Hi Wayne! Ah, if it were only that easy! A QFN component essentially is a 
"blind solder joint" so you must rely on your process to produce an 
acceptable solder joint and confirm that process consistency through 
testing. We are faced with a variety of component styles now, such a 
bottom only terminated devices, where there is no visible solder joint 
available for inspection. Using a combination of process validation, Xray 
inspection techniques and product integrity testing, you should be able to 
confirm the solder joint integrity. A very common industry myth is that we 
"inspect" quality into our electronic assemblies - the reality is that the 
inspection step is only a confirmation that your design and assembly 
processes are controlled/consistent. The JSTD-001 and IPC-610 
specifications attempt to provide as much assistance as possible. Good 
Luck.

Dave Hillman
Rockwell Collins
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Wayne Thayer <[log in to unmask]> 
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04/10/2008 09:35 PM
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Subject
[TN] FN Parts--Evidence of Wetting






Relevant IPC specs claim that no toe fillet is required for DFN/QFN parts 
and 
there is no minimum solder joint height.  The only requirement for the 
joint 
other than alignment/pad size is "evidence of wetting".  How do I get this 

evidence without a toe fillet?  I suppose if I have enough joint height I 
can 
see under the part like a BGA, but I've never seen a FN part mounted that 
high.

Would be nice if the spec included some pix/examples of this "evidence".

Any recommendations would be very much appreciated.

Thanks,

Wayne Thayer

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