Dry Joint

A dry joint is a soldered connection that never properly bonded to the metal surfaces it joins, usually because too little solder was used or the solder failed to wet and flow over the pad and lead. The result is a mechanically weak, high-resistance contact that may work at first but is prone to intermittent operation, noise, or an outright open circuit. Visually a dry joint looks dull, grainy, or cracked rather than the smooth, bright concave fillet of a good joint — one of the few defects a trained eye can catch before it ever causes a failure.

Dry joint versus cold joint

The terms are often used loosely, but a useful distinction is by cause. A dry joint generally stems from insufficient solder or poor wetting — oxidized surfaces, exhausted flux, contamination — leaving a starved, incomplete bond. A cold joint stems from the solder never reaching full melt and flow, typically because the iron or the work was too cold or the parts moved before solidification. Both are latent defects present from the moment of assembly, and both degrade further under the thermal and mechanical cycling of service, developing micro-cracks that widen with every heat-up and cool-down — the same mechanism that drives solder joint fatigue in joints that started out sound.

Why miners breed them

An ASIC miner is close to a worst-case environment for marginal joints. A hashboard swings through wide temperature ranges on every start and stop, carries brutal current through its power stages, and lives bolted to heavy heatsinks in a chassis full of fan vibration. A joint that would survive decades in a radio fails in months here. The classic presentations: a machine that hashes until warm then drops a board, a chain that disappears when the chassis is moved, an error that clears when you press on a connector. High-current paths deserve particular suspicion — PSU output terminals, board power connectors, and the solder around inductors and power stages, where a starved joint's extra resistance also means localized heating that accelerates its own demise.

Finding and fixing them

Dry joints are the textbook cause of faults that come and go when a board is tapped, flexed, or warmed — gentle, targeted mechanical persuasion while watching the kernel log is a legitimate diagnostic. Under a stereo microscope, look for joints that are dull, grainy, cracked at the fillet, or show a visible ring or gap between solder and lead. The repair is straightforward: apply fresh flux, reflow the joint at proper temperature, feed in a small amount of fresh flux-cored solder so it fully wets both surfaces, and let it cool undisturbed. On larger thermal masses, hot air or a higher-mass tip prevents the half-melt that just makes a different bad joint. Never simply "add more solder" over a defective joint — the oxide and voids stay trapped inside; rework it properly or remove and redo it.

The craftsman's takeaway

Prevention costs almost nothing at build or rework time: clean surfaces, fresh flux, an iron with enough thermal mass for the joint at hand, and the patience to let solder flow fully before withdrawing heat. On the mechanical side, strain-relieve cables so connectors don't lever their own joints, and torque board fasteners evenly so heatsinks don't preload the PCB into a bend. Most dry joints are manufactured in a hurry, one careless second at a time.

Clean, fully wetted joints are cheap insurance; marginal ones are deferred failures with interest. If an intermittent board has outlasted your patience, D-Central's repair bench hunts exactly this class of fault for a living.