JPH06256962A - Electroless ni-sn-p alloy plating solution - Google Patents

Abstract

PURPOSE:To develop an electroless Ni-Sn-P alloy plating soln. having a high content of Sn and excellent in corrosion resistance by adding the ions of Ni(II) and Sn(II) and a reducing agent to an aq. alkaline soln. contg. citric acid in a specified ratio. CONSTITUTION:Nickel sulfate or chloride as the Ni(II) ion source is added to an aq. soln. contg. citric acid so that the Ni ion concn. is controlled to 0.05-0.12mol/l and the molar ratio of the citrate ion to Ni ion to 1.3-3. Tin nitrate, etc., are further added so that the Sn(II) ion concn. is controlled to 0.002-0.004 mol/l, hypophosphorous acid as the reducing agent for the Ni and Sn ions is added so that the ion concn. is controlled to 0.1-0.3 mol/l, and NaOH, etc., are added to adjust the soln. to pH 8-12. An Ni-Sn-P alloy having a higher content of Sn than before and excellent in corrosion resistance is developed in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is directed to Ni containing a high Sn content.
The present invention relates to an "electroless Ni-Sn-P alloy plating solution" capable of stably forming a -Sn-P alloy plating film.

[0002]

2. Description of the Related Art Copper foils used for printed circuit boards have hitherto been subjected to a "rust preventive treatment" in which a Cr thin film is formed on the surface for the purpose of preventing deterioration of surface properties over time. Recently, it has been proposed to provide a thin film of Ni—Sn alloy plating because it is advantageous in terms of chemical resistance, heat resistance, solderability, etc. (for example, Japanese Patent Laid-Open No. 4-206888). Gazette).

As described above, it is well known that Ni-Sn alloy plating is excellent in corrosion resistance, and it is said that the corrosion resistance improves as the Sn content in the plating film increases. Further, in "Ni-Sn alloy plating" formed by electroless plating by reduction of hypophosphorous acid, P from hypophosphorous acid used as a reducing agent is contained in the plating film. As described above, the "Ni-Sn alloy plating containing P in the range of several% to several tens of%" is said to further improve the corrosion resistance as compared with the case of using only Ni and Sn. Of course,
Also in this Ni-Sn-P alloy plating, it was considered that the higher the Sn content, the higher the corrosion resistance.

On the other hand, according to Japanese Patent Laid-Open No. 1-169811, when a lead wire, an electronic component, or the like is soldered to a transparent conductive film containing Sn, a Ni--Sn--P alloy is deposited on the transparent conductive film. Applying electroless plating improves solderability,
It is said that a strong connection will be possible, and this Ni-Sn-P
As a means for forming an alloy electroless plating film, "the surface-roughened substrate is in an aqueous solution (90 ° C) of pH 9 containing sodium stannate, sodium citrate, nickel sulfate, ammonium chloride and sodium hypophosphite. "How to process in." Is introduced.

Further, in Japanese Unexamined Patent Publication No. 2-208816, a nonmagnetic plating layer, an underlayer such as chromium, a magnetic thin film layer of a cobalt-based alloy are sequentially formed on an aluminum alloy substrate.
In a magnetic recording medium coated with a carbonaceous protective film layer, noise is suppressed and the S / N value is improved when the non-magnetic plated layer is a Ni-Sn-P alloy electroless plated film. Is disclosed as a means for forming the Ni-Sn-P alloy electroless plating film, "the base material is nickel: 6 g /
A method of treating in an electroless plating bath (90 ° C.) of L (liter), phosphoric acid: 13 g / L, tin: 200 mg / L ”is introduced.

As described above, the Ni—Sn—P alloy plating film has various uses, but on the other hand, it has the following problems. That is, although it has been reported that a high Sn content coating with an Sn content of 48 at% (65 wt%) can be obtained by the electroplating method, the Sn content of up to 10 at Only a coating of up to about 10% was obtained, so the actual application had to be limited.

