Well sumxp,
Your PCB supplier is telling you the
truth and your customer is probably telling what he knows (who knows if
he knows the truth).
But this may be " A FAILURE TO
COMMUNICATE". If the customer is saying that he needs 50 ohms
+/- 5% for the RF board that is different than trace width +/- 5%. But
+/- 20% control on trace width will NOT get you impedance at +/- 5%, +/-
10% YES, but not 5%.
Below is our measurements in fabrication
of the various contributions to final impedance. You can see how
important thickness control is. In order to build RamBus, many had
to learn how to control impedance to +/- 2.8 ohms, but in doing so ALL
fabrication and material tolerances had to be improved. The list
of what it takes for fabrication tolerances for final impedances from +/-
10% to +/-5% is below:
My customer told me that one of the RF pcb need to
maintain the 5mils trace
width within 5% tolerance in order to achieve 50 ohms impedance.
My pcb maker said they can only control at 20%(copper etching process
capability) trace width tolerance BUT can guarantee that the impedance
is
at 50 ohms.
Please comment.Should I take the words of pcb supplier?
rgds
sumxp
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