Semiconductor packages for high performance devices with printed circuit boards having multi wiring layers such as FC-BGA have been attracting the attention in order to realize ultra-reliable and low latency communications in 5G networking. Cu wirings for the package are usually fabricated by via formation by laser for dielectric, desmear, electroless Cu seed formation, photoresist patterning, electrolytic Cu plating, resist stripping and seed layer etching. Though a desmear process can obtain enough adhesion between dielectric and Cu seed layer by anchoring effect to secure reliabilities, the interface between dielectric and Cu seed layer should be smooth to achieve low attenuation of electric signals at high frequencies. Here, instead of a desmear process, we applied an UV modification for the surface of dielectric in order to realize a smooth and high adhesive seed layer against dielectric. We obtained 0.8 kN/m of peel strength between dielectric and Cu seed layer in spite of surface roughness (Ra) of dielectric was 45 nm by nano-level anchoring effect at UV modified layer. Due to the smooth interface by UV modification, S21 value of microstrip line was 26 % improved compared to that assembled through desmear process at 60 GHz.

Semiconductor packages for high-performance devices with printed circuit boards having multiwiring layers such as flip-chip ball grid array have been attracting the attention to realize ultrare-liable and low-latency communications in 5G networking. Cu wirings for the package are usually fabricated by via formation by laser for dielectric, desmear, electroless Cu seed formation, photoresist patterning, electrolytic Cu plating, resist stripping, and seed layer etching. Although a desmear process can obtain enough adhesion between dielectric and Cu seed layer by anchoring effect to secure reliabilities, the interface between dielectric and Cu seed layer should be smooth to achieve low attenuation of electric signals at high frequencies. Here, instead of a desmear process, we applied a UV modification for the surface of dielectric to realize a smooth and high-adhesive seed layer against dielectric. We obtained .8 kN/m of peel strength between dielectric and Cu seed layer in spite of surface roughness of the dielectric being 45 nm by a nanolevel anchoring effect at the UV-modified layer. Because of the smooth interface by UV modification, the S21 value of microstrip line was 26% improved compared with that assembled through the desmear process at 60 GHz.

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