JP4147388B2 - Electroless tin plating bath for preventing copper erosion and method for preventing copper erosion - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electroless tin plating bath for preventing copper erosion, and a method for preventing copper erosion using the plating bath, a film carrier in which a copper or copper alloy fine pattern on an insulating substrate is coated with a solder resist, Provided is one that can effectively prevent copper erosion such as a flexible printed circuit board.
[0002]
[Prior art]
Tin plating is widely used in weak electrical industry and electronic industry parts as a film for improving solderability, a film for etching resist, and the like.
In particular, electroless tin organic sulfonic acid baths have been extensively studied and reported from the standpoint of ease of wastewater treatment and solubility of tin salts.
For example, JP-A-5-186878, JP-A-7-113179, JP-A-10-36973, JP-A-11-61426, JP-A-11-256350, JP-A-11-343578, etc. Discloses an electroless tin plating bath having a basic composition of an organic sulfonic acid as a bath base, a soluble stannous salt, and thioureas for promoting a substitution reaction with a copper base.
[0003]
However, when tin plating is performed on a fine pattern such as a film carrier or a flexible circuit board using an electroless tin organic sulfonic acid bath, the adhesiveness around the edge of the solder resist is lowered and partial peeling is likely to occur. The plating solution may penetrate from the edge of the solder resist to the bottom surface along the fine pattern, and may elute copper to reduce the reliability of the product.
[0004]
Examples of conventional techniques for preventing the peeling of the solder resist include the following.
(1) Japanese Patent Laid-Open No. 6-342969 (Prior Art 1)
There has been disclosed a flexible circuit board in which a tin or gold plating film is formed on a fine pattern and a solder resist is coated on the plating film to improve the adhesion of the solder resist.
[0005]
(2) Japanese Patent No. 3076342 (Prior Art 2)
A tin plating film is formed on a copper fine pattern, and this tin plating film is heated to diffuse copper, and a solder resist is applied on the tin plating film where copper is diffused in a predetermined portion excluding the terminal portion of the fine pattern. A copper / tin-containing region in which a tin plating film that does not contain copper is formed on the terminal portion and the copper diffusion concentration gradually decreases from the surface of the lower tin film toward the surface of the upper tin film. Discloses a film carrier in which the plating solution is prevented from penetrating between the solder resist and the lower tin film so as to be continuous with the upper tin film.
[0006]
[Problems to be solved by the invention]
The above conventional techniques 1 and 2 are special methods for preventing the peeling of the solder resist by coating a solder resist on the base film after forming a tin or gold film on the fine pattern. When tin plating is performed on a fine pattern of a general film carrier directly coated with a resist, it is not intended to prevent peeling of the solder resist by devising an organic sulfonic acid bath of electroless tin.
The present invention is not a technique for changing the film carrier to a special structure when forming a tin film on a fine pattern such as a film carrier or a flexible circuit board using an electroless tin organic sulfonic acid bath. A technical problem is to effectively prevent the erosion of fine patterns by modifying the composition of the plating bath.
[0007]
[Means for Solving the Problems]
The present inventors have intensively studied to effectively prevent fine pattern erosion by controlling the composition of an electroless tin organic sulfonic acid bath. As a result, the anion portion of alkane sulfonic acid was present in the bath. In this state, if the content of complexing thioureas and the molar ratio of the thioureas and soluble tin salts are conditioned within a certain range, adhesion of the solder resist on film carriers and flexible circuit boards is ensured. Therefore, it is possible to effectively prevent fine pattern erosion, and even if alkane sulfonic acid is replaced with an anion portion of borohydrofluoric acid, as long as the content and molar ratio of the above components are satisfied, copper erosion is similarly performed. The present invention has been completed.
[0008]
  That is, the present invention 1 is an electroless tin plating bath containing a soluble stannous salt, an organic sulfonic acid and thioureas.
  Soluble stannous salt (Sn²⁺Conversion) and the molar ratio of thioureas per liter is thioureas / Sn²⁺=4 . 0-8 . 4And
  The content of thioureas is2 . 2-3 . 5Mol / L,
  An electroless tin plating bath for preventing copper corrosion, comprising an anion portion of alkanesulfonic acid as the organic sulfonic acid.
[0009]
  The present invention 2 is an electroless tin plating bath containing a soluble stannous salt, an inorganic acid, and a thiourea,
  Soluble stannous salt (Sn²⁺Conversion) and the molar ratio of thioureas per liter is thioureas / Sn²⁺=4 . 0-8 . 4And
  The content of thioureas is2 . 2-3 . 5Mol / L,
  An electroless tin plating bath for preventing copper erosion, comprising an anionic portion of borohydrofluoric acid as the inorganic acid.
