A Control-Chart-Based Method for Solder Joint Crack Detection

Many researchers have used different failure criteria in published solder joint reliability studies. Since the reported timeto-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 determine which failure criterion could 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 500 V, 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-based method is very similar to that when the IPC9701A failure criterion is used. Both methods detected failure much earlier than the failure criterion of a resistance threshold of 500 V 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. The duration of the crack stage depends on the severity of the test conditions. It is recommend the control-chart-based method be used as the failure criterion because it not only monitors the average of resistance, but also monitors the dispersion of resistance in each thermal cycle