9 Factors That Lead to Signal Integrity Issues in a PCB

06 May.,2024

 

9 Factors That Lead to Signal Integrity Issues in a PCB

Contents

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Avoiding signal integrity issues in a PCB is an extremely complex task for designers. It requires a deep understanding of signal integrity design rules and techniques. With the introduction of faster logic families, the designers have realized that simple PCB layouts cannot survive the signal integrity requirements.

The high-speed designs come with peculiar signal integrity issues that can cause major problems if not treated properly. Engineers are always advised to consider certain best PCB design services to minimize signal integrity issues in the early design cycle so that expensive design iterations can be avoided.

As we proceed, we will be providing more insight on the following topics:

  • What is signal integrity in a PCB?
  • Need for signal integrity in a PCB
  • 9 factors that lead to signal integrity issues in a PCB

What is signal integrity in a PCB?

Signal Integrity (SI) signifies the signal’s ability to propagate without distortion. Signal integrity is nothing but the quality of the signal passing through a transmission line. It gives the measurement of the amount of signal degradation when the signal travels from the driver to the receiver. This problem is not a major concern at lower frequencies but is an important factor to consider when a PCB operates at a higher speed and a high-frequency (> 50MHz). In the high-frequency regime, both digital and analog aspects of the signal need to be taken care of.

When a signal propagates from the driver to the receiver, it doesn’t remain the same, whatever has been sent originally will be received with varying degrees of distortion. This signal distortion happens due to factors like impedance mismatch, reflections, transient oscillations, crosstalk, ground bounce, and jitters in PCBs. A designer’s primary aim should be minimizing such factors so that the original signal could make it to the destination with minimum distortion. Special care is also needed to maintain signal quality and to control their undesirable effects on electronic circuitry. Read our post on controlled impedance routing using Altium.

Need for signal integrity in a PCB

When we have signal integrity issues in a PCB, it may not work as desired. It may work in an unreliable manner – works sometimes and sometimes not. It may work in the prototype stage, but often fail in volume production; it may work in the lab, but no reliably in the field; it worked in older production lots, but fails in new production lots, etc. A signal is said to have lost its integrity when:

  • It gets distorted, i.e. its shape changes from the desired shape
  • Unwanted electrical noise gets superimposed on the signal degrading its signal to noise (S/N) ratio
  • It creates unwanted noise for other signals and circuits on the board

A PCB is said to have requisite signal integrity when:

  • All signals within it propagate without distortion
  • Its devices and interconnections are not susceptible to extraneous electrical noise and Electromagnetic Interference (EMI) from other electrical products in its vicinity as per or better than regulatory standards
  • It does not generate or introduce or radiate EMI in other electrical circuits/cables/ products either connected to it or in its vicinity, as per or better than regulatory standards

 

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What's Inside:
  • Explanations of signal integrity issues
  • Understanding transmission lines and controlled impedance
  • Selection process of high-speed PCB materials
  • High-speed layout guidelines

 

 

Also read: 9 HDI Considerations for Manufacturability and Cost

9 factors that lead to signal integrity issues in a PCB

Perhaps the most important cause of signal integrity issues in a PCB is faster signal rise times. When circuits and devices are operating at low-to-moderate frequencies with moderate rise and fall times, signal integrity problems due to PCB design are rarely an issue. However, when we are operating at high (RF & higher) frequencies, with much shorter signal rise times, signal integrity due to PCB design becomes a very big issue.

To learn the ways to mitigate signal integrity challenges in high-density boards, read 10 HDI PCB design tips to maintain signal integrity

Factors that contribute to signal integrity degradation in a PCB:

Generally speaking, fast signal rise times and high-signal frequencies increase signal integrity issues. For analytical purposes, we can divide various signal integrity issues into the following categories:

1. Signal degradation due to uncontrolled line impedances

Signal quality on a net depends on the characteristics of the signal trace and its return path. During travel on the line, if the signal encounters changes or nonuniformity in the impedance of the line, it will suffer reflections that cause ringing and signal distortion.

