Thermal and moisture degradation in SSL system

Currently, most of the SSL research on SSL's failure is based on thermal induced failure. This is insufficient as application such as outdoor street lighting and automotive headlights are exposed to both high humidity and temperature. This will induced additional hygroscopic stress which may induced further degradation of the SSL system. However, there is only limited studies in the literature that investigates the effect of the degradation of SSL's life due to the hygroscopic stress degradation. This is because the current thermal moisture methodology for computing combine hygroscopic and thermal stress is only limited to linear elastic analysis where linear superposition is value. In this research, numerical analysis capable of modeling nonlinear thermal and hygroscopic effect has been developed. Using this method, this paper will compare the failure of light emitting diode due to thermal mechanical with or without the additional hygroscopic stresses. This is also important since accelerated testing using increase temperature may not be sufficient due to the very narrow temperature range that it can be used to perform a valid test. Hence, by understand hygroscopic stresses induced failure in solder layer; it may enable another parameter to increases the accelerated factors during these tests.