Ultra-Thin PCB: The Ultimate FAQs Guide


This guide has everything you’re looking for about ultra-thin PCB such as classification, quality standards, co-efficient of thermal expansion, and applications, amongst others.

So, if you want to be an expert in ultra-thin PCBs, read this guide.

What is Ultra-Thin PCB?

As the name suggests, extra thin PCB is a type of printed circuit board with a smaller thickness than standard PCB.

It is lighter and more compact since it has decreased board materials and volume of copper features.

Ultra-Thin PCB is ideal for PCB applications where miniaturization and high level of reliability serve a key role.

It facilitates miniaturization with enhanced performance through higher-density PCB designs.

Ultra thin PCB

Ultra thin PCB

What are the Advantages of Ultra-Thin PCB?

The following are the main benefits of Extra-Thin PCB:

· Short Assembly Time

All lines of ultra-thin PCB are configured, which saves time during connection of excess lines.

· Smaller and Compact

This type of PCB can effectively minimize the final product volume, making it conveniently portable.

· Lighter Weight

Thinner PCB materials result in smaller vias, less copper plating, smaller spaces and lines and decreased aspect ratio of vias. This leads to a more compact and lightweight PCB product.

· Reduced Thickness

Miniaturization in the X- and Y-axis can considerably minimize the footprint of ultra-thin PCBs. However, Z direction miniaturization allows more space for supplementary components and minimize the general thickness of the circuit board.

Other benefits of ultra-thin PCB include easy assembly, good solderability, low general cost and good heat dissipation, among other factors.

The design of extra thin PCB as well compensate for the inadequacy of the PCB substrate in relations to component carrying capacity.

Which are the Types of Ultra-Thin PCB?

There are three main types of extra thin PCB including:

· Ultra-Thin Rigid PCB

There are ultra-thin rigid PCB materials for applications requiring a 2D printed circuit board.

They are usually applied as packaging substrates for integrated circuits, in which they aid in making the whole component extremely thin.

You can attain 25 microns wide spaces or lines, pitches below 175 microns, and 50 and 100 microns vias and pads diameters respectively.

· Flexible Ultra-Thin PCB

Also referred to as flex ultra-thin PCB, this is a type of extra-thin PCB manufactured using flexible laminates.

This allows folding of the PCB, which reduces the volume and surface area required to house the board, hence increasing the integration density.

Moreover, extra-thin PCB equally facilitates better bending.

This implies that it is practical bend the circuit board through smaller bend radii, making it possible to attain even tinnier volumes.

One of the main applications of ultra-thin flexible PCB due to their advanced bending capability is manufacture of cables requiring dynamic bending.

· Ultra-Thin Rigid-Flex PCB

These types of extra thin PCB feature conductors on the rigid and flexible layers of the printed circuit board.

Plated thru-holes stretch between the rigid and flexible segments and electrically link multiple layers of conductor.

Through integration of rigid sections to the flexible components, it allows you to enhance the design abilities of your ultra-thin PCB.

The rigid segments offer perfect hard mounting locations for components, chassis and connectors.

On the other hand, the flex segments provide dynamic flexing, flex-to-fit and vibration-resistance zones.

Such combination gives you multiple choices for achieving innovative solutions for the greatest demanding rigid flex PCB applications.

What are the Applications of Ultra-Thin PCB?

Here are the some of the uses of ultra-thin PCB:

  • TF Card/SIM Card
  • Medical devices such as active implants and hearing aids
  • Metro coins
  • NFC technology device
  • Automotive engine controls
  • Bar code equipment
  • Wearable
  • GPS system
  • Printers
  • Mobile phone charging module

What is Ultra-Thin HDI PCB?

High-Density Interconnect PCB is simply an ultra-thin PCB having more counts of interconnections, covering minimal space, leading to circuit board miniaturization.

The components of HDI PCB are positioned closer, reducing the board space significantly but not compromising its performance.



HDI is among the fastest advancing PCB technologies, capable of integrating smaller capture pads and vias and higher densities of connection pad.

HDI PCBs have buried and blind vias and usually comprise of microvias with diameter of 0.006 or lower.

