Connect-Contact-Plating-FinishesContacts in electronic connectors play a crucial role: they are the conductive element. Their function is to reliably and consistently transmit signals or power across the connector interface. Having the optimal application-specific contact is then critical to maintain efficiency and longevity of the connector and the overall system. The plating of the connector contacts can ultimately determine how well they function and last. There are several plating finishes available. It’s important to understand the primary differences between them, and their typical uses. Let’s take a look.

Gold is the most noble metal and is very resistant to corrosion. It is excellent for low voltage and current applications. The coefficient of friction is low, which allows mating cycle count to be high. Gold is ideal for harsh environments, and the most popular finish used in military, aerospace, medical and other mission critical applications. (10-50 u”)

Silver is also a noble metal and has the highest electrical and thermal conductivity of all metals. It also has very low contact resistance. Silver will tarnish over time, but it is reduced when contacts are mated and unmated. Thanks to its excellent conductivity, silver is used mainly for high-current contacts. (100-300 u”)

Palladium offers similar resistance to corrosion as gold. It is harder and more durable, more resistant to wear and also less costly. Palladium is diffusion resistant when plating on copper. Copper readily diffuses into gold. Some disadvantages include reduced heat resistance, weakness to strong acids and more prone to cracking. (10-30 u”)

This alloy has the advantages of palladium, but without the “fretting” issues or “brown powder” effect. Compared to palladium, palladium-nickel is less prone to cracking and is more resistant to heat and galvanic corrosion. It allows for reduced porosity and excellent solderability. PdNi followed by a gold flash offers more advantages. These include better corrosion protection and a higher number of mating cycles. It can also act as a solid lubricant. (10-30 u”)

Rhodium offers a high hardness (800 to 1000 Hv) and superior corrosion resistance. It is ideal for parts that require long-term stable contact resistance. Heat resistance is very good, and it does not oxidize in air at 500° C or lower. It is used for switch contacts, test probe parts and some connectors. (20 u”)

Unlike the above metals, tin is not in the noble category. It quickly develops an oxide layer when exposed to air. A contact system plated with tin requires greater forces and a longer wipe area to break through the oxide film. The higher coefficient of friction causes higher insertion and withdrawal forces and more wear, which limits mating cycles to less than 50. Whisker growth is a concern with close contact spacing, but whisker mitigating plating baths are available. Tin offers excellent solderability and low cost. It is a very good finish for press-fit contacts. (100-300 u”)

This finish has many similar properties as tin, without the whisker-growth. It’s melting point is altered by lead content, but overall it is relatively low. Contact resistance and corrosion resistance are similar to tin. Solderability is improved. The finish provides lubricity, excellent conductivity and good shelf-life. (100-300 u”)

(Tri-Metal Alloy) High corrosion resistance, and non-magnetic, which reduces intermodulation concerns. Low porosity. Compared to nickel, health safety is improved. A popular choice for RF connectors. (50-200 u”)

Certain applications require underplates to deliver specific properties that the finish plate may not adequately provide. Nickel, Electroless Nickel or Copper are typically used. Nickel is often used for corrosion protection. Electroless nickel contains phosphorus and increases corrosion resistance, and provides a uniform thickness. Copper is very electrically conductive. Unfortunately, it is prone to corrosion, which can be helped using a protective layer such as nickel or tin. Copper has excellent leveling and uniform deposition properties, which can help build up undersized parts.