JP2001192848A - Electroless nickel plating solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroless nickel plating solution having a good pattern precipitation and the corrosion resistance of a plating film to be deposited. SOLUTION: As to this electroless nickel plating solution, in an electroless nickel plating solution containing aqueous nickel salt, a reducing agent and a complexing agent, a sulfur-containing compound having a group expressed by the formula (1) is incorporated as an additive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an electroless nickel plating solution and an electroless nickel plating method.

[0002]

2. Description of the Related Art Conventionally, as a surface treatment for an electronic component, particularly for a portion of a printed wiring board to be subjected to soldering, bonding, and the like, a process of forming an electroless nickel plating film and then performing displacement gold plating is widely used. Is being done.

However, in recent years, when a conductive film is formed into a fine pattern and a plating film is formed with a conventional electroless nickel plating solution, plating is performed around the circuit at a portion where the pattern width of the conductive circuit is narrow. The so-called spread of the deposited plating and the so-called step plating, in which the plating is thinner at the end face and the tip portion of the circuit than at other portions, are likely to occur. In particular, recently, a printed circuit board having a very fine circuit pattern having a line width of 25 μm and a pattern width of 25 μm has been manufactured, and at present the conventional electroless nickel plating solution cannot sufficiently cope with it.

As an electroless nickel plating solution which has improved the above disadvantages, for example, Japanese Patent Application Laid-Open No. 8-269726 discloses an electroless nickel plating solution to which a specific sulfur compound having an SS bond is added. . However, with such an electroless nickel plating solution to which a specific sulfur compound has been added, improvements in plating spread and step plating have been observed, and the pattern deposition properties that can form a uniform plating film only on the required pattern portions have been slightly improved. However, the effect is not fully satisfactory. Moreover, the sulfur compound has poor heat resistance stability, and is decomposed and loses its effect when added to an electroless nickel plating solution and left for several hours after heating, which makes industrial use difficult.

Further, when the above sulfur compound is added, although the pattern deposition property is slightly improved, there is also a problem that the corrosion resistance of the formed electroless nickel plating film is remarkably reduced. For example, 0.1% on the electroless nickel plating film
After forming the replacement gold plating film of about μm, if the gold plating film is peeled off, partial or complete blackening of the nickel plating film may be observed. Objects are often detected. Further, even when blackening is not observed, unevenness may be observed in visual observation in some cases. When this portion is observed with an electron microscope, nickel is often strongly corroded. Such a phenomenon is likely to occur because the underlying nickel plating film is strongly or partially corroded by the displacement gold plating treatment, which may damage the adhesion between the nickel plating and the gold plating, or may cause poor soldering.
It may cause bonding failure.

[0006] From the above background, there is a demand for an electroless nickel plating solution having excellent pattern deposition properties and excellent corrosion resistance of a formed film.

[0007]

SUMMARY OF THE INVENTION The main object of the present invention is to:
An object of the present invention is to provide an electroless nickel plating solution having good pattern deposition properties and good corrosion resistance of a plating film to be formed.

[0008]

Means for Solving the Problems The present inventor has made intensive studies in order to solve the problems of the prior art as described above. As a result, by adding a sulfur-containing compound containing a group having a specific structure to an electroless nickel plating solution containing a water-soluble nickel salt, a reducing agent and a complexing agent, the pattern deposition property is greatly improved, and a fine circuit is formed. Even in the case of a printed wiring board having a pattern, it has been found that plating deposition and step plating hardly occur outside the circuit pattern, and that the corrosion resistance of the obtained plating film is greatly improved, and the present invention is completed here. Reached.

