Issue link: https://iconnect007.uberflip.com/i/989774
JUNE 2018 I SMT007 MAGAZINE 15 out the circuit, some of the first questions we want to ask them is what the application is, the envi- ronment, what the final config- uration of the circuit is going to look like, and how it is going to fit inside the box or the device," says Moody. "If it has circuits, we assume that it's going to trans- fer something from one end to another; it could have different height variation, it's going to start at a lower section of the box and fold and mold its way up to a higher section and understand where those aspects of the design are going to take place, where the bends are going to occur. And there are just some things you need to avoid. You can't put a component in an area of the flex circuit—even though we all talk about it being flexible—you still can't or shouldn't put a component in an area where you want to bend the circuit. "Oftentimes, the engineers come in with preconceived notions about placement, 'Well, no, it's got to go here because I need to access something now that's over here.' Well guys, you're going to have to rethink that idea, because it isn't going to last. That's really the aspect, we try to understand the applica- tion and what that final configuration is going to look like so that we can advise where you want to put stiffeners on the flex if it's just flex, or where you're going to put your components, or at least the keep-out areas where you can't or shouldn't put components." "There's one example that we ran across where the customer specified a stiffener close to a printer pad area for surface-mount. The customer would require thermal set, and that look like or how you're going to be able to fulfill it. Engineers come in with an idea; it's a conglomer- ation of a mechanical guy, and an electrical guy, and somebody else sitting down there trying to figure out what they want, and they've already selected the components, and now what to back-fill the design to meet the component requirement. And there are occa- sions when a component's been chosen that just is going to end up being problematic for the design that they're doing at the assembly aspect. It's hard to talk them out of that, so in general, I don't think there's enough empha- sis being placed on the final assembly require- ments in the initial stage of the design." Their advice to the designers? For Wettermann, it's this: "Consider how you're going to put this thing together. Somebody who is what we jokingly call the "mouseketeer", the design engineer sitting at their workstation designing a product, whether it's a wearable or a rigid-flex part that's going to go on a missile system, they likely will not have any "how-to-put-it-together" experi- ence. It's rare that this experience exists at the design level in flex. Once in a while, a consult- ing firm will get involved with the design and they'll have some experience in how the flex and rigid-flex goes together, so we invite them into the process and show them what the prob- lem is. We want to show and tell them about some of the difficulties of how the assembly is actually done. I think helps put them on the learning curve a little faster. Whether it's rigid or flex, there's a lot of people in the design community have design expertise. That's why people like David and I exist, to help put their products together." Moody adds, "I would completely agree. When we're talking to some- body and they haven't yet laid Bob Wettermann