Y. Miyazawa et T. Ariga, Influences of aging treatment on microstructure and hardness of Sn-(Ag, Bi, Zn) eutectic solder alloys, MATER TRANS, 42(5), 2001, pp. 776-782
The microstructural change and hardness, which strongly influence the life
of soldered joints, were investigated by microstructure observations for th
ree typical promising alloys as Pb free solder, Sn-3.5 mass%Ag, Sn-8.8 mass
%Zn and Sn-57 mass% Bi alloys. and Sn-38.1 mass%Pb for comparison. The sold
ers of Sn-Ag and Sn-Zn eutectic alloys and Sn-Pb eutectic alloy were found
to age-soften during storage at 25-100 degreesC (298-373 K). It seems that
the coarsening of the microstructure and re-crystallization caused the age-
softening of the Sn-Ag and Sn-Zn alloys. The hardness of the Sn-Bi eutectic
alloy hardly changed during storage at 25-100 degreesC (298-373 K) in spit
e of remarkable microstructural coarsening. It seems that the hardening eff
ect caused by solid-solution hardening of Pi into Sn-rich solution and/or t
he precipitation hardening of Bi in the Sn-rich solution compensated the so
ftening caused by the remarkable microstructural coarsening of the Sn-Bi al
loy.