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

摘要

An image in an x-ray microscope is a projected image that includes all information throughout the thickness of the object being exposed. This results in a loss of level information from the different layers. In this work, a method has been developed to distinguish the level of metal layers in multilayer 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 identifying the layer it belonged to. The sample was then moved parallel to the connecting line of the two indicator points. During the movement, the change trend in the projected distance between the indicator points was evaluated visually or by using a ruler or an image analyser. If the projected distance increases, the leading point is on the upper layer and the trailing point on the lower one. If the projected distance decreases, the leading point is on the lower layer, while the trailing point is on the upper one. For a layer structure with more than two layers, the level order can be determined by comparing each layer pair.