--fanout: leave out pins a same-net pour on their layer already joins

src/freeroute/board/items.py

@@ -119,6 +119,8 @@ class Via(Item):
     shape: object = None
     #: drill diameter in board units, when the padstack name gives it
     drill: int = 0
+    #: placed by the router's fan-out, not on the board yet: written out
+    generated: bool = False
 
 
 @dataclass
@@ -132,6 +134,8 @@ class Trace(Item):
     layer: int = 0
     half_width: int = 0
     corners: list[IntPoint] = field(default_factory=list)
+    #: placed by the router's fan-out, not on the board yet: written out
+    generated: bool = False
 
     def is_empty(self) -> bool:
         return len(self.corners) < 2

src/freeroute/cli.py

@@ -30,8 +30,11 @@ from freeroute.ses import write_ses
 #: which optional flags each engine actually implements. Anything not listed for
 #: an engine is rejected by :func:`_validate` rather than quietly ignored.
 ENGINE_OPTIONS: dict[str, frozenset[str]] = {
-    "grid": frozenset({"rip_up", "max_passes", "seed", "orders", "promote", "access", "rollback"}),
+    "grid": frozenset({"rip_up", "max_passes", "seed", "orders", "promote", "access", "rollback", "fanout"}),
-    "exact": frozenset({"shove", "diagonal", "rip_up", "max_passes", "seed", "orders", "promote", "access", "rollback"}),
+    "exact": frozenset(
+        {"shove", "diagonal", "rip_up", "max_passes", "seed", "orders", "promote", "access",
+         "rollback", "fanout"}
+    ),
     "room": frozenset({"shove", "pack"}),
 }
 
@@ -47,6 +50,7 @@ _FLAG_NAMES = {
     "promote": "--promote-failures",
     "access": "--access-cost",
     "rollback": "--no-rollback",
+    "fanout": "--fanout",
 }
 
 
@@ -183,6 +187,22 @@ def build_parser() -> argparse.ArgumentParser:
         help="grid and exact engines: least distance between the edges of any two via "
         "holes, of one net or two (KiCad's min_hole_to_hole; default 0.25)",
     )
+    parser.add_argument(
+        "--fanout",
+        nargs="?",
+        const="all",
+        choices=["all", "supply"],
+        help="grid and exact engines: before routing, give every fine-pitch pin a stub "
+        "outward past its pad row (and a via to its plane, for a plane net), committed "
+        "as copper so later routes cannot wall it in; --fanout supply: plane pins only",
+    )
+    parser.add_argument(
+        "--fanout-min-pins",
+        type=int,
+        default=32,
+        metavar="N",
+        help="with --fanout: fan out only packages with at least N fine-pitch pins (default 32)",
+    )
     parser.add_argument(
         "--jobs",
         type=int,
@@ -213,6 +233,7 @@ def main(argv: list[str] | None = None) -> int:
             ("promote", args.promote_failures is not None),
             ("access", args.access_cost is not None),
             ("rollback", not args.rollback),
+            ("fanout", bool(args.fanout)),
         )
         if asked
     ]
@@ -248,6 +269,8 @@ def main(argv: list[str] | None = None) -> int:
             "heuristic_weight": args.heuristic_weight,
             "access_cost": args.access_cost or 0.0,
             "hole_to_hole_mm": args.hole_to_hole,
+            "fanout": args.fanout or False,
+            "fanout_min_pins": args.fanout_min_pins,
             "rollback": args.rollback,
         }
     elif args.engine == "grid":
@@ -259,6 +282,8 @@ def main(argv: list[str] | None = None) -> int:
             "resolution": 1 if args.grid_resolution is None else args.grid_resolution,
             "access_cost": args.access_cost or 0.0,
             "hole_to_hole_mm": args.hole_to_hole,
+            "fanout": args.fanout or False,
+            "fanout_min_pins": args.fanout_min_pins,
             "rollback": args.rollback,
         }
     if args.engine == "room":

