JP4359907B2 - Tin-copper alloy plating bath - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tin-copper alloy plating bath, which does not contain lead that adversely affects the human body and the environment, is excellent in film composition ratio stability in a wide current density region, and can improve the appearance and denseness of the plating film. I will provide a.
[0002]
BACKGROUND OF THE INVENTION
In recent years, there has been a concern about the influence of lead on the human body and the environment. Since pure tin plating may cause whisker, development of solder plating that does not contain lead is desired.
As lead-free solder, tin-silver alloy, tin-bismuth alloy, tin-zinc alloy, etc. have been studied. For example, in the case of tin-silver alloy plating, the plating bath is easily decomposed, so that it is stable. There is a fact that it is not easy to prepare an excellent plating bath.
On the other hand, tin-copper alloy plating attracts attention in Europe and the United States, and there is a report of practical application. Tin-copper alloy has an eutectic composition with a copper content of 1.3 mol%, and its melting point is 227 ° C., and the bonding temperature is slightly higher, but it has excellent bonding strength and costs compared to tin-silver alloy and the like. Because it is low, it is a leading candidate for lead-free solder.
[0003]
[Prior art]
JP-A-8-13185 discloses at least one metal ion selected from the group consisting of (a) Sn ²⁺ ions, (b) Ag ⁺ , Cu ²⁺ , In ³⁺ , Tl ⁺ and Zn ^2+. (C) a lead-free tin alloy plating bath containing a nonionic surfactant is disclosed.
In the conventional technology, a low melting point film similar to a tin-lead alloy plating film can be obtained without using lead, and the appearance of the plating film, solderability, and ease of bath management are also excellent. Is stated.
[0004]
[Problems to be solved by the invention]
In Example 3 of the prior art (see paragraph 28 of the same publication), tin-copper composed of stannous methanesulfonate, copper methanesulfonate, methanesulfonic acid, and an ethylene oxide adduct of octylphenol ethoxylate. An alloy plating bath was also used in Example 4 (see paragraph 29 of the same publication), stannous methane sulfonate, copper methane sulfonate, methane sulfonic acid, and an ethylene oxide adduct of lauryl amine. -Copper alloy plating baths are disclosed respectively.
By the way, in the test on the plating film obtained from these plating baths, only the solder wettability at ^{2 A} / dm ² and 20 ° C. is described (see paragraphs 37 to 40 of the same publication).
[0005]
The above prior art is intended to improve the solderability of the plating film, and when plating is performed under conditions of various cathode current densities from high density to low density using this tin-copper alloy plating bath. Since the Sn / Cu composition ratio of the coating fluctuates, there is a problem in the practicality of the plating bath from the viewpoint of obtaining a tin-copper alloy coating having a stable composition ratio. For example, as described above, a low melting point tin-copper eutectic composition alloy can be obtained under the condition of a Cu composition ratio of 1.3 mol%. However, if the current density dependency on the film composition ratio is high, the composition is suitable for each application. Therefore, a tin-copper alloy plating film having a specific ratio cannot be stably obtained, and the practicality as a plating bath is lowered.
In addition, the tin-copper alloy film obtained from the above-described conventional plating bath is not necessarily sufficient in appearance and denseness, and has a problem in terms of commercial value.
An object of the present invention is to develop a tin-copper alloy plating bath that has a low current density dependency of the Sn / Cu composition ratio in a plating film and is excellent in the appearance and denseness of the film.
[0006]
[Problems to be solved by the invention]
First, the present applicant has disclosed in Japanese Patent Application No. 10-150660 a thiol such as 2,2′-dithiodianiline, 2,2′-dipyridyl disulfide, or 1,8-diamino-3,6-dithiaoctane. Silver and silver alloy plating baths containing crown ethers and the like are proposed. As one of specific examples, silver salts of organic sulfonic acid, stannous salts of organic sulfonic acid, organic sulfonic acid, dithiodi A tin-silver alloy plating bath containing aniline and a surfactant was presented.
[0007]
The present inventors have been focusing on the dithio dianiline, tin - with applying the dithio dianiline the copper alloy plating bath, in addition, ethylene oxide and the like C ₁ -C ₂₀ alkanols, phenols, naphthols, bisphenols When a specific nonionic surfactant that is an adduct of propylene oxide coexists, the Sn / Cu composition ratio of the plating film becomes extremely stable in a wide current density range from high current density to low current density. The present invention has been completed by finding out that the appearance and denseness of the plating film are improved.
