Define the Layer Stack-Up in PCB Set-Up
Set-Up is one of the important steps in PCB design, and defining layer stack-up takes a vital part in PCB set-up process. Thus we need to know the detailed information about defining layer stack-up. For different types of PCB, core material and multilayer material are different, this makes different measuring ways. For example, the core material is measured by the overall thickness of material, while the multilayer ones are respectively measured by core dielectric and the copper.
Core stack-up and foil stack-up
For multi-layers, options of defining layer stack-up are core stack-up and foil stack-up. Core stack-up is a traditional stack-up with the core material on the external layers. In contrast, foil stack-up is new method with less restriction. Take four-layer PCB board for instance, if it’s used the core stack-up, then two core materials and one layer pre-preg are required. This makes manufacturers subtract four layers copper from the overall board thickness, divide the remainder by three and use the same (or close value) thickness for the two core materials, and then leave the rest to the dielectric material. With the foil stack-up, the main part of PCB is made up with one core material and the rest is divided by the two dielectric materials.
Combination of design information and values
The information and values of layers should be conveyed to a manufacture in different ways. A graphical representation of board cross section, combined with specific manufacturing notes, provides a quick and easy method. Here is the common information used in graphical cross section:
* Layer number - Number the copper sheet using L1,L2,L3,etc
* Top silk screen - can be as short as TS.
* Bottom silk screen – can be briefly expressed as BM.
