Degradation of the die attach layer in chip-on-board packaged light-emitting diodes during temperature cycling

A noninvasive approach is used to study the die attach layer of chip-on-board (COB) packaged light-emitting-diodes (LEDs) after temperature cycling. Failure analysis of the die attach layer is performed by monitoring the changes in the thermal resistances in differential structure function curves of the COB. The results suggest that delamination occurs at the interface between the chip and die attach and fatigue voids appear in the die attach layer, which is consistent with the findings of X-ray, scanning electron microscopy and C-mode scanning acoustic microscopy analyses. Various temperature cycling experiments are carried out to apply cycling temperature stress to the LEDs to examine the influences of junction temperature and power on device failure.