JP2000178755A - Substitutional electroless gold plating liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a gold plated coating film having excellent adhesion property even to an electroless nickel-boron plated coating film by specifying the concentration of gold ion, the concentration of hydroxy carboxylic acid and the pH of an aq. solution containing a cold compound and a camplexing agent. SOLUTION: The concentration of gold ion is >=0.008 mol/l, preferably 0.01-0.02 mol/l, the concentration of hydroxy carboxylic acid is <=0.01 mol/l, preferably 0.003-0.007 mol/l and the pH is <=6.5, preferably 5-6. The gold compound is a water soluble gold compound such as cyanoaurate, chloroaurate, potassium or ammonium chloroaurate and as the aomplexing agent, hydroxy carboxylic acids, aliphatic carboxylic acids, amino carboxylic acids and amines are preferable in the case of applying the electroless plating on a metallic base material containing nickel. In a process necessary for the electroless nickel- boron plating, a substitutional gold plating is performed without electroless nickel-phosphorus plating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a substitution type electroless gold plating solution and an electroless gold plating method.

[0002]

2. Description of the Related Art In a wiring board such as a printed board, a gold plating film is formed on a component mounting portion, a terminal portion and the like of a wiring circuit in order to improve solderability and wire bonding property. In this case, generally, nickel plating is performed as a base film of gold plating for the purpose of improving corrosion resistance of a wiring circuit, preventing gold diffusion, and the like.

In recent years, high integration of semiconductor elements has rapidly progressed, and a wiring board on which the semiconductor elements are mounted has been required to have a high wiring density. Currently, electrically independent wiring patterns are mainly used. In such a case, since a portion where a plating film cannot be formed by electroplating occurs, an electroless plating method is used. Generally, after forming an electroless nickel-phosphorous film, electroless gold plating is performed. .

In general, a circuit portion of a ceramic substrate is formed by printing and baking a paste containing metal particles such as tungsten and molybdenum, and the surface of a metal such as tungsten and molybdenum is inactive. Yes, electroless nickel-phosphorus plating does not deposit.
For this reason, it is necessary to perform electroless nickel-boron plating with good deposition properties on a circuit formed using tungsten, molybdenum, or the like.

[0005] In addition, in order to improve the wire bonding property, a high coating hardness is required, and an electroless nickel-phosphorous coating (Vickers hardness of about 550 Hv) is required.
It is desired to form an electroless nickel-boron plating film (Vickers hardness about 800 Hv) having a higher hardness.

[0006] Under these circumstances, electroless nickel-
When a gold plating film is formed on a boron plating film using a conventional substitution type electroless gold plating solution, sufficient adhesion between the nickel-boron plating film and the gold plating film cannot be obtained. For this reason, a method of performing electroless nickel-boron plating, further performing electroless nickel-phosphorus plating, and then performing substitutional electroless gold plating is adopted, and the working process becomes very complicated. There is a problem.

[0007]

SUMMARY OF THE INVENTION The main object of the present invention is to:
An object of the present invention is to provide a substitution type electroless gold plating solution capable of forming a gold plating film having good adhesion on an electroless nickel-boron plating film.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above problems, and as a result, have found that a substitution type electroless gold plating solution containing a gold compound and a complexing agent has a gold ion concentration of 0.1.
A plating solution that simultaneously satisfies all the conditions of 008 mol / l or more, hydroxycarboxylic acid concentration of 0.01 mol / l or less, and pH of 6.5 or less is used, and the electroless gold plating solution is coated while maintaining these conditions. When it comes into contact with the plating, it has been found that a gold plating film having good adhesion can be formed on the electroless nickel-boron plating film, and the present invention has been completed.

That is, the present invention provides the following substitution type electroless gold plating solution and electroless gold plating method.

(1) An aqueous solution containing a gold compound and a complexing agent, wherein the concentration of gold ions is at least 0.008 mol / l, the concentration of hydroxycarboxylic acids is at most 0.01 mol / l, p
A substitution-type electroless gold plating solution, wherein H is 6.5 or less.

