Gregory,
It is all in the design and material selection, stack ups, etc.  Properly designed unit would have no problem if you tested at extreme and extended life.  However, those parts are mostly COS, it is not designed for 15 to 20 years service life.  You need to concern the unit to be replaceable at some point at either unit level or sub assembly level.  If it is not design to be swapped, that is a concern.  Its all in the design :-).    My 2 cents. (I wouldn't put my life on someone only know about paper design, I would ask at least for triple redundancy if you have any doubt.  Risk anything fall off the sky would cause nightmare). 
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----- Original Message -----
From: Gregory Munie [mailto:[log in to unmask]]
Sent: Saturday, February 23, 2013 02:39 PM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] 48-pin QFN via-in-pad solder slug problem.

I have been following this QFN discussion as about a year ago I worked a reliability problem for a QFN user.

One thing I noted is that the standoff is (of course) low. For anybody who is using QFNs: Have you done a Werner Engelmaier style mechanical reliability analysis on the parts?

Just asking. I saw them being used for avionics and was a little concerned about whether any planes I was to be flying on used QFNs. 

Greg Munie PhD
IPC Technical Conference Director
630-209-1683
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http://www.ipcapexexpo.org/
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Schaefer
Sent: Saturday, February 23, 2013 11:33 AM
To: [log in to unmask]
Subject: Re: [TN] 48-pin QFN via-in-pad solder slug problem.

I am currently working on a design with 2 similar QFNs requiring via in slug for thermal and electrical reasons.
IPC-4761 gives a good summary of methods for handling these components; IPC-4761 Type VII (filled and conductively capped) appears to be the only sure bet solution.

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