Cracks In Multilayer Ceramic Capacitors Research Articles

Resonant Acoustic Frequency Shifts Associated With Cracks in Multilayer Ceramic Capacitors

Resonant ultrasound spectroscopy (RUS) was used in this paper to measure shifts in resonant frequency that arise from the presence of cracks in barium-titanate-based multilayer ceramic capacitors (MLCCs). This paper was motivated by an industrial need for a nondestructive quality-control technique with enhanced capabilities for detecting dielectric cracks that have no initial effect on electrical characteristics of MLCCs. In this quality-control application, no information will generally be available on acoustic spectra of capacitors prior to the introduction of cracks during manufacture or mounting in devices. However, information on the distribution of frequencies of a specified resonant acoustic mode of a population of uncracked MLCCs could serve as a reference for determining whether the resonant frequency of an individual MLCC is within an acceptable range. In this paper, acoustic spectra were obtained from sets of MLCCs before and after thermal quenching that generated surface-breaking cracks in a fraction of the specimens. Three resonant modes below 1000 kHz were studied. The largest of these three resonant peaks, in the range of 575 kHz to 595 kHz in MLCCs before heat treatment, was found to be most sensitive to the presence of visible cracks. An analysis of Gaussian fits of the frequency distributions for this mode before and after heat treatment shows that approximately 71% of the visibly cracked MLCCs and less than 1% of the uncracked quenched MLCCs are rejected when the criterion for rejection is that the frequency is more than two standard deviations different than the mean frequency before heat treatment. These results show that RUS is a promising approach for nondestructive screening for the presence of cracks in MLCCs.

Detection of cracks in multilayer ceramic capacitors by X-ray imaging

A non-destructive method using X-ray imaging to find cracks in multilayer ceramic capacitors (MLCCs) mounted in different orientations with respect to the bending direction is presented. In total 300 MLCCs were investigated by 2D and 3D X-ray imaging after bending to varying levels of strain, and cross-section analysis was done to verify the findings. With X-ray imaging it was possible to not only detect the continuously cracked MLCCs, but also the cracked ones which were mounted 45° to the bending direction. These non-continuous cracks are difficult to identify even with cross-section analysis because the crack can be absent at the selected interface. None of the cracks could be identified by external optical inspection of the components using optical microscopy. The MLCCs mounted perpendicular to the bending direction were not cracked during the experiments, whereas the MLCCs mounted 45° or parallel to the bending direction were cracking at 3100 and 4300μStr, respectively. Finding cracks with a non-invasive technique such as X-ray imaging is very advantageous because of its possible implementation as a screening test in a production environment.

Nondestructive defect detection 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 by 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 arrangement. However, it is found that Joule heating of the MLC sample takes time, and therefore the thermal displacements on the MLC surface are not obvious 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 background noise in the signal so as to improve the accuracy of detection of defect locations and reduce the detection time. By introducing wavelet packet noise reduction processing, the DSCM is found to be more sensitive to and faster at detecting defects in MLC samples. Furthermore, the DSCM with wavelet packet noise reduction process can cope with the problems of edge effect, rough and warped surface, which are the limitations of the scanning acoustic microscope (SAM).