JP2000328285A - Acidic tin-copper alloy plating bath - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart a plating film having solder wettability equivalent to that of a tin-lead alloy plating bath or higher by incorporating trace eutectoidable different metal ions into Cu. SOLUTION: The plating bath preferably has the following composition: 5 to 100 g/l Sn2+ ions, 0.05 to 20 g/l Cu2+ ions (or Cu+) ions, 0.5 to 30 g/l nonionic interfacial active agent and 0.01 to 10 g/l different metal ions. The different metal ions are preferably Ni2+, Fe2+, Zn2+ and Ag+. Even if the composition in the bath is excessively small or excessively large, the assurance of good solder wettability in the plating film is difficult, and if the bath is excessively large, the crystal grain refining of the plating film progresses further and the film cures, leading to the degradation in the secondary fabricatabiity of the plating film. The plating bath regulated to a pH to <6 is used and for this purpose, alkane sulfonic acid, etc., and inorganic acid, for example, sulfuric acid, etc. are adequately used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an acid tin-copper alloy plating bath. In particular, the present invention relates to an acidic tin-copper alloy plating bath suitable for electroplating electronic components that require solder wettability of a plating film.

[0002]

2. Description of the Related Art For electronic components and the like that require soldering (electrical component terminals and printed wiring boards), electroplating is usually performed using a tin-lead alloy plating bath to improve solderability (solder wettability). Was doing. This is because the tin-lead alloy plating bath provides a plating film having a low melting point without whisker problems, has good appearance and solderability of the plating film, and is easy for bath management.

However, tin-lead alloy plating baths have problems in working environment and drainage because lead is contained in the baths, and there has been a demand for a lead-free tin-based plating bath.

Accordingly, a tin-based plating bath having the following structure has been proposed as a tin-based plating bath which provides a low melting point plating film having the same solder wettability as that of a tin-lead alloy plating bath without using lead and which is easy to manage. (See JP-A-8-13185).

"The following three components (a) to (c) (a) Sn ²⁺ ions (b) metal ions selected from the group consisting of Ag ⁺ , Cu ⁺ , In ³⁺ , Tl ⁺ and Zn ²⁺ A low-melting tin alloy plating bath containing one or more (c) nonionic surfactants and no lead. "

[0006]

However, when the present inventors select Cu as the metal ion and prepare an acidic tin-copper plating bath to perform plating on an electronic component, the solder wettability is low. -It was found to be lower than the lead alloy plating bath, and the bath stability (turbidity / precipitation) was not sufficient.

In view of the above, an object of the present invention is to provide an acidic tin-copper plating bath capable of providing a plating film having solder wettability not less than or equal to that of using a tin-lead alloy plating bath. .

Another object of the present invention is to provide, in addition to the above, an acidic tin-copper plating bath having excellent bath stability.

[0009]

An acidic tin-copper alloy plating bath according to the present invention solves the above-mentioned problems by the following constitution.

An acidic tin-copper alloy containing Sn ²⁺ ion and Cu ²⁺ ion or Cu ⁺ ion as a plating film forming component, containing a nonionic surfactant, and adjusted to an acidity of less than pH 6 It is characterized in that the plating bath contains a foreign metal ion which can be co-deposited in a trace amount with respect to the copper.

The different metal ions include Ni ²⁺ , F
one or two selected from the group ^{consisting of} e ²⁺ , Zn ²⁺ and Ag ⁺
It is desirable that the number of the metals be equal to or more than that, since such metals easily coeutect with Cu.

Further, by adopting a constitution containing a reducing organic complexing agent, it is possible to increase bath stability.

[0013]

[Detailed Description of Means] Hereinafter, the above means will be described in detail. In addition, a composition ratio etc. means a weight unit unless there is particular notice.

The acidic tin-copper alloy plating bath of the present invention contains Sn ²⁺ ions and Cu ²⁺ ions or Cu ⁺ ions as plating film forming components, contains a nonionic surfactant, and has a pH of less than 6. Is adjusted to be acidic.

The composition of each ion in the bath is Sn ²⁺ ion: 5 to 100 g / L, preferably 15 to 65 g / L.
L, more preferably 20 to 60 g / L.

