SURFACE TENSION OF SOME Sn-Pb ALLOYS: PART 1. EFFECT OF Bi, Sb, P, Ag, AND Cu ON 60Sn-40Pb SOLDER.

The maximum bubble pressure method has been used to measure the surface tension of tin, lead, and some of their binary and ternary alloys. The temperature dependence for the metals was found to be: gamma //S//n equals 604 multiplied by (times) 2( plus or minus 4. 8) minus 0. 227T (for T equals 250-340 degree C) and gamma //P//b equals 525. 9( plus or minus 4. 2) minus 0. 169T (for T equals 355-395 degree C), where gamma is the surface tension (mN m** minus **1) at temperature T ( degree C). Binary alloys did not behave as ideal solutions, showing surface enrichment by lead. Addition (all wt-%) of bismuth (0-4%) or antimony (0-5%) reduced the surface tension of 60Sn-40Pb, while copper (0-0. 6%), silver (0-2%), and phosphorus (0-0. 013%) caused it to increase. With the exception of phosphorus, these observations may be explained by reference to the surface tension of the additions, and hence their tendency to segregate at the surface of Sn-Pb solder.