Development of fluxes for selected Sn-Cu based lead-free solders

Abstract

Fluxes which are suitable for Sn-0.8Cu and Sn-0.8Cu-3Bi lead-free solder have been investigated in this paper. Fluxes were evaluated in spread test by measuring the spread areas of solders on copper substrate. The effect of flux on the intermetallic compounds (IMCs) at the interface between solder and copper substrate was studied through analyzing the morphology of IMCs of interface by electron probe microanalysis (EPMA). Results show that both NST flux (flux consists of natural rosin and SnCl/sub 2/) and SAT flux (by adding SnCl/sub 2/ into stearic acid ) can greatly improve the wetting ability of Sn-Cu based lead-free solder on copper substrate. SnCl/sub 2/ in flux influences the morphology and thickness of IMCs at the interface of solder/Cu joint. The concentration of SnCl/sub 2/ contained in fluxes also affects the spread areas of solder on copper plate.