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

Abstract

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 characterisation 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 CLine 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.

Characterization of micro-crack propagation through analysis of edge effect in acoustic microimaging of microelectronic packages

“…Finite element modelling for acoustic micro imaging of microelectronic packages was carried out in our previous research to investigate the acoustic wave propagation inside a package and the generation mechanism of edge effect [8,9] of the FEM modeling undertaken to describe the contrast in the UT-imaging of solder bumps using an SAM can be found in [8].…”

“…Figure 6, it can be seen that the Dip-Y reaches a quasi-saturation point beyond a crack of 55µm. This is due to the edge effect mainly occurring in regions at and close to the edge of the UBM structures [8]. Due to the transducer resolution limitation, current scanning acoustic microscopy cannot quantitatively evaluate small defects directly through C-scan images.…”

“…Edge effect [8] is a physical phenomenon in acoustic imaging of microelectronic packages where sample edges scatter acoustic energy leading to dark annular regions around the solder bump. This is clearly seen from the ultrasonic C-scan images shown in Figure 1.…”

Finite element modelling for the investigation of edge effect in acoustic micro imaging of microelectronic packages

“…The parameters in Equation (2) Figure 9a shows the obtained B-scan image using Model A. In order to study edge effect, a C-Line plot [4,5] as shown in Figure 9b is generated by gating the B-scan image to the desired interface, similar to real C-scan imaging. Since we are interested in the silicon die-tosolder bump interface, the gate is set to select that interface.…”

“…In our earlier study, finite element modelling was proposed to investigate acoustic propagation inside microelectronic packages, and the basic finite element model and preliminary results were reported in [4]. In [5,6], C-line plot technique was developed for characterisation of edge effects in acoustic C-scan images, in particular solder joint C-scan images. In this paper, the model is further improved by introducing the dynamic meshing, more suitable material properties, characterisation of virtual transducer, etc.…”