Hi All..
I may be naive, but over time I had two controlling factors which
guided out pwb's fabrication. The first is your drawing which dictates
the pwb's "end product requirements". The second, which has been
previously mentioned, COMMUNICATION, COMMUNICATION and
COMMUNICATION with your supplier(s). On off-loaded designs, I
required that the design service bureau, the board fabricator and the
assembler were familiar with each others processes. This could/would
eliminate CAM GUY"S creative juices from flowing to make HIS pretty
pictures.
As long as the supplier meet all end product requirement, they would be
giving some latitude to work the data base. At the start of a run, we would
meet with the supplier, if required, and they would propose their "fabrication
data modifications". With our concurrence, we would then inform the other
members of the "team" to review the impact on their cycle, as required, and
then proceed to board fab.
Our products were Mil-Spec designs and/or high end state-of-the-art designs
and our notes tended to be dynamic. If anyone in the design/fab/assemble/test
cycle offered suggestions to improve the cycle, and therefore the product, it would
be discussed and implemented, if worthy.
So, in ending (as cheers start ringing out- hee, hee ,hee), a drawing with end product
requirements and a large dose of communication with ALL those disciplines in the
product cycle to ensure that finished product equals what the customer required.
My Dime's worth.......
Bob Vanech
BVAN Enterprise
----- Original Message -----
From: Jack Olson
To: [log in to unmask]
Sent: Saturday, January 06, 2007 11:54 AM
Subject: [DC] CAM Guy Gone Wild!
A friend of mine (not on this list) asked me what I would do
about something, and I didn't know (can you imagine that?)
He is experiencing horrible problems with a product that
should have worked as designed, only to discover that the
CAM guy in China went crazy with editing! It took WEEKS
to discover what he had done.
The original design was primarily 5/5mil traces/clearances
and this guy increased the plan clearances under BGAs to
10 for some reason, claiming "More Manufacturable". He
also did all kinds of weird pad shaving and stuff which is
mysterious but probably irrelevent. The poblem was that
under the BGAs the added clearance took away return path
for signals and I think even isoalted portions of ground from
each other, and now the board won't even boot up!
Now, I know many of you are gonna say you don't let vendors
edit data, and even add notes to the drawing to prevent it.
I'm not one of those people. We use several different vendors
and if we want 5 mil traces and one vendor knows that their
process consistently over-etches traces and they want to
beef them up to 5.5 knowing that the end result will be 5,
FINE!
I am very happy when a vendor knows what to do to
give me what I want. I actually DEPEND on them to edit
whatever they need to give me my 50 ohm impedance, rather
than forcing me to specify seperate sets of detailed con-
structions to suit each of our appoved vendors. Since our
products last 20 years or more, I don't even know WHO will
be building them in the year 2020, so I DEPEND on them
to do what is necessary to make the reliable product.
That said, where do you draw the line between edits to give
the desired results, and some "wanna be a designer" CAM
guy making all kinds of "improvements"?
What should I tell my friend to do about these very expensive
boards that don't work?
Jack
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