Tin plating has been, and continues to be, the preferred surface coating for the leads on electronic components. However, tin-based plating can be susceptible to the formation of needle-like protrusions, or whiskers. If whiskers grow to critical lengths in service, they could cause electrical shorts, disruption of moving parts, and/or degraded RF/high-speed performance. For decades, small amounts of lead have been added to the tin to prevent the growth of whiskers, but elimination of lead has stimulated a review of the risks associated with the use of pure tin. This is especially a concern for high-reliability products.
Since 2001, iNEMI has had three very active — and successful — projects addressing various aspects of the tin whisker problem. The Tin Whisker Accelerated Test Project identified tests to predict whisker formation, the Tin Whisker Modeling Project focused on identifying the root causes of whiskers, and the Tin Whisker User Group developed guidelines for minimizing risk of failure from tin whiskers in high-reliability electronic applications. All three projects made significant contributions to industry's understanding of, and tools for managing, tin whiskers.
In addition to the experiments and data that our projects generated, iNEMI has become a clearinghouse for tin whisker information. We have sponsored several industry workshops that brought together some of the world's leading tin whisker researchers to share information and further industry's overall understanding of the problems. Several of these workshops were co-sponsored by IEEE's CPMT Society and the Electronic Components and Technology Conference (ECTC).
The three original tin whisker projects have now been completed and, in 2007, we organized the Tin Whisker Project, Phase II. This latest project combines teams from, and extends the results of, the Modeling and Test projects. This latest effort is continuing to develop tests that will accelerate whisker growth, using theories formulated by the previous projects to explain the formation of tin whiskers. They are also conducting experiments to test those theories.
Tin Whisker Accelerated Test Project
This effort focused on devising industry-standard tests for predicting tin whiskers. Based on the team's results from extensive testing, the iNEMI project submitted recommendations and data to JEDEC, which formed the basis of JEDEC standard JESD22-A121, Test Method for Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes (released in May 2005). This standard specifies the test conditions to be used for accelerating tin whisker growth and defines how whiskers should be inspected.
Tin Whisker Modeling
This project team was created to work on understanding why whiskers form, and how to control them. Several theories had been advanced, both within the iNEMI Modeling Project and in industry forums, and experiments were conducted to evaluate the various tin whisker theories.
Data from this project's work provided significant input for the IPC/JEDEC document JP002, Current Tin Whiskers Theory and Mitigation Practices Guideline, published in March 2006. In addition, the Tin Whisker User Group picked up many of the theories advanced by the Modeling Project and integrated them into a specification that became JEDEC standard JESD201, Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes, also published in March 2006.
The modeling group reached a point where experimental data was needed to confirm or disprove the theories advanced. The team agreed to close the existing project and work with the Test team in the Phase II project to carry out this follow-on work.
Tin Whisker User Group
The iNEMI Tin Whisker User Group, comprised of nine large manufacturers of high-reliability electronic assemblies, was organized to define tin whisker mitigation practices and acceptance testing to minimize the exposure of tin whiskers in high-reliability applications. It was the consensus of the User Group that pure tin electroplating presents a risk in high-reliability applications, and that there are cost-effective alternatives available to minimize this risk. The recommendations they developed are intended to minimize the risk of failures from tin whiskers.
The User Group published Recommendations on Lead-Free Finishes for Components Used in High-Reliability Products. In addition, they worked closely with JEDEC and IPC in the development of JESD201, Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes, as well as IPC/JEDEC joint publication JP002, Current Tin Whiskers Theory and Mitigation Practices Guideline. These standards, however, do not "solve" the tin whisker issue. In order to minimize the probability of tin whiskers creating functional or reliability problems in products, users and suppliers must employ a combination of known mitigation practices, process controls, and some level of testing.
A presentation from the iNEMI Accelerated Tin Whisker Test Project is now available for free download. The title of this presentation is: "The Effect of Temperature and Humidity Variations on Whisker Growth: Results of iNEMI Environmental Testing." A CD of the iNEMI tin whisker presentations made at ECTC 2007 is available for $75.00 at this link.
Presentation: End-of-Project Webinar for the Tin Whisker Accelerated Test Project, Phases 1-5 (June 10, 2009)
iNEMI User Group Updates Lead-Free Surface Finish Guidelines (5/24/05)
Tin Whisker Modeling Project - Interim Report (July 2003)
A History of Tin Whisker Theory: 1946 to 2004, George T. Galyon, IBM eSG Group, SMTAI International conference, September 26-30, 2004 (Chicago, IL).
