JP4305741B2 - Silver plating solution - Google Patents

Description

  The present invention relates to a substitutional electroless silver plating solution, but is preferably used for silver plating applied to a metal surface such as a copper pattern formed on the surface of a printed circuit board.

In order to improve the solderability of a metal surface such as an electronic component, a method of forming a silver plating film on the metal surface has been studied.
For example, Patent Document 1 includes a complexing agent such as silver ion and ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid and N, N, N ′, N′-tetrakis (2-hydroxypropyl) ethylenediamine, and further includes an interface. An electroless silver plating solution containing an activator, a wetting agent, a stabilizer, a fine granulating agent, a discoloration preventing agent and the like is disclosed.

  However, when this silver plating solution is used, it is possible to form a relatively thin silver plating film with a film thickness of less than 0.5 μm. However, when the processing time is increased and the film thickness of the silver plating film is increased. In addition, when the temperature of the silver plating solution is increased to increase the formation rate of the silver plating film, there is a problem in that the adhesion of the silver plating film to the base is lowered. In addition, the storage stability of the silver plating solution is not yet satisfactory, and silver is deposited in a container containing the silver plating solution during use or storage for a long period of time.

Patent Document 2 discloses a silver plating solution containing silver nitrate, an imidazole compound, methanesulfonic acid, and a dinitro aromatic compound as an oxidizing agent.
However, when silver plating is performed on the copper surface using the above silver plating solution and soldering is performed on the surface of the resulting silver plating film, the spread of the solder is insufficient and the solderability that is satisfactory There was a problem that could not be obtained.

JP-A-8-232072 Japanese Patent Laid-Open No. 10-8262

  The present invention has been made in view of such problems, and has a good adhesion to a metal surface such as an electronic component, can form a silver plating film excellent in solderability, and can be stored. An object is to provide a silver plating solution having excellent stability.

As a result of intensive studies to solve the above problems, the present inventors have found that silver ions, 3,5-dinitrosalicylic acid as the first complexing agent, and aminocarboxylic acid as the second complexing agent The present inventors have found that a silver plating solution containing at least one selected from a compound, a hydroxycarboxylic acid compound and a triazole compound can achieve the intended purpose, and has completed the present invention.

The silver plating solution of the present invention is a kind selected from silver ions, 3,5-dinitrosalicylic acid as a first complexing agent, and aminocarboxylic acid compounds, hydroxycarboxylic acid compounds and triazole compounds as a second complexing agent. By containing the above, the silver plating film has gloss, excellent adhesion to the base, and excellent solderability when soldered to the surface of the silver plating film. Since it has the feature that the storage stability of the plating solution is excellent, it can be suitably used for silver plating applied to a metal surface such as a copper pattern formed on the surface of a printed circuit board.

The silver plating solution of the present invention comprises a compound that supplies silver ions, 3,5-dinitrosalicylic acid as a first complexing agent, and an aminocarboxylic acid compound, a hydroxycarboxylic acid compound, and a triazole compound as a second complexing agent. It is the aqueous solution obtained by containing 1 or more types chosen from.

  In the practice of the present invention, typical compounds used as a silver ion source include silver acetate, silver bromide, silver carbonate, silver chlorate, silver chloride, silver iodate, silver lactate, silver nitrite, silver oxide, Examples include silver perchlorate, silver sulfate, silver sulfide, and silver thiocyanate. These silver compounds are contained at a concentration of 0.01 to 1% by weight as silver ions with respect to the silver plating solution.

The content concentration of 3,5-dinitrosalicylic acid in the silver plating solution is preferably 0.005 to 0.5% by weight. If the concentration is lower than 0.005% by weight, the gloss of the silver plating film cannot be obtained, the adhesion of the silver plating film to the base is poor, and satisfactory solderability cannot be obtained. On the other hand, when the concentration is higher than 0.5% by weight, the adhesion of the silver plating film and the gloss of the silver plating film are good, but the formation rate of the silver plating film is slow, which is not suitable for practical use.

