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April 2003

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Subject:
From:
Dave Hillman <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 9 Apr 2003 17:55:59 -0500
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Hi Charlie! Ooh, a good metallurgy question! I have also experienced
"blue" solder joints which were traced to two situations: 1) the use of
solder alloys containing high Pb compositions; 2) Sn 63 printed wiring
assemblies which have been "over etched" due to excess cleaning. We have
nicknamed the phenomena "Barney boards" in honor of Barney the purple
dinosaur. We were able to confirm (using SERA and Auger analysis) that the
blue-purpleish color is due to the surface being predominately Pb oxide
instead of being Sn oxide dominated. I'll send Steve G. a nice picture of a
"barney board" so you can compare it to your situation. We determined (for
our use application) that the condition was cosmetic in nature and would
not impact the functionality of the assembly. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]



                      Charlie Pitarys
                      <charlie_pitarys@        To:       [log in to unmask]
                      KYZEN.COM>               cc:
                      Sent by: TechNet         Subject:  [TN] Blued solder joints
                      <[log in to unmask]>


                      04/09/2003 02:56
                      PM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to
                      Charlie Pitarys






What would be the cause of blue tint, hue, specks  etc to be visible on the
surface of solder joints. Is it just alloy composition?


I have seen this in the past typically in high temp reflow /high lead
alloy, copper lead frame devices around the die attach fillet.


Now it is being seen on a 63/37 alloy solder smt reflow.


It was not seen in the past, the cleaning chemistry is buffered to protect
the metal etc. and has been in use for many years without seeing this
phenomena!


Maybe if a crappy traditional high ph saponifier was used and the solder
joint was dull and gray it would not be as noticeable?


Perhaps the copper is leaching to the surface from the tinned component
lead or HASL surface?
My suspicion is that trace amounts of copper is present on the surface of
the solder joint after reflow. That when exposed to reflow temperatures it
picks up this bluish color.


Charlie


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