JP4660806B2 - Electroless silver plating bath - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electroless silver plating bath, and provides an electroless silver plating bath that has excellent bath stability and can improve the appearance of a plating film.
[0002]
[Prior art]
In general, since the standard electrode potential of silver is extremely noble, it is not easy to stabilize silver ions in the plating bath, and the bath is decomposed and silver is likely to be precipitated. Moreover, in the actual silver plating field, since it is necessary to perform continuous operation for a long time under heating from the viewpoint of improving the productivity by increasing the deposition rate, silver ions become more unstable.
[0003]
Examples of conventional techniques for electroless silver plating baths for the purpose of stabilizing the bath and improving film properties include the following.
(1) Japanese Patent Laid-Open No. 10-130855 (Prior Art 1)
On a tin or tin alloy containing mercaptocarboxylic acid such as mercaptosuccinic acid, 3-mercaptopropionic acid, mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropanesulfonic acid, cysteine, or mercaptosulfonic acid as a complexing agent Discloses a non-cyan substituted silver plating bath for depositing a silver replacement film.
[0004]
(2) JP 2000-26977 A (Prior Art 2)
Gold, platinum containing mercapto compounds such as mercaptoacetic acid, 2-mercaptopropionic acid, 2-aminoethanethiol, 2-mercaptoethanol, glucosecysteine, 1-thioglycerol, N-acetylmethionine, or sulfide compounds as a reducing agent, A plating bath by chemical reduction deposition of a noble metal selected from silver and palladium is disclosed. These mercapto compounds have a reducing action, and also have a complexing action on noble metals such as gold, platinum, silver and palladium. Increasing the reducing agent concentration leads to an increase in the complexing agent concentration, and Stabilization is described (see paragraph 6 of the same publication).
[0005]
(3) JP 2000-309875 A (Prior Art 3)
HOCH₂CH₂-S-CH₂CH₂-S-CH₂CH₂1,2-bis (2-hydroxyethylthio) ethane represented by OH, HSCH₂CH₂-S-CH₂CH₂-S-CH₂CH₂2,2 '-(ethylenedithio) diethanethiol represented by SH, HOCH₂CH₂-S-CH₂CH₂CH₂CH₂-S-CH₂CH₂1,4-bis (2-hydroxyethylthio) butane represented by OH, HOOCCH₂CH₂-S-CH₂CH₂CH₂-S-CH₂CH₂There are two monosulfide groups in the molecule, such as 3,3 ′-(propylenedithio) dipropionic acid represented by COOH, and a C atom is present between the two monosulfide groups.₁~ C₈A substitutional electroless silver plating bath containing a water-soluble sulfur-containing compound in which an alkylene group is present is disclosed.
[0006]
[Problems to be solved by the invention]
Although the conventional techniques 1 to 3 show some improvement in the stability of the bath, there is room for further improvement, and the appearance of the silver plating film obtained from the bath is also required to be improved in terms of color tone. It is where it is done.
It is a technical object of the present invention to further improve bath stability and film appearance in an electroless silver plating bath.
[0007]
[Means for Solving the Problems]
The applicant of the present application previously described in Japanese Patent Application No. 2000-279149 (hereinafter referred to as the prior art) for the purpose of improving the aging stability of the bath and smooth co-deposition of tin and silver. An electroless tin-silver alloy plating bath containing an oxyalkylene type sulfide compound having an oxyethylene group, an oxypropylene group or an oxy (hydroxypropylene) group in the molecule adjacent to both sides or one side was proposed.
[0008]
  In the prior art 3, a water-soluble sulfur compound having two monosulfide groups is contained in the plating bath for the purpose of improving the stability of the electroless silver plating bath and the denseness of the plating film. The inventors have proposed the above prior art belonging to the same sulfide-based compound while taking into consideration the water-soluble sulfur-containing compound and the like.Oxyalkylene typeAs a result of diligent research on sulfide compounds, the compounds are not limited to electroless tin-silver alloy plating baths, but also when applied to electroless silver plating baths, they are notable in terms of bath stability and plating film appearance. The inventors have found that the present invention is effective and have completed the present invention.
