CircuiTree - February 2009 - (Page 15)

Tech Talk Dry-Film Photoresist Health and Effluent Disposal Considerations Most dry-ﬁlm resists contain acrylate monomers that form polyacrylates during exposure with UV light. These acrylate monomers are skin irritants (causing dermatitis), respiratory irritants, and sensitizers. Operators that come in contact with these monomers can develop a sensitization to acrylates, the severity of which differs widely between individuals. The skin rash that develops is quite similar to poison ivy exposure. Therefore, skin and respiratory exposure to acrylate monomers should be avoided. The monomers are found in spent developer solutions, around hot roll laminators, and, to some extent, around the exposure frame of printers during vacuum draw-down. When handling developer solutions, the operator should be wearing protective gloves such as Neoprene gloves. Exposure units should be vented to the outside, as should hot roll laminators and vacuum laminators. Laminator exhaust ﬂow rate recommendations are typically in the range of 300 cfm (8.49 m3/min [high end]) and 130 cfm (3.68 m3/min [low end]). It should be noted that the odor of the resist, or any other material, is not proportional to the level of a harmful ingredient and is therefore not a reliable indicator of safe or unsafe exposure levels. Another interesting observation we made was that the level of ozone measured that forms during UV exposure is very low and is not a cause for concern. In addition to the photosensitive resist layer, the polyester base and the polyethylene cover sheet need to be disposed of. It goes without saying that the polyester foil is not suitable for home use as packaging material, especially as food wrap, because it has been in contact with the acrylate monomers in the resist. Polyester foil has been recycled for reuse in polyester by a process called alcoholysis. In this process, the polyester chain is cleaved into ethylene glycol and terephthalic ester for reuse as building blocks for new polyester. This operation requires a large scale to be cost effective. Polyethylene can be recycled thermoplastically into shaped objects whereby the purity of the recycle stream is a consideration. The disposal of spent developer solution and stripper solution is worth discussing in more detail and will be the subject of next month’s Tech Talk. Highly alkaline strippers can attack the metal surface of the boards and cause buildup of copper, tin, and lead in the stripper solution. The spent solution should therefore be analyzed for metals before going to secondary waste treatment to assure compliance with incoming water quality standards for such treatment facilities (e.g., publicly owned treatment works [POTWs]). Disposal of spent developers and strippers in POTWs is not common in all regions of the world. It is common in the U.S. but not in Japan where most resist waste is incinerated. This explains why resists developed in Japan typically form insoluble stripper skins to minimize organic content of aqueous waste for discharge to surface waters but to cap- 797 VA Computrace CVS with unsurpassed precision • Improved bath monitoring • Reduced operating costs • Modular setup 797 VA Computrace for Cyclic Voltammetric Stripping (CVS) For the determination of organic additives such as • Brighteners • Levelers • Suppressors 6555 Pelican Creek Circle Riverview, FL 33578 Toll-free 800-727-6768 Direct 813-316-4700 info@metrohmusa.com www.metrohmusa.com circuitree.com • February 2009 CT02094Metr.indd 1 15 12/22/08 3:59:24 PM http://www.metrohmusa.com http://www.metrohmusa.com 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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