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Semi-Flex FPC: An Effective Alternative to Rigid PCBs

About Semi-Flex FPC, Circuit boards are the hearts of every electronic device in the modern world.

So, it’s no surprise they come in various designs since they perform several roles in computers, televisions, and power systems.

And an excellent example of the variant is the semi-flex FPC.

FPCs have recently garnered traction due to their easily adjustable and customizable features (without solder joints).

But what exactly is a semi-flex FPC? Don’t worry. We’ll show you.

This article will explore semi-flex FPCs and discuss how they differ from PCBs.

Table of Contents

What are Semi-Flex FPCs?

A man holding a flexible circuit board

A man holding a flexible circuit board

Flexible Printed Circuits (FPCs) are lightweight boards with numerous benefits.

First off, these circuit boards are thin, making them perfect for small-sized applications. 

Second, FBCs offer free bending and folding without damaging sensitive components.

These are only some advantages making these flexible boards one of the most popular on the market.

Semi-flex FPCs are excellent and cost-effective substitutes for their rigid counterparts. Further, producers devised this initiative to balance stiff and flexible by using more expensive polyamide-based flexible substrates.

But that’s not all. Other processes combine to make the semi-flex FPC part rigid and part flexible, like streamlining techniques and controlled-depth milling (for removing the FR4 material from bendable areas).

What’s the Composition of a Semi-Flex FPC Material?

A flex FPC

A flex FPC

An FPC’s application and end-use usually determine its material. Also, its flexibility depends on the chosen material’s ability to maintain high conductivity while resisting warping, cracking, and mechanical damage.

As a result, producers often make semi-flex FPCs from FR-4 or fiberglass materials, pouring in a blend of glass fibers and epoxy resins.

But let’s see other things that make up a semi-flex FPC’s material.

Insulating Film

Insulating films are high-density polyethylene layers made from thrusting resin through a nozzle before adding it over the FPC substrate.

Further, this HDPE film stops capacitive coupling from affecting the substrate material. Also, it blocks other circuits by electrically shielding interconnections on the top layer.

In addition, an insulating film layer provides a vapor barrier, protecting the circuit board from moisture during curing.

Electrostatic Adhesion Layer

An adhesion layer comes after the insulating film to help attach components to the board. Usually, this layer is polyimide or acrylic, allowing components like LEDs to create direct connections with the Flexible Printed Circuit.

Note: The electrostatic adhesion layer also helps save assembly time and materials.


Adding a conductive layer on top of the adhesion helps to prevent circuit warping. The coating can be epoxy resin, polyamide, or the board itself.

Note: To avoid warping effectively, apply a 100oC  solution to the conductor.

Board Enhancements

A second adhesion applied over the conductor further enhances the FPC board. Also, it reduces the chances of encountering cracking or flexural problems. Producers often make the coating from acrylic or cellulose.


The coverlay is the last plate that protects the FPC material’s underside. Manufacturers make it from polyamide or acrylic, allowing the coverlay to double as an insulation layer.

As a result, it also protects the FPC material from moisture.

Further, the coverlay provides high-temperature resistance, allowing FPC boards to work in oven and heater applications.

What’s the Difference between FPC and PCB?

PCBs are the most common circuit board types, but even the traditional variant doesn’t work for all applications. Unlike Printed Circuit Boards, FPCs can bend and flex, making them perfect for modern technology.

Further, Flexible Printed Circuits offer better heat dissipation than their traditional cousins, extending the lifespan of the electronics you use them to make.

In addition, PCBs have three types: single-sided, double-sided, and multilayered variants. On the other hand, you can categorize FPCs into semi-flex and flat flexible boards.

Wrapping up

Semi-flex FPCs are the go-to for applications requiring conductivity and flexibility. But it’s not the best choice for projects that need mechanical strength.

Since these boards are lightweight and thin, you can use them in compact devices like walkie-talkies. 

Do you have any questions on this topic? Please contact us, and we’ll be happy to help.

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Emma Lu
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