Application of finite element simulation on package failure analysis and problem solving

Finite Element Simulation is a powerful method to figure out the failure root causes in IC packaging or verify the solution proposals for problem solving. This paper presents three typical cases occurring in package development or mass production respectively regarding to die crack, wire heel crack and warpage-induced process issue. Die crack is a typical failure mode and is found frequently when qualifying a new package product. In some cases, a common phenomenon is observed in different packages with die crack issue: over-high epoxy fillets attached on the cracking die sides for all failed units. In the first case, based on the assumption that over-high fillet has more potentiality to spread the delamination to the die top edge, the simulation result reveals that the structure of over-high fillet plus the delamination at the die top edge should be a severe risk to lead to die crack. Wire heel crack is also a typical failure mode which could be observed after the temperature cycle tests. In the second case, the modeling result reveals that CTE mismatch between the gold wire and the molding compound at low temperature (-65°C) induced the thermal stress which tension the stitch bond. Delamination along the lead frame surface around the stitch bond causes the large plastic deformation at the bottom of the stitch bond and leads to wire heel crack. Thus delamination is a crucial factor that causes the heel crack. Warpage-induced process issue on production line is generally solved by equipment adjustment or process improvement. The third case provides an example with revising the substrate design to improve the BGA manufacturability. The simulation results and the assembly process with the new substrate design confirm that the redesign idea is available and successful.