JPH0544049A - Electroless tin or tin-lead alloy plating liquid and method for electroless tin or tin-lead alloy plating - Google Patents

Abstract

PURPOSE:To obtain a uniform plating film having fine precipitate particles and excellent reflowing property by incorporating an ammonium ion (quaternary ammonium ion) into an electroless tin or tin-lead alloy plating liquid. CONSTITUTION:An ammonium ion (quaternary ammonium ion) is incorporated into an electroless tin or tin-lead alloy plating liquid which contains a metal salt component comprising a soluble stannous salt or a mixture of stannous salt and lead salt, acid, thiourea or thiourea deriv., and a reducing agent. With the presence of the ammonia ion (quaternary ammonium ion), pH of the liquid is controlled and the solubility of the metal salt can be improved, and thereby, uniformity of the plating film is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acidic type coating which is preferably used for forming a tin or tin / lead alloy layer in a copper circuit of an electronic component for the purpose of improving etching resist and solderability. The present invention relates to an electrolytic tin or electroless tin / lead alloy plating solution and a plating method using the plating solution.

[0002]

2. Description of the Related Art Conventionally, electroless tin or tin / lead alloy plating has been performed on copper or copper alloy portions forming circuits of electronic parts such as printed wiring boards to improve solderability. However, with the miniaturization of electronic devices, parts and circuits have become smaller and more complicated, and some parts cannot be plated by electroplating. Therefore, an electroless tin or tin-lead alloy plating method capable of plating these portions is being studied. For example, in JP-A-1-184279, electroless tin containing organic sulfonic acid, tin and lead salts of organic sulfonic acid, sodium hypophosphite (reducing agent) and thiourea (complexing agent) as main components. -A method using a lead alloy plating bath has been proposed.

[0003]

On the other hand, recently, the mounting technology for electronic components such as integrated circuit packages has changed from the insertion mounting method (VMT) of the DIP type package to the surface mounting method (SMT) of the flat package. Therefore, it is expected that a printed wiring board with a smooth contact surface with an object to be mounted such as an integrated circuit package, that is, a printed wiring board with a highly uniform tin or tin-lead alloy plating film formed thereon is desired. Is becoming.

However, the conventional electroless tin or tin-lead alloy plating solution has coarse deposit particles and inferior uniformity of the film. Therefore, reflowability is inferior, solder supply is poor, and fine pitch is provided. It was difficult to plate an SMT compatible printed wiring board.

The present invention has been made in view of the above circumstances, and has excellent bath stability, fine deposited particles, a uniform plating film can be obtained, and it is also good for plating on fine pitch printed wiring boards compatible with SMT. It is an object of the present invention to provide an acidic electroless tin or tin / lead alloy plating solution and an electroless tin or tin / lead alloy plating method capable of coping with the above.

[0006]

Means and Actions for Solving the Problems In order to achieve the above object, the present inventor has proposed a composition of an electroless tin or tin-lead alloy plating solution capable of providing a uniform plating film with fine deposited particles. As a result of intensive studies, electroless tin containing a metal salt component composed of a soluble stannous salt or a mixture of a stannous salt and a lead salt, an acid, a thiourea or thiourea derivative, and a reducing agent. Alternatively, by containing ammonia ions and / or quaternary ammonium ions in the tin-lead alloy plating solution, a plating film having fine and uniform deposited particles and good reflow properties can be obtained, and a fine pitch SMT compatible printed wiring board can be obtained. The present invention has been completed by discovering that it can also be sufficiently applied to the plating.

Therefore, the present invention comprises a metal salt component consisting of a soluble stannous salt or a mixture of a stannous salt and a lead salt, an acid, a thiourea or thiourea derivative, and a reducing agent. Electroless tin or tin-lead alloy plating solution containing ammonia ions and / or quaternary ammonium ions, and electroless tin or tin-lead alloy plating solution, and an object to be plated in the electroless plating solution Provided is a method for electroless tin or tin-lead alloy plating, which comprises immersing and forming a tin or tin-lead alloy plating film on the object to be plated.

The present invention will be described in more detail below. The electroless tin-lead alloy plating solution of the present invention contains a soluble stannous salt or a stannous salt and a lead salt as described above.
In this case stannous ion (divalent tin ion) in the plating solution
There is no particular limitation on the tin source for supplying the above, and various tin sources can be selected, and examples thereof include organic tin stannate such as stannous methanesulfonate, stannous borofluoride, tin acetate, tin chloride, tin organic carboxylate, tin oxide. And so on. The amount of stannous ion in the plating solution is 1 to 50 g / L, especially 5 to 25
It is preferably g / L.

