JPH07268640A - Electroless gold plating method - Google Patents

Abstract

(57) [Summary] [Purpose] The establishment of a method for forming a thick gold plating film with good adhesion using a substitution type electroless gold plating solution. [Structure] A Ni-P plating base is formed on the material, and the N
In an electroless gold plating method for forming a gold plating film on an i-P plating base using a substitutional gold plating solution, Ni-
The P plating base is made into two or more Ni-P plating layers, and a metal nobler than Ni (for example, Au, A
g, Pt, Ru, Pd and Rh) is formed as a barrier layer. As shown in FIG. 1, a barrier layer made of a metal nobler than Ni is provided in the Ni-P plating film, and even if corrosion occurs, it is stopped there to prevent the corrosion from reaching the material straight. A thick Au plating film with a good adhesion of 0.3 μm or more can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of electroless gold plating by substitution, and is directed to weight reduction, downsizing and high reliability particularly for various semiconductor devices which are currently rapidly developing. The present invention relates to an electroless gold plating method capable of forming a thick gold plating film having a good adhesiveness of 0.3 to 0.5 μm on a printed circuit board for the purpose of wire bonding in a printed circuit.

[0002]

2. Description of the Related Art Copper-clad printed circuit boards, lead frames,
As typified by TAB, wire bonding of semiconductor devices and the like, gold electrode formation, etc., gold plating is very often required in electronic devices. For example, in the formation of a gold plating film for the purpose of wire bonding on a printed circuit board, there is no electroless gold plating solution that can obtain the required plating film thickness of 0.3 μm or more. Was.

However, as the pattern becomes finer, electroplating cannot be dealt with anymore, and an electroless plating solution has been demanded. In addition, although a gold plating film is obtained by electroplating for COB of a printed circuit board and is used for wire bonding, electroless gold plating is desired in view of circuit layout. In addition, conventional electro gold plating requires leads in addition to bonding pads and original circuit wiring, whereas electroless gold plating has many advantages such as the fact that these are unnecessary. From these points, there is an urgent need to establish excellent electroless gold plating technology.

The electroless gold plating has a reduction type and a substitution type. The reduction type gold plating solution contains a reducing agent in the plating solution, while the substitution type gold plating solution utilizes the difference in ionization tendency. Until now, thick plating (0.3 ~
0.5 μm) has been subjected to reduction gold plating. However, since it is an alkaline bath, it adversely affects the resist film and the substrate, so a neutral bath is required.

Under these circumstances, the substitution gold plating solution has been developed as a neutral bath in the industry including the applicant. For example, JP-A-4-314870 and JP-A-5-22
See 87541, JP-A-5-295558 and the like. The substitutional gold plating involves melting an object to be plated, and gold is deposited by receiving electrons, so that the underlying material and the material are necessarily corroded. A printed circuit board is generally formed by forming a Ni—P plating base on a copper material and then forming a gold plating film. Since substitutional gold plating is established by corroding the Ni-P base, not only the base but also the material is corroded as the corrosion progresses. This causes adverse effects such as poor appearance and poor adhesion, contamination of the liquid, and contamination of the gold film. That is, since it is substitutional type plating, since it is deposited while melting the underlayer, corrosion of Ni-P and copper of the material can occur. Since the Ni—P base is columnar crystal precipitation, the portion with a low P% erodes quickly, and the corrosion reaching the copper in the vertical direction progresses. From this, the copper surface under the Ni-P film is corroded, and the adhesion with Ni-P is deteriorated.

Therefore, the displacement plating is limited to a thin thickness to reduce erosion, and then a thick gold plating is performed using a reduction type plating solution to obtain a required gold film thickness of 0.3 μ to 0.5 μ.
The method of obtaining m is generally adopted. On the other hand, in order to obtain thickening only by substitution, two-layer plating of a low P-containing Ni layer / high P-containing Ni layer in which P% in the Ni-P coating is changed has been proposed. The lower the P% of the Ni-P coating, the more Ni
It is because the elution of gold is easy to proceed and the gold is easily replaced, but it is focused on that the dissolution is suppressed when the P% is increased. For example, Circuit Technology Vol. 8 N
o. 6 (1993) pp. 477-478. However, stabilizing the P% of the Ni-P coating,
It is not realistic from the management aspect of the two types of baths.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to use a Ni-P plating solution which is usually used, and a substitution type electroless gold plating solution which does not have the above-mentioned problems. It is to establish a method for forming a thick gold plating film having good properties.

