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August 2011

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Subject:
From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Mon, 15 Aug 2011 14:26:50 -0500
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Hi folks - one additional  possible root cause that is also related to 
cleaning. If the cleaning system/chemistry is too aggressive or if the pwa 
is over cleaned (say, like 10 exposures!), you actually produce a lead 
(Pb) rich solder joint surface with has a "blue/purple' optical effect in 
contrast to a normal solder joint which is tin rich. We used SERA analysis 
a few years ago to demonstrate this effect. Doug and I have also published 
the information in a couple of ppts at conferences - we call such pwas 
"Barney Boards" (Barney, as in the purple dinosaur on children's 
television). The optical effect is completely cosmetic and can be 
eliminated by reflow the solder joints.

I'll see if I can post the pictures.

Dave Hillman
Rockwell Collins
[log in to unmask]



Brian Ellis <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
08/13/2011 01:41 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Brian Ellis <[log in to unmask]>


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Subject
Re: [TN] Blue solder joints






This is most likely due to having a cleaning process that is almost too 
good! Most commonly seen after some kind of aqueous cleaning, followed 
by drying at temperatures above 60-70°C. The cleaning will leave 
unprotected metal (if it were solvent cleaning, it would leave a 
protective monolayer on the metal). The metal will then oxidise during 
the drying. I've seen this hundreds of times.

Brian

On 12/08/2011 21:56, Gumpert, Ben wrote:
> Technetters,
>
> I seem to remember this coming up previously, but I couldn't find it in 
the archives... What causes solder joints to have a blue tint?
>
> I have a card where most of the solder joints across the assembly have a 
blue tint to them. It's Sn63Pb37 solder on a SnPb HASL board and a variety 
of part finishes - but the pads that weren't pasted don't exhibit the blue 
color. This is the only card in the lot that has this condition, but I 
don't know what process it may have seen differently from the others.
>
> Some kind of oxide?
>
> Thanks in advance,
> Ben
>
>
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