Current density measurements in conductive polymer coated surfaces

A series of measurements mapping out the current density distributions in conductive polymer coated PC boards have been performed. For these measurements, a device called EMSCAN^TM, a planar array of 1280 virtually infinitesimal magnetic dipoles, was used. This device allows the user to scan for current hot spots on PCBs. It has been extremely useful in troubleshooting production boards and pre-production boards for electromagnetic compatibility for automotive applications. A comparison between three types of boards was made: a standard board clad with copper, a board clad with conductive polymer, and a board clad with ferrite impregnated polymer. Each board was fabricated with a centered trace that was then terminated with a 50 Ohm resistor to a ground plane on the reverse side of the board. A signal generator was connected to the input side of the trace and the trace was driven with sinusoidal signals ranging from 25 MHz-325 MHz. The use of conductive polymer coatings would be of benefit in automotive EMC applications where the relatively low cost, versus multi-layer PCB solutions, makes the polymer an attractive alternative. The question that needs answering is: how much benefit can be expected? This paper attempts a partial answer