Development of low dielectric loss polyimides and fabrication of advanced packagings for 5g applications

Recently we have developed novel polyimide adhesive sheet materials (PI sheet) which have advantages such as planarization, via-filling, low shrinkage (low stress) during curing and easy fabrication of multi-layer and cavity structures compared to spin-coating polyimide materials. The PI sheets are expected to be used in wafer level package (WLP) applications such as 5G telecommunication systems (5G) and Micro Electro Mechanical Systems (MEMS). To meet 5G and MEMS requirements, we recently have developed novel low-dielectric loss (low Df) and high mechanical properties PI sheets with good adhesion to Cu and polyimide layers on a substrate. We have achieved Df values of 0.003 and 0.007 at 20GHz for non-photosensitive (NP) PI sheet and photo-sensitive (PS) PI sheet, respectively. The use of low Df PI sheet as a redistribution layer can help realize low transmission loss due to low Df value itself and also to low conductor loss due to good adhesion to the smooth copper surface of the wiring.