Failure Analysis of Open Circuit for the LEDs of Epoxy Resin Encapsulation

The light emitting diodes (LEDs) were easy to fail due to open circuit after reflow soldering and during use. By microscope, transistor graphic instrument, C-mode scanning acoustic microscope (C-SAM), and scanning electron microscope (SEM), the causes of open circuit were mainly ascribed to the separation between the silver paste, chip electrode and lead frame and the crack of the silver paste. According to the C-SAM and Differential Scanning Calorimeter (DSC), it could be found that the epoxy resin encapsulation contains water vapor. Due to the rapid volatilization of water vapor during the reflow process, the bonding interface of the encapsulation, lead frame, the chip electrode and silver paste will cause large internal stress. It is able to lead the separation between the silver paste, chip electrode and lead frame and the crack of the silver paste.