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Evidence of the Au segregation within the crack region in laser welded Au-coated Invar material for semiconductor laser packaging is investigated. Results obtained from the metallography, scanning electron microscope (SEM) mapping, energy dispersive spectrometer (EDS) line profile, and Auger electron spectroscopy find that the cracks in the welded joints occur around the Au rich boundaries. The SEM Au mapping and EDS line profiles show that Au accumulates at the crack region. This direct observation indicates that one of the primary causes of cracks in laser welded Au-coated materials is due to the segregation of Au in the final stage of solidification. Detailed knowledge of the defect formation mechanisms in laser welded Au-coated materials is important for the practical design and fabrication of reliable optoelectronic packaging.

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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 Aucoated materials.

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