[0010]
Invention 3 is the same as Invention 1 or 2, except that the soluble stannous salt (Sn²⁺It is an electroless tin plating bath for preventing copper erosion, characterized in that the content of (converted) is 40 to 70 g / L.
[0012]
  Invention 4 provides the invention 1 or 3 described above.The alkanesulfonic acid is C₁~ C_FourAn electroless tin plating bath for preventing copper erosion characterized by being alkanesulfonic acid.
[0013]
  The present invention 5 includes the present inventions 1-4 described above.In any of the above, an electroless tin plating bath for preventing copper corrosion, wherein the thiourea is thiourea.
[0014]
  The present invention 6 includes the above-mentioned present inventions 1 to 5.In any of the above, an electroless tin plating bath for preventing copper corrosion, comprising an antioxidant such as hypophosphorous acid and its salt.
[0015]
  The present invention 7 includes the present invention 6 described above.In claim 1, the content of hypophosphorous acid and its salt is 0.1 to 1.0 mol / L, an electroless tin plating bath for preventing copper erosion.
[0016]
  Invention 8 provides the inventions 1-7.In any of the above, the electroless tin plating bath for preventing copper erosion, further comprising various additives such as a surfactant, a smoothing agent, a brightening agent, a semi-brightening agent, and a pH adjusting agent.
[0017]
  The present invention 9 includes the present invention 1-8.A copper erosion prevention method comprising immersing a copper object to be plated in any one of the electroless tin plating baths to form a tin plating film on the object to be plated without copper erosion.
[0018]
  Invention 10 provides the invention 9 described above.The object to be plated is a film carrier, a printed circuit board, a flexible printed board, or the like in which a part of a fine pattern made of copper or a copper alloy is coated with a solder resist. Is the method.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an electroless tin organic sulfonic acid plating bath in which the type of organic sulfonic acid is specified and the content of thioureas and the molar ratio of thioureas and soluble tin salts are specified. Second, there is an electroless tin plating bath in which the base acid is changed to organic sulfonic acid and borohydrofluoric acid while specifying the content and molar ratio of the predetermined component, and third, these electroless In this method, tin plating is performed on a wiring pattern of a film carrier or a flexible printed board using a tin bath to prevent copper corrosion of the wiring pattern.
In the present invention, the material of the fine pattern of the wiring is not limited to copper but includes a copper alloy.
[0020]
The first invention is an electroless tin plating bath having a basic composition of a soluble stannous salt, an organic sulfonic acid and thioureas, which satisfies the following conditions (a) to (b).
(a) As an organic sulfonic acid, it is necessary to contain an anion portion of alkanesulfonic acid.
The anionic part of alkanesulfonic acid means containing alkanesulfonic acid as a free acid and / or stannous salt of alkanesulfonic acid.
However, other organic sulfonic acids such as alkanol sulfonic acid and aromatic sulfonic acid, aliphatic carboxylic acid, or inorganic acid may coexist in the plating bath.
[0021]
  (b) Soluble stannous salt (Sn²⁺Conversion) and the molar ratio of thioureas per liter is thioureas / Sn²⁺=4 . 0-8 . 4And the content of thioureas is2 . 2-3 . 5It must be mol / L.
  In order to prevent erosion of fine patterns such as film carriers, the content of thioureas as complexing agents is adjusted to an appropriate range, and the thioureas and Sn²⁺It is necessary to control the content molar ratio of to a predetermined range. That is, thioureas / Sn²⁺When the molar ratio of Sn becomes too large, Sn²⁺The balance of interaction between thioureas and thioureas may be lost, and the erosion of copper patterns may increase.²⁺The chelating effect on the surface may increase, which may hinder the formation of an appropriate tin film. Thioureas / Sn²⁺Even if the molar ratio is appropriate, if the content of thiourea becomes too small, Sn²⁺The balance of the interaction between thioureas and thioureas is lost, and there is a risk of erosion of fine patterns.²⁺The chelating effect on water may be reduced and the bath may become unstable. Further, from the viewpoint of ensuring solubility in the bath, it is necessary to suppress the content of thioureas to a predetermined amount or less.
[0022]
As described above, the electroless tin plating bath of the present invention has a basic composition of a soluble stannous salt, an organic sulfonic acid as a bath base, and thioureas as a complexing agent.
