Prediction of Delamination Failure in Quad Flat No-Lead Packages Using Combined Experimental and Simulation Methods

摘要

In this research, finite-element analysis and failure analysis were performed to analyze delamination failure in quad flat no-lead (QFN) packages. Although a QFN is a traditional package and represents mature technology, the reliability standards of QFNs in automotive applications have become strict. The quality requirements of QFNs are increasing and require that no delamination or voids occur inside the package during the reflow process and precondition tests. Therefore, interfacial delamination is still a critical reliability issue for QFNs. Delamination failure weakens the internal structural strength of a QFN and affects the product reliability. In the interface delamination, initially generated small voids gradually expand due to hygromechanical stress during the moisture sensitivity level test. In addition, moisture penetration into the package can result in not only electrical failure but also chemical reactions that lead to corrosion. In this study, delamination occurs on the interface between the Cu pad and molding compound during the precondition tests. The available evidence indicates that the bonding strength between Ag plating on the Cu pad and molding compound is weak. Most delamination failure sites are located in the area of Ag plating according to scanning acoustic tomography (SAT) observations. To accurately predict the delamination failure in QFNs, the shear force on the molding compound/Ag plating and molding compound/Cu is combined with finite element modeling. Parametric analysis is conducted to determine the optimal design of the geometric structure in the QFN to combat delamination failure. This investigation can help improve the product reliability by preventing delamination failure in the QFN package through the analysis of the physics of failure (PoF).