Diotec Semiconductor AG

http://www.diotec.com/

Dec 18, 2025

New Application Note from Diotec Semiconductor: Thermal Considerations on Power Semiconductors

The Arrhenius law is often summarized with a simple rule of thumb: For every 10 K increase in temperature, the service life of a physical device is reduced by approximately 50%. For power semiconductors, this makes thermal design just as critical as electrical design. This application note shows how to correctly measure and calculate the junction temperature, provides tips on the correct application of thermal paste, and explains how components must be mounted correctly on the heat sink.

The impact of temperature is frequently underestimated. A junction temperature increase from 80 °C to 110 °C may appear acceptable during bench testing, yet it reduces semiconductor lifetime by a factor of eight. This is why experienced designers analyze the entire thermal path with the same rigor as the electrical path.

Data sheet thermal resistance (Rth) values are specified under idealized conditions. In real designs, junction temperature is influenced by PCB pad geometry, copper area, mounting force, thermal paste thickness, airflow, and system-level cooling. Electrical operating conditions also play a role: switching losses, reverse recovery effects, and transient load profiles all contribute to heat generation.

Field return data shows that many early failures are not caused by electrical overstress, but by insufficient thermal margins introduced during layout or assembly.

A power design is only reliable when the junction temperature is well understood and predictable. Once thermal behavior is under control, device lifetime becomes an engineering parameter—not a guess.

Download it here: Diotec's Application Note - Thermal Considerations On Power Semiconductors