Basic knowledge of connector terminal plating

1. Definition: Electroplating: It is a kind of metal electrodeposition process, which refers to simple metal ions or complex ions discharged on the surface of solid (conductor or semiconductor) by electrochemical method to reduce to metal atoms attached to the surface of the electrode, thereby obtaining a metal layer process.

2. Purpose Electroplating changes the appearance of the solid surface by changing the characteristics of the solid surface, improving corrosion resistance, abrasion resistance, enhancing hardness, and providing special surface properties such as light, electricity, magnetism, and heat.

3. Introduction to terminal electroplating knowledge Most electronic connectors require surface treatment on the terminals, which generally refers to electroplating. There are two main reasons: one is to protect the terminal reed base material from corrosion; the other is to optimize the performance of the terminal surface, establish and maintain the contact interface between the terminals, especially the film control. In other words, it makes it easier to achieve metal-to-metal contact.

Prevent corrosion:

Most of the connector reeds are made of copper alloy, and are usually corroded in the service environment, such as oxidation, sulfide, etc. Terminal plating is to isolate the reed from the environment to prevent corrosion. The plating material, of course, will not corrode, at least in the application environment.

Surface optimization:

The optimization of the terminal surface performance can be achieved in two ways. One is the design of the connector to establish and maintain a stable terminal contact interface. The second is to establish metallic contact, requiring that any surface film layer is non-existent or will be broken during insertion. There is no difference between the two forms of film layer and film layer cracking, which is the difference between precious metal plating and non-precious metal plating.

Noble metal plating, such as gold, palladium, and their alloys, is inert and has no film itself. Therefore, for these surface treatments, metallic contact is "automatic". What we have to consider is how to keep the surface of the terminal "noble", free from external factors such as pollution, substrate diffusion, terminal corrosion, etc.

Non-metal electroplating, especially tin and lead and their alloys, cover a layer of oxide film, but when inserted, the oxide film is easily broken, and a metallic contact area is established.

(1) Noble metal terminal electroplating Noble metal terminal electroplating refers to the precious metal covering the surface of the bottom layer, which is usually nickel. General connector plating thickness: 15~50u gold, 50~100u nickel. Z commonly used precious metal electroplating includes gold, palladium and their alloys.

Gold is an ideal electroplating material for Z, with excellent electrical and thermal conductivity properties. In fact, it is anti-corrosion in any environment. Due to these advantages, in connectors for applications requiring high reliability, the main plating is gold, but the cost of gold is very high.

Palladium is also a precious metal, but compared with gold, it has high electrical resistance, low heat transfer and poor corrosion resistance, but it has advantages in friction resistance. Generally, palladium nickel alloy (80-20) is used in the terminal post of the connector (POST).

The following items need to be considered when designing precious metal plating:

a. Porosity During the electroplating process, gold nucleates on numerous stains exposed on the surface. These nuclei continue to enlarge and spread out on the surface. After Z, these islands (isolated objects) collide with each other to completely cover the surface, forming a porous electroplated surface. The porosity of the gold coating has a certain relationship with the thickness of the coating. Below 15u, the porosity increases rapidly, above 50u, the porosity is very low, and the actual rate of decrease can be ignored. This is why the thickness of the electroplated precious metal is usually in the range of 15~50u. Porosity is also related to defects of the substrate, such as inclusions, laminates, stamping marks, improper stamping cleaning, and incorrect lubrication.

b. Wear and tear on the plating surface of the terminal will also cause the substrate to be exposed. The wear or life of the electroplated surface depends on two characteristics of the surface treatment: friction coefficient and hardness. The hardness increases, the friction coefficient decreases, and the life of the surface treatment will increase.

Electroplating gold is usually hard gold, containing a hardening activator, among which Co (cobalt) is a common hardening agent for Z, which can improve the wear resistance of gold.

The choice of palladium-nickel electroplating can greatly improve the abrasion resistance and life of the precious metal coating. Generally, the 20~30u palladium-nickel alloy is covered with 3u gold plating, which has good electrical conductivity and high wear resistance.

c. Nickel bottom layer Nickel bottom layer is the primary factor to be considered for precious metal plating. It provides several important functions to ensure the integrity of the terminal contact interface.

Through the positive oxide surface, nickel provides an effective isolation layer, blocking the substrate and small holes, thereby reducing the potential for corrosion of the small holes; and providing a hard layer under the noble metal plating layer. The support layer, thereby improving the life of the coating. What kind of thickness is appropriate? The thicker the nickel bottom layer, the lower the wear, but considering the cost and the roughness of the control surface, the thickness is generally 50~100u.

(2) Non-precious metal plating Non-precious metal plating is different from precious metals in that they always have a certain number of surface layers. Since the purpose of the connector is to provide and maintain a metallic contact interface, the existence of these layers must be considered. Generally speaking, for the electroplating of non-precious metals, the forward force is required to be high enough to destroy the film and maintain the terminal The integrity of the contact interface. The scrubbing effect is also very important for the surface of the terminal containing the film layer.