JPH1036973A - Electroless tin coating bath and film carrier of tab formed with tin coating film by using this coating bath - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroless tin coating bath which is high in the deposition rate of metal and good in workability and is simultaneously good in the bondability of the resulted coating film. SOLUTION: A trace amt. of a soluble salt of the metal having standard oxidation reduction potential within a range of -0.8 to +0.8 volts is compounded in a range where the tin alloy coating film is substantially not formed with the coating bath consisting of (A) a soluble salt of tin (I), (B) an acid, such as org. sulfonic acid and (C) a complexing agent. Since the specific metal soluble salt is compounded by limiting the amt. thereof to the prescribed trace amt. range, the rapidly increased film effect of the tin coating film and the good bondability are made effectively compatible. The execution of the electroless tin coating at a low temp. is, therefore, possible and the productivity is improved in addition, the effective dealing with a TAB method, etc., is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless tin plating bath for applying a tin plating film on copper or a copper alloy, and a TAB film carrier provided with a tin plating film using the plating bath. Since the deposition rate of the coating is high and the bonding property of the coating is good, the present invention provides a coating which can sufficiently cope with a high-density mounting product such as a TAB method.

[0002]

BACKGROUND OF THE INVENTION In general, tin or tin-lead alloy plating on copper and copper alloys has good solderability and good bonding properties, and is used for packages for electronic components and semiconductor devices.
(Particularly, the TAB method). However, while the above tin-lead alloy plating is excellent in terms of solderability, it gives a step to tin plating in terms of bonding, and recently there is a concern that lead may affect health and the environment.
The value of tin plating has been renewed because there is a movement to regulate tin-lead alloy plating containing lead.

[0003]

2. Description of the Related Art As a prior art of an electroless tin plating bath, Japanese Patent Application Laid-Open No. 63-230883 discloses a tin salt,
There is disclosed a plating bath having a basic composition of an organic sulfonic acid and thiourea, to which various surfactants, brighteners, and the like are added. According to the above publication, when the tin plating bath is used, the attack on the base material of copper or copper alloy is mild by using an organic sulfonic acid, and there is no pinhole due to the addition of a surfactant or a brightening agent. It is described that a tin plated film having a smooth and excellent adhesion can be obtained.

[0004]

Recently, the miniaturization, complexity, and increase in the number of pins of electronic parts have been rapidly progressing, and the performance required for electroless tin plating has been increasing. For example, TA
For electronic components such as the B method, or fine pitch printed wiring boards that support SMT (especially in the former), improvements in workability and cost reduction are strictly required every year,
In addition to performing electroless plating at a lower temperature in a shorter time, the resulting film is required to have good bonding properties and good denseness and adhesion.

However, in the electroless plating bath of the prior art, first, the deposition rate of tin is slow, and the bath temperature must be set to a high temperature of 80 ° C. from the viewpoint of workability. The bath life was short, which was economically disadvantageous. In addition, the resulting plating film does not have sufficient bonding strength and the formation of fillets is not uniform, and the bonding property is not at a level that can withstand practical use. For this reason,
It cannot sufficiently cope with high-density mounting products such as the above-mentioned TAB method, which adversely affects the reliability and production yield of products using them, and has many restrictions in preprocessing.

The present invention provides an electroless tin plating which has a high metal deposition rate and good workability, and also has excellent bonding properties of the obtained plating film, and which can mainly cope with a TAB method or the like. The technical task is to develop a bath.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the deposition behavior of an electroless tin plating bath to which various metal ions are added in small amounts. When a metal having a potential within a specific range, for example, a metal ion such as bismuth, indium, zinc, silver, lead, or copper is present in a bath within a range that does not substantially form an alloy plating film with tin. Has a remarkable phenomenon that the deposition rate of tin is increased,
It was also found that the presence of specific metal ions beyond a certain small range (even within the range where the tin alloy plating film is not formed) tends to lower the bondability of the resulting tin plating film. Then, it was found that, when the compounding ratio of the specific metal ions is suppressed within a predetermined minute range which does not exceed the upper limit, the ability to quickly increase the tin plating film and good bonding properties can be effectively achieved, and completed the present invention.

That is, the present invention comprises (A) a soluble salt of stannous, (B) an organic acid such as an alkanesulfonic acid, an alkanolsulfonic acid, an aromatic sulfonic acid, or an aliphatic carboxylic acid; In an electroless tin plating bath comprising at least one acid selected from inorganic acids such as sulfuric acid and borofluoric acid, and (C) a complexing agent, the standard oxidation-reduction potential is −
An electroless tin plating bath characterized in that a small amount of a soluble salt of a metal in the range of 0.8 to +0.8 volts is blended within a range that does not substantially form a tin alloy plating film.

