A good description of dewetting would be non uniform coverage of thick and
thin solder layers, with high contact angles to the thick bits - just as you
described.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, February 19, 2009 5:29 PM
To: [log in to unmask]
Subject: Re: [TN] dewetting
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
[log in to unmask]
Louis Hart <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
02/19/2009 10:23 AM
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TechNet E-Mail Forum <[log in to unmask]>; Please respond to
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Subject
[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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