Towards measurements of global coefficient of thermal expansion of QFN

The electronic component's thermomechanical behaviour has a major impact on the reliability of electronic assemblies. Indeed, solder joint failure is primarily due to thermal strains induced by severe thermal variation. The goal of this paper is to summarize the characterizations results obtained by Thermo-Mechanical Analysis (TMA) as a first approach to determine the global Coefficient of Thermal Expansion (CTE) of Quad Flat No-leads (QFN) components of different sizes. They were placed in a TMA analyser with a thermal profile going from −55° to 125°C. The values obtained for the out-plane measurements show another thermomechanical phenomenon. Indeed, negative and abnormally high amplitude of CTE have been measured. The mean value of the effective CTE is found at-413 ppm/°C for QFN64 and at −330ppm/°C for QFN64-6,2. The main difference between the two QFN is the die size. QFN64-6,2 has a smaller die than QFN64. Measured values decrease with the size of the components. The deflection due to warpage has been quantified by Fringe Projection Profilometry on randomly chosen QFN. For the QFN64-6,2 the mean deflection is equal to 42 μm at room temperature which is in adequation with the TMA measurements.