OK, now the games begin! :) We have two replies so far to my question
:"How big of a crack in thermally cycled solder
joints is too big of a crack?"
Werner, I am a little confused by your statement "I also assume he does not
include in "if you can detect it, it is too big!" cross-sectioning."
Could you please elaborate?
I was NOT trying to make a technical connection between BGA voiding and this
issue. I was trying to draw a parallel between the possible arguments of
what is the max largest % voiding and possible arguments about crack size.
Sorry if I confused people!
So, Werner, when does a micro-crack become a crack, in terms of size?
regards,
Bev Christian
Research in Motion
-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: June 21, 2002 7:24 AM
To: [log in to unmask]
Subject: Re: [TN] cracks in solder joints
Hi Bev, David & All T's,
While I concur with David's "big enough" statement, I also assume he does
not
include in "if you can detect it, it is too big!" cross-sectioning.
On the other hand, Bev writes "Shades of voids in BGAs... How big of a
crack in thermally cycled solder joints is too big of a crack?"
Cracks in thermally cycled solder joints have nothing to do with voids;
therefore why "Shades of voids in BGAs...". Solder exhibits micro-voids
[having nothing to do with voids] at grain boundary intersections after
about
25 to 30% of the fatigue life having been consumed, and micro-cracks along
grain boundaries after about 40%. That means about 60% of life is still
available when 'observable' micro-cracks are present.
David then says: "A better question would be how do you distinguish between
a
crack and a void?"
That one is easy, voids a roughly spherical, cracks are fractures.
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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