| The IC packaging is quite important to the semiconductor industry. In the recent decades, the semiconductor industry has made brilliant achievements owing to the rapid development of FEOL process. However, IC packaging has become the bottleneck restricting the development of electronic devices. The wafer level package (WLP) technology integrates processes such as packaging, aging, testing, and finally cutting on the wafer level, which has many advantages such as low cost, small package size, good heat dissipation and etc. Moreover, the redistribution layer (RDL) in WLP devices increases the I/O density by redistribute the pad location and improves the integration by integrating passive devices within. In this study, the influence of RDL on WLP reliability was studied, which provides reference for WLP structure design and reliability improvement.Temperature cycling test was carried out on RDL structured WLP devices of different pitch and ball size. Results showed that WLP reliability decreases with the drop of pitch size. When the pitch size is equal, the reliability decreases with smaller ball size. Three typical failure modes were found through failure analysis. Solder crack of chip side or PCB side is the main failure mode. RDL separation with UBM was found in samples only in samples with large solder size and oblique-line-shape crack was found with small solder size. Finite element analysis (FEA) indicated that stress concentration can be found where failure occurred. Stress concentration was also found inside the silicon chip, which may cause chip crack even fracture. Another kind of copper-pillar structured sample without RDL was tested to be compared with RDL structured samples, which showed lower reliability. Failure analysis indicated that the copper pillar structure used in this study affects the reliability greatly.Study on vibration reliability test was carried out with fine pitch WLP devices. A set of practical test methods was designed according to preliminary results. |
PDF Full Text Request