4 Layer Flex PCB: Your 4 Layer Flexible PCB Manufacturer


Oakley Mae

Today, the 4 Layer flex PCB is another printed circuit board that has become a staple in the electronics industry.

They’re now widely used in various industrial applications, including power, automobile components, and medical devices.

Table of Contents

What Is a 4-Layer Flex PCB?

A 4 Layer flex PCB is a circuit board consisting of four conductive layers made using polyimide instead of FR4.

Some aspects of this PCB include a top layer, a VCC (common voltage collector), and a bottom layer, all combined using holes or buried holes.  

As mentioned earlier, you’ll find these devices in many industrial applications.

That’s because they can withstand extreme heat.

Also, polyimide’s flexibility makes surface mounting much easier than your standard rigid board.

In turn, this helps to streamline the design. 

4 Layer Vs. 2 Layer Flexible PCB

Here’s a comparison between the 4 Layer and 2 Layer flexible PCB. 

Number of Layers

As far as PCBs go, layers (typically copper) are critical.

A circuit board may require a certain number of these layers to function effectively.

For instance, if a circuit board requires more than two layers to perform its function, the designer can double the layers to make it a 4 Layer PCB or even a 6 Layer. 


Usually, the complexity of a circuit board is the primary determining factor of how many layers a printed circuit board should have.

For example, you may consider yourself an expert or advanced.

So, likely you’ll require complex circuits that feature RF circuitry, long digital buses, a switch-mode power supply, and various other sophisticated connections and components. 

In that case, it’s strongly recommended that you use a 4 Layer flex PCB.

Using the 2 Layer would only lead to additional interference and radiation emission.

The other thing is that it would also compromise the signal integrity. 

On the other hand, if you want a simple circuit, then the 2 Layer flex PCB will suffice. 


The 2 and 4 Layer printed circuit boards provide the same mounting space.

That’s because you can mount the components on either side.

That means if circuit density is your only concern, then any one of these two PCBs will work just fine. 


With the 4 Layer PCB features that guarantee increased functionality, the cost can be three times higher than that of the 2 Layer PCB.

This is quite a significant difference, particularly if it’s a DIY project.

Therefore, if budget is one of your primary concerns, you should go with the 2 Layer unless your board needs complex circuitry or capability.     

Materials Used to Make 4-Layer Flexible PCBs

These materials fall under the following three categories:


The role of the adhesive is to form a bond.

See, if the base material happens to be polyamide, it can cause some issues as far as reliability goes.

Thus, in his case, the adhesive minimizes the effect of the limitations of the polyimide base. 

Base Material

Granted, most conventional PCBs comprise a metal or fiberglass base.

However, the flex versions comprise a flexible polymer using polyimide film as a substrate.

Now this material does not soften when heated.

Rather, you’ll notice that it stays flexible even after thermosetting.

On the other hand, other thermosetting resins tend to turn rigid after exposure to heat.

And this makes PI a superior material for flex PCB construction.

That said, the conventional PI film does not have optimal resistance to elements like tears and humidity.

For this reason, choosing an upgraded PI would be an effective way of eliminating such problems. 

Conductive Material

Manufacturers tend to prefer rolled annealed copper foil to regular electrodeposited copper foil.

See, this conductive material makes flex PCBs with layers ideal for industrial control equipment or other applications in the sector.

Also, it has great thickness and electrical properties, plus it’s affordable. 

4 Layer Flex PCB Stackup

Before you evaluate the 4-Layer PCB stackup, you will need to consider its component placement.

That means remembering the X, Y, and Z number of spaces between the components, as well as the spacing in which the circuit must undergo bending. 

That said, the 4 Layer flex PCB stackup is the different layers that make up the PCB during manufacturing.

Typically, it’s two inner layers with a sandwich appearance between the two outer layers. 

In most cases, you’ll find copper at the top layer, which people often call a signal layer. The bottom layer is also a copper layer. 

Considerations While Selecting 4 Layer Flex PCB Manufacturer

The following are some factors to keep in mind when selecting a manufacturer for your 4 Layer PCBs: 

  • Quality: First, check for certifications like ISO 9001 as the bare minimum. Because with such certification, you’re assured that the manufacturer has a Quality Management System (QMS). Also, they should readily avail test yields for you to review. These prove they use the appropriate materials for maximum performance, no errors, and longevity.
  • Cost: Factors like where they source materials and the technology they employ can determine the costs. For example, if the manufacturer imports, you can expect they will buy them cheaper. Then, some technologies are more expensive, so they will be higher if they use such technology. 
  • Expertise: Another factor to consider when selecting a 4 Layer flex PCB manufacturer is their experience and expertise in making 4 Layer flex circuits. Not all manufacturers have a track record of making 4 Layer PCBs. So you don’t want to order 4 Layers from a manufacturer who makes standard rigid PCBs.  

Advantages of 4-Layer Flex PCBs

The following are some advantages of featuring a 4 Layer flex PCB in your design:

  • First, use this circuit board with any connector or component you want. That’s because the compatibility of these boards is quite vast. 
  • Secondly, the 4 Layer provides higher circuit density, which enables the board to adhere to dynamic flexing requirements. 
  • Also, the stability and reliability of these PCBs are far greater than their rigid multi-layer counterparts. And the main reason for this is that they possess fewer interconnects or solder joints. In turn, this helps reduce errors that would otherwise occur. 
  • Besides its improved impedance control, signal quality, and robust operating capabilities, the 4 Layer flex PCB has the edge over other options in the market.
  • Further, these types of PCBs have a wider temperature range, which allows them to operate under environments of higher currents. This also helps to lengthen the lifespan of an electronic device.

4 Layer Flex PCB Applications

First, 4 Layer flex PCBs tend to be lightweight and have a low bend radius, making them very suitable for medical devices and various control equipment.

For example, they’re applied in interior controlling equipment such as the dashboard and ABS systems in automobiles. 

Also, these PCBs serve as one of the top-ranking utilities for the consumer electronics industry.

Thus, you’ll find them in several devices like cameras, calculators, mobile devices, and keyboards.  

4 Layer flexible circuit and an electronic surface

(Caption: 4 Layer flexible circuit and an electronic surface) 

Secondly, 4 Layer flexible PCBs mostly get applied in high-power environments.

Also, they’re thin and stiff, and all of these qualities make them a perfect fit for most industrial applications.

For example, engineers use them a lot for marine and aeronautical equipment. 

Another example where 4 Layer Flex PCBs get used is in the medical industry.

Here, they’re employed in various functions like serving as interconnects with resistors, capacitors, and circuits. 


From the information provided above, we can conclude that flexible circuits such as the 4 Layer flexible PCB are the backbone of electronic devices in several industries.

They’re not going away anytime soon, and for a good reason.

After all, they offer better and easier signal routing capabilities, are more efficient, and have improved EMI performance.