Photothermocapillary detection of conductive track ruptures on a printed circuit board coated with a protective film

The photothermocapillary (PTC) method has been proposed to detect ruptures of the copper tracks of a printed circuit board coated with a black protective film absorbing the pump laser radiation. The ruptures were simulated by obtaining parallel tracks of different lengths by etching in ferric chloride solution. The method consisted of the scanning with the pump laser of the tracks along a line perpendicular to them and passing through their midpoints, and plotting a scan-profile of the diameter of PTC signal as a function of the scan coordinate. The scan-profile was a sequence of maxima and minima the diameters of the PTC signal corresponded to the beam position in the middle between adjacent tracks and in the midpoint of the track, respectively. It was found that with an increase in the track length above a critical value, dependent on the laser beam power, the diameter of PTC signal reaches saturation. With increasing power by 1.85 times, the sensitivity of the PTC method increases by 2.57 times. The spatial resolution of the PTC method reaches tens of micrometers. Experimental results have shown that the proposed PTC method is simple and efficient for detecting of hidden defects of the copper tracks on the PCB. (paper)