6 Replies Latest reply on Nov 6, 2019 3:41 AM by Autodesk Guest

    DRC clearance error

    nav101

      I am using a library for MCP73871 battery controller. I tried two different librarys but I get the same clearance error as shown in the picture. This is qfn package where the centre is the exposed pad and is grounded.

      Changing DRC clearance does not get rid of the error. Is it a faulty library or am i doing something wrong ... MANY THANKS

        • Re: DRC clearance error
          Autodesk Guest

          On 05/11/2019 17:41, Nav Khan wrote:

          I am using a library for MCP73871 battery controller. I tried two different librarys but I get the same clearance error as shown in the picture. This is qfn package where the centre is the exposed pad and is grounded.

          Changing DRC clearance does not get rid of the error. Is it a faulty library or am i doing something wrong ... MANY THANKS

           

          There are two separate issues here.

           

          First, the four thermal vias in the centre pad are misaligned such that

          one of them is practically touching pin 13. You need to re-centre them.

          They're also not being recognised as ground vias, by the look of it,

          although the airwires suggest they are correctly named. Which version of

          Eagle are you using? I think the rules changed at some point.

           

          Second, you've got pad-to-pad clearance settings in your DRC rules that

          don't allow for this footprint. I'm not familiar with the device in

          question so I can't say whether the centre pad really needs to be as

          large as it is, or whether you need a board house that can manage very

          small clearances.

           

          In practice, even if those clearances are OK for manufacture, you may

          well need to adjust (or remove and hand-craft) the automatic solder mask

          on all the pads of a device like that.

           

            • Re: DRC clearance error
              nav101

              Hi Thanks for the response.

              The vias are non issue as I just added them to check if that would help in the clearance. So the clearance issue is still there even without the vias. I am new to this and this is my first design, I was really under the impression that the librarys available online are accurate. The manufacturing view of the device shows the central pad so large that it is touching the other surrounding pads. I should get down to designing my library...Thanks again

                • Re: DRC clearance error
                  Autodesk Guest

                  On 05/11/2019 18:58, Nav Khan wrote:

                  I am new to this and this is my first design, I was really under the impression that the librarys available online are accurate. The manufacturing view of the device shows the central pad so large that it is touching the other surrounding pads. I should get down to designing my library...Thanks again

                   

                  So, first lesson... never trust anybody else's library! This is a rule

                  that those of us who use Eagle a lot (or, indeed, use any other PCB CAD

                  software in a professional environment) find ourselves repeating on the

                  user forum. You cannot trust what you find on the web, to the point that

                  it's usually quicker just to create the part yourself than search,

                  download, and verify.

                   

                  If you're experiencing differences between the library and the board,

                  this is something of an FAQ. It's down to DRC rules. However, this is

                  mostly an issue for through-hole components, where the "annular ring"

                  setting plays havoc with newbies' expectations. In essence, the library

                  defines the minimum sizes needed for the component, while the DRC rules

                  define the capabilities of the board house for that project. If the

                  board house can't achieve the ultra-thin copper ring that the library

                  defines for a PTH pad, the board gets a fatter one. I wouldn't expect

                  that to be your problem as it doesn't normally affect SMD pads.

                   

                  The manufacturing preview may not always be fully accurate. Autodesk

                  generally say that, where there is a discrepancy, the board editor is

                  the one to trust. Or you can generate Gerber files and open them in

                  something like gerbv, which should be definitive.

                   

                  BTW, the Element14 forum, and the old CadSoft NNTP server it's linked

                  to, are not the best place for Eagle advice any more. You'd get a better

                  spread of response (including official support) from the Autodesk forum

                  at https://forums.autodesk.com/t5/eagle-forum/bd-p/3500

                   

                  1 of 1 people found this helpful
                    • Re: DRC clearance error
                      Autodesk Guest

                      Am 05.11.2019 um 21:07 schrieb Rob Pearce:

                      On 05/11/2019 18:58, Nav Khan wrote:

                      I am new to this and this is my first design, I was really under the

                      impression that the librarys available online are accurate. The

                      manufacturing view of the device shows the central pad so large that

                      it is touching the other surrounding pads. I should get down to

                      designing my library...Thanks again

                       

                      So, first lesson... never trust anybody else's library! This is a rule

                      that those of us who use Eagle a lot (or, indeed, use any other PCB CAD

                      software in a professional environment) find ourselves repeating on the

                      user forum. You cannot trust what you find on the web, to the point that

                      it's usually quicker just to create the part yourself than search,

                      download, and verify.

                       

                      If you're experiencing differences between the library and the board,

                      this is something of an FAQ. It's down to DRC rules. However, this is

                      mostly an issue for through-hole components, where the "annular ring"

                      setting plays havoc with newbies' expectations. In essence, the library

                      defines the minimum sizes needed for the component, while the DRC rules

                      define the capabilities of the board house for that project. If the

                      board house can't achieve the ultra-thin copper ring that the library

                      defines for a PTH pad, the board gets a fatter one. I wouldn't expect

                      that to be your problem as it doesn't normally affect SMD pads.

                       

                      The manufacturing preview may not always be fully accurate. Autodesk

                      generally say that, where there is a discrepancy, the board editor is

                      the one to trust. Or you can generate Gerber files and open them in

                      something like gerbv, which should be definitive.

                       

                      BTW, the Element14 forum, and the old CadSoft NNTP server it's linked

                      to, are not the best place for Eagle advice any more. You'd get a better

                      spread of response (including official support) from the Autodesk forum

                      at https://forums.autodesk.com/t5/eagle-forum/bd-p/3500

                       

                      According the data sheet the exposed pad measures 2.5x2.5 mm.

                      You can check/correct it and maybe the problem is solved.

                      So, second lesson... never trust anybody else's library! as Rob already

                      said.

                       

                      --

                      Mit freundlichen Grüßen / With best regards

                       

                      Joern Paschedag