JPH09157887A - Leadless solder plating bath and solder plating film obtained by the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a leadless solder plating bath having a compsn. approximate to the compsn. of a Zn-Sn based leadless solder alloy capable of forming a ground surface film contributing to an improvement in solder wettability and reliability of connection at the time of using the Zn-Sn leadless solder alloy in packaging operation of terminal parts, etc., in printed wiring boards and to execute soldering having reliability with the easier packaging operation of the terminal parts, etc., of the printed wiring boards by obtaining a solder film adequate as the ground surface film of the leadless solder alloy obtd. by using this bath and forming the film without contg. the lead which is harmful to the human body and poses environmental problems. SOLUTION: This leadless solder plating bath contains 5 to 40g/l tin pyrophosphate, 1 to 10g/l zinc pyrophosphate, 40 to 150g/l potassium pyrophosphate, 4 to 20ml/l hydrogen peroxide water, 0.1 to 1g/l polyethylene oxide. This solder plating film is formed by using this leadless solder plating bath. This solder plating film is adequate for treating the Zn-Sn leadless alloy having the compsn. consisting of 5 to 40wt.% zinc and 95 to 60wt.% tin.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lead-free solder plating bath capable of forming a solder plating film suitable for a Zn--Sn lead-free solder alloy treatment without containing harmful lead, and obtained by the same. Regarding solder plating film.

[0002]

2. Description of the Related Art Generally, in a printed wiring board or the like, a mounting work for soldering terminals, various components and the like is performed on a circuit surface. As a solder alloy used for these soldering operations, various lead-free solder alloys containing no lead harmful to the human body have been proposed. For example, the 1994 Journal of Electro
Various lead-free solder alloys have been proposed in nic Materials, Vol. 23 No. 8 and the like. The inventors of the present invention have also disclosed, for example, Japanese Patent Application No. 7-56691 as Sn—Ag alloys and Japanese Patent Application Nos. 6-172091 and 6-2903 as Sn—Zn alloys.
No. 62 and Japanese Patent Application No. 7-192483 have already filed.

However, when the soldering work using these lead-free solder alloys is inferior in solder wettability and solderability, the conventional Sn--Pb eutectic solder is used in the soldering work. Inevitably, a lead-free solder film cannot be obtained even when a lead-free solder alloy is used. That is, the conventional Pb-Sn solder plating film has a tin content of 5 to 95% by weight, and the solderability of the composition having a tin content of around 60% by weight is very excellent depending on the treatment method. It is said that the lead content in the film changes greatly depending on the tin content, and lead is brought into the film.

[0004]

Conventionally, as a zinc-tin alloy plating bath, for example, metal tin: 20 g / l, metal zinc:
8 g / l, organic carboxylic acid 120 g / l, conductivity aid:
Organic acid tin-zinc alloy plating bath consisting of 80 g / l, brightener: 8 ml / l, or tin (tetravalent): 24 g / l, zinc (divalent): 2 g / l, complexing agent: 60 g / l, An alkaline zincate tin-zinc alloy plating bath comprising an electrically conductive inorganic acid: 10 g / l is known. However, these are all for the purpose of rust prevention, and Z
It does not form an undercoat when an n-Sn solder alloy is used, and is not actually suitable as an undercoat.

The present invention forms a base film which can improve solder wettability and connection reliability when a Zn-Sn lead-free solder alloy is used for mounting work such as terminals of a printed wiring board. The present invention provides a lead-free solder plating bath having a composition similar to that of a Zn-Sn lead-free solder alloy, and at the same time, a solder film suitable as an undercoat of a lead-free solder alloy obtained by using this bath. The purpose of this is to form a lead-free film that is harmful to the human body and causes environmental problems, and facilitates the work of mounting the terminals, etc. on the printed wiring board, and has a reliable solder. It is intended to be attached.

[0005]

The above-mentioned object of the present invention can be achieved by using a pyrophosphoric acid-based tin-zinc-based lead-free solder plating bath. That is, the solder plating bath according to the present invention includes tin pyrophosphate: 5 to 40 g / l, zinc pyrophosphate: 1 to 10 g / l, potassium pyrophosphate: 40 to 15
0 g / l, hydrogen peroxide solution: 4 to 20 ml / l, polyethylene oxide: 0.1 to 1 g / l. By plating using this bath, zinc:
A solder plating film having a composition of 5 to 40% by weight and tin: 95 to 60% by weight, which is suitable for treatment of a Zn-Sn lead-free solder alloy, can be obtained.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the bath composition according to the present invention will be described below. First, if the amount of tin pyrophosphate is less than 5 g / l, the amount of tin is insufficient, the ratio of zinc in the plating film is outside the desired range, and the solderability and solder wettability deteriorate.
When tin pyrophosphate exceeds 40 g / l, Zn is partially undissolved, the bath liquid becomes cloudy, and the plating film composition becomes unstable. The more preferable content of tin pyrophosphate is 10 to 30 g.
/ L. When the amount of zinc pyrophosphate is less than 1 g / l, the amount of Zn is insufficient, the ratio of tin in the plating film is out of the desired range, and the solderability and solder wettability deteriorate. If the amount of zinc pyrophosphate exceeds 10 g / l, the bath liquid becomes cloudy and the plating film becomes unstable. When potassium pyrophosphate is less than 40 g / l, Zn is partially undissolved, the bath liquid becomes cloudy, and the plating film composition becomes unstable. On the other hand, when it exceeds 150 g / l, the Zn / Sn ratio in the plating film becomes unstable, and the solderability and solder wettability become unstable. 4 ml of hydrogen peroxide water
If it is less than / l, the powder of the plating film will fall off, resulting in 20 ml /
If it exceeds 1, the plating film becomes unstable. If the polyethylene oxide is out of the range of 0.1 to 1.0 g / l, the Zn / Sn ratio in the plating film becomes unstable, and the solderability,
Solder wettability becomes unstable. Is mentioned.

