Assessment of Delamination Risk During the Package Sawing Process by Simulation

Delamination at the interface between leadframe and epoxy mold compound (EMC) is a typical concern in microelectronic packaging. Deterioration after moisture penetration can result in lots of quality issues, like Cu wire corrosion during application conditions, die crack or package crack during forming and singulation processes, and Cu wedge crack during thermal cycling test (TCT). Delamination could initiate during the assembly process and propagate during moisture sensitive level (MSL) pre-conditioning, testing or customer application conditions. Among these, package sawing singulation is the key factor that can initiate delamination. Therefore, understanding the stress resulting from sawing will help to drive leadframe design and sawing process optimization to minimize delamination concerns. Numerical modeling can play a vital role in addressing the challenges; especially in predicting differences on stress for delamination with different sawing process parameters and leadframe designs. In this study, simulations are conducted using Ansys Explicit Dynamics with the blade tip modelled and half of a unit that is next to saw street attached to adhesive film. Different sawing parameters with sawing blade starting position nominal vs offset, sawing blade move down speed, and sawing blade rotational speed are studied for an optimal process window to minimize delamination. Different leadframe designs are also studied to identify the best design to minimize delamination risk during the sawing process. Simulation results show lower stress for a lower blade down speed and lower blade rotation speed, indicating lower delamination risk. While a leadframe design that use less Cu and more EMC within the saw street can also reduce delamination risk.