At 12:42 AM 6/7/01 -0700, Dwight Harm wrote:
>Since we contract out the assembly, I don't hear the gripes of the
>assemblers -- for better or for worse.
This reminds me of my least favorite response to a possible problem
situation: "No one has complained." I've seen a high percentage of
companies go out of business after I heard that from someone with authority.
Re-annotation is a complex question. It makes service easier, no doubt, but
at the expense of making engineering, in some cases, more difficult. Since
time to market is critical and many products are never serviced, it can be
a poor trade-off.
As to assembly, I've been told by some assemblers that they work from first
article anyway (i.e., a sample assembled board) so the designators make
little difference, the assemblers don't look at them. On dense SMT layouts,
designators in silkscreen on the PCB can be difficult or impossible to
position.
As a technician making the first board, I'd rather have a drawing with part
values than one with reference designators. Such a drawing could be
directly used, whereas reference designators require look-up.
So my norm is to *not* reannotate unless my client requests it. It is extra
work that *may* turn out to be worse than useless.
Consider that an engineer may have parts ordered and ready to stuff
according to designators in his schematic. He may have prepared many
different documents using the original designators. If a design is done as
Schematic, PCB, re-annotate, and then we can look at purchasing, and no
parallel documents are generated, re-annotation is harmless. But that is
not the usual case in an environment when time-to-market is crucial.
Further, the engineer may have provided design notes: "keep U5 away from
U23." These notes become unintelligible after re-annotation.
If there were an integrated design environment where *all* text referring
to reference designators would be updated, these problems might be avoided.
But we aren't there yet, and may not be there for a long time.
And now a war story, which has to do with schematic re-annotation, but
something similar could happen with PCB re-annotation. I had done a complex
design for a client, who now wanted to make some changes. He added some
parts, removed some, and moved some around. Then he re-annotated. And did
not keep the modified original.
May this never happen to you!
What I did was to write a utility to read the ASCII schematic (this was
Tango) and compare schematic part locations between the original schematics
and the revised ones; where the locations were identical, I now had a
was-is cross-reference for that part. What did not match I manually
compared. Since Tango did not suppport was-is reannotation from the
schematic to the PCB, but only in the other direction, I also wrote a
utility to do that, so I could renumber the PCB to match the new schematic.
[EMAIL PROTECTED]
Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433
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