METHOD OF FORMING A SOLDER LAYER ON PADS OF A CIRCUIT BOARD AND METHOD OF MOUNTING AN ELECTRONIC PART ON A CIRCUIT BOARD

摘要

A paste-like composition containing a lead salt of an organic acid and tin powder is applied on a pad array portion of a citcuit board. Then, the paste-like composition is heated so as to cause precipitation, thereby forming a solder layer formed of an Sn-Pb alloy substantially only on pads. This precipitation is performed in a state that a liquid pool is formed on the pad array portion when the paste-like composition is liquified by heating, and the tin powder is settled in the liquid pool. When an electronic part is to be mounted on the pads, first, preparatory solder layers are formed on the pads by the above-mentioned precipitation process. After a paste-like composition is applied on the preparatory solder layers, the electronic part is put on the paste-like composition. Then, the paste-liks composition is heated, thereby soldering leads of the electronic part with the pads.