Maw-Tyan Sheen

Post-weld-shift in dual-in-line laser package

The post-weld-shift (PWS) effect in laser welding for a dual-in-line package (DIP) with fiber pigtail to semiconductor laser connection has been studied experimentally and numerically. Experimental results show that the PWS of an optical component welded by a dual-beam laser system deforms and the welded component rotates counterclockwise as the difference of the energies between two laser beams increases. This indicates that the PWS in laser packaging can be minimized by properly controlling the laser beam-to-beam energy balance. A thermal-plasticity coupled finite-element model (FEM) has been also carried out on the analysis of the effect of PWS in laser packaging. Numerical results show that a PWS in the DIP may be introduced from an unbalanced distribution of residual stresses introduced from the solidification shrinkage. A satisfactory agreement between the experimental results and FEM calculations suggests that the FEM may provide an effective method for predicting the PWS in laser welding technique for optoelectronic packaging.

A novel fiber alignment shift measurement and correction technique in laser-welded laser module packaging

A novel measurement and correction technique employing an ultra-high-precision laser displacement meter (LDM) with a 20-nm resolution to probe the postweld-shift (PWS)-induced fiber alignment shifts in laser-welded laser module packaging is presented. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded laser module packaging can be quantitatively determined by four parameters: the lateral position (r), the position angle (/spl alpha/), the swing angle (/spl theta/), and the tilt angle (/spl psi/). Further studies show that the deformation of the lateral shift and the position angle are the dominant mechanisms that determine the fiber alignment shifts induced by the PWS. This clearly indicates that the PWS can be quantitatively corrected timely by applying a single weld spot on the negative lateral shift and the position angle to compensate for the fiber alignment shifts. In comparison with previous studies of the PWS correction by a qualitatively estimated technique, this LDM technique has significantly provided an important tool for quantitative measurement and correction to the effect of the PWS on the fiber alignment shifts in laser-welded laser module packaging. Therefore, the reliable laser modules with high yield and high performance used in low-cost lightwave transmission systems may be developed and fabricated.

Fiber alignment shift formation mechanisms of fiber-solder-ferrule joints in laser module packaging

The fiber alignment shifts of fiber-solder-ferrule (FSF) joints in laser module packaging under temperature cycle testing using PbSn and AuSn solders are studied experimentally and numerically. The measured results showed that the fiber shifts of FSP joints with the hard AuSn solder exhibited shifts two times less than that with the soft PbSn solder. This suggests that the hard solder may be more suitable for FSF assembly than the soft solder. The results also showed that fiber shifts increased as the temperature cycle number and the initial fiber eccentric offset increased. The experimental measurements of fiber shifts were in good agreement with the numerical calculations of the finite-element method analysis. The major fiber shift formation mechanisms of FSF joints in temperature cycling may come from the localized plastic solder yielding introduced by the local thermal stress variation, the redistribution of the residual stresses, and the stress relaxation of the creep deformation within the solder. Furthermore, the stress relaxation of creep deformation in solder with either 21% (PbSn solder) or 5% (AuSn solder) may have significant influence on the fiber shifts. This study has provided an optimum approach for reduction of the fiber alignment shift of FSF joints in laser module packaging under temperature cycle testing, which is to solder the fiber near to the center of the ferrule and to select the AuSn hard solder.

Effect of temperature cycling on joint strength of PbSn and AuSn solders in laser packages

The effect of temperature cycle testing on the joint strength of PbSn and AuSn solders in laser diode packages has been studied experimentally and numerically. Experimental results showed that the joint strength increased as the temperature cycle number increased initially, and then became steady after 400 cycles. The joint strengths of PbSn and AuSn solders increased about 40% to 20% after undergoing 500 temperature cycles, respectively. A finite-element method (FEM) analysis was performed on the calculation of joint strength variation of PbSn and AuSn solders in temperature cycling tests. The coupled thermal-elasticity-plasticity model was employed in the solidification and residual stresses calculation. Simulation results were in good agreement with the experimental measurements that the solder joint strength increased as the temperature cycle increased. Numerical results indicate that the increasing solder joint strength comes from the redistribution of the residual stresses within the solder during temperature cycling tests. The local yielding and the creep effects on the low melting temperature solders will make uniform the residual stresses distribution introduced in the solidification process and increasing the solder joint strength as the temperature cycle number increased. The result suggests that the FEM is an effective method for analyzing and predicting the solder joint strength in laser diode packages.

Reduction of fiber alignment shifts in semiconductor laser module packaging

The thermally induced fiber alignment shifts of fiber-solder-ferrule (FSF) joints in laser module packaging have been studied experimentally and numerically. From direct measurements of the metallographic photos with and without temperature cycling, fiber displacement shifts of up to a 0.8 /spl mu/m were found after undergoing 500 temperature cycles. Experimental results show that the fiber shifts increase as the temperature cycle number and the initial fiber eccentric offset increase. The major cause of fiber shift may come from the plastic solder yielding introduced by the thermal stress variation and the redistribution of the residual stresses during temperature cycling. A finite-element method (FEM) analysis was performed to evaluate the variation of thermal stresses, the distribution of residual stresses, and fiber shifts of the FSF joints. Experimental measurements were in reasonable agreement with the numerical calculations. Both results indicate that the initial offset introduced in the fiber soldering process is a key parameter in causing the thermally-induced fiber shift of FSF joints in laser module packaging. The fiber shift, and hence fiber alignment shift under temperature cycling tests can be reduced significantly if the fiber can be located close to the center of the ferrule.

