What is an example of a electrical connector?

Device used to join electrical conductors

Components of an electrical circuit are electrically connected if an electric current can run between them through an electrical conductor. An electrical connector is an electromechanical device used to create an electrical connection between parts of an electrical circuit, or between different electrical circuits, thereby joining them into a larger circuit.[1]

The connection may be removable (as for portable equipment), require a tool for assembly and removal, or serve as a permanent electrical joint between two points.[2] An adapter can be used to join dissimilar connectors. Most electrical connectors have a gender – i.e. the male component, called a plug, connects to the female component, or socket.

Thousands of configurations of connectors are manufactured for power, data, and audiovisual applications.[3] Electrical connectors can be divided into four basic categories, differentiated by their function:[4]

In computing, electrical connectors are considered a physical interface and constitute part of the physical layer in the OSI model of networking.

Physical construction

[

edit

]

In addition to the classes mentioned above, connectors are characterised by their pinout, method of connection, materials, size, contact resistance, insulation, mechanical durability, ingress protection, lifetime (number of cycles), and ease of use.

It is usually desirable for a connector to be easy to identify visually, rapid to assemble, inexpensive, and require only simple tooling. In some cases an equipment manufacturer might choose a connector specifically because it is not compatible with those from other sources, allowing control of what may be connected. No single connector has all the ideal properties for every application; the proliferation of types is a result of the diverse yet specific requirements of manufacturers.[7]: 6 

Materials

[

edit

]

Electrical connectors essentially consist of two classes of materials: conductors and insulators. Properties important to conductor materials are contact resistance, conductivity, mechanical strength, formability, and resilience.[8] Insulators must have a high electrical resistance, withstand high temperatures, and be easy to manufacture for a precise fit

Electrodes in connectors are usually made of copper alloys, due to their good conductivity and malleability.[7]: 15  Alternatives include brass, phosphor bronze, and beryllium copper. The base electrode metal is often coated with another inert metal such as gold, nickel, or tin.[8] The use of a coating material with good conductivity, mechanical robustness and corrosion resistance helps to reduce the influence of passivating oxide layers and surface adsorbates, which limit metal-to-metal contact patches and contribute to contact resistance. For example, copper alloys have favorable mechanical properties for electrodes, but are hard to solder and prone to corrosion. Thus, copper pins are usually coated with gold to alleviate these pitfalls, especially for analog signals and high-reliability applications.[9][10]

Contact carriers that hold the parts of a connector together are usually made of plastic, due to its insulating properties. Housings or backshells can be made of molded plastic and metal.[7]: 15  Connector bodies for high-temperature use, such as thermocouples or associated with large incandescent lamps, may be made of fired ceramic material.

Failure modes

[

edit

]

The majority of connector failures result in intermittent connections or open contacts:[11][12]

Connectors are purely passive components – that is, they do not enhance the function of a circuit – so connectors should affect the function of a circuit as little as possible. Insecure mounting of connectors (primarily chassis-mounted) can contribute significantly to the risk of failure, especially when subjected to extreme shock or vibration.[11] Other causes of failure are connectors inadequately rated for the applied current and voltage, connectors with inadequate ingress protection, and threaded backshells that are worn or damaged.

High temperatures can also cause failure in connectors, resulting in an "avalanche" of failures – ambient temperature increases, leading to a decrease in insulation resistance and increase in conductor resistance; this increase generates more heat, and the cycle repeats.[11]

Fretting (so-called dynamic corrosion) is a common failure mode in electrical connectors that have not been specifically designed to prevent it, especially in those that are frequently mated and de-mated.[13] Surface corrosion is a risk for many metal parts in connectors, and can cause contacts to form a thin surface layer that increases resistance, thus contributing to heat buildup and intermittent connections.[14] However, remating or reseating a connector can alleviate the issue of surface corrosion, since each cycle scrapes a microscopic layer off the surface of the contact(s), exposing a fresh, unoxidised surface.

Circular connectors

[

edit

]

Many connectors used for industrial and high-reliability applications are circular in cross section, with a cylindrical housing and circular contact interface geometries. This is in contrast to the rectangular design of some connectors, e.g. USB or blade connectors. They are commonly used for easier engagement and disengagement, tight environmental sealing, and rugged mechanical performance.[15] They are widely used in military, aerospace, industrial machinery, and rail, where MIL-DTL-5015 and MIL-DTL-38999 are commonly specified. Fields such as sound engineering and radio communication also use circular connectors, such as XLR and BNC. AC power plugs are also commonly circular, for example, Schuko plugs and IEC 60309.