Accordingly, the organic sulfonic acid as the bath base will be described based on the conditions (a) to (b). First, alkane sulfonic acid is an essential component as the organic sulfonic acid.
The alkanesulfonic acid can be used alone or in combination and is preferably contained in the bath as a free acid. However, it can be contained as a stannous salt of alkanesulfonic acid, and it goes without saying that both may be contained. Yes.
As described above, in the bath, in addition to alkane sulfonic acid, other aliphatic sulfonic acids such as alkanol sulfonic acid and sulfosuccinic acid, benzene sulfonic acid, naphthalene sulfonic acid, phenol sulfonic acid, naphthol sulfonic acid, Aromatic sulfonic acids such as cresol sulfonic acid may coexist, aliphatic carboxylic acids such as lactic acid, citric acid, gluconic acid and malic acid, or sulfuric acid, hydrochloric acid, phosphoric acid, silicofluoric acid, sulfamine An inorganic acid such as an acid may coexist.
[0023]
The alkanesulfonic acid has the chemical formula C_nH_{2n + 1}SO_ThreeH (for example, n = 1 to 11), specifically, methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic acid, 2- Examples include butanesulfonic acid and pentanesulfonic acid.
As alkanesulfonic acid, as shown in the present invention 5, C₁~ C_FourAlkanesulfonic acid is preferable, and specifically, methanesulfonic acid and ethanesulfonic acid are more preferable.
[0024]
The soluble stannous salt will be described based on the above conditions (a) to (b). Stannous borofluoride, stannous sulfate, stannous oxide, stannous chloride, tin pyrophosphate, tin sulfamate Inorganic soluble salts such as stannates, stannous salts of organic sulfonic acids such as aliphatic sulfonic acids and aromatic sulfonic acids, organic soluble salts such as stannous salts of aliphatic carboxylic acids, etc. Is mentioned.
As the soluble stannous salt, a stannous salt of alkanesulfonic acid is preferable according to the above condition (a).
[0025]
The thioureas coordinate with the base metals copper and copper alloy to form complex ions, shift the electrode potential of copper in the base direction, promote chemical substitution reaction with tin, and tin ions It is contained for the purpose of stabilizing.
These thioureas include thiourea, or 1,3-dimethylthiourea, trimethylthiourea, diethylthiourea (for example, 1,3-diethyl-2-thiourea), N, N′-diisopropylthiourea, Examples include thiourea derivatives such as allylthiourea, acetylthiourea, ethylenethiourea, 1,3-diphenylthiourea, thiourea dioxide, and thiosemicarbazide.
Examples of the compound having the complexing action similar to the thioureas include ethylenediaminetetraacetic acid (EDTA), ethylenediaminetetraacetic acid disodium salt (EDTA · 2Na), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid ( DTPA), triethylenetetramine hexaacetic acid (TTHA), ethylenediaminetetrapropionic acid, ethylenediaminetetramethylenephosphoric acid, diethylenetriaminepentamethylenephosphoric acid, nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), Aminotrimethylene phosphate, aminotrimethylene phosphate pentasodium salt, benzylamine, 2-naphthylamine, isobutylamine, isoamylamine, methylenediamine, ethylenediamine, tetramethylenediamine, pen Tamethylenediamine, hexamethylenediamine, diethylenetriamine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, cinnamylamine, p-methoxycinnamylamine and the like are also effective.
[0026]
  Soluble stannous salt (Sn²⁺(Conversion) and the molar ratio of thioureas per liter are thioureas / Sn²⁺=4 . 0-8 . 4It is necessary to be Sn²⁺Guarantees chelating action of thioureas againstFrom the viewpoint, 4 . 5-7 . 0 is preferred.
  The content of thioureas in the bath is2 . 2-3 . It is necessary to be 5 mol / L.The content of thioureas isProper amountIf it is more, the solubility in the bath at room temperature will be reduced, so that it will be necessary to heat the bath to ensure solubility.
  As long as the molar ratio with the thioureas is satisfied, Sn in the bath is used.²⁺The content of is not particularly limited, but as shown in the present invention 3, about 40 to 70 g / L is appropriate, preferably 45 to 60 g / L, and more preferably 50 to 60 g / L.
[0027]
The second invention (namely, Invention 2) is an electroless tin plating bath containing an anion portion of borofluoric acid instead of alkanesulfonic acid in the bath.
The anion portion of borohydrofluoric acid means containing borohydrofluoric acid as a free acid and / or stannous salt of borohydrofluoric acid. Accordingly, stannous borofluoride is also suitable as the stannous salt, as is the stannous salt of alkanesulfonic acid.
