JPH09143749A - Electroless gold plating solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop an electroless gold plating soln. good in plating film characteristic, excellent in deposition rate and capable of forming a thick plating by adding a specified complexing agent, a pH regulator and a specified compd. to the aurocyanide as the Au ion source. SOLUTION: A cyanoaurate such as KAu(CN)2 by 1-5g/l as gold, phosphoric acid, boric acid, carboxylic acid or its salt, an amine compd. such as ethylenediamine, an aminocarboxylic acid such as EDTA or its derivative, an aminosulfonic acid such as ATMP or its derivative as the complexing agent by 5-200g/l, an alkali hydroxide such as NaOH or a mineral acid such as sulfuric acid and phosphoric acid as the pH regulator by >=10g/l, a Tl compd. by 1-100mg/l and further a hydrazine compd., hypophosphite, Pb compd., thiourea, phosphite, Co compd., Bi compd., As compd., sulfite, ammonium salt, etc., are added to water. An electroless Au plating soln. good in plating film characteristic, with the Au deposition rate increased and capable of forming a thick plating having 0.5μm thickness is developed in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless gold plating solution which has good plating film characteristics, a high deposition rate, and a thickness of 0.5 μm or more.

Electroless gold plating solutions are used in fields such as terminal plating of printed boards and bonding of semiconductor devices. In recent years, as electronic devices, computer parts, etc. have become lighter, thinner, smaller and smaller, the density of printed wiring boards has also increased, and finer patterns have been developed. It is possible to plate electrically isolated and complex parts, and the thickness of the formed film is uniform. An electroless gold plating solution, which has excellent properties, is drawing attention.

Electroless gold plating solutions include substitution type and reduction type. Conventionally, plating solutions capable of thickening are reduction types, but these use a strong reducing agent in a strong alkaline region. Therefore, in addition to the problem that the stability of the liquid is a little poor, there are problems that it is difficult to use for a resin substrate, or that it penetrates into a solder resist for gold plating. On the other hand, the substitution type has the advantages that it can be plated in the neutral area, has good stability, and does not attack the resist or resin substrate.
It was difficult to thicken.

[0004]

Therefore, recently, as disclosed in Japanese Unexamined Patent Publication No. 4-371583, a substitutional gold plating solution using thiosulfate as an additive, or Japanese Unexamined Patent Publication No. As disclosed in JP-A-295558, there is proposed an electroless gold plating solution that can be applied thickly from acidic to around neutral by using a thallium compound as an additive. However, JP-A-4-371583
The plating solution disclosed in Japanese Patent Publication has a slightly poor plating film characteristic and is apt to cause pinholes, that is, if the gold plating film has many pinholes, the underlying metal diffuses to the gold plating surface, and However, the plating solution disclosed in Japanese Unexamined Patent Publication No. 5-295558 can be applied with a thickness of 0.5 μm or more. There are problems such as slow speed and lack of productivity.

It is an object of the present invention to provide an electroless gold plating solution which has good plating film characteristics, a high deposition rate in the vicinity of acidity to neutrality, and a thickness of 0.5 μm or more that can be applied.

[0006]

The electroless gold plating solution of the present inventor is an electroless gold plating solution containing a gold cyanide salt, a complexing agent and a pH adjusting agent, to which a thallium compound is added, and hydrazine is added. One or more selected from compounds, hypophosphite, lead compounds, thiourea, phosphites, cobalt compounds, bismuth compounds, arsenic compounds, sulfites, and ammonium salts are added.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As the gold cyanide salt, potassium gold cyanide (I) is usually used, but it is not particularly limited thereto. The gold concentration in the plating solution is usually 0.3 to 20 g / l, preferably 1 to 5 g / l.

As the complexing agent, those commonly used in known plating solutions can be used. Specifically, carboxylic acids such as phosphoric acid, boric acid, citric acid, tartaric acid and salts thereof, amine compounds such as ethylenediamine and triethanolamine, ED
Amine carboxylic acids such as TA and NTA and their derivatives, A
Aminosulfonic acid such as TMP and its derivative can be used. The concentration of the complexing agent is usually 5 to 200 g / l, preferably 10 to 100 g / l.

As the pH adjuster, alkali hydroxides such as sodium hydroxide and potassium hydroxide used in known plating solutions, mineral acids such as sulfuric acid, phosphoric acid and boric acid and salts thereof, citric acid and tartaric acid are used. Organic acids such as lactic acid and salts thereof can be used alone or in combination. Particularly preferred is citric acid which can be adjusted to be near neutral, and the concentration is preferably 5 g / l or more, more preferably 10 g / l or more.

