How to Model Power Electronics Equipment

6 May, 2020

Power electronics have high powered use cases ranging from automotive to railway and aerospace – and therefore require highly reliable cooling systems.

Engineers designing power electronics need to ensure that heat generated in the "IGBT" devices can be transferred away as easily as possible.

The figure below demonstrates how heat transfers from transistor through the package materials, through solder to the board and then from the board to the heat sink. The thermal resistance of a material determines how easily heat transfers through it. 

Figure 1. Heat transfer from transistor through package materials

Material selection is crucial in power electronics design; to ensure materials have low thermal resistance (high thermal conductivity), low electrical conductivity where they need to insulate, and they do not expand or contract too much during temperature changes.

It’s also important to consider the thermal resistance when heat is transferred between two touching materials. The interface between two materials is typically poor because, at a microscopic level, the surface is not smooth and there are many air gaps. Still air has a very high thermal resistance. The more changes in material, the higher the overall thermal resistance will be between the power electronics device and the heat sink or cold plate.

Figure 2. Heat Sink Surface - Direct Contact Versus TIM

Thermal interface materials are used to improve contact resistance – manufacturers provide hundreds of different options for thermal interface materials depending on the application. Greases and pastes are typically used.

Power electronics generate a large amount of heat which must then be dissipated away from the system. A fan and heat sink, or a liquid cooling system can extract the heat away from the power electronics. Cost, reliability and performance factors influence which cooling method is chosen.

To deliver a fully optimized product, these decisions need to be tackled as early as possible in the design process. Unfortunately, many designers still rely on "rules of thumb" to deal with thermal complications, which leads to "over-engineering" products, or trying to "manage out" thermal complications at the back end of their projects. Indeed, according to research from 6SigmaET, only 25% of design engineers test any thermal operation early on in their designs, while 27% wait until after a design is complete.

Simulation at All Levels 

Thermal simulation can test the thermal performance of power electronics before they are manufactured. 

By creating a simulated model in advance, engineers can test their designs using a wide variety of different materials at the click of a button. Simulation also enables designs to be tested in a massive array of different environments, temperatures and use states. This will not only help to identify potential inefficiencies, but also reduces the need for multiple real-world prototypes — further helping to decrease overall costs.

Tools like 6SigmaET make the job of pinpointing precise thermal challenges much easier, enabling more polished, thoroughly tested and overall, powerful electrical units – avoiding the need for unnecessary over-engineering. 

Put simply, the ease of use and capabilities of today’s thermal simulation tools means there is no longer any excuse to rely on "rules of thumb" when it comes to the thermal performance of semiconductors in power electronics products.

To find out more, contact us here

Blog written by: Matt Evans, Product Engineer