JPH05163579A - Gold plating method - Google Patents

Abstract

PURPOSE:To form a gold plating film with excellent adhesion to a nickel film by making nickel plating on a copper bare surface and immersing it in a water solution of a reducing agent before making gold plating with a gold plating solution containing no cyanide. CONSTITUTION:Nickel plating is made on a copper bare surface of a substrate, which is immersed in a water solution containing a reducing agent and substantially no metal ions. After water washing, gold plating is made with a gold plating solution containing no cyanide. The water solution containing a reducing agent and substantially no metal ions includes at least one of alkali borohydride, amine boranes, hypophosphorons acids, alcohols, hydroxycarboxylic acids, formalin and hydrazines and its concentration is preferably 0.01-5mol/l. It is preferable that pH be adjusted to about 7-13 and the treating temp. be about 40-90 deg.C and the treating time be about 1-30min. Thereby the adhesion between the nickel film and the gold film is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gold plating method containing no harmful cyanide compound.

[0002]

2. Description of the Related Art In general, gold plating on a printed wiring board is performed by substitution palladium plating for copper convolution, then electroless nickel plating, and then electroless gold plating. Conventionally, a highly toxic cyanide compound has been used in the electroless gold plating solution, which causes a problem in handling. That is, these cyan compounds have problems in storage and management and safety in waste liquid treatment. Therefore, in recent years, a gold plating solution that does not use a cyanide of an electroless gold plating solution has been developed.

[0003]

However, the gold plating film formed by electroless gold plating containing no cyanide on the nickel film has a remarkably weak adhesion to the nickel film. Therefore, the electroless gold containing no cyanide is used. The plating had to be applied to the surface after performing displacement gold plating containing cyan. In addition, the substitutional gold plating containing no cyanide has a weak adhesion, which hinders its practical application. The present invention provides a gold plating method for forming a gold plating film having excellent adhesion on a nickel film by gold plating containing no cyanide compound.

[0004]

According to the gold plating method of the present invention, nickel is plated on a copper substrate, which is then immersed in an aqueous solution containing a reducing agent and substantially free of metal ions, and further cyanide. It is characterized in that plating is performed with a gold plating solution containing no compound. This nickel plating method is electroplating or electroless plating, and the method is not particularly limited. The composition of the aqueous solution containing a reducing agent and containing substantially no metal ions contains at least one kind of alkali borohydride, amine boranes, hypophosphorous acids, alcohols, hydroxycarboxylic acids, formalin and hydrazines. And the concentration is 0. 01 mol / 1-5 mo
1/1, pH is adjusted to about 7 to 13 using NaOH or the like, processing temperature is 40 ° C to 9 ° C, and processing time is 1 minute to 30
Minutes are preferable. In addition, the fact that the solution does not substantially contain metal ions means that this solution is not an electroless plating solution. Generally, the metal content is 1 g / 1 or less.

Further, the composition of the gold plating solution containing no cyanide compound is as follows: 1) chloroauric acid or a salt thereof and a substituted gold plating solution containing a buffer in a substream salt and thiosulfate, or 2) chloroauric acid or its It is an electroless gold plating solution containing a salt, a sulfite, and a thiosulfate as a reducing agent and thiourea or ascorbic acid or a salt thereof as a buffer, but is not limited thereto. The cyan-free gold plating solution used may be electro gold plating.

[0006]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 Substitution palladium plating (Meltex) on a copper-clad laminated substrate having a size of 2.5 cm × 2.5 cm and a thickness of 1.6 mm
Melplate Activator 350 manufactured by K.K.
For 5 minutes, then rinse with running water for 1 minute,
Further, electroless nickel plating (Bullish Suma manufactured by Kanigen Co., Ltd.) was treated at 80 ° C. for 20 minutes. Then, it was washed with running water for 1 minute. Then, it was immersed in a treatment liquid containing a reducing agent based on the conditions shown below, and then washed with running water for 1 minute. Further, gold plating was performed, followed by washing with water and drying at 80 ° C. to obtain a sample for evaluation of adhesion. The evaluation of adhesion was performed on the following two items. Taping test: width 1c
m commercially available cello tape (trade name "Knit one cellophane sticker tape No. 29" manufactured by Nitto Denki Kogyo Co., Ltd.)
Was adhered to the surface of the sample, and then the cellote was peeled off, and the adhesion state of the gold coating on the tape surface was visually observed to evaluate the adhesion. L-type pull test: Copper sulfate electroplating was performed on the gold-plated sample surface for 2 μm, and then a circular resist having a diameter of 3 mm was formed, and the plated copper was immersed in ammonium persulfate for etching. Then, an L-shaped copper wire having a diameter of 0.9 mm was soldered to the surface of the circular copper pattern. Then, the copper wire was pulled vertically to measure and evaluate the adhesion strength. The results are shown in Table 1.

Composition of reducing treatment solution and treating conditions Sodium borohydride 2 g / 1 pH 12.5 (using NaOH) Treatment temperature 8 ° C. Treatment time 5 minutes

Composition of gold plating solution and plating conditions Sodium gold (III) chloride 5 g / 1 sodium sulfite 12.5 g / 1 sodium thiosulfate 7.5 g / 1 pH 3.5 (lactic acid used) buffer (sodium lactate) 5g / 1 Treatment temperature 80 ℃ Treatment time 20 minutes

Example 2 The same electroless nickel plating as in Example 1 above was performed, immersed in a treatment liquid containing a reducing agent under the conditions shown below, and gold plating was performed under the same composition and conditions as in Example l. Adhesion was evaluated under the conditions of 1) and 2) as adhesion evaluation samples. The results are shown in Table 1.

Composition of reducing treatment liquid and treating conditions Dimethylaminoborane lg / 1 pH 8.5 Treatment temperature 80 ° C. Treatment time 5 minutes

Comparative Example Electroless nickel plating was performed under the same conditions as in the example, and gold plating was performed without immersion in a treatment solution containing a reducing agent, and the adhesion was evaluated under the conditions 1) and 2). The results are shown in Table 1.

[0012]

[Table 1]

[0013]

As described above, according to the method of the present invention, the adhesion between the nickel coating and the gold coating is remarkably improved as compared with the case where the treatment of the comparative example is not performed.

Claims (2)

[Claims] 1. A copper substrate is nickel-plated and then:
A gold plating method characterized by immersing this in an aqueous solution containing a reducing agent and substantially not containing metal ions, and further plating with a gold plating solution containing no cyanide. 2. The reducing agent is one of alkali borohydride, amine boranes, hypophosphorous acids, alcohols, hydroxycarboxylic acids, formalin and hydrazines.
The gold plating method according to claim 1, wherein the gold plating method is more than one kind.