Andy,

I think Aric made some reasonable remarks but I would suggest that to
PERHAPS fix your problem boards, try cleaning in a pure chemistry. Suggest
Zestron, Armakleen, Kyzen although there are many others.

This should allow the aged residues to become more "washable" and you should
clean thoroughly and re-test. Are your products Class 1, 2 or 3? If 3, you
really ought to start again and wash ASAP after any soldering operation.

CSL, Robisan or Trace labs would be good contacts to review the issue in
more depth. Hope this helps.

Regards, Graham Naisbitt
__________________________________________________________________________

[log in to unmask]

Concoat Ltd
Alasan House, Albany Park
Camberley GU15 2PL UK                        http://www.concoat.co.uk

-----Original Message-----
From: lcs Mixmaster Remailer <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 21 May 1998 03:25
Subject: [TN] Ionic Contamination


>Hello Technet,
>
>A supplier made us some board-assemblies with a ionic contamination at
least twice as high as the IPC and MIL-specifications allow. This is
probably due to residues from RMA solder paste. The boards are washed after
wave soldering with water/detergent, but there is no intermediate cleaning
after the reflow soldering. It takes a couple of days before the reflow
soldered boards are wave soldered, so the paste-flux is not very cleanable
anymore.I've heard so often that bad cleaning of RMA is much worse than good
cleaning or no cleaning. I'm not sure, but this is what I think is the cause
of the problem..
>
>The question : will this ionic contamination, concentrated around the
topside-smd's, really result in early failures ? The boards are built in
hermetically sealed boxes, but will be used in a wide variety of
temperatures. There are no fine-pitch devices on the boards. Any advice or
comments are welcome.
>
>Andy
>
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