A method of distinguishing the level of features in projected x-ray images: application to multilayer printed circuit boards

An image in an x-ray microscope is a projected image that includes all info rmation throughout the thickness of the object being exposed. This results in a loss of level information from the different layers. In this work, a m ethod has been developed to distinguish the level of metal layers in multil ayer printed circuit boards (PCBs) without measurement coupons, and by the use of x-ray microscopy. To distinguish the levels of two metal layers, an indicator point was first defined on the edge of each layer and used for id entifying the layer it belonged to. The sample was then moved parallel to t he connecting line of the two indicator points. During the movement. the ch ange trend in the projected distance between the indicator points was evalu ated visually or by using a ruler or an image analyser. If the projected di stance increases, the leading point is on the upper layer and the trailing point on the lower one. If the projected distance decreases, the leading po int is on the lower layer, while the trailing point is on the upper one. Fo r a layer structure with more than two layers, the level order can be deter mined by comparing each layer pair.