What Is a Flex Circuit?

Circuit boards are one of the most important technological inventions ever to be conceived and are at the core of all modern-day electrical devices, from smartphones all the way to your washers and dryers. This mini-sized channel for charged particles serves the invaluable purpose of providing structural support to a device’s electrical components and interconnecting them through conductive pathways, signal traces, or tracks.

Developments in this technology have bred a new generation circuit board called the flexible circuit board, also known as a flex circuit. As their name suggests, a flex circuit is not confined to the limitations of your rigid traditional circuit boards and can instead bend and twist. This flexibility allows technicians to engineer a more efficient and compact design.

There are countless other benefits of a flexible circuit board, some of which will be looked at later in this article. But first, let us discuss what a flexible circuit board is and how it is constructed.

Flexible Circuit Board – An Overview

Flexible circuit boards, aka flex circuits, are often misunderstood for flex PCB, i.e., printed circuit boards that can bend. In reality however, a flexible circuit board is worlds apart from flexible PCBs in terms of fabrication, design, and functionality. As a result, designing a flex circuit based on the same rules that apply to PCBs will lead to an inaccurate circuit board, a mistake that many novice engineers tend to make.

These revolutionary circuit boards are now being used to phase out the conventional FR4 PCBs in a wide array of applications because of the many benefits they offer over their outdated counterparts. The main constituent elements of a flexible circuit board include PI base material, copper layer, adhesive layer, coverlay and occasionally, stiffeners.

The construction of a flex circuit consists of a layer of metallic traces fused atop of a dielectric layer. The metal used in the traces is usually copper owing to its high electrical conductivity, easy availability, and cost effectiveness. The thickness of the metal layer can vary; it can be as thin as below 0.0001-inches or as thick as above 0.01-inches. The thickness of the dielectric layer will usually range between 0.0005 inches and 0.01 inches.  

The common practice is to use an adhesive to fuse the metallic and dielectric layers together. However, other bonding methods like vapor deposition are also employed sometimes. Copper has the tendency to oxidize quite readily, therefore, the exposed metallic surfaces are layered with another, more inert metallic layer, solder or gold being the two most common choices thanks to a high electrical conductivity and resistance to corrosion.

A dielectric material is utilized to shield the circuitry from oxidation or electrical shorting in the non-contact sections.

Capacitance, current, mechanical resistance, chemical inertness, temperature resistance, and the type of bending are just a few of the factors that influence the material choices for the flex circuit’s composition. Seeing as there are numerous materials that meet the required material specifications, a flexible circuit board could be constructed out of virtually an endless combination of materials.

Although flexible circuit boards are more expensive than traditional rigid circuits, a rightly designed flex circuit can save you time and weight in manufacturing and will also be a more reliable and long-lasting alternative. This makes flex circuits worthwhile.

When designing a flexible circuit board to meet your specific needs, an Hemeixin expert will take into consideration all the critical requirements and parameters unique to your needs and design a flex circuit that perfectly suits your needs.

Types of Flexible Circuit Boards

A flex circuit can be divided into four different categories based on how the circuit board is layered. The four categories are as follows:

This is one of the simplest flex circuit types and consists of a thin layer of copper bonded to a flexible polyimide layer. You can access the copper layer from only one side having no access points.

  • Single-Sided Flexible Circuit Boards with Dual Access 

This flex circuit type is similar to the basic single-sided flex circuit with the exception that in this version, the conductive layer (copper layer) can be accessed from both sides.

  • Double-Sided Flexible Circuit Boards 

A double-sided flex circuit can essentially be described as a base polyimide layer sandwiched between two copper conductive layers. Electrical connections between the two layers are established with the help of through holes.

  • Multi-Layered Flexible Circuits 

Multi-layered flexible circuits are a series of single- and double-sided flex circuits interconnected with the help of through plated holes or surface mountings.

  • HDi Flex PCB

These are similar to conventional flexible PCBs but with a higher wiring density per unit area.

