Defect formation mechanisms in laser welding techniques for semiconductor laser packaging

In this work, the authors experimentally investigate defect formation mechanisms in spot-welding techniques for semiconductor laser packaging. Results obtained from the stainless-to-stainless steel joints indicate that the dimension of hole formation depends on the laser power density, and the hole disappears as the power density is below 3×10⁵ W/cm². In the stainless-to-Kovar^TM joints, surface cracks are eliminated by reducing the gold thickness from the Kovar^TM before welding, while the centerline cracks in the fusion zone are eliminated by the air gap tightness between the Kovar^TM and stainless steel. The excess laser energy is the possible cause for hole formation. The low solubility of gold in the Kovar^TM and the large air gap between the joints are the possible causes for surface cracks and enhancing centerline crack propagation, respectively. A technique for reduction of post weld shift (PWS) in semiconductor laser packaging is also presented. Preliminary reliability data demonstrated that these laser packages, which do not have hole and crack defects in the welded joints, are reliable