(2) The substitutional electroless gold plating solution according to the above item 1, which is a plating solution for forming a gold plating film on an electroless nickel-boron plating film.

(3) A substitution type electroless gold plating solution containing a gold compound and a complexing agent is prepared by adding a gold ion concentration of 0.008 mol /
l or more, concentration of hydroxycarboxylic acid 0.01 mol /
1. An electroless gold plating method on an electroless nickel-boron plating film, wherein the electroless nickel-boron plating film is brought into contact with an object to be plated, while maintaining the pH at not more than 1 and a pH of 6.5 or less.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The substitution type electroless gold plating solution of the present invention is an aqueous solution containing a gold compound and a complexing agent.

As the gold compound, a known plating solution used as a gold supply source can be used as it is. Specifically, water-soluble gold compounds such as potassium cyanide, gold cyanide such as potassium potassium cyanide, and potassium potassium cyanide, chloroauric acid, potassium salts of chloroauric acid, and ammonium salts can be used. In addition, even gold compounds having relatively low solubility such as gold cyanide, gold oxide, and gold hydroxide can be used as a gold ion source by forming a cyan complex in water by mixing with a cyan compound. These gold compounds can be used alone or in combination of two or more.

As the complexing agent, a compound which forms a complex compound with a metal component which dissolves in the plating solution by replacing with gold may be used depending on the kind of the base material forming the electroless gold plating film. . Examples of such compounds include inorganic acids such as phosphoric acid, boric acid, and polyphosphoric acid, and inorganic acids such as alkali metal salts (sodium salt, potassium salt) and ammonium salt of these inorganic acids; citric acid, gluconic acid, and lactic acid. And hydroxycarboxylic acids such as malic acid, tartaric acid and glycolic acid; alkali metal salts (sodium salt, potassium salt) and ammonium salt of these hydroxycarboxylic acids; succinic acid, fumaric acid, acetic acid, butyric acid and malon Aliphatic carboxylic acids such as acids, propionic acid, oxalic acid, formic acid, adipic acid, and maleic acid; and aliphatic carboxylic acids such as alkali metal salts (sodium salts and potassium salts) and ammonium salts of these aliphatic carboxylic acids; , Alanine, leucine, glutamic acid, aspartic acid, ethylenediaminetetraacetic acid (EDT ), Aminocarboxylic acids such as nitrilotriacetic acid (NTA), aminocarboxylic acids such as alkali metal salts (sodium salts, potassium salts) and ammonium salts of these aminocarboxylic acids; ethylenediamine, triethanolamine, tetramethylenediamine, diethylenetriamine And the like can be exemplified, and these may be appropriately selected and used.

In particular, when electroless gold plating is performed on a metal material containing nickel such as nickel, nickel-boron, nickel-phosphorus, etc., a compound which forms a complex compound with nickel may be used as a complexing agent. . Preferred examples of such a complexing agent include hydroxycarboxylic acids, aliphatic carboxylic acids, aminocarboxylic acids, and amines among the above complexing agents.

The complexing agents can be used alone or in combination of two or more.

The complexing agent concentration in the plating solution of the present invention is
Although not particularly limited, it is generally sufficient to set the amount to about 0.01 to 3 mol / l, preferably to about 0.05 to 0.5 mol / l.

The above-mentioned complexing agent not only functions to form a complex compound with the metal component eluted in the plating solution, but also acts as a buffering agent and functions to suppress the pH fluctuation of the plating solution. Seem.

The electroless gold plating solution of the present invention must have a gold ion concentration of 0.008 mol / l or more.
By setting the gold ion concentration to 0.008 mol / l or more, a gold plating film having good adhesion can be formed on the nickel-boron electroless plating film.

The upper limit of the gold ion concentration is not particularly limited, but is usually preferably about 0.03 mol / l.

The concentration of gold ions is preferably 0.01 to
It may be about 0.02 mol / l.

