Device used to join electrical conductors

This rear panel of an integrated amplifier features a variety of electrical connectors Connectors on the back of a 2018 computer

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

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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

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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

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

Failure mode Relative probability Open circuit 61% Poor contact 23% Short circuit 16%

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

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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.

NMEA 2000 cabling using M12 connectors

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

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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

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Pin sequence

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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

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Examples of keyed connectors

XLR connector , showing the notch for alignment

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

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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

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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

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Pogo pin connectors

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

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Typical crown spring plug and its female socket

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

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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

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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

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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

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  inch (6.35 mm) telephone plug
• The

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  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

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A wire and connector being crimped together with a crimping tool

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

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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

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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

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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

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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 of various types

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

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Ring style wire-end crimp connectors

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

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Blade connectors (lower half of photo). Ring and spade terminals (upper half). Bullet terminals, male and female (right-center, with blue wires)

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

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See also

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Connectors

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References

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General

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

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Introduction

This article takes an in depth look at electronic connectors.

Read further and learn more about topics such as:

• What are electronic connectors?
• Terminology used in electronic connectors
• Types of electronic connectors
• Termination methods
• And much more…

Chapter 1: What are Electronic Connectors?

Electronic connectors are devices that join electronic circuits. They are used in assembling, installing, and supplying power to electrical devices. Connectors are an important component of every electronic equipment used in industrial machinery, consumer electronics, communications, and home and commercial appliances. These devices are often overlooked, but they make every electronic product functional and complete. Most connectors are temporary or removable; some are used as permanent electrical joints.

The two main components of an electrical connector are its contacts and housing, also referred to as its plug or receptacle. The housing holds the terminals and ensures the stability of their connections. It isolates the terminals from other electronic components and prevents short-circuiting. Plugs and receptacles protect the terminals from the elements and weather and are made from insulating materials such as molded plastics or ceramics.

Additional parts may be added to a connector depending on how it will be used. Key connectors can only be inserted in a specific orientation. A lock can be placed on a connector to prevent it from being undone while sealed connectors can be used underwater.

Connector terminals are the pins that provide a continuous path for the electrical current to flow between circuits. They are made from electrically conductive materials such as brass, phosphor bronze, beryllium copper, and high copper alloy.

Chapter 2: Terminologies Used in Electronic Connectors

The terminologies used in describing the properties and specifications of electronic connectors are the following:

Electronic Connector Terminology

Electronic Connector Gender

Electronic connectors are usually found as pairs, and each half has a gender designation. The male component is called the plug, while the female component is called the jack or socket. The jack has recessed holes (socket holes) that contain the terminals and are connected to a wire, cable, or device. The terminals of the plug are inserted into the slots of the jack to enable their connection.

Keying

Most connectors can only be plugged in one orientation, as electric charges exhibit polarity. Keying is a feature of electronic connectors that avoids incorrect mating orientation. A keyway prevents mechanical and electrical damage to the pins from dangerous and incompatible connections. It also averts plugging the connector at the wrong angle or the wrong socket. A keyway helps deal with symmetrical connectors.

Locking Mechanisms

A locking mechanism holds the connector in place during mating. It prevents the connector from being displaced when bumped or jolted. It avoids accidental uncoupling of the connector during operation, which can induce damage to the electronic device. There are various types of locking mechanisms in electronic connectors, including push-pull connectors, bayonet couplings, and fine thread screw couplings.

Number of Contacts

The number of contacts refers to the number of conductive elements which make an electrical connection.

Contact Pitch

Contact pitch, or pitch, refers to the center-to-center distance of adjacent pins, usually measured in millimeters. When pins are arranged in an array, the pitch between rows and columns can be different. The contact pitch affects the compatibility of connectors.

A larger pitch means fewer terminals per connector area which reduces the tendency of electrical arcing. Electrical arcing happens when the current jumps from one pin to the other, especially if the pins are too close to each other.

Pin Numbering

Each pin of an electrical connector is serialized. A number is assigned to a specific pin based on a sequence designated by a standard. In integrated circuits, the pins are numbered in an anti-clockwise direction.

Pin Sequence

Some electronic connectors are designed such that their pins are connected in a specific sequence. A specific set of pins must be plugged first before inserting another set.

Mating Cycles

Mating cycles refer to the number of times that an electronic connector can be connected and disconnected with its counterpart while meeting all its specifications. It varies for every connector type; a USB connector can be mated thousands of times, while FFC and FPC connectors only have tens of mating cycles. The factors affecting the mating cycle include the connector material type, plating type and thickness, resistance pass/fail threshold, and mating style.

