New WLCSP scheme for device reliability improvement

Polymer film is general used for stress buffer and dielectric film for Wafer Level Chip Scale Package (WLCSP). Chemical resistance and mechanical resistance of polymer films usually get worse after several processes with chemicals or heat. Weak chemical or mechanical resistance will induce polymer film cracking. Polymer cracking further induces humidity penetration into RDL (Re-distribution Layer) or films delamination between polymer and RDL. A rapid heating and cooling environment or field induce huge stress on component or package. The polymer of WLCSP suffers film cracking when it undergoes the huge stress. Therefore, preventing polymer film cracking becomes an important topic for advance portable device application. This new WLCSP scheme focuses on highly reliable solution for a device without under-fill. This development found that this new WLCSP scheme can provide a good balance of coefficient of thermal expansion (CTE). Moreover, the new WLCSP structure is able to change the max ball strain location from Si-end side to solder ball near the printed circuit board (PCB). The new WLCSP scheme was developed to replace the ordinary WLCSP scheme is not only able to avoid polymer/dielectric layer cracking but also can provide good ball life performance.