[0009]
  That is, the present invention 1An oxyalkylene type aliphatic sulfide compound having an oxyethylene group, an oxypropylene group or an oxy (hydroxypropylene) group in the molecule adjacent to both sides or one side of one mono- or disulfide bond is contained as a complexing agent. And containing at least one compound selected from thioureas, aminocarboxylic acids, polyamines, aminoalcohols, oxycarboxylic acids, and polycarboxylic acids.An electroless silver plating bath.
[0012]
  That is, the present invention 4Invention 1 abovePrinted circuit boards, semiconductor integrated circuits, resistors, variable resistors, capacitors, filters, inductors, thermistors, crystal resonators, switches, lead wires with electroless silver plating film formed using a plating bathMore selected electronic componentsIt is.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
  First, the present invention provides a specific oxyalkylene type aliphatic sulfide compound.As a complexing agentAn electroless silver plating bath, and secondly, various electronic components in which a silver plating film is formed using the plating bath.
  In general, electroless plating can be classified into a displacement plating method based on a chemical substitution action between a metal in the bath and a base metal to be plated, and a reduction plating method in which metal ions in the bath are precipitated by the action of a reducing agent. However, the electroless silver plating bath of the present invention includes both of them.
[0015]
  Of the present inventionThe oxyalkylene type aliphatic sulfide compound functions to complex silver ions in the plating bath and stabilize it.
  The oxyalkylene type aliphatic sulfide compound is a sulfide compound having an oxyethylene group, an oxypropylene group or an oxy (hydroxypropylene) group in the molecule adjacent to both sides or one side of a mono- or disulfide bond. Specifically, the following compounds are listed.
  (1) H- (OCH₂CH₂)_Three-S- (CH₂CH₂O)_ThreeBis (triethylene glycol) thioether represented by -H
  (2) H- (OCH₂CH₂)₆-S- (CH₂CH₂O)₆Bis (hexaethylene glycol) thioether represented by -H
  (3) H- (OCH₂CH₂)_Ten-S- (CH₂CH₂O)_TenBis (decaethylene glycol) thioether represented by -H
  (4) H- (OCH₂CH₂)₁₂-S- (CH₂CH₂O)₁₂-H (bis (dodecaethylene glycol) thioether represented by
  (5) H- (OCH₂CH₂)₁₅-S- (CH₂CH₂O)₁₅Bis (pentadecaethylene glycol) thioether represented by -H
  (6) H- (OCH₂CH₂)₂₀-S- (CH₂CH₂O)₂₀Bis (icosaethylene glycol) thioether represented by -H
  (7) H- (OCH₂CH₂)₃₀-S- (CH₂CH₂O)₃₀Bis (triacontane glycol) thioether represented by —H
  (8) H- (OCH₂CH₂)₄₀-S- (CH₂CH₂O)₄₀Bis (tetracontaethylene glycol) thioether represented by -H
  (9) H- (OCH₂CH₂)₅₀-S- (CH₂CH₂O)₅₀Bis (pentacontaethylene glycol) thioether represented by -H
  (10) HOCH₂CH₂-S-CH₂CH₂2,2'-thiodiglycol represented by OH
  (11) HOCH₂CH₂CH₂-S-CH₂CH₂CH₂3,3'-thiodipropanol represented by OH
  (12) H- (OCH₂CH₂)_Five-S-S- (CH₂CH₂O)_FiveBis (ω-hydroxypentaethoxy) disulfide represented by —H
  (13) H- (OCH₂CH₂)₁₂-S-S- (CH₂CH₂O)₁₂Bis (ω-hydroxydodecaethoxy) disulfide represented by —H
