This step follows when the inner layers have been patterned with the layout and passed the AOI test. The inner layers are then bonded with pre-pregs (i.e. glas fibre mats, which have been pre-impregnated with resin) and copper foil to multilayers. The multilayer construction is different for every type.
Example: Construction of a 4-Layer ML
For the bonding, the inner layers are fitted together with compensation pads, pre-pregs and copper foil to the press tool. Under high pressure and temperature, this package is laminated together in a Vacuumchamber Laminationpress by HML
The lamination parameters are constantly being checked and documented during the process.