JP4273266B2 - Dissolving current suppression type tin alloy electroplating method - Google Patents

Description

The present invention relates to a dissolution current suppression-type tin alloy electroplating method using a lead-free tin alloy electroplating bath. By adding a dissolution current inhibitor, the dissolution current of a tin (alloy) anode is suppressed, Provided is one capable of preventing noble metals (silver, bismuth, copper) from being deposited on the anode during electrodeposition.

Tin or tin alloy plating has excellent solderability, so it is widely used in the field of industrial plating such as electronic parts and automobile parts. However, tin-lead alloy plating is subject to regulations from the viewpoint of environmental protection and safety. Moreover, tin plating has a problem of whisker generation.
Alloy plating of tin and a metal more precious than tin, such as a tin-silver alloy, a tin-bismuth alloy, or a tin-copper alloy, is a promising candidate for a tin alloy plating that does not contain lead.

The following are known as such lead-free tin alloy plating baths or plating methods.
(1) Patent Document 1
It is disclosed that a tin alloy plating bath containing a tin-silver alloy, a tin-bismuth alloy, and a tin-copper alloy contains a monoamine type compound such as an aspartic acid derivative or a glutamic acid derivative (claims 1 and 2, paragraphs). 8 and 17).
Further, Example 3 of the same document 1 has a tin-silver alloy plating bath containing sulfoethyl glutamic acid diacetic acid (see paragraph 104), and Example 7 has a tin-copper alloy plating bath containing glutamic acid diacetate ( Examples 14 and 16 describe a tin-copper alloy plating bath containing sulfoethyl glutamic acid (see paragraphs 115 and 117), respectively.

(2) Patent Document 2
In a tin alloy plating bath containing tin-silver alloy, tin-bismuth alloy, tin-copper alloy containing IB to VB group elements of 4th to 6th period of 20 to 2000 ppm as an essential component, glycine, asparagine It is disclosed to contain an aliphatic aminocarboxylic acid such as an acid or glutamic acid (see claim 16, paragraph 13).
Further, Example 9 of the same document 2 discloses a tin-bismuth alloy plating bath containing an EDTA salt (see paragraph 51). The tin-silver alloy plating bath of Example 8 and the tin-copper alloy plating bath of Example 15 did not contain aminocarboxylic acid (see paragraphs 50 and 57).

(3) Patent Document 3
In order to prevent displacement deposition of bismuth on the cathode side plating object and the tin-bismuth alloy film formed thereon, in tin-bismuth alloy electroplating at a specific range of current density, while supplying power A method is disclosed in which an object to be plated is immersed in a plating bath and pulled up from the plating bath (see claim 1).

(4) Patent Document 4
In order to prevent deposition of metals with a higher electrode potential than tin (copper, silver, bismuth, etc.) on the tin anode, an insoluble electrode is used as the anode of the electroplating bath, and it is a dissolution bath separate from the electrode bath. Discloses a method of replenishing tin by anodic electrolysis of tin (see claims 1 and 2, paragraphs 13 to 15).

(5) Patent Document 5
A tin-cobalt alloy plating bath containing an alkali stannate, an organic cobalt salt, and oxycarboxylic acids, and further containing an aminocarboxylic acid such as glycine and glutamic acid at a predetermined concentration is disclosed (claims 1 and 2). 6).

JP 2000-26991 A JP 2003-96590 A Japanese Examined Patent Publication No. 7-65207 JP 2003-105581 A Japanese Patent Laid-Open No. 9-241885

When tin or tin alloy is electroplated with a tin alloy of a noble metal (such as silver, bismuth or copper) using tin or a tin alloy anode, tin has a natural electrode potential higher than that of silver, bismuth or copper. There is a problem that silver, bismuth, copper, or the like is deposited on the tin (alloy) anode during electrodeposition because the electrode potential difference between both electrodes is large.
In order to solve such a problem, the following methods (1) to (3) can be considered in principle.
(1) First, if the noble metal is complexed with a complexing agent and the natural electrode potential of the noble metal is made lower than the natural electrode potential of tin, the above substitution can be prevented regardless of energization or non-energization. However, other than the complex of copper-thioureas and copper-specific sulfides (see Japanese Patent No. 3433291), such a complexing agent has not been found.

(2) Next, it is conceivable that the tin (alloy) anode potential is made noble than the natural electrode potential of the noble metal by energization (the above-mentioned Patent Document 4 is based on this principle).
The natural electrode potentials of silver, bismuth, and copper, and the natural electrode potentials when these are complexed are listed as follows (the potential is noble as it goes up, and it is base as it goes down). In the table below, measurement was performed using a Ag / AgCl · KCl saturated solution as a reference electrode. DTPA represents diethylenetriaminepentaacetic acid.
Natural electrode potential
Silver + 500mV
Bismuth + 100mV
Copper 0mV
Bismuth-DTPA complex -20 mV
Copper-methionine complex -150 mV
Silver-thiourea complex -300 mV
Tin -400mV
On the other hand, FIG. 4 is a polarization curve of the tin anode when no complexing agent or the like is added. Therefore, taking tin-bismuth alloy plating as an example, the natural electrode potential of bismuth is +100 mV as shown in the above table, and the anode current density at this potential is about 150 A / dm ² (ie, in FIG. 4, The dotted line extending right above +100 mV on the horizontal axis intersects the oblique polarization curve, but the dotted line extending leftward from this intersection intersects at about 150 A / dm ² on the vertical axis). If the density is made larger than 150 A / dm ^{2 and} the potential of tin is shifted more preciously than the natural electrode potential of bismuth, substitutional deposition of bismuth on the anode can be prevented.
However, for example, when lead-free plating is performed at a current density of 150 A / dm ² under an area ratio of anode to cathode of 1: 1, the cathode current density must also be 150 A / dm ^2. Realistic.
Incidentally, regarding tin-silver alloy plating, the natural electrode potential of silver is +500 mV, which is far noble compared to bismuth, and the anode current density that makes the tin potential nobler than the natural electrode potential of silver is In order to become more and more unrealistic high frequency, in actuality, for example, electroplating is performed by complexing silver with thiourea and lowering the electrode potential to -300 mV. In order to prevent precipitation, an anode current density of 30 A / dm ² or more is required (see the above table).

(3) It is conceivable to change the ratio of the anode area to the cathode area. For example, if the anode to cathode area ratio is set to anode: cathode = 1: 10, the anode current density increases to 10 A / dm ² at a cathode current density of 1 A / dm ^2. Due to the adverse effects of a) to (b), the anode area is made larger than the cathode area in actual electroplating.
(a) The anode dissolves and disappears quickly, and management is complicated.
(b) Since the distance between the cathodes is different, the current density between the cathode parts is different, and the plating film thickness varies.