  (14) H- (OCH₂CH₂)₂₀-S-S- (CH₂CH₂O)₂₀Bis (ω-hydroxyicosaethoxy) disulfide represented by —H
  (15) H- (OCH₂CH₂)₅₀-S-S- (CH₂CH₂O)₅₀Bis (ω-hydroxypentacontaethoxy) disulfide represented by —H
  (16) H- (OCH₂CH (OH) CH₂)₈-S- (CH₂CH (OH) CH₂O)₈Bis (octaglycerol) thioether represented by —H
  (17) H- (OC_ThreeH₆)_Five-(OC₂H_Four)₁₅-S- (C₂H_FourO)₁₅-(C_ThreeH₆O)_FiveBis (pentadecaethylene glycol pentapropylene glycol) thioether represented by -H
  (18) H-OCH₂CH (OH) CH₂-(OC₂H_Four)_Ten-S- (C₂H_FourO)_Ten-CH₂CH (OH) CH₂Bis (decaethylene glycol monoglycerol) thioether represented by OH
  (19) H- (OC₂H_Four)_Ten-(OC_ThreeH₆)_Three-S- (C_ThreeH₆O)_Three-(C₂H_FourO)_TenBis (tripropylene glycol decaethylene glycol) thioether represented by -H (20) H- (OC_ThreeH₆)_Five-(OC₂H_Four)₁₅-SS- (C₂H_FourO)₁₅-(C_ThreeH₆O)_FiveBis (ω-hydroxypentapropoxypentadecaethoxy) disulfide represented by —H
  (21) H-OCH₂CH (OH) CH₂-(OC₂H_Four)_Ten-SS- (C₂H_FourO)_Ten-CH₂CH (OH) CH₂Bis (ω-hydroxymonoglyceroxydecaethoxy) disulfide represented by OH
  (22) H- (OC₂H_Four)₂₀-(OC_ThreeH₆)_Five-SS- (C_ThreeH₆O)_Five-(C₂H_FourO)₂₀Bis (ω-hydroxyicosaethoxypentapropoxy) disulfide represented by —H
  (23) H- (OCH₂CH₂)₂-S- (CH₂CH₂O)₂Bis (diethylene glycol) thioether represented by -H
  (24) HOCH₂CH (OH) CH₂-S-CH₂CH (OH) CH₂Bis (monoglycerol) thioether represented by OH
  (25) H- (OCH₂CH (OH) CH₂)_Three-S- (CH₂CH (OH) CH₂O)_ThreeBis (triglycerol) thioether represented by —H
  (26) H- (OCH₂CH₂)₄₁-S-S- (CH₂CH₂O)₄₁Bis (ω-hydroxyhentetracontaethoxy) disulfide represented by —H
  (27) H- (OC_ThreeH₆)_Five-(OC₂H_Four)₂₀-SS- (C₂H_FourO)₂₀-(C_ThreeH₆O)_FiveBis (ω-hydroxypentapropoxyicosaethoxy) disulfide represented by —H
  (28) H- (OCH₂CH (OH) CH₂)_Three-S-S- (CH₂CH (OH) CH₂O)_ThreeBis (ω-hydroxytriglyceroxy) disulfide represented by —H
  (29) H- (OCH₂CH (OH) CH₂)_Ten-S-S- (CH₂CH (OH) CH₂O)_TenBis (ω-hydroxydecaglyceroxy) disulfide represented by —H
  (30) CH_Three-S-CH₂CH₂2- (Methylthio) ethanol represented by OH
[0016]
In the above formulas (1) to (9), an oxyethylene group (C₂H_FourO) is repeated in the molecule, and in the above formulas (10) to (11), an oxyethylene group or an oxypropylene group (C_ThreeH₆O) in the singular molecule.
In the above formulas (12) to (15), a repeating oxyethylene group is present in the molecule at adjacent positions on both sides of the disulfide bond, and in the above formula (16), oxy (hydroxyl) is present at adjacent positions on both sides of the monosulfide bond. Propylene) group (CH₂CH (OH) CH₂O) repeats in the molecule.
In the above formula (17), there are repeating oxyethylene groups and repeating oxypropylene groups in the molecule at adjacent positions on both sides of the monosulfide bond, and in the above formula (20), oxyethylene groups are repeated at adjacent positions on both sides of the disulfide bond. In the above formula (21), repeats of oxyethylene groups and oxy (hydroxypropylene) groups are placed in adjacent positions on both sides of the disulfide bond in the molecule. Have.
