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.

Crack formation mechanism in laser-welded Au-coated Invar materials for semiconductor laser packaging

“…An EDS trace on the cross section involving the crack region has been investigated [10]. The relative intensities of the trace elements of Fe, Ni, and Au signals show a discontinuity within the crack region.…”

“…However, the laser welding process can be influenced by the thickness of Au coating on the housing materials. An excess thickness of Au coating on housing materials in the laser welding process may cause undesirable reactions which can reduce joint strength [6]- [7] or generate cracks [8]- [10] in the welded region. Details on the effect of Au thickness on laser beam penetration in laser packaging were given in [7].…”

Defects in optoelectronic materials due to phosphorus-containing underlayer

“…7 The Invar housing materials of Invar plate, u-channel, and Invar tube with very low CTE were chosen to secure the fiber in alignment with the semiconductor laser in order to minimize the thermal stress and strain developed. 7 The Invar housing materials of Invar plate, u-channel, and Invar tube with very low CTE were chosen to secure the fiber in alignment with the semiconductor laser in order to minimize the thermal stress and strain developed.…”

“…In this work, 7 we experimentally investigated the crack formation mechanisms due to P-containing underlayer in laser spot-welding package techniques using metallogra-phy, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) mapping, EDS line profile, and Auger electron spectroscopy (AES). In this work, 7 we experimentally investigated the crack formation mechanisms due to P-containing underlayer in laser spot-welding package techniques using metallogra-phy, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) mapping, EDS line profile, and Auger electron spectroscopy (AES).…”

The principle cause of crack defects in optoelectronic materials with phosphorus-containing underlayer

“…It has been well documented that an inadequate thickness of Au on Invar or Kovar optoelectronic materials in the laser welding process can cause undesirable crack defects in the welded joints. 1,2,[5][6][7] Certainly, the detailed understanding of crack formation mechanisms in laserwelded Au-coated optoelectronic materials is important and needs to be investigated further. Prior to Au plating on optoelectronic material, a Ni underlayer coating is often applied to improve adhesion.…”