Ji Wu and Michael Pecht
CALCE Electronic Products and Systems Center
University of Maryland
College Park, MD 20742
The lead-free movement, driven by both legislation and market forces, is expected to spread to the field of electrical connector manufacturing worldwide. Lead-free solders are expected to replace tin-lead solders as contact finishes for mechanical separable connections. Determining the electrical characteristics of lead-free solder finishes, assessing the reliability of lead-free solder coatings while comparing their behavior to that of current tin-lead solder are necessary before implementing this material change in electronic separable connectors. Tin-lead solder alloys are the most commonly used non-noble contact finish materials in the electronic industry due to their low cost and ease of manufacturing. Since surface oxides of tin-lead alloys can be easily displaced by the mechanical deformation and wiping action of contact surfaces, low contact resistance can be easily obtained. However, a limiting factor in the use of tin-lead solder alloys separable connections is their susceptibility to fretting corrosion.
Similar to tin-lead alloys, lead-free alloys are also expected to show susceptibility to fretting corrosion due to their tin content. In this study, two lead-free alloys, tin silver- copper and tin-copper, as contact coatings, were investigated and compared with eutectic tin-lead alloy for their fretting corrosive behavior. An automatic contact resistance probe developed at the CALCE center at the University of Maryland was used to measure the contact resistance and introduce fretting corrosion. The effects on fretting corrosion at different temperatures and fretting amplitudes were examined in this study. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) surface analysis were performed to determine the coating oxidation and wear-out phenomena after fretting corrosion.
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