What is the ideal joint design for soldering?

The ideal joint design for soldering emphasizes clean surfaces along with an appropriate gap to promote capillary action. Capillary action is the phenomenon where liquid solder is drawn into the joint through narrow spaces, creating a strong bond between the materials. For optimal soldering, it is essential that the surfaces being joined are free of contaminants, such as dirt, oil, or oxidation, which can inhibit the solder's ability to flow properly.

A slight gap between the materials is also crucial since it allows the solder to enter the joint effectively. When the solder is applied to the joint, the heat causes it to flow into these small spaces, ensuring a good mechanical and electrical connection. Therefore, the combination of clean surfaces and a suitable gap leverages capillary action to produce a robust soldered joint. This principle is fundamental in soldering practice, making option C the correct choice.