It is possible to solder SAC balls using Pb:Sn solder.  BUT...
It is important that the profile be adjusted so the SAC balls fully melt
and there is enough time for the two types of solder to mix well,
preventing the stratification of solders often noted when this is tried.
I know of no way to check for this full mixing except through cross
sectioning polishing and either looking for PB islands in all parts of
the solder ball, and verifying by EDX that Pb is found throughout the
solder ball.  You need to be able to view the Pb islands in order to
exclude the possibility of Pb smearing over the surface when polishing.

mark

Mark Woolley

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Croslin, Robert
Sent: Tuesday, October 21, 2008 10:10 AM
To: [log in to unmask]
Subject: Re: [TN] Lead Free BGA'S

We had one of our long time CM's do exactly this on a project last year
with disastrous results.  They did it without our knowledge trying to
meet an impossible schedule.  Some of the devices passed test and began
failing immediately while others never passed.  They had to rebuild the
entire lot on their nickel.  The only positive thing was when one of our
other proposed doing the same thing recently and we were able to say
H**L NO!  Like Deac replied "It's either lead free or it AIN'T!!!!!!!!!"



Bob Croslin
The Nielsen Company

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Foster
Sent: Tuesday, October 21, 2008 11:21 AM
To: [log in to unmask]
Subject: [TN] Lead Free BGA'S

Our assembly house recently assembled some boards with Lead Free BGA's
for us and when I asked them if they used a lead free process they
responded with.

We use leaded solder (Sn63Pb37) with a hybrid oven profile to
accommodate the lead-free BGA. I hope this answers your question. Please
let me know if you have any more questions."
Is this a common process, is this a reliable process

Any input is appreciated

Thank You
John Foster


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