How To Connect Wires To Flex PCB

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Oakley Mae

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Every circuit board engineer or designer should understand how to connect wires to flex PCB.

Generally, PCB wiring involves two significant aspects: The conductors and connectors.

The conductor is essential in carrying signals and power through the circuit board, while connectors affix conductors and other components. 

While connecting wires to flex PCB, manufacturers fail to focus on essential details like the type of conductors and connectors.

And we can’t blame them since flexible PCB design and development is complex.

Worry not if you fall under this category, as we have all the necessary answers and guidelines. 

Keep reading for more on how to connect wires to flex PCB. Let’s get started. 

Table of Contents

How are wires connected to Flex PCB?

(A robotics engineer assembling a PCB)

Generally, three primary options exist for connecting wires to a flexible circuit board.

We’ll briefly highlight the options, but we will explore some of them in depth later in the article. 

  • Direct Soldering on The Board: Soldering is the cheapest option for connecting wires to a flexible PCB. But first, you should identify contact points through holes or surface mount technology. However, the solder could sometimes stick to the flexible board, making it less flexible. 
  • Terminal block: This involves soldering components on the PCB with the ability for wire connection. The most common options here include screw terminals and spring-loaded blocks. 
  • Connectors: This is a two-part system with one part soldered to the circuit and the other linked to a cable. Surprisingly, there are many connector types, as we’ll see later in this article.

How To Solder Wires To Your Flex PCB

Female engineers soldering on a PCB

(Female engineers soldering on a PCB)

Soldering is the most popular and cheapest way to connect wires to flexible circuit boards.

This method involves heating the PCB pad and the wire and, in the process melting the soldering wire.

You then allow the solder to flow to the pad and the wire. 

Generally, the solder in use is a lead-tin alloy. However, manufacturers use silver in particular situations.

You can use the soldering method when repairing, modifying, and making circuit boards. 

Below are the steps to follow when soldering wires on your flex PCB:

  1. First, clean the circuit board pad where you intend to attach the wire. Use an eraser to rub the pad until it becomes clean and shiny. Next, strip almost a quarter of an inch of your wire. 
  2. Second, melt a smaller solder on the tip of the soldering iron. Next, heat the wire end using a soldering iron for a few seconds. Bring the solder wire into contact with a bare wire and hold them in place until the solder melts. Allow the solder to flow into stranded wires. This process is what we call tinning, and it’s unnecessary for single-stranded or solid wires. 
  3. Put the end of the wire through a hole in the flexible circuit board from the component side. However, be careful not to allow the wire to touch any other component or pads on the circuit board. Also, you can bend it slightly to allow for proper soldering. 
  4. Put the soldering iron into the pad and wire end briefly until the solder melts. The solder should be enough to form a dome-shaped puddle that covers the wire and the hole. Next, remove the soldering iron from the pad but avoid moving the board. 
  5. Finally, cool the PCB soldered joint and restart the circuit board until the solder hardens. You can clip the wire end from the wire cutters. At this point, the wire will be attached permanently to your flexible circuit board. 

Wire-To-Board Connectors

A 4-pin connector cable connected to a board

(A 4-pin connector cable connected to a board)

As highlighted above, connectors are reliable for connecting wires to a circuit board.

We refer to these connectors as wire-to-board connectors, and they employ crimping technology to achieve their purpose.

Check out the different wire-to-board connector types below: 

Wafer Connectors

These connectors provide the best options for connecting wires to a circuit board.

They have a female connector which you crimp to the wire, and a male connector which you attach to your flexible circuit board.

Therefore, you don’t require soldering the female connector.

Moreover, the polarized connectors make it easier to plug into the mating connector correctly. 

Ejector Headers

These connectors have ejector mechanisms to allow for easier connection and disconnection.

They’re also polarized, making plugging into the mating connectors easier. 

FFC/FPC Connectors

Flexible flat cable (FFC) and flexible printed circuits (FPC) connectors are designed with a flexible film or plastic with a metal connector on one end.

These connectors provide a compact design and a high level of reliability. 

IDC Connectors

As the name suggests, the IDC (Insulation Displacement Contacts Systems) has a sharpened blade that strips a cable’s insulation.

Therefore, you don’t need to strip, crimp, or cut individual wires before connecting them.

Surprisingly, these cables reduce the processing time. 

Rast IDC

The Raster Anschluss Steck Technik is common in home appliances.

This connector has a numerical value representing the contact centerline spacing for a certain connector. 

Which conductor is used in flexible PCB?

A plastic flexible circuit board LCB panel

(A plastic flexible circuit board LCB panel)

A flexible circuit board requires a proper conductor to transmit power and signals.

Surprisingly, copper is the most common conductor in flexible circuit boards.

Generally, copper has preferred thanks to its high reliability, low cost, excellent conductivity, and availability. 

Copper conductors for flexible circuit boards are available in different thicknesses depending on your preference.

However, you can still use other conductors like gold, silver, nickel, and aluminum.

Unfortunately, gold and silver are costly and not economically viable for designing PCBs. 

Ways To Connect Circuit Wires Without Soldering

How can you connect flexible circuit board wires without soldering? Below are the different approaches to consider: 

  • Alligator clips method: Although this is the weakest option, it is ideal for quick and temporary solutions. You need alligator clips and two pairs of striped wires. To fix the wires, hold them parallel to each other and snap an alligator clip to hold them in place. 
  • Electrical tape: This option offers a strong connection and is perfect for permanent solutions that require insulated joints. To fix wires with this approach, lay the twisted wires onto an electrical strip and wrap the electrical tape around them for about 5-6 rounds. 
  • Hot glue: This approach offers a more robust connection that links and insulates wires. However, you’ll need a glue gun to manage this process. 
  • Crimping method: This is the strongest approach to connect PCB wires and requires a crimping tool. Fortunately, with dedication, you can quickly learn how to use the crimping tool. 

FAQ

Can you wire in Flex?

Yes! Nothing stops you from wiring in Flex.

The wiring on Flex is safe, and the Flex earth core is larger than on the cable.

Therefore, the earth loop results are somehow better. 

Can you solder to a flexible PCB?

Yes! Soldering is the most common approach to attaching components to a flexible circuit board.

Proper soldering requires a reflow temperature between 300°C to about 400°C.

You’ll need a functional soldering iron and soldering flux for good soldering. 

How are wires connected to PCB?

You can connect wires to circuit boards using any of the following options: 

  • Direct PCB soldering
  • Using terminal blocks
  • Using connectors

Conclusion

Understanding how to connect wires to the flex PCB is helpful during the design and repair.

As mentioned, PCB wiring involves the conductors and connectors.

The conductors carry power and signals in the PCB, while connectors link the conductors to the board. 

Therefore, you can connect wires to your flexible PCB by soldering, connectors, and terminals.

Surprisingly, soldering is the cheapest and most common approach most engineers and manufacturers employ.

Follow our guide above to solder wires effectively on the circuit board.