JPS60200968A - Electroless plating method - Google Patents

Abstract

PURPOSE:To improve the adhesive strength of an Ni layer as an underlayer to gold or silver when the Ni layer formed on a part to be plated by electroless plating is coated with gold or silver by substitution plating, by using a specified gold or silver plating soln. for substitution plating. CONSTITUTION:An Ni layer contg. phosphorus is formed on a part to be plated by electroless plating after forming an underlayer. A gold or silver layer is formed on the Ni layer by substitution plating with a gold or silver plating soln. for substitution plating contg. gelatin and an Se compound. A gold or silver layer of a desired thickness may be formed furthermore by electroless plating with an electroless gold or silver plating soln. contg. a B compound as a reducing agent. By this method the gold or silver layer shows remarkably improved adhesive strength to the Ni layer as an underlayer, so the reliability of the part of semiconductor housing to be bonded can be increased.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an electroless plating method C--particularly a method for plating N of precious metals made of gold or silver with extremely excellent adhesion to the plated area.
The present invention relates to an electroless plating method that can be obtained.

[Technical background of the invention and its problems]

For example, the part where a noble metal bonding wire made of gold or silver is directly bonded to a part of the lead frame, header pin, ceramic package substrate, etc. that is the external shrine of the semiconductor device's envelope, that is, the part to be plated, is in a state C2 where it is easy to bond. Therefore, a plating layer made of the same noble metal as the bonding wire, such as gold or silver, is provided.

These plating layers are super LS I, LSI, and IC.

As products such as hybrid ICs that have a high bonding density are industrialized, defective bonding in one place will cause a huge loss. It won't happen. Since these plating layers are usually provided on electrically independent parts, it is impossible to form them by electrolytic plating method C2, so electroless plating method is often suitable.

Next, to explain the conventional electroless plating method for golden metals made of gold and silver, when performing electroless plating of these precious metals,
The base is an electroless nickel plating layer formed on the part to be plated. Limbia (nickel plating containing about 10% of nickel plating) formed with an electroless nickel plating solution using salt) is commonly used because it is easy to obtain strong adhesion.

The plating solution for displacing gold or silver on this phosphorus-containing electroless nickel plating layer includes a complexing agent such as a plating solution for gold, and a plating solution for copper. It is known that the composition consists mainly of a small amount of metal compounds.

To perform displacement plating using a plating solution having the above composition, a displacement plating layer is obtained by immersing the plating solution at a high temperature of usually around 95°C for about 10 minutes. Usually, only a thin plating layer with a thickness of 0.05 to 0.1 pm can be obtained.

For this reason, after displacement plating, thick plating of 1.5 μm or more in the case of gold and 4 μm or more in the case of silver is performed using an electroless plating solution using a reducing agent.

As mentioned above, for example, electroless plating methods for forming bonding films are being established, but they lack quality stability (C).
However, there are problems that make it difficult to industrialize.

The problem is that the bonding yield varies widely due to the weak adhesion between the underlying nickel layer and gold or silver.

That is, when electroless plating is performed on a nickel plating layer using electroless gold using a reducing agent or electroless silver plating solution ζ2, there is no adhesion at all, and if the plating solution has an autocatalytic action, precipitation does not start.

In order to improve this, attempts have been made to coexist with metal group ions such as nickel and cobalt, or to add various surfactants, but there is a point where sufficient adhesion cannot be obtained. It could only be used in small quantities or for short periods of time.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and it is possible to apply gold to a suitable part to be plated even within extremely restricted conditions, such as automatic bonding with a noble metal wire C2 made of gold or silver. The purpose of the present invention is to provide an electroless plating method that enables the formation of silver and silver.

[Summary of the invention]

That is, the present invention includes a step of forming an electroless nickel plating layer containing phosphorus on a plating target area on which a base is formed, and a process of displacing gold or silver containing a C diselenium compound on the electroless nickel plating layer. Forming a gold or copper displacement plating layer using a liquid, and further depositing a desired thickness of gold or copper on this gold or silver displacement plating layer using a gold or silver electroless plating solution C2 using a boron compound as a reducing agent. This is an electroless plating method characterized by comprising at least a step of forming an electroless plating layer of silver.

[Embodiments of the invention]

Next, a second embodiment of the present invention will be described.

First, a tungsten paste is printed as a substrate to be plated to form a part to be plated, and then a tungsten layer as a base is sintered at about 1500°C. Prepare an alumina substrate with

Next (:, This alumina substrate was immersed in hydrochloric acid and then washed with water.
This is a chemical treatment that selectively deposits the next phosphorus-containing electroless nickel plating layer. As the activating liquid for application, activating liquid such as "Activating Liquid No. 3J" manufactured by Nippon Kanigen KK is convenient.

After the catalyst has been applied, the phosphorus-containing electroless nickel plating is coated with several μm of phosphorus-containing electroless nickel using water aL, the company's "Blue Schumer" solution, etc.
Let's do m2.

