JP4901168B2 - Replacement silver plating bath - Google Patents

Description

  The present invention provides a substituted silver plating bath that provides a lustrous silver-white and beautiful silver coating.

In the field of industrial plating such as electronic parts and automobile parts, tin or tin alloy plating is widely used from the viewpoint of excellent solderability, but there is a problem of whisker generation.
Silver plating has fewer whisker problems than tin and has good solderability. Therefore, the conventional technique of the substitution silver plating bath is as follows.

(1) Patent Document 1
For the purpose of improving film properties such as adhesion and corrosion resistance (paragraph 33), sulfur-containing organic compounds having two monosulfide groups in the molecule and hypophosphorous acid such as hypophosphorous acid and phosphorous acid An electroless silver plating bath containing a compound, an aldehyde compound such as formalin, a hydrazine derivative such as hydrazine and semicarbazide, and a reducing agent such as ascorbic acid is disclosed (claims 1 to 4).
The sulfur-containing compound is functionally a silver complexing agent (paragraph 10) and structurally has a hydroxyl group, a carboxyl group, etc., and 2-8 methylene groups between two monosulfide groups. (Claim 2). Specific examples of the sulfur-containing compound include 1,2-bis (2-hydroxyethylthio) ethane (HOCH ₂ CH ₂ —S—CH ₂ CH ₂ —S—CH ₂ CH ₂ OH) (paragraph 18). ).

(2) Patent Document 2
For the purpose of forming a film excellent in appearance such as denseness and adhesion (paragraphs 7 and 29), it contains a sulfur-containing organic compound having two monosulfide groups in the molecule, and the pH is 7 or less. A displacement silver plating bath is disclosed (claim 1). The bath can contain thioureas (1-150 g / L) from the viewpoint of improving (thickening) the deposition rate without impairing adhesion (claim 5, paragraphs 20-22), It describes that salts such as phosphoric acid, tripolyphosphoric acid, boric acid and acetic acid can be contained as a pH buffer (paragraph 23).

(3) Patent Document 3
A substituted silver plating bath containing thioureas (a sulfur-containing compound having a C = S bond) and an iodine compound is disclosed (claims 5 to 6).
Further, a substituted tin-silver alloy plating bath containing pyrophosphoric acids, thioureas (a sulfur-containing compound having a C = S bond) and an iodine compound is disclosed (claims 8 to 9).

(4) Patent Document 4
An electroless silver plating bath containing an aliphatic sulfide compound having one mono- or disulfide bond and one or more hydroxyl groups in the molecule as a complexing agent is disclosed for the purpose of improving the appearance of the film. (Claim 1). Aliphatic sulfide compounds include bis (triethylene glycol) thioether (H— (OCH ₂ CH ₂ ) ₃ —S— (CH ₂ CH ₂ O) ₃ —H), bis (dodecaethylene glycol) thioether (H— ( and the like _{OCH 2 CH 2) 12 -S- (} CH 2 CH 2 O) 12 -H) ( paragraph 15).
It is described that the bath can contain thioureas (Claim 3, Paragraph 25) and can contain hypophosphorous acid, phosphorous acid, etc. as a reducing agent (paragraph 27).

(5) Patent Document 5
For fibers containing sulfur-containing compounds such as thioglycolic acid, thiodiglycolic acid, thiomalic acid and thiourea as stabilizers, and hypophosphites, rossell salts, hydrazines, formates as reducing agents. An electrolytic silver plating bath is disclosed (claim 1).

(6) Patent Document 6
An electroless plating bath of an alloy containing silver and tin is disclosed (Claims 23 to 24), and the plating bath contains phosphorus-containing compounds (hypophosphites), thiols, thioureas, and nitrogen as a reducing agent. Compounds, boron-containing compounds, etc. (Claims 3 and 5), sulfur-containing compounds (mercaptocarboxylic acid, thiodicarboxylic acid, etc.), thioureas, iodine-containing compounds, polyalkylene glycols, azoles as stabilizers (Claims 6 to 9) are described.

