Multi-layered printed circuit boards (PCBs) are typically preferred because they offer high signal intensity. Of all the multi-layered types, the 2-layer PCB is the most common, as it can accommodate interconnects on both sides. Depending on the desired level of complexity, PCBs can range from two to eight layers—every increment means the addition of two more layers.
It comes as no surprise that differences exist among these layered PCB types. This article is devoted specifically to understanding the differences between 2- and 4-layer PCBs.
Comparing Stackups
The 2-layer PCB stackup can be clearly demarcated. Layer 1, or the top layer, is described as a signal layer. The 0.0014-in.-thick layer is made of copper material; the copper amounts to about 1 oz. These parameters are valid for a board whose final thickness is 0.062 in., ±10%. If the PCB manufacturer plans to make custom PCBs, then these values may differ in accordance with the desired parameters.
The 4-layer PCB stackup, on the other hand, is quite elaborate. Two inner layers, inner layer 1 and 2, are sandwiched between the top and bottom layers. From top to bottom, the 4-layer PCB stackup goes something like this:
The top, i.e. the signal layer (0.0014 in. width) is followed by a prepreg layer with a thickness of 0.0091 in. and dielectric constant of 4.2. The top layer is copper material. The prepreg layer is followed by inner layer 1 (0.0014 in.), referred to as the plane. A core sublayer is part of inner layer 1, which has a width of 0.037 in. This is followed by inner layer 2, which is another plane layer made with 1 oz. copper and is 0.0014 in. thick. Another prepreg sublayer constituting two sheets that are 0.0091 in. thick forms part of inner layer 2. The final layer, the bottom layer, is also 0.0014 in. thick, and is a signal layer as well. Interconnects are soldered and placed on the top and bottom layers.