RoHS, WEE, Pb-Free, Lead-Free, all buzzwords in this era of ultra green sensitivities. Many obstacles have had to be overcome on the path to compliance, not the least of which was an entire new line of processing equipment and processes (reflow, assembly, rework, materials development, etc.) that is necessary to work with the higher temperatures required by lead-free solders. One problem looms as a potential major issue in years to come: Tin whiskers.
Tin whiskers are the crystalline tendrils that "grow" out of the relatively high concentrations of tin in the solder alloy. NASA experimented with tin-based solders back in the 1970s for weight savings over lead-based solders. Everyone was excited, until suddenly for no apparent reason, short circuits were being discovered. Failure analysis determined that what infamously became known as "tin whiskers" were developing and were actually growing between different nodes in electrical circuit boards and connectors, and even inside integrated circuit packages.
What was intended to be a panacea for the aerospace program circuit weight reduction efforts became a nightmare since a lot of equipment was deployed before the phenomenon was discovered.
Now, thirty years later, the electronics industry is re-visiting tin-based solders in order to comply with the RoHS directives. Materials sciences and metallurgy has advanced considerably since the early tin whiskers problems, so hopefully most - preferably all - of the problems have been solved. But, don't be too sure. Not that long ago articles and letters to editors were being written by old-timers who "were there" to remind the new crop of developers about their experiences. More than a few appeared to have been previously unaware of this lurking tin whiskers menace. Yikes.
Fortunately for most of the early adopter manufacturers, we do not expect our consumer devices to last more than two or three years anyway and are never surprised if they just stop working for no apparent reason - we simply go buy a newer model that we really wanted an excuse to buy anyway. In a perverse kind of way, tin whiskers are good for the consumer market.
Avoiding Tin Whisker Reliability Problems |
By G.T. Galyon and Ron Gedney, in Circuits Assembly.
Can Nickel Barriers Eliminate Tin Whiskers?
Article by John Baliga, in Semiconductor International.
Cause of Tin Whiskers Remains Elusive | ap.pennnet.com/Articles/Article_Display.cfm?Section=Articles&Subsection=Display&ARTICLE_ID=216213
By George Galyon, Joe Smetana, and Nick Vo, in Advanced Packaging.
Controlling Tin Whiskers in Pb-free Assemblies
Two process refinements help mitigate whisker growth - in Electronic Products, by Michael Hundt.
Evaluation of Conformal Coatings as a Tin Whisker Mitigation
Strategy | calce.umd.edu/lead-free/tin-whiskers/WoodrowConfCoatPres.pdf
By Thomas A. Woodrow and Eugene A. Ledbury.
GEIA Tin Whisker Industry Standard | empf.org/empfasis/2006/mar06/geia-tin_whiskers.html
From Empfasis, by Fred Verdi.
Get Used To Tin Whiskers | reed-electronics.com/electronicnews/article/CA6332135.html
By Ed Sperling, in Electronic News.
Mitigation Strategies for Tin Whiskers | calce.umd.edu/lead-free/tin-whiskers/TINWHISKERMITIGATION.pdf
Prepared by M. Osterman CALCE-EPSC.
NASA Goddard Space Flight Center Tin Whisker (and Other
Metal Whisker) Homepage | nepp.nasa.gov/whisker
Information about tin whiskers and related research.
Overcoming Tin Whisker Problems on
Lead-free Packaging | ap.pennnet.com/Articles/Article_Display.cfm?Section=Articles&Subsection=Display&ARTICLE_ID=205979
By Melissa Grupen-Shemansky, in Advanced Packaging.
Qualification Procedure for Tin Whisker Formation in
Lead-free Connector Terminal Finishes | molex.com/cmc_upload/0/000/-12/201/WSKRTEST.pdf
Defines the test procedure & criteria for qualifying the plating finish for lead-free (Pb-free) connector terminals with respect to tin whisker formation.
Risks of Conductive Whiskers in High-reliability Electronics
and Associated Hardware from Pure Tin Coatings | calce.umd.edu/lead-free/tin-whiskers/TINWHISKERRISKS.pdf
From the Center for Advanced Life Cycle Engineering.
RoHS and Tin Whiskers: The Industry’s Next 10-Year Problem
By Chris A. Ciufo, VMEbus Systems online.
Tin Whisker Alert | calce.umd.edu/lead-free/tin-whiskers/TINWHISKERALERT.pdf
Position paper on risks to high-reliability electronics and associated hardware from pure tin coatings.
Tin Whisker Basic Info/FAQ | nepp.nasa.gov/whisker/background/index.htm
From NASA Goddard Space Flight Center.
"Tin Whisker" Crisis Threatens Global Electronic Systems
From Engadget, by Marc Perton.
Tin Whisker Debate Roars On | designnews.com/article/CA6298006.html
By Rob Spiegel, in Design News.
Tin Whisker Formation on Lead-Free Coatings
Prepared by Pete Elgren, Molex, Inc.
Tin Whisker Formation – Results, Test Methods and Countermeasures
Abstract by M. Dittes, P. Oberndorff, and L. Petit.
Tin Whisker Info "Brief" | onsemi.com/pub/Collateral/TND311-D.PDF
Application note from ON Semiconductor.
Tin Whisker Risks | calce.umd.edu/lead-free/tin-whiskers/TINWHISKERRISKS.pdf
Risks of conductive whiskers in high-reliability electronics and associated hardware from pure tin coatings.
Tin Whiskers | empf.org/empfasis/sept03/tinwisk1.htm
A publication of the National Electronics Manufacturing Center of Excellence, by Tim Ellis.
Tin Whiskers & Packaging | national.com/analog/packaging/tin_whiskers
From National Semiconductor Corp.
Tin Whisker User Group | inemi.org/cms/projects/ese/tin_whisker_usergroup.html
The iNEMI Tin Whisker User Group has defined tin whisker mitigation practices and acceptance testing to minimize the exposure of tin whiskers in high-reliability applications.
Understanding and Minimizing Tin Whiskers |
By Qian Sun and Guna Selvaduray, Chemical & Materials Engineering Department, San Jose State University.
Whisker Evaluation of Tin-Plated Logic Component Leads
Application Report by Douglas W. Romm, Donald C. Abbott, Stu Grenney, and Muhammad Khan.
Whisker Formation & Growth | atmel.com/green/documents/whisker_report_0306.pdf
Test procedure and investigation results from Atmel.