Issue link: https://iconnect007.uberflip.com/i/1507356
SEPTEMBER 2023 I DESIGN007 MAGAZINE 13 conditions, such as size, to tell you whether a rigid-flex is practical. But it may be too complicated yet for that kind of a tradeoff costing program. Exactly. at's why I created a class to teach it. For example, whenever I bend a material of some thickness around a radius, the inside radius of the band is put under compressive load and the outside radius of the band is put under tension or tensile load. e compressive load is now hardening and forcing my atoms closer together, and if I exceed the breaking strength, the tensile loads can actually tear the copper like taffy. So, we want to minimize the stresses on those bending points. Whether we're doing single-sided or double-sided flex cores, each flex core has its own coverlay and protection and I don't bond them together. e fabrica- tor can extend the length of each subsequent layer of flex. We need to know how the bend is going to be, such that when each layer bends around that corner, let's say 90 degrees, each one is under the minimal amount of stress and we don't have added incurred stress. Yes, there are multiple different stackup issues we have to deal with there. Shaughnessy: It sounds like every rigid-flex is almost a custom project every time, and communication with the fabricator is really important. You're right. One of the mantras that I say in all of my classes is, "Your fabricator is your friend." I say with all designs, even if it's a rigid design you've done 100 times, always double- check with your fabricator, because there might be something subtle in this design that he can help you with. Aer you build your stackup, you build your controlled impedance, then get your fabricator to sign off on it to make sure that all of their processes, their pro- cess controls, and process variations are taken into consideration. at way you improve your success rate, your yield, and first-pass quality of your board design. Shaughnessy: I see that you spend a lot of time talking about manufacturing in your class. What would a rigid board designer need to know about manufacturing processes for rigid-flex? For rigid-flex, there are quite a number of touch labor steps that you don't normally have in pure rigid. ink about manufacturing a rigid panel, 18 x 24 inches. ey do all the imaging, and then they come back aer the fact and cut the individual boards. With rigid-flex, in the area where the flex ribbon will be, they have to pre-machine that out of the rigid panels and have an opening there, before the flex is inte- grated into the stackup. You have a technician who's literally going by touch labor, applying a piece of coverlay material that will be either machined or laser-cut off aer it's laminated together. ere are so many more touch labor steps in rigid-flex than in pure rigid fab. Nolan Johnson: This has been very educa- tional for me. I spent a lot of time at Sunstone Circuits working with rigid boards, but not Kris Moyer