In the electroless gold plating solution of the present invention, it is necessary that the concentration of the hydroxycarboxylic acid be 0.01 mol / l or less. Conventional substitution-type electroless gold plating solutions generally have a strong complexing power for nickel in most cases when plating on nickel or a nickel alloy in order to promote the substitution between nickel and gold. Carboxylic acids are blended and the concentration is 0.0
Generally, it is about 5 to 1 mol / l. According to the plating solution of the present invention, even when hydroxycarboxylic acids are not mixed at all or when hydroxycarboxylic acids are compounded, the concentration is adjusted to 0.01 mol / l or less. It has become possible to form a gold plating film having good adhesion at a sufficient deposition rate on the electrolytic nickel-boron plating film. The concentration of hydroxycarboxylic acids refers to hydroxycarboxylic acids which are carboxylic acids containing a hydroxyl group such as citric acid, gluconic acid, lactic acid, malic acid, tartaric acid, and glycolic acid, and alkali metal salts thereof (sodium salt, potassium salt). Salt), and the total concentration of hydroxycarboxylates such as ammonium salts in the plating solution.

Hydroxycarboxylic acids need not be added at all, but in order to maintain good adhesion and to improve the deposition rate of gold plating, the concentration of hydroxycarboxylic acids should be 0.003 to 0. It is preferably about 0.007 mol / l.

Further, the plating solution of the present invention has a pH of about 6.5 or less in order to form a gold plating film having good adhesion. The lower limit of the pH is not particularly limited, and as the pH decreases, the adhesiveness tends to improve.
If the pH is too low, harmful cyan gas is likely to be generated. Therefore, the pH is preferably set to about 4.5 or more.
It is more preferable to be about H4.8 or more. In particular, p
It is preferable to use H5 in the range of about 5 to 6.

The plating solution of the present invention may be adjusted to a pH value in the above range by appropriately selecting the types of the gold compound and the complexing agent and the amounts thereof, or, if necessary, The pH may be adjusted to the above range by adding an alkali hydroxide such as sodium hydroxide, potassium hydroxide or ammonium hydroxide, or a mineral acid such as sulfuric acid, phosphoric acid or boric acid.

If necessary, a substance for maintaining the stability of gold ions may be added to the plating solution of the present invention. Examples of such a substance include cyanide compounds such as potassium cyanide and ammonium cyanide. The concentration in the plating solution may be a concentration necessary for forming a gold complex, depending on the type and concentration of the gold compound used, and may be added in excess to stabilize the gold complex. .

In order to form a gold plating film using the electroless gold plating solution of the present invention, the object to be plated may be brought into contact with an electroless gold plating solution satisfying the above conditions.
What is necessary is just to immerse the object to be plated in the plating solution.

The temperature of the plating solution when performing electroless gold plating is preferably about 55 to 95 ° C.,
More preferably, the temperature is about 2 ° C.

The material to be plated may be any material as long as the surface of the surface where the gold plating film is formed is made of a metal which undergoes a substitution reaction with gold. Examples of such a metal that undergoes a substitution reaction with gold include metals having a lower potential than gold, such as nickel, nickel alloys, palladium, palladium alloys, copper, silver, and iron.

The plating solution of the present invention is used to form an electroless gold-plated film on an electroless nickel-phosphorous plating film, an electroless nickel-boron plating film, and an electro-nickel plating film used for electronic parts and printed wiring boards. It can be suitably used for forming. In particular, it is possible to form a gold plating film having excellent adhesion on an electroless nickel-boron plating film, which was difficult to form a gold plating film having good adhesion with a conventional substitution type electroless gold plating solution. It is particularly advantageous in that respect.

In order to form an electroless gold plating film having good adhesion on an object to be plated on which an electroless nickel-boron plating film is formed, a gold ion concentration of 0.008 mol / l or more and a hydroxycarboxylic acid A substitution-type electroless gold plating solution that simultaneously satisfies all the conditions of a concentration of 0.01 mol / l or less and a pH of 6.5 or less is used. l or more,
Concentration of hydroxycarboxylic acids 0.01 mol / l or less,
It is necessary to maintain the plating solution within a pH range of 6.5 or less. If any of the conditions is out of this range during the formation of the plating film, the adhesion of the formed gold plating film is reduced.

