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Conversion of a High Reliability Exempt Product to Lead Free: Lessons Learned - 4 Years Into RoHS
Keywords: Lead Free, Reliability , DFM
Many products are exempt from the RoHS Directive including Tekelec's Processor Module and the exemption is valid until 2012 at the earliest. Tekelec is a high reliability network communications company and the Processor Module is designed to have a 25 year life in Central Office conditions in which the operational temperatures can vary between -5°C and +50°C, relative humidity can be as high as 90% and shock and vibration conditions range from transportation profiles to Zone 4 earthquake environments. The objective was to convert a limited quantity of the Processor Module to Pb-free for internal development and provide the foundation for future product conversions. The primary goal was ensure the Pb-Free version of the product had reliability metrics equal to or better than the SnPb version and the secondary goal was to do this in a cost and time effective manner. This paper provides an overview of the process used and lessons learned. Topics covered will include industry studies, Bill of Materials review, components with limited temperature ratings, key Design for Manufacturing Improvements, selection of a high reliability solder paste and wave solder flux to drastically reduce the risk of dendrite growth, product analysis by a leading university consortium, reflow profile development, a test to ensure proper wave solder spray fluxing, oblique X-Ray inspection to validate through hole solder fill, forced rework, cross sections, dye and pry tests, and thermal cycling. Lessons learned are directly applicable to military and aerospace products. The work will also include a summary of the reliability testing results of the New England Lead Free Electronics Consortium Phase IV Test Vehicle in which Tin Lead and Lead Free cards underwent vibration and thermal cycling. The thermal cycling was performed per IPC 9701 with a temperature extreme of -55 C and 125 C. All cards were cycled until a minimum of 1470 cycles.
Robert Farrell, Manufacturing Staff Engineer
Benchmark Electronics
Nashua, NH

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