JPH05222541A - Gold plating method - Google Patents

Abstract

(57) [Abstract] [Purpose] In the method of forming an electroless gold plating film on nickel, the thickness of the displacement gold plating film formed on nickel as a catalyst for electroless gold plating should be 0.1 μm or less. To improve the adhesion between nickel and gold plating film. [Structure] As shown in FIG. 1, the adhesion between nickel and the gold plating film tends to sharply decrease at a film thickness of 0.1 μm or more with respect to the thickness of the displacement gold plating film. Further, as a catalyst for electroless gold plating, the displacement gold plating film thickness is required to be 0.005 μm or more. Therefore, the displacement gold plating film thickness is 0.005
It is preferably 0.1 μm. [Effect] As a result, the adhesion between the nickel and the gold plating film is improved, the connection reliability of soldering, wire bonding, etc. is improved, and the manufacturing yield is also improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a gold plating film on nickel by electroless gold plating, and particularly to a gold plating method suitable for forming a gold plating film having high adhesion to nickel. Regarding

[0002]

2. Description of the Related Art Generally, electroless gold plating on nickel is performed as follows. That is, if necessary, the nickel surface is cleaned by treatments such as alkaline degreasing and pickling,
Then, it is immersed in a displacement type gold plating solution to deposit gold as a catalyst for electroless gold plating on nickel by utilizing the potential difference between gold and nickel. Here, the above-mentioned cleaning treatment of the nickel surface is not necessary when nickel is formed by the plating method and is continuously performed with the displacement gold plating. Next, a gold plating film having a predetermined thickness is formed by an electroless gold plating reaction by immersing it in an electroless gold plating solution containing a reducing agent and using gold deposited by the substitution reaction as a catalyst. Such a gold plating method is described in, for example, JP-A-1-180985.

[0003]

The above-mentioned conventional technique has a drawback that the adhesion between nickel and the gold plating film is reduced when the thickness of the displacement gold plating is large. If the adhesion is lowered, for example, when wire bonding is performed on the electroless gold plating film, the electroless gold plating film is peeled off, and wire bonding with sufficient strength and reliability cannot be performed. Also,
When trying to mutually diffuse gold and nickel by heat,
Both do not diffuse well and the gold repels and the gold and nickel are not evenly diffused. Furthermore, if nickel is oxidized without oxidation into nickel oxide without elution, only the gold plating film is eaten by the solder when soldering is attempted, and the problem that the solder does not spread to nickel and does not spread sufficiently Occurs.

An object of the present invention is to provide a gold plating method which secures the adhesion between gold and nickel and can perform good wire bonding, diffusion of gold and nickel, and soldering.

[0005]

The above object can be achieved by appropriately maintaining the reaction time of the displacement gold plating, which is a catalyst for electroless gold plating, that is, the displacement gold plating film thickness. The displacement gold plating film may be 0.005 μm or more as a catalyst for the electroless gold plating reaction to be performed next, and when it is deposited to be 0.1 μm or more, nickel elution or nickel along the interface between the displacement gold plating film and nickel may be performed. Oxidation proceeds excessively, and the adhesion between the two is reduced. Therefore, the thickness of the displacement gold plating film is preferably 0.005 μm to 0.1 μm, and more preferably 0.01 μm to 0.07 μm.

[0006]

The displacement gold plating deposition reaction is a reaction in which the gold ions in the plating solution receive the electrons emitted by the elution or oxidation of nickel and deposit as solid gold on the nickel surface. This nickel elution or oxidation often occurs along the interface between the deposited gold and nickel, and as the displacement gold plating reaction time increases, nickel elution or oxidation progresses, and the adhesion force between nickel and displacement gold plating increases. Will fall. At the 1st time, the adhesion strength between nickel and the displacement gold plating and the displacement gold plating film thickness of 0.07 μm or less are both 400 kg.
In contrast to the above, when it exceeds 0.07 μm, it begins to decrease and at 0.15 μm, it decreases to 200 kg or less. Thus, in order to secure the adhesion between nickel and the displacement gold plating, the displacement gold plating film thickness needs to be 0.1 μm or less, and more preferably 0.07 μm or less. The present invention is particularly effective when the nickel is a nickel-boron electroless plating film using a boron compound as a reducing agent.

