Nondestructive detection of defects in miniaturized multilayer ceramic capacitors using digital speckle correlation techniques

The novel application of a digital speckle correlation method (DSCM) was demonstrated for the in situ and nondestructive detection of cracks in small objects such as multilayer ceramic capacitors (MLC's) in surface mount printed circuit assemblies. A combined DSCM and double lens optical arrangement was employed for the measurement of minute surface deformations in MLC's. An improved cross algorithm instead of the original full-field search method was developed based on the unimodal character of the DSCM and reduced the operation time by an order of magnitude without sacrificing the measuring accuracy. The internal cracks in MLC's that contributed to the thermal displacements on the MLC surface after the electrical loading could be uniquely identified using this improved DSCM. This technique was found to be extremely sensitive to the presence of internal cracks in MLC's of different sizes ("1206", "0805", "0603", and "0402") created by thermal shock and has been shown to be more reliable and user-friendly than other conventional nondestructive techniques. A resolution of better than 20 nanometers in surface deformation measurements is achieved within 0.01 pixel resolution. The location and the size of defects, as obtained from the DSCM, correlate well with destructive physical analyses and surface temperature variation analyses performed on the respective samples.<
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