How to Choose Flex PCB Thickness for Your Electronic Device

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An essential parameter when designing any electronic device is the thickness of the flex circuit. There is no one-size-fits-all rule for selecting flex PCB thickness because it varies from project to project. As a designer, you must be aware of various factors. You will need to understand a range of thicknesses that are ideal for your application.

It is also wise to keep track of the total quantity of components that will be placed on the PCB device. Designers should keep an appropriate measurement tool with them to take accurate readings of flex PCB thickness.

Here are a few questions that you should ask yourself before determining the thickness of your flexible circuit.

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What application is the electronic device being used for?

Answering this question will help you select the most appropriate material for your flexible circuit. If you know that the device will have strenuous applications, such as a controller on an electric bike, then you need an extremely durable material that can resist the harsh outdoor elements that it will be exposed to on a continuous basis.

Some materials need to be durable enough to withstand extreme environmental stresses such as vibration, temperature, and water.

The choice of material will determine the thickness of the flexible circuit. The thickness has a direct bearing on the number of layers of circuitry that can be placed on a single flex board.

Furthermore, most electronic devices will utilize several PCBs. Add enough circuits and flex circuit thickness becomes a major limiting factor when designing devices. The thickness is particularly important if the device being manufactured has a large area. This is why designers should get acquainted with standard thicknesses for materials used in flex circuits.

A good rule of thumb is to calculate the size of the board based on the application.

Why Are Flex PCBs Useful in Electronic Devices?

The most redeemable quality of flexible circuits is their use in 3D configurations. All manners of permutations and combinations are possible with the use of flexible PCBs, which allows them to be used in a wide range of scenarios.

Flex PCBs are particularly useful in wearables, IoT devices, and smaller devices. The thickness of flex boards can be determined by studying the circuit board itself. It is common for designers to settle with 1.6mm flexible PCBs. These boards are single-sided and referred to as an Extruded Etched Board (or EEB for short).

Perhaps more importantly, these boards are smaller than the usual 1.8mm PCBs installed in most devices. Despite being thinner, they can be very expensive to manufacturers and spend longer in assembly lines.

How Flexible is the Flex Board?

A major deciding factor when choosing any flex board is how it will be used in the final product. Designers can calculate the desired bendability and flexibility of the board based on how the application moves during its life cycle.

Just because a flex PCB is ‘flexible’ doesn’t mean it is immune to denting under stress. Exceeding the threshold of flexibility can disrupt the device’s range of functionality and lead to many problems.

The board’s thickness is an important variable used to calculate the amount of bending. The following formula is often used to calculate the amount of bending: “Board thickness” multiplied by the “Bending Deflection” divided by the “Gyradius.”

This formula will allow us to calculate the amount the circuit can bend in any direction before it shatters.

Layers of Circuitry

When choosing the thickness of a flexible board, we have to consider the number of PCB layers that will be placed on the circuit. It is worth noting that the thickness of each PCB layer depends on the material and how the circuit is to be used.

Although manufacturers strive to keep board thickness to a minimum, a thicker board can be used for more applications. In other words, designers can place more components if the flexible board is thick enough.

Designers measure the thickness of each layer on circuits using ‘ounce per square foot’. For reference, 1 ounce per square foot allows the board to have nine metal layers. While it is true that you can add more layers on thinner material, the end result makes the circuit too stiff for use.

Two Layer Flexible Boards and Standard Thickness

Flexible boards are available in a wide range of thicknesses. Two layers boards have a thickness in the range of 14 to 32 mils. It is important for the circuit to stick to the total thickness established for the entire board.

Most projects will use a substrate that is 14 mils thick. Designers refer to this as a short run PCB and is available in various sizes. Designers prefer to work with boards that have a minimum thickness of 10 mils because it keeps warping to a bare minimum when soldering in tight spaces.

10 mils is a good option if you are planning to use UV-curing. It is also recommended to place at least one extra layer of circuitry. This will increase the total thickness to about 18 mil and provide room for more UV circuits on both sides of the board.

14 mils is a good range for most boards that are intended for use as prototypes of engineering projects. You can explore with thinner substrates for experimentation because they provide a good balance between durability and price.

How Thick Should Four Layer Flex PCBs Be?

A standard thickness of 32 mils is ideal for flexible circuits in any design. These boards are available in various sizes and could be single sided or double sided. The flexible board’s thickness dictates the number of layers that can be used on your project.

In practice, however, 32 mils is very thick but can be useful in devices meant for use in stressful environments.

Wrapping Up

Other factors that affect the thickness of flexible boards include the thickness of the copper itself and a range of design factors. For the most part, it is recommended to use a thinner board if you have a small circuit project.

We hope this article answers any questions you may have about the thickness of flexible boards. If you have more concerns and need a consultation with your project, get in touch with the experts at Hemeixin PCB here.

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