Laser-enhanced electroless plating of silver seed layers for selective electroless copper deposition

Copper (Cu) has been patterned using a laser direct-write metallization technique for fabrication of printed wiring boards. The approach consists of writing a silver (Ag) seed layer with a subsequent step of electroless Cu plating to increase thickness and electrical conductivity. Ag seed layers were patterned with a frequency tripled Nd:YVO₄ (λ = 355nm) laser with a spot size of approximately 50μm. Final Cu linewidths after electroless plating were found to be 150 μm with a thickness of 2 μm and electrical resistivity of 5 μΩ cm. An optimal laser power of 0.81W was found by a factorial-type design experiment. A modern prototype circuit was also patterned with this technique, demonstrating its compatibility with current resolution requirements.