What is the difference between dendrites and conductive anodic filaments on a circuit board?
Dendrites and conductive anodic filaments come from two related mechanisms: dendrites are the surface form of electrochemical migration on a circuit board, while conductive anodic filaments are its internal counterpart inside the laminate. Dendrites are branching metal structures that grow across an insulating surface from cathode toward anode and are visible under low magnification as fern-like or frost-like deposits. Dendrites can form in days under the right combination of humidity, contamination and bias.
In conductive anodic filament (CAF) formation, copper migrates along a degraded glass-fiber-to-resin interface inside the circuit board laminate, typically between plated through-holes, producing a short buried where no external inspection can see it. CAF is slower and more insidious than surface dendrite growth, and it is driven by the same three ingredients: humidity, contamination and bias.
What makes electrochemical migration possible on a circuit board?
Ionic contamination is usually what makes electrochemical migration possible on a circuit board, because humidity alone is rarely sufficient. The enabling ionic residue can be flux activators not fully removed, chloride or sulfate from handling or the environment, plating salts, or residues from a cleaning process that was itself incomplete. Those ions provide the electrolyte that electrochemical migration requires.
This makes circuit board cleanliness a measurable property rather than a matter of appearance. Ionic contamination testing and surface insulation resistance testing exist precisely because a circuit board can look immaculate and be electrically dirty. Where a manufacturing process changed — a new flux, a no-clean process treated as if it needed no control, a cleaning step removed to save cost — the change record is often where the answer to an electrochemical migration failure sits.
Does conformal coating prevent electrochemical migration on a circuit board?
Conformal coating is the standard mitigation against electrochemical migration on a circuit board, and it works when the coating is complete. Conformal coating fails where it is thin, where it did not wet a surface, where it was masked and the mask was misplaced, and around tall components that shadow adjacent areas during application.
So the useful examination in an electrochemical migration failure is not whether the circuit board was coated but whether the conformal coating covered the location that failed. Cross-sectioning through the failure site answers that directly, and conformal coating thickness and adhesion at the failure are more informative than a general statement about the coating process.
How does the service environment trigger electrochemical migration in electronic equipment?
Condensation is the practical trigger in a great many electrochemical migration service failures, and condensation is a thermal question rather than a humidity question alone. Electronic equipment that cools below the dew point of the air around it wets internally, regardless of how dry the specification claimed the environment was. Enclosures that breathe, outdoor installations, refrigerated spaces and anything subject to a daily thermal cycle are all candidates for this internal wetting.
Reconstructing the environment behind an electrochemical migration failure means reconstructing the installed conditions: enclosure sealing and drainage, heater or dehumidifier provision, ventilation, and the actual temperature and humidity history rather than the design assumption.
How is a grown short on a circuit board distinguished from other kinds of board failure?
A grown short on a circuit board is distinguished from other failures by the distinctive morphology and composition of dendrites and conductive anodic filaments. The distinction that matters is between a short that grew and one that was always there or was created by the incident under investigation. Elemental analysis identifies the migrated metal, and the metal’s distribution shows the direction of growth from cathode to anode.
Damage from an overstress event looks different from a grown short: localized melting, vaporized conductor, and damage centered on a junction rather than tracking between conductors. Where a circuit board has burned, distinguishing the initiating short from the resulting fire damage is the same cause-versus-consequence discipline that governs electrical fire work generally.
In what order should a circuit board with a suspected grown short be examined?
A circuit board with a suspected grown short should be examined non-destructively first, because most of the techniques used to examine electrochemical migration are destructive. Radiography and computed tomography (CT) locate internal features before anything is sectioned. Conductive anodic filament (CAF) formation in particular is invisible externally, and CT is often the only way to find a conductive anodic filament without guessing where to cut.
Once a failure site on the circuit board is located, cross-sectioning, scanning electron microscopy and elemental analysis characterize it. Cutting first and imaging afterward frequently destroys the evidence, because a conductive anodic filament is a feature a few microns across in a specific plane.
Can accelerated testing prove that electrochemical migration caused a failure in service?
Accelerated testing cannot prove by itself that electrochemical migration caused a failure in service: testing under temperature, humidity and bias can demonstrate that a given design and process combination is capable of the observed failure, but showing that migration can be produced under aggressive acceleration does not establish that it occurred in service. Demonstrating that capability is a genuinely strong piece of evidence, and it is also easy to overstate.
The persuasive version of an electrochemical migration reproduction pairs the accelerated test with the field evidence — the same morphology, the same location, the same migrated species — and states the acceleration factors rather than presenting a chamber result as if it were a service observation.
Why does a short caused by electrochemical migration often look intermittent at first?
A short caused by electrochemical migration often looks intermittent because a dendrite thin enough to bridge two conductors is also thin enough to fuse open when it carries current, which produces a fault that clears itself and then returns as growth resumes. A grown short rarely arrives as a hard failure. Equipment with a grown short behaves erratically for weeks, then works perfectly on a bench where the humidity is lower.
That intermittent signature is diagnostically useful rather than merely frustrating. A fault correlating with humidity, with time powered, or with a particular installed location — and disappearing under investigation — is characteristic of electrochemical migration, and it is worth pursuing as such rather than being closed as unreproducible.
Where does responsibility for an electrochemical migration failure usually land?
Electrochemical migration failures tend to resolve to process control and application rather than component quality. Design rules on conductor spacing and hole-to-hole distance, laminate selection, cleanliness control, conformal coating coverage, and the suitability of an enclosure for its environment are each traceable to a decision and a document.
That traceability is also why the manufacturing and process change records are worth requesting early in an electrochemical migration investigation. A migration failure across a population of circuit boards almost always coincides with something that changed.
This article is general technical orientation, not a failure analysis, an engineering opinion, or advice on any specific matter. Determining the cause of a particular incident requires hands-on examination by a credentialed expert.