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100-ohm diff on 2-layer PTH board

I'm designing a board with a 100-ohm diff. pair carrying LVDS. For economy, I want to make a 2-layer PTH board with a solid copper ground plane on the bottom. The PCB fab said this was impossible because of board thickness. After playing with a trace impedance calculator, I see what they mean, at least as far as normal track widths are concerned. To get 100-ohms differential on a 62 mil thick 2-layer board, I need 60 mil wide tracks spaced 40 mil apart. So my question is: what's wrong with that?

TIA

Reply to
Andrew Holme
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"Andrew Holme" schrieb im Newsbeitrag news:GBYpl.53874$ snipped-for-privacy@newsfe16.ams...

Hello,

In principle it will work. Your other traces should have a distance of 3 times the board thickness if they run in parallel over some length. That's a clearance of 0.2inch.

If you have a small board, you could use a thinner board, e.g. 20mil?

Best regards, Helmut

Reply to
Helmut Sennewald

TXline claims 55 ohms odd mode Z for your dims on FR4, which is 110 ohms diff. You could also go 30 mil traces with a 10 mil gap for 100 ohm differential, which is 50 ohms odd mode per trace.

Nothing wrong with either one.

John

Reply to
John Larkin

Agree. Controlled impedance lines anywhere between 50 and 300 ohms have even been done on double-sided phenolic. Still got some of those in the garage.

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Regards, Joerg

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Reply to
Joerg

Nothing is inherently wrong with that.

BTW, don't get fixated on differential impedance, you don't actually need it in your case:

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Dave.

Reply to
David L. Jones

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