How to Choose a Connector

Continuing our series about choosing parts, inspired by the latest version of the Common Parts Library, let’s take a close look at how to find and select connectors. In this blog, we will explain all the different types of connectors, their merits and demerits, and their popular applications. We will also recommend some commonly used connectors with high supply chain availability to help you find the right connector.

Let’s dive into the world of connectors:

Connectors  how-to-choose-a-connector how-to-choose-a-connector how-to-choose-a-connector how-to-choose-a-connector how-to-choose-a-connector

TYPES   
Connectors are used to connect power adapters, batteries, memory cards, audio, video, antenna and data interfaces in circuits and systems. This table presents a summary of some of the main connectors, how they are used, and what their properties are:

Connector
Main Applications
Properties
Part Selection
Phone  how-to-choose-a-connector Analog audio  how-to-choose-a-connector Available in 2.5mm, 3.5mm and 6.25mm sizes.
3.5mm is most common
Switchcraft’s
35RASMT series
RCA (Phono)   how-to-choose-a-connector Audio/Video  how-to-choose-a-connector
Used with yellow RCA cable for analog video,
red for right audio and white for left audio
Switchcraft’s PJR series
HDMI   how-to-choose-a-connector Digital audio/video  how-to-choose-a-connector
Type A – most common
Type C – mini-HDMI
Type D-  micro-HDMI
Type A- FCI’s 100294 series
Type C- TE’s 2013978 series
Type D- FCI’s 101182 series
Barrel  how-to-choose-a-connector Power – for development
boards like Arduino Uno
Connects with AC wall adapters
as an alternative to battery
Switchcraft’s RASM series
JST  how-to-choose-a-connector Power – with RC and Li-Po batteries VH Series – 3.96mm pitch
XH Series – 2.50mm pitch
PH Series – 2.00mm pitch
JST’s VH(LF)(SN) series,
JST’s XH-A(LF)(SN) series,
JST’s PH-SM4-TB(LF)(SN) series
USB
how-to-choose-a-connector how-to-choose-a-connector how-to-choose-a-connector         
USB-A: for terminating of cables,
USB-B: development boards,

micro-USB: consumer devices
Allows for data communication and charging,
mini-USB is slowly getting phased out
USB-A- TE’s 1734366 series
USB-B  FCI’s 61729 series
Micro-USB–  FCI’s 101035 series
Headers
 how-to-choose-a-connector how-to-choose-a-connector
To connect boards and shields Available in male and female versions,
0.1” pitch is most popular
Male headers- TE’s 4-1037 series
Female headers- TE’s 5-53423 series
Screw terminals how-to-choose-a-connector To hold wires temporarily Holds wires via adjustment of screw,
but wires can be undone easily
On Shore Technology’s  
OSTTH series
IC Sockets
 how-to-choose-a-connector how-to-choose-a-connector
DIP- ICs, resistor networks, LEDs
PLCC- ICs such as flash memory
Can be soldered directly onto a
PCB for easy replacement of ICs
DIP Socket- TE Connectivity’s
1-2199 series
BNC   how-to-choose-a-connector For video, lab and radio equipment Handles up to 4 GHz, with bayonet connection while
TNC/N uses threaded connection
TE Connectivity’s  
5-16345 series
SMA   how-to-choose-a-connector Coaxial connection in compact spaces Handles up to 18 GHz, but needs torque wrench to connect TE Connectivity’s
10525 series
Backplane  how-to-choose-a-connector Computer systems Provides a “backbone” to connect many
different circuit boards in parallel
Molex’s 850 series
D-Sub  how-to-choose-a-connector RS-232 communication, video DB-25 with 25 sockets and
DE-9 with 9 sockets most popular
TE Connectivity’s
17343 series
FFC / FPC  how-to-choose-a-connector Alternative to rigid connectors
and PCBs
Provides flexibility, but costlier than rigid PCBs FCI’s SFW series
Modular / Ethernet how-to-choose-a-connector Initially for telephone, now for Ethernet 8P8C is most common type Molex’s 48025 series
Memory  how-to-choose-a-connector Used in dev boards like
Raspberry Pi
Provides storage space on circuit boards Molex’s 503 series


