The Ups and Downs of the Flex PCB Assembly Process

Flex PCB Assembly

Since their invention, printed circuit boards of PCBs have become a significant part of our day-to-day life. As per the 21st century, PCBs are in virtually every electrical gadget you can find, ranging from laptops to smartphones and smartwatches. Their popularity and heavy utilization in the 21st century mainly come from their robustness and compactness. By using PCBs, electrical manufacturers are able to generate compact gadgets that pack a lot of power. For instance, the first computer was pretty huge, it could fill up a room, but we now have powerful computers that can rest comfortably on your lap through the power of PCBs.

Printed circuit boards come in three types, rigid, rigid-flex, and flexible PCBs. However, flexible printed circuit boards are the most space efficient of these varieties. That is primarily because of their flexible nature, which allows them to fit into tight spaces. Due to this feature, flexible printed circuit boards are mainly utilized to manufacture compact gadgets. Therefore, you can find these circuit boards in compact, powerful devices such as smartphones and smartwatches. However, flexible printed circuit boards are challenging to manufacture. Due to their flexible nature, manufacturers must utilize a unique PCB assembly process to get a functional flex PCB. So how does the flex PCB assembly process occur? And what are the benefits of flex PCBs?

What exactly is Flexible PCB Assembly?

Before you move on to the assembly of flex PCB, you must first understand the basics of printed circuit boards. PCBs are components that mechanically support and electronically connect electrical components.

Connections in a PCB depend on conductive tracks, pads, and other features, which are drawn on layers of the base material, which is mostly copper.

Flex PCB Assembly

A flexible PCB is a new type of tech that involves printing the electrical circuit on a flexible substrate. Flexible PCBs are also known as:

  • Flexible substrates
  • Flex circuit boards
  • Flex circuit

On the other hand, flexible PCB assembly is the process of efficiently assembling different components of a circuit board to generate a flexible printed circuit board. Therefore, the elements that technicians utilize to manufacture flexible printed circuit boards might differ from those they use to create rigid PCBs.

Flex circuit boards are flexible, which means you can manipulate them to achieve the shape you want. Moreover, these PCBs can fold and bend efficiently without breaking the flow of the current in the board.

The most popular flexible substrates used to generate flexible printed circuit boards include:

Advantages of Flexible Printed Circuit Boards in Electronics

Flex-printed circuit boards offer a lot of benefits to the electronics industry. These benefits include:

Weight Reduction and Packaging

Flex-printed circuit boards are flexible. Therefore they can bend and fit into tight spaces. Due to this feature, technicians design these circuit boards to cater to different mounting design densities.

Typically, the flexibility of flex circuit boards reduces this circuit’s assembly process and enhances its reliability. Moreover, this feature also makes these circuit boards robust in terms of their application areas.

Moreover, flexible printed circuit boards are the perfect solution for the movement and miniaturization of electronic products.

Flexible PCBs are thin and light. Therefore, their packaging can be substantial and straightforward. Moreover, it permits proper space utilization via its ability to bend and fold. Additionally, when dealing with flex PCBs, technicians tend to utilize three-dimensional packaging to minimize the space occupied by the circuit board.

Using flexible printed circuit boards in your device can reduce its weight immensely compared to using wires and wire harnesses. That is because these circuit boards replace wires with copper traces, lowering common errors due to bad wiring.

Reliability and Durability

Full PCB Manufacturing

Flexible printed circuit boards boost the reliability of gadgets via the elimination of common interface connections, for example, solder joints. By lowering the number of interface connections in a PCB, you also reduce the potential causes of failure, therefore, boosting the reliability of your printed circuit board.

Moreover, the ductility and low mass of flexible circuits reduce the intensity of vibration and shock, boosting the circuit board’s performance and durability.

Additionally, using polyimide, a substrate with impeccable thermal stability, to manufacture flex PCBs allows these circuit boards to be applicable in environments bearing high temperatures. Moreover, this substrate reduces the chances of a thermal mismatch occurring since compliant base films tend to put less stress on solder joints.

Flexible printed circuit boards are also pretty resistant to radiation and UV exposure. Moreover, these circuit boards are excellent components that provide impeccable resistance to different chemicals, for example, acids, oils, and gases.

Cost Saving

Flex polyimide films use up a smaller area compared to the rigid PCB layers; therefore, they reduce the cost of production materials and the size of the PCB assembly process. In the PCB assembly process, technicians require fewer parts to generate a flex PCB which lowers the overall cost of production.

The simple assembly process of flex PCBs helps manufacturers save time and reduce assembly errors. Moreover, it also reduces the complexity of carrying out tests which further cuts the cost of production.

The assembly of flexible printed circuit boards hence eliminates the chances of generating faults during the assembly process.

Applications in High-Temperature Environments

Polyimide, the material that technicians utilize to manufacture flex PCB isn’t just a perfect heat conductor; it also has impeccable thermal stability. With the utilization of this component to make flexible PCBs, this circuit board has the ability to withstand high temperatures of around 400C.

Moreover, due to the use of polyimide in flex circuit boards, they do not contract or expand unnecessarily, making them perfect for application in high temperatures.

High-Density Application

The features of materials that technicians utilize to produce flex circuit boards make them great for high-speed PCB designs. Moreover, these materials make flex circuit boards have better impedance control.

Flexible PCB assembly involves using narrow lines, making these circuit boards perfect for high-density gadgets.

Moreover, due to their compact nature, flex circuit boards leave out sufficient space on a device to add more features.

