Drop test and TCT reliability of buffer coating material for WLCSP

Portable electronic products has been extended for highperformance and high-density LSI applications in recent years. One of the major concerns of portable electronic products is performance of package during drop impact and temperature cycle test (TCT) because fracture and/or delamination of the fine joint parts are caused. In addition, in terms of process limitation or device yields, process temperature limitation is required below 200deg.C in some packaging applications. Recently, the organic passivation as polyimide, polybenzoxazole and BCB are widely used in top layer of IC chips. In terms of material development, it is interesting to clarify which material properties are most important to release the stress during TCT, drop test, and other reliability tests. In this study, TCT and drop test of WLCSP with various kinds of buffer coating material were carried out. As the results of TCT and drop test, some polymers show good reliability performance. Above all, photosensitive polyimide PIMEL^TM BL-series was lower fail rate by TCT and drop test regardless of the chip size. PIMEL^TM BL-series is 200deg.C curable material which is expected to show good reliability.