SIGNIFICANTLY IMPROVED MECHANICAL-PROPERTIES OF BI-SN SOLDER ALLOYS BY AG-DOPING

The addition of small amounts of Ag (less than similar to 0.5 wt. %) i s found to to significantly improve the ductility of the binary Bi-Sn eutectic solder. The ductility improvement, more than a threefold incr ease in tensile elongation, is observed even at a relatively high stra in rate (0.01 s(-1)). As the Bi-Sn, binary eutectic alloy tends to fai l catastrophically by brittle fracture at high strain rates, the reduc ed strain-rate sensitivity in the Ag-condaining alloy is beneficial fo r improving solder reliability on sudden impacting as might be encount ered during device assembly, shipping, or thermal shock/cycling. The o bserved increase in alloy ductility by Ag additions is attributed to a substantial refinement of the solidification microstructure.