Investigation of Package Delamination Behavior in Large Quad Flat No-Lead Package

Package delamination is a common challenge in large Quad Flat No-Lead (QFN) packages. This study investigates delamination behavior in QFNs with Ag-plated leadframes to identify the delamination mechanism. The QFN package size in this study is 11x11 mm, with the chip's Al pad connected to the Ag-plated pins of the metal leadframe by copper wire. In the final step, the chip on the metal carrier with copper wire is encapsulated by a generic mold compound (EMC) for physical protection. Scanning Acoustic Tomography (SAT) was used to identify the location and degree of delamination. Preliminary SAT results during initial development revealed significant delamination concentrated at the Ag-plated stitch finger area. Cross-sectional inspection results indicated the fracture position occurred between the mold compound and Ag layers. As the adhesion between pure Ag and the mold compound can be improved by increasing the Ag oxide thickness, this study showed that increasing die bond curing temperature by 30°C and wire bond temperature by 20°C increased Ag oxide thickness from 1.75 nm to 2.15 nm. Moisture Sensitivity Level 3 (MSL3) results revealed significant improvement in delamination. Additionally, the experiment indicated the impact of plasma cleaning on delamination. Finally, reducing the Ag plating area on the leadframe by 20% exposed roughened copper, effectively enhancing the mold compound's adhesion to the leadframe, providing a complete solution against delamination.