The two focus areas of contact material construction are the plating and the base material. Since plating garners the most attention, let’s explore the basics of the latter.
Manufacturers consider various performance factors when constructing electrical contacts. The most important are conductivity, resistance to wear (mechanical, corrosive, oxidative, etc.), production cost, and the specific application. Each elemental metal has specific qualities to take into consideration when constructing electrical components. Combined as alloys and subject to numerous manufacturing processes, the number of material options is growing rapidly.
Table of Contents:
(01) Copper and the Big Trio: Brass, Beryllium Copper, and Phosphor Bronze
(02) Silver, Stainless Steel, and Nickel
(03) Chromel, Alumel, and Constantan
(04) Gilding Metal, Cartridge Brass, and German Silver
(05) Other Alloys and Combined Metals
Copper and the Big Trio: Brass, Beryllium Copper, and Phosphor Bronze
A good starting point for understanding contact base materials is the male-pin header category where the contacts are already installed. Note the many choices in the ‘Contact Material’ filter. [click here https://www.digikey.com/products/en/connectors-interconnects/rectangular-connectors-headers-male-pins/314 ]. [Product Index > Connectors, Interconnects > Rectangular Connectors – Headers, Male Pins ]
Copper
By itself, copper is malleable, ductile, and highly conductive. In other words, it can be easily formed without cracking or breaking, can be drawn into a thin wire form, and doesn’t offer significant resistance to electricity. It has high thermal conductivity, and It can also be soldered easily. For the electronics industry, electrolytic refinement is used to turn copper into a highly conductive alloy form known as C101 (also CW004A, C11000, and Cu-ETP). Many brass and bronze metals are produced from the C101 alloy. These alloys do not have the same high level of conductivity, but in many applications, that degree of efficiency is not needed.
Brass
Brass is not just copper and zinc together in a fixed amount, but is defined as a range (15% - 40%) of copper/zinc ratios with possible inclusions of other elements. Brass is much less conductive than pure copper, but it has greater strength. The combined properties of copper and zinc give this alloy good corrosion resistance. Two very common alloy forms are copper-30% zinc and -15% zinc. The -30% zinc level is a good benchmark alloy to start with when testing a design, and the need for greater or lesser amounts of zinc can be inferred by strength, resistance to wear, and conductivity tests at this standard value. The conductivity at this -30% zinc level is about 28% of pure copper. As a raw material for contact production, zinc is much less expensive than copper, so brass is generally less costly as well.
Phosphor Bronze
As a group, bronze covers copper alloys with tin inclusions in the range of 5% to 15%. Other elements can be added to impart specific properties, and phosphorus is one of them. Most versions are tarnish and corrosion resistant. It is stronger than brass, but does not return to its original shape (spring property) as well as beryllium copper through application cycles. Phosphor bronze conductivity is around 15% of pure copper, but it has an excellent balance of strength, resistance to wear and corrosion, and electrical conductivity.
Beryllium Copper
This is an alloy of copper containing a small percentage of beryllium in the range of 0.5% to 2%. Small amounts of other elements may be added. It has good tensile strength and retains its shape under various conditions. Because of this property, it is a good choice where smaller terminals are needed, or where the application is expected to have a high number of cycles. Of these three copper-based contact materials, it is more expensive, but it gives the best combined mechanical and electrical performance.
Every connector manufacturer has a goal in mind when choosing base materials for their contacts. Here is what Samtec has to say about brass, beryllium copper, and phosphor bronze: [click here Comparing Base Metals In Connectors - The Samtec Blog ].
Silver
This element is used for its very high thermal and electrical conductivity. By itself, it has a low melting point and low mechanical strength. It also tends to tarnish, and silver atoms may diffuse into certain types of insulation when electrical fields are applied. Silver is expensive compared to more common metals such as copper or bronze, so it’s best used where the benefits justify the cost. Many silver alloys are used to impart material properties targeted towards specific applications and to overcome the shortcomings of elemental silver.
Silver contact materials are well represented in our signal and power relays:
Product Index > Relays > Signal Relays, Up to 2 Amps [click here https://www.digikey.com/products/en/relays/signal-relays-up-to-2-amps/189 ]
Product Index > Relays > Power Relays, Over 2 Amps [click here https://www.digikey.com/products/en/relays/power-relays-over-2-amps/188 ]
Stainless Steel (SS)
A combination of iron and a minimum of 11% to 12% chromium, SS is chosen mainly for its resistance to oxidation. Chromium levels affect this property, and additions of nickel or molybdenum are possible. Nickel increases the resistance to thermal stress and improves weldability. It also helps prevent corrosion caused by certain agents. This material may often be noted as ‘SS’ in documents, drawings, and descriptions.
SS is most often found in backshells and housings rather than in most contacts. It does show up in more specialized applications such as RFI and EMI products.
Here are two uncommon sources and one common application: (see the Material or Contact Material filter options)
(Not Common) Product Index > Connectors, Interconnects > Rectangular Connectors – Spring Loaded [click here https://www.digikey.com/products/en/connectors-interconnects/rectangular-connectors-spring-loaded/408 ].
