When layer information is extracted from the Altium Layer Stack Manager, each Altium layer has conductor information such as its material and its type (IE signal or plane). In addition, Altium layers holds information about the dielectric immediately below it, IE whether it is a Core or a Prepreg. The bottom layer does not have a dielectric.
The Altium layer information does not provide enough information to model a PCB. For all of our Altium products, we interprets the Altium layer information and arranged the layers into layer pairs based on the layer stack style assigned in the Layer Stack Manager.
If the PCB is assigned as Internal Layer Pairs stack up, the top layer is assigned as Prepreg with conductors on the top, the next layer is a core with conductors and the top and the bottom. This continues until the bottom layer, where a Prepreg is added with the bottom layer conductors placed on the bottom side if the Prepreg.
If the PCB is assigned as Layer Pairs stack up, the top layer is assigned as a Core with copper on the top and bottom, the next layer is a Prepreg with no conductors followed a core with copper on the top and bottom conductors. This continues until the bottom layer – this is a Core with conductors on the top and the bottom.
For Custom stack up, if the dielectric is not assigned for the layers, the program will attempt the create a suitable stack up based on the number of layers and other factors. If the dielectrics are assigned, the program will adhere to these provided it can an create appropriate set of layer pairs.
Build Up style layer stack up is not yet supported.
The board thickness is calculated from the stack up.