Issue link: https://iconnect007.uberflip.com/i/1379105
JUNE 2021 I SMT007 MAGAZINE 13 remove that oxide, there's a little haircut going on in there. You're shaving it ever so slightly. Johnson: It was silver. Now it's silver oxide. And we're taking it away. Forsythe: Most metals oxidize. Some things, like aluminum, make a very thin oxide layer and then stop because it doesn't compound. For example, aerospace people with their alu- minum—when they clean, they don't want to remove that oxide layer because it will change the dimensions on them. ey leave the oxide layer. Of course, they're not soldering. ey're screwing things together, mostly. Oxidation varies. For example, ferrous oxide (more oen known as rust) doesn't stop. Once you start to rust, it's on the way until all the iron converts to rust. Aluminum is on the other end of the spectrum. Yes, silver tends to tarnish, but sterling silver doesn't disappear. Now, once you remove that oxide layer, what happens next? It starts forming again. at's why we go through the soldering process. What are we doing? We're removing that oxide while simultane- ously forming our joint. You're essentially sol- dering with no surface effect, and some met- als take longer than others. In flash rusting you can remove all the rust. It gets wet. e whole thing will rapidly turn into rust again. So, removing that oxide layer is a surface prep step. It's repeated on purpose in jillions of processes across many industries, but we just never called it that. Johnson: Nowadays, they use water-soluble so that it is easily cleaned up. uct must function on demand or lives could be at risk. Cleaning doesn't cost that much, and it helps their reliability. ere is a range in between those extremes. You could make a case that if I'm cleaning the part, I'm preparing it for that coating, and it's true, but nobody talks about that because most people that conformal coat don't clean. at would confuse people if we talked about that. We operate in multiple industries. We oper- ate in the metal side of the aerospace and auto- motive industries, and the general metal fabri- cation; they each come with their own different language. What we call batch cleaners, they call cabinet washers. Why do they do that? I have no idea why, but they do. It's a thing. ink of our smartphones. ey used to be free in America. Sign up for two years and the phone was free. at's no longer the case. With all that great utility and these days a relatively high price, we have expectations. We want it to last longer. We don't want it to fail. Well, now maybe phones are moving on that curve from nuisance to maybe not life-threatening, and that is generally more positive for the clean- ing guy. e good news is there's lots of good technology out there that can solve these prob- lems. ere are good techniques to measure cleanliness and deliver it. We try to be deeply involved in all those areas, and that's why life is fun these days. Johnson: ere may be one place where it is, in fact, surface prep at the assembler side. For example, if boards were built with immersion silver. Now we're managing tarnish. at's not necessarily cleaning, or is it? Forsythe: Let's back up a step. You could say that simply using flux is surface prep because what the flux is there to do is to remove the oxides from the metal involved in making the joint. at's what flux does. Flux is an oxide remover. What you just described with the sil- ver that tarnished, what are we doing? We're talking about removing the oxide. When we Once you start to rust, it's on the way until all the iron converts to rust.