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Stackup problem!

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  • Stackup problem!


    I have a EVM PCB file from Spectrumdigital and I want to edit it for specific usage. But I have some problems with Stackup:
    1. When I check the DDR2 section I saw that for differential 100ohm impedance they use 5mil, 5mil for clearance and trace width and also 5mil for 50ohm single end but I can not get this impedance value with dielectric thickness changes! Only if I set the Er=2.5 the impedance is equal to 100ohm for differential and 55ohm for single end traces. But in the PCB file they explained the dielectric material is FR-4! Is there any FR-4 with Er=2.5?
    2. The layers that used in the file is different from stackup table that exist.(The ground planes is not same, and also layer count) I use the stackup table information for impedance calculation.

    Here is evm main page:
    Here is evm PCB file:

    This file was designed in Orcad and P-CAD and I imported it in Altium. It may be a problem for stackup changes!
    Have anyone a Stackup calculator to help me.

  • #2
    Did they include the exact stackup description (in PCB or as separate file)? I do not have PCAD to check it. Sometimes the PCB file may not have the stackup set correctly.


    • #3
      Thanks for your quick reply, No there is not any file about stackup.


      • #4
        Ideally, you need to know the exact stackup from their PCB manufacturer to be able to re-use their track geometry and manufacture your board then.