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AUGUST 2019 I PCB007 MAGAZINE 47 connection that will limit the rate of rinse wa- ter used for that application. It is critical that the flow restrictor, if available, not be bypassed under any condition. A process schematic of a typical etching machine and our recommendation for a new machine are included in Figure 1. The con- figuration used to reduce the flow and copper dragout in the recommended machine will re- quire a longer machine than the typical etch- ing machine. We recommend that a four-stage replenisher module be used to wash the panels with fresh etchant to remove about 99.9% of the copper before the panels enter the follow- ing rinse chamber. In Figure 1, we recommend the use of an- other four-stage module to be used as a rinse chamber following the four-stage replenisher module. This is a little unusual. In some cases, this rinse will be sent to an industrial waste pretreatment system containing a high concen- tration of ammonia. Ammonia in the incoming rinse may cause an occasional problem with that system. Our objective is to reduce the volume of this rinse water to a "drumable or truckable" volume so that this waste could be batch treated. The use of a four-stage module should meet that objective. As an alternative to the four-stage rinse mod- ule following the four-stage replenisher mod- ule, we recommend the use of a recirculating rinse module in series with a single-stage rinse module, as shown at the end of the proposed etching machine line in Figure 1. This combi- nation is used to minimize the flow from any conveyorized rinse system (where the rinse from the single station becomes the source of water for the recirculating module). This is an example of a counterflow rinse design. Conveyorized equipment can also be used for, at least, inner layer and outer layer pho- toresist stripping, inner layer and outer layer Figure 1: Modifications to inner/outer panel etching equipment.

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