An edge connector is a two-sided electrical connector that allows two printed circuit boards with terminal edges to be connected to each other. It is very common in computer hardware to have a motherboard connect to a variety of daughterboards or cards. The edge connector may also connect to a ribbon cable then to another edge connector that connects to another circuit board.
Electrical connectors make use of the pressure applied between two conductors to maintain a low resistance contact. The conductive edges of boards need a good contact with edge connector contacts, so the edges are usually plated with high-performance metals with good conductivity and good resistance to oxidation caused by humidity in air. Common metal coatings are tin, silver, and gold.
Edge connectors allow easy troubleshooting of computer hardware. For instance, the common motherboard for the desktop personal computer uses several edge connectors to connect peripherals such as hard disks, display adapters, and network interface cards. As a common practice, power supply connections are made by direct current (DC) power connectors that are separate from the data and control connectors.
A common use of the edge connector is known as a backplane. In computer systems, it is common to have a data bus and a control bus. These common connections may be made available to the backplane so that all boards can have connector edges that come in contact with these edge connectors. The result is several nodes on separate circuit boards that have common connections as required.
The currents allowed are usually low due to the limited contact pressure in edge connectors. If more current is to be allowed, several terminal positions or pins may be allocated. For instance, in the power connector edges for the backplane, the common connection may be made redundant with as many as six or more terminal positions.
In addition, the common connection may protrude forward to make contacts before any other connector edges engage. This feature prevents damage by electrostatic discharge, which happens when a loose board with non-neutral electrostatic charge is first plugged into the backplane. The latter is a reason why ground wrist straps are used when handling boards. Ground straps may be used to ground a human handler or to neutralize a charge in a new board.
Edge connectors used for computer cards are designed to plug into the earlier integrated drive electronics connector or the later peripheral component interconnect. Both of these connectors include the power supply lines, address and data buses, and other control lines. Replacement of the different types of computer interface cards, for troubleshooting and testing, is very easy to do because of the edge connectors.