Technology for Forming Micro Vias Smaller Than 20 $\mu \mathrm{m}$ with Low Surface Roughness on Build-Up Films Using UV Nanosecond Laser Drilling and Plasma Desmearing

Conventional $\text{CO}_{2}$ laser drilling and wet desmearing processes have limitations in fine via formation, while ultraviolet (UV) laser drilling enables smaller vias but cannot process polyethylene terephthalate (PET)-protected build-up films, leading to direct plasma exposure that increases filler protrusion and surface roughness. To address this, a $\mathbf{5 0}-\mathbf{1 0 0 n m}$ sputtered $\mathbf{C u}$ coating was applied to a $10 \mu \mathrm{m}$ thick Ajinomoto Build-Up Film (ABF) surface before nanosecond UV laser drilling to achieve sub-$20 \mu \mathrm{m}$ vias, and optimized plasma desmear conditions were studied to minimize via enlargement while effectively removing residues. Quick Via Pull (QVP) and 90° peel strength tests confirmed the adhesion and reliability of the via metallization on the low-roughness ABF surface, with further results to be shared in future work.