Mount

Mount refers to how an electronic connector is placed or mounted to an electrical device. The mounting types are board mount (through-hole mount, surface mount, edge mount), panel mount, and cable mount.

Termination

Termination refers to how the terminals are connected. The termination methods will be further discussed in the succeeding chapters.

Strain Relief

Strain relief is a fitting or bushing that dissipates forces acting on the electronic connector to prevent stress and damage on the connector and make it mechanically stable.

Performance Parameters

Performance parameters refer to the conditions in which an electronic connector is designed to operate safely. These parameters include the current rating, voltage rating, and temperature ratings (minimum and maximum operating temperatures).

Features of Electronic Connectors

Some types of electronic connectors possess features that enable them for special applications. Among these types are:

• Hermetically Sealed Connectors use highly engineered glass-to-metal sealing to create an airtight sealing. They are air and moisture resistant and can withstand extreme environments. They can operate safely when fully submerged in water and endure pressures up to a certain depth.
• Water-Resistant Connectors protect electronic connections from damage caused by exposure to water. Unlike hermetically sealed connectors, however, they are not designed to operate underwater.
• Moisture and Oil Resistant Connectors protect the electronic connections from damage caused by exposure to moisture and oil.
• EMI and/or RFI Filtering on connectors provides protection to electronic connectors from electromagnetic interference (EMI) and/or radio frequency interference (RFI).
• ESD Shielded Connectors protect the electronic connections from electrostatic discharge (ESD) damage.

Leading Manufacturers and Suppliers

Chapter 3: Types of Electronic Connectors

Electronic connectors are categorized based on the level of interconnection:

• Integrated circuit (IC) chip level
• IC-to-package level
• IC package-to-board level
• Board-to-board level
• Wire-to-board or subassembly-to-subassembly level
• Box-to-box level or connection between systems

Electronic Connector Types

Electronic connectors include but are not limited to the following:

Board-to-Board Connectors

Board-to-board connectors are a group of connectors that join two printed circuit boards (PCB) without using a cable. These connectors consist of a male and a female member and are assembled with PCBs via through-hole technology or surface mount technology. PCBs can be connected in a perpendicular or parallel configuration. A mezzanine connector connects PCBs in a stacking configuration, while an edge connector mates the edges of single-sided or double-sided PCBs.

Box Header Connectors

Board-to-board connectors are categorized according to their header type. In box headers, the terminals are surrounded by their header. Meanwhile, in pin headers, the terminals are exposed.

Backplane Connectors

A backplane is used as a backbone structure to connect several PCBs such that the pins of one PCB are linked to the same relative pins of another PCB. It is widely used in computers and telecommunication devices to allow data transfer between their components.

Power Connectors

Power connectors are connectors that allow electrical current to pass through them to provide power to a device. They carry either a direct current (DC) or an alternating current (AC). The common types of power connectors are the following:

Barrel Connectors

Barrel connectors, also known as coaxial power connectors, connect electronic devices to an external power source. Low voltage DC is obtained from a wall-mounted adaptor and transmitted to the electronic device through the barrel connector. These connectors are widely used in consumer electronics and are available in standard diameters and lengths.

The barrel plug consists of concentric metal sleeves separated by an insulator. The inner sleeve accepts the barrel jack pin. The barrel jack may be PCB-mounted, panel-mounted, or cable-mounted. A cantilevered spring is fitted inside the jack and pushes the outer sleeve of the plug for the inner sleeve to touch the pin.

Molex Connectors

Molex connectors were developed and patented by the Molex Connector company in the late 1950s. These connectors are commonly used to supply power to computer drives and devices. They consist of cylindrical spring-metal pins that fit into cylindrical spring-metal sockets. A Molex connector typically has 2-24 contacts, arranged in either single or double rows, which are keyed to ensure proper plugging orientation. The pins and sockets are fixed into plastic housing.

IEC Connectors

IEC connector is a category of connectors that meet IEC standards. IEC 60320 is the standard specifying the components for connecting power supply cords to electrical equipment with a voltage rating of 250 V and a current rating of 16 A. There are different types of standardized IEC connectors that vary on the current rating, temperature rating, dimensions, and number of terminals.

The components of IEC connectors come in pairs which consist of a connector (male component) and an inlet (female component); each IEC component is identified by the prefix “C” followed by a number. Examples of IEC connector components are the C13 connector and C14 inlet, which have three conductors, a current rating of 10 A, and a maximum temperature rating of 700°C.

