Planar computer tomography (PCT)

Abstract

There is an increasing demand on testing various layers of a multi-layer Printed Circuit Board (PCB) assembly. Especially the soldered joints are often the reason for the malfunction of IC board. This problem cannot be solved by 2-dimensional testing devices because of an overlapping of two different components or soldered jounkts at double side assemblies. Also in the case of Ball Grid Arrays (BGAs), only tomographic inspection systems provide the required information. Classical Computer Tomography (CT) reconstruction is based on axial rotation of the inspected object. The planar geometry of PCBs presents a problem with the necessary axial rotation for the inspection of PCB. Lateral planar movement would be better suited than rotation necessary for classical CT. Since the algorithm of Planar Computer Tomography (PCT) is well suited for parallel computers and only a few projections are needed, a significant speed-up will be achieved compared with axial (CT) and other 3D inspection tech niques. As a future extension, it is planned to add the possibility of testing even electronic devices internally because all ICs, which were soldered directly on a PCB, face the risk of being damaged due to the high temperatures of the soldering process. Therefore a final inspection for cracks and delaminations becomes more and more necessary. As a result, resolution and reliability of such testing devices has to be improved significantly