Power electronics are essential for ensuring efficient and sustainable generation, conversion and consumption of electricity.
They play a critical role in adapting renewable energy sources—such as wind turbines and photovoltaic systems—to grid frequencies, as well as setting inverter frequencies for precise control of drive train speeds.
Critical temperature limits in power semiconductors
Temperature-related issues, particularly thermo-mechanical stresses, pose significant threats to the reliability of power electronics. Strict adherence to chip temperature limits is crucial, as exceeding these thresholds can drastically reduce component lifespan.
Effective cooling strategies are therefore vital to achieve maximum power density within compact spaces. Semiconductor devices like diodes, IGBTs, and MOSFETs are typically integrated into compact power modules to meet these demands.
Surface temperatures in an IGBT casing
Thermal management with heat sinks and thermal contact materials TIM
Power modules are generally mounted on heat sinks, which dissipate thermal losses. Sometimes, a conductive base plate is inserted between the module and the heat sink to distribute heat more evenly.
Passive heat sinks rely on natural convection, while active versions use fans for forced convection, both commonly made from thermally efficient aluminum. If these methods are insufficient, advanced solutions like water cooling or heat pipes may be employed.
All these cooling mechanisms can be accurately analyzed with 3D Computational Fluid Dynamics (CFD).
When assembling the power module to the heat sink, small air bubbles remain, which greatly increase the thermal resistance.
To mitigate this, thermal interface materials (TIMs)—such as gap pads or thermal pastes—are applied. However, the actual distribution and compression of TIMs often introduce uncertainties, making precise thermal resistance difficult to estimate.
The most reliable approach is to measure this resistance directly and use it as input for further calculations.
Thermal and flow CFD calculations
The most basic CFD model includes only the device package, but more comprehensive simulations—at the board, rack, or room level—may be necessary for accurate chip temperature predictions.
Early-stage cooling design is critical; incorporating 3D CFD analysis during the concept phase allows for precise mapping of temperature and flow fields, helping to locate and eliminate hot spots.
These simulations yield rapid, actionable results, revealing opportunities for design optimization that can be validated through further thermal analysis.
Streamlines through the heat sink of an IGBT power module
Thermal models of PCBs
Printed circuit boards (PCBs) consist of multiple copper layers interconnected by vias, all embedded in an insulating substrate like FR4. From a CFD and CAD perspective, PCBs are complex geometries.
They can be modeled either in detail or simplified as anisotropic blocks. If detailed CAD data is available, it can be exported (e.g., as a STEP file),
though preparing these models for CFD can be time-consuming, even for experienced professionals. Some commercial CFD tools, such as FloEDA Bridge for FloEFD, offer automated PCB simplification, this is suitable for regular use only.
It is advisable to perform thermal simulations of power electronics as early as the concept phase, even when only the number and thickness of copper layers are known.
Standard thermal conductivity values are often insufficient, especially as thermal vias enhance vertical heat conduction.
Companies frequently create substitute thermal models for different PCB types, drawing from prior project data.
For example, an LED headlight manufacturer may maintain standard thermal conductivity values tailored for various PCB functions such as turn signals, high beams, low beams, and brake lights.
