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March 2001

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 1 Mar 2001 18:06:59 -0000
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Hello folks

Long time no posting, been kinda busy with some exciting new business
developments - more of which later - and Ingemar forced a reaction:

Given that my company name is Concoat, your heading and some of the comments
make me shudder - maybe its an earthquake in merry olde England?

Like Ingemar, I too learnt quite a lot from this issue, especially Brian
Ellis' comments regarding silicones. That was a curious one. I should have
thought, but then what do I know, that a soft "squooshy" material like
certain silicones (maybe that should be Silly-Cones?) would only react in a
"rigid" sense when subjected to kinetic energy impacts rather than the more
insidious thermal creeps!?

Anyhow, I am not entirely sure whether an underfill or a coating can -
should - ought to be used under BGA's. The issue I guess, is maintaining the
integrity of the solder joints, and maybe, just maybe, the current soldering
methodology is the weak link for these devices? Our new condensation
soldering technique - that's vapor phase to the older techies - certainly
provides for a uniform and effective soldering of such devices.

The use of a conformal coating or an underfill. Depends on the nature of the
coating and perhaps more importantly, how it is cured to avoid residual
solvent entrapment and the like. Obviously "squooshyness" is an important
factor - maybe there is scope here for more thermal dynamic work on
encapsulants, underfills and coatings - anyone for tennis?

Regards, Graham Naisbitt

[log in to unmask]
www.concoat.co.uk

Concoat Limited                     www.concoat.co.uk
<http://www.concoat.co.uk>
Alasan House, Albany Park
CAMBERLEY GU16 7PH UK
Phone: +44 (0)1276 691100
Fax: +44 (0)1276 691227
Mobile: +44 (0)79 6858 2121



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ingemar Hernefjord
(EMW)
Sent: Monday, February 26, 2001 02:52
To: [log in to unmask]
Subject: [TN] pumping concoat


Hi all,
I have triggered some BGA soldering issues last weeks and got superb
responding! We  have learnt a lot!. Among answers one warning  not using
concoat under very large BGAs, could cause pumping effects. Guess Tech-Shot
could answer as well, but more gurus  at TechNet. Graham N, he must at least
have a refresher for me. Got this b4:
1. try skip concoat, best living for BGA solderings
2. if using concoat, always underfill 100% first
3. if using concoat and no underfill first, you'll get closed in gas and
contaminations and CTE mismatch >disasters

So, my question is: is 3 above reality for some of you? Don't your balls
like such pumping?

Thx in advance
Ingemar Hernefjord
Ericsson Microwave Systems

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