[log in to unmask] wrote:
> 
>                I totally agree with all who responded to Lou Hart's
>           question about legend ink on surface mount pads.  It should
>           be unacceptable, and spec'ed out as such.  My company
>           standardly clips (removes) any legend ink falling within
>           .008" of a solderable feature, due to the tolerancing
>           required for the screen print operation.
>                I would like to take this conversation one step
>           further, however.  Why are we still using silkscreens on our
>           circuit boards (other than for hand assembly)?  When the
>           board shops clip silkscreen alpha-numerics from solderable
>           features, "R"s start looking like "P"s, "B"s like "3"s, etc.
>           Board designs are getting tighter and tighter, and there's
>           barely any room for this stuff anymore.  Folks are being
>           charged an average of $0.50 a side for silkscreens, and now
>           with double-sided surface mount, we're dealing with two
>           silkscreens, or a buck a board!  It's amazing how most of my
>           customers are looking for ways to save pennies on their
>           boards, but don't seem to mind shelling out money for
>           silkscreens which in many cases are becoming next to
>           impossible to read.  I realize that not using silkscreens
>           requires a culture change, but more and more of our astute
>           customers are taking a second look at whether or not they
>           are really needed, and some have taken the plunge and
>           discontinued their use.
>                I certainly don't want to disgruntle anyone (especially
>           inspection folks!), but maybe it's time to evaluate whether
>           silkscreens are really of any value, or simply a dinosaur
>           from the past.  Thanks for letting me throw in my $0.50!
>           Regards,
>           Tom Coyle
>           Field Services Engineer
>           HADCO Corporation____________________________________________________________

I agree with the above statement.  In a former life I bought boards 
instead of making them.  Usually when the design folks were asked why 
the silk screens were on the boards the answers ranged from we've always 
done it this way to it helps the field service staff to it helps the 
engineering lab during the proto build.  With the size (or lack thereof) 
of the legend and the increasing difficulty in locating legends where 
they can be seen after assembly (youv'e got to read it after the parts 
are on the board) my opinion is that a good assembly drawing will be 
more useful to the folks that have to make the design work after it 
breaks.  

After the designs became too tight, we managed to do away with most of 
the legend.  The opinion of many of the folks that had to work with the 
board was that the board looked better without those white blobs and 
that the Techs really could read an assembly print (surprise!).

Don Vischulis
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