Circuits Assembly - September 2008 - (Page 50)

Tech Tips development and control of the preheating profile, there is a potential for a residual solvent to remain on the assembly during exposure to the solder wave. When solvent contacts the solder wave, it explosively boils off and results in solder spattering. This spattering can result in random solder balls on the assembly. There are two concerns to address to alleviate potential issues in evaporating water off an assembly using VOC-free fluxes: one, the higher preheat profile temperature requirement. A comparison of products from a North American flux manufacturer shows required topside preheat temperature increases from 3°-10°C for a VOC-free flux versus a VOC-bearing flux. Careful profile development must be performed to ensure excess solvent is not present during contact with the solder wave. Care also must be exercised to ensure the preheat profile is not too high. This can deplete flux activity too early in the process, which can result in typical solder defects due to premature flux evaporation. Two, the type of preheat technology used. A convection-based preheater (e.g., forced air) is recommended, as it is more effective for preheating than purely radiation-based preheaters. This is because of the increased amount of energy required to evaporate water. In addition, blowing air across the bottom of a fluxed assembly expedites removal of excess water that may be present. n Bringing a world of information to you References 1. “Title 40: Protection of Environment, Part 51-Requirements for Preparation, Adoption, and Submittal of Implementation Plans, Subpart F – Procedural Requirements, 51.100: Definitions,” Access: Electronic Code of Federal Regulations (e-CFR), United States Government Printing Office. 2. “Directive 2004/42/CE of the European Parliament and of the Council,” EUR-Lex, European Union Publications Office. GET INTERCONNECTED “I’m glad I attended IPC Midwest to learn about solutions to challenges we are seeing, especially with lead free. It’s so important to have a forum like this where critical industry issues can be discussed.” Robert Cook, Technical Fellow, Visteon Corporation, Van Buren Township, Michigan If you need to see electronics assembly and PCB equipment, you need to be at this show! DESIGN PRINTED CIRCUIT BOARDS ELECTRONICS ASSEMBLY Continued from pg. 37 TM Keep up with global changes in technology, standards and customer expectations. Conclusions The experiment found: • No significant differences between SnCuNi and SAC alloy when reflowed under the same conditions. However, the SnCuNi solder is shinier, much like SnPb. • A minimum peak temperature of 240ºC is required for SnCuNi to achieve good solder coalescence. • Although time above liquidus is less for SnCuNi (higher melting point), the initial intermetallic thickness is not different from that of SAC alloy. Previous investigations showed that on account of nickel, the intermetallic does not increase as much as that of the SAC alloy after aging. n TEST References 1. Thomas Kolossa, Balver Zinn presentation on SN100C reliability. 2. Frédéric Martinez, Syed Asif Arnaud, Keith Sweatman and Tetsuro Nishimura, “Improving the Performance of the Tin-Copper Eutectic as a Pb-free Solder.” Gerjan Diepstraten is process support manager at Cobar Europe BV (cobar.com); g.diepstraten@cobar.com Sunday–Thursday, September 24–25, 2008 Renaissance Schaumburg Hotel & Convention Center Schaumburg, Ill www.IPCMidwestShow.org 50 Circuits Assembly SEPTEMBER 2008 circuitsassembly.com http://www.IPCMidwestShow.org http://www.IPCMidwestShow.org http://www.cobar.com http://circuitsassembly.com

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Circuits Assembly - September 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business Global Sourcing On the Forefront Screen Printing Better Manufacturing Reflow Soldering with a SnCu Eutectic Pb-Free Alloy Improving OEE in High Mix Facilities Effectively Managing RF Design in Utility Metering Applications Solder Joint Reliability of Different BGAs Reworked Using Low Melting Point Pb-Free Alloys Tech Tips Wave Soldering Pb-Free Lessons Learned Materials World Process Doctor Equipment Advances Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - September 2008

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