The compounds listed in the above formula have many symmetrical molecular structures centering on mono- or disulfide bonds, but the oxyalkylene-type sulfide compounds of the present invention may be compounds having different molecular structures, such as the above formula ( As shown in 30), an alkyl group or the like may be bonded to one side of a mono- or disulfide bond.
[0017]
The above aliphatic sulfide compounds can be used alone or in combination. Among them, 2,2′-thiodiglycol, bis (dodecaethylene glycol) thioether, bis (pentadecaethylene glycol) thioether, 2- (methylthio) ethanol, 1, 2-bis (2-hydroxyethylthio) ethane and the like are preferable.
The content of the aliphatic sulfide compound in the bath is 0.01 to 500 g / L, preferably 1 to 300 g / L.
[0018]
A silver salt as a silver supply source is a salt capable of supplying silver ions in a plating bath and is based on a soluble salt, but does not exclude a hardly soluble salt or the like, and any salt can be used.
Examples of the soluble silver salt include silver sulfate, silver sulfite, silver carbonate, silver sulfosuccinate, silver nitrate, silver organic sulfonate, silver borofluoride, silver citrate, silver tartrate, silver gluconate, silver sulfamate, and oxalic acid. Soluble salts such as silver and silver oxide can be used, and silver chloride which is originally poorly soluble but can ensure a certain degree of solubility by the action of sulfide compounds and the like can also be used. Preferable specific examples of the silver salt include silver methanesulfonate, silver ethanesulfonate, silver 2-propanolsulfonate, silver phenolsulfonate, and silver citrate.
The conversion addition amount of the soluble silver salt as a metal salt is 0.0001 to 200 g / L, preferably 0.1 to 80 g / L.
[0019]
The electroless silver plating bath of the present invention is basically an organic acid bath, an inorganic acid bath, or a salt-based 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, but borohydrofluoric acid or hydrogen silicofluoride. Inorganic acids such as acid, sulfamic acid, hydrochloric acid, sulfuric acid, nitric acid and perchloric acid may be used.
The acid (or salt) can be used singly or in combination, and the amount of acid (or salt) added is 0.1 to 300 g / L, preferably 20 to 120 g / L.
[0020]
The alkanesulfonic acid has the chemical formula C_nH_{2n + 1}SO_ThreeThose represented by H (for example, n = 1 to 5, preferably 1 to 3) can be used. Specifically, methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1 In addition to butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid and the like, hexanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid and the like can be mentioned.
[0021]
The alkanol sulfonic acid has the chemical formula
C_mH_{2m + 1}-CH (OH) -C_pH_2p-SO_ThreeH (for example, m = 0 to 6, p = 1 to 5)
In particular, 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1- In addition to sulfonic acid, etc. 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 and the like.
[0022]
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.
[0023]
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.
[0024]
  Of the present inventionFor electroless silver plating baths, thioureas,At least one of aminocarboxylic acids, polyamines, aminoalcohols, oxycarboxylic acids, polycarboxylic acids, etc.Added.
  These compounds have a concealing function that prevents and adversely affects the plating bath of impurity metal ions eluted from the base metal such as copper and copper alloy, and complements and promotes the stabilization of the bath, and also acts on the base metal. The effect of expanding the potential difference from silver by transitioning the electrode potential of the metal in the base direction can also be expected. Of the above compounds, thioureas belong to sulfur-containing compounds, and therefore, an action of complexing and stabilizing silver ions in the plating bath can be expected at the same time.
  The content of the above compound in the bath is 0.01 to 500 g / L, preferably 1 to 300 g / L.
  However, the substrate to which the silver plating bath of the present invention is applied is not limited to copper, copper alloy, etc., but may be other metals or alloys such as nickel, steel, tin, synthetic resin, ceramics, etc. Absent.
[0025]
The thioureas are a concept including thiourea and thiourea derivatives.
The thiourea derivative basically refers to a compound in which various substituents are bonded to one or more of nitrogen atoms or sulfur atoms of thiourea and has a molecular volume larger than that of thiourea. , 3-dimethylthiourea, trimethylthiourea, diethylthiourea (eg, 1,3-diethyl-2-thiourea), N, N'-diisopropylthiourea, allylthiourea, acetylthiourea, ethylenethiourea, 1,3-diphenyl Examples include thiourea, thiourea dioxide, and thiosemicarbazide.