The M12 connector, specified in IEC 61076-2-101, is a circular electrical plug/receptacle pair with 12mm OD mating threads, used in NMEA 2000, DeviceNet, IO-Link, some kinds of Industrial Ethernet, etc.[16][17]

A disadvantage of the circular design is its inefficient use of panel space when used in arrays, when compared to rectangular connectors.

Circular connectors commonly use backshells, which provide physical and electromagnetic protection, whilst sometimes also providing a method for locking the connector into a receptacle.[18] In some cases, this backshell provides a hermetic seal, or some degree of ingress protection, through the use of grommets, O-rings, or potting.[15]

Hybrid connectors

[

edit

]

Hybrid connectors allow the intermixing of many connector types, usually by way of a housing with inserts.[19] These housings may also allow intermixing of electrical and non-electrical interfaces, examples of the latter being pneumatic line connectors, and optical fiber connectors. Because hybrid connectors are modular in nature, they tend to simplify assembly, repair, and future modifications. They also allow the creation of composite cable assemblies that can reduce equipment installation time by reducing the number of individual cable and connector assemblies.

Mechanical features

[

edit

]

Pin sequence

[

edit

]

Some connectors are designed such that certain pins make contact before others when inserted, and break first on disconnection.[1] This is often used in power connectors to protect equipment, e.g. connecting safety ground first. It is also employed for digital signals, as a method to sequence connections properly in hot swapping.

Keying

[

edit

]

Examples of keyed connectors

A 4-pin Mini-DIN S-Video cable, with notches and a rectangular alignment pin

Many connectors are keyed with some mechanical component (sometimes called a keyway), which prevents mating in an incorrect orientation.[20] This can be used to prevent mechanical damage to connectors, from being jammed in at the wrong angle or into the wrong connector, or to prevent incompatible or dangerous electrical connections, such as plugging an audio cable into a power outlet.[1] Keying also prevents otherwise symmetrical connectors from being connected in the wrong orientation or polarity. Keying is particularly important for situations where there are many similar connectors, such as in signal electronics.[7]: 26  For instance, XLR connectors have a notch to ensure proper orientation, while Mini-DIN plugs have a plastic projection that fits into a corresponding hole in the socket (they also have a notched metal skirt to provide secondary keying).[21]

Locking mechanisms

[

edit

]

Some connector housings are designed with locking mechanisms to prevent inadvertent disconnection or poor environmental sealing.[1] Locking mechanism designs include locking levers of various sorts, jackscrews, screw-in shells, push-pull connector, and toggle or bayonet systems. Some connectors, particularly those with large numbers of contacts, require high forces to connect and disconnect. Locking levers and jackscrews and screw-in shells for such connectors frequently serve both to retain the connector when connected and to provide the force needed for connection and disconnection. Depending on application requirements, housings with locking mechanisms may be tested under various environmental simulations that include physical shock and vibration, water spray, dust, etc. to ensure the integrity of the electrical connection and housing seals.

Backshells

[

edit

]

Backshells are a common accessory for industrial and high-reliability connectors, especially circular connectors.[18] Backshells typically protect the connector and/or cable from environmental or mechanical stress, or shield it from electromagnetic interference.[22] Many types of backshells are available for different purposes, including various sizes, shapes, materials, and levels of protection. Backshells usually lock onto the cable with a clamp or moulded boot, and may be threaded for attachment to a mating receptacle.[23] Backshells for military and aerospace use are regulated by SAE AS85049 within the USA.[24]

To deliver ensured signal stability in extreme environments, traditional pin and socket design may become inadequate. Hyperboloid contacts are designed to withstand more extreme physical demands, such as vibration and shock.[20] They also require around 40% less insertion force[25] – as low as 0.3 newtons (1 ozf) per contact,[26] – which extends the lifespan, and in some cases offers an alternative to zero insertion force connectors.[27][25]

In a connector with hyperboloid contacts, each female contact has several equally spaced longitudinal wires twisted into a hyperbolic shape. These wires are highly resilient to strain, but still somewhat elastic, hence they essentially function as linear springs.[28][29] As the male pin is inserted, axial wires in the socket half are deflected, wrapping themselves around the pin to provide a number of contact points. The internal wires that form the hyperboloid structure are usually anchored at each end by bending the tip into a groove or notch in the housing.[30]

Whilst hyperboloid contacts may be the only option to make a reliable connection in some circumstances, they have the disadvantage of taking up greater volume in a connector, which can cause problems for high-density connectors.[25] They are also significantly more expensive than traditional pin and socket contacts, which has limited their uptake since their invention in the 1920s by Wilhelm Harold Frederick.[31] In the 1950s, Francois Bonhomme popularised hyperboloid contacts with his "Hypertac" connector, which was later acquired by Smiths Group. During the following decades, the connectors steadily gained popularity, and are still used for medical, industrial, military, aerospace, and rail applications (particularly trains in Europe).[28]

