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108 PCB007 MAGAZINE I NOVEMBER 2020 Introduction Sure, etching of copper foil has been in ex- istence since before through-holes were me- chanically drilled. However, as circuit density has evolved into finer and finer lines and spac- es, the mechanical and chemical aspects of etching copper have evolved as well. The pur- pose of this edition of "Trouble in Your Tank" is to provide an overview of the inner layer and outer layer etching processes. This will include chemical and mechanical aspects of each pro- cess, different chemical formulations involved, and other unique aspects of each. The Etching Process Most process problems that appear during the etching stage of printed circuit produc- tion can be traced to one of two general ar- eas. The most common and obvious cause of etching problems is the etching equipment it- A Process Engineer's Guide to Final Etching, Part 1 self, either through equipment malfunctioning or other issues, such as temperature controls and specific gravity measurement malfunction. The second most common cause of problems during the etching step are issues that occur during prior processing steps but are not de- tected until the boards are processed through the etcher. An example would be resist scum left on the board during the stripping of a plat- ing resist, which can cause uneven etching to occur. Or the defect—such as excessive under- cut, resist lifting, darkening, or etch-out of the tin etch resist—can be attributed to chemical factors (pH control, operating temperature) or other parameters, such as surface preparation, handling, and exposure/development of the photoresist. Here, I will outline some of the problems that can occur during the etching process with the most probable cause(s) and actions that can Trouble in Your Tank by Michael Carano, RBP CHEMICAL TECHNOLOGY