Thermal resistant property of siloxane-modified epoxy compositions designed for long-term and high temperature storage was investigated. In this study, we developed two siloxane-modified epoxy compositions to improve the thermal stability of current epoxy encapsulants. One composition contained silicone epoxy, and the other one was cyclic aliphatic siloxane dianhydride.
We selected triglycidyl ether terminated Phenylmethylsiloxnae-co-dimethylsiloxne (GT-1000), which was compatible with the diglycidyl ether of bisphenol A epoxy (Epon-828), to partial replaced the epoxy resin and was cured by liquid anhydride (MHHPA). In the mean time, we also synthesized 5, 5'-(1, 1, 3, 3-tetramethyl disiloxane-1, 3-dilyl)-bis-norborane-2, 3-dicarboxylic anhydride (A1) as a co-curing agent to cure Epon-828.
The thermal resistance was studied by measuring the increase of yellow index (ΔYI) after thermal treatments. In 110 °C storage experiment for 1000 h, the ΔYI of GT-1000 0.2 equivalent was 1.51, whereas Epon-828/MHHPA (Comp 1) was 6.74. Moreover, The ΔYI of the composition with higher equivalent GT-1000 was only 2.15 after 2000 hours thermal aging. In the cyclic aliphatic siloxane dianhydride co-curing compositions, when A1 was 0.05 and 0.1 equivalent, the ΔYI was 2.28 and 0.72 after 1000 h, respectively. Compared with Comp 1, both GT-1000 and A1 were effective for thermal resistance.
In IR-reflow test, the ΔYI of GT-1000/Epon-828/MHHPA= 0.5/0.5/1 was 0.65 and that of Epon-828/MHHPA was 1.49 after 260 °C for 10 seconds. The results revealed that either the siloxane-modified epoxy or siloxane-modified curing agent had excellent thermal resistant property for high performance LED applications.