Charlie

I have seen this quite often and it is actually a sign of good cleaning!
I believe that what happens is that tin is sufficiently amphoteric that,
if the solder joints are really clean, a mildly basic solution will etch
out a very thin amount of tin-rich alloy, leaving a lead-rich alloy at
the surface. As the latter is very clean, it will oxidise readily.
especially during drying. As others have said, it is purely cosmetic and
should actually be welcomed. If you don't get it, the cleaning quality
is possibly less good!

Brian

Charlie Pitarys wrote:
> 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
>
> ---------------------------------------------------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
> To unsubscribe, send a message to [log in to unmask] with following text
> in the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to
> [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to
> [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/html/forum.htm for
> additional information, or contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> -----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------