Connector knowledge: The basic performance of connectors can be divided into three main categories: mechanical performance, electrical performance, and environmental performance.
1. Mechanical Performance
In terms of connection function, insertion and extraction force is an important mechanical performance characteristic. Insertion and extraction force are divided into insertion force and extraction force (also called separation force), and the requirements for the two are different. Relevant standards specify maximum insertion force and minimum separation force, indicating that from a usage perspective, the insertion force should be low (hence the existence of low insertion force (LIF) and zero insertion force (ZIF) structures), while too low a separation force will affect the reliability of the contact. The insertion and extraction force and mechanical life of a connector are related to the contact structure (magnitude of normal force), the quality of the plating at the contact points (coefficient of sliding friction), and the dimensional accuracy of the contact arrangement (alignment).
2. Electrical Performance
The main electrical performance characteristics of connectors include contact resistance, insulation resistance, and dielectric strength.
a. Contact Resistance: High-quality electrical connectors should have low and stable contact resistance. The contact resistance of connectors ranges from a few milliohms to tens of milliohms.
b. Insulation resistance measures the insulation performance between connector contacts and between contacts and the shell, ranging from hundreds of megohms to thousands of megohms.
c. Dielectric strength, also known as withstand voltage or dielectric withstand voltage, characterizes the connector's ability to withstand the rated test voltage between contacts or between contacts and the shell.
d. Other electrical performance characteristics.
Electromagnetic interference leakage attenuation evaluates the connector's electromagnetic interference shielding effectiveness, typically tested within the 100MHz to 10GHz frequency range.
For RF coaxial connectors, there are also electrical indicators such as characteristic impedance, insertion loss, reflection coefficient, and voltage standing wave ratio (VSWR). Due to the development of digital technology, a new type of connector, the high-speed signal connector, has emerged for connecting and transmitting high-speed digital pulse signals. Correspondingly, in terms of electrical performance, in addition to characteristic impedance, new electrical indicators have appeared, such as crosstalk, transmission delay, and skew.
3. Environmental Performance
Common environmental performance characteristics include temperature resistance, humidity resistance, salt spray resistance, vibration, and shock resistance.
a. Temperature Resistance: Currently, the highest operating temperature for connectors is 200℃ (except for a few high-temperature special connectors), and the lowest is -65℃. Since current generates heat at the contact points during connector operation, causing a temperature rise, the operating temperature is generally considered to be the sum of the ambient temperature and the contact temperature rise. Some specifications explicitly define the maximum permissible temperature rise of the connector under rated operating current.
b. Moisture Resistance: Moisture intrusion can affect the insulation performance of the connector and corrode metal parts. Constant humidity and heat test conditions are 90%~95% relative humidity (up to 98% according to product specifications), temperature +40±20℃, and test time as specified by the product, with a minimum of 96 hours. Alternating humidity and heat tests are even more stringent.
c. Salt Spray Resistance: When connectors operate in environments containing moisture and salt, electrochemical corrosion may occur on the surface treatment layers of their metal structural components and contacts, affecting the physical and electrical performance of the connector. To evaluate the ability of electrical connectors to withstand such environments, a salt spray test is specified. This involves suspending the connector in a temperature-controlled test chamber and spraying it with compressed air using a sodium chloride solution of a specified concentration to create a salt spray atmosphere. The exposure time is specified in the product specification and must be at least 48 hours.
d. Vibration and Shock Resistance: Vibration and shock resistance are crucial performance characteristics of electrical connectors, especially important in specialized applications such as aerospace, rail, and road transportation. They are important indicators of the robustness of the connector's mechanical structure and the reliability of its electrical contacts. Specific test methods clearly define these characteristics. Shock tests should specify the peak acceleration, duration, and shock pulse waveform, as well as the duration of electrical continuity interruption.
e. Other Environmental Performance: Depending on the application requirements, other environmental performance characteristics of electrical connectors include sealing (air leakage, liquid pressure), liquid immersion (resistance to degradation by specific liquids), and low-pressure resistance.