I have a design that the diff-pairs (100 Ohm impedance) and single-ended (50 Ohm impedance) are routed on the same layer. To specifying the impedance, on the “Lamination Stack-up”, I am going to add the information like this; INT1 (TW=0.006” Z0=50 ohm / Z0=100 ohm DIFF-PAIR). Is this OK? enter image description here

In this case, the fabrication vendor will determine dielectric thickness based on the TW, trace spacing, and material on their own to achieve required impedance. Right?

In other case, if the trace width of the diff-pairs are different to the trace width single-ended, can I apply this way to call out?


You can do that, or you can call the diff pairs out as width and spacing. Really however you communicate well with your shop is fine. Even better if you call them at the start of your design to work on the stackup with them. Nobody knows their process like they do. It could be easier/cheaper for you to make a minor change that you wouldn't know about otherwise.

Also I'd say you should be specing your dielectric thicknesses and your over all board thickness. The shop will likely slightly adjust your widths based on what they know about their etching and lamination process.

That's another part of the Stackup that is nice to work with your shop on ahead of time.

  1. Provide a tolerance on the impedance. For example 50 +/- 3 Ohm.
  2. Have them provide back the as-built Gerber files.
  • 1
    \$\begingroup\$ @Brian_Carlton Sounds expensive. Expect more like +/-10% on inner layers and +/-20% on outer layers before it starts to get expensive. \$\endgroup\$ – Rolf Ostergaard Dec 18 '14 at 7:27

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