The cone-beam computer tomography (CT) is a new non-destructive testing method, which can be used in electronics industry. In the same manner like in the well-established x-ray microscopy the information of the inside structure of the tested sample results from the attenuation of the x-ray radiation while transition through the object. In contrast to the known principle of fan-shaped CT in medical application, the cone-beam CT uses a volumetric beam to scan the test object and therefore obtains a series of 2D images. The reconstruction of these scans leads to a 3-dimensional model of the tested object. The typical application of this method is the visualization of the inner and outer structures of electronic components, packaging and interconnection technologies, e.g. flip chip (FC) and (micro) ball grid arrays (BGA, μBGA). The radiation of an x-ray tube is usually polychromatic, which means that the x-ray photons have different energies. Low energetic radiation is better absorbed in the material than the higher energetic one. For best imaging results the cone-beam CT requires monochromatic radiation and therefore beam-hardening is performed. The resulting hardened radiation will still not be monochromatic and causes artifacts in the imaging of the object, which have to be corrected. The paper will describe the basics of computer tomography and beam hardening and furthermore discuss methods to reduce the influence of beam hardening on the imaging quality of the measured objects.
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