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Platform forum

, 01-28-2024, 08:59 PM

Hi, I would like to ask what I am doing wrong in Altium impedance setup when my value are different to values of pcb manufacturer calculator (jlcpcb)? Check the pictures please. Thank you Martin.

Robert Feranec , 01-29-2024, 03:55 PM

The most accurate track geometry for specific impedance will be always from your PCB manufacturer. Take other calculations as a reference only - theoretical values in these calculators will not consider some manufacturing factors e.g. prepreg is thinner in the final PCB, ...

, 01-29-2024, 09:34 PM

Understand.. Thank you.

, 01-30-2024, 08:37 AM

Also @Robert Feranec I would like to ask one more question about stackup and USB3 Superspeed design.
I am designing USB5744 hub. In microchip app note AN26.2 - Section 3.2.2 they said that use trace width wider than 7.5mil. And match the impedance to 85ohm. 85ohm not 90ohm?
Can I use JLC04161H-7628 stackup? Or there is necessary to use someone "better" with thinner prepreg like JLC04161H-3313?
Is it necessary use the trace width at least 7.5mil? Because calculation by JLC impedance calculator for prepreg 7628 was good (85ohm, gap 4mil, width 8.09mil) but if I tried calculate width&gap for 3313 the values for width and gap is not good for me I think... Need to use big gap about 10mil to to reach width at least 7.42mil. If there is too big gap I am not sure how to connect diff pair to IC because there is different pin spacing.
Thank you.

QDrives , 01-30-2024, 04:33 PM

You can also check Isola: https://www.isola-group.com/isostack/
The most important limitation is that they only have Isola materials.
Do note that 7628 is about twice as thick as the prepreg in the application note. 2x106, 1x2113 or 1x3313 would be a closer match.