Interfacial Reactions And Alignment For Fiber Bonding By Laser Soldering

On the premise of laser diode being positioned beforehand, the precise bonding of optical fiber to substrate is critical to the whole coupling efficiency of the device in opto-electronic packaging, therefore it is necessary to analyze factors that influence the alignment during the bonding process. Since interfacial reactions during laser soldering process is different from those during conventional overall heating means, it is necessary to investigate them to control the intermetallic compounds growth and to improve the performance of the solder joint.In present work, the microstructures formed during laser soldering process at four interfaces between two solders and two metallizations—AuSn/Au/Ti, AuSn/Au/Ni, InSn/Au/Ti, InSn/Au/Ni were investigated and the mechanisms of the interfacial reactions were analyzed. The results show that the category, morphology, quantity and distribution of interfacial microstructure depend on the input laser energy.The microstructures formed during laser process at the interface between AuSn solder and Au/Ni/Cu pad as well as that between AuSn solder and Au/Cu pad were also investigated. Furthermore, the microstructure evolution of the Au-Ni-Sn and Au-Cu-Sn ternary intermetallic compounds formed at the interfaces of AuSn/Au/Ni, AuSn/Au/Ti, AuSn/Au/Ni/Cu and AuSn/Au/Cu during aging were analyzed.The pad-solder-copper wire system was used to simulate the practical fiber bonding process to facilitate observation and measurement. The restoring force exerted on the copper wire was analyzed. The results show that the restoring force is composed of the surface tension of solder distributed along the triple line, the pressure caused by liquid solder and the annex pressure of the crook interface between solder and copper wire.Based on theory of the restoring force and the energy, different factors that have impact on the copper wire self-alignment, such as the pad shape, the solder type, the solder volume and the presetting method of solder, were investigated, respectively. An optimal solution was proposed, which provides theoretical instructions to practical fiber bonding process.