Capillary action in soldering is influenced primarily by what factor?

Capillary action in soldering is fundamentally influenced by the gap between the surfaces being joined. This phenomenon occurs when molten solder moves into the narrow spaces between the two pieces to be joined, and the size of that gap plays a significant role in the effectiveness of this process. A smaller gap allows for stronger capillary action, which helps draw the solder into the joint due to surface tension.

In addition to surface tension, the physical characteristics of the solder and the metals involved, as well as other variables like temperature, are certainly important. However, those elements do not fundamentally drive the movement of the solder into the joint. Instead, it's the narrowness of the space between the surfaces that directly enhances capillary action, thereby helping create a strong and reliable joint when soldering.