Major Types of Flex PCB Assembly Processes

When dealing with flexible printed circuit boards, you will encounter four assembly processes. These processes tend to vary primarily depending on the condition of production. These flex PCB assembly process variations are the following:

Single-Sided Flexible Circuit Assembly

The single-sided assembly process is an assembly process that involves assembling a flexible printed circuit board with a single layer. Moreover, this process consists of the utilization of metal polymers or conductors on a flexible dielectric film.

The crucial features of this circuit board are only on one side of the circuit board. Moreover, this assembly process involves the utilization of lasers or drills to generate holes in the board’s base film.

In this case, the flex PCB fabrication process might include utilizing different cover coats. However, in some cases, technicians might decide to skip the cover coats.

Double Sided Flexible Printed Circuit Board Assembly

The double-sided flexible circuit board assembly process involves assembling a flex circuit board with two circuit board layers that can efficiently conduct electricity. Moreover, to carry out this assembly process, technicians can choose to utilize plated THT (Thru-hole) or not. It will all depend on the design specification.

By carrying out this assembly process without using THT technology, technicians yield a flex circuit board with the association feature on only one side of the board.

Double-sided flexible printed circuit boards typically allow various components to be placed on either side of the circuit board.  

Multi-layer Flexible Printed Circuit Board Assembly

The multi-layer flexible printed circuit board assembly process involves assembling a flex circuit board with more than two flexible circuit layers. In this case, the different layers found on multi-layer flex circuit boards connect through THT holes.

The THT holes don’t define the circuit in the multi-layer flex circuit board; however, they provide a way for different layers to connect and communicate.

To generate the layer of these circuit boards, technicians can choose to utilize lamination depending on factors such as the design specifications. However, if the technician decides to go with the lamination, they must exempt the THT holes.

On the other hand, irregular lamination tends to be crucial to areas that need extreme levels of flexibility.

Rigid-Flex Circuit Boards Assembly

The rigid-flex circuit board assembly process involves the assembly of a hybrid flexible printed circuit board. The type of circuit board that comes out of this assembly process bears both rigid and flexible parts, hence the hybrid definition.

Moreover, these varying components stick efficiently onto the flex substrate and the board, generating a single circuit board structure.

The rigid-flex circuit board assembly process is mainly utilized to generate flex circuit boards for the following industries:

  • Military
  • Commercial

Moreover, this assembly process is excellent for low-volume production applications.

However, it would help if you kept in mind that the rigidized flexible PCB assembly process differs from the rigid-flex PCB assembly process.

The Flex PCB Assembly Process


The Flex PCB assembly process is usually divided into two main categories:

  • Automated Using Circuit Board Assembly Machine
  • Manual Flex Circuit Board Assembly

Both of these processes are efficient and help generate a functional and reliable flex circuit board.

Automated Using Circuit Board Assembly Machine

The “automated using circuit board assembly machine” process of assembling flexible circuit boards solely depends on the type of machine a technician chooses to use.

When working with these machines, you must first ensure that they are functional before assembling the flex circuit board. After you are done checking on the device, you then have to collect the components that you will be using to make your circuit board. Once you are done with this phase, you can move on to the next one, which involves configuring your machine accordingly to fit the design specification of your flexible printed circuit board assembly process.

After all this is over, the printed circuit board machine will print your flex printed circuit board design automatically on the flex substrate. The flex substrate can be polyester or polyimide, depending on your design and how you plan on using the finished product.

After this phase, the circuit board assembly machine will then punch THT holes on the flex substrate automatically. However, you can also utilize the pick-and-place gadget to mount various components on your board’s substrate efficiently.

Moreover, depending on your design specification, you can place the surface finish on the circuit board. The surface finish gives the flex circuit board a unique glowing outlook.

Advantages of using the Automated Circuit Board Assembly Machine Method

Using the “automated circuit board assembly machine” method comes with many advantages, which include:

  • Fewer human error
  • The overall cost is lower
  • It reduces time
  • It helps manufacturers achieve consistency
  • The method is suitable for the generation of flexible circuit boards in bulk

Manual Flexible Printed Circuit Board Assembly

The manual flexible printed circuit board assembly process begins with the collection of all the components you will use to produce your flex circuit board.

Some components that you might need include:

  • Silkscreen
  • Solder mask
  • Copper
  • The substrate and others

Moreover, it would help if you remembered that all the components you use to make your flex circuit board have to be flexible in nature. Furthermore, these substrates should also have impeccable heat stability.

To generate your flex circuit board design, you can utilize PCB designing software. The designing software will help you develop your board design with increased accuracy and speed. You can then use a machine to draw your design on a flexible circuit when you are done. The use of a device at this stage is crucial since it helps you achieve higher levels of accuracy. Moreover, the machine enables you to make THT holes more precisely.

When all this is done, you can choose to utilize THT tech or SMT tech to efficiently mount the electrical component on your circuit board. Once the mounting phase is done, you can carry our reflow soldering to bind the element to the board.

Once you are done, you must conduct thorough testing to ensure that the flex circuit board is functional before you decide to use it on your gadget.


Flexible circuit boards have become popular in the electronics industry. The reason behind their popularity is their ability to bend, flex and fold into different shapes, which allows them to fit into tight spaces. Therefore, using these circuit boards, you can achieve more compact gadgets that are still powerful and efficient. However, to use a flex circuit board, you must first nail the assembly process. Therefore we hope this article will help you get the flex PCB assembly process right.

Leave a Reply

Your email address will not be published. Required fields are marked *