Define the channel before comparing resin systems
Draw the path from transmitter reference plane to receiver reference plane, including package assumptions, board segments, connectors, and transitions. Assign each segment an available loss allowance over the interface's relevant frequency range. Record which parts of the model are measured and which remain estimates. This exercise may reveal that an avoidable connector or a long via stub deserves attention before the dielectric is upgraded. It also prevents paying for material performance the route never needs.
Use comparable construction assumptions
AMD's material guidance presents insertion-loss examples alongside construction and conductor assumptions. The design lesson is to compare like with like. Keep trace topology, impedance target, route length, copper treatment, and evaluation frequency consistent when evaluating alternatives. A thinner dielectric that requires a narrower trace may alter the conductor contribution. Ask for construction-specific electrical data rather than applying a resin-family average to every dielectric layer in the model.
Consider a targeted material allocation
A mixed stackup can concentrate electrical performance around critical layers, but its benefit must survive manufacturing review. Check which materials surround each signal's fields and which bonding sheets are involved. A low-loss core does not remove the influence of a less suitable adjacent prepreg. Compare a uniform material build with a proposed hybrid using the actual stackup, including symmetry and process compatibility. Keep the choice open until both electrical and fabrication consequences are understood.
Buy margin you can verify
Request a representative channel coupon when loss is a release requirement. Agree on test frequency coverage, reference planes, launch removal, and data format before fabrication. Review the result against the modeled geometry and measured dielectric thickness. If loss is worse than expected, investigate the copper model and launches before adjusting Df to force a fit. Use the resulting evidence to improve the next model rather than turning a single coupon result into a universal material rating.
- Keep candidate comparisons at equivalent impedance.
- Separate measured channel loss from datasheet loss tangent.
- Document the assumptions that support the final margin.
A construction is more than its laminate name
Dielectric · geometry + material
Core or build-up dielectric
Illustrative only. Copper thickness, dielectric construction and via spans require a reviewed stackup.
Common questions
Does the lowest Df always produce the best board?
No. Conductor loss, transitions, manufacturability, and the required electrical margin can change the preferred construction.
Can every layer use the same Dk and Df?
Only if that approximation is justified. Different glass styles, resin contents, and materials may require different layer properties.
References & further reading
Method & assumptions · General design guidance. Validate the proposed construction and acceptance criteria for your project.