The microstructure of eutectic Au-Sn and In-Sn solders on Au/Ti and Au/Ni metallizations during laser solder bonding process for optical fiber alignment

In this work, two eutectic solders: 80Au20Sn and 52In48Sn were chosen for fiber bonding through laser soldering, and scanning electronic microscope (SEM) equipped with energy dispersive x-ray detector (EDX) was used to investigate the microstructures of at four interfaces between two solders and two metallizations: Au-Sn/(Au/Ti), Au-Sn/( Au/Ni), In-Sn/ (Au/Ti), In-Sn/(Au/Ni). Results show that as for the Au-Sn solder joint a large amount of zeta-phase was formed at the Au-Sn/(Au/Ti) interface with its morphology closely related with laser input energy; while at the Au-Sn/(Au/Ni) interface scallop-like (Au,Ni)Sn appeared with a low input energy and irregular-shaped (Au,Ni) ₃Sn₂ emerged with a high input energy. As for the In-Sn solder, the IMCs at the In-Sn/ (Au/Ti) interface transformed from a Au(In,Sn)₂ layer to isolated Auln2 cubes with the increase of input energy while at the In-Sn/(Au/Ni) interface a thin layer of Au(In,Sn)₂ was formed. As the connecting layer, Ti did not react in the soldering process