Fast near infrared sintering of silver nanoparticle ink and applications for flexible hybrid circuits

Near infrared(NIR) sintering technology is a photonic sintering approach for metal nanoparticle inks, which can selectively sinter metal nanoparticle inks more quickly and efficiently, and it is also compatible with high-throughput manufacturing processes. In this paper, silver nanoparticle (AgNP) ink sintered by near infrared light at a peak wavelength of 1100nm was investigated. After only 8 seconds of exposure to NIR irradiation, resistivity of 2.78 cm was achieved for thin films printed with AgNP ink, which was only 1.7-fold higher than that of bulk silver (1.59 cm). The structure of the sintered silver film was examined by sintering printed silver nanoparticle ink samples having different thicknesses, and the results showed that AgNPs were homogeneously coalesced throughout the cross-sections of films, indicating the formation of dense silver layers. Furthermore, the morphology and electrical resistivity of the sintered AgNP film dried by NIR were compared with those of the film dried on a hot plate. It was found that drying conditions with a relatively long drying time rather than the drying temperature contributed to the reduction of voids in the film and to the improvement in its density and electrical performance. Finally, a flexible hybrid circuit integrated with a microcontroller chip on a poly(ethylene terephthalate)(PET) substrate was fabricated by screen printing with AgNP ink for interconnects, and its surface roughness and flexibility were investigated.