Enhanced Biased HAST Reliability of Polyimide for High-Density Redistribution Layers

The RDL in advanced FOWLP is approaching 1–2 μm to achieve high-density I/O. However, there is a material limitation for biased HAST reliability in conventional PI. A novel low-temperature curable photosensitive negative tone PI was developed for enhanced biased HAST reliability by redesigning key components of the formulation. The novel PI passed biased HAST for 300 h under the conditions of 3.3 V for L/S = 2/2 μm and 15 V for L/S = 5/5 μm. SEM-EDS analysis of the Cu wiring cross section after biased HAST showed no noticeable CuO formation in the novel PI. Furthermore, extrapolation by electronic field showed the possibility of passing 10 V for 168 h even with L/S = 1/1 μm. It was found that high-density RDL structures can be realized by applying this novel polyimide thanks to its high reliability.