Issue link: https://iconnect007.uberflip.com/i/1533339
62 PCB007 MAGAZINE I MARCH 2025 e side against the surface of the roller was smooth and shiny while the side away from the roller was rough. e foil was laminated to the substrate with the rough side facing down to provide more surface area for better adhe- sion to the substrate. is reduced the possibil- ity of the copper delaminating because of heat or environmental conditions, which was not uncommon. Most surface finishing was con- cerned with preparing the smooth side of the copper for maximum adhesion of fully aque- ous dry film resists. e objective of the surface prep was to remove organics and oxides from the surface that would interfere with the resist adhesion as well as to roughen the smooth surface of the copper to provide more surface area for adhe- sion. e most common way to accomplish this task was with mechanical scrubbers. Sev- eral companies provided conveyorized scrub- bers using rotating abrasive brushes with either silicon carbide or aluminum oxide, mak- ing it possible to process many circuit panels in a short amount of time. is le a bright sur- face visibly roughened by the abrasive. Alter- natives were pumice scrubbers using a volca- nic pumice slurry to scrub the copper surface, and chemical cleaning using a two-step pro- cess comprising a basic cleaning solution like a mild sodium hydroxide to remove any organ- ics, followed by an acid rinse (typically a 3–5% sulfuric acid solution) to neutralize the basic cleaner, remove any oxides, and lightly roughen the copper surface. e pumice scrubbers le the best surface for resist, but with an abrasive slurry splashing around inside, the machines tended to self-destruct. ey also sometimes le pumice particles embedded in the cop- per, which led to rejects down the line. Chemi- cal cleaning lines were longer than mechanical scrubbers and required chemical maintenance, which many wished to avoid, so mechani- cal scrubbers became the surface preparation method of choice in the 1970s. Panels came out of a mechanical scrubber looking bright, but were they really clean? One problem encountered was the abrasive particles were contained in a nylon matrix, either in a Scotch-Brite type form or in a bris- tle brush form. Under the right brush pressure, only the abrasive came in contact with the cop- per. However, too much pressure could bring the nylon in contact and smear on the copper, causing resist adhesion problems. "How clean is clean?" was a constant refrain at PCMI meet- ings in the 70s and early 80s. us, the water break test was devised, the bane of my existence. e theory was that aer cleaning, the copper surface should be able to retain any water on the surface as a thin sheet for 30 seconds before breaking into beads. If this happened, the panel was clean and ready for resist lamination. Or was it? Most of the time, that assumption was correct but other factors affect water break, so a good water break test didn't necessarily mean the surface was ideal for resist adhesion. For example, one customer complained he was getting poor resist adhesion despite water break tests that showed the water film was lasting over a minute. It turned out he was adding detergent (Dawn) to his rinse water to guarantee a good water break test. is le a slightly basic surface on