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Few clarifications needed in orcad and cadence allegro based on your videos.

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  • Few clarifications needed in orcad and cadence allegro based on your videos.

    1. What is the difference between drawing shape and drawing line?
    2. What is the difference between rats and nets?
    3. If we find a mistake in the schematic or in footprint after completing the layout, How to go about it?

    I have not completed the videos but these doubts arise in my mind. Pls let me know. Thanks

  • #2
    1) They are different objects, so different behavior e.g. if you are edditing them. Shapes are usually filled with copper, lines are just ... lines.
    2) Rats are the blue lines (the kind of virtual lines showing you which pins are connected together). Nets - I use it a lot to name different things - e.g. net name, tracks, rats, signals, ... but usually it is the specific connection which we are speaking about (e.g. it may include pads, tracks, rats connected to the same net)
    3) It is covered in the course later

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    • #3
      Thanks. I have few more questions
      1. What is the basis of selecting track width 2mm and sometimes 5mm in power nets?
      2. What was the reason for drawing rectangular shapes with vias ( around some pads connected to GND in bottom layer) and connect to ground plane?
      thank you

      Comment


      • #4
        1) I generally draw power tracks wider than other tracks. I adjust the track width based on pad width and available space.
        2) For the important capacitors it is used because high currents will flow there. For the smaller caps, you can use tracks if you like, it is not necessary to create shapes or use multiple VIAs. However, I very often use shapes and multiple VIAs as then I am always sure that the connection is fine, so I do not need to worry about it (e.g. I do not have to search for information how high currents flow there).

        Comment


        • #5
          Hi Robert

          I face some difficulties in the layout. All the left over connections are taken to different layer through vias and then you were connecting the vias together (in your videos). But I had to hover over the vias for long time for the connections to happen. Have you faced anything similar?

          Also another abnormal thing which I faced is in the schematic. Some parts (another project) when I take from library, they are invisible and if I place it on the schematic page, then it creates a lot of problem as it cannot be connected through wires bcoz it is invisible and (cannot be removed from the schematic page as well) and still will be present in pcb editor for layout. Let me know if you can help me with this.

          thank you

          Comment


          • #6
            Please, could you attach some screenshots?

            Comment


            • #7
              Hi

              I am attaching the screenshots. Pls see.
              Thanks
              Attached Files

              Comment


              • #8
                Hi
                Somehow I was able to connect the vias after hovering over the vias for some time.
                Reg the invisible part, what can be done is just type its refdes in the 'find' and see the new window with the location of the part. Double click there and the invisible part gets selected and now just press delete. But still dont know why this happened.

                thanks

                Comment


                • #9
                  1) VIA problem - maybe, did you have VIA checked in your filter when the command was active?
                  2) The invisible part - that is very unusual. What sometimes may happen, that you place component outside of schematic (e.g. if you make your schematic page smaller). However it looks to me like you had the component directly in schematic and was invisible. I do not really know how that could happen, I have not seen anything like that.

                  I am very happy you figured out everything by yourself. Great job!

                  Comment


                  • #10
                    Hi

                    How to see through holes in through hole pads in the layout? I remember you mentioned some settings to see the through hole. Can you pls mention here again?
                    Thanks

                    Comment


                    • #11
                      Setup -> Design Parameters -> Display and then check all the checkboxes with "hole" in the name

                      Comment


                      • #12
                        For through hole pads for resistors, if the hole is 1mm and dia is 1.2 mm. All the design layers, I am giving 1.2mm. Soldermask top and bottom is 1.3mm. So the paste mask at the top and bottom will be between the 1mm hole and the 1.2mm design layers, right? So I need to mention pastemask in the mask layers as 1.2mm. let me know

                        I found only mounting hole and testpoint as thru hole pads in the videos, which are actually special cases. That is why I am looking for more clarity.
                        thanks

                        Comment


                        • #13
                          I am not really sure if I would use 0.1 mm ring around pad (1.2 dia - 1 hole = 0.2 / 2 = 0.1). That seems to me maybe too small (there may not be enough space when you will be soldering the pins). If you would like to have some examples, you can have a look at our open source projects here: http://www.imx6rex.com/

                          Comment


                          • #14
                            My vias had 0.1mm ring only and DFM check asked to change these so I am going for a higher ring. Is there any way I can replace all the vias with new ones?

                            thanks

                            Comment


                            • #15
                              Ok, it is same as replacing padstack. I want to know hoe to provide a cut in the PCB to physically isolate one section from the other.

                              Regards

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