Issue link: https://iconnect007.uberflip.com/i/1002143
50 PCB007 MAGAZINE I JULY 2018 Meeker: Well, it goes in horizontal; the pan- els come off a clean line, so they're horizon- tal. We take them horizontal, we center them, then we make them vertical, so we can do dou- ble-sided coating on them, and then we dry them vertically, because that really saves a lot of space. You can have the panels on inch-and- a-half centers, or 38-millimeter centers, and then they come back out to the next process, and they get turned back to horizontal, where they're either racked or stacked or handled. Goldman: And everything from back panels, like you said, all the way down to extremely thin flex. Is that the biggest challenge? Meeker: Correct. Kojima: One of the problems with processing materials such as flexible circuits is that we can print them okay, but the drying usually would be a problem because they're so thin. And when you hang the panel inside, all of them touch each other. Circuit Automation in- vented this device called ASA, which is an an- ti-sway attachment. It attaches to each circuit board at the bottom inside the oven where the air is blowing and the panels tend to sway in the heated air. The ASAs add mass plus a phys- ical barrier, preventing the panels from touch- ing each other. Remember, the panels are wet on both sides, so they cannot touch. That's one of the unique features we have with the sys- tem, and it's what makes this machine capable of running from thick panels to very thin pan- els, like flexible circuit boards. It can go down to about a one-mil thick panel. Goldman: I know GreenSource's lot size is one, at least theoretically. But, to change between a matte and a shiny, or a different solder mask, how automated is that process? Kojima: It's all controlled by a server, and the only thing you need to do is enter the dimen- sion of the panel. Of course, the screen open- ing needs to be adjusted according to the pan- el size. That's the only manual process you'll probably need to do to set up the machine. Meeker: But changing ink is still very manual. Fortunately, at GreenSource, they're only going to use one ink. Because otherwise, to switch back and forth, you then have to change screens and squeegees. We had an automat- ic ink filler, but their plan is to go with one mask at a time, so we don't have the challenge of figuring out how to automatically switch all the wetted parts, which would be difficult to do. Matties: That would be difficult. From a circuit board design point of view, are there any con- siderations PCB design- ers should have regard- ing solder mask? Lindland: One thing that people struggle with is hole size, aspect ratio, and dam size, in terms of clearing. The oth- er thing that's difficult Figure 2: Oven and unloader.