Direct evidence of Au segregation in laser welded Au-coated Invar material

Abstract

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.