[0008]
That is, the present invention 1 includes (A) a soluble stannous salt,
(B) a soluble copper salt,
(C) an organic acid selected from organic sulfonic acids and aliphatic carboxylic acids, or an inorganic acid selected from sulfuric acid, hydrochloric acid, and borohydrofluoric acid,
(D) dithiodianiline,
(E) C ₁ ~C ₂₀ alkanols, phenols, naphthols, bisphenols selected from bisphenol A and bisphenol B, C ₁ -C ₂₅ alkyl phenols, aryl phenols, C ₁ -C ₂₅ alkyl naphthol, Ra · Rb · (MO ) P = O represented by the general formula (wherein R _a and R _b are the same or different C ₁ -C ₂₅ alkyl, one of which may be H. M represents H or an alkali metal) Addition of ethylene oxide and / or propylene oxide selected from C ₁ -C ₂₅ alkoxylated phosphoric acid, sorbitan ester, polyalkylene glycol, C ₁ -C ₂₂ aliphatic amine, C ₁ -C ₂₂ aliphatic amide A tin-copper alloy plating bath comprising a nonionic surfactant which is a product.
[0009]
Invention 2 is a tin-copper alloy plating bath according to Invention 1, wherein the organic sulfonic acid (C) is at least one of alkane sulfonic acid, alkanol sulfonic acid, and aromatic sulfonic acid. .
[0010]
Invention 3 is the tin-copper alloy plating bath according to Invention 2, wherein the alkanesulfonic acid is methanesulfonic acid.
[0011]
Invention 4 is characterized in that, in any one of Inventions 1 to 3, the nonionic surfactant (E) is an ethylene oxide adduct of α-naphthol.
[0012]
The present invention 5 includes (A) a soluble stannous salt,
(B) a soluble copper salt,
(C) methanesulfonic acid,
(D) 2,2'-dithiodianiline
(E) A tin-copper alloy plating bath characterized by containing an ethylene oxide adduct of α-naphthol.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The soluble stannous salt used in the tin-copper alloy plating bath of the present invention refers to any organic or inorganic tin salt that generates stannous ions in water, specifically, methanesulfonic acid, ethanesulfonic acid, In addition to stannous salts of organic sulfonic acids such as 2-propanolsulfonic acid and p-phenolsulfonic acid, stannous borofluoride, stannous sulfosuccinate, stannous sulfate, stannous oxide, stannous chloride Etc.
The soluble stannous salt can be used alone or in combination, and the content thereof relative to the plating bath is 0.01 to 5 mol / L, preferably 0.05 to 0.5 mol / L.
On the other hand, the soluble copper salt refers to any organic or inorganic copper salt that produces stable copper ions in water. Specifically, the organic sulfonic acid copper salt, copper sulfate, copper chloride, copper oxide, carbonate Examples thereof include copper, copper acetate, copper pyrophosphate, and copper oxalate.
The soluble copper salt can be used singly or in combination, and its content with respect to the plating bath is 0.0001 to 1 mol / L, preferably 0.0005 to 0.5 mol / L.
[0014]
Examples of the acid constituting the base of the tin-copper alloy plating bath of the present invention include organic acids such as organic sulfonic acid and aliphatic carboxylic acid, or sulfuric acid, hydrochloric acid, borofluoric acid, hydrofluoric acid, and sulfamic acid. Inorganic acids such as, but organic sulfonic acids are preferred in terms of the solubility of tin or copper, the ease of wastewater treatment, and the like.
The above acid can be used alone or in combination, and its content is 0.01 to 50 mol / L, preferably 0.1 to 10 mol / L.
[0015]
Examples of the organic sulfonic acid include alkane sulfonic acid, alkanol sulfonic acid, and aromatic sulfonic acid. The alkane sulfonic acid is represented by a chemical formula C _n H _{2n + 1} SO ₃ H (for example, n = 1 to 11). Specifically, methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, Examples include decane sulfonic acid and dodecane sulfonic acid.