[0007] Therefore, if the Sn content in the plating film obtained by electroless Ni-Sn-P alloy plating can be increased, further improvement of the film performance including corrosion resistance can be expected, and the type of substrate can be changed. It was thought that the use of electroless plating could be broadened by taking advantage of the advantage of electroless plating, which allows easy film formation without selection.

Therefore, the object of the present invention is to establish an electroless plating means capable of stably forming a Ni-Sn-P alloy plating film having a higher Sn content. Is.

[0009]

Therefore, the inventors of the present invention have made extensive studies in order to achieve the above-mentioned object, and as a result of diligent research, the following knowledge has been obtained. That is, in a Ni-Sn electroless plating solution prepared by adding divalent Ni ions and Sn ions as metal ions to an alkaline aqueous solution containing citric acid, and further containing hypophosphite ions as a reducing agent, Content of divalent Ni ion, divalent Sn ion and hypophosphite ion, and citric acid and 2
If the pH of the solution is adjusted to a specific range with alkali metal hydroxide such as NaOH, KOH or LiOH, etc., while controlling the molar ratio of valence Ni ions to a specific range It was discovered that a Ni—Sn—P alloy coating having a high Sn content, which could not be realized, can be stably formed on various substrates.

The present invention has been completed on the basis of the above-mentioned findings and the like. The "electroless Ni-Sn-P alloy plating solution
Valent Ni ion: 0.05-0.12mol / L, molar ratio of citrate ion to divalent Ni ion: 1.3 or more and less than 3, divalent Sn
Ion: 0.002 to 0.004mol / L, hypophosphite ion: 0.1
Ni-Sn with a high Sn content can be obtained by using an aqueous solution containing ~ 0.3mol / L and pH adjusted to 8-12.
-The point that a P alloy plating film can be stably formed "is a major feature.

The reasons for limiting the concentrations of the plating solution components and the pH of the plating solution in the present invention are as follows.
It will be explained together with its action and effect.

[Concentration of plating solution components]

a) Divalent Ni ion If the divalent Ni ion concentration in the plating solution is less than 0.05 mol / L, the plating reaction will be delayed, making it unsuitable for practical use, while if it exceeds 0.12 mol / L, precipitates ( Since the Sn content of the plating film) decreases, it was set at 0.05 to 0.12 mol / L.
A more preferable range is 0.06 to 0.10 mol / L. 2
The valent Ni ions may be supplied in the form of sulfate or chloride.

B) Molar ratio of citrate ion to divalent Ni ion The citrate (R) ion acts as a complexing agent for Ni ion preferentially over Sn ion, and Ni-R, Ni-R ₂ ，
It forms a chelate (complex) of Ni-R ₃ and promotes the precipitation of Sn. However, if the molar ratio of the citrate ion to the divalent Ni ion "citrate ion / divalent Ni ion molar ratio" is less than 1.3, the complexing power with respect to the divalent Ni ion decreases, so precipitation of Ni occurs. Is promoted in the precipitate
The Ni content is high, so that the plating film is better than before.
Sn content cannot be secured. On the other hand, "citrate ion / 2
When the molar ratio of valent Ni ions is 3 or more, the divalent Ni ions form a highly stable chelate with citrate ions,
Even with hypophosphite ions, they are not reduced and the plating reaction does not occur. For this reason, it has been determined that the citrate ion is contained in a molar ratio of 1.3 times or more and less than 3 times the divalent Ni ion, but a more preferable molar ratio range is 1.5 to 2.5.

Needless to say, the citric acid ion source in the plating solution may be citric acid or citrate.

