A2Z Consulting

One of the most important design aspects for power electronics applications is predicting the junction temperatures (Tj) of the silicon dies in the power semiconductors and making sure it remains within allowable range (usually  less than 125-150 ˚C). In order to allow accurate Tj prediction for power modules (IGBT and diode dies assembled in the power module), detailed 3D thermal models were developed.
In contrast to the simple steady state two-resistor models usually used (based on manufacturer’s datasheet values), the detailed model is based on the actual 3D geometry and includes the different layers (e.g. baseplate, substrate, Si dies) and TIMs (thermal interface materials, e.g. die attach, substrate attach, thermal grease). The detailed model is implemented in CFD (computational fluid dynamics) and/or FEM analysis software, and can be used to predict the transient and steady state temperatures of the different layers. 
The advantages of the detailed 3D model are:

• Provides the actual 3D temperature distribution in the power module and heatsink surface (we can get the actual temperature distribution on the Si dies instead of average “virtual junction” temperature).

• Allows consideration of the thermal coupling between adjacent dies/substrate in multi-dies modules.

• Allows consideration of the module to module thermal coupling in multi-modules assembled on a common heatsink.

• Can be used to optimize the modules layouts on the heatsink.​