Creep Corrosion

Creep corrosion is a failure mode in which a corrosion product — most commonly copper sulfide — forms on exposed metal and then migrates ("creeps") across an otherwise non-corroding surface such as solder mask or a noble-metal finish. As the conductive sulfide film spreads, it can bridge the gap between adjacent pads or traces and create leakage paths or outright shorts. Unlike dendrite growth, creep corrosion does not require a voltage bias; it is driven chemically by sulfur and moisture, which means it advances even on unpowered boards sitting in storage.

Conditions that trigger it

The recipe has two ingredients: a sulfur-bearing atmosphere and humidity. Hydrogen sulfide and related reduced-sulfur gases occur around certain industrial operations, paper mills, wastewater treatment, agricultural facilities and livestock barns, some geothermal areas, and even from off-gassing materials like some rubbers and cardboards. Combine those with elevated humidity and exposed copper or silver begins converting to sulfide, which then wicks outward across the board surface. Surface finish matters enormously: immersion-silver (ImAg) finishes are notably susceptible, producing predominantly copper sulfide with a smaller fraction of silver sulfide, while ENIG and OSP finishes generally resist better. The mechanism became prominent industry-wide when RoHS-era finish changes coincided with reports of servers and electronics failing within months in sulfur-rich sites — a reminder that a board qualified for an office can be unqualified for a barn.

Implications for miners

Mining hardware ends up exactly where creep corrosion thrives: barns and outbuildings, containers beside generators, sites near industrial or agricultural sulfur sources, unfiltered air pulled through by fans at enormous volume. An ASIC moves vastly more air per day than a desktop PC, so whatever is in that air meets the hashboard continuously — and heat-reuse deployments in living or working spaces add their own humidity swings. The visible warning signs are discolored, dark, or powdery deposits creeping outward from pads, connector contacts that darken or tarnish quickly, and unexplained leakage between adjacent nets. Any of these is worth investigating before the film bridges conductors; by the time a domain rail shows a soft short, the chemistry has been working for months.

Defenses

Control the environment first: filter intake air where sulfur sources are nearby, manage humidity, and keep boards clean — dust holds moisture against the surface and accelerates every corrosion mechanism. At the hardware level, prefer resistant surface finishes when specifying or repairing boards, and apply a protective conformal coating over vulnerable areas; a coating that blocks the atmosphere from the metal stops the reaction at its source. Immersion cooling sidesteps atmospheric corrosion entirely, which is part of its appeal in harsh sites. For boards already affected, the remedy is mechanical and chemical cleaning back to sound metal, repair of any eaten traces, then re-protection — cosmetic wiping of the deposits without removing the sulfide layer just resets the clock.

The bigger picture

Creep corrosion rewards the operator who treats siting as an engineering decision rather than an afterthought. Cheap power in a sulfur-rich building can quietly cost a fleet of boards; a filter, a coating pass, and periodic inspection under good light are trivial by comparison. For the bias-driven electrochemical cousin of this mechanism, see dendrite growth; for the thermal path to similar intermittent failures, see thermal fatigue.

Make inspection routine rather than forensic: when boards are out for cleaning or fan service, look over pad edges, connector contacts, and the tin-lead-coloured areas under good light, and keep dated photos of a known-good board as a baseline — creeping films announce themselves by change more than by appearance. Ten minutes per service interval catches in month two what otherwise becomes a dead domain in month eight.