Extra thin HDI PCBs provide better construction, layout and design choices by integrating outstanding features like microvias.

They give smaller form factor, increased functionality, and highly dense ultra-thin flex circuitry.

Moreover, though they employ thinner PCB materials, HDI boards offer improved electrical performance, better reliability and advanced extra thin PCB.

By applying HDI technology, it is possible to mount more components on either surfaces of the Ultra-thin PCB if necessary.

Additionally, with the advancement of blind via and via in pad technology, you can position smaller components nearer to each other.

This signifies quicker signal transmission and substantial reduction in crossing delays and signal loss.

The common applications of Ultra-thin HDI PCB include use in:

  • Mobile phones
  • Digital cameras
  • Medical devices
  • Laptop computers
  • Touch-screen devices
  • 4G network communications

How are Microvias Drilled in Ultra-Thin PCB?

There are three different techniques of drilling microvias in ultra-thin PCB:

1. Plasma Etching Technique

This method of microvia drilling etches PCB material for formation of hole using plasma.

With this technique, you can attain a via hole diameter of 75 µm via hole diameter on a 25 µm thick material.

However, coupled with costs on special vacuum machinery, plasma etching makes the least promising technique for via hole drilling.

2. Photo-via Drilling Technique

Photo-via technology employs lithography patterning and photo-imaginable dielectric material.

The method has promoted the advancement of ultra-thin HDI PCB.

It features a hole size of approximately 25 µm for both depth and diameter.

However, it is an expensive method of drilling ultra-thin PCB microvias because of the unique dielectric material.

3. Laser Drilling Technique

This is the most promising microvia drilling technology.

Through laser drilling, you can attain via hole diameter as low as 5 µm on a dielectric material with 5 µm thickness.

The main factors controlling this technique of microvia drilling is energy density, substrate material, wavelength, and thickness of substrate material.

It is the most preferred drilling method for microvias, which involves focusing a laser beam on an extremely small area.

The vias created incline to be as clean as those developed through mechanical drilling.

This ensure uniform deposition of plating on the vias interior.

Laser via drilling features a reduced drill speed in comparison to mechanical drilling.

The technique can be applied to effortlessly bore dense microvias in an Ultra-thin PCB, applying wavelengths spanning from ultraviolet to deep infrared.

However, the main disadvantage of laser via drilling is the limited laser beam depth that you can reliably and reproducibly drill.

When one lens is utilized for beam concentration, the depth drillable by the laser is limited because of the restricted depth of focus.

But, a collimated laser beam enables laser via drilling to a deeper depth.

Nevertheless, the challenge with it is the extremely small via size, which causes Fresnel diffraction in the beam.

This can in turn impact on the beam intensity in exceptionally deep microvia holes.

Types of vias

Types of vias

How Does Moisture Affect the Prepreg used in Ultra-Thin PCB?

Polyimidesprepregs are more sensitive to moisture than epoxies by the fact that they tend to absorb moisture from air faster.

Moisture within theprepreg does it little harm, though may lead to delamination, voids and other flaws in laminated ultra-thin PCBs.

A perfect indicator of moisture in PCB prepreg is foamy flow, which is common with polyimide because they absorb moisture faster.

Vacuum drying or storing any prepreg with desiccant at low humidity will reduce this effect.

Moisture can result in additional issues in finished ultra-thin PCB.

Excessive moisture can compromise the integrity of a multiple layer PCB under high temperature strained environments.

Therefore, it is crucial to regulate moisture even in complete bare circuit boards before solder reflow or PCB assembly process.

Moreover, controlling moisture is equally essential in finished ultra-thin PCB in case they will be eventually subjected to high temperatures.

It is advisable to vacuum dry prepregs at 29″ of vacuum for several hours.

Vacuum desiccation under room temperature is the most preferred over any form of oven drying for ordinary polyimide or epoxy PCB prepreg.

It is the best method of drying ultra-thin PCB prepreg even if the oven drying process is subjected to controlled conditions.

Oven drying may incline to enhance the prepreg, and might lead to marginal or inadequate bonds or flow.

This can cause delamination or additional failures on succeeding thermal processing.

