JP2000328286A - Tin-silver-base alloy electroplating bath - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a plating bath and to facilitate the management of the bath by incorporating at least one acid among a soluble stannous compound, soluble silver compound, thioethane compound, sulfuric acid and sulfonic acid into the plating bath. SOLUTION: The soluble stannous compound includes stannous chloride, etc., and the soluble silver compound includes silver (I) oxide, etc. The thioethane compound is a chelate agent for stabilizing the plating bath and is expressed by the general formula: R1-S(CH2CH2S)n-R2. In the formula, R1 and R2 may be the same or different and are respectively selected from -CH2OH, -C2H4OH, -C3H6OH, -CH2NH2, -C2H4NH2, -C3H6 and (n) is 1 to 3. The sulfonic acid includes methanesulfonic acid, etc. The plating bath can preferably further include a nonionic surfactant or antioxidant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tin-silver alloy electroplating bath for forming a tin-silver alloy plating film which can be used in place of a tin-lead alloy solder. In particular, the present invention relates to an acidic tin-silver-based alloy electroplating bath capable of preventing the precipitation of metal in the bath, stably maintaining the bath, and forming a bath using sulfuric acid.

[0002]

2. Description of the Related Art Environmental pollution such as groundwater pollution by lead has become a problem, and regulations on lead-containing products have been tightened.
For this reason, there has been an increasing movement to replace tin-lead alloy (solder alloy), which has been conventionally used for soldering in various products, with lead-free solder. As a lead-free solder, a tin-silver alloy having a relatively low melting point and good thermal fatigue resistance has become the mainstream. There is also known a ternary tin-silver alloy obtained by adding a third element such as bismuth or copper to a tin-silver alloy for the purpose of lowering the melting point.

[0003] In soldering electronic components and printed circuit boards, solder plating may be applied to a soldered portion in order to maintain good solderability, and if it cannot be exposed to high temperatures, electroplating is used. Is done. Conventionally, tin-lead alloy plating has been mainly used for this solder plating. However, since an electroplating bath containing a lead compound is used, it has been desired to switch the solder plating to lead-free plating. Have been.

As a lead-free solder plating, a tin-silver alloy plating is promising similarly to a soldering alloy. Particularly, when soldering is performed with a silver-tin alloy, the same alloy is used for the solder plating. Is preferred. Silver-tin-based alloy electroplating is used not only for soldering but also for electric contacts and the like.

Conventional silver-tin alloy electroplating has been generally carried out using a cyanogen bath such as a pyrophosphoric acid-cyan bath or a cyano-ammonia bath. This is the silver ion (Ag ⁺ )
A cyanide ion (CN ^-) is coordinated with and cyano silver complex
[Ag (CN)] ^- to form and stabilize silver ions in the bath,
This is to cause eutectoid silver and tin together. If silver ions in the bath are not stabilized, Ag ions and Sn
Oxidation-reduction reaction with ions (Sn ²⁺ ) occurs, and Ag precipitates, and Sn ions become unstable Sn ⁺⁴ ions and easily precipitate, so the stability of the plating bath is significantly impaired . Since silver and tin have remarkably different deposition potentials, Ag
If the ions are not stabilized, silver will preferentially precipitate first and silver and tin cannot be eutectoid together.

However, as is well known, since a cyanide is highly toxic, a silver-tin alloy electroplating bath without using a cyanide bath is desired, and many proposals have been made on a non-cyanide bath. I have. For example, pyrophosphoric acid-iodine type plating baths are disclosed in JP-A-9-296274 and JP-A-10-36995.
Nos. 10-102277 and 10-102283.

Japanese Patent Application Laid-Open No. 9-296289 discloses a plating bath of a pyrophosphate-iodine type for plating a tin-silver alloy containing bismuth and / or copper. However, electroplating baths of the pyrophosphoric acid-iodine type generally have problems in that bath management is difficult and productivity is low.

