A Study in PCB Failure Analysis
Over the course of a failure analyst’s career, he will be exposed to an extensive and varied array of devices. No matter the technology--whether they be nanoscopic silicon sensors with moving parts so small as to defy belief or massive circuit assemblies comprised of thousands of discrete components and integrated circuits--no device is completely immune to failure. Variations in process control, insufficiently robust designs, and extended abuse by an end user can all spell early doom for a device.
In our introductory article, Failure is the First Step on the Road to Success—the Failure Analysis Process we took a high-level overview of the failure analysis process, discussing the steps an analyst takes to turn a failing, rejected product into actionable knowledge for process improvement. In this column, we will see how these steps are applied to a specific failure. Naturally, examining a relatively trivial case would not provide the necessary depth of learning, so instead we choose to give an example of a failure many analysts dread: an intermittent failure on a printed circuit assembly.
In this study, a single printed circuit assembly was received as an RMA from an end-user. The end-user was able to identify the failing assembly only by swapping parts; lacking any sort of test equipment, the customer was unable to provide any detail that could help to narrow the scope of the analysis beyond the most basic of failure descriptions (“this part doesn’t work anymore”). The first step in the failure analysis process is to verify the failure; after initial photodocumentation, the assembly was put into functional testing using an application test bench. Initial results were disheartening, to say the least; the assembly functioned as designed, with supply current and output levels within specifications.