The Influence of the Cycle Frequency and Wave Shape on the Fatigue Life of Leaded Chip Carrier Printed Wiring Board Interconnections

This study employed different cycle frequencies, to determine the influence of cycle frequency on the fatigue life of leaded chip carrier printed wiring board (LCC/PWB) interconnections. Real LCC/PWB interconnections were mechanically cycled at 35°C or 125°C. The cycle frequency was varied by varying the ramp loading and unloading rates or by introducing hold times. Tests were run with equal hold times at the maximum and minimum displacements or only at the maximum displacement. The use of slower ramp cycling or the introduction in the hold times increased the plastic displacement and this decreased the fatigue life. This plastic displacement increase was corrected for, to unveil the underlying material response. The corrected data was similar to that observed in previous tests on simple, single, solder joints, where the plastic strain was kept constant while the cycle frequency was reduced. At 125°C there was a small influence of wave shape, with maximum displacement hold time tests showing the shortest fatigue lives and symmetric (maximum and minimum) hold time tests showing the longest fatigue lives. The fatigue lives of the tests run with ramp cycling were intermediate. This wave shape effect is relatively small, especially compared to the large overall influence of the cycle frequency.