To maintain the gold ion concentration in the above range,
It is sufficient to appropriately supply gold ions using a compound similar to the above-described gold compound.

In order to maintain the pH in the above range, the pH may be appropriately adjusted using the above-mentioned alkali hydroxide, mineral acid or the like.

[0035]

According to the substitution-type electroless gold plating solution of the present invention, it is possible to sufficiently coat an electroless nickel-boron plating film, which has conventionally been difficult to form a replacement gold plating film having good adhesion. A gold plating film having excellent adhesion can be formed at a high deposition rate.

Therefore, electroless nickel-phosphorous plating is performed in a process requiring electroless nickel-boron plating, which is typified when a ceramic substrate on which a circuit is formed with a paste containing tungsten or molybdenum is to be processed. Without this, it is possible to perform the replacement gold plating directly on the electroless nickel-boron plating film, and the process can be shortened and the cost can be reduced.

[0037]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples.

Example 1 A printed circuit board (5
cm × 5 cm) (effective plating area 15 cm ² ) was used as an object to be treated, and this was immersed in a degreasing solution (trade name: OPC Acid Clean 115: manufactured by Okuno Pharmaceutical Co., Ltd.) to be degreased, and the amount was 100 g / l Soft etching was performed by immersion in an aqueous solution of sodium sulfate, and then smut was removed by immersion in an aqueous solution of 10% sulfuric acid. Subsequently, a catalyst solution (trademark: I
CP Axela: manufactured by Okuno Pharmaceutical Co., Ltd.), and a catalyst for electroless nickel-boron plating is applied. )) To perform electroless nickel-boron plating. Thereby, an electroless nickel-boron plating film having a thickness of 3 μm was formed.

Next, a substitution type electroless gold plating solution having the following composition was adjusted to the pH value and temperature shown in Table 1, and the printed wiring board was immersed in the solution and the gold plating film was formed on the nickel-boron plating film. Was formed.

Potassium gold cyanide 0.015 mol / l Tartaric acid 0.005 mol / l Boric acid 0.2 mol / l EDTA · 2Na 0.1 mol / l 28% aqueous ammonia Necessity for adjusting to predetermined pH For each of the formed plating films, the deposition rate and the adhesion of the gold plating film were evaluated. The plating film thickness was measured with a fluorescent X-ray microscopic part thickness meter (“SFT-8000” manufactured by Seiko Electronics Industry Co., Ltd.). Evaluation of adhesion is based on JI
According to the 15.1 tape test method of the adhesion test method of SH-8504 plating, an adhesive tape was stuck on the plating surface, peeled off vigorously, and the presence or absence of peeling of the gold plating film was determined. These results are also shown in Table 1 below.

[0041]

[Table 1]

As is clear from the above results, according to the electroless gold plating solution having the above composition, the gold plating film having good adhesion on the nickel-boron plating film in all the pH ranges shown in Table 1. Could be formed.

Comparative Example 1 Electroless gold plating was carried out in the same manner as in Example 1 except that a substitution type electroless gold plating solution having the following composition was used and the pH and temperature were adjusted as shown in Table 2 below. Was.

Potassium gold cyanide 0.015 mol / l Tartaric acid 0.05 mol / l Boric acid 0.2 mol / l EDTA · 2Na 0.1 mol / l 28% ammonia water Necessity for adjusting to a predetermined pH For each of the formed plating films, the deposition rate and the adhesion of the gold plating film were evaluated in the same manner as in Example 1.
The results are shown in Table 2 below.

[0045]

[Table 2]

As is apparent from the above results, a plating solution containing 0.05 mol / l of tartaric acid, which is a hydroxycarboxylic acid, can form an adhesive gold plating film on a nickel-boron plating film. Did not.

