Cold Joint

A cold solder joint is a defective connection formed when solder fails to reach a high enough temperature to fully melt and properly wet the surfaces being joined. Instead of flowing smoothly and bonding metallurgically, the solder solidifies while still partly pasty, producing a joint that looks dull, lumpy, grainy, or cracked rather than bright and smoothly concave. Electrically it is a liar: it may conduct perfectly on the bench, read a few stray milliohms high, or open up entirely — and it can cycle through all three states as temperature changes.

How to recognize one

A good joint has a bright or satin finish with a clean fillet that wets up onto both the pad and the lead. A cold joint typically appears dull and rough, may show a visible crack or gap between the solder and the metal, or sits as a ball that never spread. On a repair bench the reliable combination is magnification plus measurement: inspect under a stereo microscope for the dull, grainy signature, then confirm suspicious joints with a multimeter — and remember that an intermittent joint may need gentle probe pressure or a temperature change to reveal itself. When inspection is inconclusive, a careful reflow attempt on the suspect joint is itself a diagnostic: if the fault clears, you found it.

Why hashboards breed them

Cold joints come from insufficient heat, movement before solidification, oxidized surfaces, or too little flux to allow proper wetting — and mining hardware then supplies the perfect environment for marginal joints to fail. A hashboard runs hot, cycles between hot and cold with every restart and curtailment, and vibrates under fan load around the clock. That relentless thermal cycling works marginal joints until they crack. The repair literature this site is built on catalogs the recurring victims precisely: cold joints on domain-boundary CLK resistors break the chip chain exactly at a domain boundary; cold solder on CI/BO chain resistors breaks the chain mid-domain; a cold joint on a chip's own signal-forwarding pins (CO, CLKO, NRSTO) kills everything downstream of a chip that is itself alive; and a cracked joint under the crystal oscillator produces the classic zero-chips, no-clock board. The tell in each case is the pattern: a chain that always breaks at the same chip position points to a specific joint, not a dead ASIC.

The intermittent-fault trap

The costliest property of a cold joint is that it passes tests. A board reflowed carelessly can hash flawlessly for an hour on the bench, ship, and then drop a chain two weeks later when the facility runs five degrees warmer — the fault appearing in the kernel log as chips that enumerate on some boots and not others, or a hashboard that vanishes and returns with temperature. Any fault that comes and goes with heat should put solder integrity at the top of the suspect list, alongside connectors.

The proper fix

The repair is to reheat the joint to full melting temperature with fresh flux so the solder genuinely reflows and wets both surfaces — not to poke more solder on top of a bad bond, which just buries the defect. For joints near large copper pours, use a preheater so the iron or hot air is not fighting the plane's thermal mass; starving a joint of heat is how it went cold the first time. After rework, verify continuity, then burn the board in at operating temperature rather than trusting a cold bench pass — the standard a serious bench holds itself to, and the reason a properly repaired board should be re-tested from the start of the test sequence, not just spot-checked where it failed.