Printed Circuit Board Failures – An Overview of Common Defects
Considering the relative ubiquity of printed circuit boards in modern electronics, a typical failure analysis engineer will undoubtedly see countless numbers of printed circuit board failures over the course of his or her career. At first blush, many of these jobs may seem to have very little in common – a twisted, charred circuit board from the on-board computer of a river ferry and a defective video game console could hardly be more dissimilar. While it is true that no two failure analysis jobs are alike, and that all defects have subtle nuances that make them unique, PCB failures can generally be broken down into two categories: those occuring during the manufacturing process, and those that occur after the unit has been delivered to the end user.
Manufacturing printed circuit boards is a complex task; it is not surprising, then, that there are several opportunities to accidentally introduce a defect into the product. If proper care is not taken to adhere to the exacting tolerances set forth by a designer, the result can be catastrophic failure. For example, if two metal traces are not sufficiently insulated from one another on a high-voltage board, an arc can occur, charring the board and often destroying the entire circuit. Precise standards must be observed when it comes to populating the board with components, as well; an improper selection of solder or reflow temperatures can result in poor wetting or solder bridging, either of which spells disaster for a circuit. Some of these defects may be detected during initial testing of the devices; others may not manifest until the unit has been delivered. To prevent these types of printed circuit board failures from cropping up, many manufacturers choose to sacrifice a small portion of their products for destructive physical analysis (DPA), to ensure that all specifications have been met and that there are no indicators of potential process problems.
Field failures, on the other hand, do not necessarily result from any inherent material deficiency of the product. Though in some cases a unit that was only marginally good when delivered by the manufacturer will eventually wear down and fail after a moderate amount of use, it is equally likely that a printed circuit board failure that occurs in the field has been subjected to unfavorable conditions. A PCB may have been subjected to mechanical or thermal stresses that are above and beyond what is normally expected, causing accelerated wear on the device. Even the cleanliness of the environment can make an impact on a PCB – a printed circuit board that operates in an environment with large amounts of ionic contaminants may experience corrosion causing an early life failure.
For manufacturers to continually improve their processes, it is of the utmost importance to be able to discern the former category of printed circuit board failures from the latter. It is here that failure analysis becomes incredibly valuable – by identifying process weaknesses, a good failure analysis report can provide a manufacturer with crucial data for creating better products.
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.