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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
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Brian Ellis <[log in to unmask]>
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08/13/2011 01:41 AM
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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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