Copper-clad laminate (CCL) is the core substrate of printed circuit boards (PCBs), providing mechanical support and electrical interconnection for electronic components. With the increasing demand for miniaturized and highly reliable electronic devices, high-quality microvia fabrication in double-sided CCL is essential for high-density interconnection (HDI) technology. In this study, an underwater microvia drilling method based on UV picosecond laser processing is proposed to achieve high-quality and environmentally friendly fabrication. The effects of laser power, scanning speed, and number of scans on microvia characteristics, including the heat-affected zone, roundness, taper, and surface morphology, are systematically investigated, and the synergistic mechanisms of the underwater environment—such as enhanced cooling, debris removal, and plasma confinement—are analyzed. Experimental results demonstrate that, compared with air processing, underwater laser drilling significantly reduces the entrance heat-affected zone, improves the roundness at both via entry and exit, and produces smooth sidewalls free from spatter and recast layers. Moreover, this technique eliminates the need for chemical etchants and mechanical drill bits, avoiding consumable usage and tool wear, and provides an efficient, clean, and reliable solution for microvia fabrication in CCL-based PCBs.
Guo et al. (Fri,) studied this question.