Reliability of wafer level chip scale packages (WL-CSP) under dynamic loadings

Abstract

Wafer level chip scale packaging (WL-CSP) of connectivity RF components for mobile devices has emerged as a low-cost, enabling technology. WL-CSP devices are electronic components with an exposed die that utilize a ball pitch compatible with standard surface mount technology (SMT) equipments, and common PCB design techniques. WL-CSP allows the devices to be directly mounted on the PCB of portable devices. One concern of adopting WL-CSP for mobile device applications is reliability under dynamic loading conditions, such as phone drop, due to the fragile nature of the exposed silicon die and the unique packaging designs. To mitigate this risk, a set of technical guidelines were established to qualify WL-CSP devices for mobile applications where high strain rate loading is of concern. Several failure modes unique to WL-CSP were addressed and the feasibility of the implementation of WL-CSP, directly mounted on the mobile phone board, without the application of underfill was demonstrated.