Quantification of silicone degradation for LED packages using finite element analysis

• We assumed that silicone degrades rapidly as its creep strain rate increases.
• We developed a lumen depreciation model based on creep strain rates.
• The model was applied for an engineering decision.

Light emitting diodes (LEDs) have been widely used for illumination because of their electrical efficiency and reliability. Their long lumen maintenance is not easy to be evaluated when it is compared with their efficiency because the reliability test is a time consuming task. LEDs are required to undergo many reliability tests and sometimes create failures induced by high thermo-mechanical stresses. One of the major failure modes is the lens or encapsulant crack. Therefore, the lens and encapsulant materials are required to contain high temperature stability as well as high optical properties. One of the materials for LEDs is polydimethylsiloxane (PDMS) which can have a wide range of refractive indices from 1.40 to 1.57. In this investigation, silicone degradation was quantitatively evaluated using finite element analysis. The finite element simulation showed that thermal–mechanical stress in volume of interest (VOI). As PDMS has viscoelastic properties, strain rates induced by the viscosity effect were focused and computed. Furthermore, the correlation between the strain rates and lumen depreciation was discovered, which leads to a lumen depreciation model based on the strain rates. Using the model, the tendency of the lumen maintenance for LED packages could be estimated using numerical analysis without time-consuming tests.