Use the reference design as a starting boundary

Analog Devices' RF and mixed signal layout guidance is intended to be used with the requirements of the selected components, materials and manufacturing process. This is a useful review principle: a general layout rule cannot replace the device's particular reference circuit.

Create a list of geometry to preserve, geometry that can be tuned and geometry needing simulation. Keep this list with the layout so a routing engineer does not optimize an RF transition using only digital clearance rules.

Review every transition as a small structure

Draw the RF signal and its return path through connector launches, matching pads and layer changes. Compare candidate via spans with the nearby ground connections and antipads included. Counting signal vias alone says little about the complete transition.

A thinner dielectric can create narrow trace requirements that are awkward to manufacture or assemble around component pads. Compare an achievable geometry with the performance model before committing to the stack. Avoid a nominal impedance calculation that omits the real launch.

Keep tuning and shielding practical

Reserve physical access for the matching components and a repeatable test connection. Decide whether measurements occur before or after shield installation. A test connector that cannot be reached in the assembled module may force an inconsistent fixture that obscures small design changes.

  • Document material, copper and solder mask assumptions used in modeling.
  • Review shield wall and attachment positions with the RF layout.
  • Mark antenna and matching keepouts across all affected layers.
  • Record the calibration plane and fixture used for measurements.

Control variants deliberately

If one board serves multiple radio variants, describe their component populations and matching values explicitly. Check that an unpopulated option does not leave a significant unused structure attached to the active path. Review each intended configuration rather than approving only the fully populated schematic.

Maintain a compact comparison record of simulated behavior, prototype measurements and the final fitted network. This makes the production release intelligible to another engineer and prevents a later cost reduction from silently undoing a verified RF choice.

DESIGN NOTE / SCHEMATIC

Adjacent-layer access, one connection at a time

Signal copper

Dielectric · geometry + material

Reference copper

Core or build-up dielectric

Signal copper

Illustrative only. Copper thickness, dielectric construction and via spans require a reviewed stackup.

Real smartphone circuit board illustrating compact component placement
Illustrative compact electronics example; not a product-specific manufacturing sample. © Raimond Spekking / CC BY-SA 4.0. Credits & license.

Common questions

Is the lowest loss material always the best RF choice?

Not by itself. Evaluate the required band, route length, dimensional control, bonding process and cost with a real construction. A material property is only one part of the module.

Can HDI replace RF simulation and measurement?

No. HDI changes available routing structures. The actual transitions, matching, coupling and assembled environment still need appropriate analysis and verification.

References & further reading

Method & assumptions · General design guidance. Validate the proposed construction and acceptance criteria for your project.