Hi Phil,
I have been hoping for a response from someone who has practical
experience with this, as it is interesting to me. That said, I suspect
areas of concern would be for TCE. The larger pad size takes away
solder from the bulk joint, effectively reducing the standoff height.
Again, I suspect the reduced standoff height might reduce the "flexure"
ability of the solder joint to "absorb" the TCE mismatch. And, using
a larger sphere diameter may compensate for the large pad size,
effectively raising the standoff height. Sure would be nice to do a
finite elemental analysis.
Have fun!,
Shean Dalton
Austin American Technology
www.aat-corp.com <http://www.aat-corp.com>
-----Original Message-----
From: Werner Engelmaier
Sent: 7/28/2004 1:46 PM
To: [log in to unmask]
Subject: Re: [TN] BGA pad missmatch
Hi Phil,
Land area is not the issue, solder joint geometry is. If the unequal
soldering areas create solder joint geometries with stress
concentrations, earlier
failures [everyting else can be anticipated]. This is similar to NSMD
vs. SMD
solder pads.
Regards,
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, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
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