Influence of wavelength on laser sintering characteristics of Ag nanoparticles

The purpose of this study is to develop a dry process for minute wiring or interconnections without any wet process such as chemical etching and electroplating. The process is based on the use of metal nanoparticles and their metallization by laser sintering, which will bring a desktop manufacturing of electronic circuits in view. The present paper investigates the influence of wavelength on laser sintering characteristics of Ag nanoparticles, in which a CW Nd:YAG laser (1064 nm in wavelength), a CW laser diode (980 nm), a CW green laser (532 nm) and a CW Ar⁺ laser (488 nm) are employed. Sintering mechanism as well as adhesion to a polyimide substrate is extensively investigated by FIB observation and tensile-shear testing. As a result, the lasers with visible wavelength are preferable from the viewpoint of laser output and adhesion strength because of a high absorbance of light in the NanoPastereg containing Ag nanoparticles, a dispersant and solvents. On the other hand, the near-infrared lasers yield a denser sintered structure, which leads to lower specific resistance, although it is a couple of times high compared to furnace curing.