[0009] The present invention 2 is an electroless tin plating bath characterized by further containing a surfactant in addition to the electroless plating bath of the above-mentioned present invention 1.

[0010] The present invention 3 is an electroless tin plating bath characterized by further comprising a reducing agent in addition to the electroless plating bath of the present invention 1 or 2.

A fourth aspect of the present invention is a TAB film carrier in which a TAB film carrier is immersed in the electroless tin plating bath of any of the first to third aspects to form an electroless tin plating film on a lead of the film carrier. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention 1 comprises a divalent tin salt,
It is characterized in that a small amount of a soluble salt of a metal having a standard oxidation-reduction potential within a predetermined range is mixed in a specific ratio that does not substantially form a tin alloy plating film in a plating bath containing an acid and a complexing agent as a basic composition. In the present invention 2, a surfactant is added to the bath,
The present invention 3 is obtained by additionally mixing a reducing agent. However, the range in which the tin alloy plating film is not substantially formed means that even when the plating film formed using the electroless tin plating bath of the present invention is analyzed with a fluorescent X-ray film thickness meter, metals other than tin are not detected. Means range.

The metals which are mixed in a small amount and ionized in the bath, when expressed by a standard oxidation-reduction potential, which is an electromotive force of a half cell when these are used for an electrode, are -0.8 to +0.8.
Metal within the range of 8 volts, specifically Z
n, Cr, Fe, Cd, Co, Ni, Pb, Sb, B
i, In, Cu, Hg, Ag, etc., preferably,
Bi, In, Zn, Pb, Sb, Ag, and Cu. The above metals are mixed in a plating bath in the form of a soluble salt, and various metal ions (Bi ³⁺ , In ³⁺ , Zn ²⁺ , Pb ²⁺ , Sb ³⁺ ,
Ag ⁺ , Cu ⁺ , and Cu ²⁺ ) are produced. Specific examples of the soluble metal salt are as follows.

(1) Oxides: Bi ₂ O ₃ , In ₂ O ₃ , ZnO, P
bO, Ag ₂ O, Cu ₂ O, CuO (2) halide: BiCl ₃ , InCl ₃ , PbCl ₂ ,
BiI ₃ , InI ₃ , ZnCl ₂ , ZnBr ₂ , ZnI ₂ ,
PbI ₂ , BiBr ₃ , InBr ₃ , PbBr ₂ , AgC
1, AgBr, CuCl, CuBr, CuI (3) Salts with inorganic and organic acids, and others: bismuth nitrate,
Bismuth sulfate, lead acetate, indium sulfate, zinc sulfate, indium methanesulfonate, indium ethanesulfonate, lead methanesulfonate, lead ethanesulfonate, lead 2-propanesulfonate, lead phenolsulfonate, bismuth methanesulfonate, 2 Bismuth propanol sulfonate, bismuth p-phenol sulfonate, zinc methane sulfonate, zinc p-phenol sulfonate, antimony tartrate, silver nitrate, silver methane sulfonate, silver citrate,
cupric p-phenolsulfonate, Cu ₃ P, CuSC
N, CuBr (S (CH ₃ ) ₂ )

The soluble salt of the above-mentioned trace amount of metal can be used alone or in combination. The amount of the soluble salt of the metal is generally 5 g / l or less (actually 0.0001 to 5 g / l), preferably 3 g / l.
g / l or less (actually 0.0001 to 3 g / l), more preferably 0.001 to 1 g / l. If the bath composition of the metal-soluble salt is 5 g / l or less, as described above, the composition of the resulting plating film is in a range where a tin alloy plating film is not substantially formed, and if it exceeds 5 g / l. Since the plating film has a tin alloy composition, there is a problem that the bonding property tends to decrease. In addition, although the soluble salt of the trace compounding metal is basically added to the plating bath as an independent component, other components of the plating bath, namely, acid,
When a complexing agent, a reducing agent, or various additives to be described later are prepared from the metal compound, it is not excluded that they are also used together.