[0008]

The present inventor has found that the same Ni
-P plating film from the same bath, Ni-P
As a method of enhancing the corrosion resistance of the underlayer, it was conceived to interpose a metal plating layer, which is more precious than Ni-P, as a barrier layer, and as a result of the trial, good results were obtained. Based on this finding, the present invention forms a Ni-P plating base on a material,
In the electroless gold plating method of forming a gold plating film on the Ni-P plating base using a substitutional gold plating solution,
Provided is an electroless gold plating method characterized in that an i-P plating underlayer is made up of two or more Ni-P plating underlayers, and a barrier layer of a metal nobler than Ni is formed between the Ni-P plating underlayers. . This method preferably forms a first Ni-P plated underlayer on a copper material and immerses it in a noble metal solution to form a barrier layer of a metal nobler than Ni on the first Ni-P plated underlayer. It can be embodied by forming a second Ni-P plating underlayer on the barrier layer, and then forming a gold plating film on the second Ni-P plating underlayer using a substitutional gold plating solution. The metal nobler than Ni is preferably selected from the group consisting of Au, Ag, Pt, Ru, Pd and Rh. The gold plating film has a thickness of 0.3-0.
It has a thickness of 5 μm and has excellent adhesion.

[0009]

The lower the P% of the Ni-P coating, the easier the elution of Ni, that is, the easier the gold is replaced. It is preferable that the P% is uniform and layered, but if the P% is non-uniform in the columnar crystals, elution occurs from a place where the P% is low, so that the dissolution locally reaches the material copper and progresses. Will be lost.
On the other hand, if the P% is increased, the dissolution is suppressed, but the gold displacement precipitation is reduced, and the thick gold plating film cannot be obtained. A medium P type Ni-P bath, which generally forms a 6 to 8% P film, is often used, and corrosion will occur as the gold plating thickness increases. As a countermeasure, a barrier layer made of a metal nobler than Ni is provided in the Ni-P plating film, and even if corrosion occurs, it is stopped by the barrier layer to prevent the corrosion from reaching the material straight.

[0010]

[Examples] Examples of materials targeted by the present invention include copper-clad printed boards, lead frames, TABs, semiconductor devices, transparent conductive film circuits, glass, and ceramics. Gold films for wire bonding. Formation, gold electrode formation, etc. are required, and the electric potential includes all things that are baser than gold.

As the Ni-P plating, any of commercially available ordinary Ni-P plating solutions can be used.
P content in the formed Ni-P plating film is 8 to 12%
It is possible to use any of a high P plating solution having a P content of 3 to 7%, a low P plating solution having a P content of 3 to 7%, and a medium P plating solution having a P content of 6 to 8%. In particular, it is recommended to use a medium P plating solution having good solderability. For example, Nicom-N manufactured by Nikko Metal Plating Co., Ltd. has a pH of 4.
5 is a neutral Ni-P plating solution. Plating time 5-2
A film thickness of 1 to 5 μm can be formed in 0 minutes. Ni
-P after degreasing and pickling the copper material prior to P plating
It is preferable to carry out a treatment for applying a noble metal catalyst such as d.

The barrier layer metal may be any metal that is more noble than Ni-P, and may be an extremely thin layer having a thickness of, for example, 0.01 to 5 μm so as not to impair the adhesion with the upper and lower Ni-P layers. Good. Au, Ag, Pt, Ru, Pd, R
h or the like can be used. Some examples of plating baths and their use conditions are given below: (1) Pt plating solution Chloroplatinic acid chloride: 0.2 to 0.8 g / l (Pt amount) pH: 1 to 3 Solution temperature: Room temperature Treatment time: 10 to 50 seconds (2) Ru plating solution Ruthenium sulfate: 2 to 10 g / l (Ru amount) pH: 1 to 3 Liquid temperature: room temperature Treatment time: 2 to 10 seconds (3) Pd plating solution: Chloride Palladium: 0.2 to 1.0 g / l (Pd amount) pH: 0.5 to 3 Liquid temperature: 20 to 50 ° C. Treatment time: 10 seconds to 3 minutes (4) Rh plating solution: Rhodium sulfate: 0.1 ~ 0.6 g / l (Rh amount) pH: 1 to 2.5 Solution temperature: 40 ° C Treatment time: 2 to 15 seconds (5) Au plating solution: Potassium gold cyanide: 0.1 to 0.6 g / l (Au amount) pH: 4 to 5 Liquid temperature: room temperature Treatment time: 5 to 30 seconds