Next, a gold plating layer having a thickness of about 0.1 μm is formed on this electroless nickel plating layer using a displacement gold plating solution having the following liquid composition.

This selenium solution is prepared in advance with potassium cyanide 012fi/l.
.

A mixture of 0.51/13 selenium oxide and IgN was used. The displacement plating conditions were immersion at about 95° C. for 10 minutes.

After displacement gold plating, wash with water and immediately conduct gold plating within the range of 1.5 to 2.0 μm using an electroless gold plating solution (2) using a boron compound as a reducing agent. "Aurax liquid" made by Japan Engel Häld KK is known, and thick gold plating is easy.The conditions for this gold plating are usually about 2 μm / 2 μm at 75°C with air agitation.
A plating speed of Hr is obtained.

In this way, a large number of bonding target parts having matte gold surfaces were formed on the alumina substrate.

The results of continuous automatic bonding of several hundred points using gold wire as described above for the bonded parts showed no problems, the tensile strength was uniform, and there were no accidents in which the wire broke from the gold-plated surface. .

On the other hand, a gold plating layer obtained with a substitution gold plating solution that does not contain gelatin and selenium solution peels off easily in a peel test using cellophane tape, and it is possible to achieve thick plating. However, when trying to apply thick gold plating, a blistering problem occurred, making it unusable.

Next, a second embodiment of the present invention will be described. However, since the method for forming the substrate to be plated and the phosphorus-containing nickel plating layer is the same as in the first embodiment, the explanation will be omitted.

A silver plating layer is formed on the electroless nickel plating layer using a displacement silver plating solution having the following solution composition.

The selenium solution used was the mixed solution shown in the first example.

This displacement silver plating was carried out at 95° C. for about 2 minutes, and immediately after washing with water for 6 hours, plating was carried out using an electroless silver plating solution using a boron compound as a reducing agent until a plating thickness of about 4 μm was obtained.

As this electroless silver plating solution, a solution with the following composition is used.
This is carried out at 60°C for about 1 hour.

The obtained layer to be bonded has a uniform appearance, no r, and a first layer.
Similar to the example, the bonding film has a uniform appearance;
As with the f441 example, it was found that the bonding workability and strength were uniform.

As mentioned above, the displacement plating solution to which gelatin and selenium solution have been added can be used for a long period of time with good reproducibility by replenishing the consumed gold, heptalene, etc. In addition to those in the examples, organic acid salts such as sodium nightstone and sodium citrate, phosphates, etc. can be substituted.

In addition, the underlying nickel plating solution and thick gold or silver plating solution are not limited to those in the examples, and plating solutions that use boron hydride compounds and their derivatives as reducing agents are optimal. There are boron sodium, etc., and various compositions are known.

The above-mentioned displacement plating containing a selenium solution or a selenium compound is not necessarily limited to a part of the film to be bonded, and it goes without saying that it can be widely used for decorative purposes, anti-corrosion plating, etc.

A displacement plating solution containing different metals such as nickel and cobalt and various surfactants may also be considered.

That is, for example, the plating liquid has the following composition.

The gold plating solution is a silver plating solution, and the selenium solution is the same as in the first and second embodiments.

Moreover, the selenium liquid is the same liquid as in the first and second embodiments,
If a small amount of selenium is present in this selenium solution, the adhesion to the electroless nickel plating layer containing phosphorus will be improved.

So there is no need to add too much.

The improvement of adhesion by adding gelatin and selenium solution is
This is thought to be due to the adsorption effect on the electroless nickel layer. This adsorption effect is due to the fact that gelatin with selenium ions as its nucleus selectively gathers on the bare surface of the electroless nickel layer, and prevents the adsorption of substances that inhibit the interfacial bonding between nickel and gold or silver. This is an action that involves the replacement of .

〔Effect of the invention〕

As mentioned above, according to the present invention, the adhesion to the phosphorus-containing electroless nickel plating layer is significantly improved by adding a selenium compound to the gold or silver displacement plating solution C:1. Since an electrolytically plated layer is obtained, the reliability of the bonded portion of the semiconductor envelope can be improved.

Agent Patent Attorney Inoue - Male

Claims (2)

[Claims] (1) The process of forming an electroless nickel plating layer on the part to be plated on which the base has been formed, and the step of forming an electroless nickel plating layer on this electroless nickel plating layer (gold or silver using a gold or silver displacement plating solution containing nigeratin and a selenium compound). An electroless plating method comprising at least the step of forming a displacement plating layer. (2) On the part to be plated on which the base has been formed (a step of forming a nickel plating layer and a gold or silver displacement plating solution containing gelatin and selenium compounds on this electroless nickel plating layer) A process of forming an electroless displacement plating layer of gold or silver, and electroless plating of gold or silver with a certain thickness using a gold or silver electroless plating solution using a boron compound as a reducing agent on this electroless displacement plating layer. An electroless plating method comprising at least two steps: forming a layer.