Thermal transient measurement and modelling of a power cycled flip-chip LED module

Reliability testing has become a major focus for light emitting diode (LED) systems to predict its lifetime. One common type of testing methods, which was investigated in this study, is the supply switching test (SST), also called power cycle test. In this paper, reliability testing was used to analyze failure modes appearing within a flip chip LED module. The characterization of the LED module was done by thermal transient measurement and radioscopic imaging. It was shown that the thermal transient measurement was sensitive enough to observe structural changes induced by the SST. To supply the experiments, a finite volume simulation of the LED module was carried out to analyze which physical structures in the LED module caused the changes in the measurements. Furthermore, the simulation enabled the thermal heat path to be visualized within the module via isotherms. To understand the changes seen in the measurement, two different failure type scenarios were implemented in the simulation. The effects of solder joint degradation and delamination in the printed circuit board (PCB) were analyzed and depicted by their isotherms. Conclusions about the failure roots could be drawn by comparing thermal transient measurements of a stressed LED module with its corresponding simulation of an integrated failure.