Solder balls are small spheres of solder that form around solder joints during reflow. They can cause short circuits and reliability issues.
Common causes: solder paste oxidation, incorrect reflow profile, excessive paste deposition, component placement pressure, and solder paste splattering during reflow.
Solutions: Use fresh solder paste, optimize the reflow profile (prevent too-fast ramp rates), reduce paste volume, and ensure proper stencil printing.