What is the difference between thermal resistance and thermal conductivity?

Thermal conductivity λ (W/mK) is a material property that indicates how well a material conducts heat. Thermal resistance Rth (K/W) is a system property that describes how much temperature difference arises for a given heat power in the overall system. Rth depends on material, geometry, contact interfaces and flow conditions.

Does the calculator account for contact resistance?

No. The calculator computes the total required thermal resistance from the component to the cooling medium. In practice, this consists of several partial resistances: semiconductor → package → thermal paste → heat sink → cooling medium. Each of these interfaces must be taken into account in a detailed design.

What to do if the required Rth is very small?

A very small Rth (< 0.05 K/W) means that a large amount of heat must be dissipated over a small temperature difference, practically unachievable with air cooling. Liquid cooling is required in this case. COOLTEC offers various designs from Monopress to Structureflow.

How accurate is this calculation?

The calculation is a first estimate based on simplified assumptions. It is suitable for preliminary sizing and assessment of the cooling strategy. Thermal simulations, measurements and specific geometry data are required for the final design.

Calculate Thermal Resistance

Q: What to do if the required Rth is very small?

A very small Rth (< 0.05 K/W) means that a large amount of heat must be dissipated over a small temperature difference, practically unachievable with air cooling. Liquid cooling is required in this case. COOLTEC offers various designs from Monopress to Structureflow.

Q: How accurate is this calculation?

The calculation is a first estimate based on simplified assumptions. It is suitable for preliminary sizing and assessment of the cooling strategy. Thermal simulations, measurements and specific geometry data are required for the final design.

Thermal resistance Rth is the key parameter in heat sink design. Enter power dissipation and temperature limits: the calculator instantly determines the required Rth.

Why is Thermal Resistance Critical?

Every electronic component has a maximum operating temperature that must not be exceeded. The heat sink must dissipate the generated power loss so that this limit is maintained. Thermal resistance Rth (unit: K/W) describes how efficiently a heat sink achieves this: the smaller the Rth, the more heat can be dissipated at the same temperature difference.

Rth Calculator

Power Dissipation P_V

Max. Component Temperature T_max

°C

Ambient / Inlet Temperature T_0

°C

Formula and Derivation

ΔT = T_max − T_0

The temperature difference is the maximum component temperature minus the ambient or coolant inlet temperature.

R_th = ΔT / P_V

The required thermal resistance is the temperature difference divided by the power dissipation. Unit: K/W.

Practical Calculation Example

An IGBT module has a maximum junction temperature of 70 °C. The power dissipation is 2,000 W, the cooling water inlet temperature is 20 °C.

ΔT = 70 °C − 20 °C = 50 K
R_th = 50 K / 2,000 W = 0.025 K/W

The required total thermal resistance is 0.025 K/W. This value is only achievable with liquid cooling.

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