Cu ²⁺ (or Cu ⁺ ) ion: 0.05 to
20 g / L, preferably 0.15 to 5 g / L, more preferably 0.2 to 3 g / L.

Here, if the amount of Cu ²⁺ (or Cu ⁺ ) ions is too small, the copper ratio in the composition of the plating film is too small, the melting point becomes high, and whiskers may be generated in the processed product. Conversely, if the amount of Cu ²⁺ (or Cu ⁺ ) ions is excessive, the proportion of copper in the composition of the plating film becomes excessive, crystal refinement proceeds, the plating film becomes hard, and the secondary workability of the plating film becomes poor. descend.

The composition of the metal corresponding to the ions in the plating film depends on the plating bath specifications and plating conditions, but usually, tin (Sn) / copper (Cu) = 99.9 / 0.1.
７０70/30, desirably 99.5 / 0.5 to 95/5
Becomes

The supply of these metal ions is carried out in the form of a salt compound of an organic acid or an inorganic acid described below, which is a pH regulator, from the viewpoint of solubility.

The above-mentioned nonionic surfactant is added to obtain a dense and smooth plating film with good adhesiveness as in the conventional tin and tin-lead alloy plating baths.

As the nonionic surfactant, those exemplified below can be suitably used.
30 g / L, preferably 1 to 20 g / L, more preferably 3 to 15 g / L.

If the amount of the nonionic surfactant is too small, it is difficult to obtain a dense and smooth plated film. If the amount is too large, the plated film is hardened and the secondary workability of the plated film is reduced. This hardening of the plating film results from an increase in the organic carbon content in the plating film (particularly in high current specifications).

Formula RO— (A) _m — (b) _n
Compounds represented by -H wherein, R is an alkyl group or an alkene group A and B of 1 or more carbon atoms -CH ₂ -CH ₂ -O- or -CH ₂ -CH
(CH ₃ ) —O—, wherein the position of occurrence is not limited. M and n each represent an integer of 0 to 40.
It is in the range of 40.

Formula R ₁ -Ar-O- (A) _m-
(B) _n compounds represented by -H, however, Ar is a phenyl group, R ₁ and naphthyl groups is an integer of 0 to 20 carbon atoms, an alkyl group or an alkene group A and B are -CH ₂ -CH ₂ -O -Or -CH ₂ -CH
(CH ₃ ) —O—, wherein the position of occurrence is not limited. M and n each represent an integer of 0 to 40.
It is in the range of 40.

Formula R ₃ —COO— (A) _m —
(B) _n- H wherein R ₃ is an alkyl group or alkene group having 1 or more carbon atoms A and B are —CH ₂ —CH ₂ —O— or —CH ₂ —CH
Represents (CH ₃ ) —O—, and its position is not limited.

M and n represent an integer of 0 to 40. The sum of m and n is in the range 1-40.

General formula R ₄ -N-[(A) _m- (B)
_n— H] _{2 where} R ₄ is an alkyl group or alkene group having 1 or more carbon atoms, and A and B are —CH ₂ —CH ₂ —O— or —CH ₂ —CH
Represents (CH ₃ ) —O—, and its position is not limited.

M and n represent an integer of 0 to 40. The sum of m and n is in the range 1-40.

All of these nonionic surfactants include the corresponding aliphatic alcohol, substituted phenol, β-naphthol substituted with alkyl, alkoxylated phosphoric acid, sorbitan esterified, styrenated phenol, ethylenediamine, monoalkylamine, It can be prepared by adding a predetermined number of moles of ethylene oxide and / or propylene oxide to a diphenol which may be alkyl-substituted.

Representative compounds represented by the above general formulas are shown below.

Polyethoxylates and polyethoxy-polypropoxylates of lower alcohols such as methyl, ethyl, isopropyl, butyl, hexyl and 2-ethylhexyl.

Polyethoxylates such as octylphenol, nonylphenol, α-naphthol and β-naphthol and polyethoxy-polypropoxylates.

Polyoxyethylene fatty acid esters such as oleic acid, lauric acid and stearic acid.

Polyethoxylates and polyethoxy-polypropoxylates of alkylamines such as laryl, stearyl, coconut oil and the like.