Examples of the aminocarboxylic acids include ethylenediaminetetraacetic acid (EDTA), ethylenediaminetetraacetic acid disodium salt (EDTA · 2Na), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), and triethylenetetraminehexaacetic acid (TTHA). , Ethylenediaminetetrapropionic acid, nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), metaphenylenediaminetetraacetic acid, 1,2-diaminocyclohexane-N, N, N ', N'- Examples include tetraacetic acid, aminopropionic acid, diaminopropionic acid, aminovaleric acid, glutamic acid, ornithine, cysteine, and N, N-bis (2-hydroxyethyl) glycine.
Examples of the polyamines include ethylenediamine, diethylenetriamine, pentaethylenehexamine, hexamethylenediamine, ethylenediaminetetramethylenephosphoric acid, diethylenetriaminepentamethylenephosphoric acid, aminotrimethylenephosphoric acid, and aminotrimethylenephosphoric acid pentasodium salt.
Examples of the amino alcohols include monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, and tripropanolamine.
Examples of the oxycarboxylic acids include tartaric acid, citric acid, malic acid, gluconic acid, glycolic acid, and glucoheptonic acid. When these oxycarboxylic acids are selected as the base acid to be added to the bath, this base is used. It can be used with any acid.
Examples of the polycarboxylic acid include succinic acid, malonic acid, and glutaric acid.
Other nitrogen-containing heterocyclic compounds such as 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, 2,2′-bipyridyl, 2,2 ′, 2 ″ -terpyridyl, pyridine, pyrophosphate Tripolyphosphoric acid, 1-hydroxyethane-1,1-bisphosphonic acid and the like can also be used.
[0026]
In addition to the above-mentioned components, the electroless silver plating bath of the present invention is usually used for plating baths of known reducing agents, surfactants, pH adjusters, buffers, smoothing agents, stress relaxation agents, etc. depending on the purpose. Of course, the additive can be mixed.
[0027]
As described above, the electroless silver plating of the present invention includes a reduction type plating bath. However, the reducing agent is added for the purpose of reducing the silver salt and adjusting the precipitation rate and the ratio of the precipitated alloy. , Aldehydes, Rochelle salts, reducing sugars, amino alcohols such as triethanolamine, formic acid and its derivatives, ascorbic acid and its salts, phosphate compounds, amine boranes, borohydride compounds, hydrazine derivatives, etc. Can be used together.
Examples of the aldehydes include formalin derivatives such as formalin and paraformaldehyde, glyoxylic acid and glyoxal.
Examples of the reducing saccharide include glucose, maltose, and lactose.
Examples of the phosphoric acid compounds include hypophosphorous acid, phosphorous acid, pyrophosphoric acid, polyphosphoric acid, or salts of ammonium, lithium, sodium, potassium, calcium and the like.
Examples of the amine boranes include dimethylamine borane, trimethylamine borane, isopropylamine borane, morpholine borane and the like.
Examples of the borohydride compound include sodium borohydride.
Examples of the hydrazine derivative include hydrazine hydrate, methyl hydrazine, and phenyl hydrazine.
The addition amount of the reducing agent is 0.1 to 200 g / L, preferably 10 to 150 g / L.
[0028]
Examples of the surfactant include nonionic surfactants, amphoteric surfactants, cationic surfactants, and anionic surfactants. These various surfactants can be used alone or in combination.
Examples of the anionic surfactant include alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl phenyl ether sulfates, alkyl benzene sulfonates, and alkyl naphthalene sulfonates. Examples of the cationic surfactant include quaternary ammonium salts and pyridinium salts. Nonionic surfactants include C₁~ C₂₀Alkanol, phenol, naphthol, bisphenols, C₁~ C_{twenty five}Alkylphenol, arylalkylphenol, C₁~ C_{twenty five}Alkyl naphthol, C₁~ C_{twenty five}Alkoxylphosphoric acid (salt), sorbitan ester, polyalkylene glycol, C₁~ C_{twenty two}Examples include aliphatic amides and the like obtained by addition condensation of 2-300 mol of ethylene oxide (EO) and / or propylene oxide (PO). Examples of amphoteric surfactants include carboxybetaine, imidazoline betaine, sulfobetaine, and aminocarboxylic acid.
