Issue link: https://iconnect007.uberflip.com/i/1519075
42 PCB007 MAGAZINE I APRIL 2024 I have a three-stage cascade rinse following a two-stage flood rinse on my cupric etcher. Each stage of the cascade rinse has an upper and lower spray tube. Each spray tube has 11 nozzles, each with a flow rate of 0.5 gallons per minute (gpm) at 40 psi for a total flow of 5.5 gpm per spray tube or 11 gpm for the stage. By using the flood rinse to remove most of the dragged-out etchant from the panel sur- face before the cascade rinse, I can reduce the amount of freshwater flow into the third stage from 11 gpm to about 2 gpm and still keep the water in the sump clean enough to provide a good rinse. So far, with the use of a chiller for the cooling coil and a two-stage cascaded flood rinse fol- lowed by a three-stage cascaded water rinse, we have been able to reduce the water usage in the etch system to about 2 to 3 gpm. With the flood rinse removing most of the drag-out and returning it to the etcher, and by using that water for specific grav- ity control, the contamina- tion level in the first stage of the water rinse levels out at a few hundred parts-per-million of copper (or iron for a ferric chloride etcher), down from several thousand parts-per-million. is is very treat- able and shouldn't overwhelm most treatment systems. For those with cupric chloride etchers, even further water savings are possible. e flow and copper levels in the first stage are low enough that a small ion exchange column can be added to the rinse. Water from the first stage goes through the ion exchange to remove the copper and is returned to the last stage of the cascade rinse. In this way, the water usage of the etcher is reduced to practically zero (you'll need a few gallons per hour of new water due to drag-out and evaporation) and the load on waste treatment systems is greatly reduced. A 1,000 parts per million of copper from 10 gal- lons of water than it is to remove 10 parts per million of copper from 1,000 gallons of water. More water savings can be achieved by using some of the water from the contaminated first stage for specific gravity control of the etchant instead of sending it all to waste treatment. How many stages of cascade rinse do you need? Tests have shown that a four-stage rinse is plenty. Aer four stages, you run into the law of diminishing returns where you spend a lot more effort for far fewer gains. For most, a three-stage rinse is more than adequate and doesn't take up much more space than a one- time rinse. Alkaline etchers have an advantage over cupric chlo- ride and ferric chloride etch- ers in that they have a flood rinse with replenisher solution right aer the etcher. e flood rinse is a low-pressure, recir- culated rinse that floods the surface of the panel with a replenisher solution to remove contaminants. is solution is then used for specific gravity and pH control in the etcher. By doing this, most of the etchant dragout is washed off the surface of the panel and put back in the etcher, which is where it belongs. ere is no reason you can't use this princi- ple for cupric and ferric etchers as well. A two- stage flood rinse using water instead of replen- isher solution will wash most of the etchant dragout off the panel surface and put most of it back in the etcher by using this water for spe- cific gravity control. An automatic water add to the second stage will replace the water used from the first stage for specific gravity control. Using this type of flood rinse will reduce the amount of etchant dragout going to your water rinse by about 90%. In turn, this allows even more water-saving options in that water rinse. How many stages of cascade rinse do you need? Tests have shown that a four-stage rinse is plenty.