As part of a thermal fatigue study for a PCB assembly, a conjugate heat transfer CFD analysis using Solidworks Flow Simulation was carried out to model the steady state temperature field of the PCBA board, subjected to specified ambient temperatures. The temperature field data was then transferred to ANSYS Mechanical for a consequent nonlinear static structural FEA to evaluate the plastic strains and estimate the fatigue life for critical components using the Coffin-Manson theory based on low cycle strain-life fatigue model.
Traditional hand calculation or uncoupled FEA based thermal study assumes values of heat transfer coefficient (HTC) and ambient temperature at all solid-fluid interfaces. By this means the local temperature distribution is underestimated and detrimental to accuracy of stress/strain and subsequent fatigue assessment. A coupled CFD-FEA approach is used in this study to capture the localized air flow and heating effects.