Pogo pins

[

edit

]

Pogo pin or spring loaded connectors are commonly used in consumer and industrial products, where mechanical resilience and ease of use are priorities.[32] The connector consists of a barrel, a spring, and a plunger. They are in applications such as the MagSafe connector where a quick disconnect is desired for safety. Because they rely on spring pressure, not friction, they can be more durable and less damaging than traditional pin and socket design, leading to their use in in-circuit testing.[33]

Crown spring connectors

[

edit

]

Crown spring connectors are commonly used for higher current flows and industrial applications. They have a high number of contact points, which provides a more electrically reliable connection than traditional pin and socket connectors.[34]

Methods of connection

[

edit

]

Whilst technically inaccurate, electrical connectors can be viewed as a type of adapter to convert between two connection methods, which are permanently connected at one end and (usually) detachable at the other end.[7]: 40  By definition, each end of this "adapter" has a different connection method – e.g. the solder tabs on a male phone connector, and the male phone connector itself.[3] In this example, the solder tabs connected to the cable represent the permanent connection, whilst the male connector portion interfaces with a female socket forming a detachable connection.

There are many ways of applying a connector to a cable or device. Some of these methods can be accomplished without specialized tools. Other methods, while requiring a special tool, can assemble connectors much faster and more reliably, and make repairs easier.

The number of times a connector can connect and disconnect with its counterpart while meeting all its specifications is termed as mating cycles and is an indirect measure of connector lifespan. The material used for connector contact, plating type and thickness is a major factor that determines the mating cycles.[35]

Plug and socket connectors

[

edit

]

Plug and socket connectors are usually made up of a male plug (typically pin contacts) and a female socket (typically receptacle contacts). Often, but not always, sockets are permanently fixed to a device as in a chassis connector (see above), and plugs are attached to a cable.

Plugs generally have one or more pins or prongs that are inserted into openings in the mating socket. The connection between the mating metal parts must be sufficiently tight to make a good electrical connection and complete the circuit. An alternative type of plug and socket connection uses hyperboloid contacts, which makes a more reliable electrical connection. When working with multi-pin connectors, it is helpful to have a pinout diagram to identify the wire or circuit node connected to each pin.

Some connector styles may combine pin and socket connection types in a single unit, referred to as a hermaphroditic connector.[6]: 56  These connectors includes mating with both male and female aspects, involving complementary paired identical parts each containing both protrusions and indentations. These mating surfaces are mounted into identical fittings that freely mate with any other, without regard for gender (provided that the size and type match).

Sometimes both ends of a cable are terminated with the same gender of connector, as in many Ethernet patch cables. In other applications the two ends are terminated differently, either with male and female of the same connector (as in an extension cord), or with incompatible connectors, which is sometimes called an adapter cable.

Plugs and sockets are widely used in various connector systems including blade connectors, breadboards, XLR connectors, car power outlets, banana connectors, and phone connectors.

Jacks and plugs

[

edit

]

A jack is a connector that installs on the surface of a bulkhead or enclosure, and mates with its reciprocal, the plug.[36] According to the American Society of Mechanical Engineers,[37] the stationary (more fixed) connector of a pair is classified as a jack (denoted J), usually attached to a piece of equipment as in a chassis-mount or panel-mount connector. The movable (less fixed) connector is classified as a plug (denoted P),[37] designed to attach to a wire, cable or removable electrical assembly.[38] This convention is currently defined in ASME Y14.44-2008, which supersedes IEEE 200-1975, which in turn derives from the long-withdrawn MIL-STD-16 (from the 1950s), highlighting the heritage of this connector naming convention.[36] IEEE 315-1975 works alongside ASME Y14.44-2008 to define jacks and plugs.

The term jack occurs in several related terms:

• The registered jack or modular jack in RJ11, RJ45 and other similar connectors used for telecommunication and computer networking
• The telephone jack of manual telephone switchboards, which is the socket fitting the original

  1

  ⁄

  4

  inch (6.35 mm) telephone plug
• The

  1

  ⁄

  4

  inch (6.35 mm) phone jack common to many electronic applications in various configurations, sometimes referred to as a headphone jack
• The RCA jack, also known as a phono jack, common to consumer audiovisual electronics
• The EIAJ jack for consumer appliances requiring a power supply of less than 18.0 volts

Crimp-on connectors

[

edit

]

