Hi Werner,
That is exactly the point I wanted to make. Every time a crack "coalesce" with a void, it would have to re-nucleate again and it's not an easy thing to do.
There is one sentence in your e-mail I'd be very cautious about. Some people (and a very limited number of them) they do report the presence of voids at the interface and for some strange reasons call them Kirkendall voids. As far as I know, it have not been any data published, which would show that the presence of those voids were due to the difference in the diffusion rate in between 2 different materials. So, I wouldn't call them Kirkendall voids, just now. :-)
Regards,
Vladimir
Vladimir Igoshev, Ph. D.
Senior Materials Researcher
Research in Motion
451 Phillip St.
Waterloo, ON, N2L 3X2
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-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, July 19, 2005 11:33 AM
To: Vladimir Igoshev; [log in to unmask]
Subject: Re: [TN] BGA voids
Hi Vladimir,
You are correct.
I have never seen an overstress failure of a solder joint that involved voids in the solder joint bulk volume. I have seen creep-fatigue failures in SJs with voids that did not involve the voids at all, or that went through the voids, but were not caused by them. I have even seen SJs with cracks in them where the cracks stopped at a void.
Overstress failures invariably involve the interfaces of solder joints where for a variety of reasons really weak 'links' were created; that includes interfacial failures due to Kirkendall voids.
Regards,
Werner Engelmaier
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