As the electroless gold plating solution by substitution, various kinds are known so far, as mentioned in the first document. For example, a displacement gold plating solution in which an alkali cyanide stabilizer or the like is added to a soluble gold salt is known. In the present invention, any of them can be used, but a particularly preferable example of the displacement type gold plating solution is that marketed under the trade name of KG-550. It has the following composition and conditions of use: (A) Composition KAu (CN) ₂ : 0.5-5 g / l Complexing agent: 10-50 g / l pH buffer: 10-150 g / l Additive: 1 ~ 20 ml / l (B) Usage conditions pH: 6 Temperature: 60 ° C Plating thickness: 0.5 μm / 30 minutes

According to the present invention, 0.3 to 0.5 μm thick gold plating having excellent adhesion can be performed. Prior to the displacement gold plating, it is preferable to immerse the Ni-P undercoat in a precious metal solution to perform activation treatment.

Examples and comparative examples are shown below. As an adhesion test, the peeling test is to stick a cellophane tape (made by Nitto Denko) for office work on the surface of a gold-plated printed circuit board, rub it with a cloth roll, hold the end of the tape with your fingertips, and peel off the tape all at once. went. When the Au plating film or the underlying Ni-P has poor adhesion, the plating film adheres to the tape. Further, with respect to some of the samples, the plating state was observed in detail with a scanning electron microscope.

Example 1 A Cu material was plated by the following procedure. (A) 1st Ni-P plating Ni: 5 g / l pH: 4.5 Liquid temperature: 85 ° C. Plating time: 5 minutes Film thickness: 1 μm (B) Rinse with water (C) Pt plating solution immersion Chloroplatinic acid plating solution (Pt: 0.5 g / l) pH: 2 Solution temperature: room temperature Time: 30 seconds (D) Washing with water (E) Second Ni-P plating The same as the first Ni-P plating solution is used. Plating time: 15 minutes Film thickness: 4 μm (F) Washing with water (G) Activation treatment Ruthenium sulfate: 5 g / l (Ru amount) pH: 1.0 Liquid temperature: room temperature Immersion time: 5 seconds (H) Washing with water (I) Substitution Au plating Au: 2 g / l pH: 6 Liquid temperature: 60 ° C. Time: 30 minutes Film thickness: 0.52 μm (J) Washing with water (K) Drying A thick gold plating film of 0.52 μm was thus obtained.
The result of the peeling adhesion test was good, and the cross-section observation showed no erosion reaching the copper material.

(Comparative Example 1) A single layer of Ni-P plating was used without providing a barrier layer (the same Ni-P as in Example 1).
The plating solution was used to form the same thickness as the total thickness of the first and second Ni-P plating), on which 0.55μ
m thick gold plating was applied. The procedure was as follows. (A) Ni-P plating Ni: 5 g / l pH: 4.5 Liquid temperature: 85 ° C. Plating time: 20 minutes Film thickness: 5 μm (B) Washing with water (C) Activation treatment Ruthenium sulfate: 5 g / l (Ru amount ) PH: 1.0 Liquid temperature: room temperature Immersion time: 5 seconds (D) Washing with water (E) Substitution Au plating Au: 2 g / l pH: 6 Liquid temperature: 60 ° C. Time: 30 minutes Film thickness: 0.55 μm (F ) Washing with water (G) Drying

Thus, a thick gold plating film of 0.55 μm was obtained. The result of the peeling adhesion test is poor,
As a result of cross-sectional observation, erosion reaching the copper material was recognized. Figure 2
Shows a scanning electron micrograph of a portion where adhesion failure occurred after the peeling adhesion test. It is observed that the Au layer is peeled off, the underlying Ni-P layer is exposed, and further the Cu material (black portion) underneath is exposed. Fig. 3 shows Ni-P
And shows the erosion status of Cu material. The Ni-P layer has columnar erosion portions running vertically, and the erosion extends to the Cu material.

