Factors affecting Pb-free flip chip bump reliability modeling for life prediction

The reliability of flip chip bumps remains a concern even after underfilling the gap between the chip and package substrate. A number of factors influence this reliability and it is desirable to evaluate the effect of these factors through simulations. However, underfilling introduces new material and modeling variables into the simulation methodology which need to be considered carefully. This paper reports on the study conducted to evaluate the impact of underfill material properties and modeling methodologies on solder bump response. Further, different post-processing schemes and damage indicators are evaluated to determine the best indicators for fatigue damage in solder bumps for flip chip applications. The results of these evaluations are compared with fatigue data collected on multiple package types using temperature cycle tests with in-situ resistance monitoring.