C) Divalent Sn ion If the divalent Sn ion concentration in the plating solution is less than 0.002 mol / L, the Sn content in the deposit will decrease and the Sn content in the plating film will be higher than in the past. Cannot be secured. And Sn
Ions are originally catalyst poisons for reduction reactions, but especially when the divalent Sn ion concentration in the plating solution exceeds 0.004 mol / L, the reducing power of hypophosphite ions is lost and the plating reaction does not occur. Therefore, the divalent Sn ion concentration is 0.002-0.004mo.
L / L was set, but a more preferable range is 0.0025 to 0.0035mo.
l / L.

As the divalent Sn ion source, chloride or the like is generally used. For example, the following treatment may be carried out to dissolve it before use. That is, for example, stannous chloride is dissolved in water, and a NaOH solution is added dropwise. A white precipitate is initially formed by this treatment, but the liquid becomes transparent when NaOH is added dropwise. The reaction formula in this case is as follows. _{SnCl 2 + 4NaOH → Na 2 SnO} 2 + 2NaCl + 2H 2 O used in filtration.

D) Hypophosphite ion The hypophosphite ion functions as a reducing agent for precipitating Ni and Sn, and at the same time, it also functions as a P supply source for supplying P into the precipitate. I am responsible, but the concentration is 0.
If it is less than 1 mol / L, the desired effect due to the above action cannot be obtained,
On the other hand, containing more than 0.3 mol / L is considered to be economically disadvantageous considering the effect. Therefore, the hypophosphite ion concentration in the plating solution was set to 0.1 to 0.3 mol / L, but a more preferable range is 0.15 to 0.25 mol / L. It should be noted that the hypophosphite ion may be supplied in any form of hypophosphite and hypophosphite.

[PH of plating solution] With the bath composition of the plating solution of the present invention, the reducing power of hypophosphite ions is lost when the pH of the plating solution is less than 8, while when the pH exceeds 12, Since the decomposition of hypophosphorous acid, which is a side reaction, becomes severe and adversely affects the plating operation, the pH of the plating solution was set to 8 to 12, but it is preferable to adjust it to 9 to 10.

Next, the present invention will be described more specifically by way of examples.

[Example] As a plating test plate, rolled copper foil (thickness 70μ
m, width 20 mm, length 30 mm) were prepared and subjected to usual activation treatments for electroless plating such as degreasing, pickling, soft etching and addition of Pd catalyst, and then subjected to a plating test.

The composition, pH and solution temperature of the plating solution used in the plating test are as shown in Table 1, but a 1 liter beaker was used for the formulation. And at this time, p
H adjustment was performed with NaOH. In the plating test,
The plating solution was maintained at the predetermined temperature shown in Table 1, and the activation-treated test plate was immersed in this for 10 minutes to electrolessly deposit a plating film on the surface.

[0020]

[Table 1]

Table 1 also shows the measurement results of the "composition" and "deposition rate" of the plating deposits (films) thus formed. The composition of the plated deposit was measured by a method in which the plated product was dissolved in an acid together with copper as a base material and then analyzed by ICP (emission spectroscopy). The deposition rate of plating was calculated based on the plating film thickness obtained from the weight difference before and after plating.

As is clear from the results shown in Table 1 above, when the conditions specified in the present invention are followed, a Ni-Sn-P alloy plating film having a high Sn content is practically applied by electroless plating. It can be confirmed that stable formation can be achieved with a deposition rate that does not hinder.

[0023]

[Summary of Effects] As described above, according to the present invention, a Ni-Sn-P alloy plating film having a Sn content of more than 10 atm% can be stably formed by electroless plating. The industrially very useful effect is brought about, for example, the field of application of Sn-P alloy plating can be further expanded.

Claims (1)

[Claims] 1. Divalent Ni ion: 0.05 to 0.12 mol / L, molar ratio of citrate ion to divalent Ni ion: 1.3 to less than 3, divalent Sn ion: 0.002 to 0.004 mol / L, Phosphite ion: contains 0.1 to 0.3 mol / L and has a pH of 8 to 12
Electroless, characterized by comprising an aqueous solution adjusted to
Ni-Sn-P alloy plating solution.