Here is an approach which may help you avoid a long drawn technical debate
trying to prove what seems obvious to a closed mind.

I assume that the dewetting you are experiencing is more than a small amount
and is inconsistent. On this basis the issue is that this dewetting is an
uncontrolled variable rendering the boards unsuitable for a mass production
process which
can only be assumed to work if all variables are known and controlled. This
makes the boards unfit for purpose and therefore rejectable. At the very
least acceptance of such boards would require 100% test and inspection as
there is no way of knowing when the dewetting on any one pad will go beyond
an acceptable limit. If you ask your supplier to contribute to the
additional cost of this work it may well be that they will find it cheaper
to resupply. This would not constitute a rejection and therefore may give
your purchasing people a window to jump out of...

You could fully illustrate this point  by argueing it to its logically
complete [and unreasonable] conclusion:
the different degree of solderability on each pad of every board requires
different process conditions because of their variablility and that whereas
on an individual basis each one may be considered solderable** overall this
variability clearly makes the boards unfit for the purpose for which you are
buying them namely a mass soldering process.

[**?by some to be defined process such as say individually hand soldering by
a skilled operator able to tell the degree of solderability and therefore
adjust dwell times or whatever and able to make a decision as to whether the
pad has soldered?]


Hope this helps, be interested to know what happens.

Mike Fenner
BSP, OX15 4JQ, England
T: +44 1295 722 992
M: +44 789 999 7715
F: +44 1295 720 937


-----Original Message-----
From: Kathy Palumbo <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 28 July 1999 19:26
Subject: [TN] Dewetting Issues


>Currently we are experiencing a lot dewetting issues on our HASL coated
>boards.  When tested in house they failed IPC solderability testing, and
>when tested at two outside independent labs they failed solderability
>testing at both labs.  The problem we are having is our purchasing
>department still thinks we are full of it and will not support us in
>returning the boards to the board house, and naturally the board house is
>taking our purchasing departments side and will not take the boards back
>now.
>
>Both our purchasing department and the board house are claiming "there is
no
>long term reliablity issues with dewetting".  Naturally my M.E. and Q.E.
>group disagree with their statement.
>
>What I am looking for is long term reliability studies regarding dewetting
>on typical HASL coated FR4 PCB material.  Does anyone out there know of any
>such studies, or can you steer me in the right direction?
>
>Thanks for you help in advance!
>
>Sincerely,
>Kathy Palumbo
>
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