Tin Whisker User Group Publishes Updated Set of Recommendations
January 4, 2007 // Published as a news service by IHS
The International Electronics Manufacturing Initiative (iNEMI) Tin Whisker User Group released a major update of its publication, Recommendations on Lead-Free Finishes for Components Used in High-Reliability Products.
The latest revision includes significant changes to some of the group's previous recommendations as well as the addition of new recommendations.
It is the consensus of the group that pure tin electroplating presents a risk in high-reliability applications, said iNEMI. The guidelines the group developed are intended to minimize the risk of failures from tin whiskers.
This latest update includes recommendations for component finishes for a variety of applications and reflects the best judgment of the iNEMI user group members, based on their own experiences and the available data.
The iNEMI Tin Whisker User Group consists of nine large manufacturers of high-reliability electronic assemblies including: Agilent, Alcatel-Lucent, Celestica, Cisco Systems, Delphi Electronics & Safety, Hewlett-Packard, IBM, Sun Microsystems and Tyco Electronics.
"The industry has made significant progress in standardizing its approach to tin whisker mitigation and testing," said Joe Smetana, principal engineer, advanced technology for Alcatel-Lucent and chair of the iNEMI Tin Whisker User Group.
"Three standards were released in 2005 and 2006 addressing tin whisker testing, environmental acceptance requirements and mitigation practices. The user group strongly endorses the use of these documents as part of a comprehensive strategy of mitigation practices, tin whisker testing and plating process controls, all of which are necessary to reduce the risk of failures associated with tin whiskers. However, the tin whisker issue is not solved.
"It is the user group's goal to keep this issue in the forefront and to continue to provide guidance to users and suppliers so that we can minimize the probability of tin whiskers creating functional or reliability problems with our products. As industry's knowledge and understanding of tin whiskers grows, our guidelines will evolve to reflect that new knowledge."
The latest version of the user group's publication includes new recommendations regarding issues such as corrosion, mechanical stress, use of tin over brass or tin over steel, thermal-cycled end use environments and non-columnar grain structure.
The group also expanded its discussion of bright tin, making formal recommendation regarding its use. (While bright tin is generally not recommended, the group indicates that there are some applications where it may be viable, particularly with some of the new bright tin platings and outlines specific mitigation and testing practices for its use.)
Other recommendations have been changed or updated/expanded to reflect the latest research findings. For example, the user group:
- Changed its stance on annealing of matte tin over copper, saying it can be accepted when accompanied by supporting test data.
- Updated its position on bias, noting recent data that indicates electrical bias is no longer considered a significant concern and does not require additional testing.
- Changed information about alloy 42, warning that users should be cautious in using tin finishes on alloy 42 (Fe-42Ni) lead-frames in applications where there is significant thermal cycling and noting possible mitigation practices.
- Further clarified statements about the use of tin-bismuth finishes.
The document has been reorganized to be more user-friendly. The guidelines for migrating to Restriction of Hazardous Substances (RoHS)-compliant finishes was organized into sections that discuss commonly available mitigation practices, other (less commonly available) practices, finishes that should generally be avoided, mitigation practices that require further study, applications of concern plus other considerations and recommendations.
The revised recommendations can be downloaded from the iNEMI web site athttp://thor.inemi.org/webdownload/projects/ese/tin_whiskers/Pb-Free_Finishes_v4.pdf .
Source: International Electronics Manufacturing Initiative (iNEMI).