PCB007 Magazine

PCB007-Aug2019

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48 PCB007 MAGAZINE I AUGUST 2019 photoresist developing, deburring, and panel scrubbing. Similar techniques to reduce water flow can be applied to these operations. Both the volume of wastewater and its cop- per content may be minimized by selecting a properly designed new or modifying existing conveyorized machine. The numerous options presented in this section must be evaluated on a case-by-case (and site-by-site) basis. Please be aware that some of our recommendations for waste minimization require additional floor space in the production area, that may not be currently available. Before a final decision is made to purchase or to modify a machine, it is advisable for each PCB factory to weigh the alternative equipment and operating costs. However, if the available production floor space is already stretched too thin, this comparison and its effort may be a waste of time. Use of recirculating rinse modules in the etcher and other conveyorized equipment will decrease the required flow rate of rinse water for that process step by about 50% without requiring significantly more floor space, com- pared to single-station spray rinse chambers (without recirculating rinses). In this applica- tion, fresh water is used for the final top and bottom nozzles in a rinse module. This water is collected in a sump located below the rinsing compartment. A pump recirculates this water through the first set of top and bottom nozzles (instead of using fresh water). As more fresh water enters the sump, the excess water over- flows through a pipe fitting to drain (Figure 1). Conveyorized equipment can also be used for, at least, inner layer and outer layer photo- resist stripping and inner layer and outer layer photoresist developing, deburring, and panel scrubbing. Similar techniques to reduce water flow can be applied to these operations. Immersion-type Counterflow Rinses Counterflow rinsing, employing several sin- gle-stage rinse tanks in series, is one of the most powerful waste reduction and water manage- ment techniques for inner layer processing and in the electroless copper process. These opera- tions use a cage-type carrier that holds many inner layer panels in a side by side configura- tion for processing. Immersion rinsing of pan- els is also required following the cleaner bath in the pattern plating operation and in other operations. While multiple tanks can be connected in series, we prefer using one properly designed counterflow rinse tank to minimize floor space requirements. However, this opportunity to reduce the rinse flow rate does require more floor space than a single-station rinse tank. In counter-current rinsing, after exiting the process bath, the boards move through several rinse contact stages, while water flows from stage to stage in the opposite direction. Over time, the first rinse reaches a steady-state con- centration of process dragout contaminants that is lower than the process solution. The second rinse (away from the process bath) stabilizes at even a lower concentration. This enables less water to be used to produce the same cleanliness compared to a single-station rinse tank. The higher the number of rinse sta- tions connected in series, the lower the rinse rate needed for adequate removal of the pro- cess solution from the panel. A multistage counterflow rinse system al- lows greater contact time between the panels and the rinse water, greater diffusion of the process chemicals into the rinse water, and more rinse water to encounter each panel. The disadvantage of multistage rinsing is that more steps are required as well as additional equip- ment and workspace. Generally speaking, it is impractical to use more than a four-stage rinse Before a final decision is made to purchase or to modify a machine, it is advisable for each PCB factory to weigh the alternative equipment and operating costs.

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