Thick photosensitive polyimide film side wall angle variability and scum improvement for IC packaging stress control

In this paper, we demonstrate photosensitive polyimide (PSPI) profile optimization to effectively reduce stress concentrations and enable PSPI as protection package-induced stress. Through detailed package simulation, we demonstrate similar to 45% reduction in stress as the sidewall angle (SWA) of PSPI is increased from 45 to 80 degrees in Cu pillar package types. Through modulation of coating and develop multi-step baking temperature and time, as well as dose energy and post litho surface treatments, we demonstrate a method for reliably obtaining PSPI sidewall angle >75 degree. Additionally, we experimentally validate the simulation findings that PSPI sidewall angle impacts chip package interaction (CPI). Finally, we conclude this paper with PSPI material and tool qualification requirements for future technology node based on current challenges.