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The joint strength and fracture surface of Pb/Sn and Au/Sn solders in laserdiode packages after thermal-aging testing were studied experimentally. Specimens were aged at 150°C for up to 49 days. The joint strength decreased as aging time increased. The microstructure and fracture surface of the Pb/Sn and Au/Sn solder joints showed that the joint strength decrease was caused by both the enlargement of the initial voids and an increase in the number of voids as aging time increased. The formation of Kirkendall voids with intermetallic-compound (IMC) growth of the Pn/Sn solder as aging time increased was also a possible mechanism for the joint-strength reduction. Finite-element method (FEM) simulations were performed on the joint-strength estimation of Pb/Sn and Au/Sn solders in thermal-aging tests. The coupled thermal-elasticity-plasticity model was used to simulate distributions of the thermal and residual stresses, creep deformation, and joint-strength variations in the solder joints under various thermal-aging tests. Simulation results were in good agreement with the experimental measurements that the solder-joint strength decreased as aging time increased. The result suggests that the FEM is an effective method for analyzing and predicting the solder-joint strength in laserdiode packages.

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A sulphate-activated mechanism is proposed to describe the growth of bamboo-like carbon nanotubes (CNTs) over copper catalysts using chemical vapour deposition with helium-diluted ethylene. Sulphate-assisted copper catalysts afford a high-yield growth of bamboo-like CNTs at a mild temperature, 800 °C; however, non-sulphate-assisted copper catalysts, e.g., copper acetate and copper nitrate prepared catalysts, were inert to CNT growth and only gave amorphous carbons (a-C) surrounding copper nanoparticles under the same conditions. Nevertheless, the addition of sulphate ions in the preparation step for the two inert catalysts can activate their abilities for CNT growth with remarkable yields. Furthermore, Raman spectra analysis demonstrates a linear dependence between the concentration of sulphate ions in copper catalysts and the ratio of CNT-a-C in the as-grown carbon soot. The sulphate-activated effect on CNT growth over copper catalysts could be related to a three-way interaction of sulphate ions, copper nanoparticles and support. In situ TEM images of an as-grown CNT irradiated by electron beams without the inlet of carbon sources reveal a new pathway of carbon diffusion through the bulk of copper nanoparticles and an enlarged inner-wall thickness of the on-site CNT. This carbon diffusion model over copper catalysts can provide new insights into the CNT growth mechanism over non-magnetic metal catalysts.

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In the exposure process of photolithography, a free-form lens is designed and fabricated for UV-LED (Ultraviolet Light-Emitting Diode). Thin film metallic glasses (TFMG) are adopted as UV reflection layers to enhance the irradiance and uniformity. The Polydimethylsiloxane (PDMS) with high transmittance is used as the lens material. The 3-D fast printing is attempted to make the mold of the lens. The results show that the average irradiance can be enhanced by 6.5~6.7%, and high uniformity of 85~86% can be obtained. Exposure on commercial thick photoresist using this UV-LED system shows 3~5% dimensional deviation, lower than the 6~8% deviation for commercial mercury lamp system. This current system shows promising potential to replace the conventional mercury exposure systems.