As described above, any of the above methods (1) to (3) is not realistic or has a large limitation.
On the other hand, in Patent Documents 1 and 2, a plating bath contains a specific type of monoamine compound or aliphatic aminocarboxylic acid, but a metal such as silver, bismuth, or copper is substituted on the tin (alloy) anode during electrodeposition. The ability to prevent precipitation is weak, and this point is supported by the evaluation of test examples described later for baths containing aspartic acid diacetic acid and sulfoethylglutamic acid described in the literature. Similarly, Patent Document 5 cannot be expected to have a replacement preventing effect.
The present invention smoothly prevents substitution deposition of a noble metal at a tin (alloy) anode during electrodeposition during electroplating of an alloy of tin and a noble metal (such as silver, bismuth or copper). Is a technical issue.

  The present inventors suppress the dissolution current of the tin (alloy) anode, and make the potential of the tin (alloy) anode nobler than the natural electrode potential of noble metals such as silver, bismuth and copper even at a low anode current density. As a result of diligent research on the influence of various compounds on the dissolution current of tin while referring to the above-mentioned patent documents and the like, it was found that certain amino acids have a large inhibitory effect on the dissolution current, The present invention has been completed.

That is, the present invention 1 uses a tin alloy electroplating bath for suppressing dissolution current selected from any of the following (A) to (C), and the content of the following dissolution current inhibitor with respect to the plating bath Is 0.005 to 10 mol / L, and electroplating with an anode made of tin or tin alloy,
(A) soluble stannous salt, soluble silver salt, at least one acid selected from inorganic acids and organic acids or salts thereof, glutamic acid-N, N-diacetic acid, methylglycine-N, N-di A tin-silver alloy electroplating bath containing at least one anode dissolution current inhibitor selected from the group consisting of acetic acid and salts thereof
(B) a soluble stannous salt, a soluble copper salt, an acid selected from an inorganic acid and an organic acid or at least one of its salts, methylglycine-N, N-diacetic acid, aspartic acid and their salts A tin-copper alloy electroplating bath containing at least one anode dissolution current inhibitor selected from the group consisting of
(C) soluble stannous salt, soluble bismuth salt, at least one acid selected from inorganic acids and organic acids or salts thereof, and at least one anode dissolution current inhibitor comprising aspartic acid and these salts Inhibiting dissolution current of tin-bismuth alloy electroplating bath anodes containing silver and copper to prevent substitutional deposition of silver, copper or bismuth on the anode during electrodeposition This is a tin alloy electroplating method.

The present invention 2 is an electronic component in which a lead-free tin alloy film is formed on the substrate by the tin alloy electroplating method of the present invention 1 described above .

Addition of a dissolution current inhibitor consisting of a specific glutamic acid acetic acid derivative, methylglycine acetic acid derivative, aspartic acid or a salt thereof into an electroplating bath of a tin alloy (lead-free) of tin and a precious metal than tin By doing so, these inhibitors coordinate with the tin (alloy) anode to suppress the dissolution of tin and reduce the dissolution current density of the anode (ie, lower the slope of the polarization curve of the tin anode). , The anode potential is shifted more preciously than the natural electrode potential of silver (silver, bismuth or copper) noble than tin, effectively preventing noble metal from being deposited on the tin (alloy) anode during electroplating Is.
This point will be described by taking an example of tin-bismuth alloy electroplating. As described above, since the natural electrode potential of bismuth is +100 mV, a tin anodic polarization curve when the inhibitor of the present invention is not added (FIG. 4). In the non-addition-compatible polarization curve indicated by-◆-), the potential of the tin anode does not become higher than that of bismuth unless the anode current density is set to about 150 A / dm ² or more, but the tin when the inhibitor of the present invention is added. Since the anodic polarization curve (refer to the polarization curve corresponding to the addition of the inhibitor indicated by-●-,-■-or-▲-in Fig. 1) has a lower gradient than the non-added polarization curve, the inhibitor was used. In electroplating, the anode potential of tin is nobler than the potential of bismuth (+100 mV) in an anode current density range of 13 to 16 A / dm ² or more, and bismuth can be prevented from being deposited on the anode during electrodeposition. The For example, when a diacetic acid derivative of glutamic acid (abbreviated as GLDA: corresponding to-●-in FIG. 1) is added, the anode current density is about 12.3 A / dm ² or more , and aspartic acid (abbreviated as ASP). : Corresponding to-▲-in FIG. 1), the potential of the tin anode can be made nobler than the potential of bismuth at an anode current density of about 15.5 A / dm ² or more .

The present invention firstly uses a tin alloy electroplating bath selected from any of the following (A) to (C):
(A) an acetic acid derivative of glutamic acid, an acetic acid derivative of methyl glycine, or a specific amino acid consisting of these salts as a dissolution current inhibitor for the anode, a tin-silver alloy electroplating bath for suppressing dissolution current;
(B) a tin-copper alloy electroplating bath for suppressing dissolution current to which a specific amino acid consisting of an acetic acid derivative of methylglycine, aspartic acid or a salt thereof is added;
(C) Tin-bismuth alloy electroplating bath for suppressing dissolution current to which aspartic acid or a salt thereof is added
By optimizing the concentration of the dissolution current inhibitor to a specific range and performing electroplating with a tin (or tin alloy) anode, it is possible to prevent silver, copper or bismuth from being deposited on the anode during electrodeposition. The second is an electronic component in which a tin alloy film is formed on the substrate using the tin alloy plating method.
The tin alloy of the present invention is a lead-free alloy, and lead is not contained in a metal that is nobler than tin. In the present invention, a tin or tin alloy anode is used (for example, a tin or tin-copper alloy anode is used in the tin-copper alloy plating method), and an insoluble anode is excluded.

