CircuiTree - March 2009 - (Page 19) Tech Talk centrations for a number of aqueous resists, filter flow rates, and the resulting chemical/ biological oxygen demands (COD/BOD). ions. Feed and bleed is especially effective with proprietary strippers because it helps to keep the copper level low enough that autocatalytic etching does not occur and increase the copper concentration even more. In this case, cost of treating the metals must be considered versus the cost of the stripper solution if feed-and-bleed is used. Using straight caustic solution will not complex the copper and have lower copper concentrations but may attack solder plating more rapidly. Proprietary strippers containing metal complexers may be used in circumstances where solder plating must be protected from caustic strippers, more rapid stripping is desired, or a shiny copper surface is desired. Copper concentrations for these strippers will be much higher (see Table 4): Where the organic and/or metal concentrations are too high for discharge, there are two choices. The solution can be pretreated in a batch treatment to reduce the organic strength (see Table 5) and then to precipitate the metals as insoluble complexes. Two metal-complexing materials often used to precipitate the metals from process solutions are DTC and TMT-15 The alternative to batch treatment for the removal of organics and metals is to have the solutions hauled away for incineration. The particular chemicals, order, and manner of their addition depend on the resists that are present in the stream. Care should be taken to maintain effective stirring and use slow addition of dilute precipitating materials. This will minimize the tendency of resist precipitates to form a gelatinous material. Proprietary resist treatment chemicals are being offered for the neutralization, precipitation, flocculation, and detackification of resist from spent stripper solutions to form a readily filterable precipitate. ■ References Please visit www.circuitree.com to view the references for this column. Strippers It is possible to meter the stripper into the final neutralization tank of the plant waste treatment system. This will depend on the metal concentration, what the permit discharge limits are, and whether the COD or BOD discharge will exceed them (see Table 3). Stripper solutions may require pretreatment before discharge because of copper concentrations. The copper concentration needs to be monitored and compared to the applicable regional discharge limits. If the copper concentration is too high and the stripper inexpensive, then it is possible to use a feed and bleed mode. This renews the stripper solution slowly. It constantly removes the metal ions and they never reach levels high enough to require treatment. High metal concentrations are prevented and the waste is organic with only traces of metal Karl H. Dietz is CircuiTree’s technical editor. Email karl.h.dietz@USA.dupont.com 9 circuitree.com • March 2009 19 http://www.circuitree.com http://www.wssi.com/ct http://www.wssi.com/ct http://www.circuitree.com
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