Tin Nanoparticle-Based Solder Paste for Low Temperature Processing

Abstract

Materials have shown a tendency to modify their bulk properties depending on powder particle size. Nanoparticles' coalescence temperature tends to decrease as particle size decreases. Taking advantage of this behavior, a nanoparticle-based solder paste has been developed as a proof-of-concept and is described in this paper for attaching electronic components at a lower processing temperature to avoid thermally induced damage and reduce energy consumption. Tin nanoparticles were successfully synthesized via a wet chemistry route. The synthesis consists on the use tin (II) chloride dehydrated as the Sn precursor, 1,10-phenanthroline as the surfactant, and sodium borohydride as the reducing agent. A flux system was developed based on ethylene glycol. The solder paste based on the synthesized Sn nanoparticles showed good surface wetting, but not a sufficient metal volume to produce an attachment because the paste required high flux content, thus resulting in a poor metallic load paste. By using commercially procured Sn nanoparticles the results showed acceptable coalescence of the noncapped nanoparticles at temperatures as low as 200°C with a processing time of 20 min. A reduction in processing temperature of approximately 40°C has been found when comparing the developed solder paste with typical SAC lead-free solders. The mechanical and electrical properties of the resulting structure were characterized by means of lap-shear testing and a four-wire Kelvin test showing acceptable shear strength and electrical conductivity.