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46 PCB007 MAGAZINE I AUGUST 2019 scrubber, 10 gallons/minute of DI water can be fed continuously into and out of the scrubber system reservoir… With a closed-loop system, there is no sacrificing of rinse quality to save water. Lift stations integrated with conductiv- ity sensors can automatically identify an out-of- control waste stream as it happens, allowing for quick corrections by maintenance. Also, fresh rinse-water conductivity is always DI quality." Particulate Filtration on Deburr and Panel-scrubbing Operations Deburrers are used to remove stubs of cop- per formed after the drilling of holes in double- sided and multilayer panels before they enter the copper deposition process. Scrubbers are used to remove oxides from printed circuit laminates, clean the surface prior to a surface coating to provide better adhesion and remove residuals after etching or stripping. In deburr- ing and board scrubbing, particulate materi- als are added to the water and are removed by various methods based on size and the weight of the copper particle such that the wash wa- ter becomes suitable for up to 100% recycling. The types of filtration available for this opera- tion are cloth, sand, centrifugation, and gravity settling with filtration. Etcher and Conveyorized Equipment Design Modifications Etching machines can be the single largest source of copper waste in the discharge from a PCB facility. The amount of copper discharged, and the rinse flow rate from that machine, is a function of the machine design. An older etching machine will contain a single-stage etchant replenishing module po- sitioned between the etching chamber and its continuously flowing single or multiple stage water rinse chamber. Fresh etchant is fed to the replenishing module to wash the panels, and that etchant (now containing copper washed from the freshly etched panels) then flows (in a direction opposite to the direction of the pan- el movement) into the etching chamber. The continuous water rinse can contain from 100 to 500 milligrams per liter (mg/l or ppm) of copper, depending on the configuration of the rinse module. Companies that use this type of equipment, with a single-station rinse module, normally have floor space restrictions in their production area. The etcher design affects the rate of etchant solution dragout as does the vol- ume of panels being processed and the quality of the etchant solution control. By way of comparison, adding a second stage replenisher station will reduce the range of copper dragout in the following rinse from 50 mg/l to 300 mg/l. We have observed more than one etching machine–using a four-stage replenisher module and a combination of wa- ter recirculating with a single-stage rinse mod- ule–produce a rinse effluent containing from less than 1.0 mg/l up to 2.0 mg/l of copper. That is the option that we recommend to cli- ents when etchant recycle, and copper recov- ery are not practical or economical. Use of recirculating rinse modules will de- crease the required flow rate of rinse water (by about 50%) without requiring significantly more floor space, compared to single-station spray rinse chambers (without recirculating rinses). In this application, fresh water is used for the final top and bottom nozzles in a rinse module. This water is collected in a sump lo- cated 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 overflows through a pipe fit- ting to drain. While recirculation modules are available for purchase, they can also be cus- tom-built by each PCB factory. If a PCB factory must evaluate the purchase of a new etching machine, we recommend that a photoelectric cell be included on the load module to sense when panels are being pro- cessed. This can be used to activate and deac- tivate the rinses on that machine. Water used for rinsing will begin to flow only when a pan- el enters a rinse chamber, and a timer will de- termine (based on the speed of the conveyor belt carrying the panels) when the last panel will exit that rinse chamber. The rinse water inlet connection to any rinse chamber should be fitted with a flow restrictor

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