JP-A-9-143786 discloses thiourea compounds, thiazole compounds, sulfenamide compounds, thiuram compounds, dithiocarbamic acid compounds,
Ag containing sulfur-containing compounds selected from bisphenol compounds, benzimidazole compounds, and organic thioacid compounds
⁺ Formulated as an ion displacement inhibitor, acidified the bath with alkanesulfonic acid or alkanolsulfonic acid,
A cyanide-free silver or silver alloy acid electroplating bath is disclosed.

Japanese Patent Application Laid-Open No. 9-170094 discloses a cyanide containing a sulfur-containing compound selected from a thioamide compound (thiourea compound) and a thiol compound, and acidified with alkanesulfonic acid and / or sulfamic acid. A tin-silver alloy acid plating bath containing no sulfur-containing compound is disclosed, and JP-A-10-204675 discloses a similar acid plating bath containing a sulfur-containing compound selected from an aromatic thiol compound and an aromatic sulfide compound. ing.

JP-A-10-204676 discloses an acid selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid, thiourea, a nonionic surfactant, A silver-tin alloy electroplating bath containing an additive selected from a mercapto group-containing aromatic compound, a dioxy aromatic compound and an unsaturated carboxylic acid is disclosed.

[0011]

A tin-silver alloy acid plating bath in which silver ions are stabilized by a sulfur-containing compound eliminates the above-mentioned problems associated with the pyrophosphate-iodine type plating bath. The following problems still remain in this kind of plating bath.

First, the bath containing the above sulfur-containing compound is an acidic bath and contains an acid for adjusting pH. Organic acids such as alkanesulfonic acid, alkanolsulfonic acid, and sulfamic acid are used as the acid. JP-A-10-
No. 204676 discloses sulfuric acid as an acid,
There is no example in which the acid is sulfuric acid alone.
There is only an example in which a bath was used in combination with gluconic acid). Since acids are used in very large amounts in this type of bath (eg, 100-500 g / L for organic acids), they are more expensive than sulfuric acid and have lower acidity (more use). The use of an acid significantly increases the cost of the plating bath.

An acid plating bath for electrotin plating is usually constructed using sulfuric acid. If the acid plating bath for tin-silver alloy electroplating can be similarly constructed using sulfuric acid,
The plating bath cost is considerably reduced. However, conventional tin-
When a silver alloy acid plating bath is constructed using sulfuric acid, the bath becomes unstable, so that an organic acid such as alkanesulfonic acid has to be used, which has increased the cost.

As described above, it is known that a tin-silver alloy plating bath of pyrophosphoric acid-iodine type forms a ternary alloy plating film using a plating bath containing bismuth or copper. (JP-A-9-296289). When a small amount of bismuth or copper is added to tin-silver alloy plating to form a ternary alloy plating, the melting point is lower than that of a tin-silver binary alloy, and solderability is improved. However, for a tin-silver alloy plating bath containing a sulfur-containing compound,
A tin-silver alloy plating bath capable of forming such a ternary alloy has not been known so far.

[0015] The present invention provides a silver-tin ternary alloy plating film containing a third metal such as bismuth or copper, in which the plating bath is stable even when the bath is constructed using sulfuric acid, bath management is easy. It is an object of the present invention to provide a tin-silver-based alloy plating bath capable of forming a tin-silver alloy.

[0016]

According to the present invention, the following is provided.
(1) to (4), preferably further (5) and
The above problem is solved by a tin-silver alloy electroplating bath also containing (6).

(1) Soluble stannous compound, (2) Soluble silver compound, (3) General formula: R ¹ -S (CH ₂ CH ₂ S) nR ² (wherein R ¹ and R ² are the same may be different, each -CH ₂ OH
_{, -C 2 H 4 OH, -C} 3 H 6 OH, -CH 2 NH 2, -C 2 H 4 NH 2, -C 3 H
₆ NH ₂ , n is an integer of 1 to 3), a thioethane compound represented by (4) at least one acid selected from sulfuric acid and sulfonic acid, (5) a nonionic surfactant,
(6) Antioxidants.

