Reliability of RDL structured wafer level packages

Wafer level chip scale packaging (WLCSP) is one of the most promising single chip packaging technologies due to advantages of fewer processing steps, lower cost, and enhanced device performance. Moreover, the redistribution layer (RDL) technology is an effective way to improve I/O density of IC packages. However, the reliability of WLP devices with RDL structure is greatly challenged as the pitch size going down. The RDL structure may affect the thermomechanical performance of the solder joints or silicon chips, thus causing unexpected failure. In this paper, RDL structured WLCSPs with pitch size of 500 μm were fabricated. The components with a size of 6×6 mm² were flip-chip bonded on FR-4 boards. Board level reliabilities of the WLCSP were evaluated by thermal shock test according to JEDEC standard. Furthermore, failure analysis was carried out to find out the failure mechanism and the failure related to the RDL structure was observed. The effect of RDL structure on the reliability of WLP was analyzed with the finite element simulations.