Gary,
Patterns of behavior are important in recognizing, and thus preventing,
errors. If, in your system, you see an assembly with a revision level lower
than that of the bare board, red lights and sirens are going to go off in
your head and you're going to investigate -- usually you're going to catch
and correct an error this way. It's called experience and it's the magic
dust that collects on you from just hanging around for a long time.
Unfortunately, this makes people tend hang on to old behaviors, even after
the need has passed, just to maintain the patterns we're used to. We
(draftsmen, and hence PCB Designers) are some of the world's worst about
this. "We do it this way because it's the 'right' way to do it -- we've
always done it this way and it's always worked -- stop bothering me!"
Examples are revision histories kept on drawings, "Used On" lists, avoiding
four-way connections on schematics, drawing zones, etc...
Don Walker
Visayan Inc.
[log in to unmask]
www.visayaninc.com
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Wolfe,
Robert
Sent: Wednesday, February 13, 2008 10:38 AM
To: [log in to unmask]
Subject: Re: [DC] Revision levels of PCB Assy v-v PCB Fab
Gary
Bottom line if there's a new part number involved that means it's a new part
so no reason it should not be Rev 0 for the new assembly & BOM.
The PCBA is a part with it's own rev history.
Bob Wolfe CID
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Gary M.
Koven
Sent: Wednesday, February 13, 2008 9:10 AM
To: [log in to unmask]
Subject: [DC] Revision levels of PCB Assy v-v PCB Fab
Thirty-some odd years ago when I was a novice designer, I was trained that
the revision level of a PCB assembly (PCBA) must match, or be greater than,
the revision level of the bare PCB fab.
We have a situation now with usable Rev 5 bare board glass that is being
populated for a different application, requiring a new part number for the
PCBA and the BOM.
I'm inclined to do the initial release of the new PCBA and BOM at Rev 5,
based on experience. My boss wants a Rev 0 release.
I can't remember what document originally specified the form, fit and
function rules for PCB and PCBA revision level control.
Can someone provide hard copy evidence for revision level control to
substantiate, or disprove, what I was taught back in the day?
Thanks and Best Regards,
----------------------------
Gary M. Koven, C.I.D.
Dynazign, Inc.
Charlotte, NC, USA
704.405.1234
Veteran of the Marsh School
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