WETTABILITY OF TIN-BISMUTH-SILVER SOLDER

摘要

The development of lead-free solders is urgent in view of environmental standpoints. In this work the wettability of tin-bismuth-silver solders on copper was studied. Three kinds of fluxes were used. The wettability of conventional eutectic tin-lead solder exhibited an excellent level over the other solders of tin-bismuth systems. Poor wettability of the tin-bismuth solders may be caused by the growth of dendritic copper-tin compounds at copper/solder interface, in contrast to the case of tin-lead solder The wettability was improved by the addition of silver in the solder. In this tin-bismuth-silver system, silver was abnormally concentrated at the copper / solder interface even in the initial stage of contact. The wettability of the solder and the thickness of compound formed on the copper have a good correlation; the solder containing 2 percent silver exhibited the best wettability and the formation rate of copper-tin compound on the copper was slowest.