During soldering, high temperature interaction between a liquid solder and a material to be joint is accompanied with diffusion and phase transformation, both in the solder and at the interface. Finally, these processes lead to the formation of solder joint structure responsible for utility properties of final products such as corrosion resistance.
This research is focused on structural characterization of Sn-Zn-X/Cu couples (X – alloying addition of Ag or Cu) formed at 230°C between liquid Sn-based Pb-free solders and polished Cu substrates at 230°C for 5 min contact time.
The structure and chemistry of Sn-Zn-X/Cu couples were examined under a wide range of magnifications using light microscopy and scanning electron microscopy coupled with phase identification by EDS analysis in order to understand the role of the type and amount of alloying additions on interface structure and properties.
Accelerated corrosive tests of Sn-Zn-X/Cu couples were performed by means of electrochemical methods in the sodium sulphate solution (VI) Na2SO4of about 0.5 M concentration and next leavened to pH=2 by means of concentrated H2SO4acid and the main electrochemical parameters were determined such as the corrosion current (icorr [mA/cm2]) and Tafel's coefficients, both cathodic (bc [V/dec]) and anodic (ba [V/dec]) ones.
The results are discussed taking into account the role of alloying additions on structure and chemistry of interfaces, including the presence of structural discontinuities and the formation of intermetallic compounds both in the solder and at the interface.
Acknowledgments.
The research was performed in frame of EU COST ACTION MP0602 with financial support from the Ministry of Science and Higher Education of Poland.