8 Replies Latest reply on Dec 15, 2011 5:12 AM by hgk-layout

    Donut pads

    Thomas.DeSmit

      Hi all,

       

      We use some SMT standoffs here, made by a well-known hardware maker. The recommended "footprint" for these is a donut-style pad, with a non-plated hole in the middle. We have created the cells for these in a number of different ways, none of which is ideal. Expedition does have a "donut" shaped pad, and I'm trying some test using that pad in a padstack/cell. The problem I'm running into is the fact that Expedition always insists on routing to the center of the pad/cell. In order for this to work as we'd like, the routing needs to end at the donut, not continue on into the center of the pad. The way it's working now, you'd end up with a trace across the area that we intend to be clear of copper (the small are between the inside diameter of the donut copper, and the non-plated drill).

       

      I've tried doing this two different ways; in one, I made a "thru" padstack using the donut pad and a non-plated drill in the center. Expedition wants to route to the center.

       

      Next, I tried making an SMT padstack with the donut pad and no drill. Then in the cell, I used this padstack, and added a non-plated mounting hole in the center. Expedition still insists on routing to the center.

       

      So, does anyone know how to get Expedition to recognize the donut pad as a valid start/stop point for routing?

       

      I know there are other ways to get what we want, and as I said earlier, we do have some things that work. I really want to try to find a way to make the donut pad work, as this seems like the exact scenario where that pad style would apply. It seems to me if the a donut pad is available, the software should recognize the copper donut as a valid stop/start for routing. If you have a "donut" pad, it seems you would not want copper routed through the "donut hole".

       

      Open to ideas. Thanks.

       

      Tom D

      Aeroflex

        • 1. Re: Donut pads
          jmedina

          Create donut has a custom pad and move pin origin to the edge of pad using an offset in pad description.

           

          In my case pin 1 is connected to a signal and pin 2 is connected to gnd fill.

           

           

          donut_example.PNG

          • 2. Re: Donut pads
            Thomas.DeSmit

            If we create a custom pad like this with an offset, it seems we would need to use an offset on the drill? I'm asking because I haven't tried your method yet, and I'm not sure if Mentor uses the "pin origin" for locating the drill.

             

            Does the padstack that uses this pad have a drill associated with it? It doesn't appear that it would.

             

            Thanks for the input, it does look like this is yet another way to do it, but I keep hoping there is some way to use the "donut" pad that is availble as a standard pad style.

             

            Tom D.

            • 3. Re: Donut pads
              jmedina

              Maybe try placing a non-plated mounting hole Edit > Place > Mounting hole.

              • 4. Re: Donut pads
                Thomas.DeSmit

                We do use a non-plated mounting hole for the drill. My comment/question had to do with the "offset" that was being applied in your example. If the pad "origin" is offset from the "donut" center, it seems you will need to offset the mounting hole as well, correct?

                 

                My other comment/question was asking if you have a drill associated with your donut pad?

                 

                Thanks for the input.

                 

                Tom D.

                • 5. Re: Donut pads
                  jmedina

                  No drill associasted with my example. My suggestion was to add a non-plated mounting hole as a seperate entity.

                  • 6. Re: Donut pads
                    Thomas.DeSmit

                    Well, I did figure out a way to use the "donut" style pad, without doing a "custom", and get it to route to the "donut" and not the "donut hole". I did this by applying an offset to the pad origin, and then applying the same offset to all the other pad styles in the padstack. Then another problem (bug) popped up: when you place the cell in a design, and you use the Function keys to rotate the part, the part rotates around the pad origin! But, if you rotate the cell by keying the rotation into the Properties dialog for that part, it rotates around the Cell Origin! I guess I'll try to submit this one to Mentor support. So, the short answer is; it can be done using the donut pad style, but the longer question is; should we build a padstack/cell that way. I guess that question is yet to be answered.

                     

                    Thanks again for the input on this.

                     

                    Tom D.

                    • 7. Re: Donut pads
                      jmedina

                      Thomas,

                       

                      I am glad that worked or almost worked. The reason I use custom and not the donut padstack is because I have another round pad in my application and I could not get a pad inserted into the donut pad without making it a custom pad and avoiding DRC's.

                       

                      Good Luck. I also use roatations for my application specific cells and have not seen that issue you mentioned.

                      • 8. Re: Donut pads
                        hgk-layout

                        I tried the following:

                        New Cell with total number of pins and so on.

                        Place non plated Mounting holes where needed.

                        Draw  a (non-electrical, e.g. assembly) ring around the mounting hole in the shape of the donut you want.

                        Place pins like a small SMD-pad in relation to the mounting holes where needed or wanted the routes ending.

                        The Ring should run through the pin.

                        Ask the net name of the pin, change the property of the ring to "Trace" and name it like the pin-net (net-1....).

                        Place cell-origin as needed.