Electroless Plating with UV Modification for Thermosetting Dielectric and Decay Suppression of High Frequency Transmission Property

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Abstract Semiconductor packages for high-performance devices with printed circuit boards having multi-wiring layers such as FC-BGA have been attracting attention to realize ultrareliable and low-latency communications in 5G networking. Cu wirings for the package are usually fabricated by the semi-additive process (SAP) with the de-smear process and/or the modified semi-additive process (MSAP) by using Cu film with large surface roughness. Although a de-smear process and Cu film can obtain enough adhesion between dielectric and Cu seed layer by the 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 those processes, we applied UV modification for the surface of our developed thermosetting dielectric to realize a smooth and high-adhesive seed layer against the dielectric. We obtained .5 kN/m of peel strength between dielectric and Cu seed layer despite surface roughness (Ra) of dielectric being 265 nm by the nano-level anchoring effect at UV modified layer. Because of the smooth interface by UV modification, the normalized S21 value of micro-strip line was about 29% improved compared with that assembled through Cu film with Ra of 2,400 nm at 50 GHz.