Crimped connectors are a type of solderless connection, using mechanical friction and uniform deformation to secure a connector to a pre-stripped wire (usually stranded).[1] Crimping is used in splice connectors, crimped multipin plugs and sockets, and crimped coaxial connectors. Crimping usually requires a specialised crimping tool, but the connectors are quick and easy to install and are a common alternative to solder connections or insulation displacement connectors. Effective crimp connections deform the metal of the connector past its yield point so that the compressed wire causes tension in the surrounding connector, and these forces counter each other to create a high degree of static friction. Due to the elastic element in crimped connections, they are highly resistant to vibration and thermal shock.[39]

Crimped contacts are permanent (i.e. the connectors and wire ends cannot be reused).[40]

Crimped plug-and-socket connectors can be classified as rear release or front release. This relates to the side of the connector where the pins are anchored:[20]

• Front release contacts are released from the front (contact side) of the connector, and removed from the rear. The removal tool engages with the front portion of the contact and pushes it through to the back of the connector.
• Rear release contacts are released and removed from the rear (wire side) of the connector. The removal tool releases the contacts from the rear and pulls the contact out of the retainer.

Soldered connectors

[

edit

]

Many plug and socket connectors are attached to a wire or cable by soldering conductors to electrodes on the back of the connector. Soldered joints in connectors are robust and reliable if executed correctly, but are usually slower to make than crimped connections.[1] When wires are to be soldered to the back of a connector, a backshell is often used to protect the connection and add strain relief. Metal solder buckets or solder cups are provided, which consist of a cylindrical cavity that an installer fills with solder before inserting the wire.[41]

When creating soldered connections, it is possible to melt the dielectric between pins or wires. This can cause problems because the thermal conductivity of metals causes heat to quickly distribute through the cable and connector, and when this heat melts plastic dielectric, it can cause short circuits or "flared" (conical) insulation.[40] Solder joints are also more prone to mechanical failure than crimped joints when subjected to vibration and compression.[42]

Insulation-displacement connectors

[

edit

]

Since stripping insulation from wires is time-consuming, many connectors intended for rapid assembly use insulation-displacement connectors which cut the insulation as the wire is inserted.[1] These generally take the form of a fork-shaped opening in the terminal, into which the insulated wire is pressed, which cut through the insulation to contact the conductor. To make these connections reliably on a production line, special tools accurately control the forces applied during assembly. On small scales, these tools tend to cost more than tools for crimped connections.

Insulation displacement connectors are usually used with small conductors for signal purposes and at low voltage. Power conductors carrying more than a few amperes are more reliably terminated with other means, though "hot tap" press-on connectors find some use in automotive applications for additions to existing wiring.

A common example is the multi-conductor flat ribbon cable used in computer disk drives; to terminate each of the many (approximately 40) wires individually would be slow and error-prone, but an insulation displacement connector can terminate all the wires in a single action. Another very common use is so-called punch-down blocks used for terminating unshielded twisted pair wiring.

Binding posts

[

edit

]

Binding posts are a single-wire connection method, where stripped wire is screwed or clamped to a metal electrode. Such connectors are frequently used in electronic test equipment and audio. Many binding posts also accept a banana plug.

Screw terminals

[

edit

]

Screw connections are frequently used for semi-permanent wiring and connections inside devices, due to their simple but reliable construction. The basic principle of all screw terminals involves the tip of a bolt clamping onto a stripped conductor. They can be used to join multiple conductors,[43] to connect wires to a printed circuit board, or to terminate a cable into a plug or socket.[7]: 50  The clamping screw may act in the longitudinal axis (parallel to the wire) or the transverse axis (perpendicular to the wire), or both. Some disadvantages are that connecting wires is more difficult than simply plugging in a cable, and screw terminals are generally not very well protected from contact with persons or foreign conducting materials.

Terminal blocks (also called terminal boards or strips) provide a convenient means of connecting individual electrical wires without a splice or physically joining the ends. Since terminal blocks are readily available for a wide range of wire sizes and terminal quantity, they are one of the most flexible types of electrical connector available. One type of terminal block accepts wires that are prepared only by stripping a short length of insulation from the end. Another type, often called barrier strips, accepts wires that have ring or spade terminal lugs crimped onto the wires.

Printed circuit board (PCB) mounted screw terminals let individual wires connect to a PCB through leads soldered to the board.

Ring and spade connectors

[

edit

]

The connectors in the top row of the image are known as ring terminals and spade terminals (sometimes called fork or split ring terminals). Electrical contact is made by the flat surface of the ring or spade, while mechanically they are attached by passing a screw or bolt through them. The spade terminal form factor facilitates connections since the screw or bolt can be left partially screwed in as the spade terminal is removed or attached. Their sizes can be determined by the gauge of the conducting wire, and the interior and exterior diameters.

