The successful wide application of LED lighting in general lighting market requires reduction in product cost, among which, LED packaging cost is proved to be the majority. Apparently, direct decline production expense on package can efficiently reduce the production cost. Besides, LED luminous flux increase is another way to reach the similar target. In this way, thermal management in LED packaging should be considered as to adjust luminous performance of LED. Lower junction temperature can result in higher luminous flux, especially for high power LED. Considering all the structures, die attach adhesive (DAA) is proved to have great influence on heat dissipation in LED packaging. Therefore, in order to enhance thermal dissipation, a good method is to increase the thermal conduc...[ Read more ]

The successful wide application of LED lighting in general lighting market requires reduction in product cost, among which, LED packaging cost is proved to be the majority. Apparently, direct decline production expense on package can efficiently reduce the production cost. Besides, LED luminous flux increase is another way to reach the similar target. In this way, thermal management in LED packaging should be considered as to adjust luminous performance of LED. Lower junction temperature can result in higher luminous flux, especially for high power LED. Considering all the structures, die attach adhesive (DAA) is proved to have great influence on heat dissipation in LED packaging. Therefore, in order to enhance thermal dissipation, a good method is to increase the thermal conductivity of DAA, which is exactly what we conducted in this thesis.

Specifically, multilayer graphene oxide (GO) was successfully synthesized and characterized. After adding GO into silicone DAA, the transmittance and die shear strength of the mixture were comparable with origins. The thermal conductivity performance was characterized by 3ω method and laser flash method. The former experimental results showed big deviations of the local thermal conductivity between different test places. The average results indicate there was a 66% increase in local thermal conductivity of GO-silicone DAA (0.4 ωt% GO loading), comparing with the origins. However, the laser flash method results showed there was no apparent change in overall thermal conductivity when introducing GO. Nanoscale corrugation, crumpling, wrinkling and folding of GO were found in silicone matrix, which resulted in low K_eff^∗. GO tended to be perpendicular to the heat flux, resulting in no effort on the overall thermal conductivity of the composite.

In conclusion, there are three highlights for the thesis:

1) From the viewpoint of improving thermal management so as to reduce product cost, this study successfully build up the connection between LED packaging industry and market, which will be a great guidance for LED manufacturers;

2) This study discovered the critical K_eff^∗ for LED DAA, which was 0.5W/(m ∙ K). Lower thermal conductivity values generated bad thermal dissipation while higher values led to neglectable enhancement ;

3) Controlling GO orientation is crucial to improve the thermal conductivity of GO-silicone. It is practical to reach the critical K_eff^∗ in this way, so that the final lighting cost can be reduced;