The addition amount is 0.01 to 100 g / L, preferably 0.1 to 50 g / L.
[0029]
As plating conditions using the electroless bath, the bath temperature is 40 to 90 ° C., and 50 to 70 ° C. is preferable from the viewpoint of increasing the deposition rate.
[0030]
  Invention 2Is the aboveInvention 1Articles in which a silver plating film is formed using a plating bath, specifically, printed circuit boards, semiconductor integrated circuits (including TAB film carriers, BGA substrates, etc.), resistors, variable resistors, capacitors, filters And electronic parts such as inductors, thermistors, crystal resonators, switches, connectors, lead wires, and hoop materials.
[0031]
[Action]
  In the silver plating bath of the present invention, as a complexing agentSpecific oxyalkylene typeSince there is an aliphatic sulfide compound, it acts on the silver ions in the bath to shift the redox potential of silver in the base direction and stabilize the silver ions, thereby trying to precipitate as metallic silver It is presumed that this can be prevented smoothly, and that the homogeneity of the color tone of the deposited film is promoted.
  AndThiourea, aminocarboxylic acids, etc. in the bathTo coexist,Concealing impurity ions eluted from the surface of the substrate to be plated to contribute to stabilization of the bath, and when the base metal is copper or copper alloy, thiourea acts on the base metal to oxidize it. For example, in the case of substitution silver plating, the substitution reaction seems to be promoted more smoothly because the reduction potential is shifted to the base side, thereby working to widen the difference in oxidation-reduction potential between silver and the base metal. It is.
[0032]
【The invention's effect】
  The electroless silver plating bath of the present invention is used as a complexing agent.specificOxyalkylene typeAliphaticSulfide compoundsTo useThe bath has excellent stability over time and does not decompose over a long period of time. In this case, as described above, in an actual electroless silver plating bath, from the viewpoint of productivity, it is common to operate the plating bath continuously under heating, but the present invention has high stability over time of the bath. In this plating bath, the decomposition of the bath can be suppressed and the continuous operability at a practical level can be ensured smoothly.
  In addition, since the plating bath has high stability, the appearance of the silver plating film obtained from the bath can be satisfactorily improved to form a silver film having a uniform color tone.
  In particular, the present inventionOxyalkylene typeAliphatic sulfide compounds include mercaptoacetic acids such as mercaptoacetic acid and 2-mercaptopropionic acid described in the above-mentioned prior art, mercaptoalcohols such as 2-mercaptoethanol, or sulfide bonds such as thiodiglycolic acid. However, as shown in the following test examples, the silver plating bath containing the aliphatic sulfide compound of the present invention contains other sulfur-containing compounds. Compared to baths, it is superior or even superior in terms of the stability over time and the homogeneous color tone of the plating film.
[0033]
【Example】
Hereinafter, examples of the electroless silver plating bath of the present invention will be sequentially described, and various test examples of the stability over time of each plating bath and the appearance of the silver film obtained from the plating bath will be 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.
[0034]
  Examples 1 through below8Of these, Examples 1 to6Is a single use example of an oxyalkylene type aliphatic sulfide compound, Example7-8Is a combination example of the aliphatic sulfide compoundsIt is. Also,Example5, 8IsReducing agentIt is an example of the contained reduction type plating bath, and others are examples of the substitution type plating bath which does not contain a reducing agent.
  On the other hand, Comparative Example 1 is a blank example containing no complexing agent, Comparative Example 2 is an example using thiourea as a complexing agent, and Comparative Example 3 is mercaptosuccinic acid (HOOCCH) in accordance with the prior art described above.₂-CH (SH) COOH) is used as a complexing agent, Comparative Example 4 is thiodiglycolic acid (HOOCCH) according to the prior art.₂-S-CH₂COOH), Comparative Example 5 is similarly 2-mercaptoethanol (HSCH).₂CH₂This is an example using OH).
