Silicon-based system in packaging for light emitting diodes

Silicon-based packaging for light emitting diodes (LEDs) is the tendency of packaging for improving high-power LED performance. In this paper, a simple and high efficient wafer level packaging (WLP) based on silicon with TSV is proposed. Monte-Carlo ray-trace method is implemented to analyze the effect of the size of silicone lens on light extraction efficiency (LEE). The results show that LEE of hemisphere lens is higher than that of spherical segment lens. LEE increases with radius increasing and becomes stable when radius is above 1.2 mm due to the absorption of silicon for small part of light reflected back. Temperature distribution is uniform because of high thermal conductivity of copper and silicon; however, the mismatch of CTE between them causes high thermal stress which is alleviated in TSV when it partly filled with copper from analysis by three-dimensional finite element method. Six-axis micro-tester experiment shows the nominal shear strength of the silicone lens formed on a bare silicon with four TSVs improved 10% compared with that without TSVs. Wafer level packaging for LEDs is proposed. LEDs are encapsulated with silicon substrate with four TSVs filled with copper and other four TSVs filled with silicone. The processes of silicon substrate based on MEMS technology are used. TSV is filled with copper partly by two-step electroplating in order to avoid thinning of the substrate for blind vias. The phosphor conformal coating is implemented using capillary micro-channel, which can improve the angular color uniformity and consistency of WLP. The array of silicone lens using the mould method shows high coherence and few defects.