This plating bath can further contain a soluble copper compound or a soluble bismuth compound, whereby a plating film of a ternary alloy containing copper or bismuth in addition to tin and silver can be formed.

The acidic tin-silver alloy electroplating bath according to the present invention has excellent stability and can be stored without precipitation of metal components for at least one month. When electroplating is performed using this plating bath, preferential precipitation of silver does not occur,
A tin-silver alloy plating film is formed, and the alloy composition of the plating film can be controlled by tin ions and silver ions in the plating bath. Further, the plating film has a dense, white, matte, and favorable appearance free of precipitates such as needles, dendrites, powders, and granules, burns, burns, and the like.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The plating bath of the present invention contains a soluble stannous compound, a soluble silver compound, a thioethane compound, and at least one acid selected from sulfuric acid and sulfonic acid. Contains surfactants and antioxidants. The thioethane compound acts as a chelating agent for stabilizing Ag ions and tin ions. When the plating film is formed into a ternary alloy, a bismuth compound or a copper compound is contained.

The components of the plating bath other than the thioethane compound may be those used in conventional tin-silver alloy plating baths or tin or silver plating baths. As each component, one or more compounds can be used. Hereinafter, these components will be briefly described, but are not limited to the compounds exemplified in this description.

The soluble stannous compound and the soluble silver compound are
What is necessary is just to dissolve in an aqueous solution of sulfuric acid and / or sulfonic acid. Examples of stannous compounds include sulfonates such as stannous methanesulfonate, inorganic salts such as stannous sulfate and stannous chloride, stannous gluconate, stannous citrate, and lactic acid stannate. Organic salts such as monotin are exemplified. The soluble silver compound is usually a first silver compound. Specific examples thereof include silver oxide, a sulfonate such as silver methanesulfonate, an inorganic acid salt such as silver sulfate and silver chloride, silver gluconate, and citric acid. Organic acid salts such as silver and silver lactate are exemplified.

Similarly, when a bismuth compound or a copper compound is contained in a plating bath, there is no particular limitation as long as the compound is soluble in the above-mentioned aqueous acid solution. Examples of bismuth compounds that can be used include bismuth chloride, bismuth iodide, bismuth sulfate, bismuth citrate, bismuth gluconate, bismuth methanesulfonate, and the like. Examples of copper compounds include cuprous chloride, cupric chloride, copper sulfate, copper methanesulfonate, copper citrate, copper gluconate, and the like.

A thioethane compound used as a chelating agent for stabilizing a plating bath has a general formula: R ¹ -S (CH ₂ C
H ₂ S) The compound represented by nR ² . In the formula, R ¹ and R ² may be the same or different and each represents —CH ₂ OH, —C _{2
H 4 OH, -C 3 H 6} OH, -CH 2 NH 2, -C 2 H 4 NH 2, selected from -C ₃ H ₆ NH _2, n is an integer of 1-3.

As the acid, sulfuric acid and / or sulfonic acid are used. That is, a stable plating bath can be obtained using only sulfuric acid. As the sulfonic acid, alkanesulfonic acid and alkanolsulfonic acid are preferable, but benzenesulfonic acid (eg, toluenesulfonic acid) and phenolsulfonic acid (eg, cresolsulfonic acid) can also be used. The alkanesulfonic acid and the alkanolsulfonic acid may be unsubstituted or substituted with a suitable substituent. Examples of these sulfonic acids include methanesulfonic acid, ethanesulfonic acid, isethionic acid, propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, chloropropanesulfonic acid, 2-hydroxyethane-1-sulfonic acid, 2-hydroxypentane Examples thereof include sulfonic acid, 2-sulfoacetic acid, 2-sulfopropionic acid, and sulfosuccinic acid.

