2 Replies Latest reply on Mar 5, 2018 4:38 PM by Barry_Olney

    Minimum impedance question

    Marty Fouch

      I would think that the minimum impedance is the actual trace impedance on that layer when matched. I set the diff rule to 80 ohms.

      The clocks below were set to 82 ohms differential but HL DRC is displaying 92.77 ohms on the outer layers. I read somewhere, in the information, that solder mask is not included although I loaded a stackup which does include solder mask in the layer definition. Anyway, that would only increase the impedance by about 3 ohms. Why is it reading high?


      See Pic1



        • 1. Re: Minimum impedance question

          The only parameters that should affect the impedance calculations are trace width, distance between traces and stackup.
          Considering that the trace widths and separation is not somehow altered during the import, we should start with making sure that the stack up was imported correctly.

          step two would be to make sure that in setup- > options -> general settings the tool is set to include the ER and loss tangents for metals and check for the default values since if the stack up did not come through ok, HLDRC will assume these values.

            If none of these work, it would be a good idea to look at the layout tool to make sure that the impedance value of 82 ohms is correctly derived.



          • 2. Re: Minimum impedance question

            Thanks Kanchan for your comprehensive response.

            The import was OK but I needed to adjust my stackup and remove resin flow compensation to get your impedance results.