Characterization of Micro-Crack Propagation through Analysis of Edge Effect in Acoustic Micro Imaging of Microelectronic Packages

The miniaturization and three dimensional die stacking in advanced microelectronic packages poses a big challenge to their non-destructive evaluation by acoustic micro imaging. In particular, their complicated structures and multiple interfaces make the interpretation of acoustic data even more difficult. A common phenomenon observed in acoustic micro imaging of microelectronic packages is the edge effect phenomena, which obscures the detection of defects such as cracks and voids. In this paper, two dimensional finite element modelling is firstly carried out to numerically simulate acoustic micro imaging of modern microelectronic packages. A flip-chip with a 140μm solder bump and a 230MHz virtual transducer with a spot size of 16μm are modelled. Crack propagation in the solder bump is further modelled, and B-scan images for different sizes of micro-cracks are obtained. C-line plots are then derived from the simulated B-scan images to quantitatively analyze the edge effect. Gradual progression of the crack is found to have a predictable influence on the edge effect profile. By exploiting this feature, a crack propagation characterization method is developed. Finally, an experiment based on the accelerated thermal cycling test is designed to verify the proposed method.