A Shock Vibration Calculation Method Considering Viscoplastic Behavior of Packaging Systems

With the development of electronic packaging technology to high density and miniaturization, the reliability of multi-chip packaging system under dynamic load is becoming more and more prominent. The traditional frequency domain vibration analysis method has been unable to meet the reliability assessment requirements of the packaging system due to ignoring the plastic accumulation of the space-time dimension. Therefore, this study proposes a signal conversion method for vibration calculation. The time domain shock signal conforming to the frequency domain design standard is generated by the iterative modified Fourier transform algorithm. The pure elastic finite element model of typical BGA package is used to verify the algorithm. The stress change calculated by time domain vibration can reflect the energy oscillation attenuation process of the system, and the error between the maximum stress level and the frequency domain calculation result is kept within 7%. Based on the VUMAT subroutine, the non-uniform creep-plastic behavior of SAC305 solder was described. After embedding it into the finite element model, the shock vibration calculation of pure elastic and viscoplastic models was compared. The results show that the plastic deformation mechanism absorbs the local concentrated stress. The maximum stress of the viscoelastic model of BGA solder ball is 44% lower than that of the pure elastic model, and it is close to the scientific level of material yield stress. This result shows that the proposed calculation method can provide a more accurate vibration reliability assessment of the packaging system.