Issue link: https://iconnect007.uberflip.com/i/1530610
44 PCB007 MAGAZINE I DECEMBER 2024 Whenever the need to improve etch qual- ity due to tightening customer specifications arises, the inevitable question asked early on is, "Will going to a different type of nozzle or nozzle flow rate make my etch quality bet- ter?" Unfortunately, the answer is most likely, "Probably not." (Sorry, folks.) So, why not? e fluid dynamics of flow on a horizontal plate with turbulence is extremely complicated and spraying hot acid at high velocity onto a moving horizontal plate is about as turbulent as it gets. e main problem with a horizon- tal etcher is that the etchant is sprayed onto the top surface of the panel faster than it can flow off, so the spray doesn't actually hit the surface of the panel—it hits the top of the pud- dle of etchant formed by the spray. e unifor- mity of the etch rate is affected by the thick- ness and velocity of the puddle. e puddle is thickest and moves the slowest in the cen- ter of the panel and gets gradually thinner and faster as the edges of the panel are approached. As a result, the etch rate is lower in the mid- dle of the panel and faster around the edges, and etched line widths can vary significantly between the edges and center of a panel. is is Can Changing Spray Nozzles Improve My Etch Quality? The Chemical Connection Feature Column by Don Ball, CHEMCUT