Here is some info from Hillman regarding Barney Boards like yours, Steve. More info is in the archives simply by searching "purple solder joints". It can be caused not just by overcleaning, but by cleaning with a somewhat alkaline surfactant as well.
From: "Gumpert, Ben" <[log in to unmask]>
Subject: Re: Blue solder joints
X-To: TechNet E-Mail Forum <[log in to unmask]>
To: [log in to unmask]
Subject: EXTERNAL: Re: [TN] Blue solder joints
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.
Subject
Re: [TN] Blue solder joints
> 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
--------------------------------------------------------------------------------
Item #115414 (15 Aug 2011 14:26) - Re: Blue solder joints
From: "David D. Hillman" <[log in to unmask]>
Subject: Re: Blue solder joints
X-To: TechNet E-Mail Forum <[log in to unmask]>,
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.
Subject
Re: [TN] Blue solder joints
> 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
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: Thursday, November 17, 2011 2:49 PM
To: [log in to unmask]
Subject: Re: [TN] Strange Gold?
Hi Steve,
Strange footprint as well. It appears all the leads on the left are
ground and three of the four on the right are connected to the plane
with the vias.
Anyways, isn't the picture showing that the gold turned purple due to
the heating/spread of the flux? I almost have to ask if there wasn't
something wrong with the solderpaste.
Like the others have said, how many places on the board did this happen?
Was the part removed in order to take this photo?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Thursday, November 17, 2011 10:59 AM
To: [log in to unmask]
Subject: [TN] Strange Gold?
Hi All,
Below is a photo of a SON8 footprint that was printed with SAC305 on a
gold
plated PCB and reflowed. I have never seen this before. Is this "purple
plague"? If it is, exactly what causes it?
http://stevezeva.homestead.com/Strange_Gold.jpg
Steve
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