Predictive Hydrodynamic Modeling of High-Viscosity Epoxy Flow in Ultra-Heavy Copper Cavities
Predictive non-Newtonian flow modeling prevents micro-voiding in ultra-heavy copper cavities by matching prepreg viscosity minimums to press force ramps.
Squeeze Flow Lubrication
Hydrodynamic Mechanism
Fluid mechanics models describing thin liquid film displacement between parallel closing plates establish the hydrodynamic forces opposing planar enclosure during press lamination. Squeeze flow lubrication governs how molten polymer resin escapes from between internal copper features and lamination press platens during multilayer printed circuit board fabrication. As press plates converge under hydraulic force, viscous shear stress within the thin resin film generates substantial internal pressure that opposes further platen motion.
Analytical expressions derived from the Stefan equation predict fluid velocity profiles and film thinning rates as a function of resin viscosity and applied mechanical pressure. The physical mechanism stops governing behavior when resin film thickness approaches glass fiber diameters or when thermal curing halts fluid motion.
Pressure Distribution
Internal pressure generation during plate convergence depends on board geometry, resin viscosity and closing speed. Wide copper planes generate strong squeeze flow hydrodynamic resistance, forcing molten resin outward toward lower pressure perimeter clearances. In contrast, isolated narrow traces present low fluid resistance, allowing rapid local dielectric thinning if press pressure is applied too rapidly.
Computer simulations based on squeeze flow lubrication aid tool designers in balancing inner layer copper distribution to prevent glass fabric distortion and localized thickness variations. Microsection measurements confirm that fluid squeeze forces maintain target dielectric spacing across varying copper coverage densities.
Thickness Floor
Viscous force build-up in thin polymer layers prevents direct metal-to-metal contact during multi-layer press closure. Hydrodynamic pressure developed within the squeezed fluid film balances external hydraulic force, ensuring uniform dielectric spacing over dense inner layer tracks.