Solution of Design Induced Reliability Risk for High Density Fan-Out packages

Fan-Out (FO) technologies are used for consumer electronic products generally due to the small and very thin features. Some risks would be found when the design transfer from of 2.5D Integrated Circuit (2.5D IC) or system in packages (SiPs) to the FO packages. This paper will share a case study of High Density Fan-Out (HDFO) with thermal cycle test (TCT) and the test vehicle is open/short fail. The test vehicle is examined by curve tracer (I-V), 3D X-ray, Focus Ion Beam (FIB) and Scanning Electron Microscope (SEM) to find out the failure mode. The failure mode is delamination between the u-pad layer and the Redistribution Layer (RDL) interface. The Cu oxide layer is found on the RDL sidewall. The chemical residue leads to the oxidation of Cu on the RDL surface and the poor interface would be delamination gradually during TCT. Root cause of the chemical residue was investigated in this study. The delamination issue was resolved by adding plasma clean.