On-demand gold laser-plating onto stainless steel for electrical contacts

The present study discusses the formation of a conductive film from noble metal nanoparticles onto stainless steel substrate for electrical components, such as connectors, where conventional electroplating is not applicable. The proposed “laser plating” method consists in on-demand dispensing with nanoparticle paste followed by a short-time preheating and laser sintering. The aims are fourfold: to establish sintering technology for gold nanoparticles placed on an 18%Cr-8%Ni stainless steel substrate covered with a passivation film, 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 0.8 mm and a thickness of 0.3-1.0 μm on the stainless steel substrate without any surface pretreatment; a laser with a wavelength of 915 nm enabled instantaneous sintering within one second 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, iron, chromium and nickel in the course of sintering; 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 stainless steel substrate with a high thermal conductivity; the laser-sintered gold film possesses such a good electrical property.