Edge Connectors: A Guide
An edge connector is a two-sided electrical connector used to connect two printed circuit boards with terminal edges. In computer hardware, it is very common to have a motherboard connect to an array of daughter boards or cards. The edge connector may also connect to a ribbon cable and 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 require a good contact with edge connector contacts, so the edges are typically plated with high-performance metals with good conductivity and resistance to oxidation caused by the air’s humidity. The most common metals used for this plating are tin, silver, and gold.
An added benefit of edge connectors is that they allow for relatively simple troubleshooting of computer hardware. For example, the common motherboard for the desktop personal computer uses several edge connectors to connect to peripherals including hard disks, display adapters, and network interface cards. Power supply connections are commonly made by direct current power connectors that are separate from the data and control connectors. One of the most common uses of edge connectors is as a backplane. In computer systems, it is normal to have a data bus and a control bus. These common connections may be made available to the backplane to ensure that all boards can have connector edges that come into contact with these edge connectors. This results in several nodes on separate circuit boards having common connections as needed.
Due to the limited contact pressure in edge connectors, the currents allowed are typically low. If more current needs to be allowed, several pins or terminal positions may need to be allocated. For example, in the power connector edges for the backplane, the common connection may be made redundant with as many as six or more terminal positions. Furthermore, the common connection may protrude forward to take contacts prior to other connector edges engaging. This prevents damage from electrostatic discharge, which occurs when a loose board with a non-neutral electrostatic charge is plugged into the backplane. This is also why ground wrist straps are needed when handling boards. They can 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 consist of power supply lines, address and data buses, and other control lines. Replacement of the different types of computer interface cards, such as for troubleshooting or testing, is made very easy by edge connectors.
The range of uses for edge connectors within electronics is vast. Examples of expansion peripheral technologies that use edge connectors include PCI (Peripheral Component Interconnect), PCI Express, and AGP (Accelerated Graphics Port). Many microprocessors also use edge connectors, with the processor being mounted on a card with an edge connector, instead of directly to the motherboard. Whatever use you have for edge connectors, ensure you are getting yours from a reputable source.
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