Quantifying Resin Flow Shear Dynamics in Multilayer Laminate Buildup Operations
Modelling resin squeeze flow shear kinetics during multilayer pressing prevents inner-layer trace swim and guarantees reliable dielectric clearance.
Squeeze Flow Hydrodynamics
Laminate Displacement
The lateral movement of liquefied resin between parallel plates under compressive force governs the thickness and uniformity of the dielectric layers. Squeeze flow hydrodynamics explains how the resin moves outward from the center of a board toward the edges during the lamination process. This fluid motion is driven by the pressure of the press and the resistance offered by the copper circuitry and glass reinforcement.
Accurate modeling of this flow ensures that the final board meets the specified impedance and thickness tolerances.
Pressure Distribution
Fluid pressure within the resin layers varies according to the distance from the board edge and the local density of the copper features. Areas with low copper density provide paths of least resistance, leading to faster resin movement and potentially thinner dielectric sections. Squeeze flow hydrodynamics indicates that the velocity of the resin is highest midway between the internal layers and zero at the copper surfaces due to the no-slip condition.
This velocity gradient can exert measurable shear forces on small traces, leading to displacement or deformation. Proper stackup design and the use of copper thieving help balance these internal pressures by creating a more uniform resistance to the flowing resin. The viscosity of the resin acts as a dampening factor that limits the speed of this displacement during the heating cycle.
Edge Effect
Increased flow at the periphery of the panel often results in a slight reduction in thickness compared to the center. Controlling this variation requires the use of sacrificial borders and precise pressure profiles to maintain a flat finished product.