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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