Printed Circuit Boards
Core concepts
A PCB provides mechanical support and electrical interconnection. The substrate is usually FR-4, a glass-fibre/epoxy laminate. Copper foil is patterned into tracks and pads; its thickness is often quoted by weight, with 1 oz copper being roughly 35 micrometres thick. A solder mask covers tracks to limit solder bridging, while the silkscreen prints component references and outlines. Through-hole boards use plated through-holes; surface-mount boards use pads and often vias to connect layers. Multilayer boards may have power and ground planes, which reduce impedance and improve shielding. Designers control track width, copper thickness, clearance, creepage distance and via placement. Narrow tracks have resistance, inductance and current-carrying limits; wide tracks are used for power and ground. Decoupling capacitors should be close to IC supply pins, and high-current loops should be kept short to reduce noise and EMC problems.
Traps
Do not treat the silkscreen as an electrical layer or an insulator. Solder mask is not a guaranteed safety insulation; use specified clearance and creepage. A via is an interconnection, not a test point or component. Do not choose track width only by convenience: check current, voltage drop and temperature rise. Distinguish clearance (through air) from creepage (across a surface).
Worked example
Estimate the resistance of a 50 mm long, 0.5 mm wide, 35 micrometre thick copper track. R = rho L / A, with rho = 1.7 x 10^-8 ohm m. A = 0.0005 x 35 x 10^-6 = 1.75 x 10^-8 m^2. R = (1.7 x 10^-8 x 0.05) / (1.75 x 10^-8) = 0.049 ohm. At 1 A the drop is about 49 mV. Rule of thumb: use wider copper for power and ground, and verify with the manufacturer's current-rise data.