Flexible circuit materials are important for your board’s durability and reliability.
Surprisingly, some materials have better electrical properties than others, whereas some have excellent flexibility.
Moreover, you’ll find some materials are more durable than others.
On the brighter side, most materials suit certain applications that optimize their features and characteristics.
For example, you don’t have to go with a material with high tolerance to heat if you’re using your PCB in low heat set-ups.
In today’s piece, we are looking at flexible circuit board materials and what you should consider.
Table of Contents
- What Is a Flexible Circuit Board?
- What Are the Basic Flexible PCB Structures and Materials
- Why Polyimide PCB Materials Offer The Best Flexible Design Option
- What to Consider While Choosing The Right Flexible PCB Material
- What are the Benefits of Using a Flexible PCB
- FAQs
- Why Choose FlexiPCB As Your Flex PCB Manufacturer?
What Is a Flexible Circuit Board?
Flexible circuit boards are PCBs built on bendable substrate or base materials that usually consist of polyimide, PTFE, or polyester. These boards can be categorized into different types depending on the bond between the conductive and base layers, as well as the number of layers.
Types According to the Copper-Base Bond
Adhesive Flexible PCB
This circuit board has a flexible adhesive between its substrate and base copper layers. The adhesive is usually epoxy or acrylic and is placed on either side of the core material.
Fabricators laminate the copper to the base using heat and pressure, which activate and set the adhesive to create a strong bond between the two layers. However, acrylic softens when exposed to heat, so fabricators use anchors and teardrops when building acrylic adhesive flex PCBs.
Although adhesive flex PCBs can have plated through-hole reliability issues and thicker structures, they are cheaper to manufacture.

A rigid-flex PCB stack with an adhesive flex PCB section
Non-Adhesive Flexible PCB
As the name suggests, this flex PCB doesn’t have an adhesive applied between its copper and base layers. Instead, fabricators cast the polyimide substrate layer onto the copper. The construction can either be sputtered copper on the dielectric film or cast dielectric on copper.
Regardless, both constructions primarily help to reduce the plated through-hole reliability issues that plague adhesive flex PCBs.
Other benefits include:
- Better controlled impedance
- Flatter copper pads
- Reduced board thickness
- Better flexibility
- Higher temperature ratings
- Better resistance to harsh environments
Types According to the Number of Layers
- Single-Layer Flex Circuits: These flexible PCBs are the simplest and cheapest to make because they have one conductive copper layer.
- Single-Layer, Double-Sided Flex Circuits: This PCB is similar to the single-layer type but has copper pads on both sides. It is primarily used to connect to other PCBs.
- Double Layer Flex Circuits: With two copper layers (one on either side of the substrate), this board has a medium complexity. It can accommodate more components than single-layer boards on either side.

Multilayer PCB stack-ups
- Multilayer Flex Circuits: Flexible multilayer PCBs are the most complex of these four because they have a higher circuit density distributed in more than two copper layers, which are interconnected using vias. The boards can even have multiple substrate layers to provide the necessary structural strength to the circuit.
What Are the Basic Flexible PCB Structures and Materials
The flexible PCB structure has several layers composed of different materials, which include the following.
Base Substrate
The primary roles of the substrate layer in the PCB are to provide structural strength and flexibility.
It also insulates the copper layers from each other, providing a dielectric constant that is low enough for the board’s electrical signaling requirements.
The primary base substrate materials include:
- Polyimide Film (PI): As the most commonly used substrate material in flex PCBs, polyimide has a high-temperature resistance, and its mechanical and electrical properties are remarkable.
- Polyester (PET): This material is cheaper than PI but has a lower temperature resistance, is less stable dimensionally, and provides poor solderability. However, it matches PI in tensile strength and chemical resistance properties.
- PTFE: PTFE is costlier than PI but has superior chemical resistance, thermal stability, electrical properties, weather resistance, and flame resistance.
Conductive Layers
- Copper Foil: The copper layer etched from a copper foil usually starts as an electrolytic or rolled copper foil. After production, this layer is surface-treated and roughened, and its peeling strength is enhanced on the contact surface. The other surface gets an oxidation-resistant treatment.
- Adhesiveness Flexible Copper-Clad Laminates: This conductive layer is fabricated into the dielectric but performs the same functions as the glued copper foil (to conduct power and communication signals).
Coverlay (Protective Layer)
Coverlays are insulating films layered on the conductors for protection. They also enhance the substrate layer’s strength and are usually made of polyester or polyimide (Kapton).
Adhesive Layers
This layer only applies to the adhesive flex PCB, which can have epoxy resin, acrylic, or pressure-sensitive adhesives to bond the copper foil to the substrate. Epoxy is not recommended for dynamic applications because it cures to form a relatively hard substance.
Bonding Sheets
Bondply or polyimide sheets are common in multilayer PCBs, where they separate and insulate two copper layers.
They are equivalent to prepregs and feature B-staged acrylic adhesives on either side to bond to the metal.
Stiffeners
Stiffeners are rigid reinforcing materials that are added to local sections on the flex PCB to provide mechanical support.
Typical stiffener materials include FR4, Kapton, and metal sheets (aluminum or stainless steel).
Since these reinforcements are mostly used to strengthen component areas, they must be heat and flame-resistant to withstand soldering.

