AN 958: Board Design Guidelines

ID 683073
Date 1/28/2022
Document Table of Contents

5.4.3. SMA Connectors

SMA connectors are typically used for high-speed signals because of their controlled impedance, mechanical robustness, and good signal integrity. These connectors come in the form of edge launch or vertical launch. For edge launch, the connector is connected to the board edge, the central conductor stays flush with the board, and the board is sandwiched between the ground conductors.

The vertical launch type is through-hole or surface mount. For the through-hole type, all the legs and the center conductor go through the board. For a surface mount type, the center conductor barely touches the top layer of the board.

The type of launch technique does not affect the signal quality very much. However, a long center conductor adds inductance to the transmission path and degrades the signal.

With vertical launch surface mount, you can often strip the center conductor down to below 20 mils. This stripping might be slightly harder to achieve in edge launch configuration, but the choice is dependent on the capability of the SMA manufacturers. Intel has stripped the center conductor down to less than 20 mils short in its designs. Intel uses Lighthorse Technologies and Northrop Grumman for SMA connector requirements.

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