Interfacial reaction between solder alloys and metallization during laser solder bonding process for optical fiber alignment

Optical fiber bonding is a key technique in optoelectronic packaging, and the interfacial microstructure has a significant influence on solder joint reliability. In this work, 80Au20Sn and 52In48Sn solders were chosen for fiber bonding through laser soldering, and a scanning electronic microscope (SEM) equipped with energy dispersive X-ray detector (EDX) was used to investigate the morphology and formation of microstructure at four interfaces between two solders and two metallizations: AuSn/(Au/Ti), AuSn/(Au/Ni), InSn/(Au/Ti) and InSn/(Au/Ni). Results show that a large amount of dendritic pre-eutectic ζ-phase forms at the AuSn/(Au/Ti) interface, while some needle-like (Au, Ni)₃Sn₂ forms at the AuSn/(Au/Ni) interface, an obviously continuous Au(In, Sn)₂ layer forms at the InSn/(Au/Ti) interface and an extremely thin Au(In, Sn)₂ layer forms at the InSn/(Au/Ni) interface. Moreover, the continuous Au(In, Sn)₂ layer transforms into incontinuous block-like AuIn₂ at the InSn/(Au/Ti) interface with the increase of input laser energy.