When the tin-lead alloy plating solution is used, as the lead ion source, the same salts as the above tin salts such as lead chloride, lead acetate, lead organic sulfonate, lead borofluoride, lead oxide, etc. are used. You can The amount of lead ions in the plating solution is appropriately selected according to the alloy ratio, etc., but is usually 0.1 to 50 g.
/ L, especially about 0.5 to 10 g / L.

As the acid component for dissolving these metal salts,
Condensed phosphoric acid such as organic sulfonic acid, perchloric acid, borofluoric acid, phosphoric acid, pyrophosphoric acid, polyphosphoric acid, hydrochloric acid, hypophosphorous acid, organic carboxylic acid and the like can be mentioned, and one or more of these are used. can do. Among these, organic sulfonic acids include alkane sulfonic acid, hydroxyalkane sulfonic acid, benzene sulfonic acid, naphthalene sulfonic acid and some of these hydrogen atoms are hydroxyl groups, halogen atoms, alkyl groups, carboxyl groups, nitro groups, mercapto groups. , Those substituted with an amino group or a sulfonic acid group are used, and more specifically, as the organic sulfonic acid that can be preferably used in the present invention, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 2- Propanesulfonic acid, butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid, chloropropanesulfonic acid, 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1- Sulfonic acid, 2-hydroxypentanesulfonic acid, allyls Fonic acid, 2-sulfoacetic acid, 2- or 3-sulfopropionic acid, sulfosuccinic acid, sulfomaleic acid, sulfofumaric acid, benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, nitrobenzenesulfonic acid, sulfobenzoic acid, sulfosalicylic acid, Examples thereof include benzaldehyde sulfonic acid and p-phenol sulfonic acid. The amount of these acids used is not particularly limited,
It is preferably 10 to 200 g / L, particularly 50 to 150 g / L, and the ratio of acid to metal ion is 1: 1 to 1: 1.
It is preferably 1:20, particularly preferably 1: 3 to 1:10.

The plating solution of the present invention contains thiourea or a thiourea derivative (thioamides) such as thioformamide or thioacetamide, and the presence of the thioureas makes it possible to deposit tin or a tin-lead alloy. Become. The compounding amount of thiourea is not particularly limited, but is usually 10 to 200 g, particularly 50 to 150 g per liter of plating solution.
It is preferably about g. Further, tartaric acid, malic acid, citric acid, EDTA and the like can be used together with this thiourea as a complexing agent.

A reducing agent is added to the plating solution of the present invention. As the reducing agent, hypophosphite, sodium hypophosphite, hypophosphite such as potassium hypophosphite and the like are included. It is preferably used. The amount of the reducing agent to be added can be a usual amount, and specifically, it is preferably 10 to 200 g / L, and particularly preferably about 50 to 150 g / L.

Further, the plating solution of the present invention contains a polyoxyalkyl ether type surfactant such as polyoxynonylphenyl ether and polyoxylauryl phenyl ether.
Polyoxystearyl amide ether and other pooxyalkylamide ether surfactants, polyoxyoleylamine ether and other polyoxyalkylamine ether surfactants, polyoxyethylene / propylene block polymers and other nonionic surfactants and alkyls A cationic surfactant such as an amine salt, an alkyltrimethylamine salt, or an alkyldimethylbenzylamine salt can be added, which can improve the uniformity and reflow property of the film.

The tin or tin-lead alloy plating solution containing each of the above components is acidified, and preferably has a pH of 2 or less.

The plating solution of the present invention is an electroless tin or tin-lead alloy plating solution containing each of the above components and containing ammonia ions and / or quaternary ammonium ions. The presence of ammonia ions and / or quaternary ammonium ions adjusts the pH and improves the solubility of the metal salt, thereby improving the uniformity of the plating film obtained.

The content of the ammonia ion and / or the quaternary ammonium ion is not particularly limited, but it is preferably 0.1 to 50 g / L, particularly 1 to 20 g / L. If the content is less than 0.1 g / L, a plated film having good uniformity and reflowability may not be obtained. Incidentally, these ammonia ions and / or quaternary ammonium ions are tin ions in the plating solution,
All or part of the cation components other than lead ions and hydrogen ions may be used.

These cation components are usually added to the plating solution as a salt containing these cations as a base component.
In this case, as the anion constituting the salt, condensed phosphoric acid such as organic sulfonic acid, perchloric acid, borofluoric acid, phosphoric acid, pyrophosphoric acid and polyphosphoric acid, hydrochloric acid, hypophosphorous acid, organic carboxylic acid, hypophosphorous acid An acid or the like is suitable, and it is particularly preferable to use the same acid as the above acid component in the plating solution. Specific examples of the salt containing the cation include ammonium borofluoride salt, ammonium chloride salt, ammonium hypophosphite salt, trimethylammonium hypophosphite chloride and the like.

