1996 Volume 14 Issue 2 Pages 449-453
Representative electric parts, LSI packages are turning to more fine pitch and more high pin count based on the demands of package size reduction which is coming from needs of smaller electric components. This reserch work has originated from high density LSI package surface mounting, including microjoining of leadframe on printed circuit board. In surface mounting of electric parts, solder past mass reflow line is applied to microjoining of fine pitch leadframe even less 0.5 mm pitch package outer lead on account of easy process controll and massproduction. But leadframe materials tend to smaller lead width and thinner by fine pitch photochemical etching technology propagation. This reserch work focused on reliability of fine pitch leadframe made with copper metal and Fe-42 mass% metal alloy surface mounted with solder past through long run aging.
The result of this study have shown that fine pitch surface mount with solder paste (min. 0.3 mm pitch) is capable. But after high temperature aging (150°C×1000 h in air), Pb-60Sn eutectic microstructure of solder at leadframe microjoined is segregated to Pb rich and Sn rich large grain. And copper leasds become thin by high temperature reaction with solder. It was determined that copper was damaged in high temperature circumstance.