Layer Fusion
Manufacturing stages involve the bonding of fully cured core materials to additional layers of prepreg and copper foil. During substrate core lamination, the alignment of internal features must be maintained against the forces of thermal expansion. This process creates the solid physical structure of the multi-layer board.
Press Cycle
The assembly is placed in a vacuum press where heat and pressure are applied according to a specific profile. As the temperature rises, the resin in the prepreg melts and flows into the gaps between the copper traces on the core. Maintaining a vacuum removes air bubbles and prevents the formation of internal voids that could lead to electrical failure.
The pressure must be distributed evenly across the panel to ensure a uniform thickness. Once the resin cures, the individual layers are permanently fused into a single composite plate.
Dimensional Stability
Heat causes the materials to expand at different rates, which can shift the position of the internal pads. This movement is called material shrinkage or growth and must be compensated for during the design of the artwork. Precise control of the cooling rate minimizes internal stresses that cause the board to bow or twist.
Successful lamination ensures that the holes drilled in later steps will hit the center of the internal pads.
