FOWLP-Based Flexible Hybrid Electronics with 3D-IC Chiplets for Smart Skin Display

This paper deals with a flexible 3D-IC system fabrication methodology. Mini-LEDs and 3D-IC chiplets divided from a large 3D-IC with Cu-TSVs are embedded in an elastomer PDMS based on die-first FOWLP for heterogeneously integrating them into Smart Skin Display as a biomedical/wearable FHE (flexible hybrid electronics). We address a serious die-shift issue for the tiny chips in die-first FOWLP by using a new anchoring layer technique to drastically reduce the shift within $2.7\ \mu\mathrm{m}$ including assembly positioning errors. The mechanical/electrical properties of the flexible array of 3D-IC chiplets are characterized before and after repeated bending with a curvature radius of 10 mm. In addition, stress neutral axes are designed to stably endure bending cycle applicable to the biomedical/wearable FHE with multi-level metallization.