Light emitting diodes (LEDs) are already familiar for use as lighting sources in various electronic devices and displays. LEDs have many advantages such as long life, low power consumption, and high reliability. In the future, as an alternative to fluorescent lighting, LEDs are certain to receive much attention. However, in components related to advanced LED packages or modules there has been an issue regarding the heat from the LED chip. The LED chip is still being developed for use in high-power devices which generate more heat. In this study, we investigate the variation of thermal resistance in LED modules embedded with thermal vias. Through the analysis of thermal resistance with various test vehicles, we obtained the concrete relationship between thermal resistance and the thermal via structure.
Following femtosecond (fs) laser pulse irradiation, the formation of a new type of low-spatial-frequency laser-induced periodic surface structure (LSFL) patterns, namely, omnidirectional LSFLs (OD-LSFLs) with the periodic ordering of their orientations, are investigated on Ni in this Letter. Using a liquid crystal polymer patterned depolarizer, we periodically rotate the polarization of fs laser pulses across the laser spot and create OD-LSFLs by raster scanning fs laser pulses. We also show that the period of the OD-LSFL orientation rotation can be controlled with the defocused distance, and OD-LSFLs can significantly expand the viewing angle of the structural colors in the azimuthal direction without noticeable color degradations.
Microstructure and hardness property of AgCd alloy internally oxided at 973K for 1 h - 24 h with O2 atmosphere of 3 atm was investigated. Band typed CdO phase was formed at grain boundaries, and particle typed CdO phase was formed at grain interior. In this alloy, it was found that oxygen adsorpted at surface diffuses to interior through grain boundaries, and it subsequently diffuses into grain interior during internal oxidation. No Ag exduation was found in this alloy. The thickness of oxidized layer increased with increasing holding time at given temperature. Hardness of the oxidation zone was 125 ± 5 Hv, which value is higher two times than that of the oxidation free zone. The higher hardness of oxided region than the oxidation free zone was attributed to the dispersion strengthening by CdO particles.
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