Many researchers have used different failure criteria in the published solder joint reliability studies. Since the reported time-to-failure would be different if different failure criteria were used, it would be difficult to compare the reported reliability life of solder joints from one study to another. The purpose of this study is to evaluate the effect of failure criteria on the reported thermal fatigue life and find out which failure criterion can detect failure sooner. First, the application of the control-chart based method in a thermal cycling reliability study is described. The reported time-to-failure data were then compared based on four different failure criteria: a control-chart based method, a 20% resistance increase from IPC-9701A, a resistance threshold of 500Ω, and an infinite resistance. Over 3.5 GB resistance data measured by data loggers from a low-silver solder joint reliability study were analyzed. The results show that estimated time-to-failure based on the control-chart method is very similar to that when the IPC-9701A failure criterion is used. Both methods detected failure much earlier than the failure criterion of a resistance threshold of 500Ω or an infinite resistance. A scientific explanation is made of why the 20% increase in IPC-9701A is a reasonable failure criterion and why the IPC-9701A and the control-chart based method produced similar results. Three different stages in resistance change were identified: stable, crack, and open. It is recommended that the control-chart based method be used as failure criterion because it not only monitors the average of resistance, but also monitors the dispersion of resistance in each thermal cycle over time.
Available at: http://works.bepress.com/pan/41/