Introduction

Printed circuit board (PCB) connectors allow detachably joining a board to mating connectors or cables carrying power, signals, or data. The wide variety of PCB connector types suit different applications, environments, circuit types, and design requirements.

This article explores common categories of PCB connectors and interfaces. We’ll examine board-mount connector characteristics, orientations, mounting styles, electrical properties, signal classes, and usage scenarios. Understanding PCB connector selection principles enables choosing the optimal solutions for electronics projects and products.

Connector Functionality

PCB connectors facilitate:

• Board-to-wire connections – Interface between PCB and external cables or harness.
• Board-to-board – Stacking PCBs electrically end-to-end or side-by-side.
• Board-to-panel – Mounting PCBs flush into racks, chassis, or enclosures.
• I/O interfaces – Connectors for external controls, peripherals, or instruments.
• High-speed data – Transmitting fast digital data streams.
• Power input – Delivering supply power into the PCB.

Matching connector functionality to the need is the first criterion.

Electrical Interface Types

Common PCB connector interface technologies include:

Analog/Power

• General purpose – Discrete wires for low frequency analog signals or power transmission.
• Coaxial – Shielded signal line plus ground return. For high frequency analog.

Digital Data

• Rectangular multipin – Parallel row of pins. For ribbon cables or IDC motherboard sockets.
• D-subminiature – Compact density DB connectors. RS-232 serial ports.
• RJ45 – Ethernet and datacom modular jacks for unshielded twisted pair cable.

High-Speed Digital

• USB – For connecting peripherals with the ubiquitous USB standard.
• PCI Express – Advanced PCIe data bus for boards or external devices.
• SFP – Pluggable gigabit fiber optic transceivers.

Storage

• SATA – Serial bus widely used in computer disk drive connections.
• M.2 – Compact SSD card edge connector.

Specialty

• Board stack – Stacking interconnect for mezzanine PCBs. High density vertical mounting.
• FFC/FPC – Flexible printed circuit connections from flat flex cables.

The required signal classes steer interface selection.

Connector Mounting Styles

Connectors attach to PCBs through:

Through-Hole Mounting

• Leads pass through holes in PCB.
• Requires board drilling.
• Robust mechanical attachment.

Surface Mounting

• Leads directly solder to pads on surface.
• Conserves board space.
• Reflow solder attachment.

Press-fit

• Pins press into plated through-holes.
• Gas-tight interference fit.
• No soldering.

SMT Sockets

• Surface mount connector footprint.
• Separate mating plug connector.
• Good for pluggable modules.

Edge Board Sockets

• Connect fingers grip PCB edge.
• Common for plug-in cards.

Mounting suits manufacturing constraints and connectors.

PCB Connector Orientations

Connectors attach to boards in different orientations:

Vertical Mount

• Exit board perpendicular (most common).

Right-Angle

• Exit board parallel in 90° bend.

Horizontal Mount

• Attaches flat to board surface.

Mezzanine Stacking

• Directly interconnects multiple parallel boards.

Front Mount

• Mounts to edge of board.
• Common for external instrument connections.

Orientation depends on design form factor and space requirements.

Common Types of PCB Connectors

Some of the most prevalent types of connectors used with PCBs include:

Header Connectors

• Vertical insulating housings holding pin or socket contacts.
• Friction-lock with mating socket strip or plug.
• Standard 0.1” pitch. Good for general I/O connections.

D-Sub Connectors

• Rectangular shell with arrayed crimp pin contacts.
• Secures with screws to mate with socket.
• Used for composite video, VGA, serial ports.

RJ45 Connectors

• 8P8C modular connectors for Ethernet and datacom.
• Tab-down vertical SMT footprint.
• Can have integrated magnetics.

USB Connectors

• Type A, type B, micro AB, and USB-C options.
• SMT and through-hole versions available.

Board Stacks

• Direct board-to-board interface.
• High density with mm pitch.
• Samtec, TE, Amphenol manufacturers.

FFC/FPC Connectors

• Mechanical clamping or ZIF sockets for flex cables.
• Low profile, pitch under 1 mm.

There are many other speciality connector varieties beyond this sampling.

Key Connector Specifications

Technical factors drive connector selection for fit and performance:

• Pitch – Centerline spacing between contacts. From 2.54 mm to under 1 mm.
• Current/Voltage – Current capacity and working voltage per contact.
• Interface – Type of signal lines needed. E.g. LVDS pairs.
• Speed – Maximum frequency. Important for protocols like PCIe, USB.
• Mating cycles – Lifetime durability rating.
• Contact type – Material and plating. Gold preferred for corrosion resistance.
• Temperature range
• Polarization – Keying to ensure mating alignment.
• Springs – Contact normal force and deflection range.
• Termination – Solder, press-fit, other PCB mounting styles.
• Size – Available PCB real estate and keep out regions.

Designing Connectors into PCBs

Best practices for integrating connectors in PCB design:

Schematics

• Abstract connectors into neatly labeled functional blocks rather than individual pins.

Layout

• Group related connectors together when possible.
• Ensure adequate clearance space for mating plugs.
• Use polarizing cutouts to prevent mis-plugging.

Cabling

• Plan cable bend radius exiting board.
• Support cables appropriately in enclosure.

Modeling

• Include connectors in electromagnetic simulations of PCB.

Testing

• Inspect for proper seating, alignment, and retention in prototypes.

Getting connectors designed-in robustly avoids issues and rework.

Selecting Connectors

Tips for choosing the optimal connectors:

• Match specifications to electrical, mechanical, environmental needs.
• Consider ease of assembly into production processes.
• Test samples to validate usability and performance.
• Review options from multiple vendors for alternatives.
• Leverage existing designs with proven connectors when possible.
• Seek expert guidance from component vendors.

Taking care selecting suitable connectors prevents problems arising in the field.

Conclusion

The wide variety of PCB connector types and mounting configurations allows designers to interface their electronics in the optimal way for the product and manufacturing requirements. Whether using standard interfaces like USB, press-fit pins, or direct board stacking, connectors bridge the gaps between PCBs and the outside world. Carefully considering electrical, mechanical, and assembly factors leads to robust connector integration that performs reliably throughout the product lifetime.

Frequently Asked Questions

What are considerations for connectors used in high vibration environments?

Using positive retention like screws or clips, preventing looseness in mated connectors, employing board locks, selecting ruggedized interconnections, and applying conformal coating help connectors withstand vibration.

How are high pin count connectors effectively routed on PCBs?

Using wider trace escape routing, pin grouping into bussed nets, reference planes for controlled impedance, and termination resistors help manage routing complexity for large connectors.

What are considerations for PCB connectors used in harsh environments?

Using sealed, liquid-tight connectors, avoiding dust-trapping crevices, specifying watertight board feedthroughs, considering contact plating like gold, and mechanical strain relief help connectors survive difficult environments.

How can you determine the right current rating for a power connector?

Calculate the maximum steady state and peak supply current for the PCB, consider derating and margins, and select connector current capacity above the power needs.

What are techniques to improve EMI shielding around connectors?

Using metal connector shells grounded to chassis, picking connectors with integrated shielding, surrounding connectors with plated guard traces, backside ground plane tying, and flexible contact finger gaskets help reduce emissions and ingress through connectors.