Thermal Resistance to Heat Sink Calculator
Estimate the heat-sink performance needed to keep electronics inside safe operating limits.
Thermal Resistance to Heat Sink Calculator
Enter the known values and run the calculation.
Overview
Estimate the heat-sink performance needed to keep electronics inside safe operating limits.
Use this tool to estimate the maximum sink-to-ambient thermal resistance a heat sink can have before the device exceeds its junction-temperature limit.
It is useful during first-pass power-stage design, repair review, and package replacement work when the thermal path needs a quick reality check.
The math and how it's used
The total thermal budget is (Tj max - Ta) / P in C/W.
The required sink-to-ambient value is theta SA = theta JA budget - theta JC - theta CS.
This is the back-of-the-envelope heat-flow number for deciding whether a temperature budget is even plausible before you get into a full enclosure or airflow model.
It treats the path as a lumped thermal resistance chain. Mounting flatness, interface material, airflow, copper spreading, and transient loading can all move the real temperatures.
Assumptions
This is a steady-state calculation. It does not model transient thermal impedance, airflow changes, spreading resistance, or poor mounting pressure.
If the result is very tight, use package data, heat-sink curves, and real airflow assumptions before making a hardware decision.