We have recently fabricated high-power near-ultraviolet light-emitting diodes (LED) on ceramic packages without sub-mounts, using a direct flip-chip bonding (DFCB) technique. In the ceramic packages, pad electrodes of 0.35 mm LED chips were bonded onto metalized packages using metal stud bumps. The cross-sectional microstructures of the chip/bump/ceramic of both non-degraded and degraded DFCB packages were investigated using a scanning electron microscope with energy dispersive x-ray spectroscopy. We have confirmed the presence of firm flip-chip interfaces between the stud bumps and the DFCB packages, and failure at the p-type contact layer/p-electrode interface. In addition, x-ray computed tomography (CT) and ultrasonic scanning were carried out as non-destructive inspection methods. The clacks at the interfaces of the DFCB package could be detected by ultrasonic scanning inspection, but not by x-ray CT, due to the lack of resolution.
