Laser-based conductive film forming with gold nanoparticles for electrical contacts

The present study discusses the formation of a conductive film from noble metal nanoparticles as an alternative to conventional electroplating for electrical components, such as connectors, switches, and memory cards. The proposed method consists of inkjet printing with nanoparticle paste followed by laser sintering. The aims are fourfold: to establish sintering technology for gold nanoparticles placed on a nickel-electroplated-phosphor bronze substrate, to characterize the laser-sintered film, to discuss the laser sintering mechanism, and to examine applicability to industry. The major results obtained are as follows: the laser sintering formed a gold film with a diameter of 0.3-0.8 mm and a thickness of 0.3-0.5 μm on the nickel-electroplated phosphor-bronze substrate; a laser with a wavelength of 915 nm enabled instantaneous sintering within one second in an atmosphere; the laser-sintered gold nanoparticle film had such a high adhesion to the substrate that no separation occurred after 90°-0.5R bend-peel tests; the high adhesion was attributed to interdiffusion of gold and nickel in the course of sintering; optical properties of the gold nanoparticle paste depend on preheat conditions. A relatively high-preheat temperature around 523 K produced a paste surface with a suitable absorbance of the infrared laser; and a primary sintering of the preheated gold nanoparticles with a small amount of solvents, followed by an auxiliary sintering from the substrate side made possible an efficient sintering of the nanoparticles as well as high adhesion to the substrate with a high thermal conductivity.