In the case of insulated crimp connectors, the crimped area lies under an insulating sleeve through which the pressing force acts. During crimping, the extended end of this insulating sleeve is simultaneously pressed around the insulated area of the cable, creating strain relief. The insulating sleeve of insulated connectors has a color that indicates the wire's cross-section area. Colors are standardized according to DIN 46245:

• Red for cross-section areas from 0.5 to 1 mm²
• Blue for cross-section areas from 1.5 to 2.5 mm²
• Yellow for cross-section areas over 4 to 6 mm²

Blade connectors

[

edit

]

A blade connector is a type of single wire, plug-and-socket connection device using a flat conductive blade (plug) that is inserted into a receptacle. Wires are typically attached to male or female blade connector terminals by either crimping or soldering. Insulated and uninsulated varieties are available. In some cases the blade is an integral manufactured part of a component (such as a switch or a speaker unit), and the reciprocal connector terminal is pushed onto the device's connector terminal.

Other connection methods

[

edit

]

See also

[

edit

]

Connectors

[

edit

]

References

[

edit

]

General

• Foreman, Chris, "Sound System Design", Handbook for Sound Engineers, Third Edition, Glen M. Ballou, Ed., Elsevier Inc., 2002, pp. 1171–72.

Media related to Electrical connectors at Wikimedia Commons

01 August 2020

3097

Electrical Connector is an electromechanical component that connect the electrical circuit. It is composed of a fixed female contact (socket), and a free male contact (plug). According to the shape, there are circular electrical connector and rectangular electrical connector, and each type can be subdivided based on the connection method...

Catalog

I What is Electrical Connector?

Electrical Connector is an electromechanical component that connects the electrical circuit. It is composed of a fixed female contact (socket), and a free male contact (plug). According to the shape, there are circular electrical connectors and rectangular electrical connectors, and each type can be subdivided based on the connection method.

To select a suitable electrical connector, we should carefully consider their parameters, which include the electrical, safety, mechanical, and environmental parameters. In the future, electrical connectors will develop in many directions, especially in high-speed transmission.

II Electrical Connector Types

1. Circular Electrical Connector

According to the connection method of the electrical connector and the method of fixing the connection position, the connection form of the circular connector mainly includes types of the bayonet (fast), thread, automatic locking, push-pull, straight plug and pull.

Figure 1. Circular Electrical Connectors

(1) Thread Connection

The self-locking feature of the thread is used to connect the plug and the socket. In order to achieve fast connections, some use triple threads. And to ensure the anti-loosening under the vibration and shock after the connection, a fuse set screw or ratchet wheel structure is generally used.

This structure is reliable, easy for production and use, and can ensure the reliability of the product based on the anti-loosening structure.

(2) Bayonet Connection

This type of structure has three pins spaced 120° on the outer periphery of the socket. The matching plug connecting ring is equipped with a suitable three-curve groove, and a loaded spring to ensure safe self-locking.

This structure has two forms: inner three-curve and outer three-curve, as shown in the figure below. It's fast, reliable, and easy to use.

(3) Push-pull Connection

This type of structure has three steel balls with a 120° interval on the outer periphery of the plug. The matching socket has an arc groove. When inserted into place, the steel balls always in the arc groove under the action of the external force of the spring to ensure self-locking. This type of structure can achieve a fast connection.

2. Rectangular Electrical Connector

The connection method of the plug and the socket of the rectangular electrical connector generally has two forms: straight plug and pull and thread locking type.

Figure 2. Rectangular Electrical Connector

(1) Straight Plug and Pull Type

This type of structure mainly relies on the guide mechanism of the plug and socket to connect the product, and its locking structure mainly depends on the external structure. It's mainly used in the connection between printed boards or the connection between the chassis and cabinet.

(2) Thread-Locking Type

This structure adopts the leader pin bushing of the guide mechanism of the plug and socket to achieve the guidance and locking, which mainly used in the connection between printed boards and between printed boards and cables.

III Structure of Electrical Connector

The electrical connector is composed of a fixed female contact (socket), and a free male contact (plug). The socket is fixed(welded) to the electrical components through its square (circular) disk, and the plug is generally connected to the cable. The plug and socket are connected by connecting the nut.

The electrical connector is composed of three basic units: shell, insulator, and contact body.

1. Shell

The electrical connector shell refers to the housing, nut, and tail attachment of the plug and socket. The role of the shell is to protect the internal parts of the insulators and contact bodies from damage. The positioning keyway is for the plug and the socket, and the nuts are used to connect and disconnect the socket. The tail attachment is used to protect the connection point of the wire and the contact body from damage and also used to fix the cable.

The shell also has a certain electromagnetic shielding effect. It is generally made of aluminum alloy through machining, cold extrusion, die casting. Steel shells are mostly used for glass sealing and high-temperature resistant electrical connectors.

