A method for copper direct drilling by carbon dioxide$(hbox CO_2)$laser was investigated for efficient microvia formation on the copper conducting layer of high-density interconnection (HDI) of printed circuit board (PCB). A metal–tin layer was coated on the surface of copper conductor foil to enhance the$hbox CO_2$laser energy adsorption on it. The coated surfaces were then drilled by a$hbox CO_2$laser with various pulse energies. The microvia holes were efficiently formed in good quality with one laser pulse on 9-$muhbox m$-thick polished copper conducting layer. The laser energy absorption of coated copper foils was approximately calculated. The experimental results demonstrated the potential application of the developed method in high-density interconnection printed circuit board manufacturing.
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