Ultra-thin Flexible PCB: The Ultimate Guide


Oakley Mae

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An ultra-thin flexible PCB has the characteristics of flexible printed circuit boards; it is thinner.

As a result, it is delicate and, at times, costlier to manufacture than most rigid boards.

On the other hand, it has multiple applications in devices that must be lightweight. And its demand is ever-increasing as manufacturers develop smaller devices.

Today’s guide has all the information you need to kick-start your journey with ultra-thin flexible PCBs.

We are looking at what they are, their applications, and production techniques, among other things. Let’s get going.

Table of Contents

Types of Ultra-thin Flexible PCBs

Holding an ultra-thin flexible PCB

(Holding an ultra-thin flexible PCB)

We have three main types of ultra-thin PCBs. They are as follows:

Ultra-Thin Rigid-Flex PCBs

They combine rigid and flexible architectures, giving users the best of both.

Additionally, they introduce certain features neither structure could provide on its own.

Designers can significantly improve the design capabilities of their circuits by using hard sections added to the flexible portions. 

Take, for example, when you need to capitalize the rigid areas for hard- mounting and the flex ones for vibration-resistance zones.

There’s a high chance that you would need a board that combines the characteristics of both boards.

Moreover, board mixing gives designers a wide range of options for creating original solutions for difficult situations.

Ultra-Thin Flexible PCBs

They are special ultra-thin circuit boards with excellent flexibility and resistance to vibration.

Additionally, they still retain the reliability and high density that comes with the other types of PCBs.

As such, you can use them in applications that don’t suit rigid PCBs but need the same number of components.

Also, flex circuits can assume 3D topologies, which is a significant benefit over rigid PCBs.

Ultra-Thin HDI Flexible PCBs

Ultra-thin HDI or high-density-interconnect flexible PCBs work well in applications where flexible circuits are unsuitable. They have finer features, such as micro-vias, and offer better layouts and construction.

Additionally, they have miniature form factors and dense circuitry that suit them for demanding applications.   

Applications of Ultra-thin Flexible PCBs

A UAV on patrol

(A UAV on patrol)

One area that promotes ultra-thin flexible PCBs is their endless freedom for packaging geometry.

Regardless of the installation surface shape, they will fit while retaining functionality. Additionally, we use flex circuits to substitute the wiring harness.

As a result, one flex circuit may replace several connections, wires, and hardboards at once. 

Besides, doing so hastens the assembly process as there is no longer a need to color-code and bundle wires. Doing so is beneficial as it increases the manufacturing volume and decreases installation costs.

Consequently, here are devices and applications that rely on ultra-thin flexible PCBs:

  • Wearable devices: Fitness trackers, medical monitoring devices, and smartwatches.
  • Aerospace: Unmanned aerial vehicles (UAVs), satellites, and missiles.
  • Medical devices: Sensors and implants.
  • Consumer electronics
  • LED lighting applications
  • Mobile phone charging module

Advantages of Ultra-thin Flexible PCB

A manager inspecting a flexible circuit board

(A manager inspecting a flexible circuit board)

Manufacturers design ultra-thin flexible PCBs for certain applications that may not suit larger-size circuit boards.

Additionally, some of these applications demand the PCB be thin so that it doesn’t take up too much space.

Here are the benefits that come with using ultra-thin flexible PCBs. 

Smaller Size: Ultra-thin PCBs are small and suit small, flexible devices. For instance, you can use them in wearable devices with little weight and size.

Fewer material costs: Generally, manufacturers use expensive materials like copper to make their circuit boards.

Overall, using too much material increases the manufacturing cost, translating to the buyer as an expensive product.

To cut on such, manufacturers prefer ultra-thin flex PCBs to lower production costs as they use less material.

Lightweight: Ultra-thin flex PCBs are lightweight, making them suitable for applications that have to be light. For example, medical implants and hearing aids must be as light as possible.

Better reliability: As much as the ultra-thin flex PCBs are lightweight, they are strong and reliable. It is more so in applications that generate too many vibrations or bending.

Additionally, they are less likely to break down due to thermal expansion and contractions. 

Ease of installation: Ultra-thin flex PCBs are easier to install in certain applications than rigid circuit boards.

