TDR solder mask

Am 25.01.22 um 23:08 schrieb John Larkin:

I got similar results on a JLCPCB 4 layer board. I calculated that 50 Ohms are 11.55 mil, drew it 12 mil in Altium. Seems to fit.

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The SMA launcher decal was not so good, but I was interested in the 50 Ohm line only for verifying eps-r and thickness etc. The launchers were for a 2 layer process. The streamlined boards for the LMX2594 are on the plane from HK. They also have cutouts on Layer 2 and shorter SMA center pads. The unpopulated SMA is better than the populated one. The thickness of the center pin and the solder seem to matter.

cheers, Gerhard

Makes sense; the mass of the lacquer layer can't be much, and multilayer boards, with glue layers, might have more material nonuniformity over modest length scales. Fiberglass cloth, too, can be expected to contain some weave variance.

The quickie Chinese board houses default to super thin layer 1/2 dielectrics for some reason. If you use layer 2 as ground, that makes your SMA pads capacitive anomalies. Even the cutout doesn't seem to be enough; fringing maybe.

Your trace hit 50r pretty good.

We have one 50-ohm SMA footprint that cuts away all the inner planes and plops a big copper square on the farside.

That connector has a giant center pin. The center pin in free space, not on a board, is 100 ohms!

Am 26.01.22 um 04:39 schrieb snipped-for-privacy@highlandsniptechnology.com:

That is needed to get some signal out from under a BGA. They also have a process for thicker lines. I think I will test it with a UHF LDMOS power amplifier.

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one of the next tries. Red is top = 1, blue = 2, yellow = 3 (not in this area) 4 = bottom = green.

Looks like the center pin on my board. I also have recovered some SMAs from junked wafertesters; they have REALLY small center pins and a ground tunnel / bridge with 2 hex nuts. They might fit the 12 mil line directly. Probably a solder problem even with the finest METCAL tip.

Probably Rosenberger.

The plane with the new boards has landed in .de in the night. :-)

Cheers, Gerhard

Some of the high-end connectors don't need solder. Substitute money.

New boards are always fun.

This is a nice part:

MUELLER BU-1420701851 DIGIKEY 314-1703-ND

We're paying less than $4.

A 35 mil wide trace matches the pin width, and you can bury one end of an 0603 part in that trace without adding any pad capacitance.

There's room for a couple of small parts or some silk text inside the footprint, which can be handy.