When electroless tin or tin-lead alloy plating is performed using the plating solution of the present invention, it is carried out by immersing an object to be plated such as copper or copper alloy in the plating solution of the present invention.
The temperature at that time is preferably 50 to 90 ° C, particularly preferably 60 to 80 ° C. In addition, stirring can be performed if necessary. The plating solution and plating method of the present invention are preferably used for plating electronic components such as printed wiring boards, but can also be suitably used for electroless plating of other copper, copper alloys, etc. It is a thing.

[0019]

The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example] A plating solution having the following compositions (1) to (7) was prepared, the change with time at room temperature was examined, and the turbidity of the solution was confirmed to evaluate the stability of the bath. The results are shown in Table 1.

Then, a printed wiring test board having a copper circuit formed thereon is dipped in these plating solutions at 70 ° C. for 6 minutes to form a tin or tin-lead alloy plating layer having a thickness of 5 μm on the copper circuit of the board. Was formed, and the appearance of the obtained plating film was visually inspected. The results are shown in Table 1.

Further, this substrate is charged into a reflow apparatus,
Treat at 210 ° C for 15 seconds and observe the appearance of the plating film.
To evaluate the reflowability. The results are shown in Table 1.
You The evaluation criteria for bath stability and reflowability are as follows.
As described above.Plating solution composition Plating solution (1) Methanesulfonic acid 30 g / L Stannous methanesulfonate 20 g / L Lead methanesulfonate 13 g / L Thiourea 75 g / L Hypophosphorous ammonium salt 80 g / L Citric acid 15 g / L EDTA 3 g / L pH 1.5 Plating solution (2) Ammonium methanesulfonate 50g / L Stannous methanesulfonate 20g / L Lead methanesulfonate 13g / L Thiourea 75g / L Hypophosphite ammonium salt 70g / L Citric acid 15g / L EDTA 3 g / L pH 1.8 plating solution (3) borohydrofluoric acid 20 g / L stannous borofluoride 20 g / L lead borofluoride 50 g / L thiourea 80 g / L pyrophosphate ammonium salt 200 g / L hypochlorite Trimethylammonium Phosphate Chloride 50g / L pH 1.0 Plating Solution (4) Anion Chloride 60 g / L stannous borofluoride 20 g / L lead borofluoride 50 g / L thiourea 80 g / L methylamine pyrophosphate salt 200 g / L hypophosphorous acid 50 g / L pH 1.0 Plating solution (5) Chlorination Stannous 20 g / L Lead acetate 10 g / L Hypophosphorous acid 200 g / L Thiourea 50 g / L Hypophosphorous acid ammonium salt 30 g / L pH 0.9 Plating solution (6) Stannous borofluoride 50 g / L Hoofuf Acid 200 g / L Thiourea 50 g / L Hypophosphite trimethyl ammonium chloride 30 g / L pH 0.8 Plating solution (7) Methanesulfonic acid 90 g / L Stannous methanesulfonate 20 g / L Thiourea 120 g / L Hypoxia Phosphoric acid 80 g / L Hypophosphorous tritrimethylammonium chloride 40 g / L pH 1.1 Evaluation criteria for bath stability and reflowability ◎ Very good ○ Good △ Somewhat bad × Bad

Comparative Example A plating solution having the following compositions (8) to (10) was prepared, and a printed wiring test board having a copper circuit formed thereon was immersed in these plating solutions at 70 ° C. for 6 minutes,
A tin or tin-lead alloy plating layer having a film thickness of 5 μm is formed on the copper circuit of the substrate, and the substrate is placed in a reflow apparatus.
The reflow property was evaluated in the same manner as in the examples by treating at 5 ° C. for 15 seconds and observing the appearance of the plating film. Also,
The stability of the bath and the appearance of the plating film were evaluated in the same manner as in the examples. The results are shown in Table 1. Plating solution composition Plating solution (8) Methanesulfonic acid 70g / L Stannous methanesulfonate 20g / L Lead methanesulfonate 13g / L Thiourea 75g / L Sodium hypophosphite 80g / L Citric acid 15g / L EDTA 3g / L pH 2.0 plating solution (9) borofluoric acid 20 g / L stannous borofluoride 20 g / L lead borofluoride 50 g / L thiourea 80 g / L pyrophosphoric acid 200 g / L hypophosphorous acid 50 g / L next Sodium phosphite 50 g / L pH 0.5 Plating solution (10) Boron hydrofluoric acid 20 g / L Sodium borofluoride 10 g / L Stannous borofluoride 20 g / L Lead borofluoride 50 g / L Thiourea 80 g / L Pyrophosphoric acid 200 g / L sodium hypophosphite 50 g / L pH 0.9

