In the industry, any component coming in the path of delivering control signals or power to do useful work is termed industrial connectivity. For instance, components including relays, motor starters, terminal blocks, and connectors are all typical connectivity components.
Generic connectors can use low-cost material as they merely maintain electrical continuity. However, based on operating environments, connectors are differentiated into four categories: hermetic, military, industrial, and commercial. While hermetic connectors offer maximum exclusion of their inner structural materials from the elements, military and industrial connectors handle more rugged environments with hazards including thermal shock, vibration, corrosion, physical jarring, dust, and sand. Most commercial applications do not make such extreme demands of connectors, and therefore, atmospheric and temperature conditions are the least critical factors that affect the performance of commercial connectors. This allows designers to select from different connector materials.
Brass
This is a metal alloy made from copper and zinc, with manufacturers varying the proportions to create varying properties. Although brass has excellent conductivity, it cannot withstand abrasion from many cycles of insertion and withdrawal. It undergoes crystallization under repeated stress and loses flexibility as it ages. Suitable for non-critical and low-contact-force applications, it is easy to braze, weld, solder, and crimp brass.
Beryllium Copper
With excellent electrical, mechanical, and thermal properties, beryllium copper easily resists corrosion and wear. Among all copper-based spring alloys, beryllium copper is stronger and more resistant to fatigue, while able to withstand repeated insertion and withdrawal cycles. However, it is the most expensive among all basic contact materials.
Nickel-Silver Alloys
Not always requiring plating, nickel-silver alloys resist oxidation. While contacts made of nickel-silver alloys are susceptible to stress corrosion, the extent does not exceed that of brass.
Gold
Gold, a highly stable plating material, is an excellent conductor inferior only to silver and marginally so to copper. With the lowest contact resistance and providing the best protection from corrosion, manufacturers use hard gold plating for contacts experiencing frequent insertion/withdrawal cycles. For even greater frequency of cycling, gold impregnated with graphite offers only a slight increase of contact resistance.
Silver
A general-purpose plating metal for power contacts, silver has a poor shelf life and tarnishes when exposed to the atmosphere. Although this increases the contact resistance, the oxide coating does not affect contacts carrying higher currents.
Nickel
With good corrosion resistance, nickel offers low contact resistance and fair conductivity. Therefore, it is used as an undercoat to prevent migration of silver through gold in high-temperature environments. Although it has good wear resistance, nickel may crack during crimping unless properly plated onto the base material.
Rhodium
Manufacturers use rhodium for contacts that need exceptional wear qualities. Although conductivity of rhodium is lower than that of gold or silver, the higher resistance is acceptable for thin coatings.
Tin
Providing good conductivity and excellent solderability, tin offers a low-cost finish and poor wipe resistance. This makes it the most suitable for connections requiring only very few mating cycles. Tin, not being a noble metal, will corrodes easily.
Gold-Over-Nickel
This is a widely used plating combination as it offers the surface qualities of gold, while minimizing the amount of gold required. The hard under-plating of nickel prevents migration of the base metal.