That is, the present invention provides the following electroless nickel plating solution and electroless nickel plating method. 1. In an electroless nickel plating solution containing a water-soluble nickel salt, a reducing agent and a complexing agent, the formula

[0010]

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An electroless nickel plating solution containing a sulfur-containing compound having a group represented by the formula as an additive. 2. Item 1 wherein the sulfur-containing compound is at least one compound selected from trithiocarbonates, xanthogenic acids, dithiocarbamic acids, dithiocarboxylic acids, rhodanins, mercaptothiazolines and thiurams.
Electroless nickel plating solution described in 1. 3. The sulfur-containing compound is trithiocarbonate, a soluble salt thereof,
O-alkylxanthogenic acid, its soluble salt, dialkyldithiocarbamic acid, its soluble salt, 1-pyrrolidinedithiocarbamic acid, its soluble salt, cyclopentamethylenedithiocarbamic acid, its soluble salt, phenyldithiocarbamic acid, its soluble salt, N- (dithio Carboxy) sarcosine, its soluble salt, 4-morpholinecarbodithioic acid, its soluble salt, dithioacetic acid, its soluble salt,
o-Hydroxydithiobenzoic acid, a soluble salt thereof, rhodanine, 3-ethylrhodanine, 3-aminorhodanine, 2-mercapto-2-thiazoline, at least one compound selected from tetraalkylthiuram monosulfide and tetraalkylthiuram disulfide Item 3. An electroless nickel plating solution according to item 1 or 2. 4. 4. An electroless nickel plating method, comprising: immersing an object to be plated in the electroless nickel plating solution according to any one of the above items 1 to 3.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electroless nickel plating solution of the present invention contains a water-soluble nickel salt, a reducing agent and a complexing agent as basic components.

The water-soluble nickel salt to be added to the electroless nickel plating solution of the present invention is not particularly limited as long as it is soluble in the plating solution and can provide an aqueous solution having a predetermined concentration. Specific examples of such a water-soluble nickel salt include nickel sulfate, nickel chloride, nickel sulfamate, nickel hypophosphite, and the like, and nickel sulfate is particularly preferred because of its good solubility. The water-soluble nickel salt can be used singly or as a mixture of two or more kinds. The compounding amount is preferably about 0.5 to 50 g / l, more preferably 3 to 10 g / l.

Further, as the reducing agent, various reducing agents blended in a known electroless nickel plating solution can be used. Specific examples of such a reducing agent include hypophosphorous acid; sodium, potassium, and ammonium salts of hypophosphorous acid; dimethylamine borane, hydrazine, and the like. The reducing agents can be used alone or in combination of two or more. The amount of the reducing agent is 0.01 to
It is preferably about 100 g / l, and 0.1 to 50
g / l is more preferable.

As the complexing agent, various complexing agents blended in a known electroless nickel plating solution can be used. Specific examples thereof include malic acid, citric acid, lactic acid, succinic acid, adipic acid and the like. Carboxylic acids such as sodium salts thereof, glycine, alanine, iminodiacetic acid, arginine,
Amino acid salts such as aspartic acid, glutamic acid and the like and sodium salts thereof can be mentioned. The complexing agents can be used alone or in combination of two or more. The amount of the complexing agent is preferably about 1 to 100 g / l, more preferably 5 to 50 g / l.

In the electroless nickel plating solution of the present invention, if necessary, a lead salt such as lead nitrate or lead acetate, a bismuth salt such as bismuth nitrate or bismuth acetate, or a thiodiglycolic acid may be used as a stabilizer. One or two or more sulfur compounds can be added. The added amount of the stabilizer is 0.01 to 100 in order to sufficiently exert the effect of the addition.
It is preferably about mg / l.

In the electroless nickel plating solution of the present invention, the formula

[0018]

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It is necessary to blend a sulfur-containing compound having a group represented by the formula as an additive. In the above group,
A sulfur atom bonded to a carbon atom by a single bond is bonded to another atom by an ionic bond or a covalent bond. When the sulfur atom is bonded to the carbon atom by an ionic bond, the sulfur atom is usually used in an electroless nickel plating solution. Part or all exist in dissociation into ions. Further, the carbon atom in the above group is usually bonded to another carbon atom, another sulfur atom, an oxygen atom, a nitrogen atom, or another atom.

