Complete Guide to Selecting Board-to-Board Connectors
Types of Board-to-Board Connectors
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:
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.
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.
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.
Backplane connectors: This type of connector deserves its own category, both due to its need to accommodate high data rates and very rugged construction.
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.
Selecting Board-to-Board Connectors
Now we can look at some of the points to consider when selecting board-to-board connectors. First, let`s look at some specifications, then we can think about the advantages of different connector styles.
Board-to-Board Connector Specifications
Board-to-board connectors have some electrical specifications that should be considered beyond just the connector style:
Pitch and pin count: Unless you`re designing to a specific application, or you need high speed/high frequency or high current, you`ll probably start by looking at the pitch/pin count required in the connector. With low power and low speed signaling, just about every connector can handle your power requirements while ensuring signal integrity.
Power handling: This is normally quoted as current at a specific voltage per pin. Most connectors can handle a few Amps at typical application voltages. Make sure to check the voltage as it is common to supply both power and data through a cable; you`ll want to make sure your power does not exceed the voltage rating.
Governing standard: Any industry standards on connectors can govern form factor (some examples are discussed above), or they can cover testing and application specifications. Make sure to check these to ensure your connector style will be compliant.
Environmental ratings: Specifications include power variations with humidity cycling, exposure to gases, and testing at high temperature. This gives you a good idea of where the connector can be used to ensure reliability.
Data rate/frequency limit: For high speed data channels, you`ll see a recommended data rate limit, which the vendor will determine through extensive testing. Data rate limits are just a recommendation, and you might be able to get past these in your system. Be sure to test your system thoroughly if you plan to violate a data rate/frequency specification.
Mechanical specifications: High-quality board-to-board connector datasheets may include some data on mechanical shock, vibration, pulling force, or other specs that help a designer understand ruggedness. Note that these may be listed as test results meant to comply with some industry standard.
