Spread Glass Fabric Selection and Skew Mitigation in Printed Board Manufacturing
Selecting mechanically spread glass fabric and enforcing multi-ply laminate construction mitigates intra-pair differential skew without panel rotation costs.
Lamination Pressed Thickness
Stackup Dimension
Mechanical dimensions in multilayer printed circuit board fabrication define the final thickness of the prepreg layers after they have been compressed and cured under heat and pressure in a lamination press. In high-speed designs, the lamination pressed thickness must be controlled to ensure that the characteristic impedance of the transmission lines matches the design targets. This dimension determines the separation between trace layers and reference planes.
It applies to all laminated multilayer structures, but is not used to describe the thickness of rigid core materials that do not change dimension during lamination.
Fabrication Variable
Resin flow during the pressing cycle reduces the initial thickness of the prepreg sheets as the liquid polymer fills the copper voids on the adjacent layers. Fabricators calculate this thickness change based on the copper distribution of the inner layers. This prediction allows them to select the correct prepreg style to achieve the target stackup height.
Tolerance Impact
Variations in temperature or pressure across the press plates can cause uneven thickness across the finished panel. This variation directly affects the trace impedance and the overall flatness of the board. The finished boards are measured to verify that they fall within the specified thickness tolerance.