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The conductor is the core of any cable assembly in RF and microwave transmission. Although the dielectrics and connectors are given attention, the electrical performance is essentially dependent on the purity and composition of the copper conductor. Copper and especially oxygen-free copper (OFC) is now the material of choice in high-end assemblies where signal quality, low attenuation, and long life are requisite. At Linkworld, we have 20 plus years of RF expertise and we know that in many cases, outstanding performance can be found in the conductor material. This document discusses the importance of high-purity copper conductors in finer cable assemblies.
Defining High-Purity Copper: OFC and Beyond
The main difference between high-purity copper and the ordinary electrical copper is the amount of oxygen. Oxygen-Free Copper (OFC) keeps the oxygen level at less than 10 parts per million (ppm) as opposed to copper of standard level of 200-400 ppm. The implications of this difference are far-reaching. The oxygen in normal copper forms microscopic copper oxide inclusions which hinder the flow of electrons and this reduces conductivity slightly. OFC has purities of 99.99% and better, and conductivity of about 100% or more IACS. In the most challenging applications, such sophisticated castings as Ohno Continuous Cast (OCC) result in copper of still greater purity and uniform crystal structure with no grains, so there are no grain boundaries that can influence high-frequency performance. In our high-quality assemblies, Linkworld defines OFC and OCC copper giving assurance that the conductor does not add degrading conduction to the transmitted signal.
Electrical Performance Benefits: Conductivity and Skin Effect
Conductor performance at RF and microwave frequencies is determined by the skin effect:only the current in the high frequencies exists near the conductor surface and therefore the purity of the surface becomes very important. Attenuation is directly reduced by conductivity of oxygen-free copper as it causes minimal resistive losses. With a frequency of 1 GHz, the difference between standard copper (98-99% IACS) and high-purity OFC (101% IACS) is enough to be detectable in the values of the insertion loss. Moreover, the regular grain structure guarantees the uniform behavior of the skin effect and eliminates local variations of current leading to hot spots or passive intermodulation (PIM). Such high quality assemblies have employed OFC conductors with silver plating, which further decreases the surface resistance at high frequencies. The premium assemblies of Linkworld capitalize on the material benefits to offer reduced loss and predictable performance.
Mechanical Advantages: Ductility and Reliability
Pure copper of high purity is also as mechanically advantageous as electrical. The fact that there are no oxide inclusions leaves OFC with better ductility and formability. This increased ductility plays a very important role in the manufacturing and installation process. OFC conductors have a higher resistance to tighter bend radius, without work hardening or formation of micro-cracks which cause fatigue failure. There is also enhanced resistance to stress cracking through soldering in the material where the disparities in thermal expansion may otherwise lead to reliability problems. In applications where flexing or routing work is very repetitive (e.g. test equipment or aerospace installations) mechanical robustness of high-purity copper can directly be converted into service life. Linkworld uses a purposeful choice of the OFC conductors to provide mechanical reliability equal to that of electrical performance even in extreme physical conditions.
Applications that Require High Quality Conductor Materials
The superiority of high-purity copper is worth using in some RF applications where the specification is beyond the standard material limits. The high-frequency communications (5G infrastructure, satellite links, microwave backhaul, etc.) work at frequencies in which attenuation needs to be kept to a minimum and every tenth of a decibel counts. Applications in test and measurement need predictable and continuous performance in thousands of mating cycles and flexure events. Low temperature and low outgassing properties of OFC find application in cryogenic and quantum applications. In such high-performance application requirements, the quality assemblies supplied by Linkworld have the addition of OFC and silver-plated copper conductors and provide a material base to meet the performance requirements that surpass ordinary.
One of the basic enabling technologies of high-quality RF cable assemblies is high-purity copper conductors. Oxygen-free copper is preferable because it offers superior electrical conductivity, has superior mechanical properties, and can be used with a long-term duration. Conductor quality is also becoming more and more important with the increasing frequencies and more stringent system requirements. Linkworld has more than 20 years of RF manufacturing experience, and a dedication to using the best materials, which are available to create custom cable assemblies out of the full potential of high-purity copper conductors. Get in touch with us to find out how our high quality assemblies can take your most stressful RF applications to the next level.