Flex PCB Materials and Construction

flex pcb

When it comes to electronics, there are a lot of different choices for materials and construction methods. Printed circuit boards (PCBs) are no different, with several varieties available depending on the specific application. In this post, we’ll focus on flex PCBs: what they are, what they’re used for, and how they’re constructed.

What are Flex PCBs?

Flexible printed circuit boards (Flex PCBs) are made with a flexible substrate, such as polyimide or PEEK. This gives the board the ability to bend and flex without breaking. Flex PCBs can be used in a wide variety of applications where space is limited, or flexibility is required, such as in medical devices or wearables.

One of the biggest advantages of flex PCBs is that they offer a higher degree of reliability than rigid PCBs. The flexible substrate prevents cracking and breaking from occurring with traditional rigid boards. Flexible circuit boards are also less likely to be damaged by shock and vibration, making them ideal for use in harsh environments.

Another advantage of flex PCBs is that they offer more flexibility regarding routing. The traces must be straight with traditional rigid boards, limiting the design options. With flex PCBs, the traces can be routed around corners and bends, which gives designers more freedom to create complex designs.

These advantages make them ideal for use in electronic devices that need to be able to bend or fold, such as wearable electronics, smartphones, and other portable devices.

Material Consideration for Flex PCB

Flex PCBs are made using various materials, depending on the specific application and requirements. The most common materials used in flex PCB construction are polyimide, polyetheretherketone (PEEK), and FR4.


Polyimide is a thermosetting plastic that is commonly used in the manufacture of flexible PCBs. It has excellent mechanical and electrical properties, making it an ideal material for various applications. Polyimide has high heat resistance, making it a perfect material for high-temperature environments. It is also resistant to numerous chemicals, making it an ideal material for harsh environments. Polyimide is available in various thicknesses and can be laminated with copper to create a flexible circuit board.

Polyimide has excellent mechanical properties, making it an ideal material for flexible PCBs. It has a high Young’s modulus, which is stiffer than most other plastics. This makes it suitable for applications that require flexibility, such as automotive and medical applications. Polyimide also has high tensile strength, making it resistant to tearing and stretching.

Polyetheretherketone (PEEK)

PEEK is a semi-crystalline engineering thermoplastic used as an alternative material for flexible printed circuit boards (PCBs). PEEK has several advantages over traditional materials such as polyimide and liquid crystal polymer (LCP), including higher operating temperatures, chemical resistance, and superior dimensional stability. PEEK can also be used in various applications, from medical devices to aerospace components.

PEEK is typically used as a substrate material in flexible PCBs due to its high thermal stability and ability to maintain its dimensional stability at high temperatures. PEEK can also withstand harsh chemicals and solvents, making it an ideal material for use in demanding environments. PEEK has a lower dielectric constant than polyimide, making it suitable for high-speed applications.

PEEK has superior dimensional stability compared to other flexible PCB materials, meaning that it will not warp or distort when exposed to extreme temperatures or humidity. This property makes PEEK an ideal material for aerospace and military applications where reliable performance is critical.


FR4 is a material used in the construction of flex PCB. FR4 is made from glass-reinforced epoxy laminate and has good dielectric properties, making it ideal for use in electronic circuits. FR4 is the most common material used for flex PCBs. It has good flexibility and can be bent or rolled without breaking. FR4 is also resistant to chemicals and moisture, making it ideal for use in harsh environments.

FR4 is available in various thicknesses and can be customized to meet the requirements of any application. Flexible printed circuits made with FR4 are durable and can be used in multiple applications, from consumer electronics to aerospace and defense.

FR4 is the preferred material for flex PCBs because it is strong, flexible, and resistant to chemicals and moisture. When choosing a material for your flex PCB, consider your application’s specific requirements. FR4 is a versatile material that can be customized to meet the needs of any application.

Construction Methods

The construction method used for flex PCBs can vary depending on the application and requirements. The most common construction methods are through-hole, surface-mount, and flexible printed circuit board assembly (FPCBA).

Through-Hole Construction

Through-hole construction is a method of constructing printed circuit boards. This method drills holes through the PCB, and components are inserted into these holes and soldered. This type of construction is typically used for large or complex boards where it would be difficult to solder surface-mounted components.

Through-hole construction has several advantages over surface-mount construction. The most obvious benefit is that it is much easier to solder components in place. This is because the holes provide a larger area for the solder to flow into and around the component. Additionally, through-hole construction allows taller components to be used, which can be important for some components.

However, through-hole construction also has some disadvantages. The most significant drawback is that it is much more expensive than surface-mount construction. This is because drilling holes is a costly and time-consuming process. Additionally, through-hole construction typically requires more space on the PCB than surface-mount construction.

Surface-Mount Construction

Surface-mount construction is the process of mounting electronic components onto the surface of a printed circuit board (PCB). This method is used for small, delicate components that cannot be through-hole mounted.

The process begins with soldering paste, which is applied to the pads on the PCB where the components will be mounted. The soldering paste acts as a “glue” to hold the component in place while it is being soldered.

Once the soldering paste is in place, the components are placed onto the PCB. A special tool called a pick and place machine is used to precisely place the components.

After the components are in place, the PCB is heated in an oven or with a hot air blower. This melts the soldering paste and creates a permanent connection between the component and the PCB. Surface-mount construction is a fast and efficient way to assemble PCBs. It is especially well suited for the mass production of PCBs


FPCBA is a construction method that is used for flex PCBs. Flexible printed circuit board assembly, or FPCBA, is the process of assembling a flexible printed circuit board. A flexible printed circuit board (FPCB) is made up of a thin substrate material that is coated with a conductive layer.

The conductive layer can be made of different materials, including copper, silver, or gold. The substrate can be made of different materials, including polyimide, polyester, or paper.

In this method, the components are mounted on the surface of the flex PCB and then soldered directly to the pads on the flex PCB. This allows for a more reliable connection between the component and the flex PCB.

Wrapping Up

Now that you know more about flex PCBs, you can decide if they’re the right choice for your next electronics project. If you need help with designing or manufacturing your flex PCB, be sure to contact a reputable flex PCB manufacturer. They’ll be able to help you every step of the way, from design to delivery.


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