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Managing Whiskers – Both Tin and Facial

5 March 2010 8 Comments

A big topic in the last few years has been the occurrence of (and the damage caused by) the growth of tin whiskers in high-profile and high-reliability products.  Elusive, often misunderstood, and difficult to prevent; tin whiskers have posed significant problems.  In fact, even just two weeks ago TechEye.net was speculating that tin whiskers may be behind the massive Toyota recalls. Whether the whiskers are out to race cars, or are turning into conductive plasma arcs capable of carrying hundreds of amps, it is clear that they are a force to be reckoned with and have a flair for the dramatic.tin whisker

I see a variety of similarities between Tin whiskers… and my own: Elusive, thin, short, and never helpful.  And there is always the random single hair that frustrates you to no end.

Unfortunately, the costs associated with tin whiskers in the electronics, defense, health, and aerospace industries are astronomical compared to my need to shave once every two weeks.  Failure of products due to tin whisker growth can undermine an entire mission, scrap a program, or take a life.  I think about electronic pacemakers, our men and women traveling to space, or our servicemen and women flying at Mach speeds thousands of feet above the ground.

There has yet to be a definitive ruling made concerning the cause/prevention of whiskers, although pure tin components and plating seem to exhibit the highest likelihood of developing them.  Best practices at this time are to use a tin/lead mix with no greater than 97% tin.  However, RoHS regulations are throwing a wrench into this with its demands for lead-free products.  Some RoHS frequently asked questions are answered here.

ArcDamageThis issue received significant attention at the IPC Technology Interchange this last December.  Also, the Center for Advanced Life Cycle Engineering at the University of Maryland (CALCE) and The Institute of Scientific and Industrial Research at Osaka University (ISIR) are putting on another International Symposium on Tin Whiskers this June.  The call for papers is still out.  Read more about this at PCB007. Proceedings from past Symposiums can be found here.

For a great overview of tin whiskers, be sure to check out the resources provided by NASA.  The pictures in this article have all been sourced from NASA.

Have you dealt with tin whiskers in your products/designs? What types of damage have they caused?  What are some of the things you have done to diminish the likelihood of them?

Homepage Image Original found here

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8 comments on “Managing Whiskers – Both Tin and Facial

  1. Healthy recipes on said:

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  2. Bruce on said:

    So conformal coating cannot be well controlled. I suggest to coat a number of boards, measure the resultant coating thickness, then proceed with the experiment. If a board coating is TOO thin, run it through again. The resultant graph would feature thickness on one graph axis, and propensity to grow whiskers on the other. Non-uniform coating thickness would not be an issue.

    A cursory googling on the term “conformal coating thickness gauge” produced lots of hits, including this one: http://www.defelsko.com/applications/conformal.htm.

  3. Amadeo Isart on said:

    The use of Sn-Bi alloy has proven to be rather effective in avoiding tin whiskers. I have seen internal reports from two major defense contractors (sorry no names, NDA’s in place)that will be using Bismuth at 2%.
    You also might be interested in checking the following report among the many you can Google out.

    http://www.welwyn-tt.com/downloads/pbfree/sn-whisker-report.pdf

  4. Otto J Hunt on said:

    So conformal coating cannot be well controlled. I suggest to coat a number of boards, measure the resultant coating thickness, then proceed with the experiment. If a board coating is TOO thin, run it through again. The resultant graph would feature thickness on one graph axis, and propensity to grow whiskers on the other. Non-uniform coating thickness would not be an issue.

    A cursory googling on the term “conformal coating thickness gauge” produced lots of hits, including this one: http://www.defelsko.com/applications/conformal.htm.

  5. Loretta Kish on said:

    Conformal coating is not a prosess that is easy to control! You would have to make multiple passes through the machine for thickness, that is if the contract manufacture has one. Some CM’s use a spray can.

  6. Otto J Hunt on said:

    I understand that conformal coat suppresses whisker formation, but it has to be thick. I would like to see a study that establishes a curve of coating thickness on one axis, and probability of whisker growth on the other.

  7. Loretta Kish on said:

    I certainly hope the committee on Energy and Commerce understand that the RoHos Directive could be the issue causing “Tin Whiskers!

    I always used 63%tin/37%lead for decades. Now take the lead out,which was added to stop Tin Whiskers!

  8. Loretta Kish on said:

    This is where I would start a Six Sigma Project!

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