[0016]
As the alkanol sulfonic acid, the formula _{C m H 2m + 1 -CH (} OH) -C p H 2p -SO 3 H ( e.g., m = 0~6, p = 1~5 )
In particular, 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid (2-propanolsulfonic acid), 2-hydroxybutane-1-sulfonic acid, In addition to 2-hydroxypentane-1-sulfonic acid, etc., 1-hydroxypropane-2-sulfonic acid, 3-hydroxypropane-1-sulfonic acid, 4-hydroxybutane-1-sulfonic acid, 2-hydroxyhexane-1- Examples thereof include sulfonic acid, 2-hydroxydecane-1-sulfonic acid, and 2-hydroxydodecane-1-sulfonic acid.
[0017]
The aromatic sulfonic acid is basically benzene sulfonic acid, alkyl benzene sulfonic acid, phenol sulfonic acid, naphthalene sulfonic acid, alkyl naphthalene sulfonic acid, naphthol sulfonic acid, etc., specifically, 1-naphthalene sulfonic acid, 2 -Naphthalenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, p-phenolsulfonic acid, cresolsulfonic acid, sulfosalicylic acid, nitrobenzenesulfonic acid, sulfobenzoic acid, diphenylamine-4-sulfonic acid and the like.
Among the organic sulfonic acids, methanesulfonic acid, ethanesulfonic acid, 2-propanolsulfonic acid, phenolsulfonic acid, and the like are preferable.
[0018]
The dithiodianiline is used for suppressing the current density dependency of the Sn / Cu composition ratio in the plating film, or for improving the appearance of the plating film, and the position of the SS bond to the aniline ring is not limited, Specific examples include 2,2'-dithiodianiline, 4,4'-dithiodianiline, 2,4'-dithiodianiline, and the like. The content of the dithiodianiline in the plating bath is 0.001 to 1.0 mol / L, preferably 0.005 to 0.1 mol / L.
[0019]
The above nonionic surfactant is used to remarkably improve the current density dependency of the Sn / Cu composition ratio in the plating film due to a synergistic effect with the dithiodianiline, and to further densify the plating film. .
The nonionic surfactants are, C ₁ -C ₂₀ alkanols, phenol, naphthol, bisphenol, C ₁ -C ₂₅ alkyl phenols, aryl phenols, C ₁ -C ₂₅ alkyl naphthol, C ₁ -C ₂₅ alkoxylated phosphoric acid ( salts), sorbitan esters, styrenated phenols, polyalkylene glycols, C ₁ -C ₂₂ aliphatic amines, C ₁ -C ₂₂ 2 to 300 moles of aliphatic amides such as ethylene oxide (EO) and / or propylene oxide (PO) Addition condensation. Accordingly, it may be an EO-only adduct such as a predetermined alkanol, phenol, or naphthol, an adduct of PO alone, or an adduct in which EO and PO coexist. Specifically, α-naphthol or β- Ethylene oxide adducts of naphthol (ie α-naphthol polyethoxylate etc.) are preferred.
[0020]
C ₁ -C ₂₀ alkanols for addition condensation of ethylene oxide (EO) and / or propylene oxide (PO) include octanol, decanol, lauryl alcohol, tetradecanol, hexadecanol, stearyl alcohol, eicosanol, cetyl alcohol, oleyl alcohol , Docosanol and the like.
Similarly, bisphenols include bisphenol A and bisphenol B.
C ₁ -C ₂₅ alkylphenols include mono, di, or trialkyl substituted phenols such as p-butylphenol, p-isooctylphenol, p-nonylphenol, p-hexylphenol, 2,4-dibutylphenol, 2,4, Examples include 6-tributylphenol, p-dodecylphenol, p-laurylphenol, and p-stearylphenol.
Examples of the arylalkylphenol include 2-phenylisopropylphenyl.
[0021]
Examples of the alkyl group of C ₁ -C ₂₅ alkyl naphthol include methyl, ethyl, propyl, butylhexyl, octyl, decyl, dodecyl, octadecyl, and the like, which may be at any position of the naphthalene nucleus.
C ₁ -C ₂₅ alkoxylated phosphoric acid (salt) is represented by the following general formula (a).
Ra · Rb · (MO) P = O (a)
(In formula (a), R _a and R _b are the same or different C ₁ -C ₂₅ alkyl, provided that one of them may be H. M represents H or an alkali metal.)
