Board level drop reliability study and orthotropic PCB material property test methodology

摘要

Board-level drop reliability including BGA solder joint failure, PCB cratering and Cu-trace cracking, etc., has been challenges to the whole industry for decades. The trend of consumer electronics is moving towards higher density and thinner PCB design, which raises a strong need for drop durability design. In this work, the focus is placed on board-level relaiblity of portable consumer electronics such as mobile phones. Compared to homogeneous material model, orthotropic model is a more realistic representative of a multilayer composite material like PCB. For better simulation accuracy, a novel method has been used for testing orthotropic PCB material property through acoustic vibration, laser vibrometer, and material property fitting via Hyperstudy optimization tool. A Johnson-Cook material model for solder has been used, which gives more accurate simulation results when the material is subjected to high strain rates during a drop impact. In additional, a-submodeling approach is employed for detailed solder bump and Cu pad/trace stress and strain distribution. As a conclusion, the simulation accuracy has been significantly improved by adopting the orthotropic PCB material property, J-C solder model, and sub-modeling technology, which provides a solid foundation for the lifetime prediction of various BGA and PCB failures.