src/freeroute/route/fanout.py

@@ -0,0 +1,229 @@
+"""Fan out fine-pitch pins before routing: commit each pin's way out as copper.
+
+On a dense board the pins of a fine-pitch package get walled in: their own
+neighbours' pads on either side, and other nets' copper that got there first
+across the only way out. Reserving the way out did not help (the reserved
+cells still had to be routed, and lost to congestion there); committing it
+does, which is what a person does by hand.
+
+Each fine-pitch pin of a perimeter package (QFP, QFN, LGA: pads on the edge,
+none inside) gets a straight stub outward, perpendicular to its side of the
+package, just past its pad row. A pin whose net has an inner plane also gets
+a via at the stub's end, staggered between neighbouring pins so their holes
+keep their spacing, and so reaches the plane with nothing left to route.
+Every stub and via is checked exactly against pads, keepouts, the board edge,
+copper already on the board and earlier fan-out, and left out where it would
+not fit. The result goes on the board as fixed copper of its net (marked
+``generated``), so the router starts from the stub's end or the via, and the
+session writes it out with the routes.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+import math
+
+from freeroute.board.board import BasicBoard
+from freeroute.board.items import Pin, Trace, Via
+from freeroute.geometry import IntBox, IntPoint
+from freeroute.geometry.polyline import Polyline, PolylineShape, corner_box
+
+# a package is fanned out when it has this many pins and they are this close
+_MIN_PINS = 8
+_FINE_PITCH_FACTOR = 1.2  # neighbour centres within this many (trace + 2 clearance)
+
+
+@dataclass
+class FanoutRules:
+    trace_width: int
+    clearance: int
+    via_half: int
+    via_drill: int
+    hole_to_hole: int
+    edge_clearance: int
+    signal_layers: list[int]
+    via_padstack: str
+    #: smallest package fanned out (a big dense part is where pins get walled in)
+    min_pins: int = 32
+    #: fan out plane pins only (a stub and a via each), as a person would first
+    supply_only: bool = False
+
+
+def plan_fanout(board: BasicBoard, rules: FanoutRules) -> list:
+    """The stubs and vias to put on the board before routing."""
+    half = max(rules.trace_width // 2, 1)
+    # a net may have several plane zones (a main plane and an island)
+    planes: dict[int, list] = {}
+    for z in board.get_conduction_areas():
+        if z.net_nos and not board.layer_structure.arr[z.layer].is_signal:
+            planes.setdefault(z.net_nos[0], []).append(z)
+    # copper pours on the routing layers, by net: a pad inside one is joined
+    # by the fill, and a stub there would take the room its thermal spokes need
+    pours: dict[int, list] = {}
+    for z in board.get_conduction_areas():
+        if z.net_nos and board.layer_structure.arr[z.layer].is_signal:
+            pours.setdefault(z.net_nos[0], []).append(z)
+    placed = _Placed(board, rules)
+    by_net: dict[int, list[Pin]] = {}
+    for pin in board.get_pins():
+        for n in pin.net_nos:
+            by_net.setdefault(n, []).append(pin)
+    items: list = []
+    pitch = 2 * rules.via_half + rules.hole_to_hole
+    for pins in _packages(board, rules).values():
+        centre = IntPoint(
+            sum(p.location.x for p in pins) // len(pins), sum(p.location.y for p in pins) // len(pins)
+        )
+        for k, pin in enumerate(sorted(pins, key=lambda p: (p.location.x, p.location.y))):
+            net = pin.net_nos[0] if pin.net_nos else None
+            if net is None:
+                continue
+            layer = next(layer for layer in pin.layers if layer in rules.signal_layers)
+            if any(z.layer == layer and z.polygon is not None and z.polygon.contains(pin.location)
