Customized Circuit Interconnect and Repair by Laser Seeding and Constriction-Induced Plating.

Abstract

A novel method has been developed for producing customized copper interconnections on thermally-sensitive substrates by laser seeding followed by constrictioninduced electroplating. A polyimide, polytetrafluoroethylene, or glass-epoxy substrate is first sprayed with palladium acetate solution. 500 nm thick palladium interconnects are then formed using a 514 nm argon ion laser (10 mW - 50 mW) to selectively pyrolyze the acetate film. After cleaning, the part is immersed in an acid copper electrolyte and an alternating current (0.1 Amp - 2.0 Amp) passed through the palladium seed. Joule heating produces a cathodic shift in the equilibrium potential (dε₀/dT = 0.63 mV/degree) which causes electrodeposition of copper along the seeded connection.

Cross-sectional microscopy and electrochemical polarization studies show that local plating current densities of 10 mA/cm² produce 1000 εm × 25 εm × 10 εm line geometries exhibiting excellent mechanical and electrical properties. The large process window suggests that customization and repair on lincwidths below 1 mil (25 εm) should be achievable routinely.