Optimization of thermal load distribution in accelerated temperature cycling tests for solder joint lifetime qualification tests

The cost- and time-efficient qualification process of solder joints in automotive electronic assemblies requires accelerated temperature cycling (ATC) testing. Such tests, aiming to investigate durability of solder joints in increased temperature range, are usually performed in temperature chambers on component level. In typical chambers, heat transfer imposed onto tested assemblies is driven by convection causing circulation of airflow, resulting in inhomogeneous airflow velocity and temperature distributions. These effects are expected to affect the local thermal load imposed onto the solder joint and consequently solder joints in different locations of the temperature chamber could experience different load magnitudes. Finally, the higher the temperature gradients within the test setup, the higher scatter in solder lifetime data is expected. This study proposes an approach of a test setup thermally optimized using computational fluid dynamics (CFD) simulations aiming to reduce the influence of temperature deviations on the reliability of solder joints. A transient simulation approach is applied in order to optimize the local heat transfer on the test setup during thermal cycling. Furthermore, the effect of various heating and cooling gradients on the solder joint reliability is assessed in thermomechanical finite element (FE) simulation. It is shown, that the derived test bench design provides improved airflow conditions, which significantly homogenizes and increases the local heat transfer (HTC) on the component setup board due to forced convection. Finally, the decreased transient spatial temperature gradients are confirmed by temperature measurements.