Automatically Updating Impedance Based Physical Csets After Stackup Changes.

Hi Electro.

Its not possible to auto resize the etch on the board automatically based on a stackup change. The constraints will use the stackup as a basis for their calculations by default.

On the higher tier Allegro Products, there is a utility to Resize - Re-space Diff pairs but I don't believe that is available in the Orcad Product set. On that utility you have to plug in the numbers.

Can you provide any info on your design ?. How many layers & the intended highest frequency of operation ?

Best Regards.

Hi Excellon1,

Thank you for responding.

I’m not looking to modify the etch on the board. My requirement is to update values in the Constraint Manager automatically. For example, I currently have a 50-ohm trace impedance requirement with specific stackup configuration, based on which I calculated a minimum line width of 0.2 mm and a primary differential gap of 0.26 mm.
However, my impedance/stackup configuration has now changed specifically layer thickness and dielectric constant. I understand that I need to recalculate these values, but I’m looking for a way to update them automatically in the Constraint Manager after modifying parameters like impedance, thickness, and dielectric properties, instead of manually recalculating and re-entering each value.
This is particularly important because I am working with multiple protocols on the same board, such as USB-C, HDMI, and USB 3.0. PCle, DDR5 Due to frequent stackup changes, I often need to recalculate and redefine constraints.
I hope my requirement is clear. Please let me know if you need any further clarification I’d be happy to provide more details.

Thanks and regards,

Hi Electro

I see what you are after now. So on this it will have to be a manual update of your Csets in the constraint manager so as to reflect the changes to the updated board stackup for the impedance parameters you need.

The stackup editor provides a method to calculate impedance but its just a calculator in this regard.

What I usually do is create a txt file of the various impedance parameters first, so width, spacing etc and just cut and paste the values into the cset spread sheet so as to save some manual typing. Dual monitors can be handy for such things, Cmgr on one txt file on the other.  

Best Regards.

Hi Excellon1,

Thanks for the suggestion. I am currently following the same approach.

You are absolutely correct the stackup editor provides a method to calculate impedance.

However, I was looking for a more automatic  approach that could save more  time and effort in calculating and storing the values. FYI, I am on 25.1 So just looking if there is any additional features. Thanks again for your suggestions and for taking the time to help.

Hi Electro, So I had given this some thought this evening. Allegro has very powerful scripting so as to automate common tasks, It also has Skill so as to create custom programs that can extend the functionality of the PCB editor. Skill is not my forte but scripting can be used for certain things instead.

Have you looked at creating a script so as to auto update your csets with the right values, ?. If not I can give you some details. 

Best regards.

Hi Excellon1,

Thanks for taking the time to think about this. Yes, I am also not very proficient in this skill. We can try using a script as well, if you have any suggestions, please do share; it would be great to explore them.

Additionally, I am also checking if there is anything new in 25.1 from the stackup itself to achieve the same.

Kind regards

Hi Excellon1,

Thanks for taking the time to think about this. Yes, I am also not very proficient in this skill. We can try using a script as well, if you have any suggestions, please do share; it would be great to explore them.

Additionally, I am also checking if there is anything new in 25.1 from the stackup itself to achieve the same.

Kind regards

Hi 24.1 and 25.1 has a feature that allows you to do this from the stackup. Launch the cross section editor and click on the Primary tab, You will see a column Add Physical CSet. Once selected fill in the specfied values. A Cset is calculated based on the cross section and added here and in Constraint Manager. If you need to change it, adjust the cross section then right click the CSet name and choose edit then check the box for recalculate width from Target. This will update the widths for the CSet in the cross section and in Constraint Manager. 

Hi Steve,

Thank you so much for your response. This is exactly what I was looking for.
This is really a great enhancement in the tool. I have just tried it, and it will save a lot of my time and effort.

Your help in this matter is truly appreciated. Thank you so much.

Regards,