The above-mentioned acid is preferably an organic sulfonic acid such as alkanesulfonic acid, alkanolsulfonic acid, aromatic sulfonic acid or the like, or an organic acid such as aliphatic carboxylic acid, whose reaction in the plating bath is relatively mild. However, inorganic acids such as hydrochloric acid, borofluoric acid, sulfuric acid, hydrosilicofluoric acid and perchloric acid can also be selected. The above-mentioned acids are used alone or in combination, and the amount of the acid is generally 0.1 to 200 g / l. The alkanesulfonic acid has a chemical formula of C _n H
_{2n + 1} SO ₃ H (for example, n = 1 to 5, preferably 1 to 3) can be used, and specifically, methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-
In addition to propanesulfonic acid, 1-butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid and the like, hexanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid and the like can be mentioned.

[0017] Examples of the alkanol sulfonic acid, the formula _{C m H 2m + 1 -CH (} OH) -C p H 2p + 1 -SO 3 H ( for example,
m = 0 to 2, p = 1 to 3) can be used, and specifically, 2-hydroxyethane-1-sulfonic acid, 2-
Hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1
-In addition to sulfonic acid, 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.

The aromatic sulfonic acid is basically benzene sulfonic acid or naphthalene sulfonic acid (for example, 2-naphthalene sulfonic acid), and a part of the hydrogen atom is converted to a hydroxyl group, a halogen group, an alkyl group, Those substituted with a group, a mercapto group, an amino group, a sulfonic acid group or the like can also be used. As the substituted sulfonic acid, for example, toluenesulfonic acid, xylenesulfonic acid, p-
Phenolsulfonic acid, cresolsulfonic acid, sulfosalicylic acid, nitrobenzenesulfonic acid, sulfobenzoic acid, sulfophthalic acid, diphenylamine-4-sulfonic acid, and the like.

As the aliphatic carboxylic acid, generally,
A carboxylic acid having 1 to 6 carbon atoms can be used. In particular,
Acetic acid, propionic acid, butyric acid, citric acid, tartaric acid, gluconic acid, sulfosuccinic acid and the like can be mentioned.

As the stannous salt, any soluble salts can be used, preferably salts with the above-mentioned acids,
Further, a complex salt (water-soluble) obtained by dissolving a metal or a metal oxide in the above-mentioned acid can also be used. The reduced amount of the metal salt is generally 0.1 to 200 g / l.

The receiving base metal plated with tin is:
For example, copper, copper alloy, iron, nickel, iron-42% nickel alloy, which forms a circuit pattern on the TAB method,
Zinc, aluminum, etc.

The complexing agent coordinates with the base metal such as copper or copper alloy to form a complex ion.
It is preferable to use the chelating agents (1) to (3) alone or in combination. (1) Thiourea and derivatives thereof As a derivative of thiourea, 1,3-dimethylthiourea, trimethylthiourea, diethylthiourea (for example,
1,3-diethyl-2-thiourea), N, N'-diisopropylthiourea, allylthiourea, acetylthiourea,
Ethylenethiourea, 1,3-diphenylthiourea, thiourea dioxide, thiosemicarbazide and the like can be mentioned. (2) Ethylenediaminetetraacetic acid (EDTA), ethylenediaminetetraacetic acid disodium salt (EDTA2Na), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), ethylenediaminetetrapropion Acid, ethylenediaminetetramethylenephosphoric acid, diethylenetriaminepentamethylenephosphoric acid and the like. (3) nitrilotriacetic acid (NTA), iminodiacetic acid (IDA),
Iminodipropionic acid (IDP), aminotrimethylene phosphate, aminotrimethylene phosphate pentasodium salt, benzylamine, 2-naphthylamine, isobutylamine,
Isoamylamine, methylenediamine, ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, diethylenetriamine,
Tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, cinnamylamine, p
-Methoxycinnamylamine and the like. The amount of the complexing agent is generally from 5 to 300 g / l.

The above-mentioned reducing agent is added for reducing the above-mentioned metal salt and for adjusting the deposition rate thereof. A hypophosphorous acid compound, an amine borane, a borohydride compound, a hydrazine derivative or the like is used alone or in combination. Is preferred. Examples of the hypophosphorous acid compound include hypophosphorous acid and its salts such as ammonium, lithium, sodium, potassium, and calcium. Examples of the amine borane include dimethylamine borane, trimethylamine borane, isopropylamine borane, morpholine borane, and the like.
Examples of the borohydride compound include sodium borohydride. As the hydrazine derivative,
Hydrazine hydrate, phenylhydrazine and the like can be mentioned. The amount of the reducing agent to be added is generally 5 to 200 g / l.

As the above-mentioned surfactants, nonionic surfactants, amphoteric surfactants, cationic surfactants and anionic surfactants can be used alone or in combination. Among them, nonionic or amphoteric surfactants can be used. Activators are preferred. The amount of the surfactant is generally 0.01 to 50 g / l, preferably 1 to 20 g / l.

