What are The Different Types of PCB Layers?

PCB solder mask layer
PCB solder mask layer, the green upper coating
Resource: https://incompliancemag.com

A PCB is made up of one or more layers, including the top and bottom layer (the “board”), and one or more inner layers. These PCB layers may have different functions — and made using different types of materials — depending on their position in the board. Below is what you need to know about the layers, including the functions of each.

What is a PCB Board?

Before we can delve into the inside of a PCB, let’s first define what a PCB board is. A printed circuit board (PCB) is an electronic board that’s characterized by conductive pathways or tracks on the surface. These pathways are usually made of copper, although other conductive materials may be used.

PCB circuit boards provide a framework for electrical components to be connected, and are usually made up of multiple layers that can include a substrate material, usually fiberglass or reinforced plastic, and one or more copper layers.

This allows the electrical signals to travel through the board in an organized manner, providing power and data transmission between components. The below section explains the different PCB layers, materials that make them, and their different purposes.

PCB copper layer on a simple circuit board
PCB copper layer on a simple circuit board
Resource: https://www.youtube.com/watch?v=oouC2ioivM0

PCB Layers

A PCB layer means the distinct layers of copper, substrate material and other components that are included in a PCB board. A multilayer PCB may include two copper layers, two substrate layers and one solder mask layer. These PCB layers are arranged and connected in a particular order to achieve the desired electrical connection between components. They include:

  • Substrate layer
  • Copper layer
  • Solder mask layer
  • Silkscreen layer

1. PCB Substrate Layer

The substrate layer is the base of the PCB, providing physical support and electrical insulation for the components mounted on it. PCB substrate material includes composites such as epoxy resin matrix, reinforcements consisting of glass fibers or paper, and filler materials like ceramics.

In this layer, there are conductive pathways (or traces) etched from a sheet of copper. These pathways will later become the circuit traces used to connect components. Here are a few facts about this PCB layer explained.

  • In a multilayer flex circuits designs, the PCB substrate also contains small vias (or plated holes) that electrically link various layers of the PCB.
  • The substrate layer is usually designed, manufactured and tested to meet certain standards including thermal insulation, electrical characteristics, stress tolerance and flexibility.
  • In addition to providing support for components, the PCB substrate layer also aids in dissipating heat generated by components during operation. This helps keep the circuit board cool and reliable even under extreme temperatures.
  • The PCB substrate thickness, on average, ranges at around 1.5mm depending on the board size and complexity.
  • For high frequency applications, you may want a Teflon or polyamide PCB substrate, FR4 substrate for high density applications, and FR2 for low-cost or less demanding PCBs.

2. PCB Copper Layer

The copper layer is one of the most important layers in any PCB. This layer provides electrical connection between components on the PCB, and is made from a thin sheet of copper etched to provide conductive pathways. Here’s what you need to know about this layer.

  • A PCB may be single or multilayered. Single-layered PCBs consist of two copper layers, one on each side. Multilayered PCB boards consist of three or more copper layers.
  • In the case of a multilayered type, the inner layers are sandwiched between the outer copper layers to create different pathways on the board.
  • In situations where there’s more than one PCB copper layer, the layers are connected with through-holes or vias.
  • The through-holes or vias create conductive pathways between the different layers of copper, allowing signals and power to flow freely throughout the board.

3. PCB Solder Mask Layer

Ever wondered why a printed circuit board has a green color? That green color is the solder mask. The PCB solder mask layer is typically applied to protect the copper traces (conductive paths) from oxidation that would result from exposure to air. It also helps prevent corrosion or other damage by the elements: more about this layer below.

  • Another important function of having the solder mask layer is that it also helps prevent short circuits. These would happen if the conductive traces were left open.
  • The PCB solder mask layer is typically made of a polymer material such as epoxy and can be green, blue or another color.
  • During the application process, the solder mask layer is applied to the board and then heated in order to melt and cure it. This creates an insulating film.

4. PCB Silkscreen Layer

The PCB silkscreen layer is a printed layer applied to top of a PCB that provides visual information about different components. This layer typically includes labels for components as well as other information about the board. Check out these facts about the silkscreen layer:

  • This PCB layer is normally applied to top of a PCB to provide visual information about different components. Other important information that can be seen on the silkscreen layer includes company logo, art, and other labeling.
  • The PCB silk screen layer is typically applied after the assembly process, using the silkscreen method. In this method, a mesh is used to transfer an image or design to the board.
  • The silkscreen printing technology also enables manufacturers to create finer details such as small text, symbols and lines. Most often this layer is white in color, but can be any other color, including black.

Conclusion

Different PCB layers play specific roles in providing electrical connections between components on the board. The substrate layer provides physical support and insulation, while the copper layer provides the electrical connection between components.

The solder mask layer, on the other hand, protects the board from oxidation and helps to prevent short circuits, while the silkscreen layer provides visual information about components on the board.

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