(7) Patent Document 7
For the purpose of forming a silver film on tin or a tin alloy (claim 1), (A) inorganic acid ions such as nitrate ions, (C) acetate ions, (D) A substituted silver plating bath containing sulfonate ions, (E) thioureas, (H) thiocarboxylic acid or thiosulfonic acid is disclosed (claim 1).
Further, the silver plating bath includes (a) an aliphatic dicarboxylic acid, (d) a cyclic ester compound, (f) an aliphatic mercaptocarboxylic acid as a tin complexing agent for preventing precipitation of displacement-eluting tin. (G) amine carboxylic acid, (i) condensed phosphoric acid and the like can be contained (claim 2).

(8) Patent Document 8
Cyanide containing 20 to 100 g / L of alkali salt such as alkali hydroxide and dipotassium hydrogen phosphate as buffering agent and 0.1 to 10 g / L of cyclic sulfur compound such as thiourea derivative or thiosalicylic acid and thiol A displacement silver plating bath is disclosed (claims 9-10).

JP 2000-8174 A JP 2000-309875 A JP 2002-266077 A JP 2002-356783 A JP-A-2005-105386 JP 2003-268558 A JP-A-10-130855 JP-A-5-195238

The silver plating film is ideally a beautiful and glossy silver-white film, but when plating is performed using a substitution silver bath based on a soluble silver salt and thiourea, black coarse particles are formed, Or, there is an adverse effect that unevenness of plating presumably caused by adsorption of sulfur element in thiourea occurs, and this poor appearance of the film may adversely affect solderability.
In the above Patent Documents 1 to 8, it is still not a satisfactory level in terms of obtaining a glossy silver-white plating film.
In particular, even if a silver-white plating film is obtained from the initial bath, in the bath after aging from the building bath (aging bath), the base metal elutes due to the substitution reaction, etc., which is not in the initial bath composition Since the components come in, it is difficult to obtain a silvery white film similar to that obtained from the initial bath.

  It is a technical object of the present invention to obtain a beautiful silver-white silver plating film not only in an initial bath but also in a time-lapse bath in substitution silver plating.

Patent Documents 1, 4 to 6 and the like disclose hypophosphorous acids or phosphorous acids having an antioxidant function as an additive component to the bath.
Although the present inventors belong to phosphoric acids as well as these hypophosphorous acids, etc., they are different from orthophosphoric acid, or condensed phosphoric acid such as pyrophosphoric acid and polyphosphoric acid, or a salt thereof. Paying attention to the selected specific phosphoric acid, the substituted silver bath having a basic composition of a soluble silver salt and a silver complexing agent contains the specific phosphoric acid, and the specific phosphoric acid is at a predetermined concentration or more. In the present invention, it was found that the silver film appearance can be effectively improved, and in particular, not only the film appearance obtained from the initial bath, but also the film appearance obtained from the aging bath is generally excellent.

That is, the present invention 1 is a substituted silver plating bath containing a soluble silver salt and a complexing agent comprising a sulfur-containing compound selected from thioureas, sulfides, and mercaptans.
Contains at least one phosphoric acid selected from the group consisting of orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid and salts thereof, and the content of the phosphoric acid is 0.5 to 10 mol / L This is a substituted silver plating bath.

Invention 2 is a substituted silver plating bath according to Invention 1, wherein the sulfur-containing compound is at least one of thioureas , thioglycol, thiodiglycol , cysteine, and methionine.

The present invention 3 is the substitution silver plating bath according to the present invention 1 or 2 , further comprising at least one of anionic, cationic, nonionic and amphoteric surfactants.

Invention 4 is that in any one of Inventions 1 to 3 , the replacement silver plating bath is a bath for forming a silver plating film on the substrate surface selected from 42 alloy, nickel, iron and copper. This is a featured substitution silver plating bath.