NEMA Connectors

NEMA connector is a category of power plugs and receptacles that are compliant with the standard set by the National Electrical Manufacturers Association (NEMA). NEMA standards are prevalent in North America, and some countries adapt to these standards.

The components of NEMA connectors have a unique coding system that indicates the features. The first identifier refers to the locking mechanism. If the NEMA code starts with the letter “L,” the NEMA component is twist-locking; otherwise, if the first identifier is blank, it means that the NEMA component is non-locking. The second identifier is a number before the hyphen, which refers to the NEMA type. The NEMA type indicates the number of poles (current-carrying terminals), the number of wires connected, voltage rating, and others. The third identifier is a number after the hyphen, which indicates the current rating in amperes. Lastly, the fourth identifier is a letter designation: “P” is for plugs, and “R” is for receptacles.

As previously mentioned, NEMA connectors may be non-locking or twist-locking. Non-locking NEMA connectors use straight blades in their plugs which can be easily connected or disconnected to their corresponding receptacles. Twist-locking NEMA connectors use curved blades in their plugs that can be rotated and latched into place, protecting the connector from accidental disconnection. Twist-locking NEMA connectors are ideal for industrial and commercial equipment.

Terminal Block

A terminal block is a modular, insulated block that fastens or terminates two or more wires together. It connects several terminals together, which are arranged in a long strip. Inside a terminal block is a conductive metal strip, which allows electrical conduction between the joined terminals, and a clamping system secures the terminal wires into the conductive metal strip. The wire orientation can be horizontal, vertical, or inclined at 450. Terminal blocks can be mounted on panels or DIN rails.

The types of terminal blocks can be classified into the following categories:

1. Based On The Structure

• Single feed terminal blocks are used in wire-to-wire connections. They have one input and one output contact.
• Multiple level terminal blocks have two or more levels of connection terminals. They reduce space and simplify wiring. DIN rail terminal block is an example of a multiple-level terminal block that is commonly found in power cabinets.

2. Based On The Application

• Ground Terminal Blocks
• Fused Connection Terminals
• Thermocouple Terminal Blocks
• I/O Blocks and Sensor Blocks
• Disconnect Terminal Blocks
• Power Distribution Terminal Blocks
• PCB Terminal Blocks

3. Based On The Clamping System

Screw Terminal Blocks

A screw inside the terminal block presses the wire and the strip together. Screw terminal blocks are the most common terminal blocks and can accommodate a wide range of wire sizes.

Spring-Clamp Terminal Blocks

Spring force is used to attach the wire to the strip. Spring-clamp terminal blocks are suitable for clamping smaller wires.

Push-In Terminal Blocks

Ferrules are installed on the end of the wire or conductor. They allow the connection of the wire by simply inserting it into the block. They can be insulated or uninsulated.

Barrier Terminal Blocks

A spade or ring terminal is attached to the end of the wire. The wire is fastened to the terminal by bolt and nut. Barrier terminal blocks are used in environments with high levels of vibration to prevent the loosening of wire connections.

USB Connectors

USB stands for Universal Serial Bus and are standard connectors used in data transfer and supplying power to electronic devices. They are used in smartphones, computers, and other consumer electronic devices.

A USB connector consists of a USB connector (the male component) that is plugged into the USB port (the female component). It has four or more contacts which are shielded and housed in a plastic molded strain relief. It also possesses an asymmetrical structure (except for the USB-C) which serves as the keying mechanism.

There are six versions of USBs which are the USB 1.0, USB 1.1., USB 2.0, USB 3.0, USB 3.1, and USB 3.2. The newer versions have the fastest transfer speeds. Some USB connectors can be used with USB ports of older versions (backward compatibility).

USB connectors can also be classified based on their receptacles and sizes; USB-A, USB-B, USB Mini (Mini-A, Mini B, and Mini-AB), USB Micro (Micro-A, Micro-B, and Micro-AB), and USB-C.

USB-A female is a host connector type found in computers, hubs, or devices that have peripherals plugged into them. USB extension cables can have a female A connector on one end and male A connector on the other end.

USB-A male connectors are used on keyboards and mice and have a built-in cable terminated with a USB-A male connector. They are board mountable and used on USB memory sticks.

USB-B female connectors are bulky and are used with applications where size is not important. It is a preferred removable connector and through the hole board mount connector with maximum reliability.

