Printed circuit boards can be as simple as a single routing layer with a mechanical layer PCB defining the physical dimensions of your board or as complicated as a multilayer board with all the layers outlined in this article. However, when considered individually, each layer has a very specific and simple purpose. Once you understand the purpose PCB of each layer, understanding PCB construction becomes very simple no matter how complicated the PCB board. Printed circuit boards have many different types of layers. To the uninitiated these layer types can be quite confusing, but once you have a basic understanding, you’ll see that it is all quite simple. The figure below depicts a three dimensional view of a 4-layer PCB that has two routing layers (top and bottom) and two internal planes (GND and PWR). Don’t worry if that sentence doesn’t make sense to you right now, we’ll step through each of the common layer types in this article. Below is a two-dimensional image of the same board with all layers shown on top of one another. Using this board as a reference, we’ll now dive into each of the common PCB layer types. Keep in mind that not every PCB contains all the layers listed – the need for different layer types depends on the specifics of your design. Single layer boards typically include: a mechanical layer, a keep out layer, a routing layer, an overlay layer, a solder mask layer and a solder paste layer. Multilayer PCBs contain those same layers as well as a mix of additional power planes, ground planes and more routing layers. The most common boards are 2-, 4- and 6-layer PCBs though it is not uncommon to have PCBs with over 12 layers.