In the present invention 2, thioureas and Sn are used under the same conditions as in the present invention 1.²⁺It goes without saying that the content molar ratio of and the content of thioureas are adjusted to a predetermined range. In order to effectively prevent the erosion of a fine pattern such as a film carrier, Sn is present in the presence of an anion portion of borohydrofluoric acid.²⁺This is because it is necessary to express an appropriate interaction by the combination of thiourea and thiourea.
Of course, in the electroless tin plating bath, the alkanesulfonic acid (anion portion) may be used in combination with the borohydrofluoric acid (anion portion).
[0028]
  On the other hand, in addition to the above basic components, the electroless tin plating bath may contain various additives such as known antioxidants, surfactants, brighteners, semi-brighteners, pH adjusters, preservatives as necessary. Needless to say.
  The antioxidant is Sn in the bath²⁺Hypophosphorous acid, alkane metal salts such as sodium and potassium of hypophosphite, and alkaline earth metal salts such as calcium and magnesium are preferable.
  In the plating bath, Sn²⁺And complexing to base metal and Sn²⁺In addition to thioureas that have a stabilizing effect on²⁺When hypophosphorous acid having an excellent antioxidative action coexists, it is expected that the contribution to the prevention of erosion of fine patterns such as film carriers is further increased by these interactions.
  The content of hypophosphorous acid and its salt isInvention 7As shown in the figure, about 0.1 to 1.0 mol / L is appropriate, and 0.1 to 0.7 mol / L is preferable.
  Further, ascorbic acid or a salt thereof, hydroquinone, catechol, resorcin, phloroglucin, cresol sulfonic acid or a salt thereof, phenol sulfonic acid or a salt thereof, catechol sulfonic acid or a salt thereof, hydroquinone sulfonic acid or a salt thereof, hydrazine, etc. It is effective as
[0029]
Examples of the surfactant include various nonionic, anionic, amphoteric, and cationic surfactants, which contribute to improving the appearance, denseness, smoothness, and adhesion of the plating film.
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 mono-trialkylamine salts, dimethyldialkylammonium salts, and trimethylalkylammonium 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, sulfobetaine, imidazoline betaine, sulfobetaine, and aminocarboxylic acid.
[0030]
Examples of the brightener or semi-brightener include benzaldehyde, o-chlorobenzaldehyde, 2,4,6-trichlorobenzaldehyde, m-chlorobenzaldehyde, p-nitrobenzaldehyde, p-hydroxybenzaldehyde, furfural, 1-naphthaldehyde, 2-naphthaldehyde, 2-hydroxy-1-naphthaldehyde, 3-acenaphthaldehyde, benzylideneacetone, pyridideneacetone, furfuryldenacetone, cinnamaldehyde, anisaldehyde, salicylaldehyde, crotonaldehyde, acrolein, glutaraldehyde, para Various aldehydes such as aldehyde and vanillin, triazine, imidazole, indole, quinoline, 2-vinylpyridine, aniline, phenanthroline, neocuproin, pi Phosphoric acid, thioureas, N- (3-hydroxybutylidene) -p-sulfanilic acid, N-butylidenesulfanilic acid, N-cinnamoylidenesulfanilic acid, 2,4-diamino-6- (2'-methyl) Imidazolyl (1 ')) ethyl-1,3,5-triazine, 2,4-diamino-6- (2'-ethyl-4-methylimidazolyl (1')) ethyl-1,3,5-triazine, 2 , 4-diamino-6- (2′-undecylimidazolyl (1 ′)) ethyl-1,3,5-triazine, phenyl salicylate, or benzothiazole, 2-methylbenzothiazole, 2-aminobenzothiazole, 2-Amino-6-methoxybenzothiazole, 2-methyl-5-chlorobenzothiazole, 2-hydroxybenzothiazole, 2-amino-6-methylbenzothiazole, 2-chlorobenzo Azole, 2,5-dimethyl benzothiazole, benzothiazole such as 5-hydroxy-2-methyl-benzothiazole.
[0031]
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, monocarboxylic acids such as formic acid, acetic acid and propionic acid, and boron. Dicarboxylic acids such as acids, phosphoric acids, oxalic acid and succinic acid, and oxycarboxylic acids such as lactic acid and tartaric acid are effective.
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.
[0032]
Although the conditions for electroless tin plating are arbitrary, the bath temperature is preferably 45 to 90 ° C, and more preferably 50 to 70 ° C from the viewpoint of increasing the deposition rate.
