Simulated thermal cycling of surface components on FR4 printed wiring boards using standard tin-lead solder

Thermal cycling is used as a diagnostic test for electronic equipment. It is particularly severe on solder joints that are under both compressive and tensile strain during a cycle as a result of differential thermal expansion. The electronics industry document IPC-SM-785 addresses this problem and provides means whereby joint failure can be predicted as a function of the type and number of cycles used. The method can be applied to both non-compliant ceramic chips and compliant packages on FR4 board. This paper describes the applicability of SM-785 for both compliant and non-compliant packages. Due to the change in metallurgy of solder at temperatures approaching - 20degreesC, the approach is restricted to temperatures where near eutectic tin-lead solder is in its non-elastic form. A new approach will be needed when lead-free joining becomes mandatory. (C) 2004 Kluwer Academic Publishers.