(Example 2) The noble metal immersion plating between the first and second Ni-P plating shown in Example 1 was performed under the following plating solution and conditions. The other conditions were the same. (C) Immersion in Pd plating solution Palladium chloride plating solution (Pd: 0.6 g / l) pH: 2 Solution temperature: room temperature Time: 2 minutes Thus, a thick gold plating film of 0.5 μm was obtained. The result of the peeling adhesion test was good, and the cross-section observation showed no erosion reaching the copper material. A cross-sectional photograph of the material after plating is shown in FIG. There is no erosion reaching the Cu material, Ni
The columnar corrosion of the -P second layer stops at the Pd barrier layer and does not extend therebelow.

(Example 3) The noble metal immersion plating between the first and second Ni-P plating shown in Example 1 was performed under the following plating solution and conditions. The other conditions were the same. (C) Immersion in Au plating solution Potassium cyanide plating solution (Au: 0.5 g / l) pH: 4.5 Solution temperature: room temperature Time: 15 seconds Thus, a thick gold plating film of 0.48 μm was obtained.
The result of the peeling adhesion test was good, and the cross-section observation showed no erosion reaching the copper material.

(Example 4) The noble metal immersion plating between the first and second Ni-P plating shown in Example 1 was performed under the following plating solution and conditions. The other conditions were the same. (C) Immersion in Rh plating solution Rhodium sulfate plating solution (Rh: 0.3 g / l) pH: 1.5 Solution temperature: 40 ° C. Time: 8 seconds Thus, a thick gold plating film of 0.44 μm was obtained.
The result of the peeling adhesion test was good, and the cross-section observation showed no erosion reaching the copper material.

[0022]

EFFECTS OF THE INVENTION By interposing a barrier layer during Ni-P undercoating, erosion that reaches the material during gold plating is suppressed, so that a thick Au plating film with good adhesion can be obtained. On printed circuit boards for wire bonding, a thick gold plating film of 0.3 μm or more can be obtained, which enables plating on finer patterns, aiming at weight reduction, downsizing, and high reliability. This greatly contributes to the manufacture of printed circuits and the like.

[Brief description of drawings]

FIG. 1 is an electron micrograph of the cross-sectional metallographic structure of the material after plating, showing that there is no erosion reaching the Cu material and the corrosion of Ni—P is stopped at the Pd barrier layer.

FIG. 2 shows a scanning electron micrograph of a metal structure of a portion where adhesion failure occurs after a peeling adhesion test.

FIG. 3 is an electron micrograph of a metal structure of a cross section showing the erosion state of Ni-P and Cu materials, in which the erosion portion runs vertically in a columnar shape in the Ni-P layer, and the erosion extends to the Cu material. Indicates the situation.

Claims (4)

[Claims] 1. A Ni-P plating base is formed on a material,
In the electroless gold plating method of forming a gold plating film on the Ni-P plating base using a substitutional gold plating solution,
A method of electroless gold plating, which comprises forming the i-P plating base layer into two or more Ni-P plating base layers and forming a barrier layer of a metal nobler than Ni between the Ni-P plating base layers. 2. A first Ni—P plating underlayer is formed on a copper material, a barrier layer of a metal nobler than Ni is formed on the first Ni—P plating underlayer, and a second Ni layer is formed on the barrier layer.
A non-electrolytic gold plating method, which comprises forming a -P plating underlayer, and then forming a gold plating film on the second Ni-P plating underlayer using a substitutional gold plating solution. 3. A metal that is more precious than Ni is Au, Ag, Pt,
3. The electroless gold plating method according to claim 1, wherein the electroless gold plating method is selected from the group consisting of Ru, Pd and Rh. 4. The electroless gold plating method according to claim 1, wherein the gold plating film is a thick plating having a thickness of 0.3 to 0.5 μm, and has excellent adhesion.