Flexible Multilayer PCB: The Ultimate Guide


Oakley Mae

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A flexible multilayer PCB is a circuit board combining multiple layers to form a complex board.

This is possible through the use of complex interconnection techniques like plated-through holes.

Surprisingly, these circuit boards have high-density interconnections thanks to shielding and surface mount technologies. 

Flex multilayer PCBs find applications where a one or double-layer won’t work.

But what are the multilayer circuit board applications, and how do you create one? 

This article helps you understand flexible multilayer circuit boards with a focus on their applications, benefits, and drawbacks.

Table of Contents

Multilayer Flex Circuit Boards

A flexible electronic board

(A flexible electronic board)

As mentioned, a multilayer flex circuit board combines several single and double-sided flexible PCBs.

We achieve this with complex interactions, shielding, and surface mount technologies. 

While developing multilayer flexible PCBs, you can decide to laminate them continuously.

However, we don’t recommend continuous lamination if you aim to achieve maximum flexibility. 

Generally, you can use multilayer flexible PCBs to address design challenges like eliminating crosstalk, shielding inadequacies, specified impedance requirements, extreme component density, and unavoidable crossover.

Flexible PCB Multilayer Elements

Most multilayer circuit boards have four elements as below: 

  • Conductors: Most multilayer flexible PCBs are designed with different conductor materials, including carbon, aluminum, and copper. However, of these materials, copper is the most preferred material. 
  • Insulators: Multilayer flexible PCBs have insulating layers between two PCB layers. Surprisingly, the layers can be from different materials, including polyethylene, screen-printed dielectric, polyimide, and terephthalate. However, polyimide is the most common insulating material in use. 
  • Adhesives: We use these elements to bind the layers together. In most cases, we use epoxy, acrylic, and adhesive base. The adhesiveness options offer superior electrical properties. 
  • Finishes: After you’re through with developing the circuit board, you’ll have to do some finishing. Fortunately, we have many finishes, including immersion gold, silver, tin, and carbon. 

Applications of Custom Multilayer Flexible PCB

A lady using a printer with custom multilayer flexible PCB

(A lady using a printer with custom multilayer flexible PCB)

You’ll be surprised to learn that some electronics you use now have a multilayer flexible PCB.

Check out the most common applications below:

  • Consumer electronics: Most electronics include e-readers, GPS units, tablets, PCs, and smartphones. However, you might also find them in laptops, digital cameras, desktop computers, and high-end printers. 
  • Industrial equipment: Multilayer flexible PCBs find extensive application in industrial equipment. Some equipment includes factory automation hardware, power generation equipment, and medical devices. 
  • Military/Aerospace products: Surprisingly, the aerospace and military rely heavily on flexible multilayer PCB. You’ll find them in avionic systems, wearable electronics, and communication equipment. 
  • Automotive components: Multilayer flexible circuit boards are available in different automotive components, including infotainment systems. 
  • Other applications: You’ll find multilayer flexible PCBs in robotics, renewable energy products, machinery, and buoys.

Benefits of Multilayer Flex Circuits

Engineers designing a PCB

(Engineers designing a PCB)

These circuit boards present the following advantages: 

Higher Reliability and Performance

Multilayer flexible circuit boards have higher reliability and performance than rigid circuit boards.

Therefore, you can employ them in high-end applications that require extreme reliability and performance. 

Surprisingly, their higher reliability enables them to withstand vibrations and stress, which is a significant cause of damage for traditional circuit boards.

Moreover, employing several layers provides for efficient routing of power and signals. 

Reduced Size and Weight

Multilayer circuit boards are always smaller and lighter than rigid ones.

This makes them useful when the circuit board’s weight and size affect efficiency and performance. Surprisingly, you’ll find them in aircraft and drones. 

Additionally, their multilayer constructions afford them an efficient use of space. Therefore, you can use them to design compact devices. 

Increased Signal Bandwidth and Frequency

These circuit boards provide increased signal bandwidth and frequency, critical in high data volume and high-speed applications.

Generally, the availability of advanced materials and multiple layers gives room for high-frequency routing. 

