Analysis of the stress state in QFN package during four point bending and temperature experiments utilizing piezoresistive stress sensor

This article reports a comprehensive study on four point bending and temperature experiments and their correlation with numerical simulation. The test vehicle is a printed circuit board (PCB) with 16 Quad Flat No Leads Packages (QFNs) components mounted on top and bottom side. Each QFN has 120 stress sensing cells distributed over the surface of the silicon die. In our experiments we have investigated the stress state in the QFN utilizing these piezoresisitve stress sensors for thermal, four point bending and combined loading conditions. In our study we compare these measurements with the numerical model. Stress analysis for the isothermal bending case showed that components very close to the edge are exposed to slightly higher stresses (20 %) compared to the components placed in the center of the PCB.