I am debating on what is minimum acceptable solder joint thickness for QFN-32 
packages ? Just for clarity , QFN-32 is bottom termination part with no toe 
joint due to exposed copper on toe. 

We did cross sectioning and found that solder thickness varies form 15 microns 
to 45 microns - different footprints. We are wondering what should be minimum 
acceptable thickness before we need to rework ?  Any graph or relationship to 
determine reliability of joint with respect to thickness of joint ? 

We are building Class3 products for automotive industry. No information found 
on thickness of solder joint Except for IPC-7093 (unreleased draft copy) where 
the solder thickness is mentioned as 50 microns. 

Anybody to share what should be used as minimum thickness before 
reworking ?

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