What is the characteristic appearance of a cold tin-lead solder joint?
Dark black spots
A bright or shiny surface
A rough or lumpy surface✓Correct answer
A greenish tinge
Explanation
A cold joint is one where the solder never fully melted and flowed, so it solidifies with a dull, rough or lumpy surface instead of the smooth shiny fillet of a properly heated tin-lead joint. Such a joint may look connected while being mechanically and electrically unreliable.