By blending such a sulfur-containing compound in an electroless nickel plating solution, the pattern deposition property is improved, and the plating spreads even on an object to be plated having a fine circuit pattern, such as step plating. Generation can be greatly suppressed. Further, the formed electroless nickel plating film has good corrosion resistance, and the quality of the nickel plating film is extremely reduced even when displacement gold plating is performed. Further, the sulfur-containing compound has good stability, and is compounded in an electroless nickel plating solution to obtain a normal plating temperature of 40 to 9
Even when the temperature is maintained at about 5 ° C., the above characteristics can be maintained for a long time.

The sulfur-containing compound that can be used in the present invention can be used without particular limitation as long as it is a compound having the above-mentioned group and can be dissolved in the electroless nickel plating solution within a predetermined concentration range.

Specific examples of the above sulfur-containing compounds include trithiocarbonates such as trithiocarbonate and salts thereof; O-alkylxanthogenic acids (O-ethylxanthogenic acid, O-isopropylxanthogenic acid, hexylxanthogenic acid and the like);
Xanthogenic acids such as salts thereof; dialkyldithiocarbamic acids (dimethyldithiocarbamic acid, diethyldithiocarbamic acid, etc.), 1-pyrrolidinedithiocarbamic acid, cyclopentamethylenedithiocarbamic acid, phenyldithiocarbamic acid, N- (dithiocarboxy) sarcosine, 4-morpholinecarbodithio Dithiocarbamic acids such as acids, dithiocarbamic acids such as salts thereof; dithiocarboxylic acids such as dithioacetic acid and o-hydroxydithiobenzoic acid; dithiocarboxylic acids such as salts thereof; rhodanins such as rhodanine, 3-ethylrhodanine and 3-aminorhodanine; 2
Mercaptothiazolines such as -mercapto-2-thiazoline; thiuram compounds such as tetraalkylthiuram monosulfide (such as tetramethylthiuram monosulfide) and tetraalkylthiuram disulfide (such as tetramethylthiuram disulfide and tetraethylthiuram disulfide); Can be. Among these sulfur-containing compounds, the salt of each compound may be a salt soluble in the plating solution, and examples thereof include a sodium salt, a potassium salt, an ammonium salt, a dimethylammonium salt, and a diethylammonium salt. .

Among these sulfur-containing compounds, examples of compounds having good solubility are as follows. (1) trithiocarbonates: potassium trithiocarbonate monohydrate, etc., (2) xanthogenic acids: potassium O-ethylxanthogenate, potassium O-isopropylxanthogenate, potassium hexylxanthogenate, etc., (3) dithiocarbamic acids: dimethyldithiocarbamine Sodium acid trihydrate, sodium diethyldithiocarbamate trihydrate, ammonium diethyldithiocarbamate, diethylammonium diethyldithiocarbamate, sodium 1-pyrrolidinedithiocarbamate, sodium 1-pyrrolidinedithiocarbamate trihydrate, 1-pyrrolidinedithiocarbamate Ammonium, sodium cyclopentamethylenedithiocarbamate dihydrate, ammonium phenyldithiocarbamate, N- (dithiocarboxy) sarco Emissions diammonium salt, 4-morpholine carboxamide sodium dithionite acid, (4) dithio acids: sodium dithionite acetate, o
(5) rhodanines: rhodanine, 3-ethylrhodanine, 3
(6) mercaptothiazolines: 2-mercapto-2-
(7) thiuram compounds: tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide and the like.

