Reference may be useful:
Simulation Of Microstructural Evolution During Thermomechanical Cycling In Pb-Sn Solders
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Author(s):
Michael Woodmansee, Veena Tikare
Pb-Sn solders are known to coarsen and deform heterogeneously under shear thermomechanical cycling. Solder joint failure often occurs within these coarsened shear bands. The connection between microstructure and materials properties is well documented, which leads to the conclusion that an improved understand of the interaction between stress and microstructural evolution will better enable the prediction of materials properties over time. In this paper, we simulate microstructural evolution of Pb-Sn solders using a novel two-phase version the Potts model, a kinetic Monte Carlo model that is coupled to a finite element mechanics model. Using this model, possible mechanisms for heterogeneous coarsening are explored.
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Track ID:
Paper #: W6.4
DOI:
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, April 27, 2010 10:14 PM
To: [log in to unmask]
Subject: Re: [TN] Failure fatigue photos
(1) the Pb is possibly >83 wt% alloy. Because I do not see the eutectic phase present in the joints. Possibly 90/10 Pb/Sn alloy (unless someone etched the microsection). Look like Pb rich phase is solidified 1st and Sn rich phase flowed around it.
(2) voids near the IMC observed: it could be a high resistance joints and either due to fracture (limited contact) or others (don't know what is the device nature: high power?). If it is field return or dynamic testing samples (power on during test), it might experience localized heating due to high resistance joints.
(3) Fracture along the line between the Pb rich and Sn rich phases (appear to be), it could due to grain boundary (as someone mentioned before) fracture. If it is over heating, the PbO may be preferentially formed at partially fractured surface (excessive oxidation?), enhance the crack propagation speed, and/or change the nature of the fracture.
Without knowing any history and test conditions, just shot in the dark. My 1.95 cents.
jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of vladimir Igoshev
Sent: Tuesday, April 27, 2010 7:56 PM
To: [log in to unmask]
Subject: Re: [TN] Failure fatigue photos
I just took a look at the images on a computer screen (not BB) and I think the joint could have had a lot of voiding between the bottom of the lead and pad. Otherwise, I would have a hard time to explain why the opening in the 'heel" area is much smaller then the onE between the bottom of the lead and pad.
Regards,
Vladimir
Vladimir
SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
-----Original Message-----
From: Ioan Tempea <[log in to unmask]>
Date: Tue, 27 Apr 2010 08:59:34
To: <[log in to unmask]>
Subject: [TN] Failure fatigue photos
Dear Technos,
It looks like, for the first time, I have the occasion to look at fatigue failed joints. The lab analysis we've got states this, but does not abounds in details.
One of the conclusions is "the crack propagates around harder Sn shearing the softer Pb, but the Sn and Pb zones seem fairly large for regular solder structure". Citing from Klein Wassink "During cyclic plastic deformation the microstructure inside the material changes in the zones where the deformation is concentrated. This leads to local grain growth..."
I have deposited the micro-sections on the IPCs website http://ipc-technet.groupsite.com/gallery/13116
I would need your expert opinion regarding the failure. Is this fatigue? The big pure Sn and pure Pb areas, are they normal size for fatigued joints?
Thanks,
Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] <mailto:[log in to unmask]>
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