Figure 3. Aluminum Alloy Electrical Connector

2. Insulator

The insulator consists of a pin insulator, jack insulator, interface seal body, and line seal body, etc. It is used to keep the pin and jack at the set position and create electrical insulation among each contact body and between the contact body and the shell. The interface seal body and line seal body are added to the insulator to improve the environmental resistance of the electrical connector.

In order to achieve high-temperature and low-temperature resistance, flame retardancy, and ensure the stability of the geometric dimensions of parts, most insulators are molded from thermoset plastic, and the interface seal body and the line seal body are molded from silicone rubber.

Figure 4. Thermoset Plastic Moulding

3. Contact Body

The contact body includes a male contact piece and a female contact piece sometimes called a pin and a jack. And the connection methods are divided into the welding type, the crimping type, the press-in type, and the winding type, etc., to realize circuit connection.

The pin and the jack are the key component of the electrical connector, which directly affects reliability. Most of the pin and jack are machined from elastic copper alloy materials with good conductivity, and the surface is silver-plated or gold-plated to achieve low contact resistance and anti-corrosion. Generally, there are slotted jack, wire spring jack, crown spring jack, and punched jack.

Structural characteristics:

• environment resistance

• bayonet (fast) connection

• multi-key keyway (avoid misinsertion)

• crimp connection of the contact body and wire

The shielding ring ensures 360° electromagnetic interference shielding.

IV Electrical Connector Parameters

Electrical connectors are electromechanical components that connect electrical circuits. Therefore, the electrical parameters of the connector itself are the first issues to be considered when we select the connector.

1. Electrical Parameters

(1) Rated voltage

Rated voltage is also called working voltage. It mainly depends on the insulating material used by the machine and the distance between the contact pairs. Some components or devices may not be able to perform their proper functions when the voltage is below their rated value.

The rated voltage of the connector should in fact be understood as the highest working voltage recommended by the manufacturer. In principle, the connector can work normally under the rated voltage. To reasonably choose the rated voltage, we can consider the voltage resistance (dielectric strength) of the connector, the working environment, and safety requirements. That is to say, with the same withstand voltage index, according to different working environments and safety requirements, we should choose different maximum working voltages.

(2) Rated Current

It's also known as working current. As with the rated voltage, the connector generally works normally under the rated current.

In the connector design process, the thermal design is to meet the rated current requirements. When there is a current flowing through the contact pair, due to the conductor resistance and contact resistance, the contact pair will heat up. When its heat exceeds a certain limit, it will damage the insulation of the connector and soften the surface coating of the contact pairs, causing malfunctions. Therefore, to limit the rated current, in fact, is to limit the temperature rise inside the connector within the rated value.

Figure 5. Multi-Core Electrical Connection

For multi-core electrical connectors, the current must be derated, especially in the case of large currents. For example, the φ3.5mm contact pair is generally specified to have a rated current of 50A, but it needs to be derated by 33% when it is with 5 cores, that is, the rated current of each core is only 38A. The more core, the greater the derating. The derating range can refer to Table 1.

Number of Cores

1

2

3

4

5

6

7

8

9

10

11

12

13

14

>15

Derating Rate

100

94.3

88.6

82.9

77.1

71.4

65.7

60

54.3

48.6

42.9

37.1

31.4

25.7

20

Table 1.

(3) Contact Resistance

Contact resistance refers to the resistance generated by the two conductors at the contact part. There are two issues to be noted.

First, the contact resistance index of the connector is actually the resistance of the contact pair, which includes the contact resistance and the conductor resistance of the connect pair. Usually, the conductor resistance is small, so the contact pair resistance is called contact resistance in many technical specifications.

Second, in the circuit that connects small signals, pay attention to the conditions under which the contact resistance index is tested.

There may be an oxide layer, oil stains, or other contaminants on the contact surface, and the film resistance will be produced on the surfaces of the two contacts. When the thickness of the film increases, the resistance increases rapidly, making the film layer become a poor conductor. However, the film will undergo mechanical breakdown under high contact pressure or electrical breakdown under high voltage and large current.

The contact pressure of some small-volume connectors is quite small, only in mA and mV. The film resistor is not easy to be broken down, which may affect the transmission of electrical signals.

(4) Shielding Property

In modern electrical and electronic equipment, the increasing density of components and related functions between them has imposed strict restrictions on electromagnetic interference. Therefore, the connector is often packed with a metal shell to avoid the internal electromagnetic radiation and the interference from the external electromagnetic field. At low frequencies, only magnetic materials can significantly shield the magnetic field.

