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AUGUST 2019 I PCB007 MAGAZINE 51 located properly). Solenoid valves are electri- cally actuated valves that are commonly used with conductivity controllers. A solenoid valve is either fully open or fully closed; its purpose is not to control the rate of water flow. Flow restrictors, if available, are ordered based on the desired flow rate (we recommend a 2–3-gpm flow restrictor for a two-stage coun- terflow rinse tank) and the pipe size. If a mini- mum water pressure exists in the water inlet line (about 20 psi is considered minimum), the water flow into a rinse tank should not vary although the water pressure will most likely vary. Flow restrictors are not adjustable after they are installed. By providing pipe union fit- tings for both up and down of the flow restric- tors, adjustments can be made. Flow restric- tors with flexible diaphragms are rated for a specific flow rate in a specific pipe size. Typi- cally, a 2–3-gpm flow restrictor is recommend- ed for a two-stage counterflow rinse tank. If a minimum water pressure exists in the water inlet line (about 20 lbs/in 2 is considered mini- mum), the water flow into a rinse tank should not vary, although the water pressure will most likely vary. Flow restrictors are not ad- justable after they are installed. By providing pipe union fittings both up and downstream from the flow restrictor fitting, the flow rate can be changed if necessary. We recommend installing a flexible orifice- type flow restrictor or an automated control system to maintain and monitor the inlet water flow rate to every rinse tank. Existing conduc - tivity sensors, if any, should be removed, unless they can be calibrated at least once per week. When rinse recycling or recovery equipment is to be specified, a designer must be aware of the maximum flow rate. The installation of a flow restrictor provides that assurance (if all rinse water passes through that restrictor). Reuse of Rinse Water in the Electroless Copper Process Chemical suppliers occasionally recommend the reuse of rinse water within an electroless copper line. This may require the use of pumps to transfer water from one rinse tank to an- other. As one alternative to reduce the volume of waste, we recommend that at least one of the possibilities noted in Figure 1 be tested at each facility in the short term to determine the effect. This opportunity should be discussed with the technical representatives of the chem- istry supplier for that process line before the final decision is made to implement this task. The critical element is not to recycle rinse wa- ter upstream around the catalyst. It would be useful to have a detailed chemical analysis of the rinse water before having discussions with your chemical supplier. Dragout Reduction by Using a Deionized Water Mist Spray as the Panels Are Withdrawn From a Heated Bath This should be evaluated for, at least, the brown oxide bath and the etchback bath. Installing specially designed rollers and air knives to reduce the dragout from panels being etched and following the dragout still rinse station should be considered. Some plat - ing rack designs allow the panels to be tilted to one side and the panel mounted at an an- gle (relative to the horizontal) to allow better solution drainage off the panel. This will de- crease the dragout. Eliminate the Need to Strip Racks on the Acid Copper and Tin-lead Line By using plastic-coated racks, only the tips and contactors (that electrically and physically connect and support the panel to the carrying rack), having exposed conductive metal, must be stripped. We recommend evaluating the use of racks with disposable contactors. That would eliminate the need to strip the racks and could eliminate the use of nitric acid. These types of racks are commercially available and should be addressed in the short term. Increase the Amount of Agitation in the Immersion Rinse Tanks Agitation between the panels and the rinse water can be performed either by moving the panels in water or by creating turbulence in the rinse water. Since most PCB factories operate hand rack lines, operators could easily move workpieces manually by moving the rack.