PURPOSE: To deposit solder of a uniform thickness on the pads on a board and prevent thermal deformation, by performing an electroless solder plating of a printed wiring board coated with a solder resist and thereafter making the solder eutectic.
CONSTITUTION: After a circuit 22 is formed on an insulating board 21 and pads 23 are formed, a solder resist is printed. By this printing, the circuit 22 is covered with a solder resist 24. Then, degreasing, washing in water and soft etching are carried out. The soft etching is followed by washing in water and a treatment with acid. The oxide on the surface of the pads 23 is removed by the treatment with acid. After washing in water, an electroless solder plating is performed. A solder 25 deposits on the surface of the pads 23, but the printed wiring board do not thermally deform because of a gentle condition at low temperature. After this plating, washing in water, drying and a fusing treatment are performed. This treatment is to produce eutectic of tin and lead in the solder depositing on the pads 23.
MACHIDA KOICHI
ICHIKAWA TAKAHIRO
KATAGISHI HITOSHI
SAKATA YASUHIKO
