Thermal and mechanical stability of soldering QFP with Sn-Bi-Ag lead-free alloy
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Thermal stability of the circuit boards with a quad flat package (QFP) soldered with Sn-58wt%Bi-(0, 0.5 and 1.0) wt% Ag and their microstructural features were evaluated. The addition of 1.0 wt% Ag causes the formation of large primary Ag/sub 3/Sn precipitates in the solder while no primary Ag/sub 3/Sn is found in Sn-57Bi-0.5Ag. Thermo-Calc calculation indicates that the lowest limit content for the formation of primary Ag/sub 3/Sn is about 0.8 wt%. Heat-exposure below 100/spl deg/C has no serious degradation on the joint structure for all solders. Heat-exposure at 125/spl deg/C caused serious degradation in joint strength for all alloys. The contamination of Pb from Sn-Pb surface plating on the components reduces the interface tolerance by forming ternary Sn-Pb-Bi phase melting at low temperature. Thermal fatigue between -20 and 80/spl deg/C does not have any significant influence on joint structure.
[1] K. S. Kim,et al. Effects of cooling speed on microstructure and tensile properties of Sn–Ag–Cu alloys , 2002 .
[2] Hyuck-Mo Lee,et al. A thermodynamic study of phase equilibria in the Sn-Bi-Pb solder system , 1998 .
[3] Sungho Jin,et al. Significantly Improved Mechanical Properties of Bi- Sn Solder Alloys by Ag- Doping , 1997 .