Moreover, the faster the signal rise time, the greater will be the signal distortion caused by changes in uncontrolled line impedances. We can minimize signal distortion due to reflections by reducing or eliminating line impedances changes by:

  • Ensuring that signal lines and their return paths act as uniform transmission lines having uniform controlled impedances.
  • Having signal return paths as uniform planes placed close to signal layers.
  • Ensuring that controlled impedance signal lines see matched source impedances and receiver impedances – same as the characteristic impedance of the signal line. You need to implement the right circuit board trace termination technique for this.

 

 

2. Signal degradation due to other impedance discontinuities

As we mentioned earlier, if the signal encounters a discontinuity in impedance during its travel, it will suffer reflections that cause ringing and signal distortion. Discontinuities in the line’s impedance will occur at the point of encountering one of the following situations:

  • When a signal encounters a via in its path.
  • When a signal branches out into two or more lines.
  • When a signal return path plane encounters a discontinuity, like a split in the plane when line stubs are connected to signal lines.
  • When line stubs are connected to signal lines.
  • When a signal line starts at the source end.
  • When a signal line terminates at the receiver end.
  • When signal and return paths are connected to connector pins.

And, the faster the signal rise time, the greater will be the signal distortion caused by impedance discontinuities. We can minimize signal distortion due to line impedance discontinuities by:

  • Minimizing the effects of discontinuities caused by vias and via stubs by using smaller microvias and HDI PCB technology.
  • Reducing trace stubs lengths.
  • Routing traces in daisy chain fashion rather than multi-drop branches when a signal is used at more than one place.
  • Proper terminating resistors at the source and receiver ends.
  • Using differential signaling and tightly coupled differential pairs, which are inherently more immune to discontinuities in signal return path planes.
  • Ensuring that at connectors where discontinuity occurs, signal lines are made as short and signal return paths as wide as possible.

 

3. Signal degradation due to propagation delay

Signals take finite times as they travel on a PCB from source to receiver. The signal delays are proportional directly to signal line lengths and inversely proportional to signal speed on the specific PCB layers. If data signals and clock signals do not match overall delays, they would arrive at different times for detection at the receiver, and this would cause signal skews; and excessive skew would cause signal sampling errors. As signal speeds become higher, the sampling rates are also higher, and allowable skew gets smaller, causing a greater propensity for errors due to skew.

TIP: Skew in a group of signal lines can be minimized by signal delay matching, primarily by trace length matching.

4. Signal degradation due to signal attenuation

Signals suffer attenuation as they propagate over PCB lines due to losses caused by conducting trace resistances (which increases at higher frequencies due to skin effect) and dielectric material dissipation factor Df. Both these losses increase as frequency increases, therefore higher frequency components of signals will suffer greater attenuation than do the lower frequency components; this causes a reduction in signal bandwidth, which then leads to signal distortion by the increase in signal rise time; and excessive signal rise time increase results in errors in data detection.

TIP: When signal attenuation is an important consideration, one has to choose the right type of low loss high-speed material and proper control over trace geometries to minimize signal losses.

5. Signal degradation due to crosstalk noise

A fast voltage or current transition on a signal line or return path plane may couple onto adjacent signal lines causing unwanted signals called crosstalk and switching noise on the adjacent signal lines. The coupling occurs due to mutual capacitance and mutual inductance between the traces. This mutual capacitive and inductive coupling can be reduced by increasing the space between the traces. As a thumb rule, space should be three times the trace width (3W). And as always, faster rise time signals create more crosstalk and switching noise.

Crosstalk and switching noise can be reduced by:

  • Increasing the separation between adjacent signal traces.
  • Making the signal return paths as wide as possible, and uniform like uniform planes, and avoiding split return paths.
  • Using a lower dielectric constant PCB material.
  • Using differential signaling and tightly coupled differential pairs, which are inherently more immune to crosstalk.