[0022]
Sorbitan esters include mono-, di- or triesterized 1,4-, 1,5- or 3,6-sorbitan, such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan distearate, sorbitan dioleate, Examples include sorbitan mixed fatty acid esters.
C ₁ -C ₂₂ aliphatic amines include saturated and unsaturated fatty acid amines such as propylamine, butylamine, hexylamine, octylamine, decylamine, laurylamine, stearylamine, ethylenediamine, propylenediamine, and the like.
C ₁ -C ₂₂ aliphatic amides include amides such as propionic acid, butyric acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and behenic acid.
[0023]
In addition to the above components, the tin-copper alloy plating bath of the present invention may have various additives such as known antioxidants, brighteners, semi-brighteners, complexing agents, pH adjusters, and buffering agents depending on the purpose. Of course, these can be mixed.
The antioxidant is for preventing tin in the bath from being oxidized from divalent to tetravalent. Specific examples include ascorbic acid or a salt thereof, hydroquinone, catechol, resorcin, phloroglucin, cresolsulfonic acid or The salt, phenolsulfonic acid or its salt, naphtholsulfonic acid or its salt, etc. are mentioned.
[0024]
Examples of the brightener include various aldehydes such as m-chlorobenzaldehyde, p-nitrobenzaldehyde, p-hydroxybenzaldehyde, 1-naphthaldehyde, benzylidenealdehyde, salicylaldehyde, paraaldehyde, vanillin, triazine, imidazole, indole, quinoline, 2 -Vinyl pyridine, aniline and the like.
[0025]
Examples of the semi-brightening agent include thioureas, N- (3-hydroxybutylidene) -p-sulfanilic acid, N-butylidenesulfanilic acid, N-cinnamoylidenesulfanilic acid, 2,4-diamino-6- ( 2'-methylimidazolyl (1 ')) ethyl-1,3,5-triazine, 2,4-diamino-6- (2'-ethyl-4-methylimidazolyl (1')) ethyl-1,3,5 -Triazine, 2,4-diamino-6- (2'-undecylimidazolyl (1 ')) ethyl-1,3,5-triazine, phenyl salicylate, or benzothiazole, 2-methylbenzothiazole, 2- (Methyl mercapto) benzothiazole, 2-aminobenzothiazole, 2-amino-6-methoxybenzothiazole, 2-methyl-5-chlorobenzothiazole, 2-hydroxybenzothiazole, 2- Amino-6-methylbenzothiazole, 2-chlorobenzothiazole, 2,5-dimethylbenzothiazole, 2-mercaptobenzothiazole, 6-nitro-2-mercaptobenzothiazole, 5-hydroxy-2-methylbenzothiazole, 2- And benzothiazoles such as benzothiazole thioacetic acid.
[0026]
The complexing agent is mainly for stably accelerating the dissolution of copper in a bath. Specifically, gluconic acid, glucoheptonic acid, ethylenediamine, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) ), Nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetraminehexaacetic acid (TTHA), oxalic acid, citric acid, tartaric acid, Rochelle Examples thereof include salts, lactic acid, malic acid, malonic acid, acetic acid, or salts thereof, thiourea or derivatives thereof.
Examples of the pH adjuster include various acids such as hydrochloric acid and sulfuric acid, and various bases such as ammonium hydroxide and sodium hydroxide.
Examples of the buffer include boric acids, phosphoric acids, and ammonium chloride.
[0027]
The concentration of the various additives in the tin-copper alloy plating bath of the present invention can be arbitrarily adjusted and selected in accordance with barrel plating, rack plating, high-speed continuous plating, rackless plating, and the like.
[0028]
When electroplating is performed using the tin-copper alloy plating bath of the present invention, the bath temperature is 0 ° C. or higher, preferably about 10 to 50 ° C. The cathode current density is about 0.01 to 150 A / dm ² , preferably about 0.1 to 30 A / dm ^{2. In} particular, in the tin-copper alloy plating bath of the present invention, the organic sulfonic acid bath is specified as dithiodianiline. Since the nonionic surfactant is used in combination, the Sn / Cu composition ratio of the coating can be stabilized in a wide region from a low current density to a high current density. Moreover, the pH of the bath can be applied to a region from acidic to almost neutral, but a range of weakly acidic to strongly acidic is particularly preferable.
