Layer Sequence
Planning the vertical arrangement of copper and dielectrics in a board facilitates the containment of high speed signals while managing thermal expansion. A high frequency stackup architecture incorporates specialized materials such as PTFE or low loss thermosets to maintain signal velocity at gigahertz rates. It prioritizes close proximity between signal layers and their return paths.
Designers minimize the distance to ground planes to suppress electromagnetic interference. The final drawing specifies the exactly prescribed thickness for every laminate and prepreg sheet.
Reference Control
Continuous return planes ensure that the electromagnetic waves have a stable path from the driver to the load. Inside a high frequency stackup architecture, signal paths are sandwiched between solid ground sheets to control impedance strictly. This layout prevents cross talk between neighboring conductors.
Thin dielectrics between signal and reference planes increase the coupling effect. The stackup must remain symmetrical to prevent warping during the intense heat of the reflow process.
Material Blend
Hybrid constructions combine expensive microwave materials with standard epoxy glass layers to reduce the total manufacturing cost. While implementing high frequency stackup architecture, the bonding stages must accommodate different lamination temperatures. Some high speed materials require more heat to reach adequate flow.
If the materials expand at different rates, internal stress will build up. Engineering these builds requires thorough knowledge of the glass transition temperature for every ply in the sandwich.