Advantages of Using a Flexible Circuit Board

Solves Packaging Issues and Allows for a More Compact Design

This is perhaps one of the more obvious benefits of using flex circuits, nonetheless, it is an important one. The flexible construction means that the circuit board material can be bent and wrapped around edges and corners providing a three-way connection. In addition, a flexible circuit board has no discrete parts. This means that the other internals of a device, the electrical and mechanical components can be placed in optimal positions with the flexible circuit board folded or bent around them to form connections.

This allows designers to create more innovative and compact product designs without worrying about how the internal components will be packed into the product.

Space and Weight Savings

Space, weight, and packaging are one of the most important factors that engineers must consider when designing circuit boards. This brings us to one of the most important benefits of flexible circuits which is that they can eliminate the need for heavy and bulky solder connections and wiring.

Depending on the structure, components, and the type of device the circuit is used in, flexible circuits can even offer up to 60% weight and space reduction, in doing so, substantially reducing the package size. In comparison to conventional rigid circuit boards, flexible circuits boards also offer a more sleek and compact package profile.

Reduced Assembly Costs

Since flexible circuit boards can eliminate the need for heavy and bulky wiring and solder, the total amount of wiring and solder used to manufacture the board. Less wiring and solder consequently leads to lower procurement costs, shipping charges, expense of creating numerous purchase orders, and cost of receiving, inspecting, and kitting.

In addition, less wiring and solder to put together means the boards can be manufactured at a faster pace than conventional rigid boards. This can potentially reduce the operating time of your machines and offer you energy savings as well, thereby, lowering the assembly cost of the board.

Excellent Thermal Management

Due to its unmatched flexibility, polyimide is one of the most widely employed materials in the manufacture of flexible circuit boards. In addition to being flexible, polyimide materials also offer great thermal resistance and can withstand high-temperature applications.

Thin polyimides are also good at dissipating heat resulting in a good thermal management. In addition to this, the flexible thermal adhesive used to fuse the metal layer to the dielectric material enhances the heat dissipation of the circuit board.

Good thermal performance means that the circuit can sustain peak performance for longer periods of time without slowing down the performance of the device. Because of this, an increasing number of high-power and high-frequency applications have been transitioning to flex circuits in lieu of traditional rigid boards.

Longevity

Flex circuits are more durable than their rigid alternatives thanks to their combination of highly flexible and low weight materials that allow them to withstand mechanical stress, pressures and impulsive forces caused by drops to the ground or similar events.

Furthermore, a properly designed flex circuit will be able to endure millions of flexes. This makes flexible circuits durable and long-lasting, suitable for being used in robust and industrious environments without fail.

Rigid boards on the other hand are hard and brittle, as such, they tend to crack or fracture when introduced to shocks or mechanical stresses.

Higher Current Carrying Capacity

Flexible circuits have also shown to have lower impedance and inductance. This allows flexible circuits to carry more current than rigid boards, which results in less energy being lost. Because of this, they are generally better suited to high-current devices such as motors, batteries, and power supplies.

Applications of Flexible Circuit Boards

The invaluable benefits offered by flexible circuits have earned them a place in many modern-day industries and technological devices. Here are some of the most common uses of flexible circuits:

  • Electronics

Used in: Laptops, Calculators, Cameras, Printer Heads, Computer Keyboards, Cell Phones

  • Manufacturing

Used in: Robotic Arms, Processing Machines, Sensory Equipment, Human Machine Interface (HMI) equipment, Barcode Equipment

  • Automotive

Used in: Antilock Brakes, Air Bag Systems, Engine Controls, GPS Systems

  • Medical

Used in: Hearing Aids, Pacemakers, Exercise Monitors, Heart Monitors

  • Miscellaneous

Used in: Resistors, Tower Lights, Satellites, Capacitors, Light and Motion systems, LCD Fabrication

Final Thoughts

A flex circuit is a robust and versatile element that can be used in a variety of applications, as listed above. However, a flexible circuit board is only as good as its manufacturer. Hemeixin is a trusted and reliable electronics manufacturer that offers high-precision, flexible circuit boards as well as many other electronic components. Visit our website to learn more about our services and what we can do for you.

Michael Caine

Michael Caine is the Owner of Amir Articles and also the founder of ANO Digital (Most Powerful Online Content Creator Company), from the USA, studied MBA in 2012, love to play games and write content in different categories.