Development of plating resist for FO-WLP

Abstract

We report on the latest ultra-thick photo resist to fabricate high copper pillars over 100um for FO-WLP. The new resist shows excellent coating performance to achieve 100um thickness in a single coat, or over 200um thickness with double coating, on 12 inch wafer. The resist provides good coating uniformity without bubbles, defects, wrinkles or other errors. On top of that, the new material design enables finer resolution for ultra-thick films, with an aspect ratio of 4 and beyond. We also report high copper pillars fabricated with the new THB resist. It is expected that the new ultra-thick resist will be the best candidate for FO-WLP. We will discuss the new material concept in more detail.