Hi Mike - I was thinking about degrade flux too but the other solder 
joints looked to be well formed. Still, a review of the flux/solderpaste 
is necessary as part of the root cause assessment.

Dave



From:   "Mike Fenner" <[log in to unmask]>
To:     "'TechNet E-Mail Forum'" <[log in to unmask]>, 
<[log in to unmask]>
Date:   05/07/2013 11:49 AM
Subject:        RE: [TN] Irritating ENIG Non-wetting



Agree but....
Long soaks in profiles are not such a good idea with WS pastes as they 
have
no natural body, they are mostly rheology control additives with a bit of
added oomph** - so can have hot slump issues and be quite mobile. Maybe 
part
of the problem already. 
Also it's the time of the year - spring in northern hemisphere - when some
water sol pastes fall over, especially on low throughput lines. These have
long paste out times. WS paste is vulnerable to humidity, so sitting on 
the
printer, or delays after printing before placement/ reflowing is not
helpful. If you have a marginally good situation you can go into a
marginally bad situation easily enough. 
(With solder pastes, contrary to popular belief, water soluble does not
automatically mean high activity. Just means dissolve in water. Activity
need not be any different to a resin based material. So for the possible
benefit of a simplified cleaning process, you could have more critical 
paste
handling issues)

**Apologies to formulation chemists everywhere.


Best Wishes
 
 
 
Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, May 07, 2013 5:05 PM
To: [log in to unmask]
Subject: Re: [TN] Irritating ENIG Non-wetting

Hi Steve - giving the fact that you can touch up the pads and form a good 
solder joint, you don't have a solderability issue. However, you do have a 

soldering - ability issue. Look at your two capacitor instances, you have 
a very large pad for one termination and a much smaller pad on the other 
termination with the solder paste deposit balling up on the capacitor 
termination on the large pad side. The capacitor termination is getting to 

183C before the pad and thieving all of the solder to itself. I recommend 
checking your reflow profile - good chance you need to slow down the 
conveyor speed or increase the oven temps slightly such that both the 
terminations and the pads both get to temperature equally (or within 
reason) . Your connector example could be in the same bucket depending on 
how many layers of copper it is hooked into.

Dave Hillman
Rockwell Collins
[log in to unmask]




From:   Steve Gregory <[log in to unmask]>
To:     <[log in to unmask]>
Date:   05/07/2013 10:49 AM
Subject:        [TN] Irritating ENIG Non-wetting
Sent by:        TechNet <[log in to unmask]>



Hi All,

 

We just were running some boards (ENIG finished) where we're seeing this
sporadic non-wetting on some of the pads:

 

http://stevezeva.homestead.com/PKG2.jpg

 

http://stevezeva.homestead.com/PKG3.jpg

 

http://stevezeva.homestead.com/PKG4.jpg

 

Usually it's just a few pads and the rest of the board is fine. We get
the boards in packs of 20, and it's only a couple or so out of the pack
that exhibit the problem. It's just enough to be irritating.

 

When we touch the locations up with a soldering iron they wet fine.
We're using a 63/37 water soluble paste, and the problem doesn't confine
itself to just certain pads or parts, it's random.

 

Like I said it's just enough to be irritating.....   /:o[

 

Steve Gregory

 


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________




______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________






______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________