Comparison of LED package reliability under thermal cycling and thermal shock conditions by experimental testing and finite element simulation

Abstract

High power light emitting diodes (LEDs) have begun to play an important role in many illumination applications due to their excellent performance in terms of high efficiency, low power consumption, high reliability and long life. With the rapid development of the LED industry, the reliability is becoming essential for the large scale applications of LED devices, modules and systems. Generally the thermal cycling and thermal shock test are conducted for validation the reliability performance and exposure the potential design problems during the new packaging development. In this paper, the reliability performance of the typically LED package is evaluated by the accelerated stress test under thermal cycling and thermal shock conditions. The optical degradation and electrical parameters variation of the LED package are monitored during the experiments. The thermo-mechanical responses of the LED package under thermal cycling and thermal shock loadings are investigated by sequential coupling thermo-mechanical finite element modeling interoperated with nonlinear time and temperature dependence materials properties. The stress and strain behavior of the LED package especially of the gold wire is examined. The effects of thermal gradient in the LED package during the thermal cycling and thermal shock tests and the time and temperature dependent materials property of the silicone on the reliability performance of the LED package are investigated. The physical mechanisms of failure of LED package samples are analyzed by decapulation and optical microscopic detection method. These efforts are helpful for design of reliability for the high power LED packaging development.