Examples of the nonionic surfactant include ether type nonionic surfactants such as nonylphenol polyalkoxylate, α-naphthol polyalkoxylate, dibutyl-β-naphthol polyalkoxylate, and styrenated phenol polyalkoxylate. Examples thereof include amine-type nonionic surfactants such as octylamine polyalkoxylate, hexynylamine polyalkoxylate, and linoleylamine polyalkoxylate.

Examples of the amphoteric surfactant include 2-undecyl-1-carboxymethyl-1-hydroxyethylimidazolium betaine, N-stearyl-N, N-dimethyl-N-carboxymethylbetaine and lauryl dimethylamine oxide. No.

Examples of the above-mentioned cationic surfactant include lauryltrimethylammonium salt, lauryldimethylammonium betaine, laurylpyridinium salt, oleylimidazolium salt and stearylamine acetate in the form of salts.

Examples of the anionic surfactant include alkyl sulfates such as sodium lauryl sulfate, polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene (EO12) nonyl ether sulfate, and polyoxyethylene alkyl phenyl ether sulfates. Alkyl benzene sulfonate and the like.

As for the conditions of the plating bath, the bath temperature is 45
~ 90 ° C, but from the viewpoint of increasing the deposition rate,
0 ° C. is preferred. In addition, in addition to the above-mentioned composition, for example, well-known additives shown in the following (1) to (5) can be mixed in the plating bath as needed. Antioxidants such as hydroquinone, catechol, pyrogallol, etc. In addition, pH adjusters, brighteners, semi-glossy agents, etc.

[0030]

【The invention's effect】

(1) In the present invention, bismuth having a standard oxidation-reduction potential within a predetermined range, indium, zinc, lead, antimony, silver, and a soluble salt of a specific metal such as copper are added to the plating bath in a very small proportion. Trace metal ions act catalytically in the bath, so to speak, to increase the rate of tin deposition. In addition, the crystal grain shape of the obtained tin plating film is suitable for bonding to increase the bonding strength and form a uniform fillet, so that the bonding property of the plating film can be improved. In addition, in this electroless plating, the mixing ratio of a small amount of the metal ions in the plating bath does not necessarily become the trace abundance ratio in the plating film to be deposited (as described above, the specific metal ion is The component of the plating film is substantially only tin.

In particular, according to the test examples described below (see FIG. 1),
When the plating bath does not contain the soluble salt of the metal, as shown in Comparative Examples 1a to 10a, the deposition rate of tin is naturally low, and the bonding strength and fillet forming ability are low. On the other hand, when the soluble salt of the above-mentioned metal is added to the plating bath in excess of a specific trace range (to the extent that it does not substantially lead to a tin alloy), tin precipitation occurs as shown in Comparative Examples 1b to 10b. The speed tends to increase, but the joining strength and fillet forming ability decrease. On the other hand, in the tin plating bath of the present invention (see Examples 1 to 18), a small amount of a soluble salt of a specific metal is blended in a specific range. It is possible to achieve both good bonding properties (total strength such as bonding strength and fillet forming ability). Therefore, when the electroless plating is performed using the tin bath of the present invention, the plating process can be performed at a temperature lower than 80 ° C., and the productivity is remarkably improved. Tin plating bath is T
It can sufficiently cope with high-density mounting products such as the AB system, and in turn, can improve the reliability of products using TAB (such as liquid crystal) and the production yield.

(2) As in the present invention 2, when a surfactant is additionally mixed into the plating bath, the crystal grain appearance, smoothness, adhesion, and denseness of the plating film can be further promoted.

(3) As in the present invention 3, when a reducing agent is additionally mixed into the plating bath, as described above, the deposition rate of tin is further increased, and the effect of increasing the film thickness can be further promoted.

[0034]

EXAMPLES Examples of electroless tin plating baths will be described below in order, and the deposition rate of tin when plating with the electroless bath of each example, the deposition strength of the obtained tin plating film, and the quality of fillet formation will be described. The test example of is also described.
The present invention is not limited to the following examples,
Of course, many modifications can be made without departing from the spirit of the invention.

Example 1 An electroless tin plating bath was constructed with the following composition; Stannous sulfate (as Sn ²⁺ ) 30 g / l p-phenolsulfonic acid 100 g / l hydrochloric acid 20 g / l thiourea 150 g / l sodium hypophosphite 80 g / l zinc chloride (as Zn ²⁺ ) 0.05 g / l α-naphthol polyethoxylate (EO15) 8g / l

<< Comparative Example 1a >> A plating bath of Example 1 having the basic composition and omitting zinc chloride was used as Comparative Example 1a (accordingly, the conditions for adding each component were omitted components (or
Except for the following components), except for the following components:
An electroless tin plating bath was built.