[0029]
【The invention's effect】
(1) Since dithiodianiline and a specific nonionic surfactant are used in combination in the tin-copper alloy plating bath, a tin-copper alloy film having a small current density dependency can be obtained. That is, when it does not contain both components of dithiodianiline and a specific nonionic surfactant, or contains only one of them (for example, when it contains only a nonionic surfactant, The plating bath of the present invention has a significant advantage in that the Sn / Cu composition ratio of the film can be stabilized in a wide region from a low current density to a high current density. ing.
In particular, as shown in the test examples to be described later, for example, when 2,2′-dithiodianiline and an ethylene oxide adduct of α-naphthol are used in combination in a methanesulfonic acid bath, the current density dependency is further reduced, A tin-copper alloy plating film having a composition ratio substantially corresponding to the Sn / Cu content ratio of the plating bath is obtained. Therefore, a tin-copper eutectic alloy having a Cu composition ratio of 1.3 mol% with a low melting point and high practicality can be easily obtained by preparing the bath.
[0030]
(2) As shown in the test examples described later, when dithiodianiline and a specific nonionic surfactant are used in combination with a tin-copper alloy plating bath, both components are contained or only one component is contained. As compared with the above, the appearance, denseness, smoothness and the like of the tin-copper alloy plating film can be remarkably improved, and the commercial value of the object to be plated can be increased.
The use of an organic sulfonic acid bath is advantageous in terms of the solubility of tin or copper or the ease of wastewater treatment.
[0031]
(3) The tin-copper alloy plating of the present invention is a solder plating not containing lead and has a low risk of polluting the human body and the environment. In addition, the bonding strength is high, and the cost can be reduced compared to tin-silver alloy plating, etc., and it has a bonding temperature equivalent to that of tin-lead alloy plating and can provide highly practical lead-free solder plating. .
Moreover, there is no fear of whisker generation like a tin film.
[0032]
【Example】
Hereinafter, examples of the tin-copper alloy plating bath will be sequentially described, and various test examples such as the current density dependency of the Sn / Cu composition ratio of the electrodeposited coating and the appearance of the tin-copper alloy plating coating will be described.
It should be noted that the present invention is not limited to the following examples and test examples, and can be arbitrarily modified within the scope of the technical idea of the present invention.
[0033]
In the tin-copper alloy plating baths of the following examples and comparative examples, Examples 1 to 8 are basically dithiodianiline, nonionic surfactant, concentration of soluble metal salt, or type of nonionic surfactant. Is a variety of changes.
Comparative Examples 1 to 3 are based on Example 1, Comparative Example 1 is a blank example lacking both dithiodianiline and nonionic surfactant, and Comparative Example 2 is a nonionic surfactant. This is a blank example. Comparative Example 3 is a blank example of dithiodianiline, and is based on the prior art described above (see Examples 3 to 4) in that a nonionic surfactant is contained in an organic sulfonic acid bath of a tin-copper alloy. It is assumed as a similar example.
[0034]
Example 1
A tin-copper alloy plating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 0.1974 mol / L
Copper sulfate (as Cu ²⁺ ) 0.0026 mol / L
Methanesulfonic acid 2mol / L
2,2'-dithiodianiline 0.01 mol / L
α-Naphthol polyethoxylate (EO10) 5g / L
[0035]
Example 2
A tin-copper alloy plating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 0.1974 mol / L
Copper sulfate (as Cu ²⁺ ) 0.0026 mol / L
Methanesulfonic acid 2mol / L
2,2'-dithiodianiline 0.005 mol / L
α-Naphthol polyethoxylate (EO6.7) 5g / L
[0036]
Example 3
A tin-copper alloy plating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 0.4 mol / L
Copper sulfate (as Cu ²⁺ ) 0.005 mol / L
Methanesulfonic acid 1mol / L
2,2'-dithiodianiline 0.02 mol / L
Tristyrenated phenol polyethoxylate (EO15) 3g / L
Catechol 1g / L
[0037]
Example 4
A tin-copper alloy plating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 0.2 mol / L
Copper methanesulfonate (as Cu ²⁺ ) 0.005 mol / L
Methanesulfonic acid 2mol / L
2,2'-dithiodianiline 0.02 mol / L
Polyoxyethylene nonylphenyl ether (EO15) 5g / L
Hydroquinone 1g / L
[0038]
Example 5
A tin-copper alloy plating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 0.1974 mol / L
Copper sulfate (as Cu ²⁺ ) 0.0026 mol / L
Methanesulfonic acid 2mol / L
2,2'-dithiodianiline 0.01 mol / L
Laurylamine polyethoxylate (EO10) 5g / L
Catechol 1g / L
[0039]
Example 6
A tin-copper alloy plating bath was constructed with the following composition.
