A Comprehensive Study of Crack Initiation and Delamination Propagation at the Cu/Polyimide Interface in Fan-out Wafer Level Package during Reflow Process

In the present study, the crack initiation and delamination propagation at the interface between Cu trace and polyimide (PI) dielectric layer in fan-out wafer level package (FOWLP) during reflow process is investigated through finite element simulation with incorporation of cohesive zone model (CZM). The influences of Cu trace layer number and the fully molded FOWLP structure on the interface reliability are evaluated intensively. The von Mises stress distribution in Cu trace with different line widths is also calculated. Simulation results show that crack initiation and delamination propagation are more likely to occur when the temperature exceeds glass transition temperature (Tg) of PI during reflow process. Interface damage is more prone to occur at the interface between the first layer Cu trace and PI dielectric layer, and becomes more serious as the layer number of Cu trace increases. In addition, the fully molded FOWLP structure seems to show reduced risk of interface damage. The von Mises stress distributed in Cu trace increases as its line width decreases.