Annotated Tin Whisker Bibliography and Anthology, Dr. George T. Galyon, IBM (updated November 2003, v1.2)
JEDEC Standard JESD22A121, "Test Method for Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes," published May 2005 (based on recommendations of the iNEMI Tin Whisker Accelerated Test Project)
Recommendations on Lead-Free Finishes for Components Used in High-Reliability Products (Version 3, updated May 2005), iNEMI Tin Whisker User Group
Tin Whisker Acceptance Test Requirements (NEMI Tin Whisker User Group, updated July 28, 2004) paper presentation
NEMI Team Recommends Three Test Conditions for Evaluating Tin Whisker Growth (09.26.03)
Tin Whisker Accelerated Test Project Plans Meeting at APEX (03.19.03)
NEMI's Tin Whisker Project Reports Initial Test Results, Reviews Modeling Efforts (1.21.02)
NEMI Recommends Standard Test Methods to Assess Propensity for Tin Whisker Growth, Nhat Vo, Motorola; Irina Boguslavsky, EFECT, LLC; and Peter Bush, SUNY Buffalo; SMT magazine, November 2003, pp. 36-41.
A presentation from the iNEMI Accelerated Tin Whisker Test Committee is now available for free download. The title of this presentation is: "The Effect of Temperature and Humidity Variations on Whisker Growth: Results of iNEMI Environmental Testing." A CD of the iNEMI tin whisker presentations made at ECTC 2007 is available for $75.00 at this link.
iNEMI Tin Whisker Workshop at ECTC, May 29, 2007; Reno, NV
iNEMI Tin Whisker Workshop at ECTC, May 30, 2006; San Diego, CA
iNEMI Tin Whisker Workshop, May 31, 2005; presented at ECTC; Lake Buena Vista, FL
The Integrated Theory of Whisker Formation: A Stress Analysis, G. T. Galyon (IBM eSystems Group), C. Xu (Cookson Electronics), S. Lal (FCI USA), B. Notohardjono (IBM eSystems Group) and L. Palmer (IBM eSystems Group), IEEE ECTC, May 31-June 3 (Lake Buena Vista, FL).
A History of Tin Whisker Theory: 1946 to 2004, George T. Galyon, IBM eSG Group., SMTAI International conference, September 26-30, 2004 (Chicago, IL).
NEMI Tin Whisker Projects, Ron Gedney (NEMI), Joe Smetana (Alcatel), Nhat Vo (Freescale Semiconductor, Inc.), George Galyon (IBM), Second International Conference on Lead Free Electronics, June 21-23, 2004 (Amsterdam).
NEMI Tin Whisker Test Method Standards, presented by Irina Boguslavsky (EFECT), September 25, 2003, SMTA International conference (Chicago, IL). (paper).... (presentation)
NEMI Tin Whisker Test Project, Irina Boguslavsky, SMTA International conference, September 25, 2003, Chicago, IL.
"NEMI Sn Whisker Project," Irina Boguslavsky, NEMI consultant; Peter Bush, SUNY Buffalo; Elsa Kam-Lum, Allegro MicroSystems; Mark Kwoka, Intersil; Jack McCullen, Intel; Nick Vo, Motorola; Tin Whisker Joint Meeting: NEMI, JEITA & ITRI, May 15, 2003, Tokyo, Japan. (paper) and (presentation)
"Recrystallization Principles Applied to Whisker Growth in Tin," Dr. Irina Boguslavsky, NEMI consultant, and Peter Bush, SUNY Buffalo, APEX conference, March 31, 2003, Anaheim, California.
NEMI/NIST/TMS Workshop on Tin Whiskers (March 2, 2003; San Diego, CA)
NEMI Tin Whiskers Workshop (held at the IPC Annual Meeting in New Orleans, November 7, 2002)
"Whiskers: Truth and Mystery," Irina Boguslavsky, NEMI consultant, NEMI/IPC Lead-Free Symposium, September 19, 2002, Montreal, Canada.
APEX 2002 - NEMI forum:
"Tin Whiskers Standards Committee Status," Swaminath Prasad (ChipPAC), chair, Tin Whisker Accelerated Test Project
"Tin Whisker Fundamentals Modeling Group Survey," Maureen Williams (NIST), co-chair, Tin Whisker Modeling Project
"Whisker Fundamentals Modeling Group DOE," Irina Boguslavsky (Shipley Company), co-chair, Tin Whisker Modeling Project