Why is it important to clean the surfaces before soldering?

Cleaning the surfaces before soldering is vital primarily to ensure a strong joint. When surfaces are not clean, contaminants such as oil, dirt, oxide layers, or other impurities can prevent the molten solder from properly wetting the metal surfaces. This inadequate wetting leads to poor adhesion between the solder and the base materials, resulting in weak joints that may fail under stress or thermal cycling.

A strong joint is essential for the integrity and durability of the assembly being soldered, as it directly affects the electrical, thermal, and mechanical properties of the connection. Clean surfaces allow for optimal chemical bonding and physical interlocking, which are crucial in achieving a reliable solder joint.

While rust formation and aesthetics are considerations in some contexts, they do not encompass the primary reason for cleaning in the soldering process. Similarly, while cleaning might have an impact on the speed of the process, efficiency is not the main focus; the integrity and strength of the joint is paramount.