There is a huge variation between types of connectors: they can have retaining elements like pegs, they might need selective soldering, and some are even a “hybrid” of SMT and through-hole. All of these differences can make connectors harder to assemble on a PCB, so it is important to be aware of potential manufacturing issues before choosing a connector. To help out with design for manufacturability (DFM), our friends from PCB:NG helped us pick out some things to keep in mind while choosing a connector:  
1. Avoid through-hole connectors as they incur the highest manufacturing costs. All-SMT design is typically going to be less expensive to get assembled. Even though through-hole components might seem cheaper, additional manufacturing costs typically eat up into those savings. For “hybrid” connectors, read this blog to learn more about manufacturing issues.
2. Avoid connectors that require selective soldering. In an otherwise all-SMT design, a connector that needs selective soldering requires the assembler to do an SMT/reflow pass, then do another pass with selective solder. It may require additional labor to mask out the components. All of that can drive up the price and can potentially reduce yields.
3. Prefer “pure” SMT connectors without retaining elements (such as pegs). Connectors that are SMT, but use retaining elements, are typically more expensive to place. Not all such components work well with many pick and place machines. If using retaining elements is a must, it’s a good idea to make the receiving holes as large as possible. While using SMT connectors, assemblers can and will use SMA (surface-mount adhesive) which is usually strong enough to provide more than enough physical strain relief, and typically incurs zero extra labor.

Now, let’s deep dive into the world of connectors:

I. Audio/Video Connectors  how-to-choose-a-connectorhow-to-choose-a-connector how-to-choose-a-connector

a. Phone connectors, also known as headphone jacks, are used for analog signals most commonly for audio. They come in three standard sizes: 2.5mm, 3.5mm and 6.35mm diameters. 3.5mm is most commonly used for audio cables in portable applications. It is the miniature version of the classic 6.35mm jack (which dates back to late 19th century!)
how-to-choose-a-connector

While designing a PCB, a female connector is required to connect with the headphone jack.
Part Selection: Switchcraft’s 35RASMT series for 3.5mm audio female connector [CPL]

b. RCA connectors, sometimes called phono connectors, are commonly found in audio and video equipment. They are usually color-coded with yellow for composite analog video, red for right audio channel, and white for the left audio channel.
how-to-choose-a-connector
While designing a PCB, a female RCA connector is needed to connect to a cable with RCA connectors.
Part Selection: Switchcraft’s PJR series for right angle female RCA jack [CPL]

For professional audio equipment, XLR connectors are commonly used. They can have between 3 and 7 pins and come in both female and male versions. XLR connectors look similar to DIN connectors (which are also used for analog audio signals) but are not compatible.

c. HDMI connectors are used for transferring digital audio and high definition uncompressed digital video. HDMI is a replacement for analog video standards (such as composite video with RCA jacks). HDMI connectors come in a few variants.
Type A is the most common standard and is used in most consumer devices. Type B is for very high resolution applications but is not commonly used. Type C is the mini-variant for smaller mobile devices. Type D is the micro-variant. Type E is for automotive applications and is moisture and dust resistant.

how-to-choose-a-connector

Type A, mini (type C), and micro (type D) HDMI cables

HDMI receptacles are required to connect to HDMI cables in PCBs.
Part Selection:
HDMI type-A receptacle
: FCI’s 100294 series [CPL]
HDMI type-C (mini-HDMI) receptacle: TE Connectivity’s 2013978 series
HDMI type-D (micro-HDMI) receptacle:  FCI’s 101182 series

II. Power Connectors how-to-choose-a-connector how-to-choose-a-connector

Barrel Connectors are commonly found in some consumer electronics devices and in development boards (like the Arduino Uno). They can be plugged into the wall power using AC wall adapters instead of using batteries.  
Part Selection: Switchcraft’s RASM series for current ratings upto 11A