In a conventional substitution silver plating bath having a basic composition of a silver salt and a silver complexing agent, the resulting silver film has coarse particles and turns black or has uneven color.
In the present invention, the plating bath having the above basic composition contains specific phosphoric acids selected from orthophosphoric acid, condensed phosphoric acid and salts thereof, and contains these specific phosphoric acids at a predetermined concentration or more. By eliminating the negative effects of conventional silver films, it is possible to obtain a beautiful silver film that is homogeneous and glossy silver-white.
Moreover, in the substituted silver bath of the present invention, not only the initial bath, but also a aging bath can obtain a silver-white color similar to or similar to that obtained from the initial bath, and the aging stability of the coating can be improved. Also excellent.

The present invention provides a plating bath having a basic composition of a soluble silver salt and a complexing agent comprising a sulfur-containing compound such as thioureas, sulfides, mercaptans, orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid and It is a substituted silver plating bath containing specific phosphoric acids selected from the group consisting of these salts and having a content of the phosphoric acids of 0.5 to 10 mol / L.

As the soluble silver salt contained in the substituted silver plating bath of the present invention, any soluble salt can be used as long as it is a soluble salt that produces Ag ⁺ in the bath, and there is no particular limitation, and even a hardly soluble salt is excluded. is not.
Soluble silver salts include silver sulfate, silver sulfite, silver carbonate, silver acetate, silver lactate, silver sulfosuccinate, silver nitrate, silver organic sulfonate, silver borofluoride, silver citrate, silver tartrate, silver gluconate, silver sulfamate Soluble salts such as silver oxalate and silver oxide can be used. Preferable specific examples of the silver salt include silver methanesulfonate, silver ethanesulfonate, silver acetate, silver lactate, and silver citrate.
The metal equivalent content of the soluble silver salt with respect to the plating bath is 0.0001 to 1 mol / L, preferably 0.001 to 0.5 mol / L.

The substituted silver plating bath of the present invention contains a complexing agent to stabilize silver ions in the bath. The complexing agent comprises a sulfur-containing compound such as thioureas, sulfides, mercaptans and the like. These sulfur-containing compounds can be used singly or in combination, or different types can be used together (for example, thiourea and sulfides can be used together).
Content with respect to the plating bath of a sulfur-containing compound is 0.0001-5 mol / L, and is 0.03-2 mol / L.

  The thioureas are thiourea and thio derivatives. Thiourea derivatives include 1,3-dimethylthiourea, trimethylthiourea, diethylthiourea (eg, 1,3-diethylthiourea), 1,3-diisopropylthiourea, allylthiourea, acetylthiourea, ethylenethiourea, 1,3. -Diphenylthiourea, thiourea dioxide, thiosemicarbazide, S-methylisothiourea sulfate, tributylthiourea, benzylisothiourea hydrochloride, 1,3-dibutylthiourea, 1-naphthylthiourea, tetramethylthiourea, 1-phenylthiourea, 1-methylthiourea etc. are mentioned.

  The mercaptans include cysteine, N-acetylcysteine, thioglycol, mercaptosuccinic acid, mercaptoisobutyric acid, mercaptoacetic acid (thioglycolic acid), dimercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, and 2,3 -Dimercaptosuccinic acid, mercaptoaniline, mercaptopyridine and the like.

The sulfides include methionine, ethionine, cystine, thiodiglycolic acid, thiodiglycol, 2,2'-thiobis (ethylamine), thiodipropionic acid, thiodiethanesulfonic acid, thiodipropanol, 3,3 '. -Thiobis (propylamine), thiodibutyric acid, thiodipropanesulfonic acid, bis (undecaethylene glycol) thioether, bis (dodecaethylene glycol) thioether, bis (pentadecaethylene glycol) thioether, bis (triethylene glycol) thioether, 4,7,10-trithiatridecane-1,2,12,13-tetraol, 6,9,12-trithia-3,15-dioxaheptadecane-1,17-diol, 3,6-dithiaoctane- 1,8-diol, 4,7-dithiadecane-1,10-diol, 3,6,9-triti Undecane-1,11-diol, 3,6-dithiaoctane-1,8-diamine, 3,6-dithiaoctane-1,8-dicarboxylic acid, 4,7,10-trithiatridecane-1,13-disulfonic acid diester Sodium, 3,6,9-trithiaundecane-1,11-disulfonic acid, 4,7,10,13-tetrathiahexadecane-1,16-disulfonic acid, 1,8-bis (2-pyridyl) -3 , 6-dithiaoctane and the like.
In the case of sulfur-containing compounds, from the viewpoint of more effectively obtaining a bright silver-white plating film, sulfides such as methionine, ethionine, cystine, thiodiglycolic acid, thiodiglycol, cysteine, N-acetylcysteine Mercaptans such as thioglycol, mercaptosuccinic acid, mercaptoisobutyric acid, mercaptoacetic acid (thioglycolic acid) are preferred.