[0033]
  Invention 9Is a copper erosion prevention method in which an object to be plated is immersed in the electroless tin plating bath to form a tin plating film on the object to be plated.
  Any material can be applied as long as copper or copper alloy is used for the substrate, and there is no particular limitation.Invention 10As shown in FIG. 4, a film carrier, a printed circuit board (PCB), a flexible printed board (FPC), or the like in which a fine pattern made of copper or a copper alloy is coated with a protective solder resist is preferable.
[0034]
【The invention's effect】
When a conventional electroless tin plating bath is applied to a film carrier, PCB, FPC, etc., in which a fine pattern made of copper or a copper alloy is coated with a solder resist, the adhesion of the solder resist is reduced, and the solder resist is exposed from the end of the solder resist. There was a problem that the plating solution entered the lower surface of the solder resist along the wiring pattern, and the wiring pattern suffered erosion damage due to elution of copper.
In contrast, in the present invention, a soluble stannous salt (Sn) is used in an electroless tin plating bath in which an anion portion of alkanesulfonic acid or borohydrofluoric acid is present.²⁺(Conversion) and the mixing molar ratio of thioureas and the content of thioureas are adjusted to the specified range, so even if this electroless tin bath is applied to a film carrier, etc., it ensures good adhesion of the solder resist. It is possible to effectively prevent erosion of fine patterns such as inner leads.
[0035]
  Incidentally, in the organic sulfonic acid bath of electroless tin described in Example 12 (see paragraph 56) of JP-A-11-256350 described above, thioureas / Sn²⁺The molar ratio of the thioureas is 2.10 mol / L, but it is a phenol sulfonic acid bath, and the inclusion of the anion portion of alkane sulfonic acid is essential. Out of condition.
  In the electroless tin methanesulfonic acid bath described in Example 9 (see paragraph 63) of JP-A-11-343578 described above, of course, it contains the anion portion of methanesulfonic acid and contains thioureas. The amount is also 2.14 mol / L, but thioureas / Sn²⁺The molar ratio is 8.46, which is out of the same molar ratio condition (8.4 or less) of the present invention.
  In addition, in the organic sulfonic acid bath of electroless tin described in Example 8 (see paragraph 56) of JP-A-10-36973 described in the introduction, the anion portion of methanesulfonic acid is included, and thioureas / Sn²⁺The thioureas content is 1.97 mol / L, and the content ratio of the present invention (2 . 2-3 . 5Mol / L).
[0036]
【Example】
Hereinafter, examples of the electroless tin plating bath of the present invention and copper erosion prevention test examples using the electroless plating bath 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.
[0037]
  Examples below1-12Of which, Example8-9Is an example containing the anionic portion of borohydrofluoric acid,Example 2Is an example containing an anion part of alkane sulfonic acid and an anion part of borohydrofluoric acid, and other examples are examples containing an anion part of alkane sulfonic acid.Example 3 and Examples 6-7Is an example in which alkanesulfonic acid and phenolsulfonic acid are used in combination with the base acid,Example 4Is a simple example using alkanol sulfonic acid as the base acid,Example 1WhenExample 5Is a simple example of using phenolsulfonic acid as the base acid,Example 10Is an example in which an aliphatic carboxylic acid is simply used as the base acid.Example 11Is an example in which phenolsulfonic acid and phosphoric acid are used in combination with the base acid,Example 12Is an example in which phenol sulfonic acid and aliphatic carboxylic acid are used in combination with the base acid.Example 4Has a thiourea contentUpper limitIt is an example.
[0038]
On the other hand, among Comparative Examples 1 to 4, Comparative Example 1 is a blank example not containing an anion portion of alkanesulfonic acid, and Comparative Example 2 is In accordance with Example 9 of JP-A-11-343578 described above, thioureas / Sn²⁺Comparative Example 3 is an example in which the content of thioureas is less than the lower limit in accordance with Example 8 of JP-A-10-36973 described above. In addition, when the content of thioureas exceeded the upper limit of the present invention, solubility at normal temperature was reduced, and the bath was not easy to construct.
[0040]
  Example 1
  An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.40 mol / L
P-phenolsulfonic acid: 0.80 mol / L
・ Thiourea: 2.60 mol / L
Hypophosphorous acid: 0.50 mol / L
  Thioureas / Sn²⁺The (molar ratio) is 2.60 / 0.40 = 6.50.
