Newsroom
NEMI Issues Revised Tin Whisker Acceptance Test
Requirements
HERNDON, Va. - August 30, 2004 - The National Electronics Manufacturing Initiative's (NEMI's) Tin Whisker User Group has released revised recommendations for tin whisker acceptance test requirements. The group published a draft set of recommendations in May of this year and, after actively soliciting input from suppliers, revised its recommendations based on the feedback received.
Acceptance Test Requirements
The NEMI Tin Whisker User Group is comprised of eleven large manufacturers of electronic assemblies that agree that pure tin finishes (and other high-tin content lead-free alloy finishes) present a risk of tin whisker-related failures in electronics, particularly those demanding high reliability. Seeing the need for industry-wide guidelines and criteria for accepting lead-free components in the face of uncertain technical risk, the group put together proposed recommendations that included tin whisker testing requirements and acceptance criteria for evaluating devices with tin finishes. "Industry needs common guidelines in order to reduce risk to the reliability and integrity of our products," said Joe Smetana, principle engineer, advanced technology for Alcatel and chair of the NEMI Tin Whisker User Group. "At the same time, there are a number of options for reducing the risk of tin whiskers, and we recognized the need for supplier feedback on the practicality of implementing the various approaches. Our goal was to address a complex issue in a practical manner with a justifiable approach while limiting the testing requirements in an effort to save time and money but still reducing the risk of tin whisker failures.
The NEMI Tin Whisker User Group sponsored a supplier meeting at the IEEE Electronic Components and Technology Conference (ECTC) in early June, specifically to solicit feedback on its proposal. Smetana says that the session, which generated lively debate, provided valuable input and led to the revised recommendations that are now available. Key changes made to the recommendations include:
- Changed significantly the "qualification by similarity" matrix (Appendix A), dramatically reducing the number of tests (and associated cost) required by an individual supplier.
- Eliminated the annual re-qualification requirement, replacing it with a much simpler, supplier-defined, whisker monitoring requirement.
- Eliminated requirements for control samples that produce whiskers.
- Provided options in the specification if SnPb reference samples are not used or available for baseline whisker length comparisons.
- Provided guidelines for optical inspection qualification as a possible alternative to SEM.
- Eliminated preconditioning requirements for components with nickel underplating, which cuts sample sizes for components using nickel as a mitigation practice and also reduces the test time required for these components.
- Allowed an option for bias testing (when required) to be conducted in sockets.
"As long as the fundamentals and various contributing factors to tin whisker growth are not fully understood, acceptance of lead-free tin finishes always carries some risk, particularly when relating testing to field life," explained Smetana. "However, we believe that the combination of mitigation practices, testing and plating process control reduces the risk associated with tin whiskers."
The revised acceptance test requirements have been submitted to both IPC and JEDEC to pursue release of a formal standard or guideline for tin whisker acceptance testing. Download recommendations.
About Tin Whiskers
As the electronics industry moves toward lead-free assemblies, the simple manufacturing solution is to use pure tin, or alloys with high tin content, as coatings on lead-frames. However, tin-based plating is known to be susceptible to the formation of needle-like protrusions, or whiskers under certain conditions. If whiskers grow to critical lengths in service, they could cause electrical shorts, disruption of moving parts, and/or degraded RF/high-speed performance.
Despite five decades of research, there is no scientific consensus on whisker formation and growth fundamentals. In addition, there is no standard set of tests that can accelerate whisker formation and growth and relate these tests to field conditions with any reasonable degree of certainty. As a result, it is difficult for developers to safely specify tin-based lead-free finishes for components used in their products, particularly those concerned with high-reliability and/or design life of more than five years.
Three NEMI projects are currently addressing the issues: Tin Whisker Accelerated Test, which is working to identify accelerated test(s) to predict whisker formation; Tin Whisker Modeling, which is focusing on the root cause(s) of whiskers; and Tin Whisker User Group, which is defining guidelines for minimizing risk of failure from tin whiskers in high-reliability electronic applications.
About NEMI
The National Electronics Manufacturing Initiative's mission is to assure leadership of the global electronics manufacturing supply chain. Based in Herndon, Va., the industry-led consortium is made up of more than 60 manufacturers, suppliers, industry associations and consortia, government agencies and universities. NEMI roadmaps the needs of the 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
Director of Communications
207-871-1260
cynthiaw@maine.rr.com