Effect of Au thickness on laser beam penetration in Invar-to-Invar packages

Comprehensive measurements of the dependence of the laser beam penetration 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) is done of the effect of laser beam penetration On the Au thickness in the 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 found to be reduced as the Au coating thickness increases. The likely cause for the reduction is due to the increased thermal conduction of thicker Au in the welded region. Detailed knowledge of the effect of Au coating thickness on laser beam penetration is important for practical design and fabrication of reliable optoelectronic packaging having laser welded Au-coated materials.