The substitution silver plating bath of the present invention is based on an organic acid, an inorganic acid, or a salt thereof as a base acid, but a soluble silver salt or a complexing agent may be dissolved in water to build a bath.
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 inorganic acids include borohydrofluoric acid, silicohydrofluoric acid, sulfamic acid, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, and the like.
The above acid (or salt) can be used singly or in combination, and its content is 0.1 to 300 g / L, preferably 20 to 120 g / L.

The substituted silver plating bath of the present invention needs to contain a specific phosphoric acid selected from the group consisting of orthophosphoric acid (normal phosphoric acid), condensed phosphoric acid and salts thereof.
The condensed phosphoric acid refers to pyrophosphoric acid, tripolyphosphoric acid, polyphosphoric acid (having a degree of condensation larger than tripolyphosphoric acid), chained or cyclic metaphosphoric acid, and the like.
These phosphates refer to various salts such as sodium, potassium, calcium, magnesium, ammonium, amine, sulfonate and the like.
In the present invention, the specific phosphoric acid is selected from the group consisting of orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid, and salts thereof.
The specific phosphoric acids can be used alone or in combination, and the content thereof is 0.5 to 10 mol / L, preferably 0.5 to 5 mol / L. When the content is less than 0.5 mol / L, it is difficult to impart a beautiful silver-white appearance to the silver plating film, and blackening is likely to occur.

It goes without saying that the substituted silver plating bath of the present invention can contain various additives such as known surfactants, pH adjusters, and buffering agents in addition to the above-described components.
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 the present invention 3 ).
Its content is 0.01-100 g / L, preferably 0.1-50 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 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 dicarboxylic acids such as boric acid, phosphinic acid, phosphonic acid, oxalic acid, and succinic acid, and oxycarboxylic acids such as lactic acid and tartaric acid, and ammonium chloride and ammonium sulfate. Moreover, the said buffering agent can also be combined with the specific phosphoric acids added by this invention.

The substitution silver plating of the present invention is basically performed by immersing the object to be plated in a plating solution usually for 1 second to 30 minutes to deposit a plating film to a desired film thickness. The pH is preferably 8.0 or less, and the bath may be stirred as necessary. The bath temperature is about 10 to 80 ° C., and the plating time is determined depending on the film thickness.
An object to be plated (that is, the substrate surface) to which the substitution silver plating bath of the present invention is applied is arbitrary and is not particularly limited, but is preferably selected from 42 alloy, nickel, iron or copper as shown in the present invention 4. . Therefore, when forming a silver film on electronic parts such as printed circuit boards, semiconductor integrated circuits, film carriers, resistors, variable resistors, capacitors, filters, inductors, thermistors, crystal resonators, switches, lead wires, etc. A displacement silver plating bath is preferred. However, when the substitution silver plating bath of the present invention is applied to the surface of a 42 alloy, nickel, or iron substrate, the resulting silver film can be promoted to a more beautiful silver-white color than when other substrates are selected. . Therefore, as the substrate surface to which the substituted silver plating bath of the present invention is applied, 42 alloy, nickel and iron are more preferable.

Hereinafter, examples of the substitution silver plating bath of the present invention and appearance evaluation test examples of the silver film obtained from the plating bath will be described in order.
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.

