Electronic Connectors

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.

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 700C.

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 Termination

Termination refers to the method of fastening the terminals together. The connector termination methods include the following:

The Soldering Process and Other Termination Methods

Soldering is the process of joining two or more electronic parts together by melting a solder around their contacts or terminals. It creates a strong electrical joint and can be accomplished by hand soldering, reflow soldering, or wave soldering. However, soldering is a slower process compared to other termination methods.

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 mount, the terminals are inserted into the drilled holes of the PCB and soldered on the contact pads located on the other side of the board. In surface mount, the terminals are directly soldered on the contact pads, which lie on the same side of the connector.

Crimping Method

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.

Summary

• 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.