As described above, the tin alloy electroplating bath of the present invention has a basic composition of a soluble stannous salt, a soluble salt of a metal noble than tin, and a base acid.
Any soluble stannous salt can be used as long as it is a soluble salt that generates Sn ^{2+ in} a bath, and there is no particular limitation.
Examples of the soluble stannous salt include stannous salts of organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, 2-propanolsulfonic acid, p-phenolsulfonic acid, stannous borofluoride, sulfosuccinic acid Examples include stannous, stannous sulfate, stannous oxide, and stannous chloride.
In addition, examples of metals that are nobler than tin include silver, bismuth, copper, ruthenium, gold, platinum, palladium, and the like, and silver, bismuth, and copper are preferable (see the present inventions 2-3).
These soluble salts will be described in order. For example, any soluble silver salt may be used as long as it is a soluble salt that produces Ag ^{+ in} a bath, and there is no particular limitation, and hardly soluble salts are not excluded.
Soluble silver salts include silver sulfate, silver sulfite, silver carbonate, silver sulfosuccinate, silver nitrate, silver organic sulfonate, silver borofluoride, silver citrate, silver tartrate, silver gluconate, silver sulfamate, silver oxalate, oxidation Examples include soluble salts such as silver and poorly soluble salts such as silver chloride.
Examples of the soluble bismuth salt include bismuth salts of organic sulfonic acids, bismuth salts of sulfosuccinic acid, bismuth sulfate, bismuth oxide, bismuth nitrate, bismuth chloride, and bismuth bromide.
Examples of the soluble copper salt include a copper salt of organic sulfonic acid, copper sulfate, copper chloride, copper oxide, copper carbonate, copper acetate, copper pyrophosphate, and copper oxalate.
As other soluble salts of metals more precious than tin, sulfates, halides, oxides, acetates, organic sulfonates, and the like can be used as well.
The above-mentioned soluble metal salts can be used singly or in combination, and the total concentration in the bath of the soluble stannous salt relative to the plating bath and the soluble salt of a metal noble from the tin is 0.05 to 300 g / L in terms of metal salt, Preferably it is 10-180 g / L. The mixing ratio of tin and other metals is appropriately determined according to the desired composition ratio of the tin alloy plating film.

The base acid is selected from inorganic acids, organic acids or salts thereof.
The organic acid is preferably an organic sulfonic acid such as alkane sulfonic acid, alkanol sulfonic acid or aromatic sulfonic acid, which is relatively easy to treat waste water, or an aliphatic carboxylic acid.
Examples of the inorganic acid include borohydrofluoric acid, silicohydrofluoric acid, sulfamic acid, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and the like.
Examples of these salts include sodium salts, potassium salts, magnesium salts, calcium salts, ammonium salts, and amine salts.
The above acid (or salt) can be used singly or in combination, and the content thereof is 0.1 to 300 g / L, preferably 20 to 180 g / L.

  As the alkanesulfonic acid, those represented by the chemical formula CnH2n + 1SO3H (for example, n = 1 to 5, preferably 1 to 3) can be used, and specifically, methanesulfonic acid, ethanesulfonic acid, 1-propane In addition to sulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid and the like, hexanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid and the like can be mentioned.

  As the alkanol sulfonic acid, those represented by the chemical formula CmH2m + 1-CH (OH) -CpH2p-SO3H (for example, m = 0 to 6, p = 1 to 5) can be used. In addition to hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1-sulfonic acid, and the like, 1-hydroxypropane-2-sulfonic acid 3-hydroxypropane-1-sulfonic acid, 4-hydroxybutane-1-sulfonic acid, 2-hydroxyhexane-1-sulfonic acid, 2-hydroxydecane-1-sulfonic acid, 2-hydroxydodecane-1-sulfonic acid Etc.

  The aromatic sulfonic acid is basically benzene sulfonic acid, alkyl benzene sulfonic acid, phenol sulfonic acid, naphthalene sulfonic acid, alkyl naphthalene sulfonic acid, etc., specifically 1-naphthalene sulfonic acid, 2-naphthalene. Examples include sulfonic acid, toluenesulfonic acid, xylenesulfonic acid, p-phenolsulfonic acid, cresolsulfonic acid, sulfosalicylic acid, nitrobenzenesulfonic acid, sulfobenzoic acid, diphenylamine-4-sulfonic acid, and the like.

  Generally as said aliphatic carboxylic acid, a C1-C6 carboxylic acid can be used. Specific examples include acetic acid, propionic acid, butyric acid, citric acid, tartaric acid, gluconic acid, sulfosuccinic acid, and trifluoroacetic acid.

In the present invention, a lead-free tin alloy electroplating bath contains a dissolution current inhibitor made of a specific amino acid at a predetermined concentration to suppress the dissolution current of a tin (alloy) anode, thereby precious metal for the anode. It is characterized in that it can prevent substitution deposition of (silver, bismuth or copper).
The dissolution current inhibitor used in the tin alloy electroplating method of the present invention is selected from the group consisting of glutamic acid-N, N-diacetic acid, methylglycine-N, N-diacetic acid, aspartic acid and salts thereof. That is, when the tin alloy electroplating bath type is a tin-silver alloy electroplating bath , glutamic acid-N, N-diacetic acid, methylglycine-N, N-diacetic acid and salts thereof are used as dissolution current inhibitors. Similarly, in a tin-copper alloy electroplating bath , methylglycine-N, N-diacetic acid, aspartic acid and its salt are used, and in a tin-bismuth alloy electroplating bath , aspartic acid and its salt are used.
Examples of the glutamic acid derivative, methylglycine derivative, or aspartic acid salt include sodium salts, potassium salts, magnesium salts, calcium salts, ammonium salts, amine salts, and alkyl sulfonates.
The dissolution current inhibitor of the present invention is selective in its function.For example, a different amino acid such as glycine, glutamine, asparagine, cystine, phenylalanine has little or no function of suppressing the dissolution current of the anode, Similarly, amino acids such as glutamic acid and methylglycine (that is, alanine) (that is, non-derivative amino acid itself) or aspartic acid derivatives (such as acetic acid derivatives) also have a dissolution current suppressing function. Very low (see test examples below).
The dissolution current inhibitor can be used alone or in combination, and the content thereof relative to the plating bath is 0.005 to 10 mol / L , preferably 0.05 to 2 mol / L. If the amount of the inhibitor is less than the appropriate range, the dissolution current suppression effect is reduced, and if it is too much, there is not much difference in the effect, which is a waste of cost.

