Issue link: https://iconnect007.uberflip.com/i/1417991
110 DESIGN007 MAGAZINE I OCTOBER 2021 series of clear photographs and schematics to describe three main categories: 1. Pure flex circuits, whether simple single- sided or complex multilayer, were constructed from all-flexible materials, copper-clad substrates, adhesives and bond-plies, with laminated polyimide coverlayers. In certain instances, liquid photoimageable solder mask could be used as an alternative. 2. Flex with stiffeners to add rigidity in certain areas. Different stiffening materi- als were used for different applications, temporary or permanent, in component- assembly areas or to reinforce connectors. 3. Rigid-flex, a combination of flexible and rigid materials, with flex layers incorpo- rated within the rigid areas enabling the elimination of cables and connectors to achieve more compact packaging and higher reliability. In response to Johnson's enquiry about typi- cal applications, Lackey declared that there was an unlimited number, from simple con- necting ribbons to complex devices with 90- and 180-degree turns enabling smaller-volume higher-reliability packaging. Regarding criteria for successful design and reliability, Lackey drew a distinction between static and dynamic flex, the former being bent to fit, the latter being subject to continuous motion. It was essential to recognise the actual mechanical performance requirement in a particular applica- tion and to understand bend radius in relation to the thickness of the flexible materials and the geometry and orientation of the conductors. e contribution of the mechanical designer was as fundamental as that of the electronics designer, and both could benefit enormously by involving the PCB fabricator as early as possible in the design cycle. e fabricator could advise on the choice and suitability of materials and constructions, as well as the benefits of details like cross-hatched ground planes and knowing how to properly model characteristic imped- ance. "A lot of factors to balance: here's what we can do to make this work." Lackey quoted case histories and examples of improving manufac- turing yield and reliability while saving on over- all cost. His opinions were echoed in Vardya's closing words: "If the viewer takes nothing else away from this discussion, it is to really involve your PCB fabricator right from the word 'Go.' e most important thing any designer can do in designing a flex circuit is to work with the PCB fabricator. ey will save you tons of time and you will be much better off for having done that." Finally, in answer to Johnson's question about critical things for me to keep in mind, Lackey advised giving careful consideration to what IPC classification was required, avoiding specifying name-brand material by referring to IPC slash- sheets and providing clear fabrication notes, particularly if quick turnaround was needed. In my opinion, taking the time to view this RealTime with… video is 15 minutes well- spent; excellent information professionally presented, and the opportunity to submit fur- ther questions by email. ank you ASC. To view RealTime with … American Standard Circuits: Flex and Rigid-Flex PCBs, click here. FLEX007 Pete Starkey is an I-Connect007 technical editor. The most important thing any designer can do in designing a flex circuit is to work with the PCB fabricator.