PURPOSE: To obtain a semicylindrical solder layer having uniform thickness on a pad by applying thin coat of a lead-rich solder alloy on the surface of a pad, prior to coating the paste soldered.deposit.
CONSTITUTION: After forming a lead-rich solder alloy 3 having the ratio of 3 to 7 of Sn to Pb in the thickness of 3-5um on the surface of a pad 1, a solder layer is formed by coating the paste soldered deposit of primary content of organic acid base and tin powder and by heating. As a result, a semicylindrical solder layer having an almost uniform thickness can be formed in the long direction on the pad 1, and there is no generation of solder bank or solder approach to the sides of the pad. Therefore, the solder layer, which enables to solder parts lead stably on the pad, can be formed, although formation of such solder layer has been considered impossible conventionally. Consequently, mounting of electronic parts on various shape minute pitch pads can be realized.
FUKUNAGA TAKAO
SHIROISHI HIROKAZU
KUMAMOTO SATOSHI
FUJIWARA TAKAHIRO
KONO MASANAO
HARIMA CHEMICALS INC