CircuiTree - February 2009 - (Page 16)

Tech Talk ture most of the organic content for incineration. Conversely, generating aqueous waste streams with fairly high organic loads due to soluble or partially soluble stripper skins is not such a big issue in the U.S. The dominant concern about the aqueous disposal and treatment of organic resist components is their biodegradability or compatibility with secondary waste treatment. Tests were run to demonstrate the compatibility of aqueous resist waste streams with biodegradation in secondary waste treatment.3 The bacteria of a waste treatment facility that feed on organic compounds in waste water are ﬁrst acclimated over several weeks to a steady diet of spent resist being part of the organic food. This bacteria culture is then exposed to a food stream containing the new resist to be tested for compatibility with biodegradation. The test is conducted in an electrolytic respirometer that allows the accurate measurement of the oxygen uptake of the bacteria, typically over 5 days (BOD5). The apparatus is a closed reactor (Figure 1) in which oxygen is generated by electrolysis. The amount of oxygen generated, and consumed, is proportional to the amount of current used and is measured thereby. As oxygen is absorbed into the solution, it creates a partial vacuum. This causes a shift in the level of the electrolyte, the electrolyte touches the electrodes, current begins to ﬂow, and oxygen is generated. As the pressure turns to atmospheric, the electrolyte solution shifts and no longer contacts the electrodes. The reaction products are CO2 and dead bugs that have died of natural causes, having been sustained by nontoxic organics. The CO2 generated in the reactor is adsorbed by alkali. Bacteria sludge generated in a waste treatment facility can be used as fertilizer. Cumulative oxygen demand of the bacteria culture is then plotted versus time (see Figure 2). The green curve in Figure 2 shows the base curve oxygen consumption of an acclimated bacteria culture. If the oxygen consumption increases with the addition of the test resist, one concludes that the test resist is biodegradable. If the uptake is lower after the addition of the test resist, but oxygen uptake continues, one concludes that there is some degree of inhibition to biodegradation due to the presence of the test resist. If the oxygen uptake stops after the test resist addition, one has to conclude that the test resist is toxic. If the base curve does not shift at all after the addition of the test resist, one concludes that the new material is neither considered food by the bacteria nor does it adversely affect biodegradation. Higher molecular weight acrylates fall into this category. If they are part of the sludge used as fertilizer, they will eventually degrade under the inﬂuence of heat, moisture, and UV light, just like Plexiglas. ■ References Please visit www.circuitree.com to view the references for this column. Karl H. Dietz is CircuiTree’s technical editor. Email karl.h.dietz@USA.dupont.com 16 February 2009 • circuitree.com http://www.circuitree.com http://www.mbracks.com http://www.mbracks.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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