Alkanesulfonic acid, alkanolsulfonic acid and the like can be suitably used as the organic acid used in the present plating bath, and sulfuric acid and hydrochloric acid can be suitably used as the inorganic acid.

The composition of these organic or inorganic acids in a bath is as follows:
Although it depends on the adjusted pH, it is 30 to 500 g / L, preferably 80 to 200 g / L. The adjusted pH is usually less than 6, but from the viewpoint of bath management, it should be less than pH 3, preferably less than 1.

A first feature of the present invention is that copper contains a foreign metal ion which can be co-deposited in a trace amount with copper. The dissimilar metal ions coeutect with copper to provide an effect of improving the solder wettability of the plating film.

The heterometallic ion can be co-deposited with copper.
It is not particularly limited as long as it is a functional metal. ³⁺May be, but long circumference
Is located adjacent to both sides and below copper in the periodic table
Ni which is an ion of a metal element²⁺, Fe²⁺, Zn²⁺And A
g⁺ Easily eutectoid with copper, greatly improving solder wettability
It is desirable.

The composition of these different metal ions in the bath is
0.01 to 10 g / L, desirably 0.1 to 5 g / L. Even if the amount of foreign metal ions is too small or too large, it is difficult to ensure good solder wettability in the plating film. If the amount is too large, the crystallinity of the plating film further advances and the plating film hardens, and the secondary Workability decreases.

The composition of the foreign metal ions in the plating film is 0.1 to 20%, preferably 0.5 to 10%, based on the total amount (100%) of the plating film forming metal ions.

A second feature of the present invention contains a reducing organic complexing agent. The organic complexing agent is a divalent copper ion (Cu
²⁺ ) and monovalent copper ions (Cu ⁺ ) in the bath to control the promotion of oxidation of divalent tin ions, thereby making the plating bath less turbid and less likely to precipitate, ie, plating. It has the effect of improving bath stability.

The composition of the organic complexing agent in the bath is 0.1 to 200 g.
/ L, preferably 0.5 to 50 g / L. If the content of the organic complexing agent is too small, it is difficult to obtain the effect of increasing the stability of the plating bath, and if it is too large, the current efficiency may be reduced.

Examples of the organic complexing agent include L-ascorbic acid or a salt thereof, erythorbic acid or a salt thereof, a nitrogen-containing compound such as a hydroxylamine compound and a hydrazine compound, and a sulfur-containing compound such as a thiourea compound or a thiol compound. In addition, one or more compounds among organic carboxylic acids such as hydroxycarboxylic acid can be used.

The acidic tin-copper alloy plating bath of the present invention is prepared by adding a Sn ²⁺ supply compound, a Cu ²⁺ supply compound, a nonionic surfactant, and an organic complexing agent to the acid bath according to a conventional method. To be prepared. Specifically, after adding the water-soluble tin salt, water-soluble copper salt and water-soluble dissimilar metal salt to an aqueous solution acidified with sulfuric acid, alkanesulfonic acid, alkanolsulfonic acid or the like and sufficiently dissolving the same. The plating bath is prepared by adding a nonionic surfactant.

To the lead-free solder plating bath of the present invention, in addition to the above-mentioned components, a gloss-imparting component, an antioxidant, an antifoaming agent and the like may be added as required.

In the case of a gloss type bath, as a gloss-imparting component, lower aliphatic aldehydes such as formaldehyde, acetaldehyde, paraaldehyde, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, acrylamide, methacrylamide Olefin compounds such as crotonic acid, benzaldehyde, o-chlorobenzaldehyde, cinnamaldehyde, anisaldehyde, aromatic aldehydes such as 1-naphthaldehyde, aromatic ketones such as benzalacetone, aromatic amines such as o-chloroaniline and And metal compounds such as antimonyl potassium tartrate, bismuth oxide and bismuth nitrate.

Examples of the antioxidant for tin include hydroxyphenyl compounds such as phenol, catechol, resorcin, hydroquinone and pyrogalle, L-ascorbic acid, sorbitol and the like. It is unnecessary when using an agent.

Using the acid tin-copper alloy plating bath thus prepared, electroplating can be performed under substantially the same conditions as in the case of using a conventional tin / lead alloy plating bath.

