Definition
The pump-out effect is the progressive displacement of thermal paste from between a chip and its heatsink, driven by repeated thermal cycling. As a miner heats up and cools down over thousands of cycles, the chip, board, and heatsink expand and contract at slightly different rates. That relative motion acts like a pump, working the paste outward from the center of the contact area and leaving voids behind.
Why it happens
The root cause is a mismatch in coefficient of thermal expansion between the materials on either side of the interface. Each warm-up and cool-down flexes the joint, and a fluid grease caught in that motion slowly migrates to the edges or escapes entirely. The vacated regions fill with air, an excellent insulator, so effective contact area shrinks. Volatile components in some pastes can also outgas at operating temperature, drying the compound and worsening the problem. The result over months or years is rising thermal resistance and creeping chip temperatures.
Impact and mitigation on miners
ASICs are unusually exposed to pump-out because they run hot, run continuously, and may cycle whenever a pool or power event restarts them. Symptoms include chips that once ran cool gradually drifting upward and eventually triggering protective throttling. The standard fix is straightforward but high-value: clean off the degraded paste and reapply fresh compound, or switch a gap-filling location to a pad that resists pump-out. Pastes formulated for low pump-out and avoiding over-application both extend the interval between re-pastes.
For the material involved and the protective behavior it eventually provokes, see Thermal Paste and Thermal Throttling.
In Simple Terms
The pump-out effect is the progressive displacement of thermal paste from between a chip and its heatsink, driven by repeated thermal cycling. As a miner…