What is the Typical Thickness of a Flexible Printed Circuit?

Typical Thickness of a Flexible Printed Circuit

A flexible printed circuit (PCB) is a flexible insulating material that provides electrical connectivity between components and devices. They are used in a variety of electronics and devices where space savings or dynamic flexing is desired. The PCB thickness is determined by the materials chosen for fabrication and the number of copper layers required for a specific layout. The overall thickness range is much smaller than that of rigid boards, with a maximum limit of 10 mils.

Typically, a single-layer flex PCB will have a thickness of 1 mil. Two conductive copper layers will require a minimum of 2 mils. As the design of a flex PCB becomes more complex and layers increase, the thickness will also increase. A double-layered flex circuit may be as thick as 4 or more mils. This is where a designer needs to balance complexity with thickness limitations and cost.

The total thickness of a flexible printed circuit depends on the construction techniques used. The materials selected for the insulating core and coverlay have a significant impact on the total circuit board thickness. The most common insulator and coverlay materials are polyimide and BT epoxy. Both offer a wide selection of thermal, electrical, and mechanical properties. They also feature a range of thicknesses to fit the physical requirements of a device.

What is the Typical Thickness of a Flexible Printed Circuit?

To ensure that the flex circuit is within a tolerance band, manufacturers use deadweight or electronic micrometers to measure thickness at multiple points on a cured circuit board. Deadweight micrometers are precision instruments with weighted probes that exert a consistent force and provide accurate measurements with high accuracy (+/- 1%). Electronic micrometers, on the other hand, utilize electrical sensors to digitally measure the thickness of a bare flex circuit. These tools can give a quick and accurate measurement of the flex PCB thickness in just a few seconds.

In addition to the insulator and coverlay thickness, the copper layer thickness plays a crucial role in the final PCB thickness. The thickness of the copper layer determines how well a flex circuit performs. Thinner traces will be less thermally stable and can suffer from heat damage. Therefore, the thickness of copper traces is an important factor when choosing a flex PCB for different operating environments.

The bend radius of a flex circuit also impacts the thickness of the resulting product. Larger bending radii will result in higher stress and damage to the copper, while smaller bending radii will allow for the circuit to flex with minimal strain. In order to avoid damage, a flex PCB should be designed with large bending radii and with conductors staggered on multi-layered circuits to minimize I-beaming, which can damage the copper.

Another important consideration when designing a flex circuit is the placement of plated through-holes and components. These structures can cause significant stress and cracking when a flex circuit is bent. To prevent these problems, designers should use a gradual and large bending angle for the flexible area of a circuit board and use curved bends wherever possible. Plated through-holes should be placed away from the bending area.