Two Cycle Pb/Sn Solder Evaporation
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
It is proposed to modify the standard one cycle process for Pb/Sn solder evaporation such that an equal amount of solder is evaporated in two evaporation cycles. Approximately one half of the normal charge is used for each cycle. 95 percent Pb, 5 percent Sn pellets are loaded into tantalum source cups. The evaporation system is pumped down to about 2x10/-5/ torr. RF induction heating is used to evaporate the charge. Its corresponding vapor stream is monitored by a thermocouple for end point and overheating detection. Each lot of silicon wafers receive two separate identical cycles. This process decreases the degree of melt back/overheating and thus enhances the uniformity of Pb/Sn solder pads.