+                   for z in pours.get(net, [])):
+                continue  # the pour joins it
+            direction = _outward(pin.location, centre)
+            reach = _pad_reach(pin, direction) + rules.clearance + half + rules.trace_width
+            end = _step(pin.location, direction, reach)
+            plane = planes.get(net)
+            partners = [q for q in by_net.get(net, []) if q is not pin]
+            # a signal whose other pins are all on other layers has to change
+            # layer somewhere: do it at the stub's end, away from the pads
+            elsewhere = bool(partners) and all(layer not in q.layers for q in partners)
+            if plane is None and (rules.supply_only or not elsewhere):
+                if not rules.supply_only and placed.stub_fits(pin.location, end, layer, net, half):
+                    items.append(placed.add_stub(pin.location, end, layer, net, half))
+                continue
+            # stagger the via of every other pin along the side outward
+            options = [reach + rules.via_half + rules.clearance + (k % 2) * pitch,
+                       reach + rules.via_half + rules.clearance + ((k + 1) % 2) * pitch]
+            for d in options:
+                at = _step(pin.location, direction, d)
+                if plane is not None and not any(
+                    z.polygon is not None and z.polygon.contains(at) for z in plane
+                ):
+                    continue
+                if placed.stub_fits(pin.location, at, layer, net, half) and placed.via_fits(at, net):
+                    items.append(placed.add_stub(pin.location, at, layer, net, half))
+                    items.append(placed.add_via(at, net))
+                    break
+    return items
+
+
+def _packages(board: BasicBoard, rules: FanoutRules) -> dict[str, list[Pin]]:
+    """Fine-pitch perimeter packages: many single-layer pins, close together."""
+    by_ref: dict[str, list[Pin]] = {}
+    for pin in board.get_pins():
+        if pin.shape is None or not pin.component_ref:
+            continue
+        on = [layer for layer in pin.layers if layer in rules.signal_layers]
+        if len(on) != 1:
+            continue  # through-hole pins change layer for free
+        by_ref.setdefault(pin.component_ref, []).append(pin)
+    fine = _FINE_PITCH_FACTOR * (rules.trace_width + 2 * rules.clearance)
+    out = {}
+    for ref, pins in by_ref.items():
+        if len(pins) < max(rules.min_pins, _MIN_PINS):
+            continue
+        close = sum(
+            1 for p in pins
+            if min(math.hypot(p.location.x - q.location.x, p.location.y - q.location.y)
+                   for q in pins if q is not p) < fine * 2
+        )
+        if close >= len(pins) // 2:
+            out[ref] = pins
+    return out
+
+
+def _outward(point: IntPoint, centre: IntPoint) -> tuple[int, int]:
+    """Away from the package centre, along the nearer axis (its side's normal)."""
+    dx, dy = point.x - centre.x, point.y - centre.y
+    if abs(dx) >= abs(dy):
+        return (1 if dx >= 0 else -1, 0)
+    return (0, 1 if dy >= 0 else -1)
+
+
+def _pad_reach(pin: Pin, direction: tuple[int, int]) -> int:
+    """How far the pad reaches from its centre in ``direction``."""
+    box = pin.shape.bounding_box()
+    if direction[0] > 0:
+        return box.ur.x - pin.location.x
+    if direction[0] < 0:
+        return pin.location.x - box.ll.x
+    if direction[1] > 0:
+        return box.ur.y - pin.location.y
+    return pin.location.y - box.ll.y
+
+
+def _step(point: IntPoint, direction: tuple[int, int], distance: float) -> IntPoint:
+    return IntPoint(point.x + round(direction[0] * distance), point.y + round(direction[1] * distance))