USB-B male is found at the end of a cable. They are inexpensive, which is the reason for their wide use.

USB-Mini female is found on MP3 players, older cell phones, and external hard drives as a surface mount connector. They are being replaced by USB-Micro connectors.

USB-Micro connectors have a significant size reduction and have a fifth pin for low speed signaling, which makes it possible for them to be used on USB-OTG applications.

Audio and Video Connectors Types

Audio connectors and video connectors are a broad class of electronic connectors used for transmitting audio and/or video signals. These connectors carry either analog or digital signals. These connectors are also composed of male (plug) and female (jack) components.

The signal systems for audio connectors can be monophonic (single audio channel) or stereophonic (multiple audio channels).

The types of audio and video connectors include but are not limited to the following:

Phone Connectors consist of coaxial contacts: the tip (T), ring (R), and sleeve (S). These connectors typically combine those contacts to have 3-5 contacts. They are widely used in phones, headphones, speakers, and other audio devices.

DIN Connectors are connectors that were originally standardized by the Deutsches Institut für Normung (DIN). They transmit analog audio signals. These connectors consist of three or more metal pins inside a conductive ring. A notch is present in the plug and jack that limits their mating orientation. The mini-DIN is a variation of the standard DIN connector.

RCA Connectors are connectors that carry stereo audio and video signals. These connectors consist of an outer conductor and a center or inner conductor (pin). These connectors are often color-coded: yellow for composite video and red and white for stereo audio.

XLR Connectors are connectors widely used in professional audio, video, and lighting equipment. They are circular connectors that have three to seven pins. They also contain a notch that serves as the keying mechanism.

HDMI Connectors, or high-definition multimedia interface connectors, are used in modern home entertainment devices, projectors, computer monitors, and digital audio devices. These connectors use transition-minimized differential signaling (TMDS) technology to transfer large amounts of digital data. The standard types of HDMI connectors include the standard (type A), dual-link (type B), mini (type C), micro (type D), and Automotive Connection System (type E) HDMI connectors.

DisplayPort (DP) Connectors are used to connect an audio and video source to a display device. They are used in high-definition graphic displays and are more common in computers.

DVI Connectors, or digital visual interface connectors, transmit analog and digital video signals. These connectors also use TMDS technology. They rapidly replaced the VGA connectors.

VGA Connectors have 15 pins arranged in three rows inside a trapezoidal housing. They are designed to carry analog video signals. It was developed by IBM in 1987.

Chapter 4: Electronic Connector Mounting and Terminations

There are several choices when it comes to connector mounting, which is how leads of the connector mount or fasten to the circuit board. The different types of mountings include surface mounting (SM), through the hold, hanging, cutout, and through the board. Although the terms termination and mounting are used interchangeably, there are distinct differences between them.

The term mounting refers to the overall project and how the connectors interface, fasten, and attach. Termination refers to how the connection is being made and can refer to how the connector is attached at either end.

Mounting Types

The term mount can be confusing in regard to what it is referring to. In general, it is an all encompassing term that refers to how the various connectors are attached. The many varieties of connectors require different types of mounting methods, which vary according to the terminating leads and type of connector.

• Pin Through Hole - Pin through hole mountings are used when the terminating leads are attached to a circuit board through holes placed in the board.
  
• Surface Mounting - Surface mounting attaches terminating leads using contact pads on the board.
• Panel Mounting - Panel mounting is a surface mounting where the connector is placed against a hole with connecting variations being threading or a nut to hold the connector in place.
• Hanging - With a hanging mounting, the connector is installed on the cable to which it is terminated.
• Cutout Mounting - Cutout mounting involves placing the connector at the edge of the board to take advantage of the edge placement. To provide for the mounting, the board has been cutout such that the connector can have a lower profile. The use of cutout mounting is due to the fact that there is no other space for placement.
• Through the Board Mounting - Through the board mounting is a combination of cutout mounting and panel mounting. Terminations mount through the board using holes in the board and solder on the same side as the connector’s mates as others are surface mounted to the side of the board the connectors mount from.

Termination Methods

Termination methods can vary depending on personal preference with some terminations requiring a specific type. The determining factor regarding the types of termination used for a project are dependent on the needs of the application.

Through Hole Soldering

In board-to-board and wire-to-board connections, solder terminations can be performed on through-hole mount or surface mount devices. In through-hole terminations, the terminals are inserted into drilled holes and soldered on the contact pads located on the other side of the board.