In the tin alloy electroplating method of the present invention, the addition of the specific amino acids described above can suppress the dissolution current of the anode, so that the potential of the tin anode can be maintained even if the anode current density is lower than in the conventional case of no addition. The noble metal (silver, bismuth or copper) can be shifted more preciously than the natural electrode potential, so that substitution deposition of the noble metal on the anode can be effectively prevented.
In this case, as described above, when a noble metal (silver, bismuth or copper) is complexed using a complexing agent, the natural electrode potential of the metal complex becomes lower than that of the metal itself (for example, silver The potential changes from +500 mV (no complexation) to -300 mV (complex) to the base), so adding a precious metal complexing agent to the plating bath further increases the anode current density compared to the case of no addition. It can be effectively reduced. By the way, in the present invention, the natural electrode potential of silver is far more noble than bismuth, so it is practical to use a complexing agent. It does not matter whether or not the agent is used.
Complexing agents for precious metals include aminocarboxylic acids such as ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, nitrilotriacetic acid, iminodiacetic acid, tartaric acid, citric acid, gluconic acid, lactic acid Oxycarboxylic acids such as methionine, amino acids such as cysteine, acetylcysteine, thioureas, sulfides such as thiodiglycol and thiodiglycolic acid, mercaptans such as mercaptosuccinic acid, thioglycol and thioglycolic acid, etc. Can be mentioned.
Further, as described above, when the anode area is smaller than the cathode area, the anode current density can be increased compared to the cathode current density, unlike the case of the equal ratio. As long as (a) to (b) do not occur, the anode area can be appropriately reduced from the cathode area.

  In the tin alloy electroplating method of the present invention, in addition to the above-mentioned components, a known surfactant, smoothing agent, brightening agent, semi-brightening agent, pH adjusting agent, buffering agent, preservative is added to the plating bath depending on the purpose. It goes without saying that various additives such as these can be contained.

The surfactant is contained for the purpose of assisting improvement of the denseness, smoothness, adhesion, etc. of the deposited silver film, and is a nonionic surfactant, an amphoteric surfactant, a cationic surfactant, or an anion. A system surfactant can be used alone or in combination (see Invention 4).
The addition amount is 0.01 to 100 g / L, preferably 0.1 to 50 g / L.

Specific examples of the nonionic surface active agent, C ₁ -C ₂₀ alkanols, phenols, naphthols, bisphenols, (poly) C ₁ -C ₂₅ alkyl phenol, (poly) aryl phenol, C ₁ -C ₂₅ alkyl naphthol, C ₁ -C ₂₅ alkoxylated phosphoric acid (salt), sorbitan ester, polyalkylene glycol, C ₁ -C ₂₂ aliphatic amine, C ₁ -C ₂₂ aliphatic amide and the like with ethylene oxide (EO) and / or propylene oxide (PO ) a and those engaged 2-300 mol adduct condensation, and the like C ₁ -C ₂₅ alkoxylated phosphoric acid (salt).

The C ₁ -C ₂₀ alkanol addition condensation of the above ethylene oxide (EO) and / or propylene oxide (PO), methanol, ethanol, n- butanol, t-butanol, n- hexanol, octanol, decanol, lauryl alcohol, tetra Examples include decanol, hexadecanol, stearyl alcohol, eicosanol, oleyl alcohol, docosanol and the like. Similarly, examples of the bisphenols include bisphenol A, bisphenol B, and bisphenol F. Examples of the (poly) C ₁ -C ₂₅ alkylphenol include mono-, di-, or trialkyl-substituted phenols such as p-methylphenol, p-butylphenol, p-isooctylphenol, p-nonylphenol, p-hexylphenol, 2, Examples include 4-dibutylphenol, 2,4,6-tributylphenol, dinonylphenol, p-dodecylphenol, p-laurylphenol, and p-stearylphenol. Examples of the arylalkylphenol include 2-phenylisopropylphenol, cumylphenol, (mono, di or tri) styrenated phenol, (mono, di or tri) benzylphenol and the like. Examples of the alkyl group of the C ₁ -C ₂₅ alkyl naphthol include methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl, octadecyl and the like, and may be at any position of the naphthalene nucleus. Examples of the polyalkylene glycol include polyoxyethylene glycol, polyoxypropylene glycol, and polyoxyethylene polyoxypropylene copolymer.

The C ₁ -C ₂₅ alkoxylated phosphoric acid (salt) is represented by the following general formula (a).
Ra, Rb, (MO) P = O (a)
(In the formula (a), Ra and Rb 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.)

Examples of the sorbitan ester include mono-, di- or triesterized 1,4-, 1,5- or 3,6-sorbitan such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan distearate, sorbitan dioleate And sorbitan mixed fatty acid ester. Examples of the C _{1 to} C ₂₂ aliphatic amine include saturated and unsaturated fatty acids such as propylamine, butylamine, hexylamine, octylamine, decylamine, laurylamine, myristylamine, stearylamine, oleylamine, beef tallow amine, ethylenediamine, and propylenediamine. An amine etc. are mentioned. Examples of the C ₁ -C ₂₂ aliphatic amide include amides such as propionic acid, butyric acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, behenic acid, coconut oil fatty acid, and beef tallow fatty acid. Is mentioned.

Furthermore, as the nonionic surfactant,
R ₁ N (R ₂ ) ₂ → O
(In the above formula, R ₁ represents C _{5 to} C ₂₅ alkyl or RCONHR ₃ (R ₃ represents C _{1 to} C ₅ alkylene), R ₂ represents the same or different C _{1 to} C ₅ alkyl) and the like. Amine oxides can be used.

As the cationic surfactant, a quaternary ammonium salt represented by the following general formula (b)
_{(R 1 · R 2 · R} 3 · R 4 N) + · X - ... (b)
(In the formula (b), X is halogen, hydroxy, C ₁ -C ₅ alkanesulfonic acid or sulfuric acid, R ₁ , R ₂ , R ₃ and R ₄ are the same or different C ₁ -C ₂₀ alkyl, aryl or benzyl. Or a pyridinium salt represented by the following general formula (c).
R _6- (C ₅ H ₄ N-R ₅ ) ⁺ · X ⁻ (c)
(In the formula (c), C ₅ H ₄ N is a pyridine ring, X is halogen, hydroxy, C ₁ -C ₅ alkanesulfonic acid or sulfuric acid, R ₅ is C ₁ -C ₂₀ alkyl, R ₆ is H or C _1. ~C ₁₀ represents an alkyl.)

  Examples of cationic surfactants in the form of salts include lauryl trimethyl ammonium salt, stearyl trimethyl ammonium salt, lauryl dimethyl ethyl ammonium salt, octadecyl dimethyl ethyl ammonium salt, dimethyl benzyl lauryl ammonium salt, cetyl dimethyl benzyl ammonium salt, octadecyl dimethyl Benzylammonium salt, trimethylbenzylammonium salt, triethylbenzylammonium salt, dimethyldiphenylammonium salt, benzyldimethylphenylammonium salt, hexadecylpyridinium salt, laurylpyridinium salt, dodecylpyridinium salt, stearylamine acetate, laurylamine acetate, octadecylamine acetate, etc. Is mentioned.

