Understanding PCB Layers


The printed circuit board technology has seen great strides in manufacturing and board density, but the general construction of pcbs hasn’t changed in many decades. A sheet of copper is bonded to an insulating material such as FR4. Generally these copper planes are added in pairs with a single plane of FR4 between the two copper planes. Using this technology, up to 16 layers in extreme cases can be bonded together to form the PCB.

The most simple pcb design would be a 2 layer board. This would include two copper layers on the front and the back from which your component footprints, vias, and traces would be etched away. This will allow interconnect from the components and the top and bottom planes as needed. In order to keep the pcb manufacturing costs down only place components on the top side of your board. If you’re space constrained and run out of room it is permissible to place components on the backside of the board but look carefully at the soldering technology used to manufacture the board.

Going to a 4 layer board brings about another layer that you should become familiar with. Using a pair of layers for the boards main power is called the power planes. You’ll still keep the top and bottom layers for routing your nets, and the two inner layers become your main power and ground layers. These power planes are key to making your board routable in many cases and is critical for high speed pcb design. More on that later.

One last thing to keep in mind. Cost. A small 2 layer pcb will probably cost you around $30 in very low quantity. An equivalent 4 layer board will cost about double that at $60. The more layers you add the more its going to cost. If you’re looking for a large quantity price point the 2 layer board will run you around $5 in 100 pc qty. The point here is that you should only use as many layers as your circuit design really calls for. Experience with a couple of board will be your best bet in determining how many layers you need, but until then start with 2 layers and work your way up. Any respectable pcb design software will allow you to add layers without having to start your pcb design from scratch.