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8 SMT007 MAGAZINE I JUNE 2021 Nolan's Notes by Nolan Johnson, I-CONNECT007 If It Don't Stink… My uncles had a phrase, "If it don't stink, don't stir it." It was just one of the euphe- misms they brought back from the Navy… or maybe the Army… could have been the National Guard, though. You see, coming out of high school, they had each picked a differ- ent branch to enlist. All three of them served during the Vietnam era, though none of them saw action. My Army uncle stayed stateside; my Navy uncle cruised with the Mediterra- nean fleet; my National Guard uncle was stationed in Puerto Rico. By the time I was old enough to really take in their conversations, all the salty turns of phrase from their sep- arate experiences had mixed into a vernacular unique to them and them alone. I look back on it now, and real- ize it was part of their bond with each other. at one phrase, however, about leaving things that work well enough alone, has always been a personal favorite. In my youth, that comment evoked images of a slimy, grimy 55-gallon barrel full of sludge with a threateningly crusty-looking layer seal- ing in all the putrid nas- tiness underneath. As a young boy, I could relate to the urge to poke that crust with a stick and explore deeper. And that phrase kept coming to mind as we compiled this issue on clean- ing, surface prep, and coatings. Not so much the image I had as a child, thankfully. We're leading off this issue with a detailed discus- sion with Tom Forsythe of KYZEN, who clar- ifies the differences between cleaning and sur- face preparation. ey are, he says, different in some subtle but significant ways. For exam- ple, in our context, cleaning can be defined as the non-transformative removal of contaminants from the printed cir- cuit board. Surface preparation, on the other hand, is doing something transformative to the surface to enable further processing. In other words, etching, polishing, or hot air leveling is surface prepa- ration, not cleaning. Even though they may remove contaminants, they're not cleaning. Part of Tom's con- versation also shines up the lens regarding "no clean" solder and flux products. In some applications, "no clean" is sufficient and using a no-clean protocol increases yields; in other cases, manu- facturing simply must clean or risk other contamination issues. In this case, "don't stir it" changes depending upon the specifics. Whether it's cleaning or sur- face preparation, the purpose is

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