In the present invention, among the sulfur-containing compounds having the above-mentioned groups, trithiocarbonates such as trithiocarbonic acid and salts thereof; xanthogenic acids such as O-ethylxanthogenic acid and salts thereof; dimethyldithiocarbamic acid and diethyldithiocarbamine Acid, 1-pyrrolidinedithiocarbamic acid,
Dithiocarbamic acids such as cyclopentamethylenedithiocarbamic acid, phenyldithiocarbamic acid, N- (dithiocarboxy) sarcosine and salts thereof; dithiocarboxylic acids such as dithioacetic acid and o-hydroxydithiobenzoic acid; dithiocarboxylic acids such as salts thereof; rhodanin And rhodanines such as 3-aminorhodanine; mercaptothiazolines such as 2-mercapto-2-thiazoline; thiuram compounds such as tetramethylthiuram monosulfide and tetramethylthiuram disulfide are preferable in terms of good solubility, In particular, trithiocarbonic acid, a salt thereof, O-ethylxanthogenic acid, a salt thereof, N- (dithiocarboxy) sarcosine, a salt thereof, and the like have very good solubility and are particularly suitable compounds.

The above sulfur-containing compounds can be used singly or in combination of two or more. The addition amount in the electroless nickel plating solution is preferably about 0.001 to 100 mg / l. It is more preferable to be about 0.01 to 10 mg / l. If the compounding amount of the sulfur-containing organic compound is too small, the effect of adding the compound is not sufficiently exhibited. On the other hand, if the compounding amount is excessive, the non-plating phenomenon and the turbidity of the plating solution tend to occur, which is not preferable.

The electroless nickel plating solution of the present invention is obtained by dissolving each of the above-mentioned components in water, and the pH of the plating solution when performing electroless nickel plating is preferably about 2 to 10, preferably 3 to 10. More preferably, it is set to about 7.

In order to carry out plating using the electroless nickel plating solution of the present invention, the object to be plated may be immersed in the plating solution according to a conventional method. At this time, the plating solution can be agitated and the object to be plated can be swung as necessary.

As the object to be plated, various materials conventionally subjected to electroless nickel plating can be used. For example, a metal having a catalytic property with respect to the reductive precipitation of electroless nickel plating, such as iron, cobalt, nickel, palladium, or an alloy thereof, can be used as the object to be plated. In addition, metals such as copper, which have no catalytic property for electroless nickel plating, glass, ceramics, etc.
Electroless nickel plating can be performed by attaching a metal catalyst nucleus such as a palladium nucleus according to a conventional method.

The temperature of the plating solution during electroless nickel plating is preferably about 40 to 98 ° C.,
More preferably, the temperature is about 5 ° C.

The electroless nickel plating solution of the present invention can be used for a long period of time by appropriately adding each component according to the consumption amount. The method of adding each component may be in accordance with a conventional method, and each component may be added alone, or a plurality of components may be appropriately mixed and added.

The plating film formed by the electroless nickel plating solution of the present invention is a film having a white semi-brightness or luster, and is particularly useful as a base nickel plating film for noble metal plating of printed wiring boards. It is.

[0032]

According to the electroless nickel plating solution of the present invention, the spread of plating and the occurrence of step plating are small, and even on an object to be plated such as a printed wiring board having a fine circuit pattern, only on the circuit. A uniform electroless plating film can be formed. Moreover, the formed nickel plating film has good corrosion resistance, and when performing displacement gold plating thereon,
Very little deterioration of the nickel plating film. Further, the additives have good stability and can be used continuously for a long period of time.

