Hi Lou - here is a simple way of keeping the two terms straight: 

Nonwetting:a nonwetting solderability issue is when the solder does not 
"wet" or make a metallurgical bond with the surface you are trying to 
solder

Dewetting: a dewetting solderability issue is when the solder does initial 
"wet" and makes a metallurgical bond with the surface you are trying to 
solder but then puddles/retracts on that surface similar to an oil on 
water reaction.

If you inspect a nonwetting surface under the appropriate magnification, 
you can see that no metallurgical bond was ever establish in contrast to a 
dewetting surface which will have evidence of a metallurgical bond being 
made. In many cases, the contrast requires a microscope/ good 
magnification to seen. 

The JSTD-002C, Figure 2B, page 40,  has photos of dewetting and 
nonwetting. Hope this helps.

Dave Hillman
Rockwell Collins
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Louis Hart <[log in to unmask]> 
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[TN] dewetting






TechNetters, would someone fluent in soldering and terminology please 
advise or comment? In the IPC T-50H definition of dewetting, there is 
mention of a 'thin coating of solder' on the base metal. Pictures of 
dewetting in A-600 appear to show exposed base metal. A customer is 
complaining about dewetting on some PCBs that have all surfaces covered 
with solder, thin in some regions, thick in others. I can't see clearly 
the contact angle between the thick solder and thinner areas, but it may 
not be much different from 90 degrees. To me, it appears solderability 
should be OK, but I want to understand the dewetting phenomenon better 
before discussing with the customer.

By what physical mechanism does dewetting occur? How does this mechanism 
differ from nonwetting?

Thanks for any guidance...Louis

Louis Hart
Compunetics
Monroeville, PA
USA
[log in to unmask]<mailto:[log in to unmask]>
412-858-1272


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