Classification and selection of connectors

Definition of connectors
A collective term for a device that connects two or more electrical circuits. As an electromechanical component, connectors generally work in pairs and are divided into plugs (male), sockets (female), and English plugs (or male, header); Receptacle or Socket, Jack, Female in English for socket (female).
It completes the connection and disconnection of electrical appliances through certain mechanical actions, and its main functions include:
Transmission of signals or electrical energy

Connect or disconnect a circuit

There are many ways to classify connectors, and we will focus on it in this article. However, due to the different application directions of connectors, there are contact and non-contact types. For example, fiber optic connectors and electrical connectors are contact type, while proximity switches are non-contact connectors; There are also classifications of electrical and optical signals. Today we are mainly discussing contact connectors for electrical signals.
Electronic connectors and their components are important supporting interface components in equipment, scattered throughout various systems and parts of the equipment, responsible for the transmission of signals and energy. The quality of the connection directly affects the safe and reliable operation of the entire system.
Various circuits are composed of interconnected electrical connectors, from high-frequency to low-frequency, from circular to rectangular, from high current connectors passing through hundreds of amperes to high-density connectors passing through weak signals, from ordinary printed circuit board connectors to fast separation and detachment special connectors. Almost all types of electrical connectors have been widely used in various system engineering, ensuring the normal functioning of equipment integrity.
In summary, on the one hand, in the face of various types of application scenarios, the classification of industrial connectors is also extremely complex. So with the continuous progress of technology, there are more and more connectors on the market, and the performance of different types of connectors varies greatly. Manufacturers will use materials with different characteristics to design connectors based on the application environment to ensure stable and reliable use of connectors in different environments.
On the other hand, the reliability of electrical connections directly determines the performance of equipment systems. The performance of electronic connectors is an overall performance evaluation, unlike the terminals of connectors, which can be easily evaluated from material, design, and process aspects.
Although there are numerous and complex types of connectors nowadays, making it a bit cumbersome to select for performance evaluation, the benefits of using connectors in devices are obvious:
1. Improve the production process, simplify the assembly process of electronic products with connectors, and also simplify the mass production process;
2. Easy to maintain and upgrade;
3. Improve design flexibility by using connectors to give engineers greater flexibility in designing and integrating new products, as well as in composing systems with components. The number of connector end wires and the spacing between wires make the connection more convenient and fast. It is precisely these small details that can effectively reduce the volume of electronic products, while also reducing production costs. It can effectively serve as a data line for transmission between mobile motherboards or PCBs.
With so many connectors, how do you divide them?
For any molded product, connectors are essential, such as the commonly used USB, headphone jack, Ethernet interface, or military custom interfaces that we rarely see. So, based on a wide range of markets, connector classifications are also diverse.

1. According to the functions of the internal and external connections of electronic devices, there are six levels of interconnection, as shown in the above figure:
A: Interconnection of components to packaging;
B: Interconnection between packaging and circuit boards;
C: Interconnection between boards;
D: Component to component interconnection;
E: Interconnection of components to input/output interfaces;
F: The interconnection between systems.

2. Classification by transmission signal type:
A: Power connector (transmitting power);
B: Signal connector (transmission signal);
C: High frequency connectors (transmitting data).

3. Classification according to electrical requirements:
A: Universal connectors;
B: High power connector;
C: High voltage connectors;
D: Pulse connector;
E: Low noise connectors;
F: Phase adjustment connector;
G: Precision coaxial connectors.

