Solder joint reliability analysis of wafer level CSP

Wafer level packaging technology, maintaining the same size as the die, is a true chip scale packaging technology offering smallest possible footprint and increased electrical performance. Keeping balance between cost and quality becomes an important point in WLCSP industrial practice. In our work, six kinds of WLCSP samples were designed in order to find out the real reliability contribution of UBM and re-passivation layer. A comparison result and analysis under mechanical reliability tests will be presented in this paper. The emphasis will be given to discuss the possible failure mode of each structure and the necessity of underfill dispensing.