Basics to An Electronic Connector

Connectors are a component that electronic engineering technicians often use. Its function is very simple: it sets up a bridge of communication between the blocked or isolated circuits in the circuit, so that the current flows and the circuit realizes the predetermined function. Connectors are an indispensable part of electronic equipment, and you will always find one or more connectors along the path of current flow. The form and structure of connectors are ever-changing, and there are various forms of connectors with different application objects, frequencies, power, and application environments. For example, the connector used to light a light on a court is very different from the connector used to drive a hard drive, and the connector used to ignite a rocket. But no matter what kind of connector, it is necessary to ensure that the current flows smoothly, continuously and reliably. In general terms, what the connector connects is not limited to current. In today's rapid development of optoelectronic technology, in the optical fiber system, the carrier of the signal is light, glass and plastic replace the wires in the ordinary circuit, but the optical signal connectors are also used in pathways, and they serve the same purpose as circuit connectors.

Imagine what it would be like if there were no connectors? At this time, the circuits should be permanently connected with continuous conductors. For example, if an electronic device is to be connected to the power supply, both ends of the connecting wire must be firmly connected to the electronic device and the power supply by some method (such as welding). As a result, it brings a lot of inconvenience to both production and use. For example, assuming that the battery cable is fixed and welded to the battery, the car manufacturer increases the workload for installing the battery, increasing the production time and cost. When the battery is damaged and needs to be replaced, it is necessary to send the car to a repair station, remove the old one by de-soldering, and then re-soldering the new one, which requires more labor costs. Having the connector saves a lot of hassle, just buy a new battery from the store, disconnect the connector, remove the old battery, put in the new battery, and reconnect the connector. This simple example illustrates the benefits of connectors. It makes the design and production process more convenient and flexible, reducing production and maintenance costs.

1. Improve the production process: Connectors simplify the assembly process of electronic products. The mass production process is also simplified.

2. Easy maintenance: If an electronic component fails, the failed component can be quickly replaced when the connector is installed.

3. Easy to upgrade: As technology advances, components can be updated when connectors are installed, replacing old ones with new and better components to improve design flexibility. Using connectors enables engineers to design and integrate new products and with greater flexibility when composing systems with components.

The basic structural parts of the connector include contacts, insulators, shells (depending on the variety), and accessories.

1. Contacts: It is the core part of the connector to complete the electrical connection function. Generally, a contact pair is composed of a male contact piece and a female contact piece, and the electrical connection is completed by the insertion of the female contact piece and the male contact piece.

The male contact is a rigid part, and its shape is cylindrical (round pin), square cylinder (square pin) or flat (insert). The male contacts are generally made of brass and phosphor bronze.

 

The female contact is the jack, which is the key part of the contact pair. It relies on the elastic structure to elastically deform when it is inserted into the pin to generate elastic force to form close contact with the male contact to complete the connection. There are many types of jack structures, including cylindrical type (splitting, shrinking), tuning fork type, cantilever beam type (longitudinal slotting), folding type (longitudinal slotting, figure 9), box type (square jack) as well as hyperboloid wire spring jacks and so on.

2. Insulator: The insulator is also often referred to as a base or an insert. Its function is to arrange the contacts at the required position and spacing, and to ensure the insulation between the contacts and between the contacts and the housing. Good insulation resistance, withstand voltage performance and ease of processing are the basic requirements for selecting insulating materials to be processed into insulators.

3. Case: Also known as the shell, it is the outer cover of the connector, which provides mechanical protection for the built-in insulating mounting plate and pins, and provides the alignment of the plug and socket when they are mated, thereby securing the connector to the device.

4. Appendix: Accessories are divided into structural accessories and installation accessories. Structural accessories such as retaining rings, positioning keys, positioning pins, guide pins, coupling rings, cable clamps, sealing rings, gaskets, etc. Mounting accessories such as screws, nuts, screws, spring rings, etc. Most of the accessories have standard parts and general parts.

The basic performance of connectors can be divided into three categories: mechanical performance, electrical performance, environmental performance.