For example, the bath temperature of the plating bath is about 10 to 60 ° C.
Degree, preferably about 20-30 ° C., and the cathode current density is about 0.01-100 A / dm ² , preferably about 5-
Plating can be performed at about 20 A / dm ² . Also,
As the anode, an insoluble electrode, tin or a tin alloy can be used.

The tin-copper alloy plating film obtained from the above-mentioned lead-free solder bath has a low melting point equivalent to that of a conventional tin-lead alloy, and also has good solder wettability as described later.
It can be used as a plating bath for electrical component terminals and printed wiring boards.

[0051]

The following examples, comparative examples and test examples are given.
The present invention will be described, but the present invention is not limited to these examples and the like. The pH was determined by comparing Example 6 with p.
All were adjusted to less than pH 1 except that H was about 4.

Example 1 70% -methanesulfonic acid 150 g / L tin methanesulfonate (as Sn ²⁺ ) 45 g / L copper methanesulfonate (Cu ²⁺ ) 0.6 g / L nickel methanesulfonate (Ni ²⁺ as) 0.2 g / L butyl alcohol polyethoxylates - poly propoxylate 5 g / L sodium erythorbate 5 g / L <example 2> 70% - as methanesulfonic acid 120 g / L methanesulfonic tin (Sn ²⁺ 60 g / L copper methanesulfonate (as Cu ²⁺ ) 1.5 g / L nickel methanesulfonate (as Ni ²⁺ ) 0.2 g / L cocoamine polypropoxylate-polyethoxylate 10 g / L diethylthiourea 1 g / L <example 3> 70% - and methanesulfonic acid 150 g / L methanesulfonic tin (Sn ²⁺ ) 20 g / of L copper methanesulfonate (Cu ²⁺⁾ 0.2g / L as methanesulfonic iron (Fe ²⁺⁾ 0.1g / L butyl alcohol polyethoxylates - poly propoxylate 5 g / L L-ascorbic acid 50g / L <Example 4> 70% -methanesulfonic acid 100 g / L tin methanesulfonate (as Sn ²⁺ ) 45 g / L copper methanesulfonate (as Cu ²⁺ ) 1 g / L nickel methanesulfonate (Ni ²⁺ 0.2 g / L β-naphthol polyethoxylate (EO12) 10 g / L sodium erythorbate 5 g / L methacrylic acid 0.8 g / L 1-naphthaldehyde 0.1 g / L Benzalacetone 0.2 g / L < Example 5> Sulfuric acid (d = 1.83) 100 g / L Stannous sulfate (as Sn ²⁺ ) 30 g / L Copper sulfate (Cu ²⁺ as) 0.5 g / L ferrous sulfate (Fe ²⁺⁾ 0.2g / L stearylamine polyethoxylated - Polypropylene Pishi rate 5 g / L sodium erythorbate 50 g / L <Example 6> ammonium sulfate 100 g / L Stannous sulfate (as Sn ²⁺ ) 30 g / L Copper sulfate (as Cu ²⁺ ) 0.5 g / L Nickel sulfate (as Ni ²⁺ ) 0.2 g / L Coconut amine polyproxylate-polyethoxylate 1 g / L sodium erythorbate 50 g / L ammonium citrate 150 g / L <Comparative example 1> 70% - as methane (as Sn ²⁺⁾ sulfonic acid 135 g / L methanesulfonic tin 45 g / L copper methanesulfonate (Cu ²⁺ ) 0.6 g / L butyl alcohol polyethoxylate-polypropoxylate 5 g / L <Comparative Example 2> 0% - methanesulfonamide (as Sn ²⁺⁾ acid 100 g / L methanesulfonic tin (as Cu ²⁺⁾ 45g / L copper methanesulfonate 1 g / L beta-naphthol polyethoxylate (EO12) 10g / L methacrylic acid 0 0.8 g / L 1-naphthaldehyde 0.1 g / L benzalacetone 0.1 g / L <Comparative Example 3> 70% -methanesulfonic acid 100 g / L tin methanesulfonate (as Sn ²⁺ ) 60 g / L methanesulfone Lead acid (as Pb ²⁺ ) 6 g / L butyl alcohol polyethoxylate-polypropoxylate 5 g / L Comparative Example 4 sulfuric acid (d = 1.83) 100 g / L stannous sulfate (as Sn ²⁺ ) 30 g / L Copper sulfate (as Cu ²⁺ ) 0.5 g / L Stearylamine polyethoxylate-polypropicylate 5 g / L <Plating test Plating bath stability test> Examples 1 to above
6. Using the plating baths of Comparative Examples 1 to 4, a lead frame (C7025) was plated with a thickness of about 10 μm under the conditions shown in Table 1. The stirring was performed using a cathode blocker (4
m / min) was used.

