A hole-cleaning process after opening via-holes by CO-2 laser is of great importance in build-up printed circuit boards (PCB). In this process, heavy metal solutions, such as permanganate solution, are used as oxidizing agents in usual [1]. However, the heavy metal solutions lead to a high environmental pollution. Moreover, the heavy metal solutions cannot penetrate easily into the micro via-holes (< 100 mum in diameter) because of their high viscosity. The heavy metals cannot react with residual organic compounds in the bottom of the micro via-holes.
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