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NEMI Group Releases Draft Proposal of Tin Whisker Acceptance Test Requirements
May 27, 2004 |Estimated reading time: 2 minutes
Herndon, Va. — The National Electronics Manufacturing Initiative's (NEMI) Tin Whisker User Group has released a draft proposal of tin whisker acceptance test requirements.
The User Group has developed this document to provide testing requirements and acceptance criteria for evaluating devices with tin finishes in high-reliability applications.
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 is known to be susceptible to the formation of needle-like protrusions, or whiskers, and tin whiskers are a reliability concern. They can cause electrical shorts, disruption of moving parts, and/or degraded RF/high-speed performance. Tin whiskers may grow between adjacent conductors of different potentials and cause either a transient short circuit if the whisker is burned open, or a permanent short if the whisker remains intact. At shorter lengths, whiskers may create a stub-type effect that degrades performance of high-speed/high-frequency circuits. Additionally, whiskers can potentially break loose and, as debris, cause mechanical or other electrical problems.
NEMI has previously published recommendations for test conditions for evaluating tin whisker growth and for mitigation practices to help prevent whisker formation. This latest publication combines practices established by these previous documents and adds such information as test lengths, failure criteria, number of parts and additional bias voltage testing. It provides guidelines for post finishing inspection and preconditioning; outlines a flowchart for acceptance requirements; provides a framework for a qualification test report; and defines requirements for process controls and periodic testing.
The members of this user group are large manufacturers of electronic assemblies, including consumer products, automotive, high-reliability business and telecom equipment, even space applications; and they annually purchase many millions of dollars of components.
The NEMI Tin Whisker User Group has scheduled a meeting June 2, in conjunction with the IEEE Electronic Components and Technology Conference (ECTC), in Las Vegas. At this meeting, the group will review the proposed test requirements with suppliers and solicit feedback on the practicality of implementing the various recommended mitigation and testing approaches. Supplier inputs during the meeting will be considered by the User Group for possible modifications to the test requirements.
The draft of the NEMI acceptance test requirements document is available (along with other tin whisker-related documents) on the NEMI Web site at www.nemi.org/projects/ese/tin_whisker_activities.html.
Information about the June 2 User Group meeting being held at ECTC can be found at www.nemi.org/calendar/tinwhisker_june.html.
The National Electronics Manufacturing Initiative's mission is to assure leadership of the global electronics manufacturing supply chain. For more information, visit www.nemi.org.