Board-to-board connectors come in a variety of shapes and sizes to give a modular feel to a multi-board PCB system. There are many types of common board connectors, and different vendors have their own product lines that fall generally into one of the categories listed below:
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Pin headers: Most designers are familiar with the 1-row or 2-row pin header arrangement with 1 mm pitch. There are variations on this style, including stacked pin headers. Pin headers can be shrouded and keyed (even multi-keyed) to guarantee pinouts match when boards are connected.
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Mezzanine connectors: This type of board-to-board connector joins two parallel printed circuit boards in a stacked configuration. There are many mezzanine connector styles. Note that a pin header can be used as a mezzanine connector.
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Edge card connectors: This style connector is most commonly known for its use in RAM sticks and COMs/SoMs. Really, it can be used for any board-to-board connection along a board edge, whether with a custom or standardized pinout.
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Backplane connectors: This type of connector deserves its own category, both due to its need to accommodate high data rates and very rugged construction.
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Standardized connectors: Some connectors may be developed to meet very specific industry standards beyond edge connector styles for add-in cards. Standards organizations that have defined specific connector styles include VITA (for backplanes), PCI-SIG (PCIe cards), IEEE (e.g., 1386 standard for mezzanine), JTAG, PC/104 (square-post pin headers), and Others.