  Examples of the anionic surfactant include alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl phenyl ether sulfates, alkyl benzene sulfonates, {(mono, di, tri) alkyl} naphthalene sulfonates, etc. Is mentioned. Examples of the alkyl sulfate include sodium lauryl sulfate and sodium oleyl sulfate. Examples of the polyoxyethylene alkyl ether sulfate include sodium polyoxyethylene (EO5) nonyl ether sulfate and sodium polyoxyethylene (EO15) dodecyl ether sulfate. Examples of the polyoxyethylene alkylphenyl ether sulfate include polyoxyethylene (EO15) nonylphenyl ether sulfate. Examples of the alkyl benzene sulfonate include sodium dodecylbenzene sulfonate. Examples of the {(mono, di, tri) alkyl} naphthalene sulfonate include naphthalene sulfonate, sodium dibutyl naphthalene sulfonate, and naphthalene sulfonate formalin condensate.

  Examples of the amphoteric surfactant include carboxybetaine, imidazoline betaine, sulfobetaine, and aminocarboxylic acid. In addition, sulfation of a condensation product of ethylene oxide and / or propylene oxide and an alkylamine or diamine, or a sulfonated adduct can also be used.

  Representative carboxybetaines or imidazoline betaines are lauryldimethylaminoacetic acid betaine, myristyldimethylaminoacetic acid betaine, stearyldimethylaminoacetic acid betaine, coconut oil fatty acid amidopropyldimethylaminoacetic acid betaine, 2-undecyl-1-carboxymethyl-1 -Hydroxyethyl imidazolinium betaine, 2-octyl-1-carboxymethyl-1-carboxyethyl imidazolinium betaine, and the like. Sulfated and sulfonated adducts include sulfated adducts of ethoxylated alkylamines, sulfonated Examples thereof include lauric acid derivative sodium salt.

  Examples of the sulfobetaines include coconut oil fatty acid amidopropyldimethylammonium-2-hydroxypropanesulfonic acid, N-cocoylmethyl taurine sodium, and N-palmitoylmethyl taurine sodium. Examples of the aminocarboxylic acid include dioctylaminoethylglycine, N-laurylaminopropionic acid, octyldi (aminoethyl) glycine sodium salt, and the like.

Examples of the smoothing agent, brightening agent, and semi-brightening agent include β-naphthol, β-naphthol-6-sulfonic acid, β-naphthalenesulfonic acid, benzaldehyde, m-chlorobenzaldehyde, p-nitrobenzaldehyde, p-hydroxybenzaldehyde, o-, p-) methoxybenzaldehyde, vanillin, (2,4-, 2,6-) dichlorobenzaldehyde, (o-, p-) chlorobenzaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, 2 (4)- Hydroxy-1-naphthaldehyde, 2 (4) -chloro-1-naphthaldehyde, 2 (3) -thiophenecarboxaldehyde, 2 (3) -furaldehyde, 3-indolecarboxaldehyde, salicylaldehyde, o-phthalaldehyde, Formaldehyde, acetaldehyde, paraaldehyde, butyral Dehydr, isobutyraldehyde, propionaldehyde, n-valeraldehyde, acrolein, crotonaldehyde, glyoxal, aldol, succindialdehyde, capronaldehyde, isovaleraldehyde, allylaldehyde, glutaraldehyde, 1-benzylidene-7-heptanal, 2,4 -Hexadienal, cinnamaldehyde, benzylcrotonaldehyde, amine-aldehyde condensate, mesityl oxide, isophorone, diacetyl, hexanedione-3,4, acetylacetone, benzylideneacetone, 3-chlorobenzylideneacetone, sub.pyridylideneacetone, sub.furfuridine acetone, sub.tenylideneacetone, 4- (1-naphthyl) -3-buten-2-one, 4- (2-furyl) -3-buten-2-one 4- (2-thiophenyl) -3-buten-2-one, curcumin, benzylideneacetylacetone, benzalacetone, acetophenone, (2,4-3,4-dichloroacetophenone, benzylideneacetophenone, 2-cinnamylthiophene 2- (ω-benzoyl) vinyl furan, vinyl phenyl ketone, acrylic acid, methacrylic acid, ethacrylic acid, ethyl acrylate, methyl methacrylate, butyl methacrylate, crotonic acid, propylene-1,3-dicarboxylic acid, cinnamon Acid, (o-, m-, p-) toluidine, (o-, p-) aminoaniline, aniline, (o-, p-) chloroaniline, (2,5-3,4-) chloromethylaniline N-monomethylaniline, 4,4′-diaminodiphenylmethane, N-phenyl- (α-, β-) naphthylamine, Zutriazole, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,3-benztriazine, imidazole, 2-vinylpyridine, indole, quinoline, aniline, phenanthroline , Neocuproine, picolinic acid, a reaction product of monoethanolamine and o-vanillin, polyvinyl alcohol, catechol, hydroquinone, resorcin, polyethyleneimine, disodium ethylenediaminetetraacetate, polyvinylpyrrolidone and the like.
Gelatin, polypeptone, 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 benzothiazoles are also effective as a smoothing agent.
Examples of the benzothiazoles include benzothiazole, 2-methylbenzothiazole, 2-mercaptobenzothiazole, 2- (methylmercapto) benzothiazole, 2-aminobenzothiazole, 2-amino-6-methoxybenzothiazole, and 2-methyl. -5-chlorobenzothiazole, 2-hydroxybenzothiazole, 2-amino-6-methylbenzothiazole, 2-chlorobenzothiazole, 2,5-dimethylbenzothiazole, 6-nitro-2-mercaptobenzothiazole, 5-hydroxy -2-methylbenzothiazole, 2-benzothiazolethioacetic acid and the like.

Examples of the pH adjuster include various acids such as hydrochloric acid and sulfuric acid, various bases such as aqueous ammonia, potassium hydroxide, and sodium hydroxide.
Examples of the buffer include phosphoric acids such as boric acid, phosphinic acid and phosphonic acid, phosphoric acid and tripolyphosphoric acid, dicarboxylic acids such as oxalic acid and succinic acid, oxycarboxylic acids such as lactic acid and tartaric acid, and ammonium chloride and ammonium sulfate. Can be mentioned.
Examples of the preservative include boric acid, 5-chloro-2-methyl-4-isothiazolin-3-one, benzalkonium chloride, phenol, phenol polyethoxylate, thymol, resorcin, isopropylamine, and guaiacol.
Examples of the antifoaming agent include pluronic surfactants, higher aliphatic alcohols, acetylene alcohols and polyalkoxylates thereof.