Surface Mount Termination

In surface mount termination, the leads and mounting pads are on the same side of the board. Items are placed by hand and soldered or reflow or wave soldering. Terminals are soldered on the contact pads that are on the same side as the connector.

Crimping

A crimp connection is a compression between electrical wires and cables and a crimp termination or splice band. A compressed terminal reshapes strands as if it were cold welded to form a low resistance electrical connection.

Crimping is a critical aspect of terminal connections, which, if completed improperly, can lead to electrical failures or fires. Correct wire preparation and size as well as proper termination types, tooling, and setting provide a reliable and permanent connection. The process of crimping begins with an evaluation and measurement of the wire connection cross section.

The key to proper crimping is the crimper tool, which can be a ratchet or manual crimper. The jaws of a crimper are wide enough to cover the complete surface area of the connector. Included in the jaws are crimping dies that are engineered to match the gauges of the wires to be crimped and can have color coding to show where to place the wire.

The amount of wire to be crimped should match the barrel of the connector, which is normally 0.25 inch or 0.64 cm. Once the wire is placed in the crimper, its jaws are closed and pressure is applied. With a tight grip on the wire, the crimper is pulled away removing the insulation on the wire leaving it exposed.

An important factor in regard to crimping is ensuring a firm connection between the connector and wire. This is essential for avoiding connection failure and serious damage. A minor step in the crimping process, which is twisting and tightening the exposed wire to compact it, helps to guarantee a secure fit to the connection.

The stripped exposed wire is inserted into the barrel of the connector until the insulation of the wire touches the barrel. None of the exposed wire should be visible at the entrance of the barrel or past the barrel into the tongue of the terminal.

The connector and stripped wire are placed back in the crimper die in a horizontal position with the barrel side facing upward and the flat side downward. The color of the die on the crimper should match the color of the wire’s insulation. It is essential that the slot or die match the gauge and size of the wire.

The crimper must be placed perpendicular to the connector and stripped wire such that the crimper can very firmly hold them in place. The jaws of the crimper should be placed closer to the tongue of the connector than to the insulation of the wire. Once positioned, the jaws of the crimper must be closed with great force such that the wire cannot be removed when it is pulled away from the terminal.

The terminal between the wire and connector needs to be sealed to protect it against exposure to the elements. This can be completed using electrical tape or heat shrink, which is sealed around the connection by applying heat that is sufficient to melt its plastic material.

Crimping is a process that eliminates the need for soldering wire connections and avoids potential failure associated with soldered joints that can become brittle. Terminal manufacturers supply information regarding the appropriate tooling and materials for completing a connection that should be followed to prevent wiring failures.

Ratchet crimp tools provide tactile evidence that the terminal crimp has been fully compressed and have color coding for easy identification of the proper die. Additionally, the jaws of a ratchet crimp tool will not open until the crimp between the connector and wire is sufficiently snug and tight.

Insulation Displacement Connectors

Insulation displacement connectors (IDC) have sharp blades which strip the wire insulation as the wire or cable is inserted. When the wire is properly installed, the exposed area of the wire is cold-welded to the connector terminal, which creates a secure and reliable connection. The insulation displacement method is commonly employed in ribbon cable connectors and telephone and network plugs.

Push In Termination

Push in terminations are noted for their reliability and ruggedness and can be permanent terminations or ones that can be easily released. Wires need to be stripped and pushed into the connector or a lever is used for locked in state. Aside from the push in and locked in methods, there are several variations of the push in termination configuration. Push in terminations are quite common and used with several types of connectors. The use of push in terminations is restricted to applications that do not have any vibrations that could break the connection. A vibration rating of an application is required for their use.

Conclusion

• Electronic connectors are devices that join electronic circuits. These devices are used in installing, assembling, and supplying power to electrical devices.
• The two main components of electronic connectors are the housing and the terminals.
• Electronic connectors have a male (plug) and a female (jack) component.
• Keying and locking mechanisms are important features of connectors that ensure correct and secure connections. A strain relief protects the connector assembly from mechanical stress.
• The number of contacts refers to the number of conductive elements which make an electrical connection. The contact pitch refers to the center-to-center distance of adjacent contacts or pins.
• Mounting refers to the manner of placing the connector to the electrical device.
• Termination refers to the method of fastening the terminals. The types of termination methods are soldering, crimping, and insulation displacement.
• Electronic connectors can be classified based on their level of interconnection.
• The electronic connectors discussed in this article are board-to-board connectors, power connectors, terminal blocks, USB connectors, and audio and video connectors.

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