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Thermal stress testing: putting power devices through their paces

Date: 31.07.2025

Close-up of an electric motor, highlighting copper wire coils and its metal shaft with bearings. - CSA Catapult

CSA Catapult’s state-of-the-art equipment, practical know-how and specialist expertise help businesses solve their problems when bringing compound semiconductor products to market, making those businesses — and the UK as a whole — more competitive.

A MicReD Industrial machine for GaN testing with an open lid and control monitor in a bright, clean lab setting. - CSA Catapult

Future industrial applications, in automotive and renewable energy for example, need high-performing, high-power electrical devices. Compound semiconductors make these devices smaller, lighter and more efficient, but they work hard and create a lot of heat in systems, so CSA Catapult’s team of experts need to understand how they perform in real-world conditions.

Mouhsine Fjer, senior power electronics engineer at CSA Catapult, is an expert in designing semiconductor devices, MOSFETs and diodes. He leads technical projects that enable customers to utilise the benefits of compound semiconductors in power electronics applications.

Here, Mouhsine discusses CSA Catapult’s power tester.

What is it?

The power tester is a tool used for thermal characterisation and power cycling.

Thermal characterisation is crucial for understanding and optimising the performance and reliability of power devices. It helps determine the device’s operating temperature and ensures the rated limits are not exceeded which preserves the semiconductor’s lifespan.

It aids the design of efficient cooling systems and gives accurate estimates of power losses, as these parameters are highly temperature dependent.

The tester measures how efficiently a device dissipates heat and generates detailed reports on thermal parameters in each layer of a power module, such as thermal resistance and capacitance, and storage of electric charge.

This data creates a thermal model that designers use to optimise the design of a converter.

This equipment also evaluates the reliability of power devices under thermal stress, which helps predict the lifespan of components in power converters.

Close-up of GaN electronic circuit boards and wires connected for testing or prototyping in a lab setting. - CSA Catapult

What does it do?

The power tester measures a temperature-sensitive parameter over a range of 20-80°C. Customers can specify the parameter that best suits their needs, a process that is known as calibration.

The equipment applies a heating current to the device and records its thermal response. Based on this response, it provides measurements for thermal resistance and capacitance of each component in the device. This is called a structure function.

For reliability testing, the power tester applies a high current to a device so that it reaches a specified junction temperature, then uses a cooling system to lower the temperature.

This heating and cooling process – known as a cycle – introduces mechanical stress to the device to evaluate its reliability and detect thermal aging effects, such as cracks and wire bond breaks.

The power tester can perform millions of cycles, testing up to 16 devices simultaneously with a current capacity of up to 2400 amp (A).

Who is the power tester for?

Broadly speaking, the power tester is suitable for any company developing new products. It carries out accurate thermal characterisation and helps engineers assess how efficiently components handle and dissipate heat.

The power tester supports better design choices in cooling systems, materials, and component layout. It measures the lifespan and failure rates of devices under thermal stress which accelerates testing to predict long-term performance under various bespoke conditions.

For example, a customer might design an electric motor drive with a new power module. The power tester could create an accurate thermal model and help to achieve high efficiency and reliability before market release.

In the research and development process we help customers design products that can manage higher power and dissipate heat more efficiently using compound semiconductors.

The power tester can be used on any type of semiconductor, but there is growing demand for smaller, lighter and highly efficient converters. Those compound semiconductor devices can be put into a wide variety of high-power applications, such as data centres and energy distribution. A lot of our work so far has been in the electrification of transport.

A MicReD Industrial Power Tester with control panel, GaN device, and monitor in a laboratory setting. - CSA Catapult

How is the power tester unique?

The power tester is a prime example of why the Catapult exists: to provide companies with access to state-of-the-art equipment that helps design, test and validate devices and products. For SMEs and startups, this equipment can be expensive, and not widely available in the UK.

This equipment’s validation capabilities give our customers reassurance. With the characterisation and reliability data it provides, we can share expertise that helps customers develop competitive products and grow the UK economy.

Test, characterise, commercialise.

To find out how we can help you design and validate your products and accelerate your route to market, get in touch today. 

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