The Effect of Solder Joint Microstructure on the Drop Test Failure-A Peridynamic Analysis

We investigate the drop reliability of different solder joint microstructures using a coupled board-level finite-element (FE) analysis and the microscale peridynamic (PD) simulations that can capture fracture in the heterogeneous solder joint. A new PD model for elastic behavior across a material interface is introduced and used in computing the damage and failure in the two-phase microstructure of a solder joint. This new model eliminates oscillations in strains at an interface. The microstructural geometry is digitized from the scanning electron microscopy images of experimentally tested samples. To simulate the drop test conditions, we employ the input acceleration method in the board-level FE model and calculate nodal velocities for the boundary conditions imposed on the microscale PD model. We test two different microstructures of intermetallic component (IMC) (AuSn4) and SAC305: flash and thick Au content. The results show significantly more fracture in the samples with larger Au content compared to the flash samples, which correlate well with experimental observations. The computed results show that the failure mechanism for solder joints with high Au content is a fracture through the AuSn4 IMC as well as along the interface between the inclusions and the matrix. A newly introduced measure, the quasi-damage index, estimates the locations in the microstructure of the solder joint with the highest risk for initiation of cracks and damage.