Failure-mechanism analysis for vertical high-power LEDs under external pressure

This paper presents the factors that have the greatest influence on the mechanical strength of high-power LEDs, including bonding wire modes, pressure angles, and falling speeds of the indenter. Results show that the LED strength is greatly impacted by the wire bonding modes. Two main failure modes are identified: the silicone-lens crack caused by the stress concentration and the open-circuit failure induced by fractures in the bonding wire. The fractures are all located at the top of the LED chip bond pad. The bonding wire fractures are localized in a necking in the heat-affected zone (HAZ) or formed along the edge of bonds. It is confirmed that the wire bonding modes impact the mechanical strength of the vertical LEDs. It is hoped that the findings of our work will guide further work to determine and improve the modes of bonding wires, as well as the LED installation.