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Switch units, mils to mm, inaccuracies

Leotordo

Hello,

 I've a pcb board with routing completed in Orcad PCB 17.2

Rules are: trace with 8mils, trace clearances 8mils.

I routed the board in mils and all sounds good.

Now, I've to do some change in mechanical quote (board and hole places)...but...if I switch to mm and back to mils....there are a lot of inaccuracies error...like "Clearences are 7.999mils and not 8mils"

How to solve? In Mentor PADS and in Altium Designer there aren't these problems.

Thank you

Stefano

  • Dale Peterson

    Hi, I just spent an hour experimenting with a database with only an 8 and 10 mil lines on it. I flipped the settings from mils to mm back to mils just like you did. And yes the numbers came up the same for me too.  

    But, not to worry. After changing from mm back to Mils. you need to just go back and change the "Accuracy" settings to 0. and hit OK again. All your graphical data should show nice wholesome Mil numbers. I use to run PADS a long time ago. I believe, thinking back that PADS did the same thing but, just in the background. Remember too 10mils =.254mm. If you were designing in the metric world. You would use an.25 trace width not.254. So OrCAD allows you to change the accuracy around to more flexible but, more confusing coming from a PADS environment.  

  • Leotordo
    in reply to Dale Peterson

    Hello Dale

    I agree with you about PADS behavior.

    I'll try asap your suggestions....at the moment I'm a little scared about this problem...I'm working on a board very important for us...I'll place and I'll route it in metric

    Have a nice day

    Stefano

  • Dale Peterson
    in reply to Leotordo

    Just a suggestion. Maybe you are doing this already. Try these settings- Set metric accuracy to 2 places. Mils to 0 and Inches to 3. Your metric trace and spacing should be close to what you are familiar with in Mils. to make it easier for you. So, make the metric numbers wholesome. Some examples 20 mils use .5 and 10 mils .25. And for the design grid set it to.1mm. Once in a while, you may need to place something more accurately. In these cases set the grid to .1mm. The whole industry worldwide has moved to metric. So once you go down the metric path you will never look back.

    Cheers        

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