As described above, the present invention 1 uses a lead-free tin alloy electroplating bath containing a specific dissolution current inhibitor at a predetermined concentration, and performs electroplating with an anode made of tin and tin alloy. This is a dissolution current suppression type tin alloy electroplating method capable of preventing bismuth from being deposited on the anode during electrodeposition.
In addition, the present invention 2 is obtained by applying the tin alloy electroplating method of the present invention 1 to an electronic component. That is, an electronic component in which a lead-free tin alloy film is formed using a tin alloy electroplating bath containing a specific dissolution current inhibitor at a predetermined concentration . Preferred electronic components include a printed circuit board, a semiconductor integrated circuit, Examples include resistors, variable resistors, capacitors, filters, inductors, thermistors, crystal units, switches, and lead wires.

Hereinafter, an evaluation test example of a tin anodic polarization curve with or without the addition of a dissolution current inhibitor of the present invention, an example of a tin alloy electroplating bath of the present invention containing the inhibitor, and a tin alloy electroplating of the present invention An evaluation test example of the degree of substitutional precipitation prevention of a noble metal at the anode when the method is performed will be sequentially described.
The present invention is not limited to the following examples and test examples, and it is needless to say that arbitrary modifications can be made within the scope of the technical idea of the present invention.

In a methanesulfonic acid aqueous solution, a polarization curve of tin anode (corresponding to no addition) is prepared, and then the dissolution current inhibitor of the present invention, a known compound disclosed in the aforementioned patent document or similar to the inhibitor A tin anodic polarization curve was prepared when the amino acids to be added were added, and the case of adding the inhibitor, the case of adding a known compound, or the case of no addition was evaluated.
<< Evaluation test example of tin anodic polarization curve >>
(1) Comparative addition example 1 (blank example)
First, a polarization curve of a tin anode was prepared using an Ag / AgCl · KCl saturated solution as a reference electrode in a 1 mol / L methanesulfonic acid aqueous solution.
FIG. 4 is a polarization curve in the case where the inhibitor of the present invention is not added (that is, a blank example).

(2) Addition example 1 of the inhibitor of the present invention
Next, 0.2 mol / L of glutamic acid-N, N-diacetate tetrasodium, methylglycine-N, N-diacetate trisodium and aspartic acid were respectively added to 1 mol / L methanesulfonic acid aqueous solution, The same treatment as in the above blank example was carried out to prepare a tin anode polarization curve. FIG. 1 shows the results.

(3) Addition example 2 of the inhibitor of the present invention
Further, the tin anode was polarized in the same manner as in Addition Example 1 except that the content of the inhibitor was increased from 0.2 mol / L to 0.4 mol / L based on Addition Example 1. A curve was created. FIG. 2 shows the result.

(4) Comparative addition example 2 (comparative example in which amino acids similar to compounds known in the literature or the inhibitor of the present invention were added)
In order to perform comparative evaluation with the inhibitor of the present invention, the compounds (diethylenetriaminepentaacetic acid salt, sulfoethylglutamic acid diacetic acid) disclosed in the above-mentioned patent documents 1 and 2, and amino acids similar to the inhibitor of the present invention The anodic polarization curve was examined when a class (glutamic acid, methylglycine, aspartic acid derivative) was added.
That is, about 0.4 mol / L of diethylenetriaminepentaacetic acid pentasodium salt (DTPA), glutamic acid, methylglycine, aspartic acid diacetic acid tetrasodium salt (ASDA) and sulfoethylglutamic acid diacetic acid (SEDL), respectively, A tin anode polarization curve was prepared in the same manner as in Addition Example 2 above.
FIG. 3 shows the result.

Therefore, the case where the dissolution current inhibitor of the present invention is added, the case of adding a compound known in the literature or a similar amino acid to the inhibitor, or the case of no addition is described below with reference to FIGS. Contrast evaluation.
It can be seen that the slope of the polarization curve is greatly reduced in Addition Example 1 in which the dissolution current inhibitor of the present invention is added as compared with Comparative Addition Example 1 without addition (see FIG. 4). In the comparative addition example 1 (blank example without addition: corresponding to-♦-in FIG. 4), in order to make the anode potential higher than the natural electrode potential of bismuth (+100 mV), the anode current density is about 150 A / dm ^2. However, in addition example 1, when a diacetic acid derivative of glutamic acid (abbreviated as GLDA: corresponding to-●-in FIG. 1) is used, it is about 12.3 A / dm ² or more. The diacetic acid derivative (abbreviated as MGDA: corresponding to-■-in FIG. 1) is about 13.5 A / dm ² or more, and further, aspartic acid (abbreviated as ASP: corresponding to-▲-in FIG. 1) is about 15. It was confirmed that the potential of the tin anode became nobler than the potential of bismuth at 5 A / dm ² or more, respectively. Of course, the same was true for silver and copper.
That is, as supported by the dramatic decrease in the slope of the anodic polarization curve (see the integrated diagram in FIG. 5), when the inhibitor of the present invention is added, the dissolution current of the anode is remarkably suppressed as compared with the case of no addition. It can be done.

Further, as seen in Addition Example 2 (see FIG. 2), it can be confirmed that when the inhibitor is increased from 0.2 M (M = mol / L) to 0.4 M, the slope of the polarization curve further decreases.
Taking bismuth as an example, when GLDA is used, the anode current density is about 10 A / dm ² or more, MGDA is about 12.5 A / dm ² or more, and ASP is about 14.7 A / dm ² or more. It can be seen that the anode potential is more noble than the potential of bismuth (both see FIG. 2). For example, when GLDA is added, the anode potential becomes nobler than the potential of bismuth unless it is about 12.3 A / dm ² or more at 0.2 M (see FIG. 1). It becomes noble at / dm ² or more (see FIG. 2).
This confirms that the anode current density at which the potential of the tin anode can be made nobler than the potential of the noble metal (silver, bismuth or copper) can be further lowered as the concentration of the inhibitor of the present invention increases. It was. That is, it can be estimated that the dissolution current suppressing action increases as the concentration of the dissolution current inhibitor increases.

