There is a contact point in a connector, whether through board to board or line to board connection. The contacts may be small and not easy to see, but these unobtrusive contacts are one of the most important components in any connector. When it comes to contacts, it is necessary to talk about the coating of the contacts, and to deposit another layer of metal on one metal to protect the conductivity of the connector. At present, the coating materials are gold, silver and tin, and gold and tin are commonly used. The corresponding contact points are divided into gold contact and tin contact respectively.
As a precious metal, gold will not react with other materials, and gold will not oxidize or change color in the atmosphere, and it will be durable for a long time in harsh environment, so it is very suitable to contact with the coating layer. Silver plating has the best conductivity, but the chemical properties of silver are unstable, which is easy to produce silver sulfide, thus affecting the contact discoloration, welding and other properties of the contact; general connection Because tin is cheaper and has anti-corrosion function, the texture of tin is relatively soft, which is conducive to the coordination between the plug and socket. However, due to the soft texture, it is easy to wear the electroplating surface after several times of plugging and plugging, resulting in deformation of the contact end and failure to reach the designed contact force.
Therefore, gold contact has the following three advantages:
First, gold plating improves the corrosion resistance of contacts, which means they are more suitable for harsh environments.
Second, this kind of contact is more resistant to plug and pull and is not easy to wear, so in the case of frequent plug-in, gold contact is a better choice.
Thirdly, the contact resistance of gold contact is low. Therefore, compared with tin contact, gold contact has better continuity, so it is absolutely preferred in low voltage circuit (5V and below).
In addition to these basic rules, gold (or palladium nickel) contacts must also be used for the following limitations:
Any type of analog signal (because tin contacts produce line noise)
Any unpaired connector exposed to industrial environment
Any connector whose contact spacing is less than 1 mm due to whisker growth on a pure tin plated, unannealed surface
Gold and tin contacts cannot be used in the same paired connector system. The performance of these two coatings has not been studied in depth, but the difference of standard electrode potential will lead to contact corrosion (gold = + 1.5V, tin = + 0.15v - see the appearance of copper zinc drainage tank), and the reliability will be lost.
Should the connector use gold or tin contacts? If you master these rules, you can't choose the wrong one.