Electronics > RF, Microwave, Ham Radio

JLCPCB Impedance controlled trace is not the right impedance

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kk76:

--- Quote from: Xevel on October 28, 2021, 05:15:29 pm ---JLC's calculator gives 11.55mil / 0.293mm line width for these specifications.
Saturn PCB gives a slightly different answer:
 - Microstrip, 18+18um copper, FR-4 with Er=4,6 (the dielectric constant for prereg 7628 according to JLC's page), conductor height = 0.2mm, F=2400 MHz  ==> about  0.35mm width to get 50ohms

--- End quote ---

I am about to order from JLCPCB and did just make same comparation between Saturn and JLCPCB calculator.
At first I entered 0.2mm in Saturn and wondered about difference too.
Now found that there is note under stack table: "0.2mm (7.87 mil) is nominal thickness of 7628 prepreg. Use 7.1 mil as the thickness when the controlled impedance tracks are on top/bottom, use 8.1 mil when tracks are inside."

Using a height value of 7.1 mil (with 1 oz copper) gives good match: 50.3 ohms.
ps Have not done real measurements myself.

Gerhard_dk4xp:
From my TDR measurements pictured above, I'd say that 11.5 mil is
right on spot 50 Ohms for the JLCPCB process. They say it and my
TDR measurement confirms it. Microstrip, not coplanar.
And this was without the controlled impedance option. Just leftover
space between the 4 LMX2594 Synthesizers in standard 7628 process.

---

I just made some hairpin filters for 2 and 3 GHz for 0.8mm Bungard
FR4 material in a home-etched process. The 3 GHz filter is right on
spot, the 2 GHz filter delivers exactly the same curve on the VNA
as in electromagnetic simulation, just 5 dB more loss. Weird.
And having anything that resembles a cover destroys the out-of-band
suppression. Looks like another set of ElectroMagnetic simulations.

Gerhard

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