PCB Failure Analysis - Dealing with Burnt and Mangled Boards
PCB failure analysis can be a daunting task in even the most ideal of cases. Modern printed circuit boards are densely-packed, multilayer rat’s nests of copper interconnects, integrated circuits, and discrete components. Isolating a single defect - which may often be a single splash of solder, misregistered via, or cracked copper trace - is an arduous process, requiring hours of probing and isolation to finally narrow down the point of failure. This process is taxing, to say the least; however, the problem is often compounded when the device to be analyzed is no more than a twisted, blackened hunk of burnt PCB material.
Failure analysis projects involving burnt PCBs can be potentially some of the most trying jobs to delve into. Not only does the wonderful aroma of smoky creosote pervade anything that comes into contact with the charred wreckage of circuit board, the failing sample is often incredibly fragile, making any sort of isolation techniques or probing difficult at best. In many cases, the defect itself will have been consumed in the conflagration, meaning the best that an analyst can accomplish is to identify the point where the incendiary event initiated. In these cases, the clue that unravels the mystery of the defect may come from the device’s history, rather than any particular element of the analysis.
One example of how analysis of a burnt PCB can be guided by a device’s history can be found in a project IAL worked on in which a badly burned TV remote control was analyzed. Thorough inspection of the device seemed to indicate an external source of ignition - the burned area of the board did not appear to carry high power, and did not have any sort of components that were particularly likely to fail so catastrophically. It was not until the customer revealed that the remote control may have been put in a microwave oven in an attempt to dry it out after it had been exposed to moisture that the initial observations began to make sense. To confirm that the microwave was indeed the source of failure, IAL purchased a microwave oven, placed an identical remote inside, and consulted our copy of “Cooking For Engineers” to determine the proper amount of microwave time for Flambeed Circuit Board (best served with a light caramel sauce). After a short wait, the remote was removed from the microwave, bearing damage remarkably similar to that of the failing unit.
Due to the nature of any sort of event that results in a charred circuit board, finding the root cause defect can be exceptionally difficult, if not impossible in some cases. With a full and detailed history, however, the goal of identifying the root cause of failure becomes much more attainable.
Derek Snider is a failure analyst at Insight Analytical Labs, where he has worked since 2004. He is currently an undergraduate student at the University of Colorado, Colorado Springs, where he is pursuing a Bachelors of Science degree in Electrical Engineering.