+
+
+class _Placed:
+    """Copper a fan-out stub or via has to clear, growing as fan-out is placed."""
+
+    def __init__(self, board: BasicBoard, rules: FanoutRules) -> None:
+        self.board, self.rules = board, rules
+        self.copper: list[tuple[IntBox, frozenset[int], int]] = []  # box, layers, net
+        for pin in board.get_pins():
+            if pin.shape is not None:
+                net = pin.net_nos[0] if pin.net_nos else -1
+                self.copper.append((pin.shape.bounding_box(), frozenset(pin.layers), net))
+        for net, layers, box in board.get_fixed_copper():
+            self.copper.append((box, layers, net))
+        self.keepouts = [
+            (tile.bounding_box(), o.layer, o.blocks_wires, o.blocks_vias, o.clearance)
+            for o in board.get_obstacle_areas() for tile in o.tiles
+        ]
+        self.holes: list[tuple[IntPoint, int]] = []  # centre, radius
+        for item in board.get_items():
+            if isinstance(item, Via) and item.fixed:
+                self.holes.append((item.location, (item.drill or rules.via_drill) // 2))
+        for pin in board.get_pins():
+            if pin.shape is not None and sum(1 for layer in pin.layers if layer in rules.signal_layers) > 1:
+                b = pin.shape.bounding_box()
+                self.holes.append((pin.location, min(b.ur.x - b.ll.x, b.ur.y - b.ll.y) // 2))
+
+    def _clear(self, box: IntBox, layers: frozenset[int], net: int, kind: str) -> bool:
+        grown = box.offset(self.rules.clearance)
+        for other, other_layers, other_net in self.copper:
+            if other_net != net and layers & other_layers and other.overlaps(grown):
+                return False
+        for kbox, klayer, wires, vias, needs in self.keepouts:
+            if klayer not in layers or not (wires if kind == "wire" else vias):
+                continue
+            if kbox.overlaps(grown if needs else box):
+                return False
+        outline = self.board.outline
+        return outline is None or outline.box_clear(box, self.rules.edge_clearance)
+
+    def stub_fits(self, a: IntPoint, b: IntPoint, layer: int, net: int, half: int) -> bool:
+        boxes = list(PolylineShape(Polyline([a, b]), half).tiles()) + [corner_box(b, half)]
+        return all(self._clear(box, frozenset({layer}), net, "wire") for box in boxes)
+
+    def via_fits(self, at: IntPoint, net: int) -> bool:
+        h = self.rules.via_half
+        box = IntBox(at.x - h, at.y - h, at.x + h, at.y + h)
+        if not self._clear(box, frozenset(self.rules.signal_layers), net, "via"):
+            return False
+        mine = self.rules.via_drill // 2
+        return all(
+            math.hypot(c.x - at.x, c.y - at.y) >= mine + r + self.rules.hole_to_hole
+            for c, r in self.holes
+        )
+
+    def add_stub(self, a: IntPoint, b: IntPoint, layer: int, net: int, half: int) -> Trace:
+        for box in list(PolylineShape(Polyline([a, b]), half).tiles()) + [corner_box(b, half)]:
+            self.copper.append((box, frozenset({layer}), net))
+        return Trace(net_nos=[net], fixed=True, layer=layer, half_width=half, corners=[a, b],
+                     generated=True)
+
+    def add_via(self, at: IntPoint, net: int) -> Via:
+        h = self.rules.via_half
+        box = IntBox(at.x - h, at.y - h, at.x + h, at.y + h)
+        layers = list(self.rules.signal_layers)
+        self.copper.append((box, frozenset(layers), net))
+        self.holes.append((at, self.rules.via_drill // 2))
+        return Via(net_nos=[net], fixed=True, padstack_name=self.rules.via_padstack,
+                   location=at, layers=layers, shape=box, drill=self.rules.via_drill,
+                   generated=True)

