Laser drilling of copper foils for electronics applications

Single pulse drilling of copper foils and copper-coated dielectric circuit board materials, relevant to applications in micro-electronics packaging, has been investigated here using an enhanced peak power CO₂-laser. The plasma generated during copper laser ablation, under these conditions, has been found to be self-extinguishing once the copper has been punched through, and does not materially impact the process. The analysis of the undercut formation in the copper coated laminates illustrated a direct link with the energy delivered to the dielectric after the copper has been laser ablated. Holes with zero undercut were obtained by the use of an acousto-optic modulator, used as a pulse shutter, to control the energy delivered to the dielectric. For unmodulated laser pulses, holes with zero undercut were obtained when drilling copper foils 35-µm thick. In general, when drilling copper-coated dielectrics with unmodulated pulses, holes with low undercut were obtained for peak powers < 1.2 kW. However, the stochastic nature of copper drilling dominates the process in this regime. At higher peak powers (up to 1.8 kW), a yield of 100% holes in copper is obtained, but this also results in significant undercut. © 2007 IEEE.