What is the characteristic appearance of a cold tin-lead solder joint?
The correct answer is C: A rough or lumpy surface. A cold tin-lead solder joint has a rough or lumpy surface appearance. Cold solder joints occur when the solder doesn't fully melt and flow, often due to insufficient heat, contaminated surfaces, or moving the joint before the solder solidifies. The result is a dull, grainy, rough surface instead of the smooth, shiny appearance of a good joint. For amateur radio operators, recognizing cold solder joints is important for quality workmanship and reliable connections. Cold joints are weak, have high resistance, and can cause intermittent connections or failures.
Exam Tip
Cold joint = rough or lumpy surface. Think 'C'old joint = 'C'ourse (rough) surface. Good joints are smooth and shiny. Cold joints are dull, rough, and grainy due to incomplete melting.
Memory Aid
"Cold joint = rough or lumpy surface. Think 'C'old joint = 'C'ourse (rough) appearance. Dull, grainy, lumpy surface indicates incomplete melting. Good joints are smooth and shiny."
Real-World Application
You solder a connection but the iron wasn't hot enough. The solder didn't fully melt and flow, creating a cold joint. The surface looks rough and lumpy instead of smooth and shiny. This joint has high resistance and may fail. Reheating with proper temperature creates a smooth, shiny joint that's reliable.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Dark black spots indicate burned flux or contamination, not necessarily a cold joint. Cold joints are rough, not necessarily black.
Option B: Incorrect. A bright or shiny surface indicates a good, properly made solder joint. Cold joints are dull and rough, not shiny.
Option D: Incorrect. Excessive solder (a blob) might indicate poor technique but doesn't necessarily mean a cold joint. Cold joints are characterized by rough texture, not necessarily excess solder.
题目解析
The correct answer is C: A rough or lumpy surface. A cold tin-lead solder joint has a rough or lumpy surface appearance. Cold solder joints occur when the solder doesn't fully melt and flow, often due to insufficient heat, contaminated surfaces, or moving the joint before the solder solidifies. The result is a dull, grainy, rough surface instead of the smooth, shiny appearance of a good joint. For amateur radio operators, recognizing cold solder joints is important for quality workmanship and reliable connections. Cold joints are weak, have high resistance, and can cause intermittent connections or failures.
考试技巧
Cold joint = rough or lumpy surface. Think 'C'old joint = 'C'ourse (rough) surface. Good joints are smooth and shiny. Cold joints are dull, rough, and grainy due to incomplete melting.
记忆口诀
Cold joint = rough or lumpy surface. Think 'C'old joint = 'C'ourse (rough) appearance. Dull, grainy, lumpy surface indicates incomplete melting. Good joints are smooth and shiny.
实际应用示例
You solder a connection but the iron wasn't hot enough. The solder didn't fully melt and flow, creating a cold joint. The surface looks rough and lumpy instead of smooth and shiny. This joint has high resistance and may fail. Reheating with proper temperature creates a smooth, shiny joint that's reliable.
错误选项分析
Option A: Incorrect. Dark black spots indicate burned flux or contamination, not necessarily a cold joint. Cold joints are rough, not necessarily black. Option B: Incorrect. A bright or shiny surface indicates a good, properly made solder joint. Cold joints are dull and rough, not shiny. Option D: Incorrect. Excessive solder (a blob) might indicate poor technique but doesn't necessarily mean a cold joint. Cold joints are characterized by rough texture, not necessarily excess solder.
知识点
Cold solder joints, Solder joint appearance, Soldering quality, Connection reliability
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.