<< Comparative Example 1b >> A plating bath having the basic composition of the plating bath of the above-mentioned Example 1 and having a zinc chloride compounding ratio increased to 6.0 g / l (within a range that does not lead to an alloy with tin). As Comparative Example 1b, an electroless tin plating bath was built.

Example 2 An electroless tin plating bath was constructed with the following composition; Stannous p-phenol sulfonate (as Sn ²⁺ ) 10 g / l borofluoric acid 50 g / l p-phenolsulfonic acid 50 g / l thiourea dioxide 100 g / l ammonium hypophosphite 60 g / l silver nitrate (as Ag ⁺ ) 0.008 g / l Styrenated phenol polyethoxylate (EO18) 15 g / l

Comparative Example 2a An electroless tin plating bath was constructed using the plating bath of Example 2 as a basic composition, and omitting silver nitrate as Comparative Example 2a.

Comparative Example 2b An electroless tin plating bath was constructed using the plating bath of Example 2 as a basic composition and increasing the mixing ratio of silver nitrate to 6.0 g / l as Comparative Example 2b.

Example 3 An electroless tin plating bath was constructed with the following composition; Stannous 2-propanesulfonate (as Sn ²⁺ ) 20 g / l 2-propanesulfonic acid 140 g / l diphenylthiourea 120 g / l potassium hypophosphite 80 g / l indium ethanesulfonate (as In ³⁺ ) 0 .05g / l Polyoxyethylene (EO12) nonylphenyl ether-sodium sulfate 5g / l

Comparative Example 3a Comparative Example 3 was prepared by using the plating bath of Example 3 as a basic composition and omitting the indium salt.
As a, an electroless tin plating bath was constructed.

<< Comparative Example 3b >> The plating bath of Example 3 was used as a basic composition, and the mixing ratio of indium salt was 6.0 g / l.
An electroless tin plating bath was constructed as Comparative Example 3b.

Example 4 An electroless tin plating bath was constructed with the following composition; Stannous 2-propanesulfonate (as Sn ²⁺ ) 30 g / l p-phenolsulfonic acid 120 g / l 2-naphthalenesulfonic acid 20 g / l dimethylthiourea 130 g / l calcium hypophosphite 50 g / l antimony tartrate (Sb ³⁺ 0.005 g / l Linoleylamine polyethoxylate (EO12) -polypropoxylate (PO3) 7 g / l

<< Comparative Example 4a >> Comparative Example 4 was prepared by using the plating bath of Example 4 as a basic composition and omitting the antimony salt.
As a, an electroless tin plating bath was constructed.

Comparative Example 4b The plating bath of Example 4 was used as a basic composition, and the mixing ratio of the antimony salt was 6.0 g / l.
The electroless tin plating bath was set up as Comparative Example 4b with the increased amount.

Example 5 An electroless tin plating bath was constructed with the following composition; Stannous ethanesulfonate (as Sn ²⁺ ) 30 g / l Ethanesulfonic acid 150 g / l dimethylthiourea 100 g / l hypophosphorous acid 30 g / l lead acetate (as Pb ²⁺ ) 0.6 g / l N-stearyl- N, N-dimethyl-N-carboxymethylbetaine 8g / l

Comparative Example 5a An electroless tin plating bath was constructed by using the plating bath of Example 5 as a basic composition and omitting lead acetate as Comparative Example 5a.

Comparative Example 5b An electroless tin plating bath was constructed using the plating bath of Example 5 as a basic composition and increasing the mixing ratio of lead acetate to 6.0 g / l as Comparative Example 5b.

Example 6 An electroless tin plating bath was constructed with the following composition; Stannous methanesulfonate (as Sn ²⁺ ) 20 g / l Methanesulfonic acid 100 g / l acetylthiourea 150 g / l hypophosphorous acid 20 g / l bismuth oxide (as Bi ³⁺ ) 0.001 g / l lauryl dimethylamine oxide 4g / l

Comparative Example 6a Comparative Example 6 was prepared by using the plating bath of Example 6 as a basic composition and omitting bismuth oxide.
As a, an electroless tin plating bath was constructed.

Comparative Example 6b The plating bath of Example 6 was used as a basic composition, and the mixing ratio of bismuth oxide was 6.0 g / l.
An electroless tin plating bath was set up as Comparative Example 6b.

