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July 2006

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From:
- Bogert <[log in to unmask]>
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TechNet E-Mail Forum <[log in to unmask]>, - Bogert <[log in to unmask]>
Date:
Thu, 27 Jul 2006 20:15:57 -0400
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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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