src/freeroute/route/grid_router.py

@@ -1360,7 +1360,7 @@ class GridRouter:
                 elif isinstance(item, Trace) and not item.is_empty():
                     boxes = list(PolylineShape(Polyline(item.corners), item.half_width).tiles())
                     boxes += [corner_box(e, item.half_width) for e in (item.corners[0], item.corners[-1])]
-                    piece = _FixedPiece([item.layer], boxes)
+                    piece = _FixedPiece([item.layer], boxes, trace=item)
                 else:
                     continue
                 cache.setdefault(item.net_nos[0], []).append(piece)
@@ -1482,12 +1482,13 @@ def _fixed_joins_zone(piece, zone, plane: bool) -> bool:
 class _FixedPiece:
     """One track or via already on the board, as connectivity."""
 
-    __slots__ = ("layers", "boxes", "via")
+    __slots__ = ("layers", "boxes", "via", "trace")
 
-    def __init__(self, layers, boxes, via=None) -> None:
+    def __init__(self, layers, boxes, via=None, trace=None) -> None:
         self.layers = frozenset(layers)
         self.boxes = boxes
         self.via = via  # the Via item, for a via
+        self.trace = trace  # the Trace item, for a track
 
 
 def _connected_groups(
@@ -1548,11 +1549,28 @@ def _connected_groups(
         groups[root][1].append(zone)
     for k, piece in enumerate(fixed):
         root = find(base + k)
-        if piece.via is not None and root in groups:
+        if root not in groups:
+            continue
+        if piece.via is not None:
             groups[root][0].append(_via_end(piece.via))
+        elif piece.trace is not None:
+            # a track's ends are places a route may start: a fan-out stub's
+            # far end is outside the pad row the pin sat walled in by
+            for end in (piece.trace.corners[0], piece.trace.corners[-1]):
+                groups[root][0].append(_trace_end(piece.trace, end))
     return [groups[r] for r in order]
 
 
+def _trace_end(trace, end: IntPoint) -> Pin:
+    """An end of a fixed track as a place a route may start or end."""
+    from freeroute.geometry.polyline import corner_box
+
+    return Pin(
+        net_nos=list(trace.net_nos), fixed=True, name="track", component_ref="",
+        location=end, layers=[trace.layer], shape=corner_box(end, trace.half_width),
+    )
+
+
 def _via_end(via) -> Pin:
     """A fixed via as a place a route may start or end (not a pad to route)."""
     return Pin(

src/freeroute/route/pipeline.py

@@ -88,6 +88,42 @@ def _dsn_units_per_um(dsn: DsnBoard) -> float:
     return {"um": 1.0, "mm": 0.001, "mil": 1 / 25.4, "inch": 1 / 25400}.get(dsn.unit, 1.0)
 
 
+def _place_fanout(
+    board, dsn, scale, layers, width, clearance, edge, hole_to_hole_mm, mode=True, min_pins=32
+) -> None:
+    """Put the fan-out's stubs and vias on the board, before routing."""
+    from .fanout import FanoutRules, plan_fanout
+
+    via_half = _via_half_board(dsn, scale) or max(width // 2, 1)
+    rules = FanoutRules(
+        trace_width=width,
+        clearance=clearance,
+        via_half=via_half,
+        via_drill=_via_drill_board(dsn, scale) or 2 * via_half,
+        hole_to_hole=_mm_to_board(dsn, scale, hole_to_hole_mm) or 0,
+        edge_clearance=edge or 0,
+        signal_layers=layers or [i for i, layer in enumerate(dsn.layers) if layer.is_signal],
+        via_padstack=_via_padstack(dsn),
+        min_pins=min_pins,
+        supply_only=mode == "supply",
+    )
+    for item in plan_fanout(board, rules):
+        board.insert(item)
+
+
+def _add_generated(result, board) -> None:
+    """The fan-out's copper goes into the session with the routes."""
+    from freeroute.board.items import Trace, Via
+
+    for item in board.get_items():
+        if not getattr(item, "generated", False) or not item.net_nos:
+            continue
+        if isinstance(item, Trace):
+            result.add_wire(item.net_nos[0], item.layer, list(item.corners))
+        elif isinstance(item, Via):
+            result.add_via(item.net_nos[0], item.location)
+
+
 def _via_half_board(dsn: DsnBoard, scale: int) -> int | None:
     """Half the via pad's size in board units, from the DSN's via padstack.
 
@@ -119,6 +155,8 @@ def route_dsn_board(
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
     hole_to_hole_mm: float = 0.25,
+    fanout: bool | str = False,
+    fanout_min_pins: int = 32,
     rollback: bool = True,
 ) -> tuple[RouteResult, int, list[str]]:
     """Route a parsed :class:`DsnBoard`; return the board-unit result, the scale,
@@ -130,6 +168,9 @@ def route_dsn_board(
     edge_clearance_board = _mm_to_board(dsn, scale, edge_clearance_mm)
     width_board = round(_rule_width_dsn(dsn) * scale)
     clearance_board = round(_rule_clearance_dsn(dsn) * scale)
+    if fanout:
+        _place_fanout(board, dsn, scale, layers, width_board, clearance_board,
+                      edge_clearance_board, hole_to_hole_mm, fanout, fanout_min_pins)
     result = route_board(
         board,
         resolution=resolution,
@@ -148,6 +189,7 @@ def route_dsn_board(
         via_drill=_via_drill_board(dsn, scale),
         hole_to_hole=_mm_to_board(dsn, scale, hole_to_hole_mm) or 0,
     )
+    _add_generated(result, board)
     return result, scale, [layer.name for layer in dsn.layers]
 
