Editing Printed circuit board (section)

=== Electrical properties ===
Each trace consists of a flat, narrow part of the [[copper]] foil that remains after etching. Its [[Electrical resistance|resistance]], determined by its width, thickness, and length, must be sufficiently low for the current the conductor will carry. Power and ground traces may need to be wider than [[signal trace]]s. In a multi-layer board one entire layer may be mostly solid copper to act as a [[ground plane]] for shielding and power return. For [[microwave]] circuits, [[transmission line]]s can be laid out in [[planar transmission line|a planar form]] such as [[stripline]] or [[microstrip]] with carefully controlled dimensions to assure a consistent [[Characteristic impedance|impedance]]. In radio-frequency and fast switching circuits the [[inductance]] and [[capacitance]] of the printed circuit board conductors become significant circuit elements, usually undesired; conversely, they can be used as a deliberate part of the circuit design, as in [[distributed-element filter]]s, [[Antenna (radio)|antennae]], and [[Fuse (electrical)|fuse]]s, obviating the need for additional discrete components. High density interconnects (HDI) PCBs have tracks or vias with a width or diameter of under 152 micrometers.<ref>{{cite web |url=https://www.freedomcad.com/2018/08/21/why-use-high-density-interconnect/ |title=Why Use High Density Interconnect? |date=August 21, 2018 }}</ref>