Connectors are essential components in electronics that allow detachable joining of a printed circuit board (PCB) to cables, wires, or other circuit assemblies. They facilitate quick installation, removal and replacement of boards, and provide connections to power, signals, data and other circuits.

There is an extensive range of PCB connector types that serve different applications across consumer, industrial, telecom, automotive, medical and other electronics sectors.

This article provides a detailed overview of major PCB connector categories, their characteristics, comparisons and typical applications.

Types of PCB Connectors

PCB connectors can be broadly classified based on:

• Mounting styles
• Current carrying capacity
• Termination styles
• Contact type
• Orientation
• Signal types

We will look at key connector varieties in each category and their usage.

By Mounting Style

1. Through Hole Connectors

These connectors are soldered into plated through holes on the PCB and secured using mechanical fasteners or locks. Common through hole types include:

• D-subminiature – Used for interfacing peripherals via parallel data buses. Feature multiple pin and socket contacts.
• Circular – Offer ruggedized power connections. Include types like Anderson Powerpole.
• Terminal block – Provide termination points for field wiring. Allow joining multiple wires or cables.
• Card edge – Enable insertion of a PCB edge into a slot for expansion slots in devices.

Image showing various through hole connectors.

2. Surface Mount Connectors

These connectors are soldered onto surface mount pads on the outer layers of the PCB. They maximize board space utilization. Types include:

• Header – Offer connection for board stacking or to cables via sockets. Include dual row strip headers.
• Card edge – Allows insertion of a PCB card edge for plug-in slots. May be angled or straight.
• FFC/FPC – Provides connection to flat flexible cables used in consumer devices and disk drives.
• SIM card – Used to hold subscriber identity module (SIM) cards in cellular products.

Example surface mount connectors.

By Current Carrying Capacity

1. Low Power Connectors

These handle a few amperes of current and lower voltages. Types include:

• Rectangular pin header – Simple male-female connector system for low power connections.
• JST – Interconnect various boards and components like batteries or sensors.
• USB – Provide power and communication over the ubiquitous USB protocol.
• D-subminiature – Link various computer peripherals over parallel buses.

2. High Power Connectors

These rugged connectors can carry tens to hundreds of amps for power transmission. Examples include:

• Circular (power) – Robust threaded circular connectors used to supply high currents.
• Terminal block – Allow termination of high gauge field wiring for power distribution.
• Edgelite – Edge mount solderless connectors that handle high amperage.
• Power pole – Quick connect terminals for high current 12/24V DC power links.

TE Connectivity power pins handle over 40 Amps.

By Termination Type

1. Crimp Terminals

These provide crimped wire termination that is solderless. Common examples are:

• Terminal block – Accepts pre-crimped wire ends for field wiring termination.
• Power pole – Mates with crimped contacts on high current wires.
• Flag – Crimp connectors can plug into the sides of PCB headers.

2. Solder Terminals

Require soldering of cable wires for termination. Types include:

• Header pin – Pins are soldered to wires for cable harness assembly.
• FFC/FPC – Meant for soldering flat flex cables.
• USB – Wires are soldered to USB connector pads.
• Circular – Require soldering of individual wire leads.

By Contact Type

1. Stamped and Formed

Simple connectors made from stamped/formed contacts. These include:

• Pin header – Stamped pins soldered into plated PCB holes.
• Crimp terminals – Contacts are stamped forms that crimp onto wire ends.
• Card edge – Contacts are formed sheet metal springs.

2. Machined Contacts

High reliability connectors with precisely machined contacts. Used in:

• D-subminiature – Pins and sockets are machined with gold plating.
• Circular – Contacts are machined and designed for high cycle life.

By Orientation

1. Vertical Connectors

Positioned perpendicular to the PCB surface. Examples include:

• Pin headers
• Terminal blocks
• FFC/FPC

2. Right-angle Connectors

Mounted parallel to the PCB surface. Allow stackable board-to-board connections. Some examples:

• Right-angle pin header
• Card edge connector

By Signal Type

1. Analog Connectors

Used for low level analog signals that need shielding and protection. Common types are:

• BNC – Bayonet Neill-Concelman connectors used for RF and coaxial signals.
• TNC – Threaded version of BNC connectors.
• Circular audio – Provide balanced audio connections with shielding.

