What are the plating options for high voltage connectors?

There are many options for plating terminals, generally divided into four categories: noble metals, inert metals, alloys and dispersions. The first three categories are already established and used, while decentralization is just beginning to emerge to address the need for high-power connectivity in electric vehicle charging and similar applications. We begin with a brief review of basic electroplating system concepts, then describe the properties of noble metals, inert metals, and alloys, and conclude with a brief overview of the potential advantages of dispersions.

Plating systems are typically multi-layer structures, where the top layer can be a relatively thin coating. Inert metal surfaces like tin are often found in consumer products. Industrial, military, medical and other high-performance applications often turn to precious metals. Precious metals are often used as alloys. For example, pure gold is too soft for many applications, while gold alloyed with cobalt, nickel, or iron, known as "hard gold," is used to provide greater durability (Figure 1). Other precious metals such as silver can also be used as alloys to increase hardness.

precious metals

Gold is highly conductive even at low voltages. It has excellent oxidation and corrosion resistance compared to other options. It is ideal for use in environments with high humidity or frequent heat cycles.

Silver performs well in high power applications. It is less expensive than gold and is a good choice for larger, high-current contacts.

Palladium has high electrical and thermal conductivity and is resistant to corrosion. It is harder than gold or silver, making it a good choice for applications that require more durability.

Rhodium is harder than palladium and is resistant to corrosion and acids. It is ideal for applications requiring good wear resistance and high hardness.

inert metal

Tin is non-toxic and therefore suitable for some medical applications. This is low cost and suitable for applications requiring a small number of mating cycles.

Nickel is very hard, durable and corrosion-resistant. Its combination of durability and high conductivity makes it suitable for high-use applications.

Copper is one of the most conductive metals, but it requires a protective layer to prevent corrosion. It is often used as a basis for subsequent metal plating.

metal alloy

White bronze is a non-magnetic alloy composed of copper, tin and zinc that is more conductive than nickel. It is ideal for many medical and RF connectors.

Palladium-nickel alloy is corrosion-resistant and has low contact resistance. It has good solderability and can handle a large number of mating cycles. Palladium-nickel plating often flashes gold.

Electroless nickel plating can be applied to both conductive and non-conductive surfaces. Electroless nickel plating contains up to 14% phosphorus. The higher the phosphorus content, the greater the corrosion resistance, but the hardness decreases.

Nickel-phosphorus alloy has high wear resistance and corrosion resistance. They have good weldability but have lower electrical conductivity than other alloys.

Silver graphite dispersion

Silver-graphite dispersions have been developed for use in contacts in high-power applications such as electric vehicle chargers. It combines the properties of fine silver and hard silver. The fine silver matrix provides high conductivity and the graphite increases wear resistance and supports high cycle life. Uniform and random dispersion of graphite particles is one of the keys to high durability (Figure 2).

Summarize

A wide range of plating options are available to support varying levels of conductivity, environmental ruggedness, durability and other application needs. With the development of graphite dispersion plating materials, the traditional choice between precious metals, inert metals and various alloys is expanding.