CircuiTree - February 2009 - (Page 14)

Tech Talk By Karl Dietz Fine Lines in High Yield (Part CLXI) Some Health and Efﬂuent Disposal Considerations in PWB Fabrication T ech Talk, to the best of my recollection, has never addressed the topic of workers’ health and efﬂuent disposal issues facing the PWB industry. This is not surprising because the theme “Fine Lines in High Yield” has no direct links to these important issues. However, the new restrictions on the permitting process of new PWB facilities in China, driven by environmental considerations, highlight the importance of these questions and warrant a closer look. waste streams). For some years, suppliers have been offering electroless copper baths that are EDTA-free. Immersion tin baths typically use thiourea to complex cuprous ions to shift the immersion electron exchange reaction in favor of the reduction of Sn2+ to Sn0. Thiourea was found to cause cancer in animal studies and to be teratogenic in rats. Thiourea may also interfere with waste treatment of heavy metals. For these reasons, baths containing thiourea are typically treated with oxidizing agents before disposal to chemically degrade the thiourea. Today, desmear of drilled holes uses permanganate oxidant. The use of chromic acid has completely disappeared, in part because of concern about the carcinogenic affect of hexavalent chromium. Solids Disposal/Recycling Packing materials and scrap laminate are typical solid waste components generated by PWB fabricators. The proper disposal of such solid waste, or mandatory recycling, is governed by local, state, and federal regulations. In Germany, for example, suppliers of packaged items are required to take back the packaging material. The so-called end caps of dry-ﬁlm resist packaging are often returned to the supplier for reuse. Some dry-ﬁlm resist packaging actually does not use packaging other than shrink-wrapping, eliminating the need for boxes. The cores and end pieces form an interlocking structure like Lego® pieces, forming a palletsized cubicle. There have been innovative approaches to recycling scrap laminate and circuit boards. I previously reported on a unique process operated by Fuba in Germany1 that employs a combination of techniques to separate and recycle the components of scrap boards. All materials, metals, glass ﬁber, and resin, ﬁnd a new use after proper separation—there is no residual waste stream. The separation methods employed are mechanical size reduction and classiﬁcation, magnetic and electrostatic separations. The separated materials ﬁnd new uses as ﬂame retardant building materials, paving material, or park benches, to name a few. The metal fraction is sent to a smelter for metal recovery and separation. More recently, Hall and Williams2 reported on a process for material recovery from PCBs. The boards were pyrolized at 800 °C in an oxygen-free atmosphere to yield easily separable fractions of metal, glass ﬁber, and volatile oils and gases. Plating, Surface Finishes, Desmear Acid copper plating baths typically have been agitated by so-called air sparging, a process in which air is pumped into the bath, exiting through holes in a sparger manifold as small bubbles next to both surfaces of the racked boards. When these bubbles arrive at the surface they cause the formation of sulfuric acid aerosols that constitute a health hazard, especially by interfering with what is called tracheobronchial mucociliary clearance. There are engineering solutions to avoid worker exposure to these aerosols, but a more elegant approach that also offers several technical advantages is the use of eductors (i.e., submerged jets that move the plating solution). Electroless copper has been under scrutiny for many years, a factor that has contributed to the introduction of direct metallization processes. One issue is the health concern about using formaldehyde as a reducing agent. Ventilation of these baths and monitoring for acceptable exposure levels has allowed the continued use of electroless copper based on formaldehyde, but suppliers have developed formaldehyde-free baths as an alternative where local formaldehyde regulations present a problem. Another concern is the use of EDTA complexing agent in electroless copper baths (e.g., in European countries where the discharge of aqueous efﬂuent containing EDTA is prohibited because EDTA affects the ability to remove heavy metals from the 14 February 2009 • circuitree.com Figure 1 Electric Respirometer Equipment (Source: Bioscience Inc., Bethlehem, Pa.) Biodegradable Base Curve (Without Test Material) Cumulative Oxygen Demand Inhibitory Toxic Time Figure 2 Cumulative Oxygen Demand Curves (Source: Peter. S. Strilko) http://www.circuitree.com

Table of Contents Feed for the Digital Edition of CircuiTree - February 2009

CircuiTree - February 2009 Contents Lead Wire The Wire Tech Talk Flexible Thinking Are Better PCB Design Tools and Manufacturing Enough to Stay Competitive? The Strategist Fein-Lines The Big Deal Over Fine Pitch Assembly Asian Section View From the Middle Market Outlook Technical Product Spotlights Classified Ads Upcoming Events Ad Index

CircuiTree - February 2009

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