Reflow

Reflow is the controlled melting and re-solidifying of solder used to attach or reseat chips during hashboard repair. Rather than blasting a chip with heat, a technician guides the assembly through a temperature profile, distinct preheat, soak, reflow, and cooling stages, so the solder under a BGA chip melts evenly and re-forms clean joints. On a mining hashboard, reflow is used both to remove a failed ASIC and to set a replacement, and sometimes to re-melt suspect joints that have cracked from thermal cycling.

Why the profile matters

A good reflow profile ramps temperature gradually. Too cold and the solder balls never fully liquefy, leaving cold or partial joints; too hot or too fast and the thermal shock can crack ceramic capacitors, lift pads, or warp the PCB. Lead-free solder used on modern boards has a higher melting point than older leaded alloys, narrowing the safe window and making a calibrated rework station or programmable hot-air tool essential.

Where it fits in repair

Reflow is the heating step common to most chip-level work. It is part of removing a chip, part of placing a new one, and the final step after a chip has been reballed. Done correctly, it restores the hidden connections beneath a BGA package; done carelessly, it creates new faults around the rework site.

Reflow works hand in hand with related techniques. See BGA (Ball Grid Array) for the package that makes profiled reflow necessary, and Reballing for restoring solder balls to a chip before its final reflow.

A Concrete Rework Sequence

On an Antminer hashboard, reflow sits inside a longer procedure. The heatsink over the target area comes off and old thermal paste is cleaned away. Flux is applied around the failed chip, and a hot-air station running at roughly 350–380 °C air temperature heats the site until the solder liquefies and the chip lifts free. The exposed pads are cleaned flat with solder wick and fresh flux. A replacement chip — verified on a chip-test fixture if new, or cleaned and reballed with 0.4 mm lead-free Sn/Ag/Cu balls if salvaged — is placed against the board's alignment marks and reflowed with a controlled temperature profile. Flux residue is cleaned, thermal paste reapplied, and the heatsink reattached. Lead-free alloys melt higher than the old leaded solders, which is what narrows the margin between “joints formed” and “board damaged.”

Verifying the Result

A reflow is not done when the chip sits flat — it is done when the board proves itself. The standard check is a domain-voltage sweep with a multimeter: healthy domains read within about ±50 mV of each other, a domain reading 100 mV or more low suggests a partial short, and a high reading points to an open joint. Repaired boards then go back through the full factory-style test sequence from the beginning — chip detection, pattern testing, and a burn-in under load — because a joint that passes a quick check can still fail warm. Skipping the retest is how a marginal repair ships.

When Reflow Is the Wrong Tool

Blanket “reflowing” a board with a heat gun in the hope that something reconnects is a diagnostic coin-flip, not a repair: uncontrolled heat stresses every component near the target, and a cracked joint that reconnects under heat will usually crack again within weeks of thermal cycling. If a BGA joint has genuinely failed — often visible as a cold spot on a thermal camera while neighbors run hot — the durable fix is removal, cleaning, reballing, and a fresh profiled reflow, not a surface re-melt. When a board is beyond bench equipment, a professional diagnosis is cheaper than a second failure; that is exactly what D-Central's repair intake exists for.