The Structure and Material of Connectors

The connector, also called connector assembly, is the main connecting device. Its main structure (or composition) and the corresponding materials are as follows: 

• the conductive terminal (contact)

• the housing

• the shell (depending on species)

• other hardware.

1. The housing, also known as the base or insert, is used to arrange the contacts according to the required position and spacing and to ensure the insulation property between the contacts and between the contact and the shell. Good insulation resistance, voltage resistance and machinability are the basic requirements for selecting insulating materials to be processed into insulators. The materials used are generally engineering plastics. Connectors vary greatly in size, shape and purpose, so the engineering plastics used will be different; when designing connectors, factors such as temperature-resistance, fluidity, mechanical strength, electrical performance and cost should be considered in the selection of appropriate engineering plastics. The commonly used engineering plastics are LCP, NYLON46, PBT, PPS, PCT, etc.

2. The conductive terminal also refers to the contact, which is the core part for the connector to complete the electrical connection function. Generally, the contact pairs are composed of male contacts (plug, pin and male head) and female contact (socket and female head), and the electric connection is completed through the insertion of female and male contacts.

The male contacts are rigid parts, and their shapes are generally cylindrical (circular pin), rectangular columnar (square pin) or flat (illustration). The female contact is the jack, which is the key part of the contact pairs. It relies on the elastic force, which is generated from elastic deformation when the elastic structure is inserted with the pin, to form close contact with the male contact to complete the connection. There are many kinds of socket structures, such as cylinder type(split slot and shrink mouth), tuning fork type, cantilever beam type (longitudinal slot), folding type (longitudinal slot, 9 shape), box type(square jack) and hyperboloid spring socket. They are provided for connector signal conduction.

The main functions of connectors are the signal conduction and the high inserting and extracting frequency, so they also have high requirements on the electrical conductivity and elasticity (yield strength) of contact materials. The material is mainly copper alloy, and the commonly used copper alloy types are: ① BRASS copper zinc alloy. The conductivity is good, which is about 26%-29% (IACS), and it can be divided into C2680(JIS) and C2600 according to the proportion of copper. ② With a conductivity of about 13%, PHOSPHOR BRONZE copper-tin alloy is less conductive than brass, but its flexibility is good, which is suitable for terminals with elastic requirements. According to the different tin content, it can be divided into C5111(tin content), C5191(tin content) and C5210(tin content). The higher the tin content is, the worse the electrical conductivity is and the better the elasticity is. ③ Heat-treated copper alloy such as BERYLIUM ALLOY has good conductivity and elasticity, but the price is relatively high.

As is known to all, copper is a metal that is easily oxidized. In order to protect the it from oxidation and influencing the performance of contacts, increase its wear resistance and improve the solderability, post-treatment is required. The surface shall be electroplated to ensure the terminal performance after processing the terminal or before processing raw materials. The general requirements for terminal electroplating are as follows: 

• Nickel (Ni) plating: It can prevent the base copper alloy of the terminal from oxidizing and bonding with the outer coating, and provide good electroplating performance in the subsequent electroplating process (such as gold plating or tin-lead plating);

• Gold (Au) plating: It provides conductive terminals with high wear resistance (plug resistance) and corrosion resistance;

• Tin-lead or pure tin: It can provide good solderability for welding parts of conductive terminals.

3. The shell, also known as the housing, is the outer cover of the connector, which provides mechanical protection for the inner insulation mounting plate and pin, and alignments the connector to the device when the plug and socket are plugged in, so as to fix the connector on devices.

4. Other hardware can also be called connector accessories. The hardware is designed in accordance with the product requirements for providing shell protection or fixing the connector, which can be divided into structural accessories and installation accessories. Structural accessories include clamping rings, locating keys, locating pins, guide pins, connecting rings, cable clamps, sealing rings, sealing gaskets, etc.; Installation accessories include bolts, nuts, screws, spring rings, etc. There are standard parts and universal parts in most accessories. The materials used are generally brass, phosphor copper, stainless steel or iron, and nickel, tin-lead or water washing is usually adopted in post-treatment.

The construction and materials of connectors above require the following five manufacturing techniques in processing:

• Stamping die technology. Progressive die is usually adopted in this technology;

• Plastic molding technology;

• Assemblage and automation;

• Electroplating technology, including continuous electroplating, rolling plating, hanging plating, etc.;

• Inspection and testing technology. Connectors are gradually miniaturized, PITCH and SMT, so how to effectively detect the connectors becomes a big challenge; In terms of the test, the current connector testing standards mainly include EIA364 (Electronic Industries Association of America) and MIL-STD1344A(MIL-STD American Military Standard).