2. Digital Connectors

Carry high speed digital signals between devices. These include:

• D-subminiature – Transmit parallel TTL level digital signals.
• FFC/FPC – Used for interfacing storage devices using flat flex cables.
• USB – Universal USB protocol for peripherals and hosts.
• RJ45 – For high speed Ethernet LAN connections.

This covers the major categories of PCB connectors and how they differ based on mounting, power level, contacts, orientation and signals. We will now examine some specific commonly used connectors and their typical applications.

Major PCB Connector Types and Uses

Header Pin Connectors

These consist of an insulating plastic housing with multiple through hole pins. They allow interfacing between PCBs or to cables via mating sockets. Some examples are:

Single row pin headers – Used for general I/O connections between boards and cables. Offer vertical or right-angle options.

Dual row pin headers – Provide enhanced connectivity and stacking ability. Often used for board-to-board stacking.

JST connectors – Interconnect boards or interface various electronics like batteries, sensors and display modules.

Stacking headers – Allow multiple boards to be stacked together using vertical interconnects.

Header connectors offer a versatile and simple means of connectivity in electronic devices and are available in pitches from 1.27mm to 2.54mm.

D-Sub Connectors

These connectors come in DBxx formats (DB25, DB15 etc.) with multiple pin and socket contacts. Applications include:

Linking peripherals – Used in early computers to connect keyboard, mouse, modem and other devices.

Parallel data buses – Allow high throughput parallel data transmission over multiple contacts.

VGA interfaces – Transmit analog video signals up to 2048×1536 resolution.

Serial RS-232 ports – DB9 connectors allow serial communication up to 115 kbps.

D-subminiature connectors dominated legacy computer and instrument interconnects but are now giving way to smaller and faster alternatives.

USB Connectors

Universal Serial Bus (USB) connectors provide point-to-point serial data links in devices:

USB-A – Rectangular connector found on hosts/hub ports to connect devices.

USB-B – Squarer connector installed on peripherals to plug into hosts.

USB-C – Reversible compact connector for hosts and devices. Supports USB 3.2.

Mini/MicroUSB – Used in smaller portable electronics like phones and cameras.

USB connectors and interfaces allow plug-and-play connectivity of computer peripherals and are near universal in modern electronic devices.

Circular Connectors

These rugged threaded connectors come in metal or plastic shells and are used for power and signals:

Power – Used to supply anything from a few amps up to 200+ amps for high power applications.

Coaxial – Designed for radio frequency and microwave signals up to 40 GHz.

Industrial – Rugged designs withstand harsh industrial environments. IP68 sealing available.

Audio – Made to carry balanced and shielded analog audio signals.

Circular connectors are applied anywhere robust, waterproof and vibration resistant connectivity is needed such as industrial controls, vehicles, test instruments and more.

FFC/FPC Connectors

These connectors allow interfacing flexible flat cables, circuit boards and displays in devices:

FFC/FPC Headers – Provide connection points for flat flex cable mating in devices like printers and disk drives.

FFC/FPC ZIF – Zero insertion force connectors allow smooth FFC insertion without need to apply high force.

FFC/FPC Edge card – Allow connecting display edge electrodes to circuit boards through ZIF FFC cable connectors.

FFC/FPC connectors enable compact cabling and interconnections ideal for portable electronics and display interfaces.

Terminal Blocks

Terminal blocks allow termination of multiple field wires and cables. Options include:

Screw terminal – Wires secured via screw-down mechanical fasteners for easy termination.

Spring clamp – Wires push-fit into spring loaded clamps for tool-free insertion.

Plug-in – Male-female block connections allow pre-wiring and easy field swapping.

Feed-through – Inline pass-through blocks enable connections across multiple points.

High power – Robust power blocks rated for hundreds of amps.

