Which is a common sign of overheating a solder joint?

A common sign of overheating a solder joint is discoloration. When solder is overheated, the heat can alter the physical and chemical properties of the solder material, which often results in a change in color. This discoloration typically presents as a dull, darkened surface or a varied hue, indicating that the material has been subjected to excessive temperatures.

Bubbles can also form in the solder joint when it is overheated, as they reflect the presence of gas that has been released due to the excessive heat. Cracking can happen as well, as the thermal stress may lead to fractures in the joint. However, discoloration is the most direct and visually identifiable indication of overheating, making it a key sign that one should monitor during soldering processes.

The presence of the other signs, like bubbles and cracking, does indicate overheating, but discoloration is often the first noticeable effect and is associated specifically with the degradation of the solder itself. This makes it an important aspect to look for when evaluating the quality of a solder joint.