6 Replies Latest reply on Jan 26, 2011 5:41 AM by SVETLANA_Z

    Option for ruling out of DRC special class rule for small trace lengths

    olga_g

      short trace.JPG

       

       

       

      It is obvious, that there is no need to keep special clearance rule to such short trace. It enough to keep only default manufacturing rule (4-5 mil). So for dense boards we can get mach space by taking short traces out of special clearance DRC rule given for the whole class (clock for example). There may be many such traces on layers, so for now the only possibility is to draw rule aria around them. The problem is to maintain all this frames and keep in mind to move them if trace moves (what can happen a lot during the design flow). And even more, sometimes  we have to design another board that based on existing data, but the routing might be completely different, and forgotten rule aria frame may lead even to significant mistakes. My solution is to give possibility to connect special DRC class rule to trace length. So if I set trace to trace rule 25 mil I would be able to determine the minimum length to obey it. All shorter traces will obey to default rule.

        • 1. Re: Option for ruling out of DRC special class rule for small trace lengths
          Andreas.Schaefer

          Hello Olga,

           

          the solution you would like to have is very specific.

          Our designs (also very dense) do have those issue too. And as you descibed,

          we also have defined a "miniArea" Rule scheme, to handle those areas.

           

          But, shouldn't the rule be connected somehow to the part instead of being on "short traces".

          Those short traces can occur anywhere and you will have hanger or other unusefull stuff then?

           

          On approach we are following sometimes is to define a rule scheme in library.

          As an example:

          • draw the area a critical point in the part (e.g. connector) and name it "Technology", so you know, whenever this area appears, you are allow to follow your minimum PCB technology
          • Defin rules for the "Technology" scheme in CES and your routing will obey those, without any violation of PCB Technology too.
          • Define a process, so all people know, how to define "Technology" for every new PDB.

          If you, for some reason, doe not need to define a  "Technology" scheme, e.g. your default is small enough, you can change it by tthe keyin "remap" in Expedition.

           

          Kind regards,

          Andreas

          • 2. Re: Option for ruling out of DRC special class rule for small trace lengths
            olga_g

            Hi Andreas,

             

            The part cells have two layer, and the short trace I've described theoretically may occur on every layer. You can define the rule area in cell only for outer layer or for all layers. And in the new Expedition revision you can not change the layer imported with the part, only copy it and put out of component connection. Beside, when you design a part cell you can not know exectly fanout location, so the rule aria would be larger then need.

             

            I didn't understand this sentense:

            "Those short traces can occur anywhere and you will have hanger or other unusefull stuff then? "

             

            I can't see how the DRC default rule definition for short length traces may cause to "hanger or other unusefull stuff". 

             

            • 3. Re: Option for ruling out of DRC special class rule for small trace lengths
              yu.yanfeng

              Andreas's suggestion is useful.  For your case, you can use via-via clearance setting of same net to control it.

              Yanfeng

              • 4. Re: Option for ruling out of DRC special class rule for small trace lengths
                olga_g

                Andreas didn't suggest something new. We are using rule areas include inside the parts, but this has restriction I mentioned in my previous messages (please study them carefully). Let the other Mentor users say their opinion. The administration position is clear. By the way it is nothing to do with via-via clearance or hangers, etc...

                • 5. Re: Option for ruling out of DRC special class rule for small trace lengths
                  yu.yanfeng

                  Hi

                  I may don't understand what you wanna do. If you hope to keep the clearance (distance) between via1-2 and via2-11 less than your general clearance via2via for this net type and not DRCs, my suggestion difinitely works well. I will tell you how to set it step and step.

                  If I am wrong to undstand what you wann, please describe it specific. Maybe I have another way to deal with it.

                   

                  Yafeng

                  • 6. Re: Option for ruling out of DRC special class rule for small trace lengths
                    SVETLANA_Z

                    Hi Olga, It’s great idea. But You didn't specified that this short traces are actually segments from via to via (center to center) when trace changes layers. So DRC might have option to exclude short net  segments per layer from class clearance rule.