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May 2003

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Thu, 29 May 2003 08:11:11 +0800
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Steve,

Does the board have any blind via hole groups. I had some boards once that
called for 1oz min after plating, but they had 6 blind via groups (3 from
each side) and the board was fabbed "conventionally", i.e. as a series of
through-hole sub-boards that were stacked after each group had been drilled
and plated. The end result was some (variable) copper thinkness going to
2.5 oz - considerably more than the 1 oz min called for in the stack-up,
but still acceptable according to spec.

I'm puzzled by the "skip" in your case though - any sign of any material
that might have effectively masked that portion during the plating process?

Peter



Steve Gregory <[log in to unmask]>   29/05/2003 01:53 AM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to SteveZeva

              To:  [log in to unmask]
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: [TN] Trace thickness problem...








Hi all!

I'd like your opinion on something. We're building a prototype assembly for
a customer, and discovered something at final inspection that we didn't see
when we received the bare fabs. We ordered 16-boards in four, 4-up panels.

We found a trace that has a spot where it looks like it didn't plate up
during final plating. Take a look at "Trace Thickness" at
http://www.stevezeva.homestead.com

There's 4-boards we've found that have this problem, 1 on one panel, and 3
on another panel, and of course they're all built up. The 6012 says that
thickness can't be reduced by more than 20% of the minimum conductor
thickness. I can't really tell if it's 20% or 50%.

I've sent pictures both to our customer and the fab vendor. The customer
wants the spot repaired, and there are a number of ways to do that. The fab
vendor says it's not a problem because the stack-up drawing calls out 1-oz.
copper after plating on the surface layer, and they said that there's more
like 2-oz. on the surface layer, so there shouldn't be any problem, at
least that's what I was told, I didn't speak to anyone directly. The
stack-up is on my page too, look at "Stack-up"...

The first question that comes to my mind, if 1-oz after plating was called
on the stack-up, why was 2-oz plated? Or is that normal?. The drawing
references our customers internal spec for fabrication, but it uses
MIL-PRF-55110 for references.

What are your opinions about this?

Thanks everyone!

-Steve Gregory-

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