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iNEMI Task Force Addresses Lead-free Issues
August 25, 2005 |Estimated reading time: 3 minutes
HERNDON, Va. — The International Electronics Manufacturing Initiative (iNEMI) has published recommendations for safeguarding high-reliability products' dependability as the supply chain converts to lead-free components and materials. iNEMI's High-reliability RoHS Task Force is calling for continued SnPb-compatible components availability for exempted products, and for standardized mitigation practices and testing methods to minimize tin whiskers.
"The iNEMI High-Reliability (Hi-Rel) Task Force consists of OEMs and EMS providers whose products are characterized by long service life and high-reliability requirements," says Jim McElroy, iNEMI's CEO. "Maintaining high product reliability is absolutely critical to these companies' survival. They are very concerned about the transition to lead-free and have banded together to provide a unified voice and message to the supply chain. We are currently surveying the components supply base to see if it makes sense to organize an industry forum that will bring together high-reliability users and suppliers to further discuss these needs."
Several compatibility issues have been identified as high-reliability OEMs and EMS providers try to "mix and match" lead-free components in exempted SnPb assembly processes.
"The RoHS Directive provides 'lead-in-solder' exemptions for important 'mission-critical' and high-reliability systems, ostensibly because the Commission recognized that industry does not yet have adequate field data or verified acceleration models to ensure the reliable functioning of these critical products if lead-free solders were used. Their intention was to guard against unnecessary risk in applications where failure could be anything from problematic to catastrophic," says Joe Smetana, principal engineer of advanced technology for Alcatel and chair of the iNEMI Tin Whisker User Group. "Companies that manufacture high-reliability, long-service-life systems must be assured of the availability of components that are compatible with SnPb assembly, not only to provide continued quality and performance in new products, but to maintain products already in use. Many telecom, server, monitoring and control instruments or storage products, for example, often have a field life of 10 to 25 years, and are high-end systems that customers will want to repair rather than replace."
Mike Davisson, distributed materials engineering manager for Agilent Technologies, points out that BGA components are of particular concern, noting that solder balls are designed to operate within a particular set of process and materials parameters. "Lead-free BGAs are designed to be assembled with tin-silver-copper solder paste, not SnPb solder paste. We need a continued supply of SnPb ball BGAs. We cannot take lead-free BGAs and attach them to boards using SnPb solder with today's typical assembly process. Industry experience has shown that doing so can produce lower assembly yields and less reliable interconnects," he says.
The other area of concern is tin whiskers. The predominant whisker mitigation strategy for more than 50 years has been the addition of lead to the tin plating. As lead is eliminated from electronic products, many component suppliers are proposing the use of pure tin plating as the most convenient and least costly strategy for meeting RoHS requirements. However, especially for the high-reliability user community, the pure tin strategy presents reliability risks due to the whisker-forming tendencies of pure tin and tin alloy plating. Economic realities are driving most component suppliers to offer tin and/or high tin content (>95%) lead-free finishes, and the availability of multiple surface finishes will not be a long-term option in most cases. The High-Rel RoHS Task Force has defined a set of requirements to ensure that their suppliers provide the least whisker-prone finishes possible.
"We are requiring that our suppliers employ a proven whisker mitigation strategy, such as nickel underlay or annealing," says George Galyon, senior technical staff member at IBM, and chair of the iNEMI Tin Whisker Modeling Project. "However, since mitigation techniques can vary significantly in effectiveness, we are also asking for supporting measurements — meaning testing — to provide objective evidence of mitigation efficacy."
The iNEMI Hi-Rel Task Force companies will require electronic component suppliers to implement certain recommendations for high-reliability applications. The group's recommendations are available by visiting www.inemi.org/cms/projects/ese/High_Rel_RoHS.html.