[0041]
  Example 2
  An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.29 mol / L
・ Borohydrofluoric acid: 2.50 mol / L
Dimethylthiourea: 2.20 mol / L
・ Polyoxyethylene octyl phenyl ether (EO10): 7.0 g / L
  Thioureas / Sn²⁺The (molar ratio) is 2.20 / 0.29 = 7.58.
[0042]
  Example 3
  An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.23 mol / L
・ Stannous p-phenolsulfonate (Sn²⁺As): 0.23 mol / L
・ Methanesulfonic acid: 0.24 mol / L
P-phenolsulfonic acid: 0.24 mol / L
・ Thiourea: 2.30 mol / L
Hydroquinone: 0.10 mol / L
-Octylamine polyethoxylate (EO10): 10 g / L
  The above thioureas / Sn²⁺The (molar ratio) is 2.30 / (0.23 + 0.23) = 5.00.
[0044]
  Example 4
  An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.50 mol / L
2-hydroxyethanesulfonic acid: 0.20 mol / L
・ Thiourea: 3.50 mol / L
Hypophosphorous acid: 0.60 mol / L
・ Polyoxyethylene
            -Styrenated phenyl ether (EO5): 5 g / L
  Thioureas / Sn²⁺The (molar ratio) is 3.50 / 0.50 = 7.00.
[0045]
  Example 5
  An electroless tin plating bath was constructed with the following composition.
・ Stannous ethanesulfonate (Sn²⁺As): 0.40 mol / L
P-phenolsulfonic acid: 2.50 mol / L
・ Thiourea: 2.70 mol / L
Hypophosphorous acid: 0.65 mol / L
・ Polyoxyethylene
          -Dodecyl phenyl ether (EO12): 10 g / L
  Thioureas / Sn²⁺The (molar ratio) is 2.70 / 0.40 = 6.75.
[0046]
  Example 6
  An electroless tin plating bath was constructed with the following composition.
・ Stannous ethanesulfonate (Sn²⁺As): 0.20 mol / L
・ Stannous p-phenolsulfonate (Sn²⁺As): 0.20 mol / L
Ethanesulfonic acid: 1.60 mol / L
P-phenol sulfonic acid: 1.60 mol / L
・ Thiourea: 2.40 mol / L
Hypophosphorous acid: 0.60 mol / L
・ Polyoxyethylene nonylphenyl ether (EO10): 15g / L
  The above thioureas / Sn²⁺The (molar ratio) is 2.40 / (0.20 + 0.20) = 6.00.
[0047]
  Example 7
  An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.25 mol / L
・ Stannous p-phenolsulfonate (Sn²⁺As): 0.25 mol / L
・ Methanesulfonic acid: 1.60 mol / L
P-phenol sulfonic acid: 1.60 mol / L
・ Thiourea: 2.60 mol / L
Hypophosphorous acid: 0.60 mol / L
・ Polyoxyethylene nonylphenyl ether (EO10): 10g / L
  Thioureas / Sn²⁺The (molar ratio) is 2.60 / (0.25 + 0.25) = 5.20.
[0048]
  Example 8
  An electroless tin plating bath was constructed with the following composition.
・ Stannous borofluoride (Sn²⁺As): 0.35 mol / L
・ Borohydrofluoric acid: 1.00 mol / L
P-phenolsulfonic acid: 1.50 mol / L
・ Thiourea: 2.60 mol / L
Hypophosphorous acid: 0.60 mol / L
・ Polyoxyethylene nonylphenyl ether (EO10): 10g / L
  Thioureas / Sn²⁺The (molar ratio) is 2.60 / 0.35 = 7.42.
[0049]
  Example 9
  An electroless tin plating bath was constructed with the following composition.
・ Stannous borofluoride (Sn²⁺As): 0.50 mol / L
・ Borohydrofluoric acid: 0.50 mol / L
P-phenolsulfonic acid: 2.50 mol / L
・ Thiourea: 2.30 mol / L
Hypophosphorous acid: 0.50 mol / L
・ Polyoxyethylene nonylphenyl ether (EO10): 10g / L
  Thioureas / Sn²⁺The (molar ratio) is 2.30 / 0.50 = 4.60.
[0050]
  Example 10
  An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.40 mol / L
Citric acid: 2.00 mol / L
・ Thiourea: 2.60 mol / L
Hypophosphorous acid: 0.50 mol / L
・ Polyoxyethylene
              -Octylphenyl ether (EO15): 5.0 g / L
  Thioureas / Sn²⁺The (molar ratio) is 2.60 / 0.40 = 6.50.