Examples of the second complexing agent used in the present invention include aminocarboxylic acid compounds such as glycine, nitrilotriacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, lactic acid, citric acid, salicylic acid and the like. Examples thereof include hydroxycarboxylic acid compounds having a hydroxyl group, 1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole and the like, and one or two selected from these More than one species can be used in combination.
The second complexing agent is preferably contained at a concentration of 0.1 to 40% by weight with respect to the silver plating solution. When the concentration is lower than 0.1% by weight, the gloss of the silver plating film cannot be obtained, the adhesion of the silver plating film to the base is poor, and satisfactory solderability cannot be obtained. Even if the concentration is higher than 40% by weight, the characteristics of the silver plating film are not improved, the amount of the second complexing agent is increased, and the cost of the silver plating solution is only increased.
The first and second complexing agents preferably do not form precipitates when added to the silver plating solution.

  The pH of the silver plating solution of the present invention may be selected as appropriate for the complexing agent to be used, but from the viewpoint of storage stability of the silver plating solution, practical formation rate of the silver plating film, etc. A range of 2 to 2 is preferable. When the pH is higher than 2, a silver plating film having excellent adhesion to the base and a gloss is formed, but the formation rate of the silver plating film is slow and the storage stability of the silver plating solution is impaired. On the other hand, if it is lower than 0.2, the amount of the acid used is only increased and the characteristics of the silver plating film are not improved.

In order to adjust the pH of the silver plating solution of the present invention to a range of 0.2 to 2, an organic acid and an inorganic acid can be used. Organic acids include formic acid, chloroacetic acid, 2-chloropropionic acid, glycolic acid, lactic acid, aminobenzoic acid, paranitrobenzoic acid, methanesulfonic acid, paratoluenesulfonic acid, salicylic acid, oxalic acid, maleic acid, fumaric acid, tartaric acid Citric acid, phenoxyacetic acid, phthalic acid and the like, and inorganic acids include, but are not limited to, phosphoric acid, sulfuric acid, nitric acid and the like. These acids can be used alone or in combination of two or more.
In order to adjust the pH of the silver plating solution, an alkali hydroxide such as sodium hydroxide or potassium hydroxide, aqueous ammonia, or the like can be used.

  The silver plating solution of the present invention may contain a surfactant in order to increase the gloss of the silver plating film. As the surfactant, nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene polyoxypropylene block copolymer, alkylamine polyethylene oxide and the like are preferable. The concentration of the surfactant in the silver plating solution is preferably 0.01 to 5% by weight.

As conditions for performing the silver plating treatment using the silver plating solution of the present invention, it is preferable to set the temperature of the silver plating solution to 10 to 70 ° C. About the processing time of silver plating, what is necessary is just to contact a to-be-plated object with a silver plating solution until the silver plating film of desired film thickness deposits, The contact time has the preferable range normally for 10 second-30 minutes, More preferably, it is 30 seconds to 10 minutes. Examples of the contact method between the silver plating solution and the object to be plated include methods such as immersion, spraying and coating.
In performing silver plating, it is desirable to clean the metal surface of the object to be plated in advance using an acid cleaner or a microetching agent.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these.
In addition, the chemical | medical agent used by the Example and the comparative example used the reagent generally marketed. The evaluation test method is as follows.

