Folks,
Many people responded to my recent post on tin whiskers. A few pointed out that the recent NASA report on the Toyota Unintended Acceleration Issue discussed numerous tin whiskers that were found, one implicated in a failure. The tin whiskers were emanating from tin plating.
We don’t know, however, if tin whisker mitigation techniques were used. In a mission-critical application, such as this, it would appear unwise to use RoHS-compliant electronics, especially since they are not required for automobiles. In other words, autos are exempt from RoHS. Let me be very clear: from a tin whisker perspective, I am uncomfortable with RoHS-compliant tin plating in mission-critical applications. Much more work needs to be done before such tin plating should be used in mission critical applications. In applications where RoHS-compliant electronics cannot be avoided, all tin whisker mitigation techniques should be employed, including conformal coatings.
In addition, in response to my post, a number of people pointed out the difficulty of proving a tin whisker fail and the reluctance of any manufacturer to admit that their products had them.
But my quest remains unfulfilled; the question remains:
“[W]ho knows of any verified tin whisker fails when tin whisker mitigation techniques where used? Tin whisker mitigation techniques typically use 2% bismuth or antimony in the tin, assure that the tin has a matte finish and use a nickel strike plating between the copper and the tin to minimize copper diffusion into the tin.”
Restated, here is my point. Since RoHS, quite a few people take a position something like this: With RoHS-compliant assembly, even the world of non-mission critical electronics is at considerable risk of numerous catastrophic failures, due to tin whiskers, that will cost hundreds of billions of dollars.
I still maintain, that with mitigation techniques, such as recommended by iNEMI, tin whisker control, for non-critical electronics, can be manageable. Non mission critical electronics is about 80% of the $1.5 trillion of the electronics industry.
As I pack up to leave my office today at Thayer Engineering School at Dartmouth, I am across the aisle from the chaps that provide our computers and IT support. They buy millions of dollars of electronics a year. In chatting with them they state two things:
1. They have noted no difference in electronics reliability since RoHS implementation, nearly five years ago.
2. On the very rare occasion that they get an electronics failure, it is almost always a hard drive.
Bottom line: Except for hard drives, modern electronics are very reliable for their use life.
I expect my quest will uncover some tin whisker fails, even with mitigation, but the fails will most likely be isolated and not a significant threat to the industry at large.
Cheers,
Dr. Ron
P.S. The image is from Dr. Henning Leidecker of NASA, one of the world’s leading tin whisker experts.
Ron,
all good points…
And I doubt your “quest” will likely be fulfilled…
for numerous reasons (some below).
A few additional thoughts….
a) Not everyone has excepted the tin whisker mitigation techniques mentioned as 100% effective.
I am reasonably confident they improve reliability.. but this isn’t the same as truly understanding the problem and addressing it..
We really don’t know WHY lead or bismuth stops tin whiskers… we just know it does.
We only have conjectures as to why.
poor science…
b) Soon, all industries – regardless of their ROHS requirement/status- will HAVE to use ROHS before all the technical questions are answered. reason: Market forces will require it.
the electronics component /packaging industries will not support two standards.
(why aren’t PCs considered mission critical? they are critical to my life)
result: Mission critical products will have tin whiskers (as demonstrated).
ROHS … may “get there” and with mitigation techniques may even “be there”… but a large portion of the industry isn’t convinced yet ( As you stated …”uncomfortable for mission critical products”)
It is apparent market reporting of failures ….doesn’t tell the entire story of reliability.
Did Toyota realize they had ANY tin whiskers in their electronics before the NASA report?
And NASA only had a small sample to work with…
Millions of failed electronics products that are no longer under their 1 year warranty are not going to be returned .. they are just going to the trash dump.
And Root cause failure analyst of most returned products .. isn’t very detailed.
Most returns are handled by low level techs with automated test equipment.. or less.
They simply aren’t equipped to determine the cause of an intermittent short.
As to the Thayer school’s experience….
Most PCs have a very easy life…. poor test subject for tin whisker.
Generally only operated at temperatures we people like to operate at… generally only a few components actually run warm/hot (processor, graphics processor)… bottom line.. no large temp cycles, no environmental extremes.
And they are replaced every 2-3 years (they “buy millions of dollars worth every year”)
so yes.. they are reliable “FOR THEIR LIFE” ( as short as it is)
Yes, Hard drives on PCs do fail more often.. and I doubt they research the root cause of failure on the hard drives.. could it be a tin whisker? Why assume the failure of a harddrive is ALWAYS mechanical in nature?
I have less than 50 PCs in my company.. (some embedded in production equipment) …
and I HAVE seen a reduction in reliability of the newer units.
To be honest… this isn’t a large enough quantity to be statistically significant for this discussion.
But since it comes out of my pocket.. it seems significant to me! (laugh)
BTW… Bismuth is production “by product” of lead mining.. and is estimated to be as 1/2 as rare as gold (or as Wikipedia put it.. “bismuth is about twice as abundant as gold”.
Tin whiskers with increasing RoHS compliance will continue to pose a threat in mission and life critical applications with documented failure issues in medical device, nuclear, aerospace, and now automotive to name a few; not failure events that really have made mainstream media….yet.
http://www.militaryaerospace.com/index/display/article-display.articles.military-aerospace-electronics.embedded-computing.2011.1.aem-debuts_tin_whisker.QP129867.dcmp=rss.page=1.html