Engineers Hear Reports on RoHS Compliance, Ferrites

-- Test & Measurement World, 5/2/2005 6:24:00 AM

On April 27, some 20 engineers gathered at EMC Corporation in Hopkinton, MA, for a meeting of the Northeast Product Safety Society. The meeting was a joint gathering of the IEEE EMC Society, with speakers from each group.

Dr. Richard A. Anderson of M/A com (a division of Tyco Electronics) gave a presentation on the costs and risks of compliance to the Restriction of Hazardous Substance (RoHS) directive issued by the European Union. As of July 1, 2006, electronic products sold into the EU must be free of lead (Pb), mercury (Hg), hexavalent chromium (CR⁺⁶), and other hazardous materials. The directive includes materials used to manufacture components and it includes assembly materials such as solder. Individual EU countries and even states in the U.S. (Maine and California) are adopting regulations on hazardous materials in electronic products.

Anderson explained the problems associated with replacing the widely used 63%-37% tin-lead (Sn-Pb) solder with a material that contains no lead. The most promising replacement, tin-silver-copper (Sn-Ag-Cu) requires higher reflow temperatures that Sn-Pb solder. In fact Sn-Ag-Cu solder melts at 34°C higher than SN-Pb solder. It also requires longer reflow times at temperatures 25°C higher for 35 s (vs. 10 s) needed for Sn-Pb.

Anderson's presentation included photos that explained how the higher temperatures and longer reflow times can damage materials. One photo showed inexpensive FR-4 circuit-board material, which can melt under the increased stress. The higher temperatures can cause more water vapor to dissipate from materials, which can cause them to deform. Plastics used to make connectors may deform, requiring connector manufacturers to use materials that can withstand the higher temperatures. Anderson cited other problems with Sn-Ag-Cu solder. For example, the angle at which solder joints flow onto IC leads is different than for Sn-Pb. Thus, inspectors need retraining or they may reject boards manufactured with Sn-Ag-Cu solder, thinking that the solder joints are unacceptable.

The EMC Society portion of the meeting featured a discussion of ferrite materials and how they suppress EMI. Paul Zdanowicz, product manager at Fair-Rite Products, explained how ferrites are made and how electrical signals magnetize them. He showed how different ferrite materials' impedances respond to frequency, DC bias, and temperature. He reviewed applications of ferrites and he covered equations that calculate a ferrite's ability to attenuate unwanted signals.

Numerous web sites contain information on RoHS. Here are a few that cover the basics.

Bush, Steve, "Rocky road to RoHS compliance," Electronics Weekly, March 2, 2005.
www.electronicsweekly.com/Article38897.htm.

Overview of RoHS Directive and its companion WEEE Directive
uk.farnell.com/static/en/rohs/presentations/official_pres/eratech_pres_files/frame.htm

"Top Ten Myths About RoHS"
www.rochestermicro.com/rohs_myths.html