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November 2004

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Subject:
From:
Guy Ramsey <[log in to unmask]>
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Date:
Tue, 2 Nov 2004 08:32:15 -0500
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I agree with your position. One real issue with unnecessary rework is board
damage. The soldering process exceeds the glass transition temperature of
the board. This causes a large Z axis expansion. It is one of the stress
tests for a PWB. It does not take many cycles like that to break the PTH.
Even if it doesn't break the PTH the process involves risk at a time when
the product has maximum value to the organzation.

Identify the cause, eliminate the cause where economically practical, that
is the message in the standard.
Unnecessary rework is bad.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Steve Gregory
Sent: Monday, November 01, 2004 8:02 PM
To: [log in to unmask]
Subject: [TN] Process Indicators...


Hi All!!

I've been getting into a number of debates about "Process Indicators" as
described in the IPC-610...mostly with our inspectors. I know their hearts
are
in the right place, but it seems that many times they will reject the
assemblies with "Process Indicators" back to our operators to touch them
up, so that
they look more like the "Target Condition", to be more cosmetically
pleasing.

I've tried to explain things as best I can, but find that sometimes our
operators are touching up way more solder joints than they need
too...they're
being "trained", as it were, by our inspectors. The operators know that if
something isn't "pretty" enough, it's going to come back to them...so
they're
putting more labor into product than they should.

I'm trying to find some way, any way, to be able to show our inspectors
that
to touch-up something because it doesn't look like the target condition,
doesn't mean one is making things any better...I understand that beauty is
in
the eye of beholder.

There was some talk in the past about the Intermetallic Layer being
thickened during subsequent reflow cycles, and causing fractures, but
Werner said
that he's never seen a failure because of a thick Intermetallic  layer.

Process Indicators may happen as spelled out in the -610, sometimes not
only
because of the assembly process, but because of the design, or other
factors.

I look at Process Indicators as a "Flag" to investigate whether or not the
issues can be addressed and resolved properly, if they can't be resolved,
then
it's not a defect. Am I wrong about this?

As always, TIA!

-Steve Gregory-



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