Thermal fatigue life and reliability evaluation of die attachment layer of high power LED under thermal cycling conditions

摘要

Power conservation is a very important aspect of modern-day technology. With its long life and low energy consumption, the high power light emitting diode (HP LED) has become very popular for lighting purposes. The die attachment layer is an important component of an HP LED package that is susceptible to thermal fatigue failure and therefore affects the reliability of the HP LED itself. This study uses finite element method (FEM) to simulate and analyze the mechanical behavior of an HP LED die attachment layer under thermal cycling conditions. By using the numerical results of FEM as the input for the Coffin-Manson relationship, one can predict the thermal fatigue life of the LED. It is worth noting that past studies are mostly limited to finding a fixed value for the fatigue life of a package, which cannot truly reflect the discrete qualities of real life testing. Furthermore, they cannot provide vital information such as mean time to failure (MTTF) and the failure rate of the HP LED. With this in mind, this study considers uncertainties of both geometric dimensions and material properties of the die attachment layer, regarding them as random variables, which can be simulated by the Monte-Carlo method. The sample data is then applied to the FEM analysis for evaluating fatigue life of the LED package. By using the Anderson-Darling test and probability plot, one can find the probability distribution of the fatigue life as well as information such as MTTF and failure rate of the LED package.