold plating with cyanide. Therefore, even if reduction-type electroless gold plating is performed thereafter, there is no AuCN serving as a gold nucleus, so that gold spread does not occur between patterns at minute intervals.

The cyanide-containing solution used in the present invention comprises:
As the cyanide, potassium cyanide or sodium cyanide is contained in an amount of 1 to 100 g / liter. The temperature is preferably from 10 to 40C.

Also, a surfactant is added to the cyanide solution.
１０００1000 mg / liter may be added. As the surfactant to be added, a nonionic, anionic, cationic surfactant or the like is suitable. By adding a surfactant, there is obtained an effect that the surface tension is reduced, cyan ions are easily adsorbed on the surface of the object to be plated, and AuCN is easily removed.

[0011]

[Example] Substitution type electroless gold plating bath: 4 g / liter of gold potassium cyanide (as gold) • 50 g / liter of chelating agent • 20 g / liter of organic acid salt • pH 4.0 • temperature 90 ° C. • time 10 minutes

Reduction type electroless gold plating bath: 4 g / liter of gold potassium cyanide (as gold) 8 g / liter of dimethylamine borane 5 g / liter of chelating agent 10 g / liter of organic acid salt pH 13.5 Temperature 70 ℃ ・ Time 30 minutes

Cyanide-containing solution: potassium cyanide (KCN) 1 to 50 g / liter temperature 25 ° C. immersion cleaning time 30 seconds

Using the above-mentioned substitution type electroless gold plating bath and reduction type electroless gold plating bath, electroless gold plating was performed on inner leads (interval: 100 μm) which are metal patterns of IC parts.

Then, the frame (material to be plated) after the substitution type electroless gold plating was immersed in the cyanide-containing solutions having different concentrations to be washed. In addition, what was not wash | cleaned was prepared as a comparative example. Further, a surfactant washed with a cyanide-containing solution containing 100 mg / liter of a nonionic surfactant as a surfactant was also prepared. Then
Each of them was subjected to electroless gold plating using the above-mentioned reduction type electroless gold plating bath.

Table 1: Washing KCN concentration Surfactant No gold spread state状態 ─ × Available 5 g / L ─ Available 10 g / L ─ Available 1 g / L 100 mg / L 有 り Available 25 g / L ─ Available 50 g / L ─ ○

The results are shown in Table 1. As shown in Table 1, the case where the substrate was washed with the cyanide-containing solution and then subjected to the reduction-type electroless gold plating showed no gold spread (広 が り), and the case where the substrate was not washed showed the case where the gold spread was not obtained. Occurred (x).

[0018]

According to the electroless gold plating method of the present invention,
Even with finely spaced patterns, gold spread between the patterns does not occur, which is very useful especially in the electronics industry.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-222541 (JP, A) JP-A-5-125552 (JP, A) JP-A-4-261109 (JP, A) JP-A-6-261 232136 (JP, A) JP-A-5-327188 (JP, A) JP-A-9-118986 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 18/44 C23C 18 / 42

Claims (3)

(57) [Claims] 1. An electroless gold plating method in which a material to be plated is subjected to substitutional electroless gold plating in a substitutional electroless gold plating bath containing cyanide, followed by reduction type electroless gold plating. 3. The electroless gold plating method according to claim 1, wherein after the substitutional electroless gold plating, the material to be plated is washed with a cyanide-containing solution, and thereafter, the reduction type electroless gold plating is performed. 2. A cyanide-containing solution comprising potassium cyanide or sodium cyanide as cyanide in an amount of 1 to 1;
2. The electroless gold plating method according to claim 1, wherein the content is 00 g / liter. 3. The solution containing cyanide containing 10 surfactants.
The electroless gold plating method according to claim 1 or 2, wherein the amount of the electroless gold plating is from 1000 to 1000 mg / liter.