Traces and pads

The copper of a circuit board is built from paths offset to traces, round pads and drilled holes, with every edge named after its net. The example has three nets on a pitch of 2.54 mm, each a path with a 45° jog. A trace is the path offset by half its width of 0.4 on both sides, with round ends.

import math
import planex as px

routes = {}
for k in range(3):
    y0, y1 = 2.54 * k, 2.54 * (k + 1)
    routes[f"net{k}"] = [(0, y0), (5, y0), (7.54, y1), (12, y1)]

traces = {net: px.FromPolyline(path, name=net).Offset(0.2) for net, path in routes.items()}

Check

A trace of half-width d = 0.2 covers 2d along its length L, plus two round ends of together π d². At each of the two 45° bends, a sector of d² θ / 2 is added on the outside. On the inside, the term of the length counts a kite of d² tan(θ / 2) twice, so it is subtracted once.

d, theta = 0.2, math.pi / 4
L = 5 + 2.54 * math.sqrt(2) + (12 - 7.54)
exact = 2 * d * L + math.pi * d**2 + 2 * d**2 * (theta / 2 - math.tan(theta / 2))
for net, trace in traces.items():
    print(net, "area", trace.mass, "exact", exact)

net0 area 5.344783527060708 exact 5.344783527060708
net1 area 5.34478352706071 exact 5.344783527060708
net2 area 5.344783527060707 exact 5.344783527060708

Pads and drills

Round pads of diameter 1.7 at both ends of each trace are united with the traces, and drills of diameter 1.0 are subtracted (Figure 1). The pads take the name of their net, and the drills are named drill.

copper = list(traces.values())
drills = []
for net, path in routes.items():
    for x, y in (path[0], path[-1]):
        copper.append(px.QuickSketch().Circle(x, y, 0.85, name=net).Face())
        drills.append(px.QuickSketch().Circle(x, y, 0.5, name="drill").Face())

board = px.Subtract([px.Unify(copper), *drills])
print(sorted({e.name for e in board.edges}), len(board.wires), "loops")

['drill', 'net0', 'net1', 'net2'] 9 loops

(a) Three traces

(b) The board

Figure 1: Three nets: traces, then pads united and drills subtracted