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

Abstract

Abstract 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 semi-additive process (SAP) with desmear process and/or modified semi-additive process (MSAP) by using Cu film with large surface roughness. Though a desmear process and Cu film 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 that processes, we applied an UV modification for the surface of our developed thermosetting dielectric in order to realize a smooth and high adhesive seed layer against the dielectric. We obtained 0.5 kN/m of peel strength between dielectric and Cu seed layer in spite of surface roughness (Ra) of dielectric was 265 nm by nano-level anchoring effect at UV modified layer. Due to the smooth interface by UV modification, the normalized S21 value of microstrip line was about 29 % improved compared to that assembled through Cu film with Ra of 2400 nm at 50 GHz.