Failure mechanism of solidification cracks in semiconductor laser packaging

In this work, we experimentally investigate the defect mechanisms in spot-welding technique for receptacle laser packaging. Results obtained from the stainless-to-kovar joints show that the surface cracks are eliminated by reducing the gold thickness from the kovar before welding, while the centerline cracks in the fusion zone are eliminated by the air gap tightness between the kovar and stainless. The low solubility of gold in the kovar and the large air gap between the joints are identified as the mechanisms for surface and centerline cracks, respectively. A reduction of post-weld-shift (PWS) technique in laser packaging is also presented on the basis of a detailed understanding of the welded joint quality and the defect mechanisms in the laser welding process. Preliminary reliability data demonstrated that these laser packages, which do not have hole and crack defects in the welded joints, are reliable