4 Replies Latest reply on Jun 4, 2014 7:18 AM by jduquette

    CAM Clearance errors


      I'm seeing a problem with clearances in my CAM output.  I'm using PADS Layout 9.2. 


      This is a tight board, and I've got my clearances set to 5mil.  In a number of areas of copper pour and plane (on a split/mixed layer), I get less than my required 5mil clearance in my Gerber files (in the range of 4.7 to 4.9).  When I measure the distances in layout it's right on 5mils, but my PCB manufacturer flagged the error and when I brought the Gerbers into GCPrevue (Gerber viewer) I could see the errors.  It appears ONLY around drilled pads;  surface mount pads don't seem to have any issues. 


      I noticed that in areas where there were rounded corners in the copper the copper actually bulged a little bit.  I changed my smoothing radius for copper pour from 0.1 to 0.3 and the clearance errors went away (although there still might be a bulge).  One of the strange things is that I don't see this on all pads, just SOME of the pads.  I've got my photo plotter setup in CAM set for RS-274X, leading 2, trailing 4 and absolute coordinates.


      Other than going in and manually tweaking the copper in the problem areas, what can I do to resolve this?




        • 1. Re: CAM Clearance errors

          Just to clarify, changing the smoothing radius only fixed SOME of the errors, there are still more.

          • 2. Re: CAM Clearance errors

            A guess here, but you may want to look at design rules for drill to plane, and how you set up under Options Split/Mixed plane if "Use design rules for thermals and antipads" is checked along with

            "remove unused pads" you might get different results than anticipated for set design rules.

            • 3. Re: CAM Clearance errors

              Just to stir the pot on this discussion, I am STILL having problems here.  It's all related to copper pour and planes


              One specific issue is killing me:


              In the middle a copper pour I've got a via.  I've got all my clearances set to 5mil.  Looking at the Gerber file, the clearance from one side of the via to the copper is exactly 5 mils.  On the OTHER side of the via, the clearance is about 4.8 mils.  The diameter of the via pad is exactly 55 mils, as it should be; the diameter of the opening in the copper is 64.8 mils.


              So, it looks like there's two issues here: the opening in the copper is too small, and the pad is not centered in the opening.


              I think (hope) my board house can deal with these issues, but why are they happening, and how can I avoid them?



              • 4. Re: CAM Clearance errors

                That does sound really odd.  Is there some other pad/shape on top of that via that may be confusing the pour?  Changing to transparent view might help to see it; or <Select anything> and then tab through the items at that location.


                Have you tried the ASC export and ASC import trick to see if that helps?  It really sounds like something is corrupt in the design.


                Does it improve if you change the via diameter (just as a test, not for production)?