[0051]
  Example 11
  An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.40 mol / L
P-phenolsulfonic acid: 1.80 mol / L
Phosphoric acid: 0.50 mol / L
・ Thiourea: 2.60 mol / L
Hypophosphorous acid: 0.50 mol / L
・ Polyoxyethylene
              -Octylphenyl ether (EO12): 8.0 g / L
  Thioureas / Sn²⁺The (molar ratio) is 2.60 / 0.40 = 6.50.
[0052]
  Example 12
  An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.40 mol / L
P-phenolsulfonic acid: 1.80 mol / L
Citric acid: 0.50 mol / L
・ Thiourea: 2.60 mol / L
Hypophosphorous acid: 0.50 mol / L
・ Polyoxyethylene
              -Octylphenyl ether (EO8): 10.0 g / L
  Thioureas / Sn²⁺The (molar ratio) is 2.60 / 0.40 = 6.50.
[0053]
<< Comparative Example 1 >>
An electroless tin plating bath was constructed with the following composition.
・ Stannous p-phenolsulfonate (Sn²⁺As): 0.46 mol / L
・ P-phenolsulfonic acid: 1.00 mol / L
・ Thiourea: 2.09 mol / L
-Sodium hypophosphite: 0.40 mol / L
.Alpha.-naphthol polyethoxylate (EO10): 5.0 g / L
The content of thioureas is 2.09 mol / L, thioureas / Sn²⁺(Molar ratio) is 2.09 / 0.46 = 4.56, but the anion portion of alkanesulfonic acid is not present.
[0054]
<< Comparative Example 2 >>
An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.252 mol / L
・ Methanesulfonic acid: 1.40 mol / L
・ Thiourea: 2.14 mol / L
-Sodium hypophosphite: 0.40 mol / L
.Alpha.-naphthol polyethoxylate (EO10): 5.0 g / L
The content of thioureas is 2.14 mol / L, but thioureas / Sn²⁺The (molar ratio) is 2.14 / 0.252 = 8.47.
[0055]
<< Comparative Example 3 >>
An electroless tin plating bath was constructed with the following composition.
・ Stannous methanesulfonate (Sn²⁺As): 0.25 mol / L
-Cresolsulfonic acid: 1.40 mol / L
・ Thiourea: 1.97 mol / L
-Sodium hypophosphite: 0.40 mol / L
・ Α-Naphthol polyethoxylate (EO15): 5.0 g / L
Thioureas / Sn²⁺(Molar ratio) is 1.97 / 0.25 = 7.8, but the content of thioureas is 1.97 mol / L.
[0056]
  << Evaluation test example of copper erosion prevention degree associated with tin plating film formation >>
  Therefore, a TAB film carrier patterned with SLP (a kind of electrolytic copper foil) is used as an object to be plated.Examples 1-12And each electroless tin plating bath of Comparative Examples 1 to 3 was subjected to electroless plating under conditions of a bath temperature of 65 ° C. and a plating time of 5 minutes to form a tin plating film on the inner lead.
  Then, after sticking an adhesive tape around the boundary part between the tin plating film and the solder resist in the film carrier, and quickly pulling up the tape in the vertical direction, visually observing the peeling state of the end of the solder resist, By judging the degree of exposure of the inner lead depending on whether or not the solder resist was peeled off, the superiority or inferiority of the inner lead in preventing copper erosion was evaluated.
  The evaluation criteria are as follows.
  ○: There was no peeling of the solder resist, and no exposure of the inner leads was observed.
  X: The solder resist was peeled off and the inner lead was exposed.
[0057]
  FIG. 1 shows the test results.
  Examples 1-12In both cases, the solder resist was not peeled off and the inner lead was not exposed. However, in Comparative Examples 1 to 3, the solder resist was peeled off and the inner lead was exposed.
  That is,Examples 1-12As compared with Comparative Example 1, in the organic sulfonic acid bath of electroless tin, the anion portion of alkane sulfonic acid is present in the bath.Examples 1-7, 10-12In Comparative Example 1 where only the anion portion of the aromatic sulfonic acid is present, it can be seen that the exposure of the inner lead cannot be prevented, and the copper corrosion of the inner lead can be prevented. The significance of specifying an organic sulfonic acid as an alkane sulfonic acid became clear.
  In the plating bath,Example 3, Example 4, or Example 10As shown in Fig. 5, it was found that the effectiveness does not change even if the anion portion of the alkane sulfonic acid and the anion portion of the aromatic sulfonic acid, alkanol sulfonic acid, or aliphatic carboxylic acid coexist.
