For an integrated circuit, the junction temperature is the average surface temperature. For a discrete semiconductor, the junction temperature is the temperature at the core of the semiconductor material. The formula for calculating junction temperature is:

TJ = TSub + TInit + (PwrDiss * ThermalRes)

Where:

TJ = The calculated junction temperature.

TSub = The subassembly operating temperature.

TInit = The initial temperature rise.

PwrDiss = The power dissipation.

ThermalRes = The thermal resistance.

The junction temperature that is calculated for the integrated circuit or semiconductor is used in prediction calculations. The value calculated for junction temperature can be seen in the Pi Factors window for the device. For more information, see Part Pi Factors. Because the failure rates for integrated circuits and semiconductors are highly dependent on junction temperatures, accurate temperature modeling is important.