Stannous sulfate (as Sn ²⁺ ) 0.1974 mol / L
Copper sulfate (as Cu ²⁺ ) 0.0026 mol / L
Methanesulfonic acid 2mol / L
2,2'-dithiodianiline 0.01 mol / L
Bisphenol A polyethoxylate (EO30) 5g / L
Hydroquinone 1g / L
[0040]
Example 7
A tin-copper alloy plating bath was constructed with the following composition.
Stannous ethanesulfonate (as Sn ²⁺ ) 0.1974 mol / L
Copper sulfate (as Cu ²⁺ ) 0.0026 mol / L
Ethanesulfonic acid 2mol / L
4,4'-dithiodianiline 0.01 mol / L
Tristyrenated phenol polyethoxylate (EO15)
-Polypropoxylate (PO3) 7g / L
Hydroquinone 1g / L
[0041]
Example 8
A tin-copper alloy plating bath was constructed with the following composition.
Stannous sulfate (as Sn ²⁺ ) 0.1974 mol / L
Copper sulfate (as Cu ²⁺ ) 0.0026 mol / L
Sulfuric acid 1mol / L
2,2'-dithiodianiline 0.01 mol / L
Laurylamine polyethoxylate (EO10)
-Polypropoxylate (PO3) 7g / L
Catechol 1g / L
[0042]
<< Comparative Example 1 >>
A tin-copper alloy plating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 0.1974 mol / L
Copper sulfate (as Cu ²⁺ ) 0.0026 mol / L
Methanesulfonic acid 2mol / L
[0043]
<< Comparative Example 2 >>
A tin-copper alloy plating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 0.1974 mol / L
Copper sulfate (as Cu ²⁺ ) 0.0026 mol / L
Methanesulfonic acid 2mol / L
2,2'-dithiodianiline 0.01 mol / L
[0044]
<< Comparative Example 3 >>
A tin-copper alloy plating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 0.1974 mol / L
Copper sulfate (as Cu ²⁺ ) 0.0026 mol / L
Methanesulfonic acid 2mol / L
α-Naphthol polyethoxylate (EO10) 5g / L
[0045]
<Example of current density dependency test>
Therefore, using each of the tin-copper alloy plating baths of Examples 1 to 8 and Comparative Examples 1 to 3, electroplating was carried out on a nickel substrate under a bath temperature of 25 ° C. and a cathode current density of A or B below. With respect to the obtained tin-copper alloy plating film, a current density dependency test of the Sn / Cu composition ratio of the film was performed.
(1) Current density condition A: 20 minutes at 0.5 A / dm ²
(2) Current density condition B: 3 A / dm ² for 3 minutes and 20 seconds The above test was conducted for the electrodeposition film obtained under each current density condition A or B, after dissolving each film, high-frequency plasma emission spectroscopy Quantification was performed by (ICP), and the film composition ratio was analyzed.
[0046]
The left column to the center column in FIG. 1 show the test results.
The Sn / Cu composition ratio of the electrodeposition films obtained from the plating baths of Examples 1 and 3 to 8 is between the low current density condition of 0.5 A / dm ^{2 and} the high current density condition of 3 A / dm ^2. Almost unchanged, the current density dependence of the Sn / Cu composition ratio of the electrodeposited film was found to be very small. Moreover, since a tin-copper alloy plating film having the same composition ratio as the content of the plating bath can be obtained, a tin-copper eutectic composition film having a copper composition ratio of 1.3 mol% by adjusting the bath composition, It has also become clear that a film similar to this can be formed in each example. In particular, in Example 4, it was confirmed that the copper composition ratio of the coating was increased to 2.5 mol% by increasing the copper composition ratio of the bath compared to the other examples.
On the other hand, in Comparative Example 1 lacking both components of dithiodianiline and nonionic surfactant, copper preferentially precipitates under a low current density. As a result, the Sn / Cu composition ratio of the electrodeposited film is low. It was confirmed that the dependence of the film composition ratio on the current density greatly increased with the difference between the current density condition and the high current density condition.
