Solder Creep-Fatigue Interactions With Flexible Leaded Parts

[+] Author and Article Information
R. G. Ross, L. C. Wen, G. R. Mon, E. Jetter

Jet Propulsion Laboratory, Pasadena, CA 91109

J. Electron. Packag 114(2), 185-192 (Jun 01, 1992) (8 pages) doi:10.1115/1.2906416 History: Received August 01, 1991; Online April 28, 2008


With flexible leaded parts, the solder-joint failure process involves a complex interplay of creep and fatigue mechanisms. To better understand the role of creep in typical multi-hour cyclic loading conditions, a specialized non-linear finite-element creep simulation computer program has been formulated. The numerical algorithm includes the complete part-lead-solder-PWB system, accounting for strain-rate dependence of creep on applied stress and temperature, and the role of the part-lead dimensions and flexibility that determine the total creep deflection (solder strain range) during stress relaxation. The computer program has been used to explore the effects of various solder creep-fatigue parameters such as lead height and stiffness, thermal-cycle test profile, and part/board differential thermal expansion properties. One of the most interesting findings is the strong presence of unidirectional creep-ratcheting that occurs during thermal cycling due to temperature dominated strain-rate effects. To corroborate the solder fatigue model predictions, a number of carefully controlled thermal-cycle tests have been conducted using special bimetallic test boards.

Copyright © 1992 by The American Society of Mechanical Engineers
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