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Circuit properties of the PCB


A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.
Each trace consists of a flat, narrow part of the copper foil that remains after etching. Its 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 traces. 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 lines can be laid out in a planar form such as stripline or microstrip with carefully controlled dimensions to assure a consistent 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, obviating the need for additional discrete components.

RoHS compliant PCB

The European Union bans the use of lead (among other heavy metals) in consumer items, a piece of legislature called the RoHS, for Restriction of Hazardous Substances, directive. PCBs to be sold in the EU must be RoHS-compliant, meaning that all manufacturing processes must not involve the use of lead, all solder used must be lead-free, and all components mounted on the board must be free of lead, mercury, cadmium, and other heavy metals.