<fanout />

Overview

<fanout /> groups components for escape routing: tscircuit routes their connections to exits, then connects those exits to the rest of the board. It is an alias of <breakout /> and accepts the same props. Like a breakout, it does not create a subcircuit, selector scope, or private net scope. Components inside it remain accessible through selectors such as R1.1.

Automatic fanout

Place the components to escape inside <fanout /> and define their electrical connections with <trace />. The default fanout autorouter generates exits for connections leaving the region. Use padding to give those routes room around the component pads.

const footprint = "bga36_grid6x6_p1mm_w6mm_h6mm_pad0.5mm_circularpads"

export default () => (
  <board width={24} height={14} minTraceWidth={0.1}>
    <fanout padding={1}>
      <chip name="U1" footprint={footprint} pcbX={-6} />
    </fanout>
    <chip name="U2" footprint={footprint} pcbX={6} />
    <trace from="U1.6" to="U2.1" />
    <trace from="U1.12" to="U2.7" />
    <trace from="U1.18" to="U2.13" />
  </board>
)

For explicit exit locations, place a <fanoutpoint /> inside the fanout. It is an alias of <breakoutpoint />, with the same connection, pcbX, and pcbY props.

Local dogbones

autorouter="dogbone" creates short BGA pad-to-via escapes instead of routing to a boundary. Connected signal, VCC and GND pads are included. Remaining board routing continues from the vias; fanoutRoutingLayers chooses their destination.

This 36-pad footprint connects eight pads. Only those eight receive dogbones; the other 28 remain untouched.

export default () => (
  <board width={10} height={10} layers={4} routeRemaining={false}
    minTraceWidth={0.1} minViaPadDiameter={0.4} minViaHoleDiameter={0.15}>
    <fanout autorouter="dogbone" fanoutRoutingLayers={["inner2"]}>
      <chip name="U1" footprint="bga36_grid6x6_p1mm_w6mm_h6mm_pad0.5mm_circularpads"
        connections={{
          pin1: "net.DATA0", pin6: "net.DATA1", pin8: "net.VCC", pin15: "net.GND",
          pin22: "net.CLOCK", pin29: "net.ENABLE", pin31: "net.DATA2", pin36: "net.DATA3",
        }}
      />
    </fanout>
    <pcbnotetext pcbY={4} text="8 connected pads; 28 untouched" fontSize={0.3} />
  </board>
)

For an explicit routing pass, see dogbone phase support and limitations.

Requires core 0.0.2026+ and props 0.0.672+. Use a two-dimensional SMT pad grid and an existing destination layer different from the pad layer.

Reuse saved routes

Pass pcbTracePaths to preserve edited routes and continue board routing from their exits. Keep the electrical connections and supply every pad-to-exit path. tsci build captures phase JSON in .tscircuit/autorouting-artifacts/. Copy it to your source tree before editing; use fanout-local coordinates and recheck DRC. Dogbone capture requires core 0.0.2027+.

Properties

<fanout /> accepts the layout props of <group />, plus the routing props shared with <breakout />:

Property	Description
padding	Space around the fanout region.
paddingLeft / paddingRight / paddingTop / paddingBottom	Set padding on individual sides.
autorouter	Escape router or configuration. Defaults to fanout.
pcbTracePaths	Saved port-to-exit wire/via routes covering all routing connections in the fanout.
busFanoutDirections	Maps named buses to preferred escape directions.
fanoutBoundaryPadding	Padding between source pads and the shared boundary where fanout traces terminate.
fanoutRoutingLayers	Routing layers; the destination layer for local dogbones.
fanoutPourNetMap	Maps plane layers to nets for source-only escapes; inferred from matching copper pours when omitted.

For bus direction and power-plane examples, see the breakout reference. For a larger workflow with layer planning and skew constraints, see Routing DDR.