 
@@ -197,6 +239,8 @@ def build_routing_result(
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
     hole_to_hole_mm: float = 0.25,
+    fanout: bool | str = False,
+    fanout_min_pins: int = 32,
     rollback: bool = True,
 ) -> RoutingResult:
     """Route ``dsn`` (grid track) and convert to a DSN-unit RoutingResult."""
@@ -206,6 +250,8 @@ def build_routing_result(
         route_first=route_first,
         access_cost=access_cost,
         hole_to_hole_mm=hole_to_hole_mm,
+        fanout=fanout,
+        fanout_min_pins=fanout_min_pins,
         rollback=rollback,
     )
     return _to_routing_result(route, dsn, scale, layer_names)
@@ -226,6 +272,8 @@ def route_dsn_board_exact(
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
     hole_to_hole_mm: float = 0.25,
+    fanout: bool | str = False,
+    fanout_min_pins: int = 32,
     rollback: bool = True,
 ) -> tuple[ExactRouteResult, int, list[str]]:
     """Route a parsed :class:`DsnBoard` with the exact-geometry (orthogonal,
@@ -238,6 +286,9 @@ def route_dsn_board_exact(
     edge_clearance_board = _mm_to_board(dsn, scale, edge_clearance_mm)
     width_board = round(_rule_width_dsn(dsn) * scale)
     clearance_board = round(_rule_clearance_dsn(dsn) * scale)
+    if fanout:
+        _place_fanout(board, dsn, scale, layers, width_board, clearance_board,
+                      edge_clearance_board, hole_to_hole_mm, fanout, fanout_min_pins)
     exact = route_board_exact(
         board,
         resolution=resolution,
@@ -259,6 +310,7 @@ def route_dsn_board_exact(
         via_drill=_via_drill_board(dsn, scale),
         hole_to_hole=_mm_to_board(dsn, scale, hole_to_hole_mm) or 0,
     )
+    _add_generated(exact.result, board)
     return exact, scale, [layer.name for layer in dsn.layers]
 
 
@@ -277,6 +329,8 @@ def build_exact_routing_result(
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
     hole_to_hole_mm: float = 0.25,
+    fanout: bool | str = False,
+    fanout_min_pins: int = 32,
     rollback: bool = True,
 ) -> RoutingResult:
     """Route ``dsn`` (exact track) and convert to a DSN-unit RoutingResult."""
@@ -294,6 +348,8 @@ def build_exact_routing_result(
         route_first=route_first,
         access_cost=access_cost,
         hole_to_hole_mm=hole_to_hole_mm,
+        fanout=fanout,
+        fanout_min_pins=fanout_min_pins,
         rollback=rollback,
     )
     return _to_routing_result(exact.result, dsn, scale, layer_names)

