Accurate prediction of SnAgCu solder joint fatigue of QFP packages for thermal cycling

We present an approach for the accurate prediction of the solder joint fatigue of quad flat packages (QFPs) with gullwing-shaped leads exposed to thermal cycling on board (TCoB). The derived fatigue life model is experimentally validated against more than 25 legs that differ in package size, materials, thermal cycling temperature profile and exposed pad vs. non-exposed pad type. The fatigue life model shows an accuracy of 25% and is used to analyze the sensitivity of the solder joint lifetime of QFPs w.r.t. changes in material properties and geometry.