On-Demand Infrared Laser Sintering of Gold Nanoparticle Paste for Electrical Contacts

This paper 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 in dispensing with nanoparticle paste followed by laser sintering. The aims are fourfold: 1) to establish sintering technology for gold nanoparticles placed on a nickel-electroplated phosphor-bronze substrate; 2) to characterize the laser-sintered film; 3) to discuss the laser sintering mechanism; and 4) 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 1 s in air; 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 for 60 s produced a paste surface with a suitable absorbance of the infrared laser; 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; and the film possesses such a good electrical property as that of the electroplated one in reciprocating abrasion tests.