Synthesis, Characterization, and Thermal Properties of Nanoscale Lead-Free Solders on Multisegmented Metal Nanowires

Nanoscale lead-free solders ("nanosolders") have been synthesized directly onto multisegmented metal nanowires using an electrodeposition method in nanoporous templates. The nanosolders fabricated include tin (Sn), tin/silver (Sn/Ag), and indium (In), and the diameter of the nanosolder nanowires ranges from 30 nm to 200 nm and the length from 1 to 10 mu m. The microstructures of the lead-free nanosolders on nanowires have been characterized using optical microscopy and electron microscopy including a field-emission scanning electron microscope (FESEM) and a transmission electron microscope (TEM), along with energy-dispersive X-ray spectroscopy (EDS). Thermal properties of lead-free nanosolders 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 nanosolder reflow process. The effect of base layer, barrier layer, and wetting layer on nanosolder reflow was studied, and an optimal nanowire nanosolder system with effective barrier and wetting layers was obtained. A liquid phase-based solder reflow process was developed, in which the nanosolder nanowires were assembled in a liquid medium and solder joints were formed between nanowires.