Volume Reduction
Reduction in volume of prepreg resin under temperature and pressure during the lamination cycle determines the final thickness and dielectric properties of a multilayer circuit board. Resin compression occurs as the liquefied polymer fills the internal voids between copper traces before curing into a solid state. This action reduces the thickness of the prepreg layer below its initial uncompressed state.
The amount of displacement depends on the applied pressure, temperature profile, and layout density. Accurate predictions of this behavior prevent board thickness variations.
Structural Impact
Inadequate pressure during the lamination stage results in incomplete void filling, creating trapped air bubbles that lead to delamination under thermal stress. Excessive pressure, however, squeezes out too much resin, leaving the glass cloth starved of polymer and reducing the dielectric breakdown voltage between layers. This material flow also influences the final height of high-speed transmission lines, which shifts the trace impedance away from the design target.
Balancing the squeeze out ensures a consistent insulating layer. Controlled press profiles maintain structural consistency across the panel.
Process Variable
Lamination presses monitor the displacement of the platens to calculate the resin compression in real time. Standard operating procedures dictate specific heat rise rates to match the viscosity curve of the polymer. Proper adjustment of these parameters limits thickness variance.
Consistent compression yields reliable dielectric boards.
