Microstrip Phase Velocity Fundamentals across Multi Layer Glass Stackups
Microstrip phase velocity depends on outer layer inhomogeneous dielectric fields, glass reinforcement architecture, copper roughness, and lamination compression.
Bare Board Stackup Design
Layer Geometry
Dielectric thickness and copper weight selection defines bare board stackup design before routing begins. Impedance control relies on dielectric constant values alongside prepreg resin content to maintain signal integrity across high-speed traces. Fabrication shops balance foil thickness against etch factor tolerances during outer layer imaging.
Differential pairs require precise spacing from reference planes to prevent crosstalk during lamination cycles. Microvns placement adds sequential lamination steps that increase overall manufacturing cost without adding structural rigidity.
Impedance Margin
Inner layer copper distribution prevents excessive board warpe during thermal excursions in reflow ovens. Resin rich areas fill voids between etched traces while preventing starved regions near heavy copper planes. Press parameters determine final thickness after resin squeeze out occurs during high temperature bonding.
Thermal conductivity calculations use dielectric thickness to predict internal temperature rises during continuous power delivery.
Plane Allocation
Ground plane positioning directly influences return path inductance for high speed switching signals. Signal layers routed adjacent to solid planes achieve lower electromagnetic emission levels during compliance testing. Outer layers lack adjacent reference planes on one side which increases susceptibility to radiated noise interference.
Automated optical inspection verifies copper weights before the stack goes to press. Final microsection analysis confirms dielectric thickness matches preproduction simulation targets before batch acceptance.