[0007]

EXAMPLES The present invention will be described in detail below with reference to examples.

Examples 1 to 5 On a wiring board in which a wiring pattern made of copper is formed on a glass epoxy board, degreasing with a commonly used organic solvent is performed.
After pickling with hydrochloric acid and then activation with palladium, plating was performed at 60 ° C. for 30 minutes using an electroless nickel plating solution using dimethylamine borane as a reducing agent to form a nickel plating film with a thickness of 5 μm. Was formed. After that, a displacement gold plating film is formed using a displacement gold plating solution containing potassium gold cyanide as a main component, and further sodium chloroaurate, sodium sulfite, and sodium thiosulfate are contained as main components, and thiourea is used as a reducing agent. A gold plating film was formed to a thickness of 2 μm using an electroless gold plating solution.

[0009]

[Table 1]

Both the solderability after the electroless gold plating and the wire bonding strength are good under the conditions of the present invention.
The deposited state of electroless gold plating is also good, and it fully fulfills its function as a catalyst. On the other hand, as shown in the comparative example, if the displacement gold plating film thickness is 0.001 μm or less, it is insufficient as a catalyst and uneven deposition of electroless gold plating occurs, resulting in poor solder wetting and reduced wire bonding strength. On the other hand, when the thickness is 0.15 μm, the bond strength between gold and nickel is lowered, so that the wire bondin strength is particularly lowered, and the solder wetting failure occurs.

[0011]

[Table 2]

After the heat treatment, the diffusion of gold and nickel, the solderability, and the wire bonding strength are all good under the conditions of the present invention, and the state of electroless gold plating deposition is good, and the catalyst functions sufficiently. On the other hand, as shown in the comparative example, the displacement gold plating film thickness of 0.001 μm is not sufficient as a catalyst, resulting in uneven deposition of electroless gold plating, resulting in uneven diffusion of gold and nickel, poor solder wetting,
The wire bonding strength is reduced. When the thickness is 0.15 μm, the gold-plated film is peeled off during the heat treatment due to the decrease in the adhesion between gold and nickel, and uneven diffusion occurs.
As a result, poor solder wetting and lower wire bond strength are caused.

Examples 6 to 10 A wiring board in which a wiring pattern made of tungsten is formed on an alumina board is subjected to an alkali treatment with a sodium hydroxide aqueous solution and an acid treatment with hydrochloric acid, which are generally carried out.
Then, after activation with palladium, a nickel plating film was formed to a thickness of 5 μm by electroless nickel plating using dimethylamine borane as a reducing agent. After that, a displacement gold plating film is formed by using a displacement gold plating solution containing potassium gold cyanide as a main component, and further electroless gold plating containing sodium gold sulfite and sodium thiosulfate as main components and thiourea as a reducing agent. A gold plating film was formed to a thickness of 2 μm using the solution. Further, heat treatment was performed at 750 ° C. for 10 minutes to diffuse gold and nickel.

[0014]

EFFECTS OF THE INVENTION According to the present invention, the adhesion between nickel and the gold plating film formed thereon is improved, whereby good solderability can be obtained and a high wire bonding strength can be obtained. Became. Also, in the process of heat treatment after electroless gold plating, peeling of the gold plating film due to insufficient adhesion between nickel and gold is eliminated, and a uniform and good diffusion film of nickel and gold is obtained, and soldering is performed. Good results were obtained with respect to the wire bonding strength and wire bonding strength. As a result, it has become possible to improve the connection reliability such as soldering and wire bonding and to manufacture a wiring board with a high yield.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a displacement gold plating film thickness and an adhesion force between nickel and a gold plating film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuyasu Murayama 1 Horiyamashita, Hinoyama, Hadano, Kanagawa Hitachi, Ltd. Kanagawa factory

Claims (1)

[Claims] 1. A method of forming a gold plating film on nickel using an electroless gold plating solution containing a reducing agent, wherein the thickness of the displacement gold plating film formed on nickel as a catalyst for electroless gold plating is 0. A gold plating method characterized in that the thickness is 1 μm or less.