Nonetheless, Non-woven aramid polyimide is the only exception.

Here, oven temperature not exceeding 32 degrees Celsius at 29’’ of Hg for 4 – 5 hours may help in eliminating excess moisture.

Which are the Quality Standards for Ultra-Thin PCB?

Some of the important quality standards for Ultra-thin PCB include:

  • REACH Standards
  • IPC Standards
  • RoHS Standards
  • UL Standards
  • ISO Standards
  • CE Standards
  • ITAR Standards

How Does Microvias Assist with Trace Routing in Ultra-Thin PCB?

Ultra thin PCB

Ultra think PCB

The main goal in ultra-thin PCB fabrication is to have more trace routing to smaller sections as PCB density increase with technology.

This has resulted in use of embedding vias as well as buried and blind vias in surface mounted pads.

Nevertheless, buried and blind vias are more challenging to fabricate due to the additional drilling procedures involved.

Moreover, the drilling may leave debris in the holes leading to manufacturing flaws.

Ordinary vias are equally often too broad to be integrated in the tiny surface mount pads found in modern high density PCBs.

However, microvia can assist with all these challenges:

  • Manufacturing microvias is easier in comparison to buried and blind vias.
  • Microvias in Ultra-thin PCB will fix into tinnier surface mount pads. This makes them instrumental for high pin-count gadgets such as ball grid arrays (BGA).
  • They will facilitate more trace routing about them because of their smaller size.
  • Extra thin PCB microvias can equally help in reduction of EMI and boost other signal integrity problems due to their size.

What are the Disadvantages of Ultra-Thin PCB?

Here are some of the key shortcomings of ultra-thin PCB:

High Initial Cost

Ultra-thin printed circuit boards are designed and constructed for distinct applications.

This leads to high initial cost of PCB design, layout and photographic plating.

Therefore, it is advisable not to use them in small amounts.

Difficult Changes and Repairs

Once fabricated, extra thin PCB must be modified from the configured lithography program or base map, making it hard to change.

Moreover, it has a protective layer on the surface, which should be removed prior to repairs. Removing and restoring the surface covering is a fairly challenging task.

Limited Size

Ultra-thin PCBs are often fabricated through a batch process.

Therefore, they cannot be very long and broad in size due to the restriction of production equipment size.

Easily Damaged

This type of PCB is easily destroyed by inappropriate handling. The rework and soldering of ultra-thin PCB needs handling by a trained personnel.

Are there Multilayer Ultra-thin PCBs?

Yes, you can find multilayer PCBs, which are usually 50 percent thinner than traditional multilayer PCBs.

A typical 6-layer extra thin PCB has a thickness of 260 microns, with the layers consisting of surface protection, core, pre-preg and conductive copper.

Presently, the exterior layer of a multiple layer ultra-thin PCB have 12 µm thickness for the polyimide and adhesive.

Which are the Common Dielectric Materials for Ultra-Thin PCB?

There are a wide variety of materials used in extra thin PCBs.

Materials like polyimide and polyester have been standards for the industry for several years.

Epoxy based substrates, both non-reinforced and reinforced are equally being utilized where cost is a consideration.

Other PCB materials such as aramid, glass and composite are applied for particular applications in which specific performance features are needed.

To establish the best ultra-thin PCB material for a specific application, you must understand the main performance properties of every material.

Knowing the chemical, electrical, mechanical and thermal characteristics of the material will enable you to make the right choice of base material.

Some of the mechanical features to look for include dimensional stability, tear propagation strength, tensile strength, and flexibility.

Similarly, electrical characteristics include volume resistivity, dielectric constant and dielectric strength.

The thermal features to consider include coefficient of thermal expansion, service temperature range and glass transition temperature.

Moreover, you should ensure that resistance to alkalines or acids and moisture absorption are balanced to meet the desired design characteristics.

What is the Meaning of Controlled Impedance in Ultra-Thin PCB?

Impedance control is coordinating the locations and dimensions of the PCB traces with the substrate material.

This is done to ensure that the signal strength traveling through a trace does not exceed a required range.

It is important if high-frequency signals travel on the transmission lines of the ultra-thin PCB.

