TE - White Papers

alloy as a percentage of the conductivity of pure annealed copper), and mechanical performance. It is readily available in various strengths that allow it to be used in a wide variety of applications. It does have some environmental corrosion issues, particularly with respect to ammonia that attacks brass vigorously, so some sort of plating system is strongly recommended when the end use is in such environments. Also heavily used for connector contacts is phosphor bronze, which maintains excellent long- term spring properties (without stress relaxation) and can handle higher continuous use temperatures than brass. With better spring properties than brass, phosphor bronze lends itself to smaller contacts where the enhanced spring properties can best be leveraged. A broad range of general and proprietary alloys based on phosphor bronze provide an equally broad range of conductivities and mechanical properties that are used throughout the connector industry. Phosphor bronze contacts are usually found in small and medium-pitch signal and moderate- power connectors. The last most commonly used copper alloy is beryllium copper. Beryllium copper is considered a premium material and is used where the superior spring properties are put to best use in minimizing contact size and, in applications such as aerospace or military, weight. It is significantly more expensive than the brass and phosphor bronze but has an added benefit that it can be readily heat treated to further enhance spring properties. Applications for beryllium copper are usually found in small, fine pitch telecom-type connectors. Other contact materials or configurations such as semi-exotic copper alloys also exist that are a combination of various elements. Monolithic examples of these alloys are copper-iron (CuFe) or copper-nickel-silicon (CuNiSi) alloys that provide excellent performance in those applications that can benefit from such a premium contact material. Clad materials consisting of one material bonded on top of another are also available but are used in the rarest of instances due to their cost. Another unique contact material configuration occasionally seen takes advantage of the high conductivity of electrolytic tough pitch (ETP) copper, combined with a separate spring member made of stainless or plated steel to provide the required normal force. In many high-temperature applications, such as electric oven burner elements, steel or steel alloys may be used, although conductivity is drastically reduced compared to that of copper alloys. The use of ferrous contact materials requires careful design consideration by both the connector designer as well as the designer of the product that it is used in. Inherent corrosion issues require that steel contacts must be durably and robustly plated. Contact Platings Platings can be broadly categorized into two groups: noble and non-noble materials.

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