The completed inner-layer circuit board is laminated to the outer-layer copper foil using a fiberglass resin film. Prior to lamination, the inner-layer board undergoes a blackening (oxidation) treatment to harden the copper surface and enhance insulation. The inner-layer copper surface is also roughened to ensure a good bond with the film. During lamination, inner-layer circuit boards with six or more layers are riveted together in pairs using a riveter. They are then neatly pressed between mirror-finished steel plates using a tray and fed into a vacuum laminator, where the film is hardened and bonded using appropriate temperature and pressure. After lamination, the boards are automatically aligned using an X-ray alignment locker to create holes that serve as reference holes for alignment of the inner and outer layers. Appropriate trimming is then performed on the board edges to facilitate subsequent processing.
