Defective ground plane structure for broadband crosstalk reduction in PCBs

With the advances in integrated circuit (IC) technologies, printed circuit boards (PCBs) with a large number of interconnects are commonly used. To accommodate a large number of line traces in a small area, multi-layer PCBs with tens of layers are widely adopted despite the high cost of fabrication. The density of signal transmission lines on a layer is mainly limited by the crosstalk levels between adjacent line traces. The conventional design guide states that the clearance of the line traces be kept larger than three times the width of line traces. Crosstalk between two traces can be calculated and analyzed using multiconductor transmission line equations. As per IPC2221, the minimum spacing between two traces is 1.25mm. This paper aims to bring down the minimum spacing to a level of 0.5mm by means of crosstalk reduction using defective ground plane structures.