So, you are ready to take on that project, design your Printed Circuit Board, and order your very own printed circuit board. You begin your research, only to discover that there are many types of printed circuit boards with varying amounts of layers, the most popular being two layers and four layers. Confusion sets in. If this describes your situation, don’t worry! We’ve all been there.

We’ve written up this article today to help make sense between a 4 layer and 2 layer printed circuit board. We’ll walk through the fundamentals of each so that you have a better understanding of the number of layers that work best for your project.

Printed Circuit Boards Fundamentals
Before we explore the differences between 2-layer PCB and 4-layer printed circuit boards, let’s briefly go over what printed circuit boards are made up of and how they work. This will make understanding 2 and 4 layer PCBs much easier.

Basic printed circuit boards typically comprise a thin layer of copper laminated to an insulating material known as the substrate. The copper layer is divided into separate conducting lines known as circuit traces, through a chemical etching process. These traces are what electrically connect the components that form the circuit.

The circuit pattern and components that a printed circuit board is expected to carry is usually known before you print patterns on the board. Typically components are attached to the board through soldering.

You can also get a hold of bare boards and special prototyping boards that are not customized for any particular circuit. (Check out our article on printed circuit board prototyping for more information). In addition to the copper layer(s) and substrates, a printed circuit board can also feature a protective coating that protects the copper layer from corrosion and minimizes the possibility of annoying solder shorts.

What’s a Layer in a Printed Circuit Board?
When engineers talk about “layers” they are generally referring to the copper layers on a printed circuit board.

Printed circuit boards are always manufactured in increments of two layers. If your board needs more than two layers to perform its function, you will need to increase the layer count by two, making it a 4 layer board. If 4 layers is not enough you will need a 6 layer board and so on.

Single-layer printed circuit boards

Single layer PCBs are used in simple applications, for basic electronic components in products such as printers, cameras, and power supplies. They are inexpensive and can be made much faster than other types of printed circuit boards due to their simplicity, making them popular for mass produced items. 

A single layer printed circuit board has only one conductive layer, which means that all of the components tend to be more spread out. 

2-layer (Double-sided) printed circuit board
A 2-layer printed circuit board has two copper layers. These boards, also known as double-sided boards, feature the two copper layers with the substrate material sandwiched between them in this order:

Solder mask| copper layer | core | copper layer | solder mask

Double-sided printed circuit boards can mechanically support and electrically connect components on both sides of the board. Holes, referred to as vias, are drilled through the board and are lined with copper. These allow you to connect circuits on one side of the board to circuits on the other. With this feature, you can create high-density circuits on a single board.

2-layer PCBs have plenty of room for a ground grid, which greatly reduces electrical noise. Since the price difference between double sided and single layer PCBs is negligible, and they have room to allow for more components while making routing much easier, they are more popular than single layer printed circuit boards. 

4-layer printed circuit board
4-layer printed circuit boards feature four layers of copper. These layers are laminated together with alternating layers of substrates. If we want to dive a bit deeper, a 4-layer printed circuit board comprises, in order:

Solder mask | copper layer | substrate | copper layer | substrate | copper layer | substrate | copper layer | solder mask

The top and bottom layers are the signal layers, while the inner two layers are dedicated as ground and supply planes. 4-layer printed circuit boards also feature vias. The ground and supply layers’ presence prevents electromagnetic interference (EMI) in circuits with RF components. It also provides a short return signal path, reduces the loop impedance, and provides low resistance power supply.

Multi-layer printed circuit board

Multi-layered printed circuit boards go well beyond 4 layer designs. The necessary signal layers and pin density will largely determine the number of layers your PCB needs. Printed circuit boards with six or more layers tend to be used for complex industrial machinery, healthcare technology, and other tech products that require sophisticated circuitry. Today’s printed circuit boards are commonly produced with 12 or more layers for a wide range of products and applications. PCB designs that have up to 32 layers are becoming almost commonplace.

Choosing Between 2-Layer and 4-Layer Printed Circuit Boards
Now that we’ve gone through the different features of these printed circuit boards, let’s talk about some decision factors that will help you in understanding which board to select for your project.

    • The complexity of your circuit will be the deciding factor for the number of layers your printed circuit board will require. For the go-getters that have complex circuits that feature RF circuitry, switched-mode power supply, long digital buses, and other complex components and connections, we strongly recommend 4-layer printed circuit boards. Using 2-layer boards for these kinds of circuits would not only cause emission of excessive amounts of radiation and interference, but signal integrity would also be compromised. If you are making a simple circuit, a 2-layer printed circuit board is recommended.
  • Cost. While 4-layer printed circuit boards are great for their functionality, they can cost up to three times more than their 2-layer counterparts. That’s a significant increase in price, especially for DIY and hobby projects. So when budget is a concern, you can choose to go for 2-layer boards, unless your board requires complex circuitry and capability requirements.

