Quality inspection of multi layer ceramic micro devices is a challenging task for large-scale production. Detection of embedded cavities, metal strips or defects within a sintered multi layer alumina ceramic stack is one of the research areas under investigation in the EU-Multilayer project. Since visible light is highly scattered in the turbid alumina, traditional optical imaging techniques fails and acoustic microscopy requires the structure to be soaked in a liquid for good acoustic coupling. In this paper we investigate the performance of optical coherence tomography (OCT) as a candidate for inspection of alumina films. To understand how deep we can “see” through the alumina material, an optical scattering model is built up based on the study of microstructure of the sintered alumina sample. The investigated sample has high purity, more than 1% porosity and an average pore size of 0.8 µm. By applying optical coherence tomography (OCT) to a sintered tapered alumina ceramic sample for the first time, a depth profile of sample is obtained with high resolution. The maximum detectable thickness was is 0.26 mm using an OCT system with center wavelength at 1.3 µm and axial resolution of 12 µm.

For an emerging market a mass and cost-effective production of non-silicon micro devices requires an in-process and accurate 3D monitoring to assure the quality. Optical coherence tomography (OCT) providing high-resolution contactless imaging is used to inspect the surface quality of a laser-machined alumina ceramic layer. Quantitatively the root mean square (rms) roughness is measured by traditional means and provides input parameters to theMonte Carlosimulation of OCT method. We found that the quality of both free and embedded surfaces of the highly-scattering alumina ceramic material can be evaluated by OCT.

Large-scale and cost-effective manufacturing of ceramic micro devices based on tape stacking requires the development of inspection systems to perform high-resolution in-process quality control of embedded manufactured cavities, metal structures and defects. With an optical coherence tomography (OCT) system operating at 1.3 mu m and a dedicated automated line segmentation algorithm, layer thicknesses can be measured and laser-machined channels can be verified in alumina ceramics embedded at around 100 mu m depth. Monte Carlo simulations are employed to analyze the abilities of OCT in imaging of the embedded channels. The light scattering parameters required as input data for simulations are evaluated from the integrating sphere measurements of collimated and diffuse transmittance spectra using a reconstruction algorithm based on refined diffusion approximation approach.