Development of C-Line plot technique for the characterization of edge effects in acoustic imaging: A case study using flip chip package geometry

• Numerical modelling and simulation of acoustic wave propagation in flip chip packages
• Development of C-Line plot technique for the characterization of edge effects in acoustic imaging
• Edge effect in acoustic images of flip chip packages is mainly attributed to the UBM structure.
• Investigated the impact of the transducer focal point and the spot size on the edge effect

Edge effect is a common phenomenon observed in acoustic micro-imaging of microelectronic packages. In this paper, using flip chip package geometry as a test vehicle, finite element modelling is carried out to study the fundamental mechanism of the edge effect phenomenon. C-Line plot technique is developed for the characterization of edge effects in acoustic C-scan images, in particular solder joint C-scan images. Simulated results are compared to experimental results. Results reveal that edge effect generation is mainly attributed to the under-bump-metallisation structure. In addition, through analysis of the C-Line profile of edge effects, the impact of the transducer focal point and the spot size on the edge effect is investigated. Results show that slight off-focus can reduce the severity of the edge effect in which image sharpness is a trade-off.