[0039]
  《Example 1>>
  An electroless silver plating bath was constructed with the following composition.
  Ethanesulfonic acid silver (Ag⁺As) 2g / L
  2-hydroxypropane-1-sulfonic acid 60 g / L
  Thiourea 20g / L
  Bis (dodecaethylene glycol) thioether 30g / L
[0040]
  《Example 2>>
  An electroless silver plating bath was constructed with the following composition.
  Silver nitrate (Ag⁺As) 1g / L
  Methanesulfonic acid 70g / L
  1,3-dimethylthiourea 15g / L
  Bis (pentadecaethylene glycol) thioether 40g / L
[0041]
  《Example 3>>
  An electroless silver plating bath was constructed with the following composition.
  Silver methanesulfonate (Ag⁺As) 4g / L
  Methanesulfonic acid 75g / L
  Diethylthiourea 35g / L
  Thiodiglycol 30g / L
[0042]
  《Example 4>>
  An electroless silver plating bath was constructed with the following composition.
  Silver citrate (Ag⁺As) 1g / L
  Methanesulfonic acid 80g / L
  Thiourea 30g / L
  2- (Methylthio) ethanol 20 g / L
[0043]
  《Example 5>>
  An electroless silver plating bath was constructed with the following composition.
  Silver methanesulfonate (Ag⁺As) 1g / L
  Methanesulfonic acid 50g / L
  EDTA 25g / L
  Bis (dodecaethylene glycol) thioether 25g / L
  Hydrazine sulfate 30g / L
[0044]
  《Example 6>>
  An electroless silver plating bath was constructed with the following composition.
  Silver sulfamate (Ag⁺As) 5g / L
  Methanesulfonic acid 60g / L
  Thiourea 10g / L
  Bis (dodecaethylene glycol) thioether 35g / L
  Lauryl alcohol polyethoxylate (EO15 mol) 1g / L
[0045]
  《Example 7>>
  An electroless silver plating bath was constructed with the following composition.
  Silver methanesulfonate (Ag⁺As) 3g / L
  Methanesulfonic acid 90g / L
  Allylthiourea 10g / L
  Bis (dodecaethylene glycol) thioether 25g / L
  Thiodiglycol 10g / L
  Dibutyl-β-naphthol polyethoxylate (EO15 mol) 1g / L
[0046]
  《Example 8>>
  An electroless silver plating bath was constructed with the following composition.
  Silver methanesulfonate (Ag⁺As) 3g / L
  Methanesulfonic acid 50g / L
  EDTA 20g / L
  Bis (dodecaethylene glycol) thioether 15g / L
  2- (Methylthio) ethanol 10 g / L
  Formalin 40ml / L
  Laurylamine polyethoxylate (EO10mol) 0.1g / L
[0047]
<< Comparative Example 1 >>
An electroless silver plating bath was constructed with the following composition.
Silver methanesulfonate (Ag⁺As) 1g / L
Methanesulfonic acid 50g / L
[0048]
<< Comparative Example 2 >>
An electroless silver plating bath was constructed with the following composition.
Silver methanesulfonate (Ag⁺As) 1g / L
Methanesulfonic acid 50g / L
Thiourea 30g / L
[0049]
<< Comparative Example 3 >>
An electroless silver plating bath was constructed with the following composition.
Silver methanesulfonate (Ag⁺As) 1g / L
Methanesulfonic acid 50g / L
Mercaptosuccinic acid 20g / L
[0050]
<< Comparative Example 4 >>
An electroless silver plating bath was constructed with the following composition.
Silver methanesulfonate (Ag⁺As) 1g / L
Methanesulfonic acid 50g / L
Thiodiglycolic acid 30g / L
[0051]
<< Comparative Example 5 >>
An electroless silver plating bath was constructed with the following composition.
Silver methanesulfonate (Ag⁺As) 1g / L
Methanesulfonic acid 50g / L
2-mercaptoethanol 10g / L
[0052]
  As described above, electroless silver plating is basically performed continuously for a long time under heating from the viewpoint of improving productivity. Thus, the silver plating baths of the above examples and comparative examples were held for a long time under heating to evaluate the aging stability of the plating bath.
