Phase Delay Instability from Temperature Dependent Glass Matrix Anisotropy in PAM4 Stackups
Temperature-driven phase delay drift in PAM4 stackups stems from the thermal expansion coefficient mismatch between glass fibers and resin matrix.
Lamination Pressure
Mechanical Force
Compressive stress applied during the bonding of multilayer circuit boards ensures the complete consolidation of the prepreg and the conductive layers. Proper lamination pressure forces the liquefied resin into the gaps between the copper traces and pushes out any trapped air. This step is conducted inside a vacuum-assisted press to prevent the formation of bubbles or oxidized surfaces.
Resin Flow
Movement of the epoxy or polyimide depends on the balance between the applied pressure and the viscosity of the material at a specific temperature. If the lamination pressure is too low, the resin will not fully encapsulate the glass fibres, leading to weak bonds and potential delamination. High pressure can cause excessive resin squeeze-out, resulting in a board that is thinner than the design specification and potentially starved of dielectric material.
Bonding Strength
Adhesion between the layers is achieved through the chemical crosslinking of the resin under the influence of heat and force. The pressure must be maintained throughout the heat-up and soak phases to ensure that the interface between the copper and the dielectric remains intact. Monitoring the pressure profile throughout the cycle allows the manufacturer to detect equipment malfunctions that could compromise the long-term reliability of the board.