Electroless copper films deposited onto laser-activated aluminum nitride and alumina

Metallization of ceramic substrates by laser activation and subsequent electroless deposition has been demonstrated recently in aluminum nitride and alumina. However, the bond strength between the electroless copper and the ceiamic substrate is weak (less than 14 MPa). Low temperature annealing of electroless copper films deposited on substrates activated at low laser energies strongly increases the adhesion strength. The effectiveness of the annealing for improving the metal-ceramic bonding is dependent upon the laser treatment performed on the substrate prior to deposition. Faster deposition kinetics are obtained for both substrates by increasing the laser energy density. On the other hand, an increase in the laser energy density leads to poor adhesion strengths. The dislocation microstructure produced during laser irradiation in aluminum nitride is analyzed as a possible cause of laser activation. Free aluminum produced by laser irradiation of aluminum nitride and of alumina is discussed as another factor of laser activation. The chemical and microstructural changes taking place in the near-surface region as a consequence of laser-induced processes are correlated with adhesion enhancement promoted by the annealing treatment.