  <Example of stability test of electroless silver plating bath over time>
  That is, the above Examples 1 to8In addition, each electroless silver plating solution of Comparative Examples 1 to 5 was placed in a 1 L beaker, and placed in a water bath set at a constant temperature of 50 ° C. and kept warm for 250 hours. ) Stability over time was visually evaluated by observing the degree of state.
[0053]
The evaluation criteria for the temporal stability are as follows.
◯: The plating bath was stable at the time of 250 hours, the transparency was high, and there was no change compared to the initial bathing time.
Δ: Turbidity and precipitation occurred between 50 hours and 250 hours, and the plating bath was decomposed.
X: Turbidity and precipitation occurred by 50 hours, and the plating bath was decomposed.
[0054]
  The left column of FIG. 1 shows the test results.8Were all evaluated as ○. That is, the plating bath containing the aliphatic sulfide compound of the present invention was stable without being decomposed over a long period of 250 hours or more under heating at 50 ° C., regardless of the type and concentration. In general, in a plating bath containing a reducing agent, silver ions become unstable and easily precipitate.5, 8In addition, excellent bath stability over time was revealed.
  On the other hand, in Comparative Example 1 containing no complexing agent, the bath was naturally decomposed, and in Comparative Example 2 containing thiourea as the complexing agent, turbidity and precipitation occurred during 50 to 250 hours. . Further, in Comparative Examples 3 to 5 containing mercaptosuccinic acid, thiodiglycolic acid, or 2-mercaptoethanol based on the above-described prior art, the time of occurrence of turbidity was slower than in Comparative Example 2. From the point of view of bath stability, turbidity and the like occurred by 250 hours.8The advantage of was revealed.
[0055]
  Therefore, each of the above Examples 1 to8In addition, each electroless silver plating bath of Comparative Examples 1 to 5 was kept at 50 ° C., and a test piece of a TAB film carrier patterned with VLP (a kind of electrolytic copper foil) was immersed for 5 minutes to electroless silver plating. Went.
  The appearance of each silver plating film obtained was visually observed, and the film thickness (μm) of the film was measured with an instrument.
[0056]
<< Example of appearance evaluation test for plating film >>
The appearance of the silver plating film was evaluated based on the following criteria.
○: A white appearance with a uniform color tone and a metallic luster.
X: Spots such as brown and brown, color unevenness were observed, and the color tone was uneven.
[0057]
  The center column of FIG.8Were all evaluated as ○. As described above, since the plating baths of the examples have high temporal stability, it is clear that this stability contributed to the formation of an excellent coating appearance.
  On the other hand, Comparative Example 1 has an apparent poor appearance, and also in Comparative Example 2, thiourea cannot be as effective in stabilizing silver ions as the aliphatic sulfide compound of the present invention, and has a poor appearance. there were. As for Comparative Examples 3 to 5, the coating appearance was improved to some extent as compared with Comparative Example 2, but fine color unevenness was observed, and the color tone was less uniform than Examples 1-12. .
[Brief description of the drawings]
FIG. 1 to Example 18And it is a graph which shows the test result of the time-dependent stability of each electroless silver plating bath of Comparative Examples 1-4, the external appearance of the silver plating film | membrane obtained from each plating bath, and a film thickness, respectively.

Claims (2)

An oxyalkylene type aliphatic sulfide compound having an oxyethylene group, an oxypropylene group or an oxy (hydroxypropylene) group in the molecule adjacent to both sides or one side of one mono- or disulfide bond is contained as a complexing agent. An electroless silver plating bath comprising at least one compound selected from thioureas, aminocarboxylic acids, polyamines, aminoalcohols, oxycarboxylic acids, and polycarboxylic acids . A printed circuit board, a semiconductor integrated circuit, a resistor, a variable resistor, a capacitor, a filter, an inductor, a thermistor, a crystal resonator, a switch, and a lead wire on which an electroless silver plating film is formed using the plating bath of claim 1 Electronic parts .

Images