The study of thermal properties and thermal resistant behaviors of siloxane-modified LED transparent encapsulant

In this study, we selected triglycidyl ether terminated Phenylmethylsiloxnae-co-dimethylsiloxne (GT-1000) which was compatible with the diglycidyl ether of bisphenol A epoxy (DER331) to partial replace the epoxy resin and was cured by liquid anhydride (MHHPA). We also synthesized 5, 5´-(1, 1, 3, 3-tetramethyl disiloxane-1, 3-dilyl)-bis-norborane-2, 3-dicarboxylic anhydride (Al) as a co-curing agent to cure DER331 with MHHPA. DER331 and Al and MHHPA were dissolved in equivalent ratio of 1/0.2/0.8 and cured. The Tg of the siloxane dianhydride co-cured composition is 150.7deg.C and the increase of yellow index (DeltaYI) was only 0.72 after 110deg.C 1000 hours storage test. In the mean time, we also incorporated the siloxane structure into the main chains of LED encapsulant through the tri-epoxy groups GT-1000. When GT-1000 was added 0.2eq, the Tg of the siloxane epoxy cured composition was 120.0deg.C and the coefficient of thermal expansion (CTE) was 87.07ppm/deg.C. The TMA result infers that the tri-functionality of GT-1000 can raise the crosslink density and enhance thermal mechanical property. The DeltaYI of 0.2eq GT-1000 was 1.51 after 110deg.C 2000 hours test. The high thermal storage results reveal that both of GT-1000 and Al are effective methods for thermal resistant needs. Moreover, the DeltaYI of 0.2eq of GT-1000 was 0.07 and DER331/MHHPA was 1.49 after IR-reflow at 260deg.C for 10 seconds. The results reconfirm the siloxane-modified epoxy encapsulants present excellent thermal resistant properties for high performance LED applications.