So, you are ready to take on that project, design your circuit, 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 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.
2-layer 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.
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.
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.
- Circuit density. 2-layer and 4-layer printed circuit boards provide equal amounts of mounting space as components can be mounted on both sides of these boards. Any one of them would suffice if circuit density is your only consideration.
- 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.
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.