I agree Werner. But should the user (assembler) be the one to figure this? Or
should the manufacturer determine if this is necessary and what the
difference should be? 

-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]] 
Sent: Monday, 20 June 2005 10:46 PM
To: [log in to unmask]
Subject: [TN] Moisture sensitivity levels...

Hi Steve,
Even that is not the whole story. In J-STD-020 & 033, MSL levels are
established. however, no differentiation is made as to the difference in the
soldering
temperatures for SnPb-soldering and LF-soldering. The MSLs mean different
things depending on the soldering temperature, since at higher temperatures
the
same moisture level will result in higher vapor pressures and thus more
destructive forces. Thus, some sort of de-rating system, i.e.,
MSLx(SnPb)=MSL[x+2](LF); thus, e.g., MSL3(SnPb)=MSL5(LF), needs to be
developed.

Werner

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