Issue link: https://iconnect007.uberflip.com/i/1530610
48 PCB007 MAGAZINE I DECEMBER 2024 the same spray pressure compared to the lower flow rate nozzle, but not much change in etch quality. is is because, while the droplet sizes get bigger for a higher impact force, the flow rate has also increased, leading to a deeper etchant puddle. e higher impact force verses the deeper puddle tend to cancel each other out. Some have thought that changing to a lower flow rate nozzle with a smaller droplet size might be an advantage as the spaces between the lines get tighter and tighter. A smaller droplet size might be better at getting into smaller spaces. A 0.75 gpm (2.8 lpm), 70° cone spraying 40 psi (2.7 bar) has an average drop- let size of around 950 µm compared to an aver- age droplet size of about 1200 µm for a 1.5 gpm (5.7 lpm), 70° cone nozzle at the same pressure. Yes, the droplet size is smaller but still gigan- tic compared to a 50 µm space between circuit lines, so there probably won't be much effect on etch quality. Also, the relationship between flow rate and droplet size still applies. Lower flow rates mean less puddle but with smaller droplet sizes and less impact force that tend to cancel each other out. Cone nozzles vs. fan nozzles for etching has always been a favorite subject for debate ever since I started in the business in 1974. e argument in favor of fan nozzles has always been that they have a higher impact because the spray is directed at a much smaller area. Because of this, they should be more effi- cient at getting fresh etch solu- tion to the panel surface through the puddle and therefore give a better etch quality. A fan nozzle does have a higher impact/unit area at the surface, but the area of impact is long and narrow, so each part of the panel spends a relatively short time under the direct impact. e impact/unit area for the cone nozzle is much less but applied for a longer period of time over a much larger area. If you multiply the impact/unit area by the total area of the spray coverage for each nozzle with the same flow rate and spray angle, you will find that the total spray force is about the same. Other variables must be considered in spray design, so the best spray design for cone noz- zles is different from that for fan nozzles. Given the proper spray system design, I have never seen any difference in etch quality between cone and fan nozzles. e whole source of debate arose because fan nozzles don't work as well in a system designed for cone nozzles and vice versa. In conclusion, you probably won't see much improvement in etch quality by just changing nozzles. However, it's a relatively easy change to make so there is no harm in trying different nozzle combinations if you wish to satisfy your curiosity. PCB007 Don Ball is a process engineer at Chemcut. To read past columns or contact Ball, click here.