Example 7 An electroless tin plating bath was constructed with the following composition; Stannous toluenesulfonate (as Sn ²⁺ ) 30 g / l propionic acid 180 g / l thiosemicarbazide 90 g / l calcium hypophosphite 50 g / l copper p-phenolsulfonate (as Cu ²⁺ ) 0.075 g / l stearylamine Acetate 8g / l

Comparative Example 7a An electroless tin plating bath was constructed using the plating bath of Example 7 as a basic composition and omitting the copper salt as Comparative Example 7a.

Comparative Example 7b An electroless tin plating bath was constructed using the plating bath of Example 7 as a basic composition and increasing the mixing ratio of the copper salt to 6.0 g / l as Comparative Example 7b.

Example 8 An electroless tin plating bath was constructed with the following composition; Stannous methanesulfonate (as Sn ²⁺ ) 30 g / l cresol sulfonic acid 120 g / l thiourea 150 g / l sodium hypophosphite 80 g / l zinc methanesulfonate (as Zn ²⁺ ) 3.00 g / l lauryl Alcohol polyethoxylate (EO15) 7g / l

Comparative Example 8a An electroless tin plating bath was constructed by using the plating bath of Example 8 as a basic composition and omitting the zinc salt as Comparative Example 8a.

Comparative Example 8b An electroless tin plating bath was constructed by using the plating bath of Example 8 as a basic composition and increasing the mixing ratio of zinc salt to 6.0 g / l as Comparative Example 8b.

Example 9 An electroless tin plating bath was constructed with the following composition; Stannous methanesulfonate (as Sn ²⁺ ) 0.25 mol / l Methanesulfonic acid 0.8 mol / l p-phenolsulfonic acid 0.1 mol / l Thiourea 1.4 mol / l hypophosphorous acid Sodium 0.5 mol / l cuprous oxide (as Cu ⁺ ) 0.0025 mol / l 2-undecyl-1-carboxymethyl-1-hydroxyethylimidazolium betaine 5 g / l

Comparative Example 9a An electroless tin plating bath was constructed by using the plating bath of Example 9 as a basic composition and omitting the copper salt as Comparative Example 9a.

Comparative Example 9b An electroless tin plating bath was constructed by using the plating bath of Example 9 as a basic composition and increasing the mixing ratio of the copper salt to 6.0 g / l as Comparative Example 9b.

Example 10 An electroless tin plating bath was constructed with the following composition; 2-hydroxyethanesulfonic acid-stannous (as Sn ²⁺ ) 50 g / l ethanesulfonic acid 140 g / l diethylthiourea 130 g / l lead ethanesulfonate (as Pb ²⁺ ) 0.05 g / l hexynylamine polyethoxy Rate (EO10) 6g / l

Comparative Example 10a Comparative Example 10a was prepared by using the plating bath of Example 10 as a basic composition and omitting the lead salt.
An electroless tin plating bath was constructed.

Comparative Example 10b An electroless tin plating bath was constructed by using the plating bath of Example 10 as a basic composition and increasing the mixing ratio of lead salt to 6.0 g / l as Comparative Example 10b.

Example 11 An electroless tin plating bath was constructed with the following composition; 2-hydroxypropane-1-stannous sulfonate (as Sn ²⁺ ) 35 g / l 2-hydroxypropane-1-sulfonic acid 110 g / l acetylthiourea 175 g / l bismuth p-phenolsulfonate (as Bi ³⁺ ) 0.5 g / l 1,1-bis (4-hydroxyphenyl) ethane-polyethoxylate (EO10) 10 g / l

Example 12 An electroless tin plating bath was constructed with the following composition; Stannous methanesulfonate (as Sn ²⁺ ) 0.25 mol / l Methanesulfonic acid 0.4 mol / l p-phenolsulfonic acid 0.4 mol / l Allylthiourea 1.2 mol / l cuprous oxide 0.0005 mol / l (as Cu ⁺ ) Octylamine polyethoxylate (EO8) 10 g / l

Example 13 An electroless tin plating bath was constructed with the following composition; Stannous methanesulfonate (as Sn ²⁺ ) 0.20 mol / l ethanesulfonic acid 0.7 mol / l p-phenolsulfonic acid 0.2 mol / l diethylthiourea 1.6 mol / l cuprous oxide 0.0025 mol / l (as Cu ⁺ ) lauryl dimethylamine oxide 4 g / l

