>>> David Ricketts <[log in to unmask]> 07/09/97 04:45pm >>>
Thomas Kropski wrote:
> 
> What is the smallest reasonable text size for silkscreen text. Text
> height, width, and thickness. With design density increasing, we would
> still like to have as many ref des possible.  From a PCB designer,
> what tooling parameters are acceptable for good resolution on the
> finished products.


The only real limitation to silkcreen is your PCB fabricator. We have
successfully used 40 mil high by 6 mil stoke width with the right
vendor. Older eyes may require help, but the text is completely readable
and clear. Our typical text size is 60 x 10 and 50 x 8. Our software
does not control the width.

As to the suggestion of eliminating silkscreen altogether by Tom Coyle,
that is a tempting but limited view. Every company will have different
products and priorities. Saving $1 per panel could cost $thousands in
assembly and rework errors. If your engineers get everything right every
time, and you use pick and place machines for assembly with every
single
part, including through-hole parts on both sides of the PCB, and do not
add discrete wiring at a later assembly, who needs silscreen? :)

David
-----------------------------------------------------------------------------
To all:

Why not consider getting rid of the solder-masks as well as the
silk-screen. Add two layers (just pads or smt lands and fanout pattern)
for the outer layers and get on with life utilizing the less expensive
boards. Also, when utilizing this technique, why not just etch your
reference disignators. From what I have been led to believe, the cost
advantage is seen when having to utilize over 6 or so layers.
You would just make a 6 layer board into an 8 layer. It would be
interesting to get some feed-back on this. I used to work for a military
contractor that initially was doing pcbs masked with dry-film. The thinking
then was to avoid the masks using this technique. The extra "pads-only"
layers allowed for etched-in reference designators. Any thoughts
regarding costs/trade-offs would be appreciated.

John Swinehart
BFGoodrich Avionics Systems, Inc.



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