PCB Failure Analysis: Working From the Mechanism
Boards fail in the field for a small number of reasons, and most of them are present in the design long before the failure occurs. A failure analysis that begins with the mechanism rather than with the component reaches the cause faster.
Start With the Mechanism
A failure has a mechanism: a crack, a corrosion product, a void, a short, an open or a damaged device. Identifying the mechanism narrows the possible causes, and the identification is done by examination rather than by reasoning.
The examination begins with the unaided eye and continues under magnification. A surprising proportion of failures are visible as a discoloured joint, a lifted pad or a crack across a component body. Our board quality notes describe the appearance criteria.
Non-Destructive Examination
Optical inspection under magnification, X-ray and, where available, acoustic microscopy cover most of the non-destructive ground. Each has a resolution limit and each is blind to something.
X-ray sees inside a package but not a joint that has not merged; acoustic microscopy sees delamination but needs a coupling medium; optical inspection sees the surface but nothing beneath it. The choice follows from the suspected mechanism. Our BGA inspection notes compare the methods.
<img src="https://www.gopcba.com/wp-content/uploads/2026/08/pl149813980-oem_fast_turn_custom_pcb_rigid_enig_printed_circuit_board_quick_turn.webp" alt="Microsection of a failed solder joint under a microscope” />
Electrical Localisation
Where the failure is an open or a short, localising it electrically narrows the search to a small area before any destructive step is taken. A time domain reflectometer shows the distance to a discontinuity along a trace, which is often enough to identify the location.
For a short, a current injection with a sensitive detector finds the path by the field it produces. Both techniques preserve the board so that the evidence is not destroyed by the search.
Destructive Analysis and Sectioning
Sectioning exposes the internal structure of a joint or a hole and is the definitive method for plating and solder defects. The section has to be prepared carefully, because a poorly polished section introduces artefacts that look like defects.
The location of the section is the important decision. Sectioning through the failure preserves the evidence, while sectioning through a nearby good joint confirms what the process normally produces.
Chemistry and Contamination
Where corrosion or electrochemical migration is suspected, the analysis becomes chemical. Ionic contamination, halide residues and flux activators are each detectable, and each has a characteristic appearance.
The pattern of the corrosion indicates the mechanism. Dendrites growing between conductors indicate a metal migration, while a uniform tarnish indicates an environmental exposure. Our copper surface notes describe the related processes.
Thermal and Mechanical Evidence
A joint that has been cycled shows a crack that propagates from the interface, while one that has been overloaded shows a ductile tear. The two are distinguished under magnification, and the distinction tells you whether the cause is thermal or mechanical.
The location of the crack also carries information. A crack at the corner furthest from the neutral point of the package indicates thermal fatigue, while a crack at the same location on every board indicates a mechanical cause.
Process Records and Correlation
The analysis is only complete when the failure is correlated with the process that produced it. The panel identifier, the material batch, the plating parameters and the assembly profile are the records that make the correlation possible.
Without them, the analysis can identify the mechanism and not the cause, and the same failure will recur. Our traceability marking notes describe the records.
Corrective Action and Verification
A corrective action that is not verified is a hypothesis. The verification is a repeat of the test that produced the original failure, on a sample built with the correction applied.
Where the original failure took a long time to appear, the verification uses an accelerated test that reproduces the same mechanism rather than waiting for the same duration. Choosing that test is part of the corrective action.
Process Control and Verification
On a design of this kind, failure analysis is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.
The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.
Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch. Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end.
Process Control and Verification
On a design of this kind, failure analysis is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.
The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.
Process Control and Verification
On a design of this kind, failure analysis is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.
FAQ
Should the failed board be cleaned before examination? It should be photographed first, then cleaned only where the cleaning does not destroy the evidence. Contamination is itself evidence, and removing it before it is characterised loses the information.
How many samples are needed? One sample is enough to identify a mechanism and not enough to establish a rate. Where the failure is intermittent, several samples are needed before the cause can be distinguished from coincidence.
What does gopcb provide for a failure investigation? We provide the process records for the panel, the material certificates, the coupon data and, where the board is returned, a section through the failed area. We also compare the failure with the process records of the surrounding batches to see whether the cause is local.
