Flexible Circuit Thickness: The Ultimate Guide

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Oakley Mae

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About Flexible Circuit Thickness, Most electronic companies are now discarding traditional circuit boards for flex PCB thanks to the flexible circuit thickness and flexibility.

Surprising, flexible PCB allows you to bend and fold without damage.

However, when designing an electronic device, you should understand how thick your flexible circuit board should be.

We are sure the flexible circuit thickness will determine the number of components on your board.

But how do you select the right PCB thickness? And what factors will affect the standard circuit board thickness? 

This article answers all questions you might have about flexible circuit thickness. 

What Is A Flexible PCB?

A digital camera that uses flexible PCB

(A digital camera that uses flexible PCB)

This is a circuit board that you can bend, twist, or fold to your desired shape. This circuit can fit into tight spaces, thus crucial in developing compact devices.

Surprisingly, you can also form flexible circuit boards into layers and use them in different environments. 

Moreover, flex circuit boards have a higher temperature range making them ideal for use even in harsh environments.

Furthermore, their reduced weight and size make them common for wearable products.

However, circuit boards are more challenging and take longer to manufacture.

Consequently, you’ll buy them more expensively than a traditional rigid circuit board. 

Understanding PCB Bendability/Flexibility

Plastic strip flexible PCB

(Plastic strip flexible PCB)

The flexible circuit board you select will determine how you use your electronic device.

Surprisingly, you can evaluate the flexibility you need depending on the movement your use case will require.

However, letting your board flex a lot will make it dent or bend under pressure, translating into serious problems later.

This happens more if you use your device in an environment having many fluctuations. 

Fortunately, there is a formula to help you calculate the bending amount you’ll need.

This is given by multiplying the bending deflection with the board thickness and dividing it by the gyration radius.

Therefore, you’ll get a rough estimate of how much its parts can bend before they break. 

Flex Circuit Thickness Versus Layer Count

The first thing you must consider when selecting the circuit board thickness for your application is the number of layers you need on the board.

Surprisingly, the thickness of each layer depends on the material and how you use the circuit board. In most cases, thicker layers allow you to have more applications and pack more devices on your board. 

Generally, we refer to layer thickness on a circuit board by a certain standard called ounce per square foot. In most cases, you’ll meet 1 oz/ft², which allows for almost nine metal layers on the PCB.

However, expect such a board to be as stiff as a piece of plywood

Two-Layer Circuit Board Thickness

As highlighted, circuit boards come in different thicknesses for various functions.

For example, a standard two-layer circuit board comes with a minimum and maximum thickness of 14 mils and 32 mils, respectively.

Surprisingly, each PCB layer has a minimum thickness that you should maintain throughout your circuit board. 

However, 14 mil is the perfect substrate thickness for most projects, and we refer to it as a short-run circuit board. This thickness finds application in audio circuits and electric guitars. 

We recommend a 10 mil circuit board if you intend to apply UV-curing. This thickness limits warping problems, especially when you solder in tight spaces.

Moreover, we recommend 14 mil thickness for engineering samples and prototypes

The Standard Four-layer Circuit Board Thickness

The perfect thickness for four-layer boards is 32 mil.

Surprisingly, it’s available in different sizes, with single and double-sided being the most common.

The board’s thickness depends on the number of layers you need to achieve your design objective.

Four-layer and 32 mil circuit boards find applications in audio amplifiers or electronic devices designed to work under high temperatures. 

Factors Affecting Standard Circuit Board Thickness

Engineers inspecting circuit board

(Engineers inspecting circuit board)

Several factors will influence the choice of your circuit board thickness. Check them out below: 

Copper PCB Thickness

To begin with, an 8oz copper circuit board is enough for most electronics.

Generally, the copper board thickness will affect your circuit board’s cost, flexibility, appearance, and size.

And since copper is the main circuit board material, its thickness is critical. 

We recommend a thicker copper circuit board if your electronic device requires extremely flexible connections.

Surprisingly, thicker copper boards don’t resist electrical current like the thinner options.

However, you might find them extremely expensive and consumes more space. 

Trace PCB Thickness

Generally, the trace circuit board thickness influences your electronic device’s overall size.

Therefore, thicker traces adds the circuit board area necessary for components and shielding.

If your device requires few traces, we recommend a thinner trace thickness. A 10 mil trace will work well in such a case. 

Design Factors

While selecting a circuit board thickness, you should consider your design needs.

For example, if your project is large, go for a thicker substrate or circuit board to ensure your board is strong enough to withstand damage.

However, a small circuit project would require a thinner board that you can manufacture quickly and cost-effectively. 

Quality Factors

Every time you buy circuit board materials, you must ask yourself several questions.

For example, is the material bio-degradable?

Do they contain any impurities? Will the materials harm people or the environment? 

First, purchase and use substrates that are perfect for your design. For example, all electronic guitars require you to use thicker substrates. 

Manufacturing Factors

When you get to the point of developing a physical PCB, order the right circuit board materials. We recommend buying such materials from a local store or sending the design directly to a manufacturer. 

Manufacturing companies usually have professional technicians and engineers who understand circuit designs better. Surprisingly, they might help you create circuit schematics or specifications. 

Advantages of Flex Boards

A bend flexible PCB

(A bend flexible PCB)

  • The main advantage of flexible circuit boards is that you can bend and twist them for applications that rigid boards aren’t useful. Therefore, they find major applications in developing devices with tighter spaces. 
  • They have less weight and space. Therefore, you can use them to develop wearables and compact devices. 
  • They have increased usability.
  • They have a higher density that lets you place more components on the circuit.
  • These circuit boards have increased durability, which makes them perfect in situations where rigid PCBs are likely to break.

Flex Circuit Copper Thickness Requirements

Every end user must specify their circuit board’s copper thickness since it impacts the current carrying capacity, impedance, and thermal performance.

Consequently, these factors will impact the flexible circuit boards’ reliability and functionality. 

Therefore, the functional requirements to consider include the following: 

  • The minimum connector area thickness to guarantee robust contact
  • The adequate current carrying capacity related to the trace’s cross-sectional area
  • The thermal properties directly related to the trace profile and metal type
  • Proper conductivity that depends on the trace’s metal type and cross-sectional area
  • The copper cross-sectional area drives proper high-speed circuit impedance

FAQ

Does a flexible circuit board thickness matter?

Yes! Circuit board thickness will determine how you use the board. Generally, thin circuit boards are always flexible, perfect for tighter spaces.

On the other hand, thicker boards have better structural integrity. However, this makes them heavier, thus taking up more space. 

How thick is a flexible PCB?

Flexible PCB thickness ranges between 14 mils and 32 mils. However, the average thickness for single-layer circuit boards is 14 mils while that for four-layer boards is about 32 mils. 

What is the minimum thickness of a flexible PCB?

Generally, the standard two-layer PCB has a minimum and maximum thickness of 14 mils and 32 mils, respectively. Surprisingly, a 14 mil circuit board will serve you well for any project. 

How thick is flexible PCB copper?

Most flexible circuit boards use copper weights of 0.5oz and 1oz translating into 7 mils and 14 mils, respectively. However, you’ll also come across a maximum copper weight of 2oz. 

Conclusion

As highlighted, understanding how thick your flexible circuit board is, is critical to design an electronic circuit.

This way, you can know how many components you can add to your devices and how much you can bend them.

By now, you should know that the copper and trace circuit board thickness, design factors, and manufacturing factors will likely affect your PCB thickness.

Generally, a 14 mil circuit board is enough to handle almost any functionality.