Sequential Analysis of Drop Impact and Thermal Cycling of Electronic Packaging Structures

Electronic packaging structures go through complicated loading history such as power on-off, vibration and drop impact during the storage and serving conditions processes. All these loading applications result in the deformation and possible damage accumulation in the packaging structure of the electronic device. Considering that the thermal cycling is a standard procedure for evaluating the mechanical reliability of a packaging, we systematically investigate the combination effect of the drop and thermal cycling on the reliability of the packaging structures by using the finite element analysis. Compared with the transient analysis of drop impact, the analysis duration for thermal cycling is significantly prolonged. A representative Ball Grid Array (BGA) packaging structure is adopted to perform the sequential analysis. The strain rate and temperature dependent visco-plastic properties are considered for the Sn-3.0Ag-0.5Cu (SAC305) solder material at the solder joints. Those material properties have been validated against published experimental data. Firstly, the numerical analysis of the packaging structures subject to drop impact is conducted to obtain the distribution of plastic deformation and strain. As the plastic deformation and strain are not recoverable after the loading application, those distributions can be utilized as initial strain conditions to be imported into the subsequent analysis under thermal cycling. In the second analysis step, a temperature profile between -50°C and 125°C is applied to the packaging structure to predict the deformation and strain during the thermal cycling. The thermal fatigue life is evaluated using the Coffin-Manson model based on the predicted increment of equivalent plastic strain in the critical solder joints. More importantly, the effect of drop-impact damage on the thermal deformation and thus on the fatigue life is discussed by correlating the drop impact, thermal cycling and fatigue life as a closed loop.