The preferred bath concentrations of the above components are as follows: Stannous compound: 1 to 100 g / L as Sn concentration, particularly 10 to 10 g / L
60 g / L; ・ Silver compound: 0.01 to 80 g / L as Ag concentration, particularly 0.1 to 10
g / L; ・ Copper or bismuth compound (if used): Cu or
Bi concentration of 0.01 to 50 g / L, especially 0.1 to 10 g / L; total metal concentration: 5 to 100 g / L, especially 10 to 80 g / L; chelating agent (thioethane compound): 0.1 to 200 g / L,
In particular, 0.5 to 80 g / L; ・ Acid (sulfuric acid and / or sulfonic acid): 50 to 400 g / L
, Especially 80-300 g / L.

The pH of the plating bath of the present invention is usually strongly acidic, lower than 1. When the acid is sulfuric acid, the acid concentration may be lower than when sulfonic acid is used. For example,
A concentration of about 60-80% of the concentration when sulfonic acid is used is sufficient. If the concentration of the acid or the concentration of the chelating agent is too low, the bath becomes unstable and precipitation tends to occur. If the concentration of the chelating agent is too high, the appearance of the deposited plating film may deteriorate.

The plating bath of the present invention contains one or two of various additives conventionally added to a tin-silver alloy electroplating bath or a silver electroplating bath or a tin electroplating bath.
More than one species can be added if desired. Examples of such additives include brighteners, antioxidants and the like.

As the brightener, those which have been used as brighteners for tin plating or silver plating can be used. For example, nonionic surfactants, anionic surfactants, water-soluble polymers (eg, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, etc.), ketones (eg, benzal acetone, acetophenone), aldehydes
(Eg, formalin, valeraldehyde, salicylaldehyde, vanillin, etc.).

Preferred brighteners are nonionic surfactants. Examples of the nonionic surfactant include the following: General formula: R—O— (A) n —H (where R is an alkyl group or an alkenyl group, and A is —CH ₂ CH ₂ O— ( = ethyleneoxy _{group), -CH 2 -CH (CH 3} ) O- (= propyleneoxy group),
And an alkylene oxide adduct of a saturated or unsaturated alcohol represented by the formula: R'-Ar-O- (A) n-H (wherein R is an integer of 1 to 40). 'Is hydrogen or an alkyl or alkenyl group, Ar is an aromatic hydrocarbon group such as phenyl or naphthyl, and A and n are the same as those described above), and alkylene oxide adducts of phenol or naphthol or alkyl or alkenyl phenol or naphthol; An alkylene oxide adduct of a saturated or unsaturated fatty acid represented by the general formula: R-COO- (A) n-H (wherein R, A and n are the same as described above); general formula: RN [( A) n-H] ₂ (wherein R, A and n
Is the same as the above), which is an alkylene oxide adduct of a saturated or unsaturated aliphatic amine.

Specific examples of the above nonionic surfactants are as follows: Ethylene oxides of saturated or unsaturated alcohols such as methanol, ethanol, isopropanol, butanol, hexanol, 2-ethylhexanol and allyl alcohol. (EO) adduct or ethylene oxide /
Propylene oxide (EO / PO) adduct; EO adduct such as octylphenol, nonylphenol, α-naphthol, β-naphthol or EO / PO
Adducts; polyoxyethylene esters of saturated or unsaturated fatty acids such as oleic acid, lauric acid and stearic acid; EO adducts of saturated or unsaturated aliphatic amines such as laurylamine, stearylamine, coconut oil amine or EO / PO Adjunct.

The concentration of the brightener, in particular, the nonionic surfactant in the plating bath may be the same as in the prior art, and is preferably 0.1 to 50 g.
/ L, especially 1 to 30 g / L.

In order to prevent the oxidation of stannous ion (Sn ²⁺ ) in the plating bath, it is preferable that an antioxidant generally added to the tin plating bath is also contained in the plating bath of the present invention. Examples of such antioxidants include phenol,
Examples include hydroxyaromatic compounds such as catechol, resorcinol, hydroquinone, and pyrogallol, L-ascorbic acid, and sorbitol. The concentration of the antioxidant in the bath is generally about 0.5 to 10 g / L.

The balance of the plating bath of the present invention is water. The plating conditions of the tin-silver alloy electroplating bath of the present invention are not particularly limited, but preferred plating conditions are as follows.