On the other hand, when the comparative addition example 2 which added the amino acid similar to the compound well-known to a literature or the inhibitor of this invention is seen (refer FIG. 3), for example, even if diethylenetriaminepentaacetic acid (DTPA) is added, anodic polarization The slope of the curve was almost the same as in the case of no addition (see the integrated diagram in FIG. 5), and no inhibitory action on dissolution current was observed. In addition, in the addition example of sulfoethyl glutamic acid diacetic acid (SEDL), the slope of the anodic polarization curve is slightly lower than that in the case of no addition (see the integrated diagram in FIG. 5). Even when the anode is added, if the anode current density is not more than about 130 A / dm ^2, the potential of the tin anode will not be nobler than the potential of bismuth (+100 mV), compared to the case of no addition (about 150 A / dm ² or more). However, it is still unrealistic high current density.
Furthermore, even when glutamic acid, methylglycine, or a diacetic acid derivative of aspartic acid (ASDA) was added, only intermediate results between the DTPA and SEDL were shown.
That is, in the case of this comparative addition example 2 (see FIG. 3), the slope of the anodic polarization curve is almost the same as that in the case of no addition, or only a slight decrease is observed, and the addition is made at the same concentration (0.4M). In contrast to the addition example 2 of the inhibitor of the present invention (see FIG. 2), the inhibitor of the present invention is as shown by the dramatic decrease in the slope of the anode polarization curve (see the integrated diagram of FIG. 5). It is clear that the compound has a significant advantage over these known compounds and similar amino acids of the inhibitor in terms of the dissolution current suppressing effect.

Then, the Example of the tin alloy electroplating bath containing the inhibitor of this invention by which the dissolution current suppression function was confirmed, and the comparative example of the same plating bath which does not contain the said inhibitor are shown below.
<< Example of tin alloy electroplating bath >>
Among Examples 1 to 6 below, Examples 1 and 2 are examples of tin-silver alloy electroplating baths, Examples 3 and 5 are examples of tin-bismuth alloy electroplating baths, and Examples 4 and 6 are tin- It is an example of a copper alloy electroplating bath. Example 1 is an example in which an acetic acid derivative (salt) of glutamic acid is used as a dissolution current inhibitor, Examples 2, 4 and 6 are examples of using an acetic acid derivative (salt) of methylglycine, and Examples 3 and 5 are asparagine. This is an example of using an acid (salt).
On the other hand, among Comparative Examples 1 to 3, Comparative Example 1 is a blank example of a tin-silver alloy electroplating bath that does not contain the inhibitor, and similarly, Comparative Example 2 is a blank example of a tin-bismuth alloy electroplating bath. Example 3 is a blank example of a tin-copper alloy electroplating bath.
A tin-silver alloy electroplating bath to which aspartic acid was added was referred to as Reference Example 1, and a tin-bismuth alloy electroplating bath to which an acetic acid derivative of glutamic acid was added was also shown as Reference Example 2.

(1) Example 1
A tin-silver alloy electroplating bath was constructed with the following composition.
2-hydroxyethanesulfonic acid stannous (as Sn ²⁺ ) 40 g / L
Silver methanesulfonate (as Ag ⁺ ) 1g / L
Methanesulfonic acid (as free acid) 100g / L
Thiourea 5g / L
Glutamic acid-N, N-tetrasodium diacetate (0.4 mol) 140 g / L
1-methyl-2-naphthol polyethoxylate (EO18 mol) 7 g / L
Catechol 1g / L

(2) Example 2
A tin-silver alloy electroplating bath was constructed with the following composition.
2-hydroxyethanesulfonic acid stannous (as Sn ²⁺ ) 40 g / L
Silver methanesulfonate (as Ag ⁺ ) 1g / L
Methanesulfonic acid (as free acid) 100g / L
Thiourea 5g / L
Methylglycine-N, N-trisodium diacetate (0.4 mol) 110 g / L
1-methyl-2-naphthol polyethoxylate (EO18 mol) 7 g / L
Catechol 1g / L

(3) Example 3
A tin-bismuth alloy electroplating bath was constructed with the following composition.
2-hydroxypropanesulfonic acid stannous (as Sn ²⁺ ) 60 g / L
Bismuth methanesulfonate (as Bi ³⁺ ) 3g / L
2-hydroxypropanesulfonic acid (as free acid) 150 g / L
Aspartic acid (0.4 mol) 53 g / L
Diethylenetriaminepentaacetic acid 17g / L
Tristyrenated phenol polyethoxylate (EO22 mol) 10g / L
Hydroquinone 0.7g / L

(4) Example 4
A tin-copper alloy electroplating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 20g / L
Copper methanesulfonate (as Cu ²⁺ ) 1.5g / L
Methanesulfonic acid (as free acid) 100g / L
Methylglycine-N, N-trisodium diacetate (0.4 mol) 110 g / L
Nonylphenol polyethoxylate (EO23 mol)
-Polypropoxylate (PO3 mol) 10 g / L
2-mercaptobenzothiazole 0.5 g / L

(5) Example 5
A tin-bismuth alloy electroplating bath was constructed with the following composition.
Stannous sulfate (as Sn ²⁺ ) 40g / L
Bismuth 2-hydroxypropanesulfonate (as Bi ³⁺ ) 2g / L
2-hydroxyethanesulfonic acid (as free acid) 110 g / L
Sulfosuccinic acid 20g / L
Sodium aspartate (0.2 mol) 31 g / L
Sodium propylnaphthalenesulfonate 0.5g / L
Octylphenol polypropoxylate (PO5 mol)
-Polyethoxylate (EO15 mol) 8g / L
Sodium dodecyldiaminoethylglycine 1g / L
4-Carboxybenzotriazole 0.01 g / L

(6) Example 6
A tin-copper alloy electroplating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 40g / L
Copper sulfate (as Cu ²⁺ ) 1g / L
Methanesulfonic acid (as free acid) 100g / L
Methylglycine-N, N-diacetic acid (0.2 mol) 41 g / L
Methionine 25g / L
1-hydroxyethyl-2-alkylimidazoline 1 g / L
Polyoxyethylene (EO26 mol)
-Polyoxypropylene (PO30 mol) block copolymer 3g / L
Dodecylamine polyethoxylate (EO18 mol) 5g / L
2-mercaptobenzothiazole 0.1 g / L
Catecholsulfonic acid 0.8g / L

(7) Reference example 1
A tin-silver alloy electroplating bath was constructed with the following composition.
Stannous ethanesulfonate (as Sn ²⁺ ) 25g / L
Ethanesulfonic acid silver (as Ag ⁺ ) 0.6g / L
Ethanesulfonic acid (as free acid) 80g / L
Thiourea 3g / L
Aspartic acid (0.2 mol) 27 g / L
Bisphenol F polyethoxylate (EO19 mol) 3g / L
Dodecyldimethylbenzylammonium chloride 0.3g / L
Sodium hydroquinone sulfonate 0.5g / L

