Yes but a long time ago.

What happened is that the top side surface mount QFP's had very little over
board clearance. The top side was assembled first using SMT. After this the
through hole was loaded and wave soldered. The flux was water wash active.

What happened is that the first thing the board sees is the wave solder
fluxer which coats the via hole (and this is worst if it is not a spray
fluxer). Then along comes the wave. The solder wets to the via and drives
the flux up onto the top board surface. Subsequent washing failed to remove
the residue due to the low clearance between the QFP and the board.

The boards started to fail in the field. When the QFP's were removed the
traces and vias underneath were corroded and turning black.

The condition was worse in high current density areas, just after the supply
line entry point to the board and gradually became less pronounced the
further away from the supply rail as the current draw became lower.

Anyhow, not sure this helps you but that's what I saw in 1993 and I know
that the field recall internal cost to the large company concerned was
around 4 million dollars at that time.

Kind regards,

John

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of No Name
Sent: Tuesday, July 25, 2006 3:11 PM
To: [log in to unmask]
Subject: [TN] Vias under parts

Has anybody had any experiences with open vias underneath parts?
Specifically, have you ever seen flux from the no-clean wave process
become trapped under the parts and cause long term field failures?

Thanks.

Henry J. Rekers B. Eng
Senior Manufacturing Engineer
Power Monitoring and Control

Schneider Electric
2195 Keating Cross Road,
Saanichton, BC, V8M 2A5
Tel: 1-(250) 652-7100 ext. 7510
Fax: 1-(250) 544-2390

http://www.schneider-electric.com/

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