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96 DESIGN007 MAGAZINE I OCTOBER 2020 multilayer designs could reduce the clutter and cost of a medium heavy-copper FR-4 PCB. When designing bendable, heavy-copper flex buss bars, the copper must be thick enough to support the attachment fingers. The fingers could fit into a slot on the base FR-4 PCB or be surface mounted by bending the fingers at 90 degrees. A bendable, heavy-copper flex circuit can snake around the surface of a PCB, verti- cally supplying power and carrying heavy cur- rents, creating a standard PCB with the bend- able power board designed to carry the current throughout the entire rigid FR-4 PCB. Single, double, and multilayer heavy-copper flex designs could reduce the clutter and cost of a medium heavy-copper FR-4 printed circuit. When a bendable, heavy-copper flex circuit is used for the previously noted PCB buss bar and plated with 10 oz. of copper, it will possess considerable strength. You can bend it into any shape, including 3D shapes, and it will retain that shape due to the thickness of the copper. A bendable, heavy-copper circuit can with- stand a small number of flex cycles. However, it is not designed to flex repeatedly. A properly designed and manufactured bendable, heavy- copper flex circuit of 6 oz. copper can bend as far as 360 degrees, in as little as one-inch diam- eter, for a few times—enough to shape and sol- der the heavy-copper flex circuit to the PCB base board. Some mechanical attachment device is suggested to keep the circuit in the desired shape if it utilizes 4 oz. of copper or less. The heavy-copper, flex-based, buss bar can have plated vias, as well as multiple traces and circuitry (Figure 2). Some buss bars have com- ponents designed onto the surface, but they must be placed clear of any bend area. When a heavy-copper flex PCB is used for a power supply, buss bar, and plated with 10 oz. of copper, it will possess considerable strength and weight with higher-than-normal reliabil- ity. FLEX007 John Talbot is president of Tramonto Circuits. To read past columns or contact Talbot, click here. Figure 2: Heavy flex circuit with 6 oz. of copper on both sides.