Cathode current density: 0.1 to 50 A / dm ² , Temperature: 15 to 40 ° C. (at room temperature), Anode: Soluble anode such as tin, silver, tin-silver alloy, or platinum, platinum-plated titanium material, Insoluble anode such as carbon.

The substrate to be plated is not particularly limited as long as it has electroconductivity capable of electroplating. In the case of an insulating substrate, for example, electroplating can be performed by coating the surface with a metal by electroless plating or the like to impart conductivity. The plating bath of the present invention is particularly suitable for tin-silver alloy plating of electronic components requiring soldering, such as chip components, hoop materials, lead frames, semiconductor packages, bumps, and printed circuit boards.

The plating method may be a rack method or a barrel method, or a high-speed plating method using a hoop, a jet or the like. The cathode current density is preferably set appropriately within the above range according to the plating method.

[0038]

EXAMPLES The tin-silver alloy electroplating baths of Examples and Comparative Examples are shown below. All the plating baths had a pH of less than 1. In the plating bath composition shown below, 98% sulfuric acid was used as the sulfuric acid, and the amount of the sulfuric acid was shown in terms of H ₂ SO ₄ concentration.

[0039]

Example 1 An acidic tin-silver alloy electroplating bath having the following composition (the remainder being water) was prepared. The 3,6-dithiaoctane-1,8-diol used as a chelating agent in this plating bath is:
In the above formula, R ¹ = R ² = —C ₂ H ₄ OH, where n = 1.

[0040]

[Table 1]

[0041]

Example 2 An acidic tin-silver alloy electroplating bath having the following composition (the remainder being water) was prepared.

[0042]

[Table 2]

[0043]

Example 3 An acidic tin-silver alloy electroplating bath having the following composition (the remainder being water) was prepared. In this example, since methanesulfonic acid was used as the acid, the acid concentration was higher than in Examples 1 and 2. 3,6-dithiaoctane-1,8-diamine used as a chelating agent in this plating bath is represented by the above general formula.
R ¹ = R ² = -C ₂ H ₄ NH ₂ , where n = 1.

[0044]

[Table 3] Component concentration (g / L) Sn ²⁺ (supplied as stannous methanesulfonate) 40.0 Ag ⁺ (supplied as silver methanesulfonate) 2.5 Methanesulfonic acid 140.0 3,6-dithiaoctane-1,8 -Diamine 10.0 EO (20 mol) adduct of β-naphthol 10.0 Catechol 2.0

[0045]

Example 4 An acidic tin-silver-bismuth alloy electroplating bath having the following composition (the remainder being water) was prepared.

[0046]

[Table 4]

[0047]

Example 5 An acidic tin-silver-copper alloy electroplating bath having the following composition (the remainder being water) was prepared.

[0048]

Table 5 Component concentration (g / L) Sn ²⁺ (supplied as stannous methanesulfonate) 40.0 Ag ⁺ (supplied as silver methanesulfonate) 2.5 Cu ²⁺ (supplied as copper methanesulfonate) 0.3 Methane Sulfonic acid 140.0 3,6-Dithiaoctane-1,8-diol 10.0 EO (15 mol) adduct of coconut oil amine 15.0 Resorcinol 2.0

[0049]

Comparative Example 1 Electroplating of an acidic tin-silver alloy having the following composition (the remainder being water) is the same as in Example 1 except that no chelating agent (3,6-dithiaoctane-1,8-diol) was added. A bath was prepared.

[0050]

[Table 6]

[0051]

Comparative Example 2 An acid tin-silver alloy electroplating bath having the following composition (the remainder being water) was prepared in the same manner as in Example 2 except that the conventional chelating agent was changed to trimethylthiourea.

[0052]

[Table 7]

[0053]

Comparative Example 3 The same procedure as in Example 3 was carried out except that the chelating agent was changed to a conventional thiourea.
A silver alloy electroplating bath (the remainder was water) was prepared.