<< Example of Substitution Silver Plating Bath >>
Among Examples 1 to 13, Examples 1 to 4, 6, 8 to 10 and 13 are examples using orthophosphoric acid or a salt thereof as a specific phosphoric acid, and other examples are using condensed phosphoric acid or a salt thereof. This is an example. Examples 1 to 6, 9 to 10 and 13 are examples using mercaptans as sulfur-containing compounds, Examples 8 and 11 are examples using sulfides, Examples 7 and 12 are examples using thiourea It is. Examples 1 to 3 are examples in which the concentration of phosphate was changed while the concentration of mercaptans was kept constant. Examples 3 to 4 are examples in which the concentration of the mercaptans was changed while keeping the concentration of phosphate constant.
On the other hand, among Comparative Examples 1 to 5, Comparative Example 1 is a blank example containing only a sulfur-containing compound and no specific phosphoric acid. Comparative Examples 2-3 are blank examples containing only phosphoric acids and no sulfur-containing compounds. Comparative Examples 4 to 5 include both sulfur-containing compounds and phosphoric acids, but the phosphoric acid concentration is less than 0.5 mol / L.

(1) Example 1
A substitution silver plating bath was constructed with the following composition.
Silver acetate (as Ag ⁺ ) 0.05 mol / L
Sodium dihydrogen phosphate 0.50 mol / L
Thioglycol 0.30 mol / L

(2) Example 2
Silver acetate (as Ag ⁺ ) 0.05 mol / L
Sodium dihydrogen phosphate 1.00 mol / L
Thioglycol 0.30 mol / L

(3) Example 3
Silver acetate (as Ag ⁺ ) 0.05 mol / L
Sodium dihydrogen phosphate 2.00 mol / L
Thioglycol 0.30 mol / L

(4) Example 4
Silver acetate (as Ag ⁺ ) 0.05 mol / L
Sodium dihydrogen phosphate 2.00 mol / L
Thioglycol 1.00 mol / L

(5) Example 5
Silver methanesulfonate (as Ag ⁺ ) 0.10 mol / L
Disodium dihydrogen pyrophosphate 1.00 mol / L
Cysteine 0.10 mol / L

(6) Example 6
Silver methanesulfonate (as Ag ⁺ ) 0.10 mol / L
Phosphoric acid 2.00 mol / L
Cysteine 0.50 mol / L

(7) Example 7
Silver lactate (as Ag ⁺ ) 0.10 mol / L
Metaphosphoric acid 0.50 mol / L
Thiourea 0.30 mol / L

(8) Example 8
Silver methanesulfonate (as Ag ⁺ ) 0.05 mol / L
Phosphoric acid 2.00 mol / L
Methionine 0.30 mol / L

(9) Example 9
Silver methanesulfonate (as Ag ⁺ ) 0.10 mol / L
Phosphoric acid 1.00 mol / L
Thioglycolic acid 0.30 mol / L

(10) Example 10
Silver methanesulfonate (as Ag ⁺ ) 0.10 mol / L
Phosphoric acid 1.00 mol / L
2-mercaptobenzothiazole 0.30 mol / L
Polyoxyethylene alkyl ether
-Sulfate ester salt (EO10 mol) 10.0 g / L

(11) Example 11
Silver acetate (as Ag ⁺ ) 0.10 mol / L
Disodium dihydrogen pyrophosphate 1.00 mol / L
Thiodiglycol 0.30 mol / L
Dibutyl-β-naphthol polyethoxylate (EO8 mol) 10.0 g / L

(12) Example 12
Silver acetate (as Ag ⁺ ) 0.10 mol / L
Disodium dihydrogen pyrophosphate 1.00 mol / L
Thiourea 0.30 mol / L
Decyldimethylbenzylammonium chloride 10g / L

(13) Example 13
Silver nitrate (as Ag ⁺ ) 0.10 mol / L
Sodium dihydrogen phosphate 1.00 mol / L
Cysteine 0.30 mol / L
Polyoxyethylene nonylphenyl ether (EO10 mol) 10.0 g / L

