There are a number of good reasons for not silkscreening a PCB. Silkscreen
is a source for errors that can delay fabrication. It is an extra process
step usually manual that adds cost to a PCB. Incorrectly applied it can be a
contaminant in solder joints (silkscreen on pads). Any or all of these maybe
a good reason for leaving it off.
If I were creating a PCB with no silkscreen I would make an effort to
identify polarization of components. The convention has been square pad for
pin 1 on through-hole discreet and dip parts. We use an extended pin for
SMT ICs and a hash mark for SMT discreets. In addition to parking
polarization We supply a component placement map that identifies the
placement of all components with copper features shown for orientation.
I know this doesn't make life easier for the assembler but sometimes you
gotta' do what you gotta' do.
Jeffrey A. McGlaughlin
Sr. PCB Designer
Battelle Memorial Institute
Columbus Ohio
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-----Original Message-----
From: Rick Thompson [SMTP:[log in to unmask]]
Sent: Monday, 14 February, 2000 12:36
To: [log in to unmask]
Subject: Re: [TN] Silkscreen, Pin-1 markings, etc....
Steve,
FWIW, we actually get quite a few boards without silkscreen or with
minimal
silkscreen, not including all components. When we get it, its
usually done
because of lack of usable space for marking, even away from the
components.
Ideally in those cases, we get both X/Y data information for
programming and
a marked up assembly drawing showing the locations for inspection.
It's not
what we'd want if given the choice, but it's usually workable.
As for the square pad on pin 1, while it's pretty common, I don't
think it's
any kind of standard. Again, we see a variety of uses for square
pads, not
always indicating pin 1. Enough so that we discourage our operators
from
making that assumption unless there's some other corroboration with
other
markings or the customer verifies that is the case.
Rick
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Stephen R.
Gregory
Sent: Monday, February 14, 2000 4:13 PM
To: [log in to unmask]
Subject: [TN] Silkscreen, Pin-1 markings, etc....
Hi ya'll!
Is there anything that says a board should have silkscreened
reference
designators on them, or pin-1 markings or indicators (like a square
pad for
PTH locations) incorporated into the design?
I know there sometimes isn't room to put a reference designator
right next
to
a location, but in those cases I've seen the designer find room
someplace
else on the board and then arrange the reference designators in the
order
that the parts are in, then have a line going to the beginning of
that row
of
components. What I'm talking about usually I see when passive
components are
so tightly spaced there's no other way.
I've hardly ever run across boards that didn't have some sort of way
you
could tell what goes where...I've seen maybe 2 or 3 boards in all
the time
I've been working, and that's including the board I have now.
So is there some sort of requirement, or is it just good sense to
make
things
easier to build?
Thanks!
-Steve Gregory-
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