JST Connectors are another common way to power up circuit boards, especially for rechargeable batteries, like Lithium ion Polymer (Li-Po) batteries. They are compact and sturdy, and can be very difficult to disconnect.  
JST connectors vary by their pin-to-pin pitch (spacing) and number of positions. Let’s look at some of the common ones:
I. VH series – Pitch: 3.96mm; Current rating: 10A; Voltage rating:250V  
With a large current carrying capacity, these are used with signal, power supply and output circuits.
II. XH series – Pitch: 2.50mm; Current rating: 3A; Voltage rating: 250V
The spacing on the XH series is very close to 0.1” (2.54mm) and works with 0.1” male header pins in various perfboards and breadboards. JST-XH connectors are commonly used with RC batteries for balance charging.
III. PH series – Pitch: 2.00mm; Current rating: 2A; Voltage rating: 100V
These are used for high density connection of wires to printed circuit boards. Many Li-Po batteries come with JST-PH connectors to connect to the circuit boards.

Since there are different series, it can be confusing to identify the exact series of a specific connector. It is good to check the exact pitch, as well as the number of positions of a JST connector before buying.

IEC connectors are commonly used for AC power input. IEC-to-wall cables are widely available and are commonly used with PCs and lab equipment.

Part Selection:
VH series: JST’s VH(LF)(SN) series for 2 to 10 positions [CPL]
XH series: JST’s XH-A(LF)(SN) series for 2 to 20 positions [CPL]
PH series: Through Hole: JST’s PH-K-S(LF)(SN) series for 2 to 16 positions [CPL]
PH series: SMD: JST’s PH-SM4-TB(LF)(SN) series for 2 to 16 positions [CPL]

III. IC and Component Sockets how-to-choose-a-connector how-to-choose-a-connector how-to-choose-a-connector

DIPs, which stands for dual-in-line packages, are popular packages for integrated circuits (ICs), resistor networks, LED displays and DIP switches. A DIP package device can be mounted on a PCB either by using through-hole soldering or by using DIP sockets. DIP sockets allow easy replacement of devices and prevent risk of damage during soldering. A SIP, or single-in-line package, has only one row for connecting pins and is not as popular as DIP.
Part Selection: TE Connectivity’s 1-2199 series

A PLCC, or plastic leaded chip carrier, is a four-sided flat integrated circuit (IC) package. A PLCC IC can either be surface-mounted or installed on a PLCC socket, which is especially useful when an IC needs to be removed on a regular basis or when the IC needs stand-alone programming like flash memory devices.   

PGAs, or pin grid arrays,  are also IC packages. These can provide more pins than the older DIP packages. PGA sockets can be used to mount ICs.

IV. RF/Coaxial Connectors  how-to-choose-a-connector how-to-choose-a-connector how-to-choose-a-connector how-to-choose-a-connector how-to-choose-a-connector

BNC Connectors are one of the most commonly used coaxial connectors with applications in video wiring, laboratory test equipment, and radio equipment.  They are constant impedance connectors, which is particularly useful for RF applications since they provide same impedance throughout the cable’s length, with 50Ω the most widely used value. They can handle signal frequencies of up to 4GHz.
Part Selection: TE Connectivity’s 5-16345 series

TNC connectors are similar to BNC, except BNC connectors use bayonet connections while TNC connectors use threaded connections. This makes TNC connectors more robust. They operate more reliably at higher frequencies.

N connectors are larger versions of TNC connectors and are used in applications where RF performance is very important. They can handle higher signal frequencies — up to 11 GHz (precision designs can reach 18 GHz). Frequency response-wise, they are similar to TNC connectors, but they are tougher because of their larger size.

SMA connectors are compact and can operate up to 18 GHz. A torque wrench is usually required to connect them. If cables need to be connected/disconnected more often, BNC connectors are usually a better choice over SMA connectors. Other than SMA connectors, there are SMB and SMC connectors which are smaller. SMB connectors can operate up to 4 GHz.
Part Selection: TE Connectivity’s 10525 series

U.FL connectors are used when the space is critical — the connection is only 2.5mm high. Male U.FL connectors are soldered directly to PCB boards and can handle frequencies up to 6GHz.
Part Selection: Hirose’s U.FL-R-SMT series

V. USB Connectors how-to-choose-a-connector how-to-choose-a-connector how-to-choose-a-connector

USB (Universal Serial Bus) is an industry standard developed in the mid-1990s and USB connectors are common in many consumer products. Most USB cables have one end terminating with a USB-A male connector and they connect with host USB-A female connectors which can be found on most devices that support peripherals.

