Dendrite Growth

Dendrite growth is the formation of branching, tree-like metallic deposits that bridge between conductors on a circuit board. Unlike tin whiskers, which grow from internal stress alone, dendrites are the product of electrochemical migration (ECM): they require the simultaneous presence of moisture, ionic contamination, and an applied voltage bias. Together these form a thin electrolyte film across which metal dissolves at the positive conductor, migrates as ions, and re-deposits as a conductive filament growing toward the negative conductor.

The four-stage mechanism

ECM typically progresses through four stages: electrolyte-layer formation (humidity condensing over ionic residues), metal dissolution at the anode, ion migration across the film under the electric field, and metal deposition at the cathode, where the characteristic branching structure grows back toward the anode. As dendrites lengthen they lower the surface insulation resistance between conductors, first causing leakage currents and erratic behaviour, ultimately a hard short. The short can be dramatic: a thin dendrite carrying real current often vaporises itself, leaving an intermittent fault that clears and re-forms — one of the most maddening failure signatures a repair bench encounters. Of the common board metals, silver is the most susceptible, followed by tin and copper, which is why immersion-silver finishes and certain flux residues warrant extra care.

Drivers on real mining hardware

The main accelerants are high humidity (commonly cited above roughly 60% RH), ionic residues such as unremoved flux, and tight conductor spacing under bias. Mining hardware collects all three. Hashboards live in basements, garages, sheds, and containers where humidity swings daily; fans pull dust — often hygroscopic and ionic — across densely packed boards that hold a permanent DC bias whenever powered. Repairs add their own risk: every BGA rework or hand-soldered fix leaves flux behind, and activated residues left uncleaned under a component are a textbook dendrite nursery. A board that fails weeks after an otherwise good repair frequently traces back to exactly that.

Prevention and cleanup

Prevention centers on removing what dendrites need. Clean thoroughly after any rework — isopropyl alcohol and a brush at minimum, proper board wash for serious work — so no ionic residue remains under bias. Control the room: keeping RH moderate in the mining space does more for board longevity than most operators realise. Layout-level defenses (spacing, solder mask, surface-finish choice) are set by the manufacturer, but conformal coating is an owner-accessible barrier for boards destined for damp environments, and full immersion in dielectric fluid via immersion cooling removes the moisture film entirely — one of its quietly underrated benefits. If you find grey-black feathery traces between pads during inspection, clean them off completely, identify the moisture and contamination source, and fix that before re-powering, or the growth simply restarts.

For closely related failure modes, see our entries on creep corrosion and tin whiskers, and compare the assembly-time defect of a solder bridge — a short present from day one, versus the dendrite's short that grows in the field.

A bench checklist

A few habits keep dendrites theoretical instead of expensive. Inspect under magnification at an angle after every repair — dendrites are thin, semi-transparent, and easy to miss face-on, hiding along solder-mask edges and under component bodies. Use no-clean flux as directed or clean it anyway; "no-clean" means low-activity residue, not residue that is safe under bias in a humid shed. When a board arrives with water damage or visible corrosion, wash and dry it thoroughly before first power-up, because applying bias to a contaminated wet board is precisely the recipe that grows filaments in minutes. And log ambient humidity where your machines live: a ten-dollar hygrometer is the cheapest insurance in the entire failure-prevention toolkit.