Hi Werner, A sibgle crack is a result of a non-uniform loading but that is what happens in solder joints almost all the time and in the joints on SMD pads in particular. With all due respect, I don't think that once a ckack is created its kinetic can be described only based on the fatigue-damsge accumulated in the bulk of solder. Regards, Vladimir ________________________________ From: Werner engelmaier To: Igoshev, Vladimir; [log in to unmask] Sent: Thu Dec 11 18:26:54 2008 Subject: Re: [TN] Xbox360 BGAs Hi Vladimir, A single crack signifies a non-uniform loading condition/stress concentration geometry. Even than, "accumulation of creep-fatigue damage" is still the life-time controlling process. Werner -----Original Message----- From: Igoshev, Vladimir <[log in to unmask]> To: TechNet E-Mail Forum <[log in to unmask]>; Werner engelmaier <[log in to unmask]> Sent: Thu, 11 Dec 2008 9:42 am Subject: RE: [TN] Xbox360 BGAs Hi Werner, That is a completely different story J and "Yes" it is one possible scenario where the life time prediction can be made based on "accumulation of creep-fatigue damage". In other words, to predict the life time one would have to know the rate of accumulation of total damage (voids, as I wouldn't call them cracks in that particular case) distributed throughout the joints. However, in many-many case a single crack starts growing in a joint, finally causing its failure. That is the scenario I was referring to in my original e-mail and "accumulation of creep-fatigue damage" my not be the life-time controlling process. Regards, Vladimir -----Original Message----- From: TechNet [mailto:[log in to unmask] <mailto:[log in to unmask]> ] On Behalf Of Werner engelmaier Sent: Wednesday, December 10, 2008 10:05 PM To: [log in to unmask] Subject: Re: [TN] Xbox360 BGAs Sorry, that's what comes from doing things waiting for an airplane- should have been "...micro-voiding at grain boundary intersections,..." Werner -----Original Message----- From: Igoshev, Vladimir <[log in to unmask]> To: [log in to unmask] Sent: Wed, 10 Dec 2008 4:26 pm Subject: Re: [TN] Xbox360 BGAs Hi Werner, I got used to calling it grain boundary triple junction (it's just probably different terminologies). However, since I know what you meant I'm confused with the whole sentence: "In any case, grain coarsening comes first, micro-voiding and grain boundary intersections next...", triple joints are there to begin with. Regards, Vladimir ________________________________ From: Werner engelmaier [mailto:[log in to unmask] <mailto:[log in to unmask]> ] Sent: Wednesday, December 10, 2008 4:21 PM To: Igoshev, Vladimir; [log in to unmask] Subject: Re: [TN] Xbox360 BGAs Hi Vladimir, "Grain boundary intersections" occur where 3 or more grain boundaries come together. Purely metallurgically speaking, things get more messy on a scale smaller than grain size, but in terms of SJ rel consideration on the grain-size level is sufficient.