Considerations for a robust moisture performance of a flip chip in package for lead-free soldering

This work provides a comprehensive study on several approaches to obtain a robust lead-free flip chip package. The influence of materials, chip passivation, package configuration and cleaning processes were investigated to provide insights on the effectiveness of each approach to improve the moisture sensitivity level (MSL) performance. Results showed that the underfill/flux compatibility to the chip passivation has a strong influence on the MSL performance. Furthermore, it was observed that the unmolded version generally has a better MSL performance than the molded flip chip in package (FCIP) for a given material combination. However, there is no strong correlation between MSL performance and material properties. The plasma cleaning and defluxing processes were introduced to assess any potential improvement in MSL performance. Based on the results, plasma cleaning was found to be effective in improving the MSL performance. Defluxing evaluation showed potential for MSL performance improvement provided the defluxing process is well controlled. It is also worth noting that with the right underfill/flux/passivation combination, plasma cleaning may not be necessary to achieve the same MSL performance. In summary, this paper has emphasized the importance of mold compound/underfill/flux/passivation compatibility and the effectiveness of an optimized plasma cleaning or defluxing process to improve MSL performance. This study has also sucessfully demonstrated that MSL 1 performance can be achieved with the right choice of materials combination without additional cleaning processes.