Microelectrochemical corrosion studies on lead-free Sn-Ag-Cu solder alloys

Oliver von Trzebiatowski ,  Jolanta Janczak ,  Thomas Suter 

Empa, Materials Technology and Research (Empa), Überlandstrasse 129, Dübendorf 8600, Switzerland

Abstract

New solder alloys are being developed for electronic devices in order to replace traditional solder materials that contain harmful lead. A research group of the Empa is involved in developing new Sn-Ag-Cu based solder alloys. Particles are specially added in order to enhance the joint mechanical performance. The preliminary results show that there is a great potential for improvement of the mechanical properties of Sn-based solders especially of the creep resistance by the particle reinforcement. Whereas intensive studies focused on the physical, electrical and mechanical behaviour, no corrosion data are available at moment. Thus, the goal of this work is to characterize the corrosion behaviour of lead-free Sn-3.8Ag-0.8Cu alloys with and without different reinforcing particles. Electrochemical corrosion measurements in 1 M NaCl solution showed similar pitting potentials for all alloys, at around -430 mV (SCE). However, a quite strong variation of the corrosion potential and the passive current was observed. Although the new solder alloys show heterogeneous microstructures with reinforcing particles, intermetallic inclusions and pores, the corrosion behaviour is improved compared to the Pb-Sn standard solders. In order to further enhance the corrosion stability, microelectrochemical measurements are being performed to localize pitting initiation sites. It is assumed, that compositional and structural heterogeneities, like pores or particles trigger the onset of localize corrosion. An electrochemical microcell using microcapillaries filled with electrolyte is used to perform electrochemical tests on structures down to 0.5 μm. Preliminary microelectrochemical experiments on pore and particle free zones revealed a significant better corrosion behavior. The pitting potentials were shifted several 100 mV to higher values. At the moment we are trying to clarify the detrimental influence of pores and particles on the corrosion behaviour of Sn-Ag-Cu solder alloys.

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Presentation: oral at E-MRS Fall Meeting 2005, Symposium H, by Oliver von Trzebiatowski
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-06-14 14:21
Revised:   2009-06-07 00:44
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