Fluid Displacement
Lateral movement of liquid epoxy between layers follows predictable physical laws when high vertical pressure is applied. Analyzing squeeze-flow mechanics explains how resin fills the complex spaces around thick inner copper layers during lamination. This behavior is driven by the decrease in resin viscosity that happens at elevated temperatures before the start of the final cure.
It dictates how much thickness will be maintained in the central insulating layers after the press sequence is complete.
Dynamic Interaction
High local pressure near dense circuit features forces the fluid into open areas where the resistance to movement is lower. Understanding squeeze-flow mechanics requires a model of the interaction between the laminate geometry and the non-Newtonian nature of the resin. As the press applies force, the material moves outwards toward the edges of the panel until the chemical reaction increases its molecular weight.
If this flow is too aggressive, it will wash away small features or leave starved areas with insufficient glass-to-resin ratios. Engineers choose prepreg materials with low flow characteristics for high density builds to minimize these shifts.
Control Limit
Balancing the press force with the material viscosity allows fabricators to hold stack heights to tight tolerances. Incorrect application leads to excessive corner squeeze where the resin is completely removed from the perimeter zones.
