Solid state lighting technology has achieved great progress especially in white light emitting diodes (LEDs). The LEDs exhibit many advantages such as long lifetime and high light efficiency. Moreover, they are environmental friendly compared to the conventional light sources. However, the key issue in widespread application of white LEDs is packaging technology. High light efficiency requires the white LEDs endure a high working temperature which will accelerate the thermal aging of packaging materials. Traditionally, epoxy resins are used in white LED packaging. However, under long time exposing to high temperature, epoxy resin will result in an obvious discoloration and yellowing phenomenon which will adversely affect the light efficiency of white LEDs. So the rapid developme...[ Read more ]

Solid state lighting technology has achieved great progress especially in white light emitting diodes (LEDs). The LEDs exhibit many advantages such as long lifetime and high light efficiency. Moreover, they are environmental friendly compared to the conventional light sources. However, the key issue in widespread application of white LEDs is packaging technology. High light efficiency requires the white LEDs endure a high working temperature which will accelerate the thermal aging of packaging materials. Traditionally, epoxy resins are used in white LED packaging. However, under long time exposing to high temperature, epoxy resin will result in an obvious discoloration and yellowing phenomenon which will adversely affect the light efficiency of white LEDs. So the rapid development of white LED technology requires the packaging materials with better performance in thermal resistance and optical transmission.

Compared to epoxy resin, silicone is a kind of novel packaging material for white LEDs. Its excellent performances including high light transmittance, low water absorption and non-discoloring behavior attract numerous attentions of white LED manufactures. What's more, the good thermal stability property makes it suitable even in high-power LED application. However, there are still some reliability issues of silicone application in white LED packaging, such as fracture, delamination and chemical corrosion. Thus the evaluation and selection of silicone for LED packaging are very important.

In this study, some major failure modes of silicone in white LED packaging are discussed. To better understand the performance of silicone, a series of test methods are set up to evaluate its mechanical, thermal and chemical properties. Corresponding simulation models are used to verify the test results. Some common properties such as transmittance and infrared spectrum are also demonstrated and studied in this paper. Finally, a practical methodology has been proposed to serve as guideline for silicon selection in white LED packaging.