1997 Volume 15 Issue 4 Pages 600-606
For higher reliability of bonding of outer leads to TCP (Tape Carrier Package), research has been done on temperature changes in the wettability of leads, coated with Au, Sn and Sn-Pb, by Sn-Pb eutectic solder. From changes in the wetting force according to the wetting balance method, an apprent activation energy is obtained, with the speed of degradation of wettability defined, dependence on coating thickness measured, and a formula to obtain permissible temperature aging time presented. The speed of degradation is lowest with Au ; it rises much more with Sn. It has been determined that the difference between Sn-Pb and Sn comes from the fact that degradation due to diffusion of Cu (the core meterial of the lead), in the coated layer is more influential than that due to surface oxidation. By forming lap shear joints with test pieces that possess zero wetting force, it is proved that bonding is possible, and that the speed of degradation of strength can be defined like that for wettability.