Laser-enhanced electroless plating has been a forcus of interest as a maskless selective plating technique. This study was designed to elucidate the optimum conditions under which a uniform electroless nickel film could be obtained under irradiation by an argon ion laser. Highly selective metal spots were observed in the region of laser irradiation on polyimide film activated by palladium.
The amount of deposits was roughly proportional to irradiation time, and the deposition rate was approximately 4 times higher than in conventional electroless nickel plating. Electroless nickel plating without the activation process was possible selectively at the site of laser irradiation, but the films deposited were not uniform.
The deposition rate during laser beam irradiation depended on the pH of the plating solution, as in conventional electroless nickel plating. Using unactivated substrates, virtually no deposits were observed when pH was less than 5.
Generally the plating spots were of the same size as the laser beam, but when laser power was reduced, the plating spots were smaller than the diameter of beam.
Laser irradiation also had an influence on deposit structure. Laser-enhanced electroless deposits showed several sharp X-ray peaks caused by crystalline nickel differing from the broad pattern associated with the amorphous structure. This seemed to be related to the reduction of the phosphorus content in the deposits as a result of laser irradiation.