A proper solder joint looks smooth, shiny, and slightly concave, while a cold joint often looks dull, grainy, or uneven. You might also see cracks or gaps where the solder didn't bond well. Tilting the board under light helps reveal surface texture and any hidden flaws. ● Texture: A good joint is smooth and shiny (especially with SnPb solder). It usually occurs in hand-soldering or repair work. A cold solder joint forms when the solder does not properly bond the component lead to the pad—typically due to inadequate heat, oxidation, or poor technique. Imagine your production line is running smoothly, but your latest batch. A cold solder joint happens when there is improper bonding between a solder and a solder-surface interface because of either incomplete melting or lack of fusion of the solder. Joints obtained through this process. When solder doesn't melt properly during soldering because of not heat from the solder wire or iron or when the connection is disturbed before the solder sets correctly its called a cold solder joint issue. This can lead to a connection, between PCB components, which might look dull and rough.
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