9 Replies Latest reply on Jun 15, 2013 2:15 PM by hgibbons

    Strange behavior from Paste Mask Pads

    cbedard

      Imagine a thru hole connector that is going to be placed by automated SMT equipment on a PCB.  Since it is going to be placed with automation and reflowed you'd also want solder paste on the PCB (in the holes) while it's being inserted.  Thus you would want solder paste openings in your solder paste stencil. To get openings in your stencil, you'd want "something" associated with the opening presumably on the Paste Mask Top (assuming the connector is inserted into the PCB from the top side) layer in the pad stack.  The easiest thing for the "something" to be would be a Pad right?

       

      Why will CAM not pick up Paste Mask Pads for thru holes?  If there is no drill associated with the pad stack (an SMT pad) a Paste Mask Pad shows up just fine in CAM but if it has a drill associated with the pad stack you MUST Associate Copper on the Paste Mask Layer to get anything to show up.

       

      Why, why, why??  I'd prefer to just be able to handle this via the Pad Stack than have to draw Copper shapes and Associate them.

       

      Thanks for any info!

       

      Chris

        • 1. Re: Strange behavior from Paste Mask Pads
          DenisL

          This behavior is a product of how the CAM routine 'sees' paste mask. When a CAM document is defined as a paste mask, only "SM" parts are allowed in the output. The easiet way to work around this issue is to redefine the CAM output as a "General" layer rather than a "Paste" layer. Then be sure to make all the same item selections as were made on the paste layer.

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          • 2. Re: Strange behavior from Paste Mask Pads
            jduquette

            By default every pad with a zero drill (i.e. SMD pad) gets the pad shape copied to the paste layer. I believe if you define the paste mask layer for this 'special' through hole component it will get openings on the paste layer.  Just be careful that it is also going to get paste for every board that you use it on whether you want the paste or not.

             

            Are you attempting to avoid the wave solder process that would typically be used for a through hole component? Have you asked your assembly house if this is going to work?

            • 3. Re: Strange behavior from Paste Mask Pads
              sabitha.jamal

              Hi

               

               

                 Since this is the special type process ,we need to give a additonal information to work this in solder paste layer . For making stencil layer it is using solder paste layer for the all SMD pad ,if you required the SMD process for all components including through hole components ,select only the soldering pad of through hole components and add paste layer property as the same size of top layer's annualr ring for through hole pads.Then in solderpaste layer there will have all SMD pads and Through hole pads and it will work in CAM .

                 But in Process, remember to use high thickness stencil for getting good solder for thorugh hole joins.Hope it will clarify your query.

               

               

              Thanks and Regards

              sabitha

              • 4. Re: Strange behavior from Paste Mask Pads
                Pete

                Using paste and reflow for through hole parts is not common.   I, for one, appreciate that Mentor didn't make it the default!  This way, only the minority who are using that process need to create a special padstack, rather than making the majority do it!

                 

                Yes, you have to add a Paste Mask Top shape to your padstacks.

                • 5. Re: Strange behavior from Paste Mask Pads
                  cbedard

                  Thanks for all of the information!

                   

                  It sounds like a couple of solutions got smashed up together there though.

                   

                  While I now understand there is a "rule" in the way PADS is programmed to prevent a Paste Mask Pad from showing up on a pin with a drill size bigger than zero I disagree with having that rule in the first place.  I think it should be left to the user to present a paste feature or not regardless of drill.  Is there a situation that Mentor is trying to prevent by not allowing paste for pins with drills, or did it "just not make sense so we didn't allow it?"  If there is a good reason to not do it, then that's OK... I just don't know of one.

                   

                  So the layer defined as Paste Mask or General fix.  I think the layer type solution got confused with defining what type of CAM document the "Paste Mask Top" CAM output file would be.  The Paste Mask Top Layer still needs to be defined as a Paste Mask Layer so it can keep associative properties to allow PADS to see when a part is on the top or bottom side of the PCB.  However I did confirm that changing the CAM Document from a Paste Mask Document to a Custom Document does in fact allow pads defined on Paste Mask Layers to show up even for pins with drills.  So that is a viable solution.

                   

                  Yaa!  Simple solution.  Custom CAM Document instead of a Paste Mask Document.  Strange to me that PADS is programmed this way but it does work.

                   

                  Thanks!

                  • 6. Re: Strange behavior from Paste Mask Pads
                    cbedard

                    Pete I think you missed it a little bit.  I agree that the process is not common.  But allowing users to utilize Paste Mask Pads even on pins with drills does not make life harder for any user.  There would be no additional configuration that you need to do because of this.  I'm not suggesting that when a new terminal is added to a decal that it automatically have a paste mask pad.  I'm only saying that if I do choose to define a pad on that layer, that it be available in CAM.  ...which has been shown to be possible by defining the CAM document as Custom instead of Paste Mask.

                    • 7. Re: Strange behavior from Paste Mask Pads
                      cbedard

                      Paste Mask Pads can be output on pins with drills simply by defining the CAM Document as Custom instead of Paste Mask.

                      • 8. Re: Strange behavior from Paste Mask Pads
                        Pete

                        I never needed to do this before, so I never noticed.  So I tried it.  It DOES appear to be a bug!  I added a Paste Mask top definition to a PTH padstack, I changed my CAM setup to include pads on the paste mask top layer - and got no pads!   That IS different than any other CAM layer setup.

                        • 9. Re: Strange behavior from Paste Mask Pads
                          hgibbons

                          There is not a good reason for that as a general rule.  We successfully (> 1 million units) used through-hole reflow on connectors.  It takes considerable care to get the patterns right to reflow successfully.