(14) Comparative Example 1
Silver acetate (as Ag ⁺ ) 0.05 mol / L
Thioglycol 0.30 mol / L

(15) Comparative example 2
Silver nitrate (as Ag ⁺ ) 0.10 mol / L
Sodium dihydrogen phosphate 0.50 mol / L

(16) Comparative Example 3
Silver acetate (as Ag ⁺ ) 0.10 mol / L
Phosphoric acid 0.50 mol / L

(17) Comparative example 4
Silver acetate (as Ag ⁺ ) 0.10 mol / L
Pyrophosphate 0.40 mol / L
Thioglycol 0.30 mol / L

(18) Comparative Example 5
Silver lactate (as Ag ⁺ ) 0.10 mol / L
Phosphoric acid 0.30 mol / L
Cysteine 0.20 mol / L

<< Example of film appearance evaluation test by substitution silver plating >>
Then, about each substitution silver plating bath of the said Examples 1-13 and Comparative Examples 1-5, by immersing the test plate made from 42 alloy in the shape of 25 mm x 25 mm on the conditions of plating temperature 50 degreeC and 30 second, The surface of the test plate was subjected to substitution silver plating, and the following test evaluations (a) to (c) were performed.
(a) Appearance evaluation test of the plating film obtained from the initial bath The appearance of the plating film obtained from the silver bath immediately after the construction bath (initial bath) was visually observed, and the superiority or inferiority of the appearance of the film was evaluated according to the following criteria. .
○: Glossy silver-white color was exhibited.
X: Black color was exhibited or color unevenness occurred.

(b) Evaluating stability of coating appearance over time Observing the appearance of each plating coating obtained from an initial bath and a silver bath (aging bath) after a period of time from the building bath, the change over time of the plating bath The superiority or inferiority of the stability of the film appearance (referred to as the stability of the film appearance over time) associated with was evaluated according to the following criteria.
The time-lapse bath refers to a bath in which surplus components not in the initial composition are mixed because the base metal is dissolved by a substitution reaction with the passage of time from the building bath.
○: The appearance of the plating film obtained from the time-lapse bath was not changed compared to the appearance of the film obtained from the initial bath.
(Triangle | delta): The external appearance of the plating film obtained from the time-lapse | temporal bath changed from silver white to the silver color with a little blackishness compared with the film external appearance obtained from the initial stage bath.

(c) Comprehensive evaluation of film appearance The results of the appearance test (a) of the plating film (the film obtained from the initial bath) and the temporal stability test (b) of the film appearance were comprehensively evaluated according to the following criteria. .
○: Excellent in the appearance of the film obtained from the initial bath and excellent in the temporal stability of the appearance of the film.
Δ: The film appearance obtained from the initial bath is excellent, but the temporal stability of the film appearance is slightly retreated.
X: The film appearance obtained from the initial bath is inferior.
However, in the case where the evaluation of the film appearance obtained from the above initial bath is x, it is natural that the evaluation with the aging bath is not considered to be more than the initial bath. The test was not conducted, and therefore, the overall evaluation was x.

The table below shows the test results.
Film appearance of initial bath Stability over time Comprehensive evaluation Example 1 ○ ○ ○
Example 2 ○ ○ ○
Example 3 ○ ○ ○
Example 4 ○ ○ ○
Example 5 ○ ○ ○
Example 6 ○ ○ ○
Example 7 ○ △ △
Example 8 ○ ○ ○
Example 9 ○ ○ ○
Example 10 ○ ○ ○
Example 11 ○ ○ ○
Example 12 ○ △ △
Example 13 ○ ○ ○
Comparative Example 1 × −− ×
Comparative Example 2 × −− ×
Comparative Example 3 × −− ×
Comparative Example 4 × −− ×
Comparative Example 5 × −− ×