Example 14 An electroless tin plating bath was constructed with the following composition; a small amount of indium salt. Stannous p-phenol sulfonate (as Sn ²⁺ ) 30 g / l cresol sulfonic acid 95 g / l diphenylthiourea 155 g / l potassium hypophosphite 70 g / l indium ethane sulfonate (as In ³⁺ ) 0.15 g / L

Example 15 An electroless tin plating bath was constructed with the following composition; Stannous methanesulfonate (as Sn ²⁺ ) 0.25 mol / l ethanesulfonic acid 0.8 mol / l p-phenolsulfonic acid 0.1 mol / l diethylthiourea 1.4 mol / l cuprous oxide (As Cu ⁺ ) 0.0025 mol / l potassium hypophosphite 0.5 mol / l linoleylamine polyethoxylate (EO12) -polypropoxylate (PO3) 7 g / l

Example 16 An electroless tin plating bath was constructed with the following composition; Stannous 2-propanesulfonate (as Sn ²⁺ ) 0.18 mol / l p-phenolsulfonic acid 0.6 mol / l sulfuric acid 0.1 mol / l thiourea 1.5 mol / l hypophosphorous acid 1.0 mol / l cuprous oxide (as Cu ⁺ ) 0.002 mol / l dibutyl-β-naphthol polyethoxylate (EO15) 8 g / l

Example 17 An electroless tin plating bath was constructed with the following composition; Stannous methanesulfonate (as Sn ²⁺ ) 0.25 mol / l Methanesulfonic acid 0.8 mol / l p-phenolsulfonic acid 0.1 mol / l Thiourea 1.4 mol / l hypophosphorous acid Sodium 0.5 mol / l cuprous oxide (as Cu ⁺ ) 0.0025 mol / l polyoxyethylene (EO12) nonyl ether-sodium sulfate 5 g / l

Example 18 An electroless tin plating bath was constructed with the following composition; an example of a small amount of a combination of a lead salt and a bismuth salt. Stannous ethanesulfonate (as Sn ²⁺ ) 30 g / l Methanesulfonic acid 150 g / l Ethylenethiourea 180 g / l Hypophosphorous acid 10 g / l Lead 2-propanesulfonate (as Pb ²⁺ ) 0.04 g / l Bismuth methanesulfonate (as Bi ³⁺ ) 0.035 g / l t-butanol polyethoxylate (EO10) 12 g / l

Then, a test piece of a TAB film carrier prepared by VLP (a type of electrolytic copper foil) was immersed in each of the tin plating baths of Examples 1 to 18 and Comparative Examples 1a and 10a and 10b, and TAB under the processing conditions of 10 ° C for 10 minutes.
Was subjected to electroless plating. Then, the deposition rate of tin during the electroless plating was measured by the thickness of the tin after 10 minutes, and the resulting tin plating film was visually examined for plating appearance such as gloss and denseness.

The two columns on the left in FIG. 1 show these results. However, the evaluation criteria for the deposition rate and plating appearance are as follows. (1) Evaluation criteria of deposition rate ○: Film thickness of 1.0 μm or more △: Film thickness of 0.6 to 1.0 μm ×: Film thickness of less than 0.6 μm (2) Evaluation criteria of plating appearance ○: Matte ×, uniform and good appearance and dense crystal particle appearance ×: Black or gray non-uniform appearance, coarse crystal particle appearance

On the other hand, each TAB plated with matte tin
Bond the film carrier of the above on a predetermined copper plate,
The state of fillet formation and bonding strength were examined.

<< Example of Fillet Forming State and Bond Strength Test >> Bonding Machine (TCW manufactured by Avionics)
Using -115A), an inner lead of each TAB was bonded to a copper plate plated with gold of 0.5 μm under the conditions of a load of 50 g / unit inner lead, a temperature of 450 ° C., and a time of 5 seconds. Then, the state of formation of fillets around the inner leads after bonding was observed from a bird's eye view with a magnifying glass.
Further, a simple test of the peeling strength (peeling strength) of the lead was performed by pulling one end of the inner lead after bonding until the end was broken in a direction perpendicular to the copper plate, and examining the breaking mode.

