Stackup is the soul of Multi-layer PCB.it refers to the arrangement of copper layers and insulating layers that make up a PCB prior to board layout design.Stackup information includes the layers order,which is layer 2,,which is layer 3.Many customers sent us gerber file without stackup or layer order information. That means we can not proceed the PCB. If you do not have customs stackup ,you also need to provide layers information to PCB manufacturers.
Here is an example. TOP/inner 1/Plane1/Bottom,or CMP/LY2/L15/Bottom. So we can know inner 1 or LY2 is layer 2. The core material and Prepreg is flexible for us to meet the final thickness.
Another important information is one core for 4 Layer PCB,2 cores for 6 layers PCB and 3 cores for 8 layers PCB.The dielectrical (Prepreg)thickness should not be more than 0.3mm, otherwise, we have to use more than two Prepreg material with higher cost.