Phase change materials

A PCM thermal interface is a thin film that is solid at room temperature (so it ships and installs like a thermal pad) but softens or melts at a defined transition temperature — typically 50–60 °C for polymer-based grades. On the first heat cycle the material flows into the microscopic surface irregularities of the heat source and heatsink, achieving a bondline approaching that of thermal grease (10–50 µm). Once cooled below the transition it solidifies again, locking the contact in place. The result is grease-like contact resistance with pad-like installation simplicity, and no pump-out under thermal cycling.

Pick a PCM when you want grease-level contact resistance without the assembly mess or long-term pump-out risk. Common cases: server CPU/GPU integrated heat spreaders, laptop / desktop OEM cooling stacks, and any high-volume assembly where dispensing grease in line is impractical but a thermal pad's bondline is too thick. Skip PCM when (a) the surface is rough enough that even melted PCM can't fill the gap (use a pad), or (b) the operating temperature stays below the phase-change point so the material never softens (use grease).

TIC800M is a bismuth-tin alloy that goes through a true solid-liquid phase change above 60 °C and re-solidifies below 57 °C. Thermal conductivity is 18.9 W/m·K — 2–4× the best polymer PCM and 5× typical silicone grease. The trade-off: it is electrically conductive, so it must be used only on isolated package surfaces (no bare PCB traces nearby), and the phase-change temperature is fixed by the alloy chemistry. Use cases: laser diode pumps, high-current SiC modules, and any place where polymer PCM thermal resistance becomes the bottleneck.

Pick a transition temperature 10–20 °C below the device's typical operating junction temperature so the PCM reliably softens during normal duty. Most CPUs and GPUs run their lid at 60–80 °C in service, so a 50–60 °C polymer PCM is the standard choice. Industrial power modules running 80–100 °C continuously may benefit from a higher-transition formulation; ask your applications engineer. The transition temperature is independent of the maximum operating temperature, which can be much higher (TIC800K continues to function up to 125 °C).

Polymer PCMs leave a tacky residue after one heat cycle that can be wiped clean with isopropanol, similar to grease. Metal PCM (TIC800M) re-solidifies into a thin shell that requires careful peel-and-clean. Re-applying a fresh PCM after the original is removed restores the joint — but on metal-PCM joints inspect for surface alloying with the heatsink (some platings react over long service). For OEM-volume designs, plan one-time install and don't budget for field rework.

PCM films ship on different carriers: aluminum foil (TIC800A-AL — improves spreading uniformity), polyimide / Kapton MT (TIC800D, TIC800P, TIC800K — gives mechanical robustness and chemical resistance), stainless-steel film (TIC800G-ST — for higher mechanical stress), and freestanding flexible-solid (TIC800A, TIC800G, TIC800H — maximum thermal performance, requires careful handling). Polymer or metal carrier choice usually follows assembly automation needs more than thermal performance — most polymer carriers add < 5 % to net thermal resistance.