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Dross Short
A solder whisker or dross short can be found after soldering due to either a poorly maintained solder bath or incorrectly set exit section of the Lambda wave. If a solder bath is poorly maintained, dross can be present in the ducting below the solder surface. When the wave operates any dross can emerge randomly in the wave and contact the board. In the case of the back flow on a lambda wave the solder should flow at the same speed as the board. The board displaces any surface oxides on the surface of the wave before it can contact the base of the board. If the wave drops the board will contact the surface oxide.