Prepreg Rheology Control in Thin Core Laminate Stacks
Precise control of prepreg minimum viscosity and press temperature ramp rates prevents core squeeze out and micro voiding in thin laminate stackups.
Controlled Impedance Stackups
Structural Arrangement
Layered configurations of dielectric materials and copper conductors maintain a specific electromagnetic relationship to ensure signal integrity in high speed circuits. These controlled impedance stackups define the exact thickness of prepreg and core materials relative to the trace widths and copper weights. Designers use these calculations to match the characteristic impedance of the transmission lines to the requirements of the active components.
Fabrication Precision
Manufacturing tolerances for etched copper and dielectric thickness must be tightly managed to prevent signal reflections or timing errors. In controlled impedance stackups, a variation of even one mil in spacing alters the electrical performance of the trace. Fabricators include test coupons at the edge of the panel to verify the actual values against the design targets.
Time domain reflectometry measurements provide the data needed to confirm the finished board meets the customer specification.
Dielectric Configuration
Dielectric constant and dissipation factor influence how energy travels through the board layers. High frequency designs often require specialized glass weaves and resin systems to minimize signal loss. These controlled impedance stackups must account for the resin flow during lamination which changes the final distance between planes.
Errors in material substitution or layer orientation result in boards that cannot support the intended data rates.