Nondestructive detection of defects in multilayer ceramic capacitors using an improved digital speckle correlation method with wavelet packet noise reduction processing

The nondestructive detection of defects in multilayer ceramic capacitors (MLCs) in surface mount printed circuit board assemblies has been demonstrated using an improved digital speckle correlation method (DSCM). The internal cracks in MLCs that contribute to the thermal displacements on the MLC surface after DC electrical loading may be uniquely identified using this improved DSCM combined with double lens optical management. However, it is found that Joule heating of the MLC sample takes time, and therefore the thermal displacements on the MLC surface are not pronounced at the beginning of the DC electrical loading. In order to shorten the detection time and increase the resolution of the DSCM, a wavelet packet noise reduction process is introduced into the DSCM technique. This new algorithm is used to reduce the signal background noise in order to improve the defect location detection accuracy and reduce the detection time. By introducing wavelet packet noise reduction processing, the DSCM is found to be more sensitive to and faster at defect detection in MLC samples.