2. Safety Parameters

(1) Insulation Resistance

Insulation resistance refers to the resistance value generated by the leakage current in or on the surface of the insulation part when a voltage is applied. It is mainly affected by insulation materials, temperature, humidity, stain, and other factors. The insulation resistance value provided on the electrical connector sample is generally the index value under standard atmospheric conditions. And in some environments, the value will decrease.

We should pay attention to the test voltage value of the insulation resistance. According to the formula:

insulation resistance (MΩ) = voltage applied to the insulator (V)/leakage current (μA),

different voltages will have different results. In the test, the applied voltage is generally 10V, 100V and 500V.

(2) Withstand Voltage

The withstand voltage is the critical voltage that the mutually insulating parts of the contact pairs or parts between the insulating parts and the ground can withstand without breakdown within a specified time, which is higher than the rated voltage.

It is mainly affected by the contact pair distance, creepage distance and geometric shape, insulator material, ambient temperature and humidity, and atmospheric pressure.

(3) Flammability

Electrical connectors can't work without the current, which may cause a fire. Therefore, the connector is required not only to prevent ignition, but also to self-extinguish in a short time once it ignites and catches fire. When choosing, pay attention to the electrical connector with flame retardant, self-extinguishing insulating material.

3. Mechanical Parameters

(1) One-foot Separation Force and Total Separation Force

The contact pressure is an important indicator of the electrical connector, which directly affects the contact resistance and the amount of abrasion loss. In most structures, it is quite difficult to directly measure the contact pressure, so we measure it through the separation force of one foot.

For contact pairs with circular pinholes, a standard pin with a specified weight is usually used to test the clamping ability of the jack. The diameter of the standard pin is -5μm shorter than the lower limit of the pin diameter.

The total separation force is generally twice the upper limit of the one-foot separation force. When the total separation force exceeds 50N, it is quite difficult to plug and pull manually. Of course, for some test equipment or occasions with special requirements, we can choose zero insertion force connector, self-releasing connector, and so on.

(2) Mechanical Life

The mechanical life of the electrical connector refers to the life for plug and pull, which is usually specified as 500 to 1000 times. When reaching the specified mechanical life, the contact resistance, insulation resistance and withstand voltage of the connector should not exceed the specified value.

Strictly speaking, mechanical life is a vague concept. It should have a certain relationship with time. 500 times in 10 years and 500 times in one year is obviously different. It's just that there is no more economical and scientific way to measure it by now.

(3) Number of Contact Pairs and Pinholes

First, the number of contact pairs depends on the needs of the circuit, and at the same time, the connector volume and the total separation force must be considered. The more contact pairs, the larger the volume, and the greater the total separation force. When high reliability is required and the volume is allowed, two contact pairs can be connected in parallel to improve the reliability of the connection.

In the plug and socket of the connector, the pin and the jack can generally be interchanged. For example, if the socket needs to be charged frequently, you can choose the socket with the jack. Because of the socket with the jack, the charged contact is buried in the insulator, which is relatively safe because we can not touch it easily.

Figure 6. The Plug and Socket

(4) Vibration, Impact, and Collision

We should mainly focus on the electrical continuity of the contact pairs under vibration, impact, and collision at specified frequency and acceleration. The contact pair will instantaneously turn off under this dynamic stress. The specified instantaneous turn-off time is generally 1μs, 10μs, 100μs, 1ms, and 10ms.

So how can we identify if there is an instantaneous turn-off failure? It is currently believed that when the voltage drop across the closed contact pair exceeds 50% of the power electromotive force, it can be determined that the contact pair has failed. In other words, there are two conditions for judging whether an instantaneous turn-off occurs: duration and voltage drop, both of which are indispensable.

4. Environmental Parameters

Environmental parameters mainly include ambient temperature, humidity, rapid temperature change, atmospheric pressure, and corrosive environment. The environment in which the connector is used, stored, and transported has a significant impact on its performance, so the connector must be selected according to the actual environmental conditions.

(1) Ambient Temperature

The metallic and insulating materials of the connector determine the working temperature of the connector. The high temperature will damage the material, causing a decrease in insulation resistance and pressure resistance. Besides, it can make contact pair lose elasticity, accelerating oxidation and plating deterioration. The general ambient temperature is -55-100℃, which may be more specific on special occasions.

(2) Humidity

Relative humidity greater than 80% is the main cause of the electric breakdown. The humid environment causes the absorption and diffusion of water vapor on the surface of the insulator, which can easily reduce the insulation resistance to below the MΩ level. Long-term exposure to high humidity will cause physical deformation, decomposition, and escape of products, resulting in respiratory effects, electrolysis, corrosion, and crack. Especially for the electrical connectors outside the equipment, moisture, water seepage, and pollution are considered.

