On-demand laser-sintering of copper micro-particles on ferrite/epoxy resin substrates for power electronics devices

Thick copper wiring on ferrite/epoxy resin substrate was carried out by laser sintering of the paste prepared with 1 μm-diameter copper micro-particles and organic solvents. A 532 nm-wavelength Nd:YVO4 green laser has a high adsorption both to the copper micro-particle paste and to the ferrite/epoxy resin substrate are used for laser ablation of the substrate and laser sintering. From the microscopic observations and property evaluations of the laser-processed ferrite/epoxy resin substrate with copper, the following conclusions are obtained: (1) The paste prepared with 1 μm-diameter copper and organic solvents made it possible a small-volume dispensing as well as a good laser sintering; (2) The use of 532 nm-wavelength Nd:YVO4 green laser has a high adsorption both to the copper micro-particle paste and to the ferrite/epoxy resin substrate, resulting in the formation of the laser-sintered film with 20 μm in thickness and 15 μΩ·cm in specific resistance. No damage to the substrate occurred; (3) The adhesion between the sintered film and the substrate is attributed to the removal of the surface epoxy layer by laser ablation. Copper micro-particles penetrate to the exposed ferrite particles, being mechanically locked with each other at the interface; (4) The scratch test with a cotton swab and the peel test with an adhesion tape show that no separation took place at the interface.