[Evaluation method of silver plating film]
(1) Appearance: The color and gloss of the silver plating film surface were observed visually. It is known that the higher the gloss of the silver plating film is, the better the adhesion between the silver plating film and the base is, and the higher the gloss of the silver plating film is preferable.
(2) Film thickness of silver plating film: measured using a fluorescent X-ray film thickness meter.
(3) Adhesion of the silver plating film: The surface of the silver plating film with a width of 10 mm x 10 mm is cut into 1 and 2 mm at intervals of 1 mm using a cutter knife, and 100 cells are made. Was attached, peeled off at once, and the number of peeled squares was determined. The smaller the number of peeled cells, the better the adhesion of the silver plating film.
(4) Solder spreadability test: A silver-plated test piece is heated and humidified for 60 hours under conditions of 60 ° C / 95% RH, and then an infrared reflow device (product name: MULTI-PRO).
306, manufactured by Vitronics), reflow heating at a peak temperature of 250 ° C. was performed once. Then, using a metal mask with an opening width of 1.20 mm and a thickness of 150 μm, cream solder was printed on the center of the conductor, and reflow heating was performed under the same conditions as described above to perform soldering. The cream solder used was a tin-silver-copper lead-free cream solder (manufactured by Senju Metal Industry Co., Ltd., trade name: M705-221BM5-42-11, composition: 95.65 / 3.0 / 0.5% by weight) is there. About the obtained test piece, the length of the solder which spread on the conductor was measured. The longer the solder spread, the better the solderability.
(5) Storage stability of silver plating solution: The silver plating solution was put in a plastic container, sealed, and stored at 40 ° C. The number of days until silver was deposited on the inner wall of the plastic container was measured visually, and the longer the number of days, the better the storage stability of the silver plating solution.

[Example 1]
Table 1 shows silver nitrate, 3,5-dinitrosalicylic acid as the first complexing agent, citric acid monohydrate as the second complexing agent, and polyethylene glycol monooleyl ether (n≈10) as the surfactant. 1 kg of a substitutional electroless silver plating solution was prepared by dissolving in ion-exchanged water so that the concentration (unit: wt%) described in (1) was obtained. The resulting plating solution had a pH of 1.9.
A single-sided copper-clad laminate (base material: FR4, copper foil thickness: 35 μm, 50 mm × 50 mm × thickness 1.6 mm) subjected to degreasing, soft etching and water washing is immersed in the silver plating solution adjusted to 40 ° C. The copper surface of the laminate was subjected to silver plating while the laminate was rocked for 3 minutes at a speed of 1 second per stroke. Next, the laminate was pulled up from the silver plating solution, washed with water, and dried with warm air to obtain a test piece for evaluation.
About the obtained test piece, the silver plating external appearance, the film thickness of the silver plating film, and the adhesiveness of the silver plating film were evaluated. The test results obtained were as shown in Table 1. .
Similarly, on the copper surface of the above-mentioned single-sided copper-clad laminate (circuit part: 10 copper foil (conductor) parts having a size of 0.8 × 20 mm formed at 1 mm intervals) on which a test circuit was formed, silver Plating treatment was performed, and a solder spreadability test was performed on the obtained test piece. The test results obtained were as shown in Table 1.

[Examples 2-3, Comparative Examples 1-4]
For pH adjustment, except that 60% nitric acid or sodium hydroxide was used, a silver plating solution was prepared according to the raw material chemicals and concentrations shown in Table 1, and a test piece was prepared in the same manner as in Example 1. An evaluation test was conducted.
The test results obtained were as shown in Table 1.

According to the test results in Table 1, the silver plating solutions of the examples were composed of silver ions, 3,5-dinitrosalicylic acid as the first complexing agent, and aminocarboxylic acid compound and hydroxycarboxylic acid as the second complexing agent. By containing at least one selected from acid compounds and triazole compounds, the silver plating film has gloss, excellent adhesion to the ground, and solderability when the surface of the silver plating film is soldered Furthermore, it has the characteristics that the storage stability of the silver plating solution is excellent.

Claims (1)

A silver plating solution containing silver ions, 3,5-dinitrosalicylic acid as a first complexing agent, and one or more selected from an aminocarboxylic acid compound, a hydroxycarboxylic acid compound and a triazole compound as a second complexing agent. The silver plating solution is characterized in that the pH of the silver plating solution is in the range of 0.2-2.