Selection and Characterization of Photosensitive Polyimide for Fan-Out Wafer-Level Packaging

Fan-out wafer-level packaging (FOWLP) is one of the most popular microelectronics packaging technologies. Redistribution layers (RDLs) are employed to expand chip pads beyond the chip edges. Photosensitive polyimide (PI) is widely used in RDLs fabrication. But it also introduces some issues during the thermal cycling test or highly accelerated stress test, for example, warpage, peeling, blistering, and even cracking. In order to reduce these risks at the materials selecting stage, four common dielectric materials–PI A, B, C, and phenolic resin D were investigated in their thermomechanical properties and surface characteristics. And a design of the experiment on process improvement was conducted. The experimental results show that material A owning excellent elongation exceeding 30%, acceptable curing temperature below 260 °C, and low coefficient of thermal expansion (CTE) at 52 ppm/K is more suitable to be adapted as dielectric in RDLs compared with other materials chosen in this article.