John:

This is a subject that IPC has avoided.  The last specification that I can remember was in the
+/-0.020" area, which is not adequate for today's designs.  You must decide what you want for
your legend.  Conventional, screened legend can maintain somewhere between +/-0.015 to 0.010 inch
(optimum conditions).  If you are willing to pay for LPI legend, you should experience +/-0.005".

The real question is why do you need tight registration tolerances?  Automated assembly equipment
doesn't use legend to assemble the boards, and once the parts are on the boards most modern
designs can't be read.  IMO, legends on modern designs should only be used for warnings, assembly
identification, test points, and similar designations.  Assembly drawings (scaled larger than
1:1) should be used for component identification.

Don Vischulis
[log in to unmask]

John Bauer wrote:

> Is there a specification that specifies the registration tolerance of the
> silkscreen legend to the PWB?

snip --------------------------------------

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