Lead-free low melting solder with improved mechanical properties and articles bonded therewith

摘要

We have made the surprising discovery that small amounts of Ag below 1% by weight are effective in making Bi-Sn alloys less strain-rate sensitive without deleteriously affecting the melting character of the alloy. A Pb-free solder composition comprising at least 40%by weight Bi, between 40% and 60% Sn, and between 0.05 and 1% Ag is effective to increase the total elongation of the solder by at least 20% under the same processing conditions. Moreover the solder is free of undesirable Ag-containing phases with a melting point in excess of the 183 DEG C melting point of the Pb-Sn binary eutectic alloy. In a preferred embodiment, the composition comprises 54.75%Bi, 45%Sn, and 0.25%Ag.