The center column in FIG. 1 shows the result of the fillet formation state, and the second column from the right in FIG. 1 shows the result in the break mode. However, the fillet formation state and each evaluation standard of the peeling test are as follows. (1) Evaluation criteria of fillet formation state ：: Continuously formed in a uniform shape over the entire circumference of the lead △: Fillet was formed but discontinuous ×: No fillet was formed ( 2) Peeling test evaluation criteria ○: Lead breaks ×: Breaks at interface between lead and gold plating

<< Individual Evaluation and Overall Evaluation of the Test Results >>
Regarding the deposition rate of tin from the electroless plating bath (film-enhancing effect), Examples 1 to 18 were all evaluated as ○, and Comparative Examples 1a to 10a in which a soluble salt of a predetermined metal such as bismuth and indium was not mixed were used. All were evaluated as x. Comparative Examples 1b to 10b in which the predetermined metal salt was blended at 6.0 g / l
Are mostly evaluations of Δ to ○, and Comparative Examples 1a to 10
The film-enhancing effect was recognized as compared with a. On the other hand, as for fillet formation, all of Examples 1 to 18 were evaluated as ○, whereas Comparative Examples 1a to 10a were all evaluated as x, and Comparative Examples 1b to 10b were all evaluated as x to △. Was. Regarding the peeling test, all of Examples 1 to 18 were evaluated as ○, whereas Comparative Examples 1a, b to 10a, and b were all evaluated as X, and the difference between the example and the comparative example was most apparent. Appeared.
Furthermore, regarding the plating appearance, all of Examples 1 to 18 were evaluated as ○, whereas Comparative Examples 1a to 10a were evaluated as は except for one example of X, and Comparative Examples 1b to 10b were evaluated as ○. Except for the two cases, the others were evaluated as x.

Comprehensively evaluating the individual results described above, as shown in the rightmost column of FIG. 1, Examples 1 to 18 have a high tin deposition rate and uniform fillet formation, Had a particle shape suitable for bonding, and the bonding strength of the resulting plating film was also high. That is, in each of the examples, a soluble salt of a predetermined metal such as bismuth or indium is blended in the electroless plating bath in a specific minute range, so that both the effect of increasing the thickness of tin and the bonding property of the plating film can be well balanced. And the overall evaluation was ○. Therefore, the electroless plating can be performed at a low temperature, the productivity of the plating process is improved, and it is possible to sufficiently cope with a high-density mounting product such as a TAB method. Further, the plating films obtained in the respective examples had good appearance.

On the other hand, Comparative Example 1 in which the predetermined metal was not added
Samples a to 10a had relatively good plating appearance, but had a low tin deposition rate, were inferior in bondability such as fillet formation and bonding strength of the plating film, and were all evaluated as x. Also, when the above-mentioned predetermined metal is blended (although within a range that does not substantially lead to alloying with tin) beyond the trace range of the present invention, the tin deposition rate does not increase as seen in Comparative Examples 1b to 10b. Although it is faster than the case of addition, it is inferior in fillet formation and bonding strength of the plating film. In other words, both the effect of increasing the film thickness of tin and the bonding property of the plating film could not be achieved at the same time, and the overall evaluation was x. Therefore, when a small amount of a soluble salt of a metal is added to the electroless tin plating bath within a range that does not lead to a tin alloy, the type of the metal is limited to a specific type, and the salt of the specific metal is contained in a predetermined minute range. If it is contained within the range, the effect of increasing the film thickness of tin and the bonding property of the plating film can be both satisfactorily achieved, and the above test results strongly indicate this.

The criteria for the comprehensive evaluation in FIG. 1 are as follows. ：: plating bath in which all evaluation items are △: plating bath in which one of the evaluation items is △ or × ×: plating bath in which two or more of the evaluation items are ×

[Brief description of the drawings]

FIG. 1 shows Examples 1 to 18 and Comparative Examples 1a and 10b
5 is a table showing the results of tin deposition film thickness, fillet formation state, peeling test, plating appearance, and comprehensive evaluation in a and b.

Claims (4)

[Claims] (A) a soluble salt of stannous tin; (B) an organic acid such as an alkanesulfonic acid, an alkanolsulfonic acid, an aromatic sulfonic acid, or an aliphatic carboxylic acid, or hydrochloric acid, sulfuric acid or hydrogen borofluoride At least one acid selected from inorganic acids such as acids, and (C) an electroless tin plating bath comprising a complexing agent, wherein a metal having a standard oxidation-reduction potential in the range of -0.8 to +0.8 volts is soluble. An electroless tin plating bath characterized in that a small amount of salt is blended within a range that does not substantially form a tin alloy plating film. 2. An electroless tin plating bath further comprising a surfactant in addition to the electroless plating bath according to claim 1. 3. An electroless tin plating bath characterized by further comprising a reducing agent in addition to the electroless plating bath according to claim 1. 4. A TAB film carrier in which a TAB film carrier is immersed in the electroless tin plating bath according to claim 1 to form an electroless tin plating film on a lead of the film carrier.