On Pb-Free Reliability and its Doubters

I was at SMTAI (Surface Mount Technology Association International) in late September. As mentioned, I chaired a session on Alternative 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 lead-free thermal cycle reliability as a function of silver content and compared the results to SnPb reliability.

Both papers concluded that as far as thermal cycle reliability is concerned

SnPb < SAC105 < SAC305 < SAC405

Coyle’s paper summed it 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. (See Coyle’s figure. Data curves to the right are more reliable.)

Henshall’s paper also showed that the addition of dopants, to improve shock resistance, in SAC105 does not reduce thermal cycle life.

So, it appears, at this time, that, from a thermal cycle and drop shock perspective, it is looking more and more like SAC-based solders out perform SnPb solders in these two reliability arenas.

At the end of the session a noted lead-free curmudgeon came over to introduce himself.  We have had a jovial disagreement on several blogs, etc., in the past re: lead-free status and issues, but had not met in person. I should mention that this person is a college graduate, a former technical leader at several influential technological companies, and he owns a PE license. I asked him what he now thought about lead-free reliability after hearing the talks. He claimed that he is a little less likely to think that Pbfree reliability is a disaster. He still refuses to purchase lead-free products. He buys old units (pre-2006) on eBay.

I mentioned that over $2 trillion of electronics has been placed in the field since 2006 with no unusual reliability issues. I then went on to say that a RoHS-compliant product is much more likely to fail due to a non-RoHS related issue. He did not disagree. So then I asked him why he won’t use RoHS compliant electronics. His answer: “I just don’t trust them.”


Dr. Ron

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About Dr. Ron

Materials expert Dr. Ron Lasky is a professor of engineering and senior lecturer at Dartmouth, and senior technologist at Indium Corp. He has a Ph.D. in materials science from Cornell University, and is a prolific author and lecturer, having published more than 40 papers. He received the SMTA Founders Award in 2003.

5 thoughts on “On Pb-Free Reliability and its Doubters

  1. Your Feedburner account has been hi-jacked, I suspect. When I click on Link from my Google Reader account to read about reliability in this article, I instead get a fake ‘scanning for malicious content’ screen. Since the regular blog is okay, I can only guess that the problem is with Feedburner. The redirect goes to a URL based on aoreguard.in . Hope this info is helpful to fixing the problem.

  2. Ron,

    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.

    In the Thursday session at 2010 SMTAI, where the results of the current NASA/DoD 13 company consortium started being reported, Raytheon reported in the combined harsh thermal vibration – “in general, tin/lead finished components soldered with tin/lead solder were most reliable. In general, tin/silver/copper was less reliable than tin/lead soldered controls.”

    Also, in Rockwell’s preliminary report on straight harsh envronment testing of the same boards, “In general, preliminary results show the the Sn/Pb solder out performed the two lead-free solder alloys”.

    Finally, in Boeing’s report on straight vibration (harsh cycle) – “The results of this study suggest for many component types, the lead-free solders tested are not as reliable as eutectic solder with respect to vibration”.

    Recognize that the use of lead-free solder requires ENGINEERING, and an understanding of the stresses of the use environment.

    For what it’s worth, I DO buy lead-free consumer items, as there lead-free has a proven record of performance. But, I will do my utmost to prevent Department of Defense from buying fighter planes or helicopters with lead-free electronics.

    Dennis Fritz
    SAIC, Inc

  3. I have serious issues with the article on a number of points.
    Only one test program, the iNEMI program, supports a ranking of:
    SnPb < SAC105 < SAC305 < SAC405
    ALL other test programs show:
    SAC105 < SAC205 < SAC305 < SnPb ? SAC405
    There is a consistent bias/systematic error in the iNEMI data against SnPb solder joint reliability that has never been explained.
    HOWEVER, solder joint reliability is only a small part of the total picture. This needs to include tin whiskers, of course. It further needs to include what the much higher soldering temperatures required for Pb-free solders do the PCBs and components.

  4. Pingback: Some Consensus on SAC at Circuits Assembly blog

  5. Hello,

    What are the Constants for a Coffin-Manson equation for SAC 305?

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