The main tolerance for Top to Bottom PCB Thickness is not the Copper thickness
variation. The final Copper thickness varies a bit by design, stack-up and via
barrel plating requirements. Good manufacturers can manage up to +/-5µm Copper
thickness variation, +/-10% are usually met by every Manufacturer.
This is very little compared to the laminate thickness tolerances. There are
three thickness tolerance classes defined in the IPC, and there also 10% is the
average. The tightest tolerance is in the 5-7% range (depending on the final
thickness of the laminate. This is then the overall thickness measured
including Copper foil on top and bottom, thus for impedance calculations the
nominal core thickness given by the manufacturer must not be used as the
dielectric thickness in your impedance calculator.
So for a 2-Layer PCB there is the 10% Laminate thickness (and 10% tolerance),
the plating thickness (and 5% tolerance), the Solderresist thickness (approx.
25µm) and tolerance (+/-10µm) that results in the final Thickness and tolerance
of your PCB.
For Multilayer Boards an overall thickness tolerance of 10% can be achieved by
most PCB Manufacturers when they use Class L/M Laminate and Prepregs (that’s
the most accurate IPC thickness Class).
Hope this helps.
BR
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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
Auftrag von Doug Brooks
Gesendet: Montag, 23. November 2015 00:35
An: SI
Betreff: [SI-LIST] Copper plating
This is a question primarily for PCB board fabricators, or anyone who has
specifically made accurate measurements:
What is the typical thickness tolerance on plated copper. That is, if I specify
a plated thickness of 1.0 Oz (nominally 1.3 mils), what is the range (board top
to board bottom, board front to board back, etc.) of actual thickness I can
expect.
I am guessing it is about 50%. I will not associate your company name with your
answer!! I am not trying to get sales pitches or anything --- just honest
assessments.
Thanks
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