Reliability and failure analysis study of multi-die embedded micro wafer level packages
Main objective of this study is to design and development of multi-die embedded micro wafer level packages (EMWLP) reliability test vehicles. Such as, the laterally placed die EMWLP and the vertically stacked thin die EMWLP. For reliability evaluation, EMWLPs have been subjected to both environmental and mechanical reliability tests as per JEDEC standards. These reliability tests include highly accelerated stress testing (HAST), thermal Cycling (TC), moisture sensitivity testing level 3 (MSL3), board level TC and drop tests. In case of drop tests evaluation, two types of pad finishes, ENIG & OSP have been used. During reliability tests both test vehicles have exhibited better performance without any electrical failures. But in case of HAST reliability test, delamination issue in two packages have been observed. Detailed failure analysis has been carried out on delaminated packages to find out the root cause for the different modes of delamination failures. Non-destructive and destructive techniques have been employed to investigate the failures in EMWLP's and this includes electrical testing, Scanning Acoustic Microscopy (SAM), micro-sectioning and Scanning Electron Microscopy (SEM). Delamination interface has been identified as passivation-RDL interface. Thermo-mechanical simulation study has been carried out over both test vehicles to locate higher stress concentration regions in the packages and finally to correlate with experimental reliability and failure analysis results.