Hi Dave,
I read the paper and have to say that I respectfully disagree with your
statement that solder "doesn't follow the basic principles of fracture
mechanics".
The paper is good indeed and the data indicate that reduction in the
lifetime of the ENIG joints after 1x reflow was simply due to reduction
of the cross-sectional are of the "gage section" because of the voids. A
rough estimate shows that a void of that size located close to the
UBM/solder interface reduces the cross-sectional area by almost 25 %
(based on the diameter of the UBM opening and the void size). Therefore,
I'd say that the principles of fracture mechanics still stand :-)
As far as the original question is concerned (voiding), then I believe
the answer is our favorite one: "it depends". If void do not reduce the
cross-sectional area and they are not adjacent to one of the interfaces
(board or UBM), then the answer is "NO".
Regards,
Vladimir
________________________________
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Friday, February 22, 2008 2:33 PM
To: TechNet E-Mail Forum; Igoshev, Vladimir
Cc: [log in to unmask]
Subject: Re: [TN] Shrink hole voids
Hi Vlad! Sorry to disagree but you are applying classic crack initiation
and growth theory on a material that doesn't follow those basic
principles. The voids in solder joint neither initiate crack growth nor
blunt crack growth. It would make a materials engineers life soooo much
easier if solder just behaved like steel. Richard Coyle published an
outstanding paper that covers this topic in great detail. I recommend
that folks read the following paper:
R. Coyle, et al, "The Effect of Process Voiding on BGA Solder Joint
Fatigue Life Measured in Accelerated Temperature Cycling", SMTAI
Conference Proceedings, September, 2007
Dave Hillman
Rockwell Collins
[log in to unmask]
"Igoshev, Vladimir" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
02/22/2008 12:34 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Igoshev, Vladimir" <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] Shrink hole voids
Hi David,
Think of rivets on a plane or ship. They are there to prevent a crack
from propagating. A hole (or void) will do the same trick. It does not
create a stress concentration (particularly in a ductile material like
solder) and therefore it can stop a crack ("swallowing" it). You can
take a look at the basics of Fracture Mechanics if you want to.
Regards,
Vladimir
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Tremmel
Sent: Friday, February 22, 2008 1:29 PM
To: [log in to unmask]
Subject: [TN] Shrink hole voids
Hello TechNet Gurus,
I read an article that say that a shrink hole void (hot tear or sink
hole)
is not a crack, does not impact reliability, does not continue to grow
under
thermo-mechanical stresses.
This seems to go against my common sense and would venture to say adds
to
solder creep fatigue.
Would anyone like to comment on my comment and/or offer a link to where
I
can find more information?
I am a poor country and your two cents goes a loooooong way.
As always, thank you in advance.
Thank you,
David Tremmel
Value Recovery
847 858-5540 - Cell
847 557-9574 - Office
847 557-9573 - Fax
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