New-Tech Europe Magazine | Q1 2020

Manufacturing magic takes multilayer flexible printed circuits to extraordinary lengths

By Philip Johnston, CEO, Trackwise

Until few companies could manufacture flexible printed circuits (FPCs) of more than a couple of metres in length. However, new manufacturing techniques now enable the design and production of multilayer FPCs of unlimited length. This is opening up a world of new applications that previously had to be served using conventional and bulky wire harnesses. From a concept first postulated by inventor Albert Hanson in patents of 1902 and 1903, FPCs now represent a multi-billion dollar, global market. Incidentally, the term ‘printed circuit’ is a little misleading because FPCs, like their rigid counterparts, are manufactured using a subtractive recently, very

process whereby copper is chemically etched from its substrate to leave the conductive circuit elements. It’s not printed onto the substrate, so FPCs should not be confused with recent innovations in ‘printed electronics’. Substrates are made from a variety of materials. Polyesters and polyimides have been popular, but other advanced polymers are now emerging, particularly thermoplastic versions which can be laminated onto fabric or operate at very high temperatures. FPCs may be single- or double-sided, or, for higher density interconnects, multilayer. Multilayer FPCs are typically formed from several single- or double- sided flexible circuits bonded together with conductive and insulating layers and plated through to form a compound interconnected device.

In the application, flexible circuits may be static or dynamic. They can be ‘flexed-to-fit’ into the required housing, enabling complex circuitry to be embedded in curved and aerodynamic structures. Alternatively, in a dynamic design a circuit may be flexed in operation, such as connecting through a hinged assembly like a car door hinge. A single FPC can replace not only ribbon cable, discrete wiring or complex wiring harnesses, but also connectors and even conventional, rigid printed circuit boards (PCBs). FPCs save weight and space, and often reduce costs while improving circuit performance. What’s more, taking advantage of the 3D nature of FPC technology, circuits can be folded and shaped to fit specific form factors, which might be impossible

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