(8) Reference example 2
A tin-bismuth alloy electroplating bath was constructed with the following composition.
2-hydroxypropanesulfonic acid stannous (as Sn ²⁺ ) 60 g / L
Bismuth methanesulfonate (as Bi ³⁺ ) 3g / L
2-hydroxypropanesulfonic acid (as free acid) 150 g / L
Glutamic acid-N, N-tetrasodium diacetate (0.2 mol) 70 g / L
Diethylenetriaminepentaacetic acid 17g / L
Tristyrenated phenol polyethoxylate (EO22 mol) 10g / L
Hydroquinone 0.7g / L

(9) Comparative Example 1
A tin-silver alloy electroplating bath was constructed with the following composition.
2-hydroxyethanesulfonic acid stannous (as Sn ²⁺ ) 40 g / L
Silver methanesulfonate (as Ag ⁺ ) 1g / L
Methanesulfonic acid (as free acid) 100g / L
Thiourea 5g / L
1-methyl-2-naphthol polyethoxylate (EO18 mol) 7 g / L
Catechol 1g / L

(10) Comparative example 2
A tin-bismuth alloy electroplating bath was constructed with the following composition.
2-hydroxypropanesulfonic acid stannous (as Sn ²⁺ ) 60 g / L
Bismuth methanesulfonate (as Bi ³⁺ ) 3g / L
2-hydroxypropanesulfonic acid (as free acid) 150 g / L
Diethylenetriaminepentaacetic acid 17g / L
Tristyrenated phenol polyethoxylate (EO22 mol) 10g / L
Hydroquinone 0.7g / L

(11) Comparative Example 3
A tin-copper alloy electroplating bath was constructed with the following composition.
Stannous methanesulfonate (as Sn ²⁺ ) 20g / L
Copper methanesulfonate (as Cu ²⁺ ) 1.5g / L
Methanesulfonic acid (as free acid) 100g / L
Nonylphenol polyethoxylate (EO23 mol)
-Polypropoxylate (PO3 mol) 10 g / L
2-mercaptobenzothiazole 0.5 g / L

<< Evaluation test example for prevention of substitutional precipitation at the anode when the tin alloy electroplating method is implemented >>
Therefore, using the tin alloy electroplating baths of Examples 1 to 6 , Comparative Examples 1 to 3 and Reference Examples 1 to 2 , electroplating was performed under the following conditions, and the appearance of the tin anode after electrodeposition was By visually observing, the degree of prevention of substitution deposition of silver, bismuth or copper at the anode was evaluated according to the following criteria.
[Electroplating conditions]
Anode: Tin Cathode: Copper Cathode current density: 20 A / dm ²
Anode area / cathode area = 1/1
Bath temperature: 35 ° C
Electrolysis time: 100 minutes Evaluation criteria are as follows.
○: No discoloration of the anode was observed, and tin metallic luster was maintained.
X: The anode was discolored and the tin metallic luster was remarkably lost.

The table below shows the test results.
Anode appearance Anode appearance Example 1 ○ Comparative Example 1 ×
Example 2 ○ Comparative Example 2 ×
Example 3 ○ Comparative Example 3 ×
Example 4 ○
Example 5 ○
Example 6 ○
Reference example 1 ○
Reference example 2 ○

According to the above table, in Comparative Examples 1 and 2, the tin anode became black-gray or black, and silver or bismuth was clearly substituted and deposited on the anode. Further, in Comparative Example 3, the tin anode changed to a bronze color, and copper substitution deposition was clearly confirmed. On the other hand, in Examples 1 to 6 , no discoloration of the anode was observed at all, and the anode retained the beautiful metallic luster of tin, effectively replacing the deposition of silver, bismuth or copper on the anode. It was confirmed that it could be prevented.
On the other hand, in the above-mentioned polarization curve test example, when the inhibitor of the present invention is added, the dissolution current of the tin anode is suppressed to lower the slope of the anodic polarization curve, and the anode current density is lower than when no additive is added. Thus, it was confirmed that the potential of the tin anode can be changed more preciously than the natural electrode potential of the noble metal (silver, bismuth or copper).
The above table confirms the effectiveness of the dissolution current suppression effect by this inhibitor. It is actually the cathode current density (20 A / dm ² ) normally used in high-speed plating, and the anode area: cathode area = 1: 1. It has been found that when electroplating is performed, substitution deposition of silver, bismuth or copper on the tin anode during electrodeposition can be reliably prevented.

FIG. 4 is a polarization curve diagram of a tin anode when the dissolution current inhibitor of the present invention is added (addition amount is 0.2 mol / L: corresponding to addition example 1 (see paragraph 47 above)). It is a polarization curve figure of a tin anode when the dissolution current inhibitor of the present invention is added (addition amount is 0.4 mol / L: corresponding to addition example 2 (see paragraph 48)). When a known compound or an amino acid similar to the inhibitor of the present invention is added (addition amount is 0.4 mol / L: corresponding to comparative addition example 2 (see paragraph 49)), is there. It is a polarization curve figure of the tin anode of the case where the dissolution current inhibitor of the present invention is not added (corresponding to Comparative addition example 1 (see paragraph 46)). It is the integrated figure which put together the polarization curve figure of the tin anode of the case where the dissolution current inhibitor of this invention is added, the case where a well-known compound etc. are added, and the case where it does not add.

Claims (2)

Using a tin alloy electroplating bath for suppressing dissolution current selected from any of the following (A) to (C), and a content of 0.005 to 10 mol of the following dissolution current inhibitor with respect to the plating bath / L, by performing electroplating with a tin or tin alloy anode,
(A) soluble stannous salt, soluble silver salt, at least one acid selected from inorganic acids and organic acids or salts thereof, glutamic acid-N, N-diacetic acid, methylglycine-N, N-di A tin-silver alloy electroplating bath containing at least one type of anode dissolution current inhibitor selected from the group consisting of acetic acid and salts thereof
(B) a soluble stannous salt, a soluble copper salt, an acid selected from an inorganic acid and an organic acid or at least one of its salts, methylglycine-N, N-diacetic acid, aspartic acid and their salts A tin-copper alloy electroplating bath containing at least one anode dissolution current inhibitor selected from the group consisting of
(C) a soluble stannous salt, a soluble bismuth salt, at least one acid selected from inorganic acids and organic acids or salts thereof, and at least one anode dissolution current inhibitor comprising aspartic acid and these salts Tin-bismuth alloy electroplating bath containing
A dissolution current-suppressing tin alloy electroplating method characterized in that the dissolution current of the anode is suppressed to prevent silver, copper or bismuth from being deposited on the anode during electrodeposition.   An electronic component having a lead-free tin alloy film formed on the substrate by the tin alloy electroplating method according to claim 1.

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