The joint strength and microstructure of fluxless Au/Sn solders in InP-based laser-diode packages after thermal-aging testing were studied experimentally and numerically. Specimens were aged at 150°C for up to 64 days. The joint strength decreased as aging time increased. The microstructure and fracture surface of the 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 the aging time increased. Finite-element method (FEM) simulations of joint strength were in good agreement with experimental measurements. Both experimental and numerical results indicate that the enlargement of the initial voids and an increase in the number of voids, caused by stress concentration as the aging period increased, resulted in the weakness of joint strength. The effect of temperature-cycling testing on the power variation of the InP laser diodes using fluxless Au/Sn solders was also studied. It was shown that the laser diodes operated in the stable condition up to 500 cycles.
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.
The post-weld shift (PWS)-induced fiber-alignment shifts of fiber-ferrule clip (FFC) joints in butterfly laser packaging by using laser-welding techniques and a high-magnification, video-probe camera system were studied experimentally and numerically. The measured results show that the fiber shifts of FFC joints with a 5-µm gap between the clip and ferrule exhibited shifts less than that without a gap. This suggests that the 5-µm gap design may be more suitable for FFC joints in laser packaging. The experimental measurements of fiber shifts in FFC joints were in reasonable agreement with the numerical calculations of the finite-element method (FEM) analysis. The major fiber-shift formation mechanisms of FFC joints in the laser-welding process may come from the mismatch of the thermal expansion coefficient, the solidification shrinkage, and the residual stresses within the FFC joint, but solidification shrinkage is the dominant cause. This study demonstrates that the FEM is an effective method for predicting PWS-induced fiber-alignment shifts in lasermodule packaging.
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