Porosity reduction in inkjet-printed copper film by progressive sintering on nanoparticles

This work demonstrates a progressive three-step sintering for inkjet-printed copper (Cu) nanoparticles. For the inkjet-printed Cu thin films, the proposed processes of sequential low-pressure drying, near-infrared sintering, and intense pulsed light (IPL) reduction ensure high nanoparticle compactness, complete Cu sintering, and low oxygen content, respectively. Experiments showed that the highest Cu conductivity resulted from a combination of 65.7% improvement on surface roughness, 37.3% porosity reduction, and 91.7% oxygen elimination provided by the proposed method. Enhanced adhesion between the Cu and the substrate confirmed by mechanical examinations indicated other benefits of this progressive sintering. In addition, the cracks that resulted from different thermal expansions in the Cu thin film and the substrate during IPL reduction were quantified, and the results explained the degraded electrical performance of the Cu thin films that had been processed beyond the optimal condition.