tests/route/test_fanout.py

@@ -0,0 +1,78 @@
+"""--fanout: fine-pitch pins get their way out committed before routing."""
+
+from __future__ import annotations
+
+from freeroute.board import build_board
+from freeroute.board.items import Trace, Via
+from freeroute.dsn import parse_dsn
+from freeroute.route.fanout import FanoutRules, plan_fanout
+from freeroute.route.pipeline import route_dsn_board_exact
+
+# a 12-pad package, 3 pads a side at 0.5 mm pitch, over a GND plane on In1;
+# pad 1 (left side, top) is GND, the rest are signals to far connector pads
+_SIDES = {
+    "L": [(-2000, y, 0) for y in (500, 0, -500)],
+    "R": [(2000, y, 0) for y in (500, 0, -500)],
+    "T": [(x, 2000, 90) for x in (-500, 0, 500)],
+    "B": [(x, -2000, 90) for x in (-500, 0, 500)],
+}
+_PADS = [p for side in "LRTB" for p in _SIDES[side]]
+
+
+def _dsn():
+    pins = "\n      ".join(
+        f"(pin {'padv' if r else 'padh'} {i + 1} {x} {y})" for i, (x, y, r) in enumerate(_PADS)
+    )
+    far = " ".join(f"(place C{i} {3000 + 2000 * (i % 5)} {-12000 - 2000 * (i // 5)} front 0)" for i in range(11))
+    nets = "(net GND (pins U1-1))\n    " + "\n    ".join(f"(net S{i} (pins U1-{i + 2} C{i}-1))" for i in range(11))
+    return f"""(pcb pkg (parser) (resolution um 10) (unit um)
+  (structure
+    (layer F.Cu (type signal)) (layer In1.Cu (type power)) (layer In2.Cu (type power))
+    (layer B.Cu (type signal))
+    (boundary (path pcb 0  -15000 15000  25000 15000  25000 -25000  -15000 -25000  -15000 15000))
+    (plane GND (polygon In1.Cu 0  -14500 14500  24500 14500  24500 -24500  -14500 -24500  -14500 14500))
+    (via "Via[0-3]_450:200_um") (rule (width 150) (clearance 150)))
+  (placement (component Q (place U1 0 0 front 0)) (component P {far}))
+  (library
+    (image Q
+      {pins})
+    (image P (pin padc 1 0 0))
+    (padstack padh (shape (rect F.Cu -400 -125 400 125)) (attach off))
+    (padstack padv (shape (rect F.Cu -125 -400 125 400)) (attach off))
+    (padstack padc (shape (rect F.Cu -500 -500 500 500)) (attach off))
+    (padstack "Via[0-3]_450:200_um" (shape (circle F.Cu 450)) (shape (circle B.Cu 450)) (attach off)))
+  (network {nets}))"""
+
+
+def _rules(dsn):
+    s = dsn.resolution.value
+    return FanoutRules(trace_width=150 * s, clearance=150 * s, via_half=225 * s, via_drill=200 * s,
+                       hole_to_hole=250 * s, edge_clearance=0, signal_layers=[0, 3],
+                       via_padstack="Via[0-3]_450:200_um", min_pins=8)
+
+
+def test_every_pin_gets_a_stub_outward_past_its_pad():
+    dsn = parse_dsn(_dsn())
+    board = build_board(dsn)
+    items = plan_fanout(board, _rules(dsn))
+    stubs = [i for i in items if isinstance(i, Trace)]
+    assert len(stubs) == 12
+    for stub in stubs:
+        a, b = stub.corners
+        pin = next(p for p in board.get_pins() if p.location == a)
+        pad = pin.shape.bounding_box()
+        # outward: the stub ends further from the package centre, outside its pad
+        assert abs(b.x) + abs(b.y) > abs(a.x) + abs(a.y)
+        assert not (pad.ll.x <= b.x <= pad.ur.x and pad.ll.y <= b.y <= pad.ur.y)
+
+
+def test_a_plane_pin_gets_a_via_and_needs_no_route():
+    dsn = parse_dsn(_dsn())
+    board = build_board(dsn)
+    items = plan_fanout(board, _rules(dsn))
+    assert len([i for i in items if isinstance(i, Via)]) == 1
+    exact, _scale, _ = route_dsn_board_exact(dsn, resolution=2, fanout=True, fanout_min_pins=8)
+    gnd = next(i + 1 for i, n in enumerate(dsn.nets) if n.name == "GND")
+    assert not any(f[0] == gnd for f in exact.result.failed)
+    assert exact.drc_clean
+    assert len(exact.result.vias.get(gnd, [])) == 1  # the fan-out's, written out

tests/test_cli.py

@@ -159,6 +159,7 @@ def test_cli_supported_combinations_are_accepted(tmp_path):
         "promote": ["--promote-failures", "2"],
         "access": ["--access-cost", "5"],
         "rollback": ["--no-rollback"],
+        "fanout": ["--fanout"],
     }
     for engine, options in ENGINE_OPTIONS.items():
         for option in options: