Calculate thermal requirements for power components, regulators, and semiconductors.
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| Material | θcs (°C/W) | Notes |
|---|---|---|
| Thermal Paste (standard) | 0.5 - 1.0 | Most common, easy to apply |
| Thermal Paste (high-end) | 0.2 - 0.5 | Metal oxide or silver-based |
| Thermal Pad (silicone) | 1.0 - 3.0 | Easy handling, fills gaps |
| Thermal Pad (graphite) | 0.3 - 0.5 | Reusable, compressible |
| Mica + Paste | 0.4 - 0.9 | Electrical isolation |
| Direct Contact (no TIM) | 1.5 - 5.0+ | Not recommended |
Heat flows from the semiconductor junction through thermal resistances to the ambient environment. Each interface adds resistance, limiting how much power can be dissipated safely.
Junction temp equals ambient plus heat rise through all thermal resistances.
This is your total allowable thermal resistance from junction to ambient.
No fan required. Relies on rising hot air. Best for low to medium power.
Fan provides constant airflow. Much better thermal performance.
Water or coolant carries heat away. Best for high power density.
Copper or aluminum plates spread heat over larger area.
Sealed tubes with phase-change fluid for efficient heat transport.
Peltier coolers can actively pump heat. Needs heat sink on hot side.
| Package | θjc (°C/W) | θja (no sink) | Common Use |
|---|---|---|---|
| TO-220 | 0.5 - 2.0 | 50 - 70 | Power MOSFETs, regulators |
| TO-247 | 0.3 - 0.7 | 35 - 50 | High power MOSFETs, IGBTs |
| TO-263 (D2PAK) | 0.5 - 2.0 | 40 - 70 | SMD power devices |
| TO-252 (DPAK) | 1.0 - 3.0 | 50 - 100 | SMD regulators, MOSFETs |
| SOT-223 | 10 - 20 | 100 - 150 | Small regulators |
| SOT-23 | 50 - 100 | 200 - 350 | Small signal transistors |
| QFN (exposed pad) | 1 - 5 | 25 - 50 | ICs with thermal pad |
| BGA (with lid) | 0.1 - 0.5 | 15 - 30 | Processors, FPGAs |
Note: Actual values vary by manufacturer and specific device. Always check the datasheet.