Test Screening of Solder Joints Under Combined Cyclic Thermal and Bending Load for Automotive Applications

The cost and time efficient qualification process of solder joints' reliability in automotive electronic assemblies requires accelerated temperature cycling (ATC) testing. This work introduces a load-dependent reliability assessment method on board level for solder joints of multilayer ceramic capacitors (MLCC) under superimposed cyclic thermal and 3-point bending load. For this purpose, a testing setup is developed, which enables statistical testing of solder connections under accelerated load scenarios. The solder joints are monitored online by means of impedance measurement until failure. In this work, solder joint failure of a large amount of MLCC 1206 components is experimentally investigated, where the following lifetime influencing factors are studied: solder volume variation and MLCC 1206 components from different suppliers.The resulting lifetime of solder joints with volume variation reveals, that under the same loading conditions smaller solder joints show a significantly lower survival probability compared to solder joints with larger volumes. Furthermore, significant differences in solder joint lifetime between components from the two different suppliers are observed.In order to derive a load-dependent failure criterion using measurement data, finite element (FE) simulation is performed under consideration of test boundary conditions. In this way, printed circuit board (PCB) deformation is determined, taking into account both the thermal and mechanical induced strains. It is shown, that the relationship between calculated load-dependent PCB strain amplitudes and experimentally detected solder joint failures are described by a power law leading to component Woehler curves for different failure probabilities.