>We are having a significant problem with quickturn cards coming
>in  overetched, and we're trying to understand some things about
>the process of  etching.
>  One question that has come up is:  Is it possible for
>  etching to be greater in one area of the card over another?
> If so, how is this >possible,  and what are the design
> considerations for this?  Some here contend that every
> feature should etch down by the same nominal amount, say
> .002 inch, whether the feature is an .008 trace or a  large
> ground plane, since the whole PCB is exposed to etchant at the
> same  time.  Is there fault in this thinking ?

Even etching across the panel requires close attention to the
process variables (spray pressures, temperature, chemistry). Many
companies run a test panel of bare copper to check for even
etching on a daily or shift schedule in addition to all the
other checks. On a large card even etching definitely needs to be
watched.

Design considerations are:
-Use the thinnest copper foil call out you can down to half
ounce.
-Try not to use 'isolated' copper features with nothing
around them. They can over-etch.
-Lines parallel to the board edges work better.
-In general finer lines are easier to make than fine spaces. I'd
rather have a 4 mil line with a five mil space than a 5 mil line
with a 4 mil space. Above 6 mil line and spaces most operations
don't have an issue with this.





[log in to unmask]
Hallmark Circuits Inc.
San Diego, Ca.

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