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PCB/PCBA knowledge
Single-layer vs. Double-sided vs. Multilayer FPC – What is the Difference

FPC, flexible printed board, also known as “flexible PCB”.

As the name suggests, the biggest feature of FPC is that it is flexible enough. Compared with the conventional rigid PCB, FPC is very thin, bendable and flexible, and can withstand millions of dynamic bending without damaging the wires. FPC can be moved and stretched arbitrarily according to the requirements of the space layout, realizing three-dimensional assembly, and achieving the effect of integrating component assembly and wire connection.

With the development of high-end miniaturized electronic products such as mobile phones, notebook computers, consumer drones, and smart watches, the market demand for FPC is increasing, and at the same time, the requirements are also getting higher and higher. PCB manufacturers are accelerating the development of thinner, lighter and higher-density FPCs.

Like PCB rigid boards, FPC is also divided into single-layer, double-sided, and multi-layer according to the number of superimposed circuit layers. But what is the difference between single-layer vs. double-sided vs. multilayer FPC?

Table of Contents

Single-layer FPC

Single-sided flexible PCB (FPC) is the simplest flexible board, it has only one layer of chemically etched conductive pattern. It is usually processed on the basis of two raw materials: “substrate + transparent glue + copper foil” and “protective film + transparent glue”.

Single-layer FPC

First, on the raw material of “substrate + transparent glue + copper foil”, chemical etching and other processes are performed on the copper foil to obtain the desired conductive pattern circuit; then, on the raw material of “protective film + transparent glue”, the protective film is drilled to expose the corresponding pads; after cleaning, the two raw materials are combined by rolling; finally, the exposed pads are electroplated with gold or tin to protect the board. In this way, a whole piece of single-layer FPC is ready. According to the needs, generally, the whole piece of FPC will be stamped and divided into small flexible boards of corresponding shapes.

The base material used by FPC is generally polyimide (PI), but not limited to, it can also be polyethylene terephthalate, aramid fiber ester and polyvinyl chloride.

Double-sided FPC

Double-sided FPC is to have a layer of conductive patterns etched on both sides of the insulating base film to increase the wiring density per unit area. Generally, when the wiring of the circuit is more complicated and the single-layer FPC cannot meet the wiring requirements, the double-sided FPC will be selected.

Double-sided FPC

Compared with single-layer FPC, the biggest difference between double-sided FPC is the addition of a via structure to connect two layers of copper foil (that is, two layers of conductive patterns) to form a conductive path. Drill holes on the base material and copper foil first, and then plate a certain thickness of copper after cleaning, and the via holes are completed. The subsequent manufacturing process is almost the same as that of the single-layer FPC. Similarly, double-sided FPC will also be covered with a protective film on both sides to protect the wires and indicate where the components are placed.

Multilayer FPC

Multi-layer FPC is to press multi-layer single/double-sided FPC together, form metallized holes through drilling and electroplating, and form conductive paths between different layers. In this way, no complicated welding process is required.

Multilayer FPC

Compared with single/double-sided FPC, multilayer FPC has higher reliability, better thermal conductivity, and more convenient assembly, but it loses the excellent flexibility of single/double-sided FPC. However, there is also a compromise option, that is flexible multi-layer FPC.

Flexible multi-layer FPC is manufactured on a flexible insulating substrate, and its finished product is specified to be flexible. This structure usually bonds the two sides of many single-sided or double-sided microstrip flexible PCBs together, but its central part is not bonded together, so it is highly flexible. In order to have a high degree of flexibility, a thin, suitable coating such as polyimide can be used on the conductor layer instead of a thicker laminate cover.

Single-layer vs. double-sided vs. multilayer FPC – applications

  • Single-layer FPC is mostly used in the fields of industrial control and electronic instruments with relatively simple lines.
  • Double-sided FPC is widely used in mobile phones, automotive instruments and other products.
  • In high-end consumer electronics, multi-layer FPCs are often seen. A typical example is the smartphone we “hold” every day.

Conclusion

These are all about the difference between single-layer vs. double-sided vs. multilayer FPC. From a market point of view, China’s FPC market is very broad. On the one hand, the FPC industry in mainland China has developed rapidly, and a number of local FPC manufacturers with initial scale and leading technology have emerged.

On the other hand, FPC has a wide range of downstream applications. Needless to say, mobile phones, tablet computers, wearable devices, automobiles, etc., the emerging consumer drones have also seen a surge in demand in recent years. UAVs have light and thin requirements for core components, and the FPC consumption of a UAV is more than 10 pieces.

As a highly reliable multi-layer PCB manufacturer in China, IBE can not only produce rigid PCBs, but also provide high-quality FPC manufacturing services. Whether it is single-layer/double-sided/multi-layer FPC, IBE can manufacture and produce. In addition, IBE also provides rigid-flex PCBs and HDI-type rigid-flex boards containing blind buried holes to meet the diverse needs of the market.

you asked we answer

Single-sided FPC is the simplest flexible board, it has only one layer of chemically etched conductive pattern. It is usually processed on the basis of two raw materials: “substrate + transparent glue + copper foil” and “protective film + transparent glue”.

Double-sided FPC is to have a layer of conductive patterns etched on both sides of the insulating base film to increase the wiring density per unit area. Generally, when the wiring of the circuit is more complicated and the single-layer FPC cannot meet the wiring requirements, the double-sided FPC will be selected.

Multi-layer FPC is to press multi-layer single/double-sided FPC together, form metallized holes through drilling and electroplating, and form conductive paths between different layers. 

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