Redistribution-Layers for Fan-Out Wafer-Level Packaging and Heterogeneous Integrations

Redistribution layers (RDLs) are the most integral part of wafer-level packaging (WLP) [1, 2], especially for fan-out wafer-level packaging (FOWLP) and heterogeneous integrations [3]. For FOWLP, the RDLs are the interconnections between the chip or chips and the solder balls to be attached to the PCB (printed circuit board). For heterogeneous integrations, the RDLs are the interconnections between the chips (lateral communications) and the next level of interconnections (vertical communications) such as the TSV-interposer, package substrate, solder balls, and PCB. In this study, six major methods in fabricating the RDLs are presented. These are: (1) organic RDLs (polymer and ECD [Electrochemical deposition] Cu + etching), (2) organic RDLs (photosensitive polymer and ECD Cu + etching), (3) inorganic RDLs (PECVD [plasma enhanced chemical vapor deposition] and Cu-damascene + CMP [chemical-mechanical polishing]), (4) hybrid RDLs (first organic RDLs and then inorganic RDLs), (5) bridge RDLs, and (6) fan-out on substrate RDLs. Many examples will be given and some recommendations will also be provided.