Reliability study on chip capacitor solder joints under thermo-mechanical and vibration loading

Abstract

In this work we present the results on a reliability study on chip capacitor solder joints. The components were tested under three different loading conditions. First, temperature shock tests were conducted on a set of various chip capacitor components. Tested components were evaluated for the occurred damage and the causing damage mechanisms. Using finite element analysis (FEA) the accumulated solder joint creep strain per cycle was determined and used to establish a life time model based on the Coffin-Manson approach. Second, another set of components was exposed to vibration loading. These components were tested in the as cast and isothermally pre-aged condition. The vibration experiments were accomplished at room and elevated temperature. The evaluation focused on the occurred damage as well as the causing damage mechanisms again. FEA was utilised to determine the maximum von Mises stress of the solder joints. Life time and stress data were merged to define the parameters for a Basquin life time model for the vibration load cases. In a third step sequential experiments were accomplished. Temperature cycling with subsequent vibration loading and vice versa was done. Observed cycles to failure were compared to the results from the temperature shock and vibration experiments. A reduction in crack initiation as well as failure cycle count was observed. The damage mechanism was studied as for the single load experiments. Temperature shock testing was proofed to cause dominant shear loads within the solder joints. Observed cracks appeared to be based on creep deformation. In contrast, vibration causes dominant tensile and compression within the solder joint. The cracks showed a refined grain zone at their boarder pointing to an at least partly plastic deformation cause. Combined loads revealed superposed damage mechanisms. Both pre-ageing before as well as vibration experiments at elevated temperatures significantly enhance the solder joint damage. However, the combination of vibration and temperature cycling proposes the damage process even stronger. Solder joint life time reveals to be significantly shorter after vibration pre-ageing and subsequent temperature cycling tests than after temperature shock experiments.