While an engineering student, I spent a few summers working for Parlex (now Johnson Electric), a company that manufactured flexible circuits. Most circuits were the typical sizes that you see every day. Trackwise, a company based in Tewkesbury, U.K., announced that it has shipped what the company claims is the world’s longest multilayer flexible circuit at 26 m (85 ft.). The company said in a press release that the cable was designed for an unmanned solar-powered aircraft.

Trackwise flex

Trackwise employees show the longest flexible circuit you’ve ever seen. (Image: Trackwise)

According to the press release, the unmanned aerial vehicle (UAV) has a flexible circuit that’s based on a polyimide substrate. You may know the material by its trade name of Kapton. The circuit’s planar structure, according to the company, dissipates heat better than conventional wiring. That provides for higher current-carrying capacity for a given weight of copper conductor. The company did not say how much current the circuit can pass because that’s product-specific.

Trackwise currently produces these long circuits in two, four, and six layers. As with all flex circuits, pads can be designed to provide access points at any location. In this instance, the primary application is to replace wiring harnesses, reducing weight. In the photo below, a Trackwise employee uses a DMM to measure electrical isolation (resistance).

Trackwise flex PC

Testing the long flex circuit for electrical isolation requires only a multimeter. (Image: Trackwise)

Most flex circuits are etched onto a single sheet of Kapton-backed copper, often several to many circuits on a sheet, depending on the circuit size. Clearly, sheet size is an issue here. The people at Trackwise have to stitch together the long circuit in sections. Even so, Trackwise had to work with its equipment manufacturers to develop modified production equipment to accommodate the large circuit sections.