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What information do I need from the PCB manufacturer to create a 50 ohm impedance trace on my 6-layer PCB?

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  • \$\begingroup\$ Most PCB houses will do this for you if you identify the tracks that need to be impedance matched. If you need to do it yourself then you’ll need to know the thickness of the dielectric between the tracks and the ground plane, and the dielectric coefficient of the dielectric itself. Provided that the ground plane is relatively large, the tracks are much longer than their width and so on you can usually ignore the other factors. \$\endgroup\$
    – Frog
    Oct 6 at 10:13
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If it's a prototype/small quantity ask about their standard stackup for 6-layer. That can save you time and money. For example, here are the standard stackups for PCBway, from their web page (they vary depending on copper thicknesses you choose).

You can then use an online calculator to determine the trace dimensions.

enter image description here

Then you will generally want to tell them that you would like the impedance controlled, and they may make small changes to get within the tolerance that you require (tight tolerance is more costly, of course). You can skip this step but it's more of a gamble. In the case of a 100 x 150mm board for 5 pieces, the increase is from $212 USD to $368 USD according to their calculator and as of this date.

Their standard tolerance is

±10%,50Ω and below:±5Ω

enter image description here

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You will need the following information to then obtain certain parameters such as dielectric thickness etc to estimate your 50 Ohms impedance :

  1. Work out if you can the required PCB stack-up for the 6-layer PCB
  2. Let the PCB manufacturer know of your intention to request the manufacture of a 6-layer board. If this is a standard PCB they make, they can immediately give you the dielectric thicknesses you can then use in you calculations. (they may just let you know of the stack-up from which you can get thicknesses etc.)
  3. Once you have all manufacturing dimensions you can go ahead an calculate your Tx-line width.
  4. At manufacturing you can let the manufacturer know you need "controlled impedances" for some of your PCB traces so that they can ensure constant, and accurate trace dimensions and tolerances etc.

Generally speaking it is fairly easy to get all this from a good PCB manufacturer prior to placing an order, but some may require that you first place an order and that you accept making payment ... good luck

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