[0033]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. Example 1 An electroless nickel-nickel plating solution having the following compositions was prepared. (Plating bath 1 of the present invention) Nickel sulfate 5 g / l (as nickel metal) Sodium hypophosphite 20 g / l Citric acid 10 g / l Adipic acid 10 g / l Potassium trithiocarbonate 0.1 mg / l pH 4.6 Bath temperature 80 (Plating bath 2 of the present invention) Nickel sulfate 5 g / l (as nickel metal) Sodium hypophosphite 20 g / l Malic acid 10 g / l Succinic acid 10 g / l N- (dithiocarboxy) sarcosine diammonium salt 1.5 mg / l Lead nitrate 0.5 mg / l (as lead metal) pH 4.6 Bath temperature 80 ° C (Plating bath 3 of the present invention) Nickel sulfate 5 g / l (as nickel metal) Sodium hypophosphite 20 g / l Malic acid 10 g / L succinic acid 10g / l lead nitrate 0.5mg / l (as lead metal) thiodiglycolic acid 20mg / l 1-pyro Lysine dithiocarbamic acid 0.1 mg / l pH 4.6 Bath temperature 80 ° C (Plating bath 4 of the present invention) Nickel sulfate 5 g / l (as nickel metal) Sodium hypophosphite 20 g / l Citric acid 10 g / l Adipic acid 10 g / L Lead nitrate 0.5mg / l (as lead metal) 3-Aminorhodanine 1.0mg / l Tetramethylthiuram monosulfide 0.5mg / l pH 4.6 Bath temperature 80 ° C (Plating bath 5 of the present invention) Nickel sulfate 5g / L (as nickel metal) Sodium hypophosphite 20 g / l citric acid 10 g / l adipic acid 10 g / l lead nitrate 0.5 mg / l (as lead metal) tetraethylthiuram disulfide 0.5 mg / l o-hydroxydithiobenzoate Acid 2.0 mg / l Potassium O-ethyl xanthate 5.0 mg / l pH 4.6 Bath Temperature 80 ° C (comparative plating bath 1) Nickel sulfate 5 g / l (as nickel metal) Sodium hypophosphite 20 g / l citric acid 10 g / l adipic acid 10 g / l lead nitrate 0.5 mg / l (as lead metal) pH 4.6 Bath temperature 80 ° C (comparative plating bath 2) Nickel sulfate 5 g / l (as nickel metal) Sodium hypophosphite 20 g / l Citric acid 10 g / l Adipic acid 10 g / l Lead nitrate 0.5 mg / l (as lead metal) Thiodiglycolic acid 5 mg / l pH 4.6 Bath temperature 80 ° C (comparative plating bath 3) Nickel sulfate 5 g / l (as nickel metal) Sodium hypophosphite 20 g / l citric acid 10 g / l Adipic acid 10 g / l Lead nitrate 0.5 mg / l (as lead metal) Sodium thiosulfate 1 mg / l pH 4.6 Bath temperature 80 ° C (Comparative plating 4) Nickel sulfate 5 g / l (as nickel metal) Sodium hypophosphite 20 g / l citric acid 10 g / l adipic acid 10 g / l lead nitrate 0.5 mg / l (as lead metal) sodium dithionate 5 mg / l pH 4.6 Bath temperature 80 ° C. After preparing 1 liter each of the plating baths 1 to 5 of the present invention and the comparative plating baths 1 to 4, the electroless nickel plating film was evaluated by the following method.

As an object to be plated, a material (about 4 cm × 4 m) having a polyimide pattern as a base material and a copper pattern having a line width of 20 μm and a slit width of 25 μm formed thereon for evaluation of plating spread and step plating was used. A test substrate (approximately 5 cm × 5 cm) having an epoxy resin as a base material and copper patterns of various shapes formed thereon was used for evaluating the adhesion of the displacement gold plating and the discoloration after the gold was peeled off.

First, after the object to be plated was degreased, it was immersed in a catalyst solution containing hydrochloric acid and palladium (ICP Axela, manufactured by Okuno Pharmaceutical Co., Ltd.) for 1 minute at room temperature. After being washed with running water, it was immersed in each of the above-described electroless nickel plating solutions while stirring with air at room temperature to form an electroless nickel plating film having a thickness of about 4 μm.

Each of the obtained samples was dried with a drier, and the spread of nickel plating outside the copper pattern was visually observed. Furthermore, the presence or absence of step plating was evaluated by observing the cross section.