Controlled impedance is crucial for signal integrity: it refers to signal propagation without distortion.

Since complex antennas, processors and other components are mounted directly onto the PCB surface, the signal speed switching on the board surges.

This makes the electrical properties of the signal transmitting tracks very crucial.

Therefore, most designs of ultra-thin PCB require impedance control.

Why is Coefficient of Thermal Expansion in Ultra-Thin Rigid PCB?

The CTE of the rigid laminate is among the most essential features of Ultra-thin PCB substrate materials.

Poor matching with silicon die can result in cracks, which greatly affect PCB manufacturing and components assembly onto the substrate.

Furthermore, issues with thermal expansion may as well result in failures when using the PCB.

Ultra-thin PCB substrate materials equally should have excellent high-frequency features to attain the needs of modern high-speed PCB applications.

What is the Purpose of Shielding in Ultra-Thin PCB?

PCB shielding requires that it is enclosed on either sides using a material layer that functions as barrier to EMI radiation or absorption.

The layers are linked to ground to ensure harmless dissipation of any EMI.

Most electronic assemblies that employ ultra-thin PCBs are reactive to either emission or absorption of electromagnetic interference.

When the EMI goes unregulated it can adversely affect the functioning of the board and in severe cases totally hinder it from working.

For most types of ultra-thin PCB, EMI shielding is an instrumental parameter that guarantees the general performance of the end product.

There are various types of shielding techniques available that allows you to achieve all the mechanical and electrical requirements of the PCB.

What is the Difference Between Single-sided Ultra-Thin PCB and Double-sided Ultra-thin PCB?

Single-sided ultra-thin PCB has the components and conductive copper mounted fixed on one edge of the board, with conductive wiring on the other surface.

They are the commonly fabricated types of ultra-thin PCB due to their simplicity and basic nature.

Some of the common applications of single-sided extra thin PCB include use in calculators, printers, camera systems, and radio equipment among others.

Conversely, double-sided ultra-thin PCB has two-sided traces having a bottom and top layer.

They can fit the components and conductive copper on either surfaces of the board, which enables traces to pass over one another.

This leads to a high-density circuitry without the necessity for point-to-point soldering.

Since these types of ultra-thin PCB are more sophisticated compared to single-sided versions, they can be more challenging to fabricate.

However, the advantages of double-sided PCBs greatly surpass the disadvantages.

Double-sided boards are among the most common types of ultra-thin PCB, since they facilitate production of more sophisticated boards.

This benefits applications in higher technology electronics and PCB uses.

The common applications of double-sided ultra-thin PCB consist of use in vending machines, car dashboards, lighting systems, and amplifiers among other applications.

Which are the Important Consideration During Construction of Ultra-Thin PCB?

Let’s look at some of the important factors to consider during manufacturing of ultra-thin PCB:

· Use Experienced Manufacturer

It is important to seek the services of an experienced PCB manufacturer having advanced engineering skills.

This is due to the fact that ultra-thin PCB materials need unique fabrication technology, design approaches, among other considerations.

· Precise Registration Procedures

You can use advanced methods like laser direct imaging with extra thin PCB materials.

However, highly accurate registration processes are needed since the features are usually tinnier when you use a thinner PCB material.

· Proper Handling

Correct handling during Ultra-thin PCB assembly is more crucial than with ordinary materials.

This is because thinner substrate materials can result in warpage and greater flexibility.

The smaller pads and reduced dimensions need higher precision during assembly.

Moreover, with ultra-thin PCB materials, it can be more challenging to mount finalized circuitry onto the board without damaging them.

Therefore, it is vital to discuss early with your PCB manufacturer about handling requirements and quantity of units in a delivery panel.

· Cost of Manufacturing

The extra fixtures and handling required with ultra-thin PCB materials increase handling and assembly costs.

Nonetheless, lower material and process costs can assist in balancing these.

You can reduce the cost of materials by using less copper.

Consulting the engineering team during design can aid in ensuring cost-efficient solution that satisfy your performance requirements.

Depending on your unique specific needs, Venture Electronics offers custom ultra-thin PCBs.

Contact us now for competitive prices and high performance ultra-thin PCB solutions.

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