Issue link: https://iconnect007.uberflip.com/i/1533339
MARCH 2025 I PCB007 MAGAZINE 63 the copper that the resist he was using at the time absolutely did not like. As the industry evolved in the 1990s, other weaknesses in using mechanical scrubbing as surface preparation for resist adhesion became apparent. Scrubbing hardened the copper, making it more brittle with a tendency to crack, which caused problems with flexible circuits. As the number of layers in multilayer boards increased, the substrates became thin- ner. Engineers discovered the scrubbing pro- cess stretched the dimensions of these thinner substrates in the direction of travel through the scrubber, so it became more difficult to cor- rectly line up the layers properly in the mul- tilayer lamination process, especially as the layer count got higher. As a result, mechani- cal scrubbers gradually fell out of favor, and chemical cleaning became the surface prep of choice. Between 1975 and 1985, we sold more than 600 mechanical scrubbers. Between 2014 and 2024, we sold six. Dry films and laminates have improved since those early days. Now, I prefer to get reverse- treated foils (RTF) for testing, which are lami- nated with the rough side out, something that wouldn't have been considered in the early 70s. is provides an excellent roughened sur- face profile for resist adhesion and is worth the extra cost because no micro-etch is needed, just a simple acidic cleaner to remove any oxide or conversion layers. e panel is then ready to laminate, making it easier than even the old mechanical scrubber. ese days we receive very few questions on surface prep for resist adhesion, so maybe we finally have a handle on this type of surface prep. PCB007 Don Ball is a process engineer at Chemcut. To read past columns or contact Ball, click here.