If your installation surface is tight, you are better off going with ultra-thin flex PCBs.

High flexibility: Ultra-thin PCB’s characteristic lessens the tension on the solder joints & flex circuit. Excellent ductility assists the flex circuit in tolerating harsh operating circumstances.

Furthermore, they can withstand acceleration and vibration of particles that may be difficult for rigid PCB joints. 

Disadvantages of Ultra-thin Flexible PCB

A PCB assembly line in a factory

(A PCB assembly line in a factory)

Ultra-thin PCBs have disadvantages that make them unsuitable for certain applications. Here are the major ones. 

Manufacturing challenges: Ultra-thin PCBs are delicate circuit boards requiring specialized manufacturing equipment. Moreover, you’ll need the skills to operate the equipment and set precise tolerances.

Signal integrity: Since ultra-thin PCBs are very thin, they are prone to manufacturing errors. Additionally, their flexibility can cause signal integrity issues such as crosstalk and signal loss.

All these factors will contribute to signal degradation and introduce electrical noise into the circuit. 

Low trace capacity: The thin nature of the PCBs may reduce the size of the traces you can add.

Consequently, this limits their functionality to certain applications and only suits some. 

Cost: You’ll need specialized equipment to manufacture ultra-thin PCBs.

Therefore, you’ll find that the start-up cost is expensive, especially if you incorporate the cost of special materials.

Techniques To Drill Microvias Into Ultra-thin Flexible PCB

Here are the techniques to drill micro-vias into an ultra-thin flexible PCB:

Photo-via Drilling: It is a technique using photo-imaginable dielectric materials and lithography patterns. Moreover, its hole size is a miniature 25 micrometers in diameter and depth. 

Plasma Etching: It is a technique that uses special vacuum equipment to drill micro-vias. With it, you can drill a 75 µm hole that’s 25 µm in diameter.

Laser Drilling: The laser technique can drill holes 5 µm in diameter on a 5 µm dielectric material. 

Considerations While Manufacturing Ultra-thin Flexible PCB

Engineers in a consultation process

(Engineers in a consultation process)

Important factors to consider when manufacturing ultra-thin flexible PCBs include:

The manufacturer: If you lack sophisticated equipment to make manufacturing easier, seek a proven manufacturer’s services. 

Registration processes: Use state-of-the-art methods to register your ultra-thin flexible PCBs. The reason is that they’re thin and have little manufacturing tolerances.

Handling: Ultra-thin flexible PCBs are delicate and need precise handling during manufacturing. 

Manufacturing costs: Ultra-thin flex PCBs are delicate, and their handling increases manufacturing costs. Luckily, you can reduce such by adopting cost-effective manufacturing techniques.


Why is shielding important in Ultra-thin Flexible PCB?

The fact that PCBs work in demanding environments exposes them to interferences that may lower the signal quality.

Consequently, manufacturers enclose the ultra-thin PCBs with a layer that shields them from absorption and EMI radiation.

Additionally, your PCB can suffer from different problems that necessitate shielding. 

First, manufacturers use metal foil shielding to protect an ultra-thin PCB from EMI. Second, they apply a conductive coating to the board’s surface to absorb or block EMI.

Thirdly, they can use conductive enclosure shielding to enclose the entire circuit from radiation.

And lastly, they can use conductive tape to wrap around the PCB.

What is an Ultra-Thin HDI PCB?

An ultra-thin HDI PCB is a type of circuit board that is thinner than traditional PCBs.

Moreover, they use micro-vias that allow the boards to accommodate a higher density of components than most ultra-thin boards.

Micro-vias are small holes on the PCB that manufacturers fill with conductive material for more connections.

Consequently, you’ll find that it has applications in devices where space is at a premium.

Final Remarks

We’ve gone through the most important aspects of ultra-thin PCBs concisely.

If you’re designing a system without space, consider using these boards. They are lightweight and reliable, more so in areas with many vibrations. 

Additionally, you can use them for applications that generate a lot of heat unsuitable for rigid PCBs.

And if you need a PCB with a higher density of connections, go with the High-Density Interconnect printed circuit boards.