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54 PCB007 MAGAZINE I AUGUST 2022 ing has come to a nearly perfect etch factor was when the PERI-etch process was discovered. e PERI-etch process, also known as powder- less etching, was a process that was developed by the Platemakers Educational and Research Institute (PERI) to improve the manufacturing process of copper letterpress printing plates 1 . is process consisted of an additive to an etching solution that would form a film to pro- tect the sidewalls to prevent them from being etched. Powderless etching gave some promis- ing results of sidewalls from nearly vertical to 30–40 degrees from vertical with no undercut- ting. Although it gave some promising results for the plate-making industry, some draw- backs limited its wide use in the PCB industry. It was primarily not adopted in PCB produc- tion because the additive was meant to work in ferric chloride (FeCl 3 ). Ferric chloride is an etchant that is some- times used for PCB fabrication, but it is not oen used because the regeneration chemistry is inefficient for large-scale PCB production. Since ferric chloride is based on iron, it is best suited for iron-based metals because it makes regeneration and waste treatment simple and efficient. With copper etching, regeneration of the ferric chloride would not be able to sustain a steady etch rate. As copper content accumu- lates in the ferric chloride, etch rates decline even with regeneration. Once regeneration becomes ineffective in a large-scale etch pro- cess, like PCB fabrication, the profitability of the etch process quickly declines. Since regen- eration cannot be performed efficiently, there was never enough reason to justify using pow- derless etching in large-scale PCB production. What Could Ideal Etch Factors Mean for SAP? If somehow you could get both the regener- ation of cupric chloride and the vertical side- walls of powderless ferric chloride etching, I think we would see a dramatic change in the PCB industry. Currently, using the semi-addi- tive process (SAP) is the most practical way to obtain fine features. However, if sideways etch can be efficiently inhibited in the etchants we use today (cupric chloride and alkaline cupric chloride), SAP may not even be necessary in most cases. If you are unfamiliar with SAP, it can be summarized as a process where a cop- per-plated panel undergoes a selective plat- ing process to form desired features on top of the copper that was already present. Once the features are plated onto the base copper, that panel gets etched to remove the base copper, thus leaving behind only the features that were added. Finding a way around SAP would mean skipping many long and costly steps in the PCB fabrication process. Without requiring SAP to obtain fine features, PCB shops would require less plating equipment and fewer resources to perform plating (i.e., chemicals, trained per- sonnel, time to plate, and operating space). Conclusion Although this would be a major game changer in the PCB industry, we seem to be far from obtaining a practical solution with ideal etch factors. e best etch factor with a PCB etchant is the 4:1 ratio you get from maintain- ing alkaline cupric chloride in its top condi- tion. It begs the question of whether it is possi- ble for copper etching to advance so much that you can get both efficient regeneration capabil- ities and near perfect etch factors. In the past, we have gotten close to obtaining ideal etch factors, but we did not have the right etchant. Perhaps we could get there with new efforts in chemistry research. If obtaining this quality of etchant is possible, could it ever be enough to replace SAP? PCB007 References 1. "Member's Handbook," Platemakers Educa- tional and Research Institute Inc. (Print) Christopher Bonsell is a chemical process engineer at Chemcut. To read past columns, click here.