JP2001279485A - Solder plating method for printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder plating method for a printed circuit board in which, in a printed circuit board having the two kinds of connecting uses for a solder packaging connecting terminal part and a contact point connecting terminal part, a shielding board is not required contact point connecting terminal part in a reflowing stage of solder packaging, and also a smooth surface can be maintained even after solder reflowing. SOLUTION: In this solder plating method for a printed circuit board, a solder plating solution in which the contains tin metal ions 10 to 100 g/L, lead metal ions 5 to 50 g/L, and organic acids 100 to 200 g/L, and solder plating is performed in such a manner that current density is controlled to 1/10 to 0.1 (A/dm2) of the concentration of the tin metal ions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder plating method which is excellent in connection reliability and productivity in a printed wiring board in which solder mounting connection terminals and contact connection terminals are mixed.

[0002]

2. Description of the Related Art Generally, an epoxy resin printed wiring board,
A hard or soft printed wiring board such as a flexible printed wiring board is provided with a connection terminal portion for electrically connecting a plurality of electronic components, and ones having different connection methods and connection uses are mixed. Often. These connection terminals are subjected to surface treatment according to the purpose and use of the connection. Usually, however, the eutectic solder plating having a tin: lead content of 6: 4 is applied to the solder-mounted connection terminals. It is considered that bright nickel-hard gold plating is optimal for the connection terminal portion.
However, when a plurality of surface treatments are performed in accordance with the connection method, the number of steps for plating resist and the like increases, and the cost increases due to a decrease in productivity. For this reason, if the printed wiring board is a contact connection terminal part which is used only in the assembling stage and has relatively few insertion / removal, the surface treatment of the solder mounting connection terminal part is prioritized, and the tin: lead content is 6: 4, eutectic solder plating is often used. In recent years, due to the remarkable development of solder mounting technology, a method of printing an electronic component by printing a solder paste and performing a solder reflow process has become common. Has the following problems. That is, in order to perform a solder reflow treatment at a temperature higher than the solder melting temperature (usually, a treatment at a reflow peak temperature of 200 to 240 ° C. for 1 to 4 seconds), the eutectic solder plating of the contact connection terminal portion is also melted and required for contact connection. In some cases, the resulting smoothness may be impaired. For this reason, when soldering such a printed wiring board, a heat shield plate was installed at the contact connection terminal part to prevent melting of the solder plating, but the productivity decreased and it was difficult to manage the solder reflow conditions. Met.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a printed wiring board having two kinds of connection purposes, a solder mounting connection terminal portion and a contact connection terminal portion, which is shielded on the contact connection terminal portion in a solder mounting reflow process. It is an object of the present invention to provide a method for solder plating a printed wiring board which does not require a board and can maintain a smooth surface state even after solder reflow.

[0004]

According to the present invention, a tin metal ion concentration is 10 to 100 g / L, and a lead metal ion concentration is 5 to 100 g / L.
Using a solder plating solution having a concentration of 50 g / L and an organic acid concentration of 100 to 200 g / L, plating with a current density of 1/10 to 0.1 (A / dm ² ) of the tin metal ion concentration value, A method for solder plating a printed wiring board, wherein a plating film is formed. In particular, the thickness of the solder plating film is 1 to 4 μm.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below. The tin metal ion concentration used in the present invention is 10 to 100.
g / L, lead metal ion concentration 5-50 g / L, organic acid 1
The solder plating solution having an essential component of 00 to 200 g / L may contain an additive, a brightener, and the like as other components as necessary. The tin metal ion concentration is
100 g / L is preferable, and if it is out of this range, the gloss and physical properties of the deposited film, and the life of the plating solution are significantly reduced, which is not preferable. When plating a panel such as a printed wiring board, considering the running cost due to the removal of the plating solution out of the plating bath and the variation in the thickness of the plating film due to the current distribution, the tin metal ion concentration is Preferably, it is 15 to 60 g / L. On the other hand, the lead metal ion concentration is more preferably 7 to 30 g /
L is desirable, and if it is out of this range, the precipitation ratio of the eutectic solder is remarkably deviated.

[0006] The organic acid is an organic acid such as alkanolsulfonic acid, and the organic acid concentration is preferably 100 to 200 g / L. Outside of this range, the tin metal ion concentration and the lead metal ion concentration become unstable, which is not preferable. Additive,
As the brightener, there are generally nonionic surfactants, organic amines, aldehydes, ketones, alcohols, etc.
Generally, it is not particularly limited as long as it is commercially available for a eutectic solder plating solution having a tin: lead content of 6: 4. When the solder plating is performed using the solder plating solution, the current density is 1/10 to 0. 0 of the tin metal ion concentration value.
1 (A / dm ² ) is preferred. Outside this range, unevenness is generated on the plated surface after reflow, or sufficient gloss cannot be obtained, which is not preferable. In the case of a solder plating solution containing a brightener, an optimum current density may be set according to the gloss range of each brightener. The tin metal ion concentration value in the present invention refers to a tin metal ion concentration value in a plating solution during use. By using the plating solution used in the present invention and performing plating treatment at the current density, the resulting precipitated particles of solder plating are unlikely to cause electrolysis of water in the plating solution, so that the hydrogen atom plating film And a stable crystal comprising tin and lead particles is obtained. The thickness of the plating film to be obtained is 1 to 4 μm in consideration of the surface tension fluidity when the solder is melted by heat in the processing at a peak temperature of 200 to 240 ° C. for 1 to 4 seconds, which is the processing condition of solder reflow.
It is desirable to set to. As a result, a plated film having a smooth surface state can be obtained even after solder reflow. 1 to
The thickness of the plating film of 4 μm can be obtained by performing the treatment at the treatment current in the plating solution for 0.2 to 80 minutes while rocking or jet stirring with 2 to 6 m / min.

[0007] The present invention will be specifically described with reference to the following examples. Using the solder plating solution having the chemical concentration shown in Table 1,
The flexible printed wiring board is processed under the current density conditions described above, a solder plating film of 3 to 4 μm is formed, and the peak temperature is 2
The appearance of the solder plating surface was observed after solder reflow at 40 ° C. for 4 seconds. The organic acid used was alkanolsulfonic acid.・ After solder reflow, no unevenness on the solder plating surface: ○ Some unevenness on the solder plating surface: △ Unevenness on the entire surface of the solder plating: × . From this result, it can be seen that the solder plating film treated at a current density (A / dm ² ) of 1/10 of the tin metal ion concentration value has no unevenness on the plating film surface after the solder reflow.

[Table 1]

[0008]

According to the present invention, there is provided a printed wiring board having a connection application between a solder mounting connection terminal portion and a contact connection terminal portion.
Even without using a shielding plate to shield the melting of the solder plating on the contact connection terminal part in the solder reflow processing step of solder mounting, the solder plating method of the printed wiring board having a plating film with a smooth surface state even after solder reflow Yes, connection reliability,
Excellent productivity.

Claims (2)

[Claims] 1. The method according to claim 1, wherein the tin metal ion concentration is 10 to 100 g /
L, using a solder plating solution having a lead metal ion concentration of 5 to 50 g / L and an organic acid concentration of 100 to 200 g / L, the current density is 1/10 to 0.1.
A solder plating method for a printed wiring board, wherein a plating process is performed at 1 (A / dm ² ) to form a solder plating film. 2. The method according to claim 1, wherein the thickness of the solder plating film is 1 to 4 μm.