Packaging of electronic modules through completely dry process

In order to establish technology of packaging electronic modules, we investigated conditions for laser sintering of Ag nanoparticles, and evaluated characteristics of the sintered film. First, we plotted minute patterns on a copper substrate by ink-jet printing, and then employed an NdYAG laser to metalize the nanopaste in a short time. The Ag nanoparticles (5 nm in average diameter) dispersed in organic solvents were solidified to form coarse agglomerates of about 0.05-0.5 mum with a pulsed laser, or about 0.05 mum by CW mode. We carried out a bend-peel test to find that no separation occurred at the interface between the sintered Ag film and the substrate. Adhesive strength of the laser-sintered pattern on the Cu substrate is higher or equal to than that obtained by furnace sintering. An SIM observation of FIBed cross-sections revealed that the laser-sintered film is as thin as less than 0.5 mum, and has a porous structure. As for wiring a polyimide substrate, the use of water-repellant is indispensable for ink-jet printing. Three-step laser sintering enables us to make Ag wires on the polyimide film at a low laser power, which leads to less thermal damage to the substrate.