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52 PCB007 MAGAZINE I AUGUST 2019 However, the effectiveness of this depends on the cooperation of the operator. Agitating the rinse tank by using oil-free low-pressure air (from a blower, not an air compressor) is the most efficient method for creating effective turbulence during rins - ing operations. This type of agitation can be performed by pumping filtered air into the bottom of a rinse tank through a pipe dis- tributor (air sparger). Air volumes typically recommended are 3–4 cubic foot per minute per square foot of rinse tank surface area. The delivered pressure should be about 1 psi for every 21 inches of liquid depth. Not ev - ery rinse tank should be agitated. There may be selected rinses that will produce excessive foam when agitated. Care should be used be- fore agitating rinse tanks. Dragout Reduction Bath dragout reduction can reduce recovery equipment and operating costs. Withdraw the panels slowly to allow ample drainage. The faster an item is removed from a process bath, the thicker the liquid film is on the panel, and the greater the dragout volume will be. The removal of racks containing panels is opera- tor-dependent (unless automated hoists are used); therefore, the amount of dragout from each bath will be operator-dependent. The time allowed for drainage can be inadequate if the operator is rushed to remove the rack from the process bath and place it in the rinse tank. However, the installation of a rail above the process tank and the requirement that the operator place all racks on the rail for at least 10 seconds will reduce the dragout. However, there are a few operations where concern about oxidization of the panel will not allow this method to be used to reduce the dra- gout. Etcher Design In the last section, we described the prop- er design for an etcher. In that case, a four- stage replenisher module reduced the dragout of etchant contaminated with copper more ef- ficiently than a two-stage replenisher module. However, the four-stage (or even a three-stage) replenisher module requires more floor space than a two- or a single-stage module. If etchant recycling is contemplated, the etcher itself may be redesigned (eliminating the need for a re- plenisher module). Increasing Dwell Time Holding the panels over the process bath re- duces the dragout. One can accomplish this ei- ther by slowly withdrawing the panels from a process bath or by installing a rigid supporting device to hang the rack with the panel over the process tank, for a period, before proceeding to the rinse tank. Use of Automated Control and Wet Processing Systems Computerized process control systems can be used for panel handling and process bath monitoring to prevent unexpected decomposi- tion of a process bath, controlled rinse flow, and uniform panel withdrawal from each pro- cess bath. Since these systems require a sig- nificant capital expense for initial installation, only large PCB companies will incorporate this alternative into their manufacturing process. Drip Pans A drip pan (also called a drain board) is one of the simplest methods for dragout re- covery. The drip pan will capture drips of pro- cess solution from racks and panels as these are transferred between tanks. Drip pans not only save chemicals and reduce rinse water re- quirements, but they also improve housekeep- ing by keeping the floor dry. We also stress the need for double containment of all plumbing Not every rinse tank should be agitated. There may be selected rinses that will produce excessive foam when agitated.