A case of performing a plating treatment using the above-described solder plating bath of the present invention will be described. First, after degreasing the surface of a copper plate or the like for a printed wiring board which is an object to be plated, it is pickled with a sulfuric acid solution. The concentration of the sulfuric acid solution used for this pickling treatment is about 2 N, and the temperature is room temperature (25 ° C.) for 30 to 2 minutes. After pickling, the sulfuric acid solution is removed by washing with water.

After the pretreatment, the object to be plated is subjected to electrolytic plating using the solder plating bath according to the present invention. The plating treatment conditions are: current density: 1 to 10 A / dm ² , bath temperature 20 to 5
Electrolysis is performed at 0 ° C. for a treatment time of 2 to 10 minutes and at a pH of 7.5 to 9.5. When the current density exceeds 10 A / dm ² , the plating film thickness is not constant and the desired film thickness of 2 to 5 μm cannot be obtained. On the other hand, if the current density is less than 1 A / dm ² , the desired film thickness cannot be obtained and the solder wettability deteriorates. Bath temperature is 2
If the temperature is lower than 0 ° C, the deposition rate is not stable, and if the temperature exceeds 50 ° C, a film non-forming portion is generated. If the pH is less than 7.5, the deposition of the plating film becomes unstable, and if it exceeds 9.5, the non-plated film formation portion occurs.

A lead-free Zn-Sn solder film is obtained on the surface of the object to be treated, which has been treated with the bath of the present invention as described above. The composition of this film is Zn: 5 to 40% by weight,
Sn: 95 to 60% by weight. This film has solderability and solder wettability equivalent to those of a film formed using a conventional Sn-Pb-based solder plating bath, and is similar to the conventional lead-free solder alloy composition described above. It has a film property extremely suitable for performing solder mounting work using the lead-free solder alloy. In the coating film obtained by the plating bath of the present invention, if the Zn content is less than 5% by weight, the solderability and the solder wettability are significantly reduced. On the contrary, even if the Zn content exceeds 40% by weight, the solderability and the solder wettability are deteriorated, and practical use cannot be endured.

To solder various components and the like on the plating film obtained by the present invention using a lead-free solder alloy,
Since the plating film of the present invention acts as a base film during soldering, and has a film composition similar to that of a solder alloy,
Soldering work can be performed very easily without using special flux.

[0011]

EXAMPLES The present invention will be described below with reference to examples. After degreasing a copper test piece having a length of 10 cm, a width of 6.5 cm and a thickness of 0.3 mm with an organic solvent such as acetone, a 2N sulfuric acid solution is used and the acid is kept at room temperature (25 ° C.) for 30 seconds to 2 minutes. A pretreatment consisting of washing and then washing with water was carried out. Next, electrolytic treatment was performed using the plating bath having the bath composition shown in Table 1 under the same conditions shown in Table 1.

The test piece on which the obtained plating film was formed was tested for solderability and solder wettability by MLL-STD.
It was evaluated based on the 883D standard (solder wettability according to the meniscograph method). The evaluation was performed by comparing with a film formed using a conventional Sn-Pb-based plating bath. The results are shown in Table 1. The results obtained by the same electrolytic treatment using a conventional plating bath are also shown in Table 2 for reference.

[0013]

[Table 1]

[0014]

[Table 2]

From Table 1, all the plating films formed by using the plating bath of the present invention showed the same solderability and solder wettability as the films formed by using the conventional Sn-Pb type solder plating bath.

[0016]

According to the present invention as described above, it has extremely suitable solderability and solder wettability for soldering terminals or components to a printed wiring board or the like using a lead-free solder alloy. Provided is a plating bath capable of obtaining a lead-free solder plating film. Therefore, the plating film formed by this is a lead-free alloy, which is similar to a lead-free solder alloy when soldering work by soldering on it. It acts as a base film having a composition, the solder mounting work can be easily performed, the reliability of connection is improved, and the film does not contain lead harmful to the human body at all, and there is no possibility of causing environmental pollution.

Claims (2)

[Claims] 1. Tin pyrophosphate: 5-40 g / l, zinc pyrophosphate: 1-10 g / l, potassium pyrophosphate: 40
Lead-free solder plating bath containing ~ 150 g / l, hydrogen peroxide water: 4-20 ml / l, polyethylene oxide: 0.1-1 g / l. 2. A solder plating film formed by using the lead-free solder plating bath according to claim 1, wherein zinc: 5 to 4
Zn with a composition of 0% by weight, tin: 95-60% by weight, Zn
-A solder plating film suitable for Sn-based lead-free solder alloy processing.