Copper is the default choice when selecting a metal for many electrical applications. However, electrical contacts made from brass usually perform better, providing they're plated with a conductive material. Hartford Technologies manufactures brass balls for electrical contact applications. This blog post addresses the benefits of brass, why it needs plating, and what must be considered to ensure good conductivity and adherence.

Why Brass in Electrical Contacts?

The electrical conductivity of copper is bettered only by silver, but while copper is less expensive it's also soft and ductile. This makes it a poor choice in contact applications where it deforms easily. Alloying copper with zinc produces a harder metal: brass.

Increasing the proportion of zinc in the copper improves hardness, formability and machinability, but at the expense of electrical conductivity. Brass metal balls used in contact applications typically contain less than 30% zinc and conductivity is around 1/3rd that of copper.

Plating for Conductivity

Increased resistance - the flipside of lower conductivity - means less efficient current flow and more heat. To overcome this, Hartford plates precision balls for electrical contact applications with either gold or silver.

Silver has the lowest electrical resistance of any metal, and also the highest thermal conductivity. Together, these attributes make it the first choice for electrical applications. However, silver can tarnish in some circumstances, making gold, with conductivity only slightly inferior to that of copper, an alternative. 

A second reason for selecting gold plate on precision metal balls is that gold offers a higher degree of ductility. This can help in making good electrical contact.

Achieving Conductivity and Adherence

Electroplating entails placing the brass balls into a molten metal salt bath. Applying an electrical current moves atoms from the bath onto the surface of the balls. Current duration, and to a lesser extent, intensity, determine the thickness of coating developed.

The plating process is optimized to maximize throughput while ensuring good adherence of the metal being applied. It's also important to minimize variability in plating thickness as variation increases cost and diminishes ball precision. 

Adhesion depends on the cleanliness of the metal balls. Electroplating therefore begins with thorough cleaning. This consists of an alkaline treatment followed by an acid pickle. Pickling removes any remaining surface oxides that would limit adhesion of gold or silver. Brasses with a particularly high lead content will go through a two-part pickling process that removes any free lead on the surface.

In silver plating increased adhesion is achieved by performing a silver "strike" prior to the main plating treatment. A "strike" is a very thin flash coating forming a layer to which the main coating can adhere.

Substrate First

The key to making precision balls for electrical contact applications is to start with a high quality substrate. Hartford Technologies are leaders in the manufacture of metal ball bearings used for both friction reduction and in electrical contacts. Balls are manufactured in materials ranging from brass and stainless steel to glass and ceramics. Contact Us to learn more.