Comprehensive Design Analysis Of Thick FR-4 QFN Assemblies For Enhanced Board Level Reliability

Abstract

Quad Flat No-lead package (QFN) is one of the most cutting-edge technologies emerged in the market, exhibiting high performance and efficiency with unparalleled cost effectiveness. QFN, a leadless package, is an ideal choice for applications where size, weight thermal and electrical characteristics are critical, particularly in mobile and handheld devices. Applications like automotive, defense and high current circuits require the package to be mounted on thick printed circuit boards (PCB). But using thick PCBs (>3mm) is detrimental to the package reliability. The motivation of this work is to understand the effect of several package parameters affecting reliability and optimize the QFN package to improve reliability for application on thick boards. Initially, the FE modeling methodology in ANSYS APDL was studied to gain insight on mesh/solution/analysis controls. ANSYS APDL model was leveraged to benchmark ANSYS Workbench model in order to create a consistent reliable model and propose best practices for modeling in ANSYS Workbench. The material properties of the PCB were determined using Instron Micro tester, Digital Image Correlation technique (DIC) and Thermal Mechanical Analyzer (TMA). Next, several material/dimensional parameters affecting QFN reliability on thick board were studied and chosen for optimization. Finally, Multi design variable optimization (MDVO) was performed to propose the optimum design parameters to reduce solder damage in thick boards QFN assemblies.