Also in Comparative Example 2 lacking the nonionic activator, the preferential precipitation of copper under a low current density could not be suppressed, and the current density dependency of the film composition ratio was large.
Comparative Example 3 is an example similar to the prior art described above in that it lacks dithiodianiline and contains a nonionic activator, but in this case as well, as in Comparative Example 2, the current density dependency was large. .
Therefore, a tin-copper alloy plating bath using a combination of dithiodianiline and a specific nonionic surfactant has a Sn / Cu composition ratio of the electrodeposited film as compared with a plating bath lacking both or one of them. The superiority in terms of current density dependency was remarkable, and it was found that the film composition ratio could be satisfactorily stabilized in a wide current density range from high current density to low current density.
In Example 2, since the content of dithiodianiline is lower than in other Examples, it is considered that the current density dependency of the film composition ratio is slightly increased, but the dependency is higher than that of Comparative Examples 1 to 3. The improvement was obvious.
[0047]
On the other hand, FIG. 2 shows the current densities obtained by extracting the plating baths of Example 1 and Comparative Examples 1 to 3 as representative examples and changing the plating baths in the range of 0.5 to 5 A / dm ^2. It summarizes the relationship with the copper composition ratio of the electrodeposited film.
Also in FIG. 2, it was possible to confirm again the remarkable lowering effect on the current density dependency of the film composition ratio when the dithiodianiline and the nonionic surfactant were combined.
[0048]
<< Example of film appearance test >>
About the said electrodeposition film | membrane of each said tin- copper alloy obtained from the plating bath of the Example and the comparative example, the state of the film | membrane surface was observed visually and the film | membrane external appearance test was done.
The evaluation criteria are as follows.
○: Uniform white appearance.
X: Color unevenness was recognized and the color tone was grayish.
The right column of FIG. 1 shows the result.
Although the electrodeposition films of Examples 1 to 8 were all evaluated as “good”, the evaluations of Comparative Examples 1 to 3 were inferior.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a chart showing results of a current density dependency test and a film appearance test on electrodeposited films obtained from the tin-copper alloy plating baths of Examples 1 to 8 and Comparative Examples 1 to 3, respectively.
FIG. 2 is a graph showing the relationship between the current density and the copper composition ratio of the electrodeposited film for the tin-copper alloy plating baths of Example 1 and Comparative Examples 1 to 3.

Claims (5)

(A) a soluble stannous salt,
(B) a soluble copper salt,
(C) an organic acid selected from organic sulfonic acids and aliphatic carboxylic acids, or an inorganic acid selected from sulfuric acid, hydrochloric acid, and borohydrofluoric acid,
(D) dithiodianiline,
(E) C ₁ ~C ₂₀ alkanols, phenols, naphthols, bisphenols selected from bisphenol A and bisphenol B, C ₁ -C ₂₅ alkyl phenols, aryl phenols, C ₁ -C ₂₅ alkyl naphthol, Ra · Rb · (MO ) P = O represented by the general formula (wherein R _a and R _b are the same or different C ₁ -C ₂₅ alkyl, one of which may be H. M represents H or an alkali metal) Addition of ethylene oxide and / or propylene oxide selected from C ₁ -C ₂₅ alkoxylated phosphoric acid, sorbitan ester, polyalkylene glycol, C ₁ -C ₂₂ aliphatic amine, C ₁ -C ₂₂ aliphatic amide A tin-copper alloy plating bath comprising a nonionic surfactant which is a product. The tin-copper alloy plating bath according to claim 1, wherein the organic sulfonic acid (C) is at least one of alkane sulfonic acid, alkanol sulfonic acid, and aromatic sulfonic acid. 3. The tin-copper alloy plating bath according to claim 2, wherein the alkane sulfonic acid is methane sulfonic acid. The tin-copper alloy plating bath according to any one of claims 1 to 3, wherein the nonionic surfactant (E) is an ethylene oxide adduct of α-naphthol. (A) a soluble stannous salt,
(B) a soluble copper salt,
(C) methanesulfonic acid,
(D) 2,2'-dithiodianiline
(E) A tin-copper alloy plating bath comprising an ethylene oxide adduct of α-naphthol.

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