A test piece was prepared by cutting one pin (dimension: t0.125 × 0.5 mm) of the outer lead portion of the plated lead frame.

The solder wettability of each test piece to which the flux NS-828A (manufactured by Nippon Superior Co., Ltd.) was adhered was measured using a Nurebara tester. In addition,
The solder bath used was a 250 ° C. melting solder SN100C (manufactured by the company).

The stability of the plating bath was determined immediately after the bathing and in the bath 5
After standing for a day, the presence or absence of turbidity / precipitation was visually determined.

<Results and Evaluation> It can be seen that Examples satisfying the requirements of the present invention are excellent in bath stability and solder wettability. And it turns out that each Example shows the same solder wettability as the case where a tin-lead alloy bath is used.

[0057]

[Table 1]

Claims (9)

[Claims] 1. A plating film-forming component containing Sn ²⁺ ions and Cu ²⁺ ions or Cu ⁺ ions,
An acid tin containing a nonionic surfactant and containing a different metal ion which can be co-deposited in a trace amount with respect to the copper in an acid tin-copper alloy plating bath adjusted to an acidic pH of less than 6. -Copper alloy plating bath. 2. The method according to claim 1, wherein the different metal ions are Ni ²⁺ , Fe ²⁺ ,
An acidic tin-copper alloy plating bath, which is one or more selected from the group ^consisting of Zn ²⁺ and Ag ⁺ . 3. The acidic tin-copper alloy plating bath according to claim 1, wherein the following composition is an essential component, and the pH is adjusted to less than 6 with an organic acid or an inorganic acid. (a) Sn ^{2+ 5 to} 100 g / L (b) Cu ²⁺ (or Cu ⁺ ) 0.05 to 20 g / L (c) Foreign metal ion 0.01 to 10 g / L (d) Nonionic surfactant 0.5-30g / L 4. The acidic tin-copper alloy plating bath according to claim 3, which has the following composition and is adjusted to a pH of less than 3 with an organic acid or an inorganic acid. (a) Sn ²⁺ 15 to 65 g / L (b) Cu ²⁺ (or Cu ⁺ ) 0.15 to 5 g / L (c) Heterogeneous metal ion 0.1 to 5 g / L (d) Nonionic surfactant 5 to 15 g / L 5. The acidic tin-copper alloy plating bath according to claim 4, which is a sulfonic acid bath or a sulfuric acid bath. 6. An acidic tin-copper alloy plating bath according to claim 1, further comprising a reducing organic complexing agent. 7. The acidic tin-copper alloy plating bath according to claim 6, wherein the following composition is an essential component, and the pH is adjusted to less than 6 with an organic acid or an inorganic acid. (a) Sn ^{2+ 5 to} 100 g / L (b) Cu ²⁺ (or Cu ⁺ ) 0.1 to 20 g / L (c) Heterogeneous metal ion 0.01 to 10 g / L (d) Nonionic surfactant 2 to 30 g / L (e) Reducing organic complexing agent 0.1 to 200 g / L 8. An acid tin-copper alloy plating bath according to claim 7, comprising the following composition and adjusted to a pH of less than 3 with an organic acid or an inorganic acid. (a) Sn ²⁺ 15 to 65 g / L (b) Cu ²⁺ (or Cu ⁺ ) 0.15 to 5 g / L (c) Heterogeneous metal ion 0.1 to 5 g / L (d) Nonionic surfactant 5 to 15 g / L (e) Reducing organic complexing agent 0.5 to 50 g / L 9. The acidic tin-copper alloy plating bath according to claim 8, which is a sulfonic acid bath or a sulfuric acid bath.