A flexible PCB with a stiffener on the component area
Finish and Coating
Surface finishes of flex PCBs can include treatments like HASL, ENIG, or ENEPIG. On the other hand, protective coatings can be coverlays, photo-imaged dry films, liquid photo-imaged polymers, or cover coats.
Why Polyimide PCB Materials Offer The Best Flexible Design Option

(Holding a flexible circuit board)
Polyimide is a popular material for manufacturing flexible PCBs. Here are the reasons that boost its popularity:
Flexibility: These highly flexible materials allow bending to different shapes without breaking.
Therefore, they are the best options for use in tight spaces and compact electronics.
High-temperature resistance: Surprisingly, these materials are heat-resistant.
Therefore, you can employ them in applications that need heat-resistant materials.
Chemical resistance: Besides being heat and temperature resistant, these materials are also chemical-resistant.
The materials resist solvents and acids that they may come across after installation.
Consequently, it is ideal for use in applications where the board may interact with harsh chemicals.
Low water absorption: Polyimide PCB materials have low water absorption.
In other words, they are waterproof, which helps prevent damage to the board from moisture exposure.
What to Consider While Choosing The Right Flexible PCB Material
Electrical Properties
It would help to consider a material’s electrical properties before manufacturing your PCb.
The dielectric constant will show the amount of electrical energy the circuit board will have.
Furthermore, use a material with low dielectric constants as insulators and covers for the copper traces.
Also, ensure that the material retains its dielectric constant throughout its lifetime.
Thermal Properties

(A circuit board IC burns)
Flexible PCBs generate heat as current passes through the conducting paths.
The heat results in thermal stress, which may cause the materials and components to disintegrate faster.
Moreover, the heat can result in expansion, causing cracks and, eventually, circuit board failure.
Chemical and Mechanical Properties
The kind of environment for using a circuit board will be crucial when assessing its chemical resistance.
You want a material with excellent chemical resistance and minimal moisture absorption.
Additionally, engineers should seek materials with flame-retardant characteristics, meaning they won’t burn for long during combustion.
Also, choose a material with sufficient flexural strength to maintain the physical load.
Moreover, it should retain its flexibility and bent angle over the lifespan of the circuit board.
Signal Performance
Even when the frequencies rise, signal performance should remain consistent with low signal loss. The materials should have a low dissipation factor (DF) for this benefit.
What are the Benefits of Using a Flexible PCB

(Inspecting a flexible PCB at a quality check station )
Optimizing the space available in modern-day devices calls for using flexible PCBs. They are getting increasingly popular due to several benefits, including:
Saving Space: You can twist and roll flexible PCbs without risking that you may damage them. Consequently, manufacturers design them to fit into tight spaces, which the rigid PCBs would not.
Additionally, they can follow complex three-dimensional (3D) shapes, making them ideal for portable devices like wearables.
Lightweight: If you’re designing a system and weight is an important consideration, use flexible PCBs. They are lighter in weight than rigid PCBs while still being equally reliable.
Durability: Flex PCBs last longer than rigid PCBs due to their flexibility. Moreover, they are less likely to break under shock and vibrations.
Better Reliability: Flexible PCBs offer better signal integrity and impedance control than rigid PCBs. As a result, they are more reliable, especially for long-term use.
Easy to install: You can bend, twist, and fold a flexible PCB to fit into various configurations. Therefore, they are easier to install and integrate into electronic products.
Environmental Resistance: Flexible PCBs can withstand extreme weather conditions that the rigid PCBs may struggle against.
For instance, they are more tolerant of moisture, chemicals, and extreme temperature.
FAQs
Are flexible PCB materials affordable?
Generally, flexible PCB materials cost more than those we use to manufacture traditional rigid PCBs.
However, the cost may vary depending on factors that include design complexity and volume of production.
But that’s not to mean that they are not affordable.
Special flex PCB materials like coverlays, conductive inks, and adhesives may be affordable.
Moreover, the cost of these materials keeps getting cheaper as their production process improves.
Additionally, the benefits of using flex PCBs may outweigh their initial costs in the long run.
Is it possible to make a rigid-flex PCB?
Yes, you can make a printed circuit board that bends the characteristics of both flexible and rigid PCBs.
Typically, the boards combine multiple layers of flexible PCBs with one or more rigid PCBs through a lamination process.
Thus, the flexible sections twist to fit a certain shape, while the rigid parts provide additional support and stability.
Does material Affect flexible PCB performance?
Yes, the type of material you will use can affect the performance of your flexible PCB.
In other words, your choice of materials affects the board’s flexibility, durability, thermal stability, and electrical performance.
For instance, most flexible PCBs use polyimide for its excellent chemical resistance, thermal stability, and flexibility.
If you use any other material that downgrades the board, you risk lowering its performance.
Why Choose FlexiPCB As Your Flex PCB Manufacturer?
You should consider the three E’s when choosing your flex PCB manufacturing partner. These are equipment, expertise, and experience.
Our Capabilities
FlexiPCB has invested heavily in quality machinery to build adhesive, non-adhesive, single, double, and multilayer flexible circuit boards to the highest quality standards.
These PCBs require special care and precision during handling, so state-of-the-art machinery is necessary.
On expertise, our trained staff undergo regular standardization testing to ensure they are capable of designing, manufacturing, and assembling flex PCBs to meet the most recent standards.
This is also important because it ensures boards coming from our production lines can be sold to different markets globally.
Lastly, we have the required experience to build these boards because we have been in this business since 2007.
From our company’s inception to date, our goal has been to provide high-quality and innovative flexible PCB solutions to our customers.
Cooperation With Trusted Flexible PCB Material Suppliers
When building flex PCBs, materials are critical factors to consider, and we only source them from trusted suppliers, who we’ve come to build business relations with over time.
These relations ensure we get only the best quality materials for each layer and at good discounts, benefits which we pass directly to our customers.
Therefore, you can expect high-quality, functional, and reliable flex PCB products from us at reasonable costs. Contact us to get started on your order today!