[0054]

[Table 8] Component concentration (g / L) Sn ²⁺ (supplied as stannous methanesulfonate) 40.0 Ag ⁺ (supplied as silver methanesulfonate) 2.5 Methanesulfonic acid 140.0 thiourea 4.0 EO of β-naphthol 20 mol) adduct 10.0 catechol 2.0

[0055]

[Experimental results] 1. Stability of plating bath Each of the acidic plating baths of the above Examples and Comparative Examples was placed in a glass bottle with a lid, allowed to stand at room temperature, and visually observed for precipitation after 1 hour, 1 week and 1 month. Judged by. The results (○: no precipitation, ×: precipitation) are shown in Table 9 below.

[0056]

[Table 9]

As can be seen from Table 1, the tin-silver-based alloy acidic plating bath of the present invention using a thioethane compound as a chelating agent is similar to the case where methanesulfonic acid is used, even if the bath is constructed using sulfuric acid. , And could be stored for one month or longer without precipitation. In contrast, in Comparative Example 1 in which no chelating agent was present, a precipitate was formed within one hour. The chelating agent is methylthiourea,
In Comparative Example 2 in which a bath was prepared using sulfuric acid, precipitation occurred in one month, and the plating bath became unusable. In Comparative Example 3 in which the chelating agent was thiourea, precipitation occurred in the plating bath in one week even when the bath was constructed using methanesulfonic acid.

2. Hull Cell Test Using the plating bath of the above example, a tin-silver alloy electroplating was performed on a copper plate or a 42 alloy (42% Ni-Fe alloy) plate in a Hull cell under the following conditions.

Energization: 3 A × 3 minutes Temperature: 25 ° C. Anode: Tin plate The deposition ratio of each metal of the tin-silver alloy plating film at the position of 5 A / dm ^{2 in} the obtained Hull cell pattern was determined by atomic absorption spectrometry. The results of the analysis are shown in Table 10 below (the balance being tin). Each of the plating films had a dense and good appearance in the white matte portion of the Hull cell pattern.

[0060]

[Table 10]

As can be seen from Table 10, not only the tin-silver binary alloy plating film but also the tin-silver-copper or tin-silver-bismuth ternary alloy plating film can be formed by the tin-silver alloy plating bath of the present invention. It can be formed, and the content of the alloy element in the plating film can be controlled by the composition in the plating bath.

[0062]

According to the present invention, an acidic tin-silver alloy electroplating bath which is stable even when a bath is constructed using sulfuric acid, can be stored for a long time without precipitation, and is easy to manage the bath is realized. it can. Thereby, the cost of electroplating tin-silver alloy can be reduced. The electroplating bath of the present invention suppresses the preferential precipitation of silver, so that not only tin-silver binary alloy but also tin-
A plating film of a ternary alloy such as silver-copper or tin-silver-bismuth can also be formed, and the plating film thus formed has a dense white matte appearance.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sahisa Senda 50 Nobacho, Noda-cho, Kariya-shi, Aichi F-term in Yuken Industry Co., Ltd. (Reference) 4K023 AB04 AB34 BA06 BA29 CA01 CB05 CB08 CB33 4K024 AA21 BB09 BB11 CA01 CA02 GA14

Claims (3)

[Claims] (1) a soluble stannous compound, (2) a soluble silver compound, (3) a general formula: R ¹ -S (CH ₂ CH ₂ S) _n -R ² (wherein R ¹
And R ² may be the same or different and each represents -CH
_{2 OH, -C 2 H 4 OH} , -C 3 H 6 OH, -CH 2 NH 2, -C 2 H 4 NH 2, -
Selected from C ₃ H ₆ NH ₂ , wherein n is an integer of 1 to 3), and (4) at least one acid selected from sulfuric acid and sulfonic acid. A tin-silver alloy electroplating bath. 2. The method according to claim 1, further comprising: (5) a nonionic surfactant;
(6) The tin-silver alloy electroplating bath according to claim 1, which contains an antioxidant. 3. The tin-silver alloy electroplating bath according to claim 1, further comprising a soluble copper compound or a soluble bismuth compound.