Issue link: https://iconnect007.uberflip.com/i/1073397
24 FLEX007 MAGAZINE I JANUARY 2019 multidimensional space they envisioned and were attempting to explain. That function of envisioning the not-always- easily perceived is summoned here, but for a much less complex purpose than defining space and time. My specific purpose is, "How to tease a three-dimensional circuit from a two-dimensional copper-clad panel and do so reliably?" That should be job one in nearly every flex-circuit design. So how does one carry out the task and make 2D into 3D reliably? Here are some suggestions. Be warned in advance that there are no pat answers to the question posed. Each design inevitably has its own set of requirements and challenges, but there are a few steps that are common: 1. Define the end-product shape, size, and volume: This is the primary constraint for the design—the canvas for the painting. An individual or team has the job of defining the shape and volume of the product. Often, that job is constrained in some manner either by limitations of space where the electronics are going to be put to use or by a mandate from marketing or management. Steve Jobs, it has been said, was intimately involved in the design of the iPod and iPhone in terms of the size and shape and other design features along with its functionality. He did not exe - cute the design and manufacture by himself, however. He created a significant challenge for designers, and flexible circuits were vital to achieving the goal. In fact, the use of flex - ible circuits was arguably crucial to making it happen as they were indispensable to the interconnection of the various high-density connecting elements of the electronics in the product (Figures 1 and 2). 2. Identify all components and make selections carefully: Many years ago while working for a major aerospace company, I was part of a group tasked with making a circuit that needed to fit in a very small predefined space. To say that it was difficult was to understate the case. The devices chosen for use with the design were rated for reliability, but they were very large. It was as if someone had measured the volume of each of the individual components and their collective volume, and, also knowing the volume of the space available and seeing they matched, they decided it was possible. It wasn't quite that bad but it seemed that way. Moreover, the design chosen was a rigid-flex, which was not very common at the time and the processing was not well understood. The product was built and had several overlapping flex arms designed to interconnect to bulkhead connectors inside the space. Trying to assemble the circuit was a nightmare, and because there was little additional length on the arms, many of the circuits broke during the assembly process. It was eventually solved by a combination of selecting different components and getting some relief on the size of the box by making it slightly larger. The takeaway is that the early decisions can have a knock-on effect of significance. 3. Use paper doll mockups of the proposed layout: Available CAD tools can lay out circuit patterns and allow them to be modeled for interferences in the application. However, a simpler method—at least for first-pass approx- Figure 1: View of an iPhone's internal electronic elements layout upon opening the device (folding interconnections between the halves enabled by flex circuits). (Source: Tech Insights)