(3) Rapid Temperature Change

The rapid temperature change test is to simulate the actual use of the connector device from a cold environment to a warm environment or to simulate the situation of a sudden change in the ambient temperature of a spacecraft or detector. Sudden changes in temperature may cause cracking or layering of the insulating material.

(4) Atmospheric Pressure

At high altitudes with thin air, the plastic emits gas to contaminate the contact pair, and the corona increases, the pressure resistance performance decreases, causing a short circuit fault. When the altitude reaches a certain value, the performance of the plastic deteriorates. Therefore, when unsealed electrical connectors are used at high altitudes, they must be derated. The recommended voltage derating factor at low pressure is shown in Table 2.

Height h/m

Pressure p/102Pa

Derating Rate

>

≤

<

&ge;

-

2000

-

795

1

2000

3000

795

700

0.74

3000

4000

700

620

0.67

4000

5000

620

540

0.61

5000

6000

540

470

0.51

6000

7000

470

410

0.44

7000

8000

410

355

0.38

8000

9000

355

305

0.33

9000

10000

305

265

0.30

Table 2.

(5) Corrosive Environment

We should choose connectors with corresponding metal, plastic, and plating structures according to the corrosive environment of the electrical connector. For example, for connectors used in salt-spray environments, if there is no corrosion-resistant metal surface, the performance will deteriorate rapidly. And in an environment with a considerable concentration of SO2, it is not appropriate to use connectors with silver-plated contact pairs. In hot areas, mold is also an important issue.

V Butt Joint Method

The butt joint method refers to the connection method between the contact pair and the wire or cable. Reasonable selection and proper use of butt joint methods are also important aspects of using and selecting electrical connectors.

1. Welding

The most common type of welding is tin soldering, and the most important thing for it is the continuity between the solder material and the soldered surface. Therefore, for electrical connectors, solderability is important.

Tin alloys, silver, and gold are the most common coatings on the soldering end of connectors. The reed contact pair has a welding end of solder tab, punching solder tab, and notched solder tab type, while the pinhole contact has a drilled arc notch type for the common welding end.

2. Crimping

Crimping is a technique to connect wires to contact pairs for compressing and displacing metal within the limits. Good crimping can produce intermetallic fusion flow so that the wires and contacts material deform symmetrically. This kind of connection is similar to a cold welding connection, which can get better mechanical strength and electrical continuity, and can withstand more severe environmental conditions.

At present, it is generally believed that crimping is better than soldering, especially on high-current occasions. Special crimping tools or automatic or semi-automatic crimping machines must be used in crimping. And the wire barrel should be selected correctly according to the cross-section of the wire. It should be noted that crimping is a permanent connection and can only be used once.

3. Winding

Winding is to wind the wire directly on the winding post of the angular contact. The wire is wound under the tension, and pressed into and fixed at the corners of the winding post to form an airtight contact. There are several requirements for wire winding:

• the nominal value of the wire diameter should be in the range of 0.25mm -1.0mm;

• when the wire diameter &le; 0.5mm, the elongation of the conductor material is &ge; 15%;

• when the wire diameter is > 0.5mm, the elongation of the conductor material is &ge; 20%.

Tools for winding include wire wrap tools and fixed winding machines.

4. Puncture Connection

Puncture connection, also known as insulation displacement connection(IDC), is a novel end technology invented in the United States in the 1960s with high reliability, low cost, and ease of use. It has been widely used in various electrical connectors for printed boards and is suitable for the connection of ribbon cables.

Figure 7. Example of IDC connectors in a small module

It is not necessary to strip the insulation layer of the cable during the connection, instead, penetrate the tip of the U-shaped contact spring of the connector into the insulation layer to make the cable conductor slide into the groove of the contact spring and be clamped so that a tight electrical connection is formed between them. It requires only simple tools but must use cables with a specified wire gauge.

VI Development Characteristics

The electrical connector is developing in the direction of

● miniaturization, high density, and high-speed transmission;

● high-performance and high-frequency technology;

● high-voltage, high-current electric

● anti-interference technology, modular technology, and lead-free technology.

In the case where the speed of the traditional parallel synchronous digital signal is about to reach its limit, the high-speed serial method is a good solution. This makes low voltage differential signaling (LVDS) become the primary next-generation high-speed signal level standard. The selection of high-speed electrical connectors has also become the main problem to be solved for high-speed signal interconnection.

Several key technologies used in the development of high-speed electrical connectors include:

● The differential signal, noise-free signal, and ground layer technology are used to reduce crosstalk;

● To adjust the lead of the connector, we can change the delay difference caused by the unequal physical distance between the input and output of the connector;

● In order to obtain maximum transmission efficiency, the characteristic impedance value of the connector should match that of the transmission circuit.