Failure analysis and reliability reinforcement on gold wire in high-power COB-LED under current and thermal shock combined loading

We experimentally and theoretically investigated the failure mechanism of gold wire in high-power COB-LED (chip on board-light-emitting diode) under thermal shock and current combined loading. The samples with electric current were tested under thermal shock loading and the failure modes were analyzed. After the silicone resin dissolved, metallographic microscope was used to observe the failure position of gold wires, the fracture was found occur at the neck of the bond between the first solder joint and gold wire. In the simulation, the characteristics for three types of COB-LED gold wires were studied. We detected some unusual phenomenon such as plastic deformation in the part near the chip which experienced decline instead of rise under low temperature loading. It should, however, be on the rise according to regular speculate. Moreover, results indicate that the strain of failure position reaches 2% (the place where the maximum strain occur on device), which is in great accordance with the experimentally-achieved failure point position. The validity of qualitative and quantitative analysis for LED failure evaluation can be enhanced by the testification between numerical and experimental approach. It implies that we can improve the reliability of COB-LED by using the method which proposed in this work.