Abstract: Resin overflow in the interior cavity of a multilayer substrate assembly during lamination is restricted and controlled by a plug inserted into the cavity prior to bonding. The plug is shaped to mate with the stepped vertical profile of the cavity. The plug may include sections of materials of different hardness to support the stepped vertical profile of the plug and to facilitate removal of the plug after lamination. The plug may also include textured surfaces to facilitate removal of the plug. Pressurized gas is introduced at the interface between the plug and the cavity surface to dislodge the plug and a vacuum may be applied to the top of the plug to facilitate removal. The cavity may also be coated with layer of photo sensitive material to protect the metal bonding surfaces in the cavity from damage by the plug and to prevent particulate contamination during lamination.