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What are steps to build an Impedance controlled Layer Stack-up?

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  • What are steps to build an Impedance controlled Layer Stack-up?

    Hello everyone, recently I have been working on a 10 layer board that has 6 Signal and 4 Power Plane Layers. Signals in each Signal Layer should be 55 ohm controlled impedance. After placement and before routing I asked my PCB manufacturer to share the required 10 Layer 55 ohm controlled stack-up so that I route the Signal layers as per his specs. However, the manufacturer suggested to make a rough 55 ohm layer stack-up that would later be tweaked as per their own capabilities. I resorted to Altium 19 Impedance calculator and managed to build a 55 Ohm signal layer stack-up by changing values of FR-4 Thickness, Track width randomly just to meet 55 Ohm criteria.

    Would anyone please guide me proper required steps to build a controlled impedance layer stack-up and all other considerations that I need to have in mind. Attached is my layer stack-up.

    Click image for larger version

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  • #2
    Please, be aware, your stackup may need to support not only 55OHM Single ended impedance, but also other standard impedance such 90OHM & 100OHM Differential. When you play with your stackup, you may need to include calculation of track geometry also for these.

    I am not sure how good the Altium impedance calculator is (maybe it works just fine), but I usually use Saturn PCB Toolkit (Free software):

    Based on the results from Saturn PCB I then create a suggested stackup and PCB manufacturer will tweak it.