Page 12 - 2019 How-to-Specify E-Book
P. 12

Five Things to Consider When Specifying Metal Contact Materials
Steve Smashey, President, and Mike Conte, General Manager, SOS Engineering, Inc.
Small details in the quality and construction of interconnects can make a big difference in a system’s performance capabilities. This is especially true with regard to an interconnect’s contact structure and, more specifically, its contact material. There are many factors to consider when specifying metal contacts, most of which — including mechanical performance, electrical performance, machinability, physical size constraints, cost, and availability — fall under the general umbrella of application requirements. In harsh environments, for instance, higher quality materials must be used to ensure consistent operational integrity, reliability, and durability.
Selecting the right materials for the male pins and female sockets in given application can be challenging, as it can be difficult to strike the right compromise between so many variables. When considered within the context of the application at hand, five considerations: tensile strength, current-carrying capabilities, cost, availability, and machinability can help identify which metal contact material will provide the best all-around solution.
 A graphical comparison of the machinability, tensile strength, cost, and current-carrying capacity of four common contact materials: brass, phosphor bronze, leaded nickel copper, and beryllium copper.
Tensile Strength
Higher quality materials inherently produce spring contacts with more tensile strength. Tensile strength is vital for the reliability and durability of interconnects that serve applications with high mating cycles and a long operating lives because it ensures that female (socket) contacts spring back into place after each mating and unmating cycle, and proper placement ensures reliable connectivity for the next mating cycle.
Brass is commonly sourced for sockets used in commercial applications, while harsh-environment applications typically use leaded nickel copper or beryllium copper (BeCu). Phosphor bronze is also commonly used in harsh environments, as it has a higher tensile strength — and therefore better spring properties — than brass. However, its tensile strength is still not good enough for socket contacts smaller than 20 gauge. As such, both brass and phosphor bronze are not typically used for miniature connector contacts.
Contact size is also a consideration when choosing the material. Larger contacts usually have thicker walls, which helps to make sockets less susceptible to losing their spring properties. As a result, in many applications, large contacts can be made of lower quality, less costly materials.

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