Example 2 A substitution type electroless gold plating solution having the following composition was prepared at a solution temperature of 90 ° C.
Except for using H5.5, electroless gold plating was performed in the same manner as in Example 1.

Potassium gold cyanide 0.015 mol / l Citric acid 0.005 mol / l Succinic acid 0.1 mol / l Triethanolamine 0.1 mol / l 28% aqueous ammonia for adjusting to pH 5.5 Required amount For each of the formed plating films, the deposition rate and the adhesion of the gold plating film were evaluated in the same manner as in Example 1.
The results are shown in Table 3 below.

[0049]

[Table 3]

As is clear from the above results, according to the electroless gold plating solution of the present invention, a gold plating film having good adhesion was obtained regardless of the film thickness.

Since the surface area of the object to be plated is small,
After completion of the plating for 120 minutes, the concentration of gold ions, the concentration of citric acid, and the pH were almost the same as those at the start of plating, and during the plating treatment, these conditions were kept almost the same as those at the start of plating.

Comparative Example 2 A substitution-type electroless gold plating solution having the following composition was prepared at a solution temperature of 90.degree.
Except for using H5.5, electroless gold plating was performed in the same manner as in Example 1.

Potassium gold cyanide 0.015 mol / l Citric acid 0.05 mol / l Succinic acid 0.1 mol / l Triethanolamine 0.1 mol / l 28% aqueous ammonia For adjusting to pH 5.5 Required amount For each of the formed plating films, the deposition rate and the adhesion of the gold plating film were evaluated in the same manner as in Example 1.
The results are shown in Table 4 below.

[0054]

[Table 4]

As is apparent from the above results, according to the plating solution containing 0.05 mol / l of citric acid, which is a hydroxycarboxylic acid, even when a thin plating film of about 0.07 μm is formed. In addition, the adhesion of the gold plating film was insufficient.

Example 3 A substitution type electroless gold plating solution having the following composition was prepared as shown in Table 5 below.
The gold ion concentration was changed in the range described in
Electroless gold plating was performed in the same manner as in Example 1 except that the temperature was set at 5.5 ° C. and the pH was 5.5.

Potassium gold cyanide 0.003 to 0.02 mol / l Tartaric acid 0.005 mol / l Glycine 0.1 mol / l EDTA · 2Na 0.1 mol / l 28% aqueous ammonia Adjust to pH 5.5 For each of the formed plating films, the deposition rate and the adhesion of the gold plating film were evaluated in the same manner as in Example 1.
The results are shown in Table 5 below.

[0058]

[Table 5]

As is clear from the above results, when the concentration of gold ions in the plating solution was 0.008 mol / l or more, a gold plating film having good adhesion could be formed on the nickel-boron plating film. When the gold ion concentration was lower than this, the adhesion of the gold plating film became insufficient.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K022 AA42 BA03 BA04 BA14 CA06 CA28 DA01 DA03 DB03 DB04 DB07 5E343 BB23 BB24 BB55 CC46 CC71 CC78 DD33 GG11 GG20

Claims (3)

[Claims] 1. An aqueous solution containing a gold compound and a complexing agent, wherein the concentration of gold ions is 0.008 mol / l or more, the concentration of hydroxycarboxylic acids is 0.01 mol / l or less, and the pH is 6.5 or less. A substitution type electroless gold plating solution, characterized in that: 2. The substitution type electroless gold plating solution according to claim 1, which is a plating solution for forming a gold plating film on an electroless nickel-boron plating film. 3. A substitution-type electroless gold plating solution containing a gold compound and a complexing agent, a gold ion concentration of 0.008 mol / l or more, a hydroxycarboxylic acid concentration of 0.01 mol / l or less, and a pH of 6.5. A method for electroless gold plating on an electroless nickel-boron plating film, wherein the method is brought into contact with an object to be plated on which the electroless nickel-boron plating film is formed, while maintaining the following.