What can wiping a joint while it is still hot cause in the bond between the solder and the base metal?

Wiping a joint while it is still hot can lead to the development of a crack in the bond between the solder and the base metal. When the joint is heated, the solder melts and flows into the joint, forming a bond with the base metal. However, if you disturb or wipe the joint while it's still hot, you can cause the solder to cool unevenly. This rapid cooling can introduce stress and create a crack, compromising the integrity of the joint.

It's crucial to allow the solder to cool and solidify completely before handling the joint. This ensures a strong and durable bond, as both the solder and base metal will have time to settle and form a proper joint without introducing stressors that can lead to cracks.