Thermal Cycling Durability Assessment and Enhancement of FBGA Package for Automotive Applications

The essential functions provided by electronic packaging are, among many others, mechanical protection of the fragile electrical device subjected to harsh environmental and operational loads, electrical connection and isolation for electronic components within a system, and thermal dissipation paths for the functioning heat generating silicon chip. In the past, these functions had normally been achieved by traditional lead frame based packages such as SOIC, DIP, QFP and QFN. In many cases, while addressing reliability and thermal issues a traditional lead frame based package can easily consume 4-5 times more space than the active device it contains, resulting in a remarkable waste of the precious package footprint. In this regard, BGA (Ball Grid Array) technology is a more desirable packaging alternative due to its intrinsic size reduction capability and highly favorable electrical performance. Nevertheless, it is well known that the board level ATC (Accelerated Thermal Cycling) test performance of BGA packages is worse than its lead frame counterparts since its interconnects are much more rigid. Therefore, to ensure the reliability and durability of its solder joints is a critical task when developing a BGA package for automotive applications, where safety is extremely demanding.This paper initially investigates the solder joint reliability of the FBGA package for automotive applications during board level ATC test through Finite Element Analysis (FEA). Experiments were then carried out to assess the accuracy of the FEA model. It is found that the predictions made by the FEA simulation do not match the actual test result. The failure pattern suggests that it could be related to the excessive package warpage during testing. Viscoelastic behavior of the polymer based materials was then characterized and taken into account. The updated FEA model is found to have much better simulation result. To validate this approach, packages with standard and low CTE core materials were built and tested. Good agreement is found between the simulation and testing results. Significant improvement of the package fatigue life is observed with low CTE substrate core materials.