Circuits Assembly - November 2008 - (Page 29)

Cover Story • Whisker testing using Jedec standards (JESD-201, Class 2). should be an ongoing activity for the materials team. Obsoles• Lead spacing evaluation. cence analysis of SnPb components should help identify when a Component lead spacing is reviewed and risk assessed based component is going end-of-life (EOL). Leveraging a component on typical Sn-whisker length. Lead spacing guide: engineering team, the OEM can select second sources or alter• >1 mm whiskers are not an issue. nates, purchase last-time buys, or redesign to eliminate obsolete • 500 µm to 1 mm some concern; testing required. materials, in addition to potentially costing down the product. • <500 µm – must use NiPdAu/Ni underlay/anneal/fuse or Many of these actions may require revalidation of the product. reflow/A42 substrate. The OEM should also monitor the BoM for lead-finish Once supplier feedback is received, a decision matrix is used changes as components are converted to RoHS compliant. CircuitWorks Ad:Khaki Fields_CA 8/19/08 10:59 AM Page 1 Many component suppliers may convert, as an example, to a matte tin or SnBi finish for components that can be used in either soldering process. Because these components are backwards comparable, the manufacturer might only provide these components in that lead finish or package style. The medical OEM should ensure the lead finish alloy is consistent with International Electronics Manufacturing Initiative (iNEMI) recommendations for reduced Sn-whisker growth. The iNEMI consortium has proposed a test to promote and accelerate whisker growth, but the test’s validity remains unproven. JEDEC/IPC Joint Publication JP002 is another document to reference, along with JESD22-A121 and JESD201.6 We have found some suppliers do not provide PCNs when bringing lead finishes in compliance with RoHS. It may be prudent to use XRF to monitor incoming components to ensure the leadframes are SnPb. Tin Whiskers Tiny strands of tin can grow and short with adjacent materials. The root causes are unknown, but lead has been used as a mitigation method for whisker growth for decades. For medical OEMs, the primary risk is the growth of whiskers from a component leadframe and potentially shorting to the adjacent leadframe. Even if the component is soldered with SnPb solder, if the component leadframe is RoHS-compliant (i.e., contains no lead), then tin whiskers could grow between these adjacent leads. This would occur above the SnPb solder joint. Medical OEMs’ products should be analyzed for Sn-whisker risk and mitigation activities conducted. Analysis typically includes: • Lead finish identification. • Review of any available Sn-whisker test results. circuitsassembly.com CircuitWorks Benchtop Repair and Prototype Solutions ® CircuitWorks® conveniently packaged and precision dispensing products makes your circuit board repair and prototyping faster, easier and more accurate. Conductive Adhesives • Flux Dispensing Pens • Precision Cleaning Pens Conductive Lubricants • Lead-Free Solutions • Precision Contact Lubricants Conductive Ink Pens • Heat Sink Compounds • Protective Overcoats Contact ITW Chemtronics today for more information about the complete CircuitWorks® product line. Call our technical hotline at 770-832-4401, or email us at askchemtronics@chemtronics.com. CALL NOW! Nothing Cleans Like Chemtronics 800-645-5244 / 770-424-4888 • www.chemtronics.com Chemtronics®, CircuitWorks® and Nothing Cleans Like Chemtronics™ are registered trademarks or trademarks of ITW Chemtronics. ©2008 All rights reserved. Circuits Assembly NOVEMBER 2008 29 http://www.chemtronics.com http://www.chemtronics.com http://www.circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - November 2008

Circuits Assembly - November 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business On the Forefront Screen Printing Better Manufacturing RoHS Conversion for Medical Devices Supporting Full-Service Customer Requirements at the Regional EMS Level Speed Thrills Tech Tips Wave Soldering Process Doctor Pb-Free Lessons Learned The Defects Database Getting Lean Materials World Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - November 2008

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