What is a characteristic appearance of a cold tin-lead solder joint?

• A. A rough or lumpy surface
• B. A smooth and shiny surface
• C. A clear and transparent surface
• D. A dull and even surface

Answer: (A)

A characteristic appearance of a cold tin-lead solder joint is a rough or lumpy surface. This type of joint occurs when the solder does not melt adequately or fails to fuse properly with the components being joined. The insufficient heat results in poor adhesion, which manifests as a non-uniform, often uneven surface texture. This roughness is a visual indication that the solder has not flowed properly, leading to a weak joint that may not provide reliable electrical conductivity.

When solder joints form properly, they should generally appear smooth and shiny, indicating a good bond between the solder and the surfaces being connected. A clear and transparent surface is not typical of any solder joint, as solder is opaque. A dull and even surface may suggest a properly cooled joint but does not convey the incorrect cooling or melting issues associated with cold solder joints. Therefore, recognizing the rough or lumpy texture is critical for identifying potential problems in soldering techniques.