Hi Vlad! Sorry, I didn't mean to imply that there is free silver on the
surface. The microstructure of a Sn96Ag4 solder joint can be Sn phase with
in a Sn-Ag3Sn eutectic matrix or it can be Sn phase with lots of Ag3Sn
intermetallic needles. I don't know what the influence the Sn with have on
the Ag3Sn eutectic in terms of oxidation but I was guessing that
potentially a Ag sulfide might come into play (Ag sulfide has a purplish
appearance). Another guess would be that Paul has a Sn oxide species that
the Ag is influencing such that it has a darker visual appearance than
typical. Either idea may be way off base too but looking at what Paul had I
thought I would venture a couple of guesses. Any reason you are leaning
toward XPS analysis instead of Auger analysis?
(That's probably way more metallurgy discussion than some of the Technet
crew was looking for but the SnAg system is much more "interesting" than
the SnPb system).
Dave Hillman
Rockwell Collins
"Vladimir
Igoshev" To: "TechNet E-Mail Forum." <[log in to unmask]>, <[log in to unmask]>
<[log in to unmask] cc:
> Subject: RE: [TN] Blue leads
12/16/2003 11:00
AM
Dave,
Why do you think it may be some silver based "film"? It shouldn't be any
"free" silver in the solder alloy (there is almost nothing in the solid
solution), but only the intermetallics. I think XPS can be run to figure
out what is on the surface.
Regards,
Vladimir Igoshev,
Research in Motion
-----Original Message-----
From: Dave Hillman [mailto:[log in to unmask]]
Sent: Monday, December 15, 2003 5:37 PM
To: [log in to unmask]
Subject: Re: [TN] Blue leads
Hi folks! Well, as Steve mentioned, the typical "blue" tint seen on a
solder joint is the result of Pb oxide dominating the solder joint surface
instead of the usual Sn oxide. Overcleaning is a classic way of producing
"Barney pwbs" but since Paul is using an Sn96Ag4 solder alloy we can't be
dealing with Pb oxide. I don't know of any Sn oxide species that are "blue"
in appearance. My guess is that the blue appearance is due to some Ag
surface species - silver sulfide can have a "blueish" appearance. If you
had a flat enough surface you can use the SERA equipment to identify some
silver surface species (silver oxide, silver chloride, silver sulfide).
I'll see if any of my references can provide any help. A majority of the
time these types of observations have only cosmetic impact and not a
product integrity impact (someday the bright and shiny myth will be
extinct!).
Dave Hillman
Rockwell Collins
[log in to unmask]
Steve Gregory
<[log in to unmask] To: [log in to unmask]
M> cc:
Sent by: TechNet Subject: Re: [TN] Blue
leads
<[log in to unmask]>
12/15/2003 03:23
PM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to
SteveZeva
Hi Paul!
I had an experience with what we called "Blue Solder" once, but it was
traced
back to our cleaning process...you can see a picture of it on my web page
at:
http:www.stevezeva.homestead.com and look at "Blue Solder". What we
discovered was that the airknife cycle in between the wash and rinse cycle
was drying
out the chemistry on the solder joints before we could get it rinsed of.
Once
we shortened the airkife cycle, the appearance went away. This was dealing
with
63/37 solder too, not SN96 solder...
Dave Hillman has some pictures on my page next to the "Blue Solder" one, he
called "Barney Boards" because of the purple appearance of the solder. I
can't
quite remember what the situation was with that...maybe he will see this
and
refresh our memories.
-Steve Gregory-
> We just ran a long time heat run at 175C on a board made with Sn96/4Ag.
> The leads turned blue.
>
> I don't have my CRC handy. What caused the blue? Is it silver halide? IS
> there another tin oxide I am not aware of which turns blue? Or even
> copper?
>
>
>
>
> Paul Stolar
> Materials/Reliability Engineer
> Manufacturing Reliability Lead Engineer
> Baker Atlas
> 713-625-5376
>
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