IPC-2581 Number Precision

Jonathan,

When I import or export stuff, I would set units of my PCB design database to match whatever format I'm dealing with. In your case, go to "setup/design parameters from the menu bar. Then select the design tab. Play with the "User units" and "accuracy settings" to get the desired results that you need. It should solve your problem I hope.

Good luck

Dale

Hi again,

If you don,t mind me asking.

What supplier or fabricator requires the resolution you are looking for. Settings way beyond every ones process capabilities are unnecessary,. Especially if they can/t hold it anyway.

When it comes to copper weights using a setting in Mils set to a accuracy to 1 is fine. If you spec 1/2 copper weight you will need this setting because it is .7 mils as an example.

So going forward, my recommendation is to let your system round off your data in Mils in your case using the accuracy setting of 1. 2 would be really an over kill.

The accuracy is driven from the database accuracy. By default, with Mils, you get 2dp, or 5dp in Inch, you can set a User Preference for Drawing to allow Mils to 4dp and accept the warning that some artwork formats won't support this, then set the Design Parameters for an Accuracy of 3, or 4 (as required) and the cross-section will output Inch to 6dp, or 7dp, accordingly. What any other tool might make of the data is another question.

Dale,

Thanks for all of the feedback. I understand how you are approaching this in your last post. Unfortunately I do not define the processes that we incorporate. I left out a lot of irrelevant details in my original post. I am a software engineer and I am writing a Skill script to automate a process that is manually performed by our PCB Designers. We obtain an Excel Spreadsheet from our PCB Technologist outlining the stackup that is to be used. The Designer then manually updates the Cross Section in Cadence with this data. We want the data in Cadence to be identical to the data in the spreadsheet so that we can replicate simulation results.

Revisiting your first post you actually were correct. The design parameter accuracy was set to 2 decimal places(the max). When you export the IPC2581 it takes the thickness in mils (ex 0.625) and rounds the number to 2 decimal places (0.63) and then converts it to inches (0.00063) for the IPC file.

At the time I was unaware that there was a User Preference which needed to be toggled on to increase accuracy. To access this preference you go to Setup -> User Preferences. In the new window select the Drawing folder in the left pane. In the right pane there is the Preference "drawing_4mils" which needs to be checked. Now when you go back to the Design Tab in the Design Parameter Editor windows (Setup -> Design Parameters), the Accuracy in the Size section can be increased to 4 decimal places instead of just 2. Now when you export the IPC you retain 4 decimal places instead of just 2 which retains the number in my previous example. This obviously is not an acceptable solution and just exacerbates what you were discussing in your second post.

Thanks for the help! Now I'm off to work on a new solution.