 

 

6. Signal degradation due to power and ground distribution network

Power and ground rails or paths or planes have very low, but FINITE nonzero impedances. When output signals and internal gates switch states, currents through power and ground rails/paths/planes change, causing a voltage drop in power and ground paths. This will decrease the voltage across the power and ground pins of the devices. The higher the frequency of such instances, and faster the signal transition times, and the higher the number of lines switching states simultaneously, the greater is the voltage decrease across power and ground rails. This will reduce signals’ noise margins, and if excessive, would cause devices to malfunction.

To reduce these effects, the power distribution network has to be so designed as to minimize the power system’s impedance:

  • Power and ground planes should be placed as close together and as near to the PCB surface as possible. This will reduce via inductances.
  • Multiple low inductance decoupling capacitors should be used across power and ground rails and they should be placed as close to device power and ground pins as possible.
  • Use device packages with short leads.
  • The use of thin high-capacitive cores for power and ground considerably increases the capacitance and reduces impedance between power and ground rails. Read how we can reduce parasitic capacitance in PCB layout.

7. Signal degradation due to EMI/EMC

EMI/EMC increases with frequency and faster signal rise times. Radiation far-field strength increases linearly with frequency for single-ended signal currents, and squarely with differential signal currents. Read PCB design guidelines for EMI and EMC for a detailed explanation.

TIP: EMI can also be reduced by reducing the current loop area.

 

Signal Integrity eBook

6 Chapters - 53 Pages - 60 Minute Read

What's Inside:
  • Impedance discontinuities
  • Crosstalk
  • Reflections, ringing, overshoot and undershoot
  • Via stubs

 

 

8. Signal integrity issues due to via stub and trace stub

A via stub is the part of a via which is not used for signal transmission. A via stub acts as a resonant circuit with a specific resonant frequency at which it stores maximum energy within it. If the signal has a significant component at or near that frequency, that component of the signal will be heavily attenuated due to the energy demands of the via stub at its resonant frequency. In the example depicted below, part A of the via is used for signal propagation from the conductor C1 on an outer layer to the conductor Cn on an inner layer. But the part B of the via is extraneous – thus, is the via stub. Learn more about Via Stubs and Their Effects on Signal Attenuation and Data Transfer Rates here.

The long stub traces may act as antennas and consequently increase problems to comply with EMC standards. Stub traces can also create reflections that negatively affect signal integrity. Pull-up or pull-down resistors on high-speed signals are common sources of stubs. If such resistors are required then route the signals as a daisy chain.

9. Signal integrity issues due to ground bounce

Due to excessive current drawn the circuit’s ground reference level shifts from the original. This is due to ground resistance and interconnect resistance such as bonding wires and traces. The ground voltage levels at different points in the ground will, therefore, be different. This is known as a ground bounce as ground voltage will vary with the current.

Techniques for decreasing ground bounce:

  • Implement decoupling capacitors to local ground.
  • Incorporate serially-connected current-limiting resistors.
  • Place decoupling capacitors close to the pins.
  • Run proper ground.

The signal’s rise time is a critical parameter in SI issues. To attain a desired signal integrity level, we should focus on impedance control, attenuation, ground bounce, propagation delay, and EMI/EMC. Signal integrity measures should be adopted during the design phase of a PCB because we cannot afford to come up with a new design every now and then. It is better to treat it beforehand rather than let it ruin your device’s performance in real-time. Check this post on How to Achieve a Robust PCB Design Workflow for Signal Integrity? to gather more information on PCB designing for signal integrity.

 

PCB Transmission Line eBook

5 Chapters - 20 Pages - 25 Minute Read

What's Inside:
  • What is a PCB transmission line
  • Signal speed and propagation delay
  • Critical length, controlled impedance and rise/fall time
  • Analyzing a PCB transmission line

 

Electrical connector

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.

Media related to Electrical connectors at Wikimedia Commons

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