PC Board Troubleshooting

by Frank Bryson
Bryson Infrared Technologies

THE PROBLEM
A printed circuit board manufacturer had problems when a batch of boards failed quality control testing.  Unfortunately, classical techniques were unable to pinpoint the problem or locate the offending component(s).  Thermal imagers allowed them to pinpoint and correct the problem.
THE SOLUTION
A board from an accepted batch and one from the failed batch were powered on a test setup and infrared images were taken of each by a thermal imager. Visual comparison of the thermal images immediately showed that several components on the failed board were operating at significantly different temperatures than the identical components on the accepted board. This was to be expected since previous traditional testing had shown abnormal voltages and power consumptions at several components. When the abnormally warm components on the failed board were observed closely we found that while one of these appeared identical to it’s duplicate on the acceptable board, its markings revealed that it was designed to operate at a higher voltage than specified. This component was generating more power than the circuit design could tolerate, causing improper operation of itself and other components. This finding explained both the malfunction of the board and the temperatures differences that the thermal image displayed.
The image produced by the thermal imager at the far left is that of the acceptable board, while that in the middle is of the failed board. The common color vs. temperature scale associated with these images can be used by the observer to visually determine the operating temperature of any component on either board.

The image to the right displays the thermal differences between the two images above. This image was generated by digitally subtracting the image of the accepted board from that of the failed board. Note that the scale to the left of the image relates color to a plus or minus temperature difference, rather than the absolute temperature as shown in the other images. Using this scale the observer can see if components on the failed board are operating at temperatures above or below their counterparts on the acceptable board.
The component at the top of the image is the source of the manufacturer’s problem. It is identical in size and shape to its proper counterpart, however since it is designed to operate at a different voltage than the design specified it caused problems throughout various circuits.

To view a list of thermal imagers used for these types of applications, please visit http://www.flirthermography.com/cameras/series/1010/.

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