Further, the plating object for evaluating the adhesion of the displacement gold plating and the discoloration after the gold was peeled off was subjected to electroless nickel plating by the above-mentioned method, and then to a thickness of 0.1%.
A substituted gold plating film of 0.3 μm or a substituted gold plating film of 0.3 μm was formed. As the replacement gold plating solution, a plating solution commercially available under the trade name of OPC Muden Gold manufactured by Okuno Pharmaceutical Co., Ltd. is used, and a gold plating film having a predetermined film thickness is formed at a solution temperature of 85 ° C. Substituted gold plating was carried out. Next, after the obtained sample was dried with a dryer, a cellophane tape was attached to the sample, and the sample was peeled off to evaluate the adhesion between the nickel plating film and the gold plating film. Thereafter, the gold plating was peeled off by immersing it in a gold peeling solution containing potassium cyanide and an oxidizing agent for 3 minutes, and the nickel plating film after the gold plating was peeled was evaluated by visual observation with a stereoscopic microscope for black discoloration and unevenness. .

The results are shown in Tables 1 and 2 below.

[0039]

[Table 1]

[0040]

[Table 2]

As is evident from the above results, in the plating baths 1 to 5 of the present invention, an electroless nickel plating film excellent in adhesion, corrosion resistance and pattern deposition property of displacement gold plating was formed in all plating baths. Was done. After leaving each plating bath at 80 ° C. for one week, the same plating test was performed. However, the plating baths 1 to 5 of the present invention showed the same performance as that at the time of building.

On the other hand, in the comparative plating baths 1 and 2, the formed nickel plating film has poor adhesion to the replacement gold plating, and the surface state after the gold plating film is peeled off becomes darker as the gold plating becomes thicker. And the tendency of the appearance unevenness becoming strong was recognized. Further, protrusion of the nickel plating out of the copper pattern and step plating were observed.

In the comparative plating baths 3 and 4, slight protrusion of nickel and step plating were observed, and the obtained nickel plating film had very poor adhesion to the gold plating film. Black discoloration and appearance unevenness were observed.

For the comparative plating baths 3 and 4, a plating solution was prepared again and left at 50 ° C. for one day.
After leaving for a while, the same test was performed,
It was confirmed that the spread of the plating and the occurrence of step plating increased, and the effect of adding the additive was reduced.

As can be seen from the above results, the electroless nickel plating solution of the present invention has good pattern deposition properties,
The formed electroless nickel plating film has good corrosion resistance. Furthermore, even if it is heated and left, it can be used stably for a long time without a decrease in performance.

Claims (4)

[Claims] 1. An electroless nickel plating solution containing a water-soluble nickel salt, a reducing agent and a complexing agent, wherein the compound has the formula: An electroless nickel plating solution characterized by containing a sulfur-containing compound having a group represented by the formula as an additive. 2. The method according to claim 1, wherein the sulfur-containing compound is at least one compound selected from trithiocarbonates, xanthogenic acids, dithiocarbamic acids, dithiocarboxylic acids, rhodanins, mercaptothiazolines, and thiurams. Electroless nickel plating solution. 3. The method of claim 1, wherein the sulfur-containing compound is trithiocarbonate, a soluble salt thereof, an O-alkylxanthic acid, a soluble salt thereof,
Dialkyldithiocarbamic acid, its soluble salt, 1-pyrrolidinedithiocarbamic acid, its soluble salt, cyclopentamethylenedithiocarbamic acid, its soluble salt, phenyldithiocarbamic acid, its soluble salt, N- (dithiocarboxy) sarcosine, its soluble salt, Morpholine carbodithioic acid, its soluble salt, dithioacetic acid, its soluble salt, o-hydroxydithiobenzoic acid, its soluble salt, rhodanine, 3-ethylrhodanine, 3-aminorhodanine, 2-mercapto-2-thiazoline, tetraalkylthiuram monosulfide The electroless nickel plating solution according to claim 1, wherein the electroless nickel plating solution is at least one compound selected from the group consisting of and a tetraalkylthiuram disulfide. 4. An electroless nickel plating method comprising immersing an object to be plated in the electroless nickel plating solution according to claim 1.