Newsroom
NEMI's Tin Whisker Project Reports Initial
Test Results, Reviews Modeling Efforts
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APEX (San Diego, Calif.) - January 21, 2002 — The Tin Whisker Test Method Standardization Project, organized by the National Electronics Manufacturing Initiative (NEMI) to address the problem of "tin whiskers" in lead-free assemblies, is reporting results from its first round of tests in an industry forum at APEX this week. Initial results point to various combinations of thermal cycling and temperature-humidity conditions as accelerants of whisker growth, depending on substrate material. The project will also present data gathered - and conclusions drawn - about the cause of tin whiskers.
The Tin Whisker Project, chaired by Swaminath Prasad of ChipPAC, and co-chaired by Jack McCullen, Intel, and Mark Kwoka, Intersil, grew out of NEMI's Lead-Free Project, where it was recognized that component leads would require lead-free solderable surfaces. While pure tin is the most promising component termination in terms of cost and performance, it tends to "grow whiskers" - small protrusions of metal that seem to grow out of a solder joint or pad. These whiskers can become large enough to short leads and cause equipment malfunction and are, therefore, a reliability concern. There is currently no industry-accepted accelerated test that can predict tin whisker growth, and no way to ensure the reliability of a given plated component design.
NEMI's Tin Whisker Project is addressing this problem with efforts that will help industry understand the causes of the tin whisker phenomenon and predict its occurrence. The group is working to identify or develop standard accelerated tests that can be used to predict the propensity of a given material to grow whiskers. In addition, a sub-group is assembling a database of information to provide a basic understanding of, and develop a model for, the mechanism(s) behind tin whiskers. If the reason for tin whisker growth is understood, then there is hope it can be controlled.
"Without an industry accepted test methodology, component suppliers have no way to assure their customers of the reliability of their products," said Swaminath Prasad. "They sorely need some means of ensuring that a given lead material and plating combination is reliable. For the long term, we need a complete understanding of why this phenomenon occurs and how to control it."
Over the last six months, the test standards group has devised a test plan, constructed hardware and tested ICs and passive components. Initial test results indicate that the combination of temperature, temperature and humidity, and thermal cycling accelerate the growth of tin whiskers on passives (capacitors) and brass coupons (brass substrates with tin plating) significantly, and to a lesser degree (which may be insignificant), on typical component lead designs with pure tin plating. The whisker propensity is also found to be significant in areas where there are scratches on the plated surface.
In parallel with testing, the modeling project, chaired by Irina Boguslavsky, Shipley Company, and Maureen Williams, NIST, has been working to understand the causes of tin whisker formation. This group has done an extensive literature compilation, surveys of suppliers and users, and research in stress measurement methods, and has come to some basic conclusions regarding the root cause of tin whiskers. Information gathered to date indicates that the compressive stress in the plated layer seems to be the predominant factor influencing whisker growth. These results, along with the planned design of experiment (DOE), will be presented at the APEX forum this week.
About NEMI
The National Electronics Manufacturing Initiative's mission is to facilitate leadership of the North American electronics manufacturing supply chain. Based in Herndon, Va., the industry-led consortium is made up of more than 60 electronics equipment manufacturers, suppliers, industry associations and consortia, government agencies and universities.
NEMI roadmaps the needs of the North American electronics industry, identifies gaps in the technology infrastructure, establishes implementation projects to eliminate these gaps (both business and technical), and stimulates standards activities to speed the introduction of new technologies. The consortium also works with government, universities and other funding agencies to set priorities for future industry needs and R&D initiatives. For additional information about NEMI, visit www.nemi.org.
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For further information:
Cynthia Williams
cwilliams@nemi.org
phone: 207-871-1260