Pb-Free Sky is Not Falling


Although a few have suggested that lead-free reliability is an oxymoron, currently most people that have studied the reliability of SAC3XX and SAC105 Pb-free solders would conclude something akin to what Denny Fritz wrote in response to one of my posts:

No one I know will dispute your ranking of SAC better than SnPb solder using the commercial temperature cycle [Dr. Greg] Henshall uses – 0C to 100C. But, harsh environment electronics have to perform to either -40C or -55C, and most use a top end cycling temperature of 125C. IT IS IN THAT WIDE THERMAL CYCLE TESTING THAT SnPb outperforms SAC solders.

It is interesting to consider however, that almost all discussions on lead-free solder reliability are based on lab-based thermal cycling and drop shock testing. What about field results? It occurred to me that I knew someone who might have an answer.

Vahid Goudarzi is a Director of NPI Advanced Manufacturing Technology at Motorola and owns a Six Sigma Black Belt. He was the technical leader in Motorola’s efforts for lead-free and RoHS compliant assembly in its mobile phone products. There are few people I know that are more knowledgeable in electronics assembly than Vahid. Motorola was a very early adopter of lead-free, seeking the advantage of tighter lead spacings that lead-free allows. So, Vahid has been working on lead-free processes since the late 1990s. Motorola has been shipping lead-free mobile phones since 2001. With over 100 million mobile phones in the field since then, Motorola has quite a bit of lead-free field data. I asked Vahid if he could comment on these data. Here is his response:

In general, the reliability of lead-free solder is equal or better than leaded solder except for BGA/CSP/WLCSPs. The high silver content in SAC387 resulted in poor drop performance of these packages as the joints are very brittle. This issue can be addressed by reducing the Ag content of the solder balls.

Being an early adopter, Motorola qualified the near-eutectic SAC387 solder. So, with SAC387 and SAC105 solder balls, Motorola’s field data (for about ten years and over 100 million mobile phones) shows equal or better reliability than leaded solder. While these data do not necessarily support other applications, they are encouraging.

Another encouraging thought is that, since its debut (with RoHS now about to celebrate its fifth anniversary),  about $4 trillion worth of lead-free electronics have been manufactured with no shocking reliability problems.

Although admittedly anecdotal, the IT folks at Dartmouth’s Thayer School of Engineering have purchased over a million dollars in lead-free electronics since RoHS. They have noticed no difference in reliability. This is enough gear, and time, to have the beginnings of statistical confidence. Compare this to the advent of Microsoft’s Vista, it was viewed by these folks as a step backward and they immediately took action to prevent Dartmouth from adopting it. Yet, lead-free adoption went by unnoticed. The biggest reliability problem with PCs is still hard drive failure.

So concerning lead-free field reliability: The sky is not falling!

Best Wishes,

Dr. Ron

Some Consensus on SAC

Back in November, I posted comments on lead-free availability. In this post, I mentioned that I chaired a session at SMTAI on Alternate Alloys. At this session, Greg Henshall presented a paper on the  Low Silver BGA Sphere Metallurgy Project. This paper was a collaborative effort of six companies.  In addition, Richard Coyle presented an overview of the work of three companies titled “The Effect of Silver Content on the Solder Joint Reliability of a Pb-free PBGA Package.” Both projects evaluated Pb-free thermal cycle reliability as a function of silver content and compared the results to SnPb reliability.

Both papers concluded that, as far as 0oC to 100 oC thermal cycle reliability is concerned, in their experiments

SnPb < SAC105 < SAC305 < SAC405

Coyle’s presentation summed it up best: “Each of the SAC alloys outperformed the SnPb eutectic alloy in every test, including the long, 60 min. dwell time test. This tends to diminish the argument that SAC is less reliable than SnPb.”

To be clear, it was two papers by two different groups coming to the same conclusion. It would probably be a stretch to say that the conclusions of either group were “almost unique”.

Denny Fritz responded to this blog post with this point: “No one I know will dispute your ranking of SAC better than SnPb solder using the commercial temperature cycle Henshall uses – 0C to 100C. But, harsh environment electronics have to perform to either -40C or -55C, and most use a top end cycling temperature of 125C. IT IS IN THAT WIDE THERMAL CYCLE TESTING THAT SnPb outperforms SAC solders.”

Denny’s point is well- taken. I believe it can be said that SAC alloys have demonstrated acceptable reliability in commercial, non harsh environments (i.e., mobile phones, PCs, consumer electronics, etc.). However, it cannot be said that acceptable reliability for SAC has been established for military (RoHS exempt) and harsh (i.e., automobile engine compartment) environments.

A short time ago, Werner Engelmaier wrote an article on this topic (Global SMT, vol. 11, no. 1, January 2011, pp. 38-40), referring to my post he said: “Of course, ‘Dr. Ron’ selectively picks data agreeing with the point of view he held from the inception of the Pb-ban under RoHS on a plot with an expanded x-axis overemphasizing the differences and supporting a solder joint reliability ranking of SnPb < SAC105 < SAC305 < SAC405.”

Ouch! My motives were not quite so nefarious, I chaired a session and wanted to share the conclusions.

However, Werner makes good points in his article, data exist disagreeing with this reliability ranking and he suggests some good points on how to conduct reliability tests so that comparisons can be made between data sets.

In reading some of his other articles, I was delighted to find that we actually agree on the state of lead-free reliability in thermal cycle testing. Here is a statement of his circa 2008 (Global SMT, vol 8., no. 8, August 2008, pp. 46-48.): “It has been 2 years since the infamous ban of Pb-solders under RoHS. What have we learned? For solder joints, no dramatic differences in reliability are apparent. The data bases for LF-solders have grown, the favored LF-solders might be shifting, and no reliability model exists as of yet. Nevertheless, progress has been made.”

Best Wishes,

Dr. Ron