Effect of Au thickness on laser beam penetration in semiconductor laser packages

Comprehensive measurements of the dependence of the weld width, penetration depth, and joint strength on the Au coating thickness in laser welding techniques for semiconductor laser packages are presented. The results obtained from the Invar-Invar joints show that the welded joints with thick Au coating exhibit narrower weld width, shallower penetration, and hence less joint strength than those the package joints with thin Au coating. A finite-element method (FEM) has been carried out on the effect of Au thickness on laser beam penetration in Invar-Invar joints. This method has been employed successfully to predict the laser beam penetration in laser welded Au-coated materials that the weld width and the penetration depth are reduced as the Au coating thickness increases. The likely cause for the reduction is the increased thermal conduction of thicker Au in the welded region. In addition to Au coating, the effect of Ni coating on laser beam penetration is also presented. Detailed knowledge of the effect of Au coating thickness on laser beam penetration is important for the practical design and fabrication of reliable optoelectronic packaging having laser welded Au-coated materials.

An optimum approach for reduction of fiber alignment shift of fiber-solder-ferrule joints in laser module packaging

The results of experimental and numerical investigations leading to an optimum approach for the reduction of fiber alignment shift of fiber-solder-ferrule (FSF) joints in laser module packaging under temperature cycling test is presented. Using a novel image capture camera system as a monitor probe and the Sn -based solders as bonding materials, we have achieved the minimum fiber eccentric offsets of 8 and 20 /spl mu/m in FSF joints with the PbSn and AuSn solders, respectively. After a 500-temperature cycling test, the fiber alignment shifts for these small initial fiber eccentric offsets of FSF joints were found to be 0.7 and 0.3 /spl mu/m with the PbSn and AuSn solders, respectively. The measured fiber shifts were in good agreement with the numerical results of the finite-element method (FEM) analysis when both the residual stresses and the creep deformation within the solder were considered. This study have demonstrated that by soldering the fiber near to the center of the ferrule, and hence minimizing the fiber eccentric offset, the fiber alignment shifts of FSF joints in laser diode module packaging under temperature cycling test can be reduced significantly.

Crack formation mechanism in laser-welded Au-coated Invar materials for semiconductor laser packaging

Crack formation mechanism in laser-welded Au-coated Invar materials for semiconductor laser packaging is investigated experimentally and numerically. Experimental results obtained from metallography, scanning electron microscope (SEM), SEM mapping, and energy dispersive spectrometer (EDS) line profile show that high concentration of Au composition accumulate near the crack region. The cause of Au accumulation may come from the segregation of Au along the track region. A finite-element method (FEM) is performed on the calculation of thermal stresses during spot-welding for Au-coated Invar materials. Numerical results show that the high tensile stresses of the Au segregation layer generated by rapid solidification shrinkage is the possible cause for crack formation. Both experimental and numerical results suggest that the crack formation mechanism in laser-welded Au-coated optoelectronic materials is directly related to the combined effects of the Au segregation and high tensile stresses induced by the strain shrinkage during the final stage of solidification.

Post-weld-shift in semiconductor laser packaging

Post-weld-shift (PWS) in laser welding technique for a package (DIP) with fiber pigtail to laser connection has been studied experimentally and numerically modelled. Experimental results show that the PWS of optical component welded by a dual-beam laser welding system shifts more to the counterclockwise as the energy difference of the laser beam increases. This indicates that the PWS in laser packaging can be minimized by properly controlling the laser beam energy delivery. A finite-element method (FEM) has been carried out to analyse the effect of laser beam energy variation on PWS in laser packaging. A satisfactory agreement between the experimental results and FEM calculations suggests that the FEM provides one of the effective methods for predicting the PWS in laser welding technique for optoelectronic packaging.Post-weld-shift (PWS) in laser welding technique for a package (DIP) with fiber pigtail to laser connection has been studied experimentally and numerically modelled. Experimental results show that the PWS of optical component welded by a dual-beam laser welding system shifts more to the counterclockwise as the energy difference of the laser beam increases. This indicates that the PWS in laser packaging can be minimized by properly controlling the laser beam energy delivery. A finite-element method (FEM) has been carried out to analyse the effect of laser beam energy variation on PWS in laser packaging. A satisfactory agreement between the experimental results and FEM calculations suggests that the FEM provides one of the effective methods for predicting the PWS in laser welding technique for optoelectronic packaging.

Thermal stresses in box-type laser packages

The effect of Au coating on thermally induced stresses in box-type semiconductor laser packages was investigated by a finite-element method (FEM). The simulated results showed that Invar–Invar joints with Au coating have maximum stresses two times higher than joints without Au coating. This is due to the different coefficients of the thermal expansion (CTE) between dissimilar materials of Invar and Au, resulting in higher stresses. Maximum stresses were also found to be increased as the Au thickness increased. This effect is attributed to the increase in the thermal gradient in the welded region provided by the increased thermal conduction of the thicker Au coating layer. These results suggest that both the difference in CTE between dissimilar materials and higher thermal conduction of Au coating layer have an important impact on thermally induced stresses for optoelectronic packages having laser-welded Au coated materials.