Infrared (IR) Soldering of Metallic Nanowires

In this work, we used infrared (IR) heating as a new soldering method for the melting and joining of metallic nanowires. IR soldering method is a non-contact soldering method with focused heating area and the soldering process can be done within a few seconds without spreading too much unnecessary heat to the surrounding so as to protect polymer or other low melting temperature or heat sensitive substrates. Lead-free nano-solders can be used for the assembly and joining of nanowires for nanoelectronics and device applications. In order to control the nano-solder melting process and form reliable solder joints, fundamental study of solder melting behavior and morphology change is necessary in order to optimize the IR soldering process. Pure tin (Sn) solder was used as a model solder material, and both Sn nanowires and multi-segment nanowires which have two Sn segments on both ends, were tested by the IR soldering method. Nanowires were synthesized by using electrodeposition method in nanoporous polycarbonate (PC) templates or anodic aluminum oxide (AAO) templates. After electrodeposition, the nanowires were cleaned and deposited on the surface of silicon wafer for IR treatment. The melting behavior and morphology change were examined by field-emission scanning electron microscope (FE-SEM). The dramatic morphology change of Sn segments and Sn nanowires was observed when proper choice of flux, operating time and temperature were applied. The soldering process parameters were then optimized in order to obtain spherical solder balls for complete solder reflow. Finally, multi-segment nanowires were melted and soldered by IR soldering.