TIN WHISKERS – Electronic’s Dirty Little Secret
 
  Certainly in today’s news there is no shortage of crisis warnings:  from environmental to political:  from natural to man-made disasters.   It is, therefore, with no great glee that I write this article.  Rather, I hope it is a caveat not to put all our electronic chickens in the same basket.  The stark truth is that most equipment containing microchips are extremely vulnerable to a normal function of science:  crystallization  (also referred to as 'tin whiskers.')
 
      Computers contain thousands of micro-circuits and chips that perform so many critical tasks in everyday life, that we’ve surely taken them for granted.  Take for instance, your daily routine:  the alarm clock keeps you from being fired; your microwave fires up your morning biscuit; your car (with its myriad diodes and relays) gets you to work; you get a call on your cell phone; your entire work day is spent on electronic equipment; and you relax at the end of it all by veging in front of digital cable.  Ho-hum.   Now comes the kicker:  there are little conductive crystalline structures that naturally form on tin.  Tin is used on most all circuitry to bridge circuits and allow a constant flow of conductivity.  These 'whiskers' are stiff and can be fairly long.  They grow in a straight line, allowing an unintentional bridge to be formed between circuits.  The result is often a short circuit.
 
    We’ve all seen the byproducts of a short circuit:  that awful fizz & smell when the car dies; a TV blowup in a cloud of smoke.  Tin whiskers (or dendrites if you prefer) have the potential to grow across the tin lines on the chips and bridge two unlike electric currents.  The result is a short circuit.  And it fries the chip.  Goodbye piece of equipment in most cases, or at the very least: goodbye to that section of affected circuitry and/or software.    Sometimes other unaffected microchips will allow the device to partly function, giving the false illusion that the equipment is working properly.  Other times, both the cause and effect are undetermined, making the device perform erratically for no apparent reason.
 
       Tin whiskers can grow to be 10 mm in length (roughly 1/10th the length of a cigarette. )  Considering how densely packed most circuits are, this distance is more than sufficient to ‘lay across the tracks’ so to speak, and cause either a permanent or transient short circuit or a metal vapor arc.   Imagine the effect of igniting a lighter and you have the same effect of what happen when metal vapor arcs ignite.    Instead of a ‘fire’, however, hundreds of amperes can be released in a highly conductive ionic plasma.  This is NOT good for your equipment.
 
     At the very least, the contamination from the constant growth of tin whiskers allow debris and scarring of the boards and chips.   If optical elements are inside the device, they could be affected.  Isolated conductors may also be connected accidentally by the floating detached whisker fragments.
 
     This problem has been known as early as the 1940’s.  The tin whisker effect is also present in several other similar ‘weak’ metals.   One element that seems immune from this is lead.  Industry efforts to purify the dangers associated with lead has resulted in the self-enforced banning of lead in circuitry anymore.  Furthermore, the initial efforts to contain tin whiskers utilized a process called ‘pure tin plating’ which only exacerbated the situation.   The very plating process of trying to protect the circuitry has created an additional problem yet to surmount.  The element Zinc is also extremely prone to whiskers and is also found in electronic components.
 
        Interesting enough, the world’s biggest supplier of tin is China, who also is a leader in microchip production.   The plating process was an attempt to protect the circuitry, but instead has turned into its own worst enemy.  Most computer equipment, cell phones, and digital equipment are plated in some way to keep oxidation (rust) or some form of contamination from forming.
 
        The effects of tin whiskers has already been heavily felt in the communications industry.  At least three complete satellite failures and five more partial failures have been directly attributed to whisker failure.  It’s possible that the latest space station electronic problems may be at least partially Mr. Whisker’s fault.   In 1998 tin whiskers brought the Galaxy 5 satellite’s communications to a screeching halt.  The $250 million unit was responsible for 40 million pages and countless ATM machines.  It took most of a week for all these systems just to reroute their immense networks to another satellite. 
 
     Whiskers have also crippled the military in several instances.  There is ample document that radar systems, missile defense systems, and critical relays within nuclear stations have already been short circuited by the growth of tin whiskers.  Pacemaker failure is being explored by the Food and Drug Administration (FDA.).   The largest ramification is in the Aviation industry.  Do we really want plants to fall from the skies because some tin got crystallized?    UNISYS published a document detailing zinc whiskers that could also have affected main-frame computers and server systems. (Source:  Unisys World Monthly--November 2002)
 
       So people are planning for this eventuality, right?  Right?  Wrong.  The European Union has recently passed the Restriction of Hazardous Substances (RoHS) which promotes tin plating in an effort to be ‘green’ in the field of manufacturing.   Talk about pouring fuel on the fire!   A partial combination of lead and tin will help immensely in alleviating the whiskering problem.  But everyone knows that ‘lead’ is dangerous and can’t be used!   Even a 3% lead mix to tin exceeds the recommendations of the EU ordinance.   Once more the blind try to lead the ‘sighted.’  
 
     All is not lost:  there may be other ways around the problem without using lead.  Not all the factors that contribute to the growth of tin whiskers are  known.   Replating the circuits is an tedious and expensive procedure.  Solder dips with lead on the tin pathways seem to slow the effect.   Other polymers can possibly be used to coat the circuits but currently they all have drawbacks that prohibit mass integration.   The problem seems to primarily lie in circuits that were developed 10 years ago when tin-plating was at its peak.   The only solution in many cases, like the satellite occurences, is just to wait for the eventual failure or short circuit to occur.    Some of NASA’s best minds are involved in the solutions as evidenced by the abundance of NASA articles published on the subject.
 
     Once more, in an effort for security, man has put his life in the hands of the natural happenstances of chemistry.  These tiny titans: tin whiskers, have opened a world of questions that are already affecting us every day of our modern technology-driven life.  This is an important topic that I believe you will see in the news much more in the days yet to go.  I believe it is important that we, as consumers, get a heads-up on this as soon as possible.

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Written by Jeff Feezle of Macafeez
(C) 6/15/2007 
 
 Photo courtesy of Andre Pelham- NASA Goddard Space Center.