Introduction to Connectors
1.Definition of Connectors
Connectors, also known as interconnect devices, are components used to connect two active devices. Connectors, commonly referred to as plugs and sockets, are typically used in electrical applications to transfer electrical current or signals. Some well-known brands for connectors include JST, Tyco Electronics, Toshiba, Molex, and others. The interface where the male and female ends make contact and transmit information or electric current is also referred to as a connector.
2.Benefits of Connectors
2.1 Streamline Production Processes
Connectors simplify the assembly process of electronic products and facilitate mass production.
2.2 Ease of Maintenance
When a specific electronic component fails, having connectors allows for quick replacement of the faulty component.
2.3 Facilitate Upgrades
With the advancement of technology, connectors enable the updating of components with newer and more advanced ones, replacing the older ones.
2.4 Enhance Design Flexibility
The use of connectors provides engineers with greater flexibility in designing and integrating new products and systems with various components.
3.Basic Performance of Connectors
The basic performance of connectors can be categorized into three main types: mechanical performance, electrical performance, and environmental performance. Mechanical lifespan is an important aspect of connector performance. It measures the durability of the connector and is evaluated based on whether the connector can successfully fulfill its connection function (e.g., contact resistance) after a specified number of insertion and withdrawal cycles.
3.1 Mechanical Performance
In terms of connection functionality, insertion force and withdrawal force (also known as separation force) are important mechanical performance factors. The requirements for insertion force and withdrawal force are different. Relevant standards specify maximum insertion force and minimum separation force. Generally, low insertion force (LIF) or zero insertion force (ZIF) structures are preferred to minimize insertion force, while separation force should be sufficient to ensure reliable contact. Insertion and withdrawal forces, as well as mechanical lifespan, depend on factors such as contact structure (normal force), coating quality on contact surfaces (coefficient of friction), and dimensional accuracy of contact arrangements (alignment).
3.2 Electrical Performance
The main electrical performance factors of connectors include contact resistance, insulation resistance, and dielectric strength.
►Contact resistance: High-quality connectors should exhibit low and stable contact resistance, typically ranging from a few milliohms to tens of milliohms.
►Insulation resistance: It measures the insulation performance between contact elements and between contact elements and the shell of the connector, typically in the range of several hundred megohms to several teraohms.
►Dielectric strength: Also known as withstand voltage or insulation voltage, it indicates the ability of the connector to withstand the rated test voltage between contact elements or between contact elements and the shell.
►Other electrical performance factors may include electromagnetic interference leakage attenuation, which evaluates the electromagnetic interference shielding effect of the connector. For coaxial connectors, additional electrical indicators such as characteristic impedance, insertion loss, reflection coefficient, and voltage standing wave ratio (VSWR) are considered. With the development of digital technology, high-speed signal connectors have emerged to connect and transmit high-speed digital pulse signals. Consequently, new electrical performance indicators such as crosstalk, delay, and skew have been introduced.
3.3 Environmental Performance
Common environmental performance factors for connectors include temperature resistance, humidity resistance, salt spray resistance, vibration resistance, and impact resistance.
►Temperature resistance: The highest operating temperature for connectors is currently 200°C (excluding certain special high-temperature connectors), while the lowest temperature is -65°C. As connectors generate heat at the contact points during operation, resulting in temperature rise, the working temperature is typically considered as the sum of the ambient temperature and contact temperature rise. Some specifications explicitly define the maximum temperature rise allowed under rated operating current.
►Humidity resistance: Moisture ingress can affect the insulation performance of connectors and corrode metal components. Constant damp-heat test conditions typically involve a relative humidity of 90% to 95% (or up to 98% based on product specifications) and a temperature of +40±20°C, with a minimum test duration specified in the product requirements, often no less than 96 hours. Alternating damp-heat tests are more stringent.
►Salt spray resistance: When connectors operate in environments with moisture and salt content, their metallic structural parts and contact surfaces may undergo galvanic corrosion, affecting the physical and electrical performance of the connectors. To evaluate the connector’s ability to withstand such environments, salt spray tests are conducted. Connectors are suspended in a temperature-controlled test chamber, where compressed air with a specified concentration of sodium chloride solution is sprayed, creating a salt fog atmosphere. The exposure time is determined by product specifications, typically lasting at least 48 hours.
Vibration and impact resistance: Vibration and impact resistance are important performance indicators for connectors, particularly in special application environments such as aviation, aerospace, railway, and road transportation. These indicators assess the mechanical robustness and electrical contact reliability of connectors. Relevant test methods provide specific requirements for peak acceleration, duration, pulse waveform, and the duration of electrical continuity interruption.
►Other environmental performance factors: Depending on specific requirements, connectors may also have additional environmental performance considerations, such as sealing (air leakage, liquid pressure), immersion in specific liquids (resistance to specific chemicals), low air pressure, etc.
4.Categories of Connectors
Although the categorization of connector products may appear somewhat confusing, from a technical standpoint, connectors can be divided into two basic types:
►Based on the outer structural form: Circular and rectangular (cross-section).
►Based on working frequency: Low frequency and high frequency (with 3MHz as the boundary).
According to the above classification, coaxial connectors belong to the circular category, and printed circuit board (PCB) connectors belong to the rectangular category (historically, PCB connectors were separated from rectangular connectors to form a distinct category). Currently popular rectangular connectors have a trapezoidal cross-section, which approximates a rectangle. The division between low frequency and high frequency at 3MHz aligns with the frequency division of radio waves.
Regarding other classification criteria such as application, installation method, special structures, special performance, etc., many different types can be identified and often appear in publications and promotional materials. However, these classifications usually serve to highlight specific features and applications, without exceeding the basic classification principles outlined above.
Considering the technological developments and practical considerations of connectors, as well as their universality and related technical standards, connectors can be categorized into the following types:
►Low-frequency circular connectors
►Rectangular connectors
►PCB connectors
►Coaxial connectors
►Fiber optic connectors.