Male USB-B, mini-USB or micro-USB connectors are commonly found at the other end of the USB cables and are used for charging/communication between computers and peripheral devices.

how-to-choose-a-connector
USB-A, USB-B and micro-USB cables

Female USB-A, micro-USB, mini-USB and USB-B connectors are used to connect with USB cables for data communication/charging. Mini-USB is slowly getting phased out and being replaced by micro-USB in mobile devices.
Part Selection:
USB-A female connector: TE Connectivity’s 1734366 series [CPL]  
USB-B female connector:  FCI’s 61729 series [CPL]
Micro-USB female connector: FCI’s 101035 series [CPL]

VI. Headers and Terminal Blocks  how-to-choose-a-connector how-to-choose-a-connectorhow-to-choose-a-connector

Headers, which come in both male and female versions, are commonly used to connect expansion boards. They can also be used with jumpers. Cables with female headers are available and can be connected with the male headers on the boards. The most common pin headers are 0.1” single or double row connectors, the standard pitch of a breadboard. Headers are commonly used in most prototype boards, like Arduinos.   

Terminal Blocks are useful for connecting wires to a circuit board. Screw terminals hold wires and allow temporary connections to PCBs. This happens through the adjustment of a screw. Care needs to be taken as wires can be undone fairly easily.

Part Selection:
Male headers: TE Connectivity’s 4-1037 series for 1 to 80 positions [CPL]
Female headers: TE Connectivity’s 5-53423 series for 3 to 10 positions [CPL]  
Screw terminal blocks: On Shore Technology’s OSTTH series for 2 to 12 positions


Other Connectors

VII. Backplane connectors: how-to-choose-a-connector    

These are used to connect several connectors in parallel, such that pins on one connector are linked to corresponding pins on other connectors. They provide a “backbone” for connecting many different PCBs together to make up a system.  
Part Selection: Molex’s 850 series

VIII. D-subminiature (D-sub) connectors:how-to-choose-a-connector
These have two or more parallel sockets with a D-shaped metal shield surrounding it to provide mechanical support. The most popular D-sub connectors are DB-25 connectors, which have 25 sockets, and DE-9 connectors, which have 9 sockets. They are most commonly used as video connectors and in RS-232 serial communication. However, they are getting replaced by much smaller and cheaper USB, Thunderbolt, and HDMI connectors.        
Part Selection: TE Connectivity’s 17343 series
IX. FFCs (flexible flat cables) and FPCs (flexible printed circuits):how-to-choose-a-connector
These provide an alternative to rigid PCBs and connectors. They are used in applications where space is critical, such as cellular telephones. While they provide flexibility, they are more costly and harder to use than rigid PCBs.
Part Selection: FCI’s SFW series

X. Modular/Ethernet connectors:how-to-choose-a-connector
Modular connectors were initially designed for telephone wiring, but are now usually used for Ethernet connections. 8 position 8 contact (8P8C) modular connectors are preferred for Ethernet over twisted pair. In this context, the 8P8C connector is frequently referred to as an RJ45 connector, but this is technically incorrect – RJ45 is a telephone system standard.
Part Selection: Molex’s 48025 series  

XI. Memory connectors:how-to-choose-a-connector
Memory connectors are used to connect SD and SIM cards on circuit boards. Development boards like the Raspberry Pi have an inbuilt SD or a micro-SD card slot to provide storage space without a computer.
Part Selection: Molex’s 503 series

Apart from these, there are solar / photovoltaic connectors, fiber optic, card edge connectors and automotive connectors among others, which provide unique advantages in different applications. However, in most projects you are likely to see the connectors discussed in this guide. If you have any comments or suggestions, drop us a note in our Slack room or in comments below. Be sure to check out the other blogs in this series: how to select a capacitor, resistor and inductor.

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