Board Level Reliability Study of WLCSP with 5-Sided and 6-Sided Protection

Creating die protection is a key characteristic of molded afer-level-chip-scale package (mWLCSP) comparing to wafer-level-chip-scale package (WLCSP). Sidewall crack is a common defect mode on WLCSP. Therefore, molding compound or backside lamination (BSL) layer is applied at die periphery to increase package protection. Innovative 5-sided mWLCSP and 6-sided mWLCSP are proposed to create package protection and strength. In 5-sided mWLCSP, compound covers five sides of die surface, including die sidewall and backside. In 6-sided mWLCSP, compound covers five sides of die surface, including die sidewall and die active side. BSL covers die backside to achieve 6-sided protection.In this study, WLCSP and 5-sided mWLCSP are comprised of one RDL, one Polyimide (PI) layer, one under bump metal (UBM) layer, and Ball-Grid-Array (BGA) balls; 6-sided mWLCSP is comprised of one RDL, molding compound which is filled at RDL space, one PI layer which is covered on top surface of RDL and molding compound, one UBM layer, and BGA balls. Board level reliability (BLR) test is applied to evaluate package protection performance. BLR tests are comprised of TCT condition G (- 40~125 °C ) and drop test with acceleration 1500G. Stress simulation on die, UBM neck, and ball are applied to generate optimized BLR package structure. Simulation results obtain 6-sided mWLCSP can reduce 12% stress on die, 35% stress on UBM neck, and 47% stress on ball, comparing to WLCSP. 5-sided mWLCSP can reduce 6% stress on ball, but increase 3% stress on die and perform the comparable stress on UBM neck comparing to WLCSP.From BLR drop test results, both 6-sided mWLCSP and 5-sided mWLCSP show comparable results to WLCSP. From BLR TCT results, 5-sided mWLCSP shows comparable results to WLCSP, but 6-sided mWLCSP shows significant improvement on 1st failure performance comparing to WLCSP. From BLR results, innovative 6-sided mWLCSP can improve die protection and BLR performance comparing to WLCSP.