Reliability of visible GaN LEDs in plastic package

This work presents the results of extensive high-current accelerated aging tests carried out on blue and white InGaN/GaN LEDs packaged with the usual epoxy encapsulation (lamps) in order to investigate both package degradation and chip-related failure modes. As a result, the following package related failure modes were identified: (i) in blue lamps, high current levels and high junction temperatures, induce degradation of the epoxy material in contact with the heated device surface, leading to the formation of an opaque layer on the device surface; (ii) in white lamps tested at high current levels converting phosphors degradation has been observed, suggesting degradation of their white light converting efficiency; (iii) contact resistance increasing induced by die attach degradation has been observed in both white and blue lamps, finally (iv) plastic carbonization has been observed along the wire bonding suggesting power- or temperature-related cover plastic degradation that can contribute to the observed optical power degradation