Oxygen-free copper

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Oxygen-free copper, commonly abbreviated as OFC, is a manufacturing process of copper cables. The process produces more pure copper, resulting in slightly higher conductivity than cables manufactured from unprocessed copper.

A variation of the oxygen-free copper manufacturing process called linear crystal oxygen-free copper, abbreviated LC-OFC, also increases purity between crystal boundaries, resulting in longer crystallites (grains) and therefore lower resistance. However, Single Crystal Copper also exists with only one grain per crystal.

These kinds of cables are often used in high-end audio equipment and other fields where retention of analog signal is important. While manufacturers insist that the difference in resistance is significant, most professionals and audiophiles believe that there is no perceivable difference and that the claim of "oxygen-freeness" is just a sales argument to trick consumers into paying more.^[1] The difference in resistance is quite small (about 20%) and is usually dwarfed by the resistance of the connectors and other factors. Also the most commonly used grade of "oxygen-free" copper, C10200, is the lowest grade available and does not provide all the features of the better grades.^{[citation needed]}

Oxygen Free Copper is available in two basic categories:

First, copper can have the oxygen reduced or made 'Free' of oxygen by addition of flux agents such as Phosphorus when the copper is in a molten state. This produces a basic high quality refined copper for general usage. This grade is not recommended for electrical or electronic applications. It is used to make sheet, rod, and similar bulk copper items.

Second, copper can be further refined in a multi-step process which includes electro-chemical followed by induction heating combined with an inert gas atmosphere until molten. This second refining process produces several additional grades of very high purity Oxygen Free Copper. Among these grades are: C10100 and C10200, referred too above, for electronic applications..

The C10100 copper grade is the finest. It often is offered as 'Certified Electrical Grade'. The Oxygen content is no more then 5ppm. Importantly, C10100 has no more than 3ppm of Phosphorous. The presence of Phosphorous increases the electrical resistance of copper.

In the case of electrical measurements, such as the resistance, both C10100 and C10200 are expected to be fully annealed ( soft or 'dead-soft' ) copper, unless otherwise specified in the measurement. Any hardening of the copper will increase the resistance and affect other electrical measurements.

The C10200 copper is considered to be 'Regular Grade’ Oxygen Free Copper. It is an excellent copper which satisfies many Electronic needs. The Oxygen content is no more than 10ppm. The C10200 copper does exhibit approximately 1% less conductivity due to impurities such as Phosphorous.