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Laser Drilling of Copper Foils for Electronics Applications

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4 Author(s)
Colin J. Moorhouse ; Sch. of Eng. & Phys. Sci., Heriot Watt Univ., Edinburgh ; Francisco J. Villarreal ; Howard J. Baker ; Denis R. Hall

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 CO 2-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-mum 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 1.8kW), a yield of 100% holes in copper is obtained, but this also results in significant undercut

Published in:

IEEE Transactions on Components and Packaging Technologies  (Volume:30 ,  Issue: 2 )