Better Power Efficiency

Multilayer circuit boards route power more efficiently than rigid circuit boards. Therefore, you can use them in applications that require a long battery life. 

Better Environmental Compliance

Since these circuit boards route power and signals effectively, they reduce the emission of electromagnetic interference and radiation.

We can only say they’ll make significant contributions in the future, especially since the world is going green. 

They’re Durable

Multilayer circuit boards are designed with a high-quality base.

Also, they have good thermal stability, making them withstand higher temperatures than rigid PCBs.

Therefore, they’re likely to last longer than their traditional counterparts. 

Better Heat Dissipation

Multilayer flexible circuit boards are thin, thus having a high surface area-to-volume ratio.

This provides a shorter thermal path. Therefore, they dissipate heat better than rigid circuit boards, thus, higher efficiency. 

Multi-Layer Flexible PCB Drawbacks

Despite these PCBs’ many benefits, they also have drawbacks. Let’s check them out:

High Cost

The whole process of designing and wiring a multilayer flexible circuit board is complex and expensive.

Therefore, you might have to purchase them more expensively than traditional circuit boards.

Consequently, they’re rarely used, and you’ll only find them in some special applications. 

Restricted Finished Product Size

The production equipment size always limits multilayer flexible circuit board production.

Therefore, you can’t make them very wide or very long. 

Low Yield Rate

As highlighted, multilayer circuit boards undergo a complex manufacturing process.

Therefore, they have a high finished product scrap rate. Consequently, the overall price of flexible circuit boards increases. 

Circuit Damage Due to Improper Assembly

If by any chance you operate the assembly personnel improperly, the flexible circuit board will get damaged.

Surprisingly, any rework or soldering will require serious professional operations. 

Tips for Developing The Best Multilayer Flexible PCB for Your Project

Photo robotic soldering for multilayer PCB

(Photo robotic soldering for multilayer PCB)

The main focus of any multilayer circuit board design is the stack-up.

The layer stack-up has several selections or choices guided by manufacturing, deployment, considerations, and functionality. 

Optimize The PCB Size

Some factors determine your circuit board’s optimal size, including the component size and number and where you seek to mount the PCB.

Other factors include your preferred manufacturer’s tolerance for clearances, drill holes, and spacing. 

Optimize The Layer Design

You should base your layer design on the signal types. Moreover, consider the impedance requirement using controlled or fixed impedance. 

Optimize The Via Selection

The type of visa you will inform the circuit board’s quality and the fabrication process’s complexity.

You can choose between through-hole, via-in-pad, buried, and blind vias. 

Optimize The Material Selection

We recommend choosing the best circuit board material layer-by-layer.

However, ensure the stack’s ground plane and signal layers distribution is symmetric and promotes good signal integrity. 

Optimize The Circuit Board Manufacturer

Finally, choose the best manufacturer for your flexible multilayer board.

Always prioritize a manufacturer with the right equipment and technicians. Moreover, they should test the circuit board after fabrication. 


Are multilayer flexible circuit boards expensive?

Yes! Multilayer circuit boards go through a complex and expensive manufacturing process.

Therefore, expect to buy them more expensively than a rigid circuit board. 

Why should you use a multilayer flexible PCB?

Generally, multilayer circuit boards present several benefits, some of which you’ll never find in other circuit boards. For example, they’re highly durable and boast better heat dissipation.

Also, they have less weight and size than rigid ones, thus being useful in the design of compact devices. 

When using flexible multilayer boards, expect high reliability and better performance. 

What’s the difference between a multilayer and a single-layer PCB?

You can tell the difference between a single and multi-layer circuit board from their name.

A single-layer circuit board has a single base material layer or substrate.

On the other hand, a multi-layer circuit board has multiple layers. 


As we’ve seen, flexible multilayer PCBs are circuit boards with multiple layers to form a complex circuit.

These circuit boards have come in handy in eliminating crosstalk and shielding inadequacies. 

Although complex and expensive to design, flex multilayer circuit boards are highly reliable and provide increased power efficiency.

Surprisingly, they boast better heat dissipation functionality than other options. 

And if you follow our tips above, we guarantee you’ll create a reliable flex multilayer circuit board.