All these factors should be taken into consideration before you make a decision on what type of printed circuit board your project requires.

Some additional aspects to contemplate when designing a PCB include: 

  • How to maximize functionality while minimizing required space
  • How durable your PCB needs to be (the more layers your printed circuit board design has, the more durable your PCB will be)
  • Cost and affordability of both the PCB itself and your finished product
  • Turnaround time for manufacturing 

If you’re having difficulties determining whether you should choose a 2- or 4-layer PCB design for your project, you can compare the design options to evaluate the functionality and cost. There are often pros and cons to either choice, and creating multiple designs allows you to get a more accurate idea of the differences between the two. 

2-Layer PCB Advantages and Disadvantages

Advantages

  • Lower Cost – double sided PCBs are less expensive than 4-layer designs. This difference can be considerable depending on the number of units you intend to order. 
  • Simpler Design and Production – simpler design and production not only means you get your printed circuit boards faster. The simpler your design is, the less vulnerable it is to costly errors during the design or manufacturing process. In certain applications, the ability to repair your PCB at a later date is also important; when compared to more complex 4-layer PCBs,  it is inherently easier to repair double sided printed circuit boards. 
  • High Volume – Whenever projects require mass production, eliminating unnecessary layers is vital. If your project is going to be a high-volume order, 2-layer boards are typically preferred to optimize manufacturing speed, cost, and efficiency. 
  • Short Lead Time – For large and small projects, a shorter lead time is often required to quickly make a prototype. 2-layer PCBs have an advantage over other multilayer printed circuit boards, because they are extremely fast to produce. 

Disadvantages

  • Simplistic Design – Oftentimes opting for a double sided circuit board means sacrificing some bells and whistles. A 4-layer PCB has more room for more components and routing options, while a 2-layer PCB typically has a simple design. 
  • Slower Speed and Lower Operating Capacity – If speed is an issue, the more layers, the better. Depending on the application, you may find that 2 layers isn’t enough to give you the necessary speed and capacity for your project. The jump from 2 layers to 4 layers includes considerably more speed and operating capacity. 
  • Larger Size and Higher Weight – Despite 4-layer printed circuit boards having more layers, double sided PCBs are typically quite large and bulky in comparison to make room for components and leads. If you need to fit your printed circuit board into a compact space, adding more layers is often the best design choice. 

4-Layer PCB Advantages and Disadvantages

Advantages

  • Useful for More Complicated Projects – The more complex your project is, the more useful you will find the additional layers of a 4-layer PCB. Being able to increase your creative design choices including layouts, routing, and additional components, gives you the opportunity to make the best end product possible. 
  • High Quality – For even simple products that demand the highest quality, going from a 2-layer to a 4-layer PCB design is an obvious choice. If cost is not an issue, 4-layer boards offer a higher quality result. 
  • Added Power – The ability to handle more power is a considerable advantage for 4-layer PCBs. When you are deciding whether you need a double sided or 4-layer printed circuit board, keep in mind how much power your design will require.  
  • Increased Durability – The more layers your design has, the more durable your PCB will be. A 4 layer design will be much more substantial than a 2-layer printed circuit board, despite typically being smaller in size. 
  • Smaller Size and Lighter Weight – While many people conflate a larger number layers with a larger sized board, 4-layer boards are actually often much smaller and lighter than 2-layer PCBs. This is because they require less room for components and wiring. 

Disadvantages

  • Higher Costs – Since 4-layer PCBs use more materials and are more difficult to manufacture, they can be quite a lot more than 2-layer printed circuit boards. When costs are an issue, minimizing the number of layers is usually the best option. 
  • More Complicated Design and Production – When you need to quickly design and produce printed circuit boards for a project, the more layers you have, the longer each step of the process is going to take. 
  • Less Availability – You will find that the more complex your design is, the harder it is to find a manufacturer who can accommodate your needs. That being said, 4-layer designs are very common these days, so this becomes more of an issue as your PCB designs begin to get even more complicated. 
  • Longer Lead Times – For projects that are in a time crunch, adding layers to your design isn’t ideal. The smaller your timeframe is, the more important it will be to use as few layers as possible for your project. 
  • More Complex Repairs – Double-sided printed circuit boards have an advantage over 4-layer designs when it comes to ease of repairs. While everything is essentially exposed on 2-layer designs, any necessary repairs for 4-layer PCBs are going to be more difficult. For some applications, this is extremely important and should be taken into consideration.  

The Takeaway
2-layer and 4-layer printed circuit boards offer different levels of functionality but are both beneficial for different types of projects. Ultimately, the choice between a 4 and 2-layer board primarily comes down to the specs of your project and the complexity of your circuit and the budget requirement you have for your project.