Microstrip vs stripline
Microstrip vs stripline — differences and when you choose each.
| Level | ● screening |
| Track | SI & high-speed |
| Really testing | Speed, loss, EMI and crosstalk. |
Going deeper
Extra explanation that is not in the book: worked numbers, where people go wrong, and how to say it in the room.
The number that bites in practice — delay, not length. Microstrip in FR4 runs at about 145 ps/in; stripline at about 170 ps/in. A 10-inch route is 1.45 ns on top and 1.70 ns inside — 250 ps apart. If two signals of one group take different layers, match delay, not length. Most layout tools can do this if you set it up.
Worked example — far-end crosstalk. In microstrip the signal travels partly in air and partly in FR4, so the capacitive and inductive coupling don't cancel; far-end crosstalk grows with coupled length. In stripline the field is all in one dielectric, so FEXT nearly vanishes. Long parallel buses therefore belong inside.
Where people go wrong
- Forgetting solder mask: it lowers microstrip impedance a few ohms and adds loss.
- Assuming outer-layer copper thickness is exact — plating adds variation, so impedance tolerance is worse on the outside.
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