In this paper, in order to develop a low silver content lead-free solder with
good overall properties, a newly designed solder alloys of
Sn-0.3Ag-0.7Cu-20Bi-xCe type, with addition of varying amounts of rare earth
Ce (0.05 mass%, 0.1 mass% and 0.2 mass%) were studied. The melting
temperature of Sn-0.3Ag- 0.7Cu can be decreased substantially through
addition of 20 mass% Bi; while the segregation of Bi element in the
microstructure of the as-cast alloys can be relieved by micro-alloying with
trace amount of rare earth Ce. Besides, aging treatments (160?C held for 6 h)
of these solder alloys imply that appropriate amount of Ce addition can not
only depress the diffusion induced aggregation of Bi in the microstructure
but promote the homogenization during annealing. Compared with Bi-free
Sn-0.3Ag-0.7Cu solder, Sn-0.3Ag-0.7Cu- 20Bi exhibits better wettability. More
excitingly, the wetting property of Sn-0.3Ag-0.7Cu-20Bi can be further
improved by doping little amounts of Ce, especially 0.5 mass%, in which case
the spreading area of the solder can be increased to the largest extent. On
the whole, the present study reveals that Sn-0.3Ag-0.7Cu- 20Bi-xCe
(x=0.05-0.1) is a promising lead-free solder candidate considering the
microstructure, melting temperature and wetting properties.