Features

Extruded Flat Cables vs Round Cables

Highly flexible flat cables have many advantages over flexible round cables in constant motion and confined area applications. Round cables incorporate single and multiple bundles of insulated wires and are usually surrounded by several layers of other materials. The inner bundle is usually surrounded by a wrapped textile material, fillers or an inner jacket to minimize internal heating caused by friction caused by flexing, bending and twisting of the cable. In shielded round cables, there are additional protective layers consisting of low-friction wraps, additional inner jackets, braided copper, fillers and even lubricating agents such as talc. With the inclusion of more layers and materials, the cable increases in size and weight, which results in a less flexible cable.

Eliminating unnecessary insulation, fillers and tapes reduces the bulk and physical volume of flat cables. In addition, their low profile enables them to hug surfaces and take advantage of tight, or normally-unused space and exhibit much flexibility. A rectangular cross-section allows flat cables to stack, or layer, with almost no wasted dead space between cables, providing maximum conductor density for a given volume.

Flat cables have greater surface-to-volume ratio than their round cable counterparts, consequently having higher efficiency in dissipating heat. This allows a higher current level for a given temperature rise and conductor cross-section.

The spacing of conductors in the extruded flat cable never changes as the cable moves. Thus cable impedance, inductance, capacitance, time delay, crosstalk, and attenuation all remain constant. Similarly, the conductors in the cable all have the same physical and electrical length. This, coupled with the fact that the dielectric dimensions stay constant, means that signal skewing and differential time delays between signals in the cable stay at a minimum.

Extruded flat cables and flat cable assemblies form an inherently high-density interconnect system. Packing density of flat cable is higher than is possible with round cables. The fact that conductors can be visible in the Flexx-Sil™ extrusion simplifies coding, inspection, and tracing circuits for trouble shooting.

Extruded Flat Cables vs Flex Circuit

Flex Circuits offer engineers some useful properties, but sometimes they are used in applications that require more capabilities than they can offer. Despite the “Flex” in flex circuits, the flexing capability in the flat form factor is limited. Unlike flexible flat cables designed for millions of continuous flex cycles, Flex Circuits tend to be stiff and are very fragile. They can easily be dented, cracked, bent and damaged from exposure to severe turbulence, vibration, impact, long term flexing, mechanical stress and improper handling.

Where flat cables can incorporate different components within its profile, Flex circuits are typically limited to single conductors only. For applications exposed to EMI/RFI, shielding is attained by using neighboring conductors or flat shield planes above and below the circuit traced layer resulting in larger and very stiff assemblies. Flat cables can incorporate single shielded power conductors, twisted shielded data and Ethernet pairs, coax, triads and shielded cable bundles.

The initial tooling costs for Flex Circuits are high. Once made, tooling is expensive to change and new tooling may be required to accommodate application modifications. Flat extruded cables typically require a one-time $250 tooling charge, which is inexpensive compared to tooling used to manufacture Flex Circuits.

Similar to molded flat cables, Flex Circuits are individually produced and the size is fixed according to the tooling; whereas, extruded flat cable is manufactured in continuous bulk lengths and can be cut to suit various applications.

Flex Circuits can be used in small spaces where equivalent round cables won't fit and can be shaped to fit the installation path. Flat extruded cables meet these requirements as well. Custom shaped flexible flat cables allow for very precise cable routing without folding, kinking or pinching. The custom shape of the flat cable also contributes to the elimination of signal failures due to physical stress at the cable connector.

This article was written by Rich Buchicchio, National Sales & Marketing Manager, Cicoil (Valencia, CA). For more information, Click Here.

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