If necessary, a cyan compound such as sodium cyanide or potassium cyanide may be added to the plating solution of the present invention as a substance for maintaining the stability of gold ions.

As the thallium compound, lead compound, cobalt compound, bismuth compound and arsenic compound, chlorides, sulfates, nitrates, acetates, oxides and the like can be used, but they are limited to water-soluble substances. Not a thing. The amount added is 0.1 to 10000 mg / l, more preferably 1 to
100 mg / l is good.

As the hydrazine compound, hydrazine sulfate, hydrazine hydrochloride and the like can be used. As the addition amount,
It is preferably 0.1 to 50 g / l, more preferably 1 to 30 g / l. The addition amount of thiourea is 0.1 g / l or more,
More preferably, it is 1 g / l or more.

As hypophosphite, phosphite and sulfite, sodium hypophosphite, calcium hypophosphite,
Examples include sodium phosphite, sodium sulfite, and potassium sulfite, but the present invention is not limited to these and can be used.
The addition amount is 0.1 to 50 g / l, more preferably 1 to 30 g / l.

Examples of the ammonium salt include ammonium chloride and ammonium sulfate, but the ammonium salt is not limited to these and can be used. The amount of addition is 1 g / l or more,
More preferably, it is 5 g / l or more.

When applying the electroless gold plating solution of the present invention, degreasing, pickling, and
Etching and activation treatment can be performed. The pH of the electroless gold plating solution of the present invention is preferably about 5 to 7 from the viewpoint of solution stability and plating deposition rate, but is not limited to the above. The temperature of the plating solution is preferably 50 to 90 ° C, more preferably 70 to 90 ° C. Also, the load of the plating solution is 3 dm ² It is preferably within 1 / l from the viewpoint of plating deposition rate. When the plating solution of the present invention is used, the surface of the object to be plated may be preliminarily subjected to known underlayer gold plating of about 0.1 μm, and then the gold plating of the present invention may be performed thereon.

[0016]

[Example] (Basic composition) ・ KAu (CN) ₂・ ・ ・ ・ ・ ・ 2.5 g / l ・ EDTA ・ 2Na ・ ・ ・ ・・ ・ ・ ・ ・ ・ ・ ・ 20g / l ・ Citric acid ・ 2Na ・ ・ ・ ・ ・ ・ 20g / l ・ pH adjuster ・ ・··· Add various additives of the present invention shown in Table 1 to an amount to bring the pH to about 6 and perform electroless nickel plating on a copper plate of 5 cm ² square. A certain ICP nicolone (trade name, manufactured by Okuno Seiyaku Co., Ltd.) was performed, and then gold plating was performed with the plating solution of the present invention at 85 ° C. for 1 hour while stirring. The load at that time was 1 dm ² / l.
The gold plating film thickness was measured with a fluorescent X-ray film thickness meter. In addition, the quality of the gold plating film was evaluated by observing the gold plating surface with a microscope after exposing the prepared sample to nitric acid for 3 hours, and evaluating the number of pinholes within a certain area. Table 1 shows the results.

[0017]

[Table 1]

As is clear from Table 1, the plating solution of the present invention has a plating deposition rate of 5 to 8 as compared with Comparative Example 1 of the basic bath.
1.4 times that of Comparative Example 2 in which the thallium compound alone was used.
~ 2.4 times faster deposition temperature. In Comparative Examples 5 and 6 without thallium compound, the plating deposition rate is slow, and it can be seen that the effect is increased by using them together. In addition, Comparative Examples 3 and 4 are, due to the effect of sodium thio,
Although the plating deposition rate increases, the film properties are poor and the number of pinholes is large, and the plating solution of the present invention has a significantly small number of pinholes.

[0019]

As described above, the electroless gold plating solution of the present invention has excellent plating film characteristics, a high deposition rate, and a thickness of 0.5 μm or more, and is currently required. It is possible to satisfy the characteristics of gold plating.

Claims (1)

[Claims] 1. An electroless gold plating solution containing a gold cyanide salt, a complexing agent and a pH adjuster, to which a thallium compound is added, and a hydrazine compound, hypophosphite, lead compound, thiourea An electroless gold plating solution comprising one or more selected from phosphates, cobalt compounds, bismuth compounds, arsenic compounds, sulfites, and ammonium salts.