Terminal blocks simplify wiring, distribution, troubleshooting and maintenance in industrial controls, power distribution, facilities and instrumentation systems.

Card Edge Connectors

These connectors mount on the edge of a PCB and mate with sockets to provide expansion slots and modular boards. Types include:


Single edge – Interface one side of the PCB card edge.

Dual edge – Contact both sides of the inserted PCB.

Solder mount – Through-hole soldering directly to PCB.

Surface mount – Allow SMT mounting parallel to board surface.

Card edge connectors are used to add modular functionality via daughterboards and I/O expansion cards in devices and instruments.

This provided an overview of some of the most common PCB connector varieties and their typical applications. We will now summarize the key differences between connector types.

Comparison of Connector Attributes

Connector	Mounting	Signals	Power	Contacts	Termination	Orientation	Cost
Header pin	Through-hole	Digital, analog	Low	Stamped pins	Solder	Vertical	$
D-sub	Through-hole	Digital, analog	Low-medium	Machined pins/sockets	Solder	Vertical	$
USB	SMT	Digital data	Low	Formed pins	Solder	Vertical	$
Circular	Bulkhead	Power, RF signals	High	Machined pins/sockets	Solder	Straight	$$
FFC	SMT	Digital data	Low	Stamped pins	Solder	Vertical	$
Terminal block	Through-hole	Power, field signals	High	Stamped	Crimp, screw	Vertical	$
Card edge	Through-hole/SMT	Digital data, expansion	Low-medium	Stamped pins/springs	Solder	Right angle	$

This summarizes some key attributes like mounting, signal types, power handling, contact types, termination methods, orientation and relative cost. These factors determine suitability for different applications.

Conclusion

There is a diverse variety of PCB connector types that cater to the immense range of applications in electronics:

• Mounting styles include through-hole, surface mount, and panel mount using screws or rivets. Through-hole mounts are robust while SMT saves board space.
• Current ratings range from connectors carrying a few amps to hundreds of amps for high power transfer. Contact size and material determine max current.
• Termination can be by soldering or crimping. Soldering provides optimal connectivity while crimping allows fast field wiring.
• Contacts are manufactured by stamping, forming or machining. More processing increases reliability and durability.
• Orientations include vertical and right-angle. Right-angle save space in board stacking.
• Analog signals demand specific connectors to avoid interference. Digital links permit more connector flexibility.
• Factors like size, durability, isolation and bandwidth determine connector selection for the application.

In summary, the connector type must be matched to the mounting, data rates, power levels, mechanical space, operating environment and cost targets of the design. Careful connector selection ensures the PCB interfaces properly with cables, peripherals and other system electronics throughout its service life.

Frequently Asked Questions (FAQ)

Q1. How are connectors specified for a PCB design?

Relevant connector parameters like number of contacts, pitch, mating orientation, termination method, voltage and current ratings, interface standards, mechanical dimensions, operating temperature etc. need to be defined based on signal types and application environment. These drive the connector selection.

Q2. What are key considerations when selecting PCB connectors?

Important criteria are signal types (digital, analog), transmitted power, voltages, contact reliability and durability, contact plating and material (gold, tin), insulation rating, polarization and mating, mounting style (TH, SMT, panel mount), environmental sealing rating (IPxx), operating temperature range, and mechanical stability.

Q3. What are some best practices for the PCB-connector interface?

Use generous connector contact pad sizes on the PCB, sufficient clearance around the connector, proper solder mask gapping from pads, and conformal coating on the board section exposed outside the connector. Ensure connector mounting is mechanically secure.

Q4. How can the reliability of PCB-connector mating cycles be determined?

Connectors are specified for a given minimum number of insertion/removal cycles. This depends on factors like contact plating material, contact wiping and normal force, contact fabrication technique and mechanical design. More expensive connectors exceed 100,000+ cycles.

Q5. What are some alternatives to using connectors on a PCB?

For permanent connections, wires or cables can be directly soldered to pads on the PCB edge. Board stacking can employ soldered bus pins instead of connectors. Traces can be routed to an edge fingerprint connector. For serviceability, sockets allow components to be plugged in.