Modeling Slip Velocity and Pressure Gradients across Smooth Copper Foils
Modelling slip velocity and pressure gradients across smooth copper foils prevents resin starvation and locks dielectric thickness tolerances during lamination.
Pressure Gradient
Driving Force
Variations in physical pressure across a distance determine the direction and speed of fluid movement within a confined space. A measurable pressure gradient represents the physical difference in force per unit area that drives the movement of resin between internal board layers. During the multilayer lamination process, this gradient forces the liquefied resin to flow from high-pressure zones in the center toward the lower pressure at the edges.
This movement is necessary to encapsulate the copper traces and eliminate any air pockets.
Resin Distribution
Flow rates increase when the difference in pressure between two points becomes larger. A steep pressure gradient is needed to move resin into narrow gaps between fine-pitch conductors. If the force is too low, the resin will not reach the tightest spaces before it begins to cure.
Lamination Uniformity
Vacuum-assisted presses reduce the absolute pressure at the board perimeter to enhance the effect. This setup creates a more effective pressure gradient that pulls the resin into the furthest corners of the layout. Even distribution of the copper across the layer helps to maintain a consistent force profile.
Inconsistent pressure leads to thickness variations and potential signal integrity issues in the finished product. Proper board design uses thieving patterns to ensure that the fluid behaves predictably across the entire surface area.