Trace Current Carrying Capabilities
During the electrical design process of a printed circuit board, the width and thickness of a specific trace needs to be sized to handle the expected current passing through it. The Association Connecting Electronics Industries (formerly the Institute for Printed Circuits) has developed IPC-2221 and IPC-2152, industry-standard documents for calculating PCB trace widths to manage temperature rise. The problem is the documents do not account for real PCB's that have multiple layers with multiple power and ground layers which help dissipate the heat. Therefore, using the documents results in very conservative design. They also do not account for what happens when traces carrying high current are next to each other or cross on different layers. These cases result in higher temperatures than the documents will predict. If there is a transient fault condition with significantly higher current passing through the trace, this condition cannot be handled.
Because of these deficiencies, we have been developing a tool that can be used to predict trace temperature rise on your board, accounting for all layers, vias and your thermal boundary conditions. If you do have a fault condition, you can predict your board temperatures as a function of time.
Simply change the current of the fault trace then solve the transient condition.
The model accounts for the thermal capacitance of each layer, trace, plane, via as well as components on the board surfaces.
The maximum temperature of each defined trace is automatically plotted.
Start by importing the ODB++ file of your board.
Import a text file that has the net name, current and layer.
Fix edge temperature or define natural convection.
The small hot and cool spots on the board surface shown below are due to vias connected to internal layers.
After building a full 3D mode accounting for every layer, trace, plane and via, solving for temperatures, which typically takes less than a minute, board surface temperatures are displayed.
You can also display the actual trace temperatures. You can see that traces are anything but isothermal due to the influence of other heated traces and traces and planes on other layers.
The tool is still under development. If you have any questions or would like to try it, please contact us at info@harleythermal.com.
