Solder balls can be observed after wave-, selective- and reflow soldering, yet the mechanisms for their formation are different in each case. In wave-and selective soldering, the balls form during the separation of the withdrawing solder from the joint. If at that moment the solder mask is softened, the danger exists that the balls attach to the soft mask. Solder balls in the reflow process have their origin either in evaporating humidity which had been absorbed by the paste, or through capillary action which is pulling solder particles underneath components. During the drop of the component into the now liquid solder paste, this excessive solder is being pushed out from underneath and forms the balls at the side of the components.