  Furthermore, instead of alkane sulfonic acid, even if the anion portion of borohydrofluoric acid is present in the bath, it is possible to prevent copper corrosion of the inner lead as well.Examples 8-9It is clear fromExample 2Of course, it is effective even if both anion portions of alkanesulfonic acid and borohydrofluoric acid coexist.
[0058]
  ThenExamples 1-12Compared to Comparative Example 2, the thioureas / Sn²⁺The molar ratio of4 . 0-8 . 4ofExamples 1-12In Comparative Example 2, which exceeds this upper limit, the exposure of the inner leads cannot be prevented. Therefore, in the point of preventing the copper corrosion of the inner leads, the electroless tin in the organic sulfonic acid plating bath In this case, it became clear that it is important to specify the content molar ratio below a predetermined value.
  further,Examples 1-12Compared to Comparative Example 3, the thioureas2 . 2-3 . 5Contains in the range of mol / LExamples 1-12Then, you can prevent the peeling of the solder resist,2 . 2In Comparative Example 3 with less than mol / L, the exposure of the inner lead cannot be prevented, so that the content of thiourea is specified within a predetermined range in the electroless tin organic sulfonic acid plating bath in terms of preventing copper corrosion of the inner lead. The importance of making it clear became clear.
[0059]
All of the above points prevent the peeling of the solder resist when tin plating is performed on a TAB film carrier with a copper fine pattern covered with a solder resist using an electroless tin organic sulfonic acid plating bath. In order to prevent copper erosion of fine patterns, it is possible to specify an alkane sulfonic acid as an organic sulfonic acid that supplies anions, and thioureas / Sn.²⁺It was confirmed that it is necessary to specify each of the molar ratio of thiourea and the content of thiourea. In addition, it was confirmed that even if an anion portion of borohydrofluoric acid was present instead of alkanesulfonic acid, the copper erosion of the fine pattern could be similarly prevented as long as other specific conditions were satisfied.
[Brief description of the drawings]
[Figure 1]Examples 1-12It is a graph which shows the result of the copper corrosion prevention evaluation test of an inner lead at the time of forming tin plating in the film carrier of TAB using each electroless tin plating bath of Comparative Examples 1-3.

Claims (10)

In an electroless tin plating bath containing a soluble stannous salt, an organic sulfonic acid, and a thiourea,
Molar ratio per unit liter of soluble stannous salt (Sn ²⁺ equivalent) and thioureas are thioureas / Sn ²⁺ = 4. 0~8. 4;
The content of thiourea is from 2.2 to 3.5 mol / L,
An electroless tin plating bath for preventing copper erosion, comprising an anion portion of alkanesulfonic acid as the organic sulfonic acid. In an electroless tin plating bath containing a soluble stannous salt, an inorganic acid and thioureas,
Molar ratio per unit liter of soluble stannous salt (Sn ²⁺ equivalent) and thioureas are thioureas / Sn ²⁺ = 4. 0~8. 4;
The content of thiourea is from 2.2 to 3.5 mol / L,
An electroless tin plating bath for preventing copper erosion, comprising an anionic portion of borohydrofluoric acid as the inorganic acid. 3. The electroless tin plating bath for preventing copper erosion according to claim 1, wherein the content of the soluble stannous salt (in terms of Sn ²⁺ ) is 40 to 70 g / L. _{4. The} electroless tin plating bath for preventing copper erosion according to claim _{1, wherein the} alkane sulfonic acid is a C1-C4 alkane sulfonic acid. The electroless tin plating bath for preventing copper erosion according to any one of claims 1 to 4 , wherein the thiourea is thiourea. Electroless tin plating bath for preventing copper corrosion according to any one of claims 1 to 5, characterized in that it contains an antioxidant such as hypophosphorous acid and salts thereof. The electroless tin plating bath for preventing copper erosion according to claim 6 , wherein the content of hypophosphorous acid and its salt is 0.1 to 1.0 mol / L. Furthermore, various additives, such as surfactant, a smoothing agent, a brightener, a semi-gloss agent, and a pH adjuster, are contained, The copper erosion prevention agent of any one of Claims 1-7 characterized by the above-mentioned. Electroless tin plating bath. A copper erosion prevention characterized by immersing a copper object to be plated in the electroless tin plating bath according to any one of claims 1 to 8 to form a tin plating film on the object to be plated without copper erosion. Method. The object to be plated according to claim 9 is a film carrier, a printed circuit board, a flexible printed board or the like in a form in which a part of a fine pattern made of copper or a copper alloy is coated with a solder resist. Copper erosion prevention method.

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