Abstract
Acoustic microimaging (AMI), a technology for high-resolution imaging of materials using a scanning acoustic microscope, has been widely used for non-destructive testing and evaluation of electronic packages. Recently, the internal features and defects of electronic packages have reached the resolution limits of conventional time domain or frequency domain AMI methods with the miniaturization of electronic packages. Various time-frequency domain AMI methods have been developed to achieve super-resolution. In this paper, the sparse representation of AMI signals is studied, and a constraint dictionary-based sparse representation (CD-SR) method is proposed. First, the time-frequency parameters of the atom dictionary are constrained according to the AMI signal to constitute a constraint dictionary. Then, the AMI signal is sparsely decomposed using the matching pursuit algorithm, and echoes selection and echoes reconstruction are performed. The performance of CD-SR was quantitatively evaluated by simulated and experimental ultrasonic A-scan signals. The results demonstrated that CD-SR has superior longitudinal resolution and robustness.
Highlights
Acoustic microimaging (AMI) can evaluate the surface layer, sub-surface layer and internal structure of materials with non-destructive, precision and high sensitivity
AMI signals with different degrees of overlap can be obtained by the above simulation model, and are used to test the performance of sparse representation (SR) and constraint dictionary-based sparse representation (CD-SR) methods in improving the longitudinal resolution
When the amplitude error or position error of the reconstructed echo is greater than 30%, it is considered that the method cannot correctly reconstruct the echo before the overlap
Summary
AMI can evaluate the surface layer, sub-surface layer and internal structure of materials with non-destructive, precision and high sensitivity. It has been used in the fields of microelectronics [1], materials science [2], technical science [3], etc. Considering the penetration depth and resolution, the ultrasonic frequencies required for electronic packages detection are 20–200 MHz. Recently, electronic packages have been evolving towards ultra-miniaturization and ultra-high density, which creates challenges for their AMI. When the thickness of the layer is less than or equal to the length of the ultrasonic wave, the echo overlap and waveform distortion of the adjacent interface are caused by insufficient longitudinal resolution. While increasing the ultrasonic frequency can improve longitudinal resolution, it means greater attenuation and lower penetration
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