Journal of SMT Article


Authors: Ji Wu and Michael Pecht
Company: University of Maryland - CALCE
Date Published: 4/1/2002   Volume: 15-2

Abstract: The lead-free movement, driven by both legislation and market forces, is expected to spread to the field of electrical connector manufacturing. Lead-free solders are expected to replace tin-lead solder as contact finishes for mechanical separable connections. Determining the electrical characteristics of lead-free solder finishes and comparing their behavior to that of current tin-lead solders is necessary for assessing of the reliability of lead-free electronic separable connectors.

In this study, the contact resistance versus contact force characteristics of tin-silver-copper (SnAgCu) and tin-lead (SnPb) solder separable contact interfaces were measured and compared. An automatic contact resistance probe developed at the CALCE center was used to measure the contact resistance. The effect on contact resistance of different aging conditions, including mixed flowing gas, steam, and dry heat aging was examined. Energy dispersive spectroscopy (EDS) surface analysis was performed on selected samples to determine the nature of the surface films. Overall, the tin-silver-copper lead-free solders tested in this study have similar contact resistance behavior when compared with tin-lead eutectic solder for all aging conditions. The MFG aging test and EDS analysis results show that the tin-silver-copper lead-free solder coating is not sensitive to corrosive gases like chlorine and hydrogen sulfide.

Key words: Lead-free solder, contact resistance, aging.

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