Degradation of silicone in white LEDs during device operation: A finite element approach to product reliability prediction
Silicone, which is a very common material for Light Emitting Diode (LED) packaging components like lens, casting and housing, undergoes degradation during high temperature and current operation. Indeed, electrical and optical losses cause material shrinkage and hardening, inducing mechanical stress within the LED assembly, which can end up into crack formation in silicone. In order to evaluate the reliability of LED package regarding the silicone crack, a degradation material model is developed, which is based on the experimental investigation of the mechanical properties of silicone during degradation. A coupled thermo-optical model is used for the calculation of the temperature distribution in the device during steady-state operation. The crack reliability model, which is build combining the stress simulation results based on finite element approach and the visual inspection of the corresponding LED package during steady-state operation, is used to estimate the package lifetime depending on the operation conditions.