[0024]

[Table 1]

As is clear from the results shown in Table 1, the electroless tin or tin-lead alloy plating solution of the present invention can form a uniform plating film with fine deposited particles. It was confirmed that the plated printed wiring board was excellent in reflowability and the like, and was sufficiently compatible with fine pitch SMT.

[0026]

As described above, according to the electroless tin or tin-lead alloy plating solution and plating method of the present invention, a plating film having fine and uniform deposited particles and excellent reflowability can be obtained. It is possible to satisfactorily support plating on fine pitch printed wiring boards compatible with SMT.

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[Procedure amendment]

[Submission date] July 8, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

These cation components are usually added to the plating solution as a salt containing these cations as a base component.
In this case, as the anion constituting the salt, condensed phosphoric acid such as organic sulfonic acid, perchloric acid, borofluoric acid, phosphoric acid, pyrophosphoric acid and polyphosphoric acid, hydrochloric acid, hypophosphorous acid, organic carboxylic acid, hypophosphorous acid An acid or the like is suitable, and it is particularly preferable to use the same acid as the above acid component in the plating solution. Specific examples of the salt containing the cation include ammonium borofluoride, ammonium chloride, ammonium hypophosphite, tetramethylammonium hypophosphite, and the like.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

Further, this substrate is charged into a reflow device,
The reflow property was evaluated by treating at 210 ° C. for 15 seconds and observing the appearance of the plating film. The results are shown in Table 1. The evaluation criteria for the bath stability and reflow property are as follows. Plating solution composition Plating solution (1) Methanesulfonic acid 30 g / L Stannous methanesulfonate 20 g / L Lead methanesulfonate 13 g / L Thiourea 75 g / L Hypophosphorous acid ammonium salt 80 g / L Citric acid 15 g / L EDTA 3 g / L pH 1.5 Plating solution (2) Ammonium methanesulfonate 50 g / L Stannous methanesulfonate 20 g / L Lead methanesulfonate 13 g / L Thiourea 75 g / L Ammonium hypophosphite 70 g / L Citric acid 15 g / L EDTA 3 g / L pH 1.8 plating solution (3) borohydrofluoric acid 20 g / L stannous borofluoride 20 g / L lead borofluoride 50 g / L thiourea 80 g / L pyrophosphate ammonium salt 200 g / L hypophosphite tetramethylammonium 50 g / L pH 1.0 plating solution (4) A chloride Monium salt 60g / L Stannous borofluoride 20g / L Lead borofluoride 50g / L Thiourea 80g / L Methylamine pyrophosphate salt 200g / L Hypophosphorous acid 50g / L pH 1.0 Plating solution (5) Chlorination Stannous 20g / L Lead acetate 10g / L Hypophosphorous acid 200g / L Thiourea 50g / L Hypophosphorous ammonium salt 30g / L pH 0.9 Plating solution (6) Stannous borofluoride 50g / L Hoofuf Acid 200 g / L Thiourea 50 g / L Tetramethylammonium hypophosphite 30 g / L pH 0.8 Plating solution (7) Methanesulfonic acid 90 g / L Stannous methanesulfonate 20 g / L Thiourea 120 g / L Hypoxia phosphoric acid 80 g / L hypophosphite tetramethylammonium 40 g / L pH 1.1 bath stability and reflow criterion ◎ very good ○ There △ slightly bad × bad

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Teruyuki Hotta 1-5-1, Exit Hirakata, Osaka Prefecture Central Research Institute, Uemura Industrial Co., Ltd. (72) Tohru Uetama 1-5 Exit, Hirakata, Osaka No. 1 Uemura Industrial Co., Ltd. Central Research Institute

Claims (2)

[Claims] 1. Electroless tin or tin containing a metal salt component comprising a soluble stannous salt or a mixture of a stannous salt and a lead salt, an acid, a thiourea or thiourea derivative, and a reducing agent. The electroless tin or tin-lead alloy plating solution containing ammonia ions and / or quaternary ammonium ions in the lead alloy plating solution. 2. An electroless tin or tin comprising immersing an object to be plated in the electroless plating solution according to claim 1 to form a tin or tin-lead alloy plating film on the object to be plated. -Lead alloy plating method.