Thermal Capacitance

Time Constant

Lag in the temperature rise occurs because the material must absorb energy before it can pass it on. Increasing the thermal capacitance of a heat sink allows it to handle short bursts of high power. This buffer prevents the junction temperature from exceeding its limits during transients.

Material Property

Copper and aluminum are frequently selected for their specific combination of density and heat capacity. In a thermal model, thermal capacitance is represented by a capacitor connected to the ground. The value depends on the volume of the material in the heat path.

Transient Behavior

Dynamic simulations use these values to predict the thermal behavior under cycling loads. Thermal capacitance is the primary factor in determining the cooling time of a system after the power is removed. Designers balance the weight of the system against the required thermal storage.

The verification of these properties involves measuring the rate of temperature rise under a constant heat load.