Bending Simulation of BGA SMT Assemblies and Application to System Level Drop Simulation

This paper will examine the displacement and strain behavior of solder joints during static and dynamic bending. Simulation has shown that four point dynamic bending test result in a higher accumulation of plastic strain than static bending at equivalent board strains. This is important as the yielding and failure of lead-free solder joints occurs primarily at the joint package interface. Solder joint strains are on the order of magnitude higher than printed circuit board (PCB) bending strains at the edge of the package. Additionally, a method for using solder joint stretch has been developed for measuring joint response. Utilizing the concept of solder stretch, a technique for using equivalent beam models for the solder joints in a system level drop will be introduced. Results for three different beam model strategies will be given. The results show these techniques are valid and their use will greatly increase the ability to determine package impact reliability during the design stages.