Investigation of printed wiring board testing by using planar coil type ECT probe

A new application of eddy current testing techniques for investigating trace defects on printed circuit boards is proposed. A test probe consisting of a meander type exciting coil is used to induce eddy currents. The following three experiments are conducted: measuring the induced signal when a circuit trace is cut; measuring the induced signal for a number of traces placed in parallel and with a cut in the centre trace; measuring the induced signal for two back to back right angle traces. The experimental results reveal that it is possible to clearly detect defects and that the signal response obtained is strongly associated with a particular defect pattern. The signals obtained from a high density patterned board have a complicated signal signature and are therefore difficult to interpret. This complexity can be avoided by comparing the signal signature of a known good board with a defective board. The difference signal gives a clear indication of a trace defect.