While no two PCB defects are identical, almost all PCB failure analysis jobs can be broken into three distinct phases. The first of these phases is the inspection phase. Upon receiving a malfunctioning printed circuit board, an analyst spends time visually characterizing the sample, answering several questions about its condition and construction. Have the manufacturer's specifications been met for parameters like via registration and metallization spacing, and could failure to meet these specifications result in catastrophic failure (for example, if the board is used to handle extremely high voltage and current)? Are there burn marks, discolorations, reflowed solder, or other anomalies that may give an indication as to the general location of a defect? After answering these and countless other questions, the analyst is ready to move on to the next phase of the job and isolate the location of the failure.
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In the isolation phase of a PCB failure analysis, the analyst uses a variety of tools to narrow down the location of a defect. Isolation can take many forms, depending on the failure mode; for example, the analyst may choose to image the failing device using an infrared camera and compare it to a unit that functions properly, attempting to find any anomalous "hot spots" that may indicate leakage paths between traces or shorts between layers of the board. To look for an open, an analyst could use Time-Domain Reflectometry (TDR), using precise equipment designed specifically for testing the reflection of a high-frequency signal and identifying the location of open circuits. With the results from the inspection and isolation techniques in hand, the analyst can move on to the final stage of the analysis.
Once the analyst has completed inspection and isolation techniques, he or she usually has a theory about what sort of defect is causing the device to malfunction. The verification phase is where an analyst attempts to prove this theory. This phase may be non-destructive (for example, Auger spectroscopy may be used to confirm the presence of ionic contamination) or more destructive, involving a cross-section through the failure site or even parallel delayering of the board, in a similar fashion to how integrated circuits can be deprocessed. Once the analyst has verified the failure, their findings can be summarized in a report and delivered to the customer, who can then improve their processes or design to prevent recurrence of the problem.
PCB failure analysis can be of immense value to a manufacturer, whether they are responsible for making circuit boards themselves or merely use them in their final product. IAL offers PCB failure analysis services for precisely this reason; by making our years of expertise available to the customer, we greatly increase the chances of successfully resolving a given issue and implementing effective corrective actions.