4. Classified by working frequency:
High frequency connectors, high-frequency coaxial connectors, video connectors, coaxial converters, impedance converters, matching size converters, gender converters, microstrip coaxial converters, waveguide coaxial converters, matched load connectors, low-frequency connectors, printed circuit board connectors, ribbon cable connectors, integrated circuit connectors, hybrid connectors, etc.
5. Classified according to environmental conditions (the figure above shows waterproof connectors):
A: Sealed connectors;
B: High water pressure sealing connector;
C: High vacuum sealed connector;
D: Three prevention connectors;
E: Radiation resistant connectors;
F: High temperature connectors;
G: Low temperature connectors.
6. Classified by appearance:
Circular connectors, commonly used in military equipment; The rectangular connectors (mainly in the form of bayonets (quick), threads, automatic locking, push pull, direct insertion and pull, etc.) have a wide range of applications and are developing rapidly. Many board level connectors belong to rectangular connectors. There are generally two forms of connection between plugs and sockets: direct insertion and direct extraction, and thread locking
Circular connector
Rectangular connector

7. Classification according to application direction:
A: RF connectors;
B: Fiber optic connectors;
C: Non contact connectors (such as proximity switches, etc.)

The above classifications are all classified based on external or application attributes, and the specifics vary from manufacturer to manufacturer. Although NEDA has established classification standards for connector component packaging, with the advancement of technology, connector classification has become more complex. However, in terms of communication connectors, due to the cooperation of software protocols, there are indeed few changes and can be effectively distinguished.
A. Multi wire cable connectors, including DB connectors, DIX connectors, and DIN connectors.
B. Twisted pair connectors, including RJ45 and RJ11 connectors;
C. Coaxial cable connectors include T connectors, BNC connectors, and terminal resistors.

Carrying capacity
When choosing a connector for power signal transmission, attention should be paid to the current carrying capacity of the connector, and a derating design should be adopted, while also paying attention to the insulation and voltage resistance between the pins.
structure size
The overall size of the connector is very important, and there are certain space limitations for connection in the product, especially for connectors on single boards, which cannot interfere with other components. Choose the appropriate installation method based on the usage space and installation location (installation includes front and rear installation, and installation and fixation methods include rivets, screws, circlips, or quick locking of the connector itself) and appearance (straight, curved, T-shaped, circular, square).
impedance matching
Some signals have impedance requirements, especially radio frequency signals, which require stricter impedance matching. Impedance mismatch can cause signal reflection, thereby affecting signal transmission. There are no special requirements for the impedance of connectors in general signal transmission.
shield
With the development of communication products, EMC is increasingly valued. When selecting connectors, a metal shell is required, and the cable needs to have a shielding layer. The shielding layer should be connected to the metal shell of the connector to achieve shielding effect. Injection molding can also be used to wrap the plug part with copper sheet, and the shielding layer of the cable should be welded together with the copper sheet.
Anti Misinsertion
There are two aspects to preventing incorrect insertion: on the one hand, the connector itself rotates 180 degrees, and the signal is incorrectly connected due to misalignment. In this case, it is necessary to choose the anti incorrect insertion connector as much as possible, or adjust the relative position relationship of the connector to make the assembly unique; On the other hand, in order to reduce the variety of materials, several signals use the same connector. In this case, it is possible to plug the A plug into the B socket. It is important to note that if this situation can cause serious consequences (non simple alarm, destructive), the A and B interfaces must be selected as different types of sockets (such as A being male and B being female).
reliability
The connector is used to connect signals, so the connection part should be reliable (such as surface contact is better than point contact, needle hole type is better than leaf spring type, etc.).
Universality
In the selection process of connectors, it is necessary to choose universal materials as much as possible, especially between products of the same series. The selection of connectors has strong universality, reducing material types, increasing quantity, reducing costs, and reducing supply risks.
Usage environment
When connectors are used in outdoor, indoor, high temperature, high humidity, salt mist, mold, cold and other environments, there are special requirements for connectors.
Insertion and unplugging frequency
The plugging and unplugging of connectors have a certain lifespan. After reaching the limit of plugging and unplugging times, the performance of the connector will decrease. When selecting connectors for some signal interfaces that require frequent plugging and unplugging, it is important to pay more attention to the number of times the connector is plugged and unplugged.
Live condition
Choose a pin or hole type connector based on whether it is constantly charged or not.
Comprehensive consideration
In the process of selecting connectors, various factors are not independent and often interact with each other. Therefore, we need to comprehensively consider and choose the most suitable connector in the connector selection process. The quality of selection will affect the product to varying degrees at different stages.