When the appearance of the film in the initial bath was examined according to the above table, the evaluation of the appearance of the film was inferior in Comparative Example 1 that contained only the sulfur-containing compound and no specific phosphoric acid. Even in Comparative Examples 2 to 3 containing only specific phosphoric acids and no sulfur-containing compound, the evaluation of the film appearance was similarly inferior.
On the other hand, in Examples 1 to 13, a glossy and beautiful silver-white plating film was obtained, and it was recognized that the film appearance was excellent. Therefore, in order to obtain a glossy silver-white plating film, it was confirmed that a sulfur-containing compound that is a complexing agent of silver and a specific phosphoric acid need to coexist.
Comparative Examples 4 to 5 contain both components of a sulfur-containing compound and specific phosphoric acids as in the present invention, but the concentration of phosphoric acids is 0.30 to 0.40 mol / L, and the appearance of the film is Evaluation was inferior. Therefore, when Comparative Examples 4 to 5 are compared with Examples, it is not sufficient to make phosphoric acid coexist with a sulfur-containing compound in order to improve the appearance of the silver film, and the concentration of phosphoric acid is 0.50 mol / L. It was confirmed that it was necessary to increase the above.

Examples 1 to 3 are examples in which the concentration of mercaptans (thioglycol) was kept constant and the concentration of phosphate (sodium dihydrogen phosphate) was changed to 0.50 to 2.00 mol / L. Since the evaluation of the film appearance in the initial bath was excellent, it can be seen that if the concentration of phosphoric acid is 0.50 mol / L or more, a shiny silver-white plating film can be obtained.
On the other hand, Examples 3 to 4 are examples in which the concentration of the phosphate (sodium dihydrogen phosphate) was kept constant and the concentration of the mercaptans (thioglycol) was changed from 0.30 to 1.00 mol / L. In Example 5, the concentration of mercaptans (cysteine) is 0.10 mol / L. Therefore, in order to obtain a shiny silver-white plating film, the concentration of the sulfur-containing compound is phosphoric acids. It is understood that it is not necessary to include it at the concentration level, and it may be small.

The examples are not only excellent in the appearance of the film in the initial bath, but generally, the tin film obtained from the aging bath is also glossy silver-white, which is the same as the film in the initial bath, and is excellent in terms of the aging stability of the film. I understood that.
In detail, in Examples 1-6, 8-11, and 13 using mercaptans and sulfides as the sulfur-containing compound, not only the film appearance in the initial bath is excellent, but also the stability of the film over time. Also excellent. However, in Examples 7 and 12, in which thiourea was used as the sulfur-containing compound, the stability of the plating bath itself was good due to the excellent complexing effect to silver ions, but the silver film obtained from the aging bath was Slightly blackish silver.
Therefore, when Examples 1 to 13 were comprehensively evaluated in terms of both the appearance of the film in the initial bath and the stability over time of the film, the sulfur-containing compound was subjected to the conditions under which the sulfur-containing compound and the specific phosphoric acid coexist. It was found that when mercaptans and sulfides were selected, the overall evaluation was excellent, while when thioureas were selected as the sulfur-containing compound, the overall evaluation was somewhat retreated.
On the other hand, since it is unlikely that the evaluation of the film appearance in the aging bath is more than the evaluation in the initial bath, in Comparative Examples 1 to 5 inferior to the evaluation of the film appearance in the initial bath, the evaluation in the aging bath is performed. Therefore, the overall evaluation of Comparative Examples 1 to 5 was low.

Claims (4)

In a substituted silver plating bath containing a soluble silver salt and a complexing agent comprising a sulfur-containing compound selected from thioureas, sulfides, and mercaptans,
Contains at least one phosphoric acid selected from the group consisting of orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid and salts thereof, and the content of the phosphoric acid is 0.5 to 10 mol / L A substituted silver plating bath characterized by that. The substituted silver plating bath according to claim 1, wherein the sulfur-containing compound is at least one of thioureas , thioglycol, thiodiglycol , cysteine, and methionine. The substituted silver plating bath according to claim 1, further comprising at least one of an anionic, cationic, nonionic, and amphoteric surfactant. The replacement silver plating bath is a bath for forming a silver plating film on a substrate surface selected from 42 alloy, nickel, iron and copper, according to any one of claims 1 to 3 . Replacement silver plating bath.