I think you have entered the strange zone of dewetting, which is not the
same as non wetting.
It is quite possible that something has changed to allow poor or
marginal initial wetting, which on re-exposure causes non wetting. It
would be interesting to see what happens if you simply double the
initial exposure time - you might then go straight to non wetting.
Dewetting is usually, but not always a function of some sort of
contamination.
Regards
Mike Fenner
Indium Corporation
T: + 44 1908 580 400
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F: + 44 1908 580 411
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Braddock, Iain
Sent: 08 April 2004 15:54
To: [log in to unmask]
Subject: Re: [TN] Strange phenomenon!
Thanks Werner,
The reflow temperature measured at the lead I/F is 215C. These boards
have
been built for the last 2 years without this problem but now there is.
If the joints are rerun with a soldering iron the problem goes away but
this
is a cumbersome, non value added activity which I am trying to address.
I am considering having the failed joints analysed by one of the
universities that specialise in Auger / SIM microscopy.
Regarding your last comment, if the lead / foot wasn't solderable at all
would you expect the formation of a joint ie. a nice meniscus as we
have,
though obviously a weak metallurgical bond I wouldn't have thought so!
Regards,
Iain.
-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: 08 April 2004 13:05
To: [log in to unmask]
Subject: Re: [TN] Strange phenomenon!
*** WARNING ***
This mail has originated outside your organization,
either from an external partner or the Global Internet.
Keep this in mind if you answer this message.
Hi Iain,
Remember, that what you are soldering to in Alloy 42 is the 42% nickel
in
it.
As such you need to raise the reflow temperature some 15 to 20°C over
what
is
needed for Cu.
Also, there occasionally apppears Allloy 42 that is not solderable
at
all; thus, your gullwing feet are simply encased in solder without any
metallurgical bond.
Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com
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