Wetting properties of the Pb-free solder candidates of binary Sn-Zn (4.5, 9, 13.5, 90, 95 wt.% Zn) and ternary Sn-Zn-X systems (X – Al, Cu) in contact with various substrates were examined using the following variables: testing conditions (method, procedure, temperature), the type and amount of alloying elements, the type of flux as well as substrate material (Cu, Ni and laminates covered with either Sn or Ni/Au of 100 nm thickness). Two testing methods were applied: 1) wetting balance method and 2) sessile drop method coupled with contact heating procedure. In order to avoid Zn evaporation, all tests were performed in air with a flux at the temperature of 230-450°C.After wettability tests, the solder/substrate couples were used for structural characterization of interfaces by optical and scanning electron microscopy coupled with EDS analysis. The results obtained show a good agreement of the contact angle measurements done by two selected methods, i.e. the test method does not affect the contact angle values if testing condition are the same. Moreover, independently on the type of examined substrates, the flux type presents a key factor for wetting properties of Zn-containing alloys. Therefore, contrary to the solder alloys of SAC family, the SnZn and SnZnX alloys require more aggressive fluxes. If the flux is properly selected, Zn-containing alloys exhibit wetting properties comparable to those of SAC solders.
Acknowledgements
The research has been done in frame of COST MP0602 Action on Advanced Solder Materials for High Temperature Application. Financial support from the Ministry of Science and Higher Education of Poland is also acknowledged.