Solder/solder joint for low temperature reflow by multi plating method

The electrolytic multi plating method (EMPM) of Bi and Sn was studied as the approach that supplied Sn-Bi solder. Ni/Bi/Sn and Cu/Bi/Sn coupon were prepared to compare the influence of the different under layer for Bi dispersion. And then, these coupons were jointed under 170 or 190 ^o C with the coupon which plated electrolytic Sn-Ag. When it’s jointed under 190 ^o C, uniform Bi dispersion in the solder was confirmed for the coupon by multi plating method from SEM observation and EDS analysis, which was similar to one by solder paste method[1]-[2]. Also, after the heat soak test under 100 ^o C for 500 hours, Bi aggregation and some cracks were observed in the solder near the Ni deposit for the coupon of Ni/Bi/Sn. On the other hand, Bi was dispersed to the center of the solder for the coupon of Cu/Bi/Sn and no cracks were observed.