This is why the reasoning that you have an exemption to RoHS is not the
most logical position since the industries with the critical mass are
the determining factor. 

Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED 
           76 Technology Drive - POB 1890 
              Brattleboro, Vermont 05302
                Voice - 802.257.4571 ext 21
                    Fax - 802.257.0011
                       <http://www.vtcircuits.com/> 
                           

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of - Bogert
Sent: Thursday, July 27, 2006 8:16 PM
To: [log in to unmask]
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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