I'm also in the MIL game, and I recognize all what you say. Our company have
cooperated with Universal for a period on this matter, and we have found
that the situation is not that pessimistic. Lots of testings have shown few
reliability incidents, and we have recommended soldering process windows to
follow now, even if the 100% truth won't be found until after 10-20 years
from today.

If you know the ingredients for the sponge cake, it's easy to make one or
one million. However, if the ingredients vary, you will get all sorts of
cakes. That is our dilemma today. You can't be sure what you get, even if
you buy according to MIL std, Gidep, QPL or whatever. The thicker the
purchase documentation, the bigger the uncertainty about what you will get,
because MIL is not handled by MIL specialists any more, but by COTS
suppliers and others. So, we have to check all incoming lots for solder
status: wheather we got SnPb or Leadfree and what  kind of Leadfree. Not so
hard a job, but adding costs, which is not popular these days.

We apply this daily, and we have had very few problems, although we have to
deal with mixed production, SnPb and Leadfree. As MIL suppliers, we can go
on with Pb as  long as we need, but on the other hand, we can't be standing
still while others are moving, even MIL folks need to accept changes.

And don't forget this: even old, handsome SnPb can cause problems that make
you mad !

Inge

PS. I opened  my Creative Touchpad to see what's under the kilt. I must say,
we MIL people have a lot to learn. If we had to produce such products, the
price would be a magnitude higher, and the quality...stop now...keep your
mouth...joking. In fact, I've dropped my touchpad from standing upright, and
it works still. MIL quality with cheapast possible components! Extreme
miniturization and new models every year, and still high functionality. Just
wonder if they are LF or not?


----- Original Message -----
From: "- Bogert" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, July 28, 2006 2:15 AM
Subject: [TN] BGAs; SnPb vice SAC Balls


July 27, 2006

Folks, I have a dilemma regarding the transition to Pb free.

As a military user, we have no intention of transitioning to Pb free
assembly soldering at this time, and probably never, unless industry can
positively provide documented evidence, based on accelerated life testing
acceleration factors, that establish that the use of Pb-free solders, such
as SAC, will provide a product that will meet the same reliability life
requirements that Pb based solders have been proven to meet, and that this
level of reliability can be easily and consistently achieved on the
production floor without hiring a "Rocket Scientist" or a team of 20 people
to establish the soldering process using Pb-free.

Given this, I am frustrated by some BGA manufacturers apparent "Don't give a
dam attitude" about the military users of BGA'S since some folks are
eliminating Pb from solder balls in favor of alloys such as SAC.  Appears
they are more interested in their bottom line industrial and commercial
customers than us military folks.  This is understandable since us military
folks constitute a very small % of their overall business.

Although some manufacturers will still provide Pb BGA balls, some will only
provide SAC balls.  Also if Pb balls are requested, there may be long lead
times involved.

There have been published test studies done that show that if one solders
BGA's having SAC balls in an assembly soldering process using traditional
Sn63 solder, an unreliable solder joint may exist.

Based on the above, our current intent is to prohibit the use of any BGA
that does not use SnPb balls.

My question is, which is the least reliable alternative.  That is, allowing
BGA'S with SAC balls soldered using Sn63 solder, or having someone take the
BGAs and have the SAC balls replaced with SnPb balls?

What suppliers have the capability of doing this ball replacement?

My preference is to stick with the prohibition on non-Pb BGA balls.  The
down side of this is that by doing this, we may not be able to take
advantage of new technology parts that may only use SAC balls.

This Pb free issue is driving up costs.  Since about 50% of the part
manufacturers are eliminating Pb from their part finishes without changing
their part numbers, we are forced to implement XRF testing of parts received
by our OEMs to verify they contain the 3% Pb mandated by most military
specifications.

Just because it is a mil spec part does not mean one will not get Pb free
part terminations.  There have been several recent GIDEP Alerts that
indicate that some mil parts contained pure tin finish, in violation of the
mil spec.

While my experience to date is that part manufacturers who have transitioned
to a Pb free finish such as pure tin have implemented tin-whisker mitigation
methods, there is no guarantee that all folks have done this.  Additionally,
even though JP002 tin whisker mitigation methods can reduce the risk for
growing tin whiskers, if one uses pure
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tin, there is no positive guarantee that a tin whisker will never grow.

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