(Not Common) Product Index > Connectors, Interconnects > Terminals – PC Pin Receptacles, Socket Connectors [click here https://www.digikey.com/products/en/connectors-interconnects/terminals-pc-pin-receptacles-socket-connectors/324 ].
(Common) Product Index > RF/IF and RFID > RFI and EMI – Contacts, Fingerstock and Gaskets [click here https://www.digikey.com/products/en/rf-if-and-rfid/rfi-and-emi-contacts-fingerstock-and-gaskets/945 ].
Nickel
Nickel is a fair conductor of heat and electricity. It is resistant to corrosion, and aside from contact plating, it is often used to create alloys with specific properties.
It has a significant amount of use in card edge and edgeboard connectors in the form of an alloy or in combination with other metals: (see the Contact Material filter options)
Product Index > Connectors, Interconnects > Card Edge Connectors – Edgeboard Connectors [click here https://www.digikey.com/products/en/connectors-interconnects/card-edge-connectors-edgeboard-connectors/303 ].
Chromel, Alumel, and Constantan
Chromel, Alumel, and Constantan are ‘named’ alloys with specific compositions. On the Digi-key site, a search for any of these will show mixed results, and most will be in “Multiple Conductor Cables” where thermocouples are the targeted application. These materials are very commonly used in the construction of certain element types of thermocouples, but that information isn’t always listed in the manufacturer documentation, and therefore neither on our site.
Product Index > Cables, Wires > Multiple Conductor Cables (Conductor Material filter) [click here https://www.digikey.com/products/en/cables-wires/multiple-conductor-cables/473 ].
Product Index > Sensors, Transducers > Temperature Sensors – Thermocouples, Temperature Probes [click here https://www.digikey.com/products/en/sensors-transducers/temperature-sensors-thermocouples-temperature-probes/513 ]
Chromel
This alloy is seen in very specific types of products. The composition is approximately 90% nickel and 10% chromium. It can tolerate a temperature range of -452C to +1100C. It is used for the positive Type E and Type K conductors in thermocouples and associated products.
Alumel
This alloy has very specific applications. The composition is approximately 95% nickel, 2% manganese, 2% aluminum, and 1% silicon. It has good thermal conductivity and electrical resistivity, so like Chromel, it is used to construct type K thermocouples and related products.
Constantan
The composition of Constantan is usually 55% copper and 45% nickel. It has a consistent resistivity over a wide range of temperatures, so along with Chromel and Alumel, it is used to construct thermocouples and associated products.
Gilding Metal, Cartridge Brass, and German Silver
Gilding Metal
The alloy ratio of 95% copper and 5% zinc is referred to as gilding metal. As the name implies, the sheet form is often used in hammered metalworking, but also in items such as ammunition and artillery jackets. Beginning in 1944, gilded metal shell casings were melted down as a raw material for making pennies until 1946. Like other brass metals, the zinc content directly affects conductivity, and the -5% zinc version has one of the highest levels in marketed brass contact materials.
Product Index > Connectors, Interconnects > Rectangular Connectors – Headers, Male Pins (Contact Material filter) [click here https://www.digikey.com/products/en/connectors-interconnects/rectangular-connectors-headers-male-pins/314 ].
Cartridge Brass
This is a specific alloy ratio of approximately 70% copper and 30% zinc (C26000). The name ‘cartridge brass’ is derived from its traditional role in ammunition construction. It nonetheless retains the same types of qualities associated with brass of a similar copper-zinc ratio.
This material has some presence in common headers: (see the Contact Material filter options)
Product Index > Connectors, Interconnects > Rectangular Connectors – Headers, Male Pins [click here https://www.digikey.com/products/en/connectors-interconnects/rectangular-connectors-headers-male-pins/314 ].
German Silver
Also called “nickel silver”, German Silver does not contain silver at all. Instead, it is composed mainly of copper, zinc, and nickel. It has desirable properties such as strength and corrosion resistance. A small number of D-Sub contacts on the Digi-key site use this as the base material.
Product Index > Connectors, Interconnects > D-Sub, D-Shaped Connectors – Contacts (Contact Material filter) [click here https://www.digikey.com/products/en/connectors-interconnects/d-sub-d-shaped-connectors-contacts/332 ].
Other Alloys and Combined Metals
In some cases, the contact material may be listed in ways that are not entirely clear. More research may be needed to determine the exact composition. The description may be the same as the material by a different name, but these are taken from manufacturer documentation, so they are copied directly to our site.
Any material listed as “alloy” should have more details regarding the actual composition. Examples are copper alloy, nickel alloy, brass alloy, aluminum alloy, copper magnesium alloy, etc.
Some materials are listed as two separate metals, but it is not clear if this is an alloy or used separately in the construction. In general, this implies an alloy. Examples are titanium copper and copper zinc.
Materials listed together, but separated by commas, might be used separately in the construction, but the data should still be verified. An example is Copper, Nickel, Tin Alloy.
For further exploration, try a general search for “contacts” from the Digi-key home page, and look for many categories within the Connectors, Interconnects group. [click here https://www.digikey.com/ ].
{Coming Soon: Where to find contact base material data.}