Temporal pulse shaping for smoothing of printed metal surfaces

The surfaces of laser-induced forward transfer (LIFT) printed metal structures show typical roughness characteristic of the metal droplet size (3 to 10 μ m). Submicron voids are often observed in the bulk of such printed metal structures with consequences on the mechanical strength, chemical resistivity, and electrical conductivity. We present the results of our efforts to reduce surface roughness and bulk voids by controlled laser melting. We have used temporally shaped pulses from a fiber laser tunable in the range from 1 to 600 ns in order to improve the quality of LIFT printed copper and aluminum structures. For the best case shown, roughness was improved from R_RMS = 0.8 μ m to RRMS = 0.2 μ m and the relative percentage of the voids was reduced from 7.3% to 0.9%.