Lead-free nano-solders on metallic nanowires: Synthesis, characterization, and thermal reflow properties

Solders and soldering techniques are widely used in microelectronics assembly and packaging. With the emergence of nanomaterials and nanotechnology, new enabling tools have to be developed for nanoscale assembly and integration. Lead-free nano-solders have received significant attention in recent years and have shown promise in the assembly and integration of micro- and nano-electronics devices. In this project nano-soldering techniques were explored in the assembly and integration of nanowires.;Nano-solders were synthesized directly onto multi-segmented metallic nanowires using an electrodeposition method on nanoporous templates with diameters ranging from 30 nm to 200 nm. Optical microscopy, electron microscopy (SEM and TEM) and energy-dispersive x-ray spectroscopy (EDS) were used to characterize tin-based lead-free solders with different nano-solder compositions and structures. Differential scanning calorimetry (DSC) was used to measure the melting point of tin nanowires, and there was no significant melting point drop for the nano-solder nanowires with a diameter of 50 nm and a length of 5 mum. Thermal properties of the lead-free nano-solders on nanowires were characterized using a temperature programmable furnace tube under a controlled atmosphere. It was found that nitrogen plays an important role in the nano-solder reflow process. The effect of a base layer, a barrier layer and a wetting layer on nano-solder reflow was studied, and an optimal nanowire nano-solder system with effective barrier and wetting layers were obtained. A liquid phase based solder reflow process was developed, in which the nano-solder nanowires were assembled in a liquid medium and solder joints were formed between nanowires.;The multi-functional nanowires with nano-solders, when combined with self-assembly or directed assembly techniques or AFM and Dip-Pen nanolithography (DPN)-based techniques, may provide new enabling tools in the integration of nanoelectronics, nano-optics, sensors, and biomedical devices.;Keywords. Lead-free nano-solders, nanoelectronics, nanowires, solder reflow, self-assembly, green nano-manufacturing.