Abstract: A method and apparatus for cleaning printed electrical circuit boards having surface mount components by ultrasonic energy in the frequency range between 300 kHz and 1.0 MHz. The ultrasonic energy is produced by an array of piezoelectric wafers mounted to the inside surface of an immersible transducer assembly which, in turn, is disposed in a tank accomodating a bath of cleaning liquid. The ultrasonic energy provided by the transducer assembly and the circuit board to be cleaned are disposed to cause the ultrasonic wave beam to be incident upon a board to be cleaned at an angle of 90.+-.60 degrees relative to the surface plane of the board. This arrangement will remove solder flux residue and other contaminants from spaces ranging from 0.001 to 0.010 inch present underneath a surface mount component.