A PCB is mostly made up of multiple layers of the substrate, copper layering, small holes drilled into the device, solder mask, a coating (quite often in tin-lead), multiple components, before being fused together. Although, when put this way, developing a PCB doesn’t seem like it involves too much. However, the actual creation process is extensive, as you must be precise with every calculation to avoid malfunction.

A prepreg (pre-impregnated) is one of the main materials used in multilayer boards and is what holds the cores together. It is composed of fiberglass impregnated with resin (an epoxy-based material). The layers get pressed together at a temperature to create the required board thickness.

The prepreg and core quite often get mixed up. However, they are two separate components of the PCB. The core of the PCB is the FR4 layers of copper traces and glass-reinforced epoxy laminate sheets. Once heated, the prepreg holds the core of the PCB and the layers together. The role of the prepreg is to fuse etched cores together or to glue a copper foil to an etched core. You will find a layer of prepreg between each layer of the PCB.

The most frequently used PP parameters are as below:

Most Common Core thickness (mm): 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.6, 2, 2.4
Copper foil thickness (um): usually 18, 35, 70, 105

The prepreg is not just an important part in the PCB manufacturing process, it is a necessity if the board has multiple layers. Without the prepreg, there would not be anything holding the different layers together. The prepreg and core are two different parts of the PCB. For starters, the core is an FR4 material with copper traces. Whereas, the prepreg is fiberglass impregnated with resin. It is the prepreg that holds the core together on the PCB.

What is DFM, DFA and DFX? http://henengconsult.com/dfm-dfa-and-dfx/