1. Mechanical perfermance: As far as the connection function is concerned, the insertion force is an important mechanical property. The insertion force is divided into the insertion force and the extraction force (the extraction force is also called the separation force), and the requirements of the two are different. In the relevant standards, there are provisions for the maximum insertion force and the minimum separation force, which means that from the point of view of use, the insertion force should be small (thereby a structure with low insertion force LIF and no insertion force ZIF), and if the separation force is too small, will affect the reliability of the contact.

Another important mechanical property is the mechanical life of the connector. Mechanical life is actually a durability index, which is called mechanical operation in the national standard GB5095. It takes one insertion and one extraction as a cycle, and judges whether the connector can normally complete its connection function (such as contact resistance value) after the specified insertion and extraction cycle.

The insertion force and mechanical life of the connector are related to the contact structure (positive pressure), the coating quality (sliding friction coefficient) of the contact part, and the dimensional accuracy (alignment) of the contact arrangement.

2. Electrical performance: The main electrical properties of connectors include contact resistance, insulation resistance and electric strength.

(a) Contact resistance: A high-quality electrical connector should have a low and stable contact resistance. The contact resistance of connectors varies from a few milliohms to tens of milliohms.

(b) Insulation resistance: an index to measure the insulation performance between the contacts of an electrical connector and between the contacts and the shell, and its magnitude ranges from hundreds of megohms to several gigaohms.

(c) Dielectric strength: or withstand voltage, dielectric withstand voltage is to characterize the ability of the connector to withstand the rated test voltage between the contacts or between the contacts and the shell.

(d) Other electrical properties: EMI leakage attenuation is to evaluate the electromagnetic interference shielding effect of the connector, and electromagnetic interference leakage attenuation is to evaluate the electromagnetic interference shielding effect of the connector, generally tested in the frequency range of 100MHz~10GHz.

 

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, in order to connect and transmit high-speed digital pulse signals, a new type of connector, namely high-speed signal connector, has appeared. Correspondingly, in terms of electrical performance, in addition to characteristic impedance, some new electrical indicators have appeared. Such as crosstalk, transmission delay, time delay and so on.

3. Environmental performance: Common environmental properties include temperature, humidity, salt spray, vibration and shock.

(a) Temperature resistance: At present, the maximum working temperature of the connector is 200°C (except for a few high-temperature special connectors), and the minimum temperature is -65°C. Since the current generates heat at the contact point when the connector is working, resulting in a temperature rise, it is generally believed that the operating temperature should be equal to the sum of the ambient temperature and the temperature rise of the contact point. In some specifications, the maximum temperature rise allowed by the connector at the rated operating current is clearly specified.

(b) Moisture resistance: The intrusion of moisture will affect the insulation performance of the connector and corrode metal parts. The constant damp heat test conditions are relative humidity 90%~95% (according to product specifications, up to 98%), temperature +40±20℃, and the test time is at least 96 hours according to product regulations. The alternating damp heat test is more severe.

(c) Salt spray resistance: When the connector works in an environment containing moisture and salt, its metal structural parts and the surface treatment layer of the contact parts may cause galvanic corrosion, which affects the physical and electrical properties of the connector. To evaluate the ability of electrical connectors to withstand this environment, the salt spray test is specified. It is to hang the connector in a temperature-controlled test box, and spray the sodium chloride solution with the specified concentration with compressed air to form a salt fog atmosphere. The exposure time is specified by the product specification, at least 48 hours.

(d) Vibration and shock: Vibration and shock resistance are important properties of electrical connectors, especially in special application environments such as aviation and aerospace, railway and road transportation. An important indicator of contact reliability. There are clear provisions in the relevant test methods. The shock test shall specify the peak acceleration, duration and shock pulse shape, as well as the time of interruption of electrical continuity.

 

(e) Other environmental properties: According to the requirements of use, other environmental properties of electrical connectors include sealing (air leakage, liquid pressure), liquid immersion (the ability to resist deterioration of specific liquids), low air pressure, etc.