Which of the following can cause a Cold Solder Connection?

A cold solder connection typically occurs when the solder does not melt properly and fails to create a good bond between the components and the solder pad. Excessive impurities in the solder can significantly contribute to this issue. When there are too many impurities, they can interfere with the solder's ability to flow and adhere properly, leading to weak joints that may not conduct electricity effectively.

In contrast, using high-quality solder material, thorough cleaning, and appropriate heat application during the soldering process are practices that help ensure a proper solder joint is formed. High-quality solder typically has better melting characteristics and bonding capabilities, while sufficient cleaning removes contaminants that could inhibit solder flow. Appropriate heat application ensures that the solder melts correctly without overheating the components or pads.