Thermal simulation of high frequency electronic products

Passive components Filters Electronic Design Automation & Electronics Multiphysics
By David Lee | 05/07/2021

What is the power handling capacity of an electronic product? 

Simply put, it is the power level that a device can support before it fails. Generally speaking, the average and peak powers determine the power handling capacity of the product. Failure can occur abruptly due to dielectric breakdown that results in arcing, or it can happen more slowly due to thermal runway heating. To protect against such failures, systems are usually designed with a safety margin such that they operate in a dynamic range well below the damaging power levels.  

A SolidWorks model of a microwave tunable filter 

Average power 

It is well known that RF and Microwave power heats electronic products due to conductor and dielectric losses. That is why heat sinks and fans are essential to dissipate the heat.  If the average power exceed some threshold and/or the ventilation is not adequate, the “magic blue smoke” is produced.   

Peak power 

All dielectrics, including air, have a maximum electric field strength above which ionization occurs resulting in corona and sparking.  It is the well-known dielectric breakdown.  This phenomenon happens if the applied power is too high or if the spacing, i.e. air gap, between components is too small.   

The HFWorks solution 

To ensure the reliability of electronic products while avoiding the need for costly experimental setups, HFWorks provides the virtual test bench that can accurately quantify the power-handling capacity of a product based on peak and/or average power levels. At the pre-processing level, the user is able to specify the breakdown electric field value for the all dielectrics as well as the thermal properties for both dielectrics and conductors. For a given total input power level, i.e., combined over all ports, a safety factor is calculated by comparing the resulting electric field strength to the specified breakdown value at each point in the model.  The safety factor distribution is then plotted on the entire model. Regions where the safety factor equals or exceeds 1.0 will produce arcing and the other will operate safely. To assess the power handling from a thermal standpoint, the thermal loads due to conductor and dielectric losses are computed everywhere in the model for user-specified input power levels at the ports and are automatically fed into the built-in thermal solver. Taking into account additional user-defined thermal constraints such as convection, radiation, or temperature, HFWorks then finds the thermal results, i.e., temperature distribution, temperature gradient and heat flux, throughout the electronic device. The hot spots where thermal runaway heating that may lead to failure can then be easily identified.

Temperature distribution in the filter 

Summary and takeaways 

HFWorks stand outs in handling the power-handling of electronic products.  By borrowing from structural engineering, it introduces and computes a safety factor that guides designers to the high-risk areas of their designs.  In addition, using its built-in thermal solver, HFWorks streamlines the computation of thermal results based on the user input power and locates the hot-spots in the design that are at risk of runaway heating failure. Using these capabilities, the electronics engineer would excel in handling the power-handling of their electronic products hands-down.   

Safety factor distribution –a cross section-