7 Replies Latest reply on Mar 4, 2010 6:07 AM by Niki

    PCB Decal Pads with no Soldermask or Pastemask openings

    mkaszynski

      Can anyone tell me how to create a pad on a PCB decal that can be tied to the GND net but which has no soldermask or pastemask openings?  Much appreciated.

       

      Mike Kaszynski

      Stillwaterm, MN

        • 1. Re: PCB Decal Pads with no Soldermask or Pastemask openings
          john

          Like this:

           

           

          1. Go to File > CAM.
          2. Select the solder mask or paste mask document, click the Edit button.
          3. Click the Options button from the Edit Document window.
          4. In the section called "Suppress" enter the reference designator prefixes  or specific reference designators of the components you do not want pads displayed for. You can include multiple reference designator prefixes or specific reference designators by separating them with a comma.
          5. Place a check mark in the box for "Exclude Pads", click OK, and Save the CAM document.
          6. When you preview the document and output the gerbers the pads you specified will be suppressed.

           

          FYI, this came from SupportNet, a very good source for answers to questions like yours:

           

          http://supportnet.mentor.com/reference/technotes/public/technote.cfm?tn=mg33331

           

          Or go to the Listserver, an almost better resource (you can interface with some very experienced designers there):

           

          http://www.mentor.com/products/pcb-system-design/design-flows/pads/listservers.cfm?dt=Regional%20User%20Groups#

           

          JM

          • 2. Re: PCB Decal Pads with no Soldermask or Pastemask openings
            naiwu.yuan

            Hi, John

             

            It is useful to know the function. Furthurmore, could only several pads in a components is suppressed?

             

            Thank You

             

            Regards

             

            Yuan

            • 3. Re: PCB Decal Pads with no Soldermask or Pastemask openings
              Niki

              I don't know  why did you do that?  Is it the sme to no PCB Dcal ?

              • 4. Re: PCB Decal Pads with no Soldermask or Pastemask openings
                john

                Yes, but you would need to have built your Decals with padstacks (aka define soldermask pad(s) and/or solderpaste pad(s) for the surface pad(s)).

                 

                If you do pad stacks, I would say not to use the default oversize function. Based on conversations I've had with some fabricators, I would reccommend that the default soldermask opening should be 6 mils (~0.15mm) over the pad size (for example, a 0.060" RD pad would get a 0.066" mask opening).There are exceptions to this of course, but they will normally be defined by the engineer or by the MFR data sheet. Some examples of exceptions would be ganged openings for QFPs, a reduced opening (like 4 mils or less) on high-density BGAs, reduced or removed mask openings for vias, oversize openings on fiducials or mounting holes, things like that

                 

                Unless you always use the same shop, or are captive to a company that does its own assembly and know exactly what the shop wants, I would make the solderpaste pad 1:1 to the SMT pad, and allow your assembler to redefine those as they see fit.

                 

                You can then edit the Decal at the board level to selectively remove or modify soldermask and/or solderpaste for specific pads on specific parts (much like how you can modify specific anti-pads and/or thermal connections now).

                 

                Otherwise, you would need to edit the Gerbers using CAM350 or a similar program. Do-able, but, IMHO, not really a good idea.

                • 5. Re: PCB Decal Pads with no Soldermask or Pastemask openings
                  mkaszynski

                  On one particular tiny quad package I am using the only way to connect all of the ground pads is from the center of the part by using a via in the center and pouring copper over the inside.  But this part also has a square pad in the center of the part.  (usually connected to copper for heat transfer but not in the case of this part)  I do not want to change the decal to remove the center pad.  The manufacturer indicates that the center square pad is not to be connected to ground.  So I have a decal with a center pin pad that I don't want solder or paste mask openings.  Thanks for all of the advise.

                  • 6. Re: PCB Decal Pads with no Soldermask or Pastemask openings
                    naiwu.yuan

                    HI, John

                     

                    It is lovely to learn your introduction, every functions work very well. which bring more flexibility for PCB design.

                     

                    However, the selection of "pins with associated copper" didn't work, please refer to attached picture. That means, even I select the tick marked box. Only pads but not including associated copper is display in past mask layer of gerber file.

                     

                    My Pads version is "Pads 2007". Could you please answers it is my wrong operation or a bug in the software.  

                     

                    Thank You

                     

                    Regards

                     

                    Yuan

                    • 7. Re: PCB Decal Pads with no Soldermask or Pastemask openings
                      Niki

                      That is good method to deal with this issue! Thanks for your explanation,