Hi Gebhard,
Mr. Zuverlässigkeit is here; Lee gave an excellent answer, so I did not see 
the need for my 5-cents.
At this moment, you have stomped my with IPC White Paper called "Design for 
Success"—when and where was it published?
And I do not see the need to specify a maximum barrel wall thickness, 38 [µm] 
or otherwise. Typically copper thicknesses are too low. In order to get 
knee/corner/shoulder cracks you need a large amount of land rotation; if you have 
large plating thickness in the PTH you also have a great Cu thickness at the 
surface pad—this would resist land rotation. Now, if you prevent plating on the 
surface, then...yes
Just like Lee, I have seen PCB reliability to suffer with the higher LF 
soldering temperatrures and the demand on PCB quality [drilling, Cu plating 
uniformity, copper plating ductility, adequate copper thickness (1 mil or better yet 
1.2 mil)] go up. 
That is why I have written my White Paper "Recommendations for PCB FAB Notes 
and Specifications in Printed Circuit Board Drawings for SnPb and Lead-Free 
Soldering Assemblies, the Qualification of PCB Shops and Activities to Assure 
Continued Quality." 


Werner



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