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.
Inner Layer Copper Shift
Registration Error
Mechanical displacement of conductive patterns occurs during the high pressure bonding of multilayer circuit boards. Inner layer copper shift describes the movement of etched traces or planes away from their intended coordinates before the resin fully cures. This deviation can cause misalignment between the layers and the subsequently drilled holes.
Fabrication facilities use pins or optical alignment systems to minimize this movement during the layup process.
Mechanical Cause
Hydraulic forces exerted by flowing resin during the lamination cycle push against the vertical edges of the copper features. As the epoxy liquefies under heat and pressure, it acts as a lubricant that allows the internal copper foil to slide or distort. The magnitude of inner layer copper shift depends on the density of the circuitry and the thickness of the prepreg layers.
Large copper planes are generally more stable than narrow, isolated traces that offer less resistance to the moving fluid. Vacuum lamination presses help reduce this effect by ensuring uniform pressure distribution and removing air that could cause localized turbulence. Even with these controls, small movements are inevitable and must be compensated for during the design of annular rings.
Compensation Strategy
Scaling factors applied to the artwork before imaging account for the predictable shrinkage and movement of the laminate material. Fabricators measure the actual displacement in test batches to refine these offsets for high density production runs.