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July 2010

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Subject:
From:
David R1 Nelson <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, David R1 Nelson <[log in to unmask]>
Date:
Wed, 14 Jul 2010 14:50:11 -0500
Content-Type:
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text/plain (124 lines)
I would also theorize that the mechanical strength of the parylene
strengthens the solder joint. We saw increased resistance to low cycle
fatigue on boards coated with this versus over other coatings or a
baseline with nothing under the parts. It wasn't as good as underfill but
was a slight improvement over nothing at all. Sorry guys, data not
available.




From:
Douglas Pauls <[log in to unmask]>
To:
[log in to unmask]
Date:
07/14/2010 02:44 PM
Subject:
Re: [TN] Underfill as a Remedy for Electro Migration?
Sent by:
TechNet <[log in to unmask]>



Ken,
Yes, the parts were as underfilled as I could get them.  There was some
voiding and open areas as the liquid coating shrank when the solvents
escaped.

The forces come from CTE mismatches that accumulate through the bulk of
the material.  I would not expect Parylene or other chemical vapor
deposition coatings to have the same issues.  Lesser CTE values and far
less bulk.

Doug Pauls



Ken Harp <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
07/14/2010 12:07 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Ken Harp <[log in to unmask]>


To
[log in to unmask]
cc

Subject
Re: [TN] Underfill as a Remedy for Electro Migration?






I have a tangential question for Doug regarding the BGA thermal cycling
performed with conformal coating as underfill...it looks like the BGAs in
question were completely underfilled with conformal coating (from the
board
up to the underside of the BGA package).  Is this correct?  Any
experience(s)
with the effects on solder joint fatigue/reliability when using thin film
vapor
condensate parylene coating in leiu of acrylic or Loctite products for BGA


underfill?

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