Substrate cassette for ultrasonic cleaning

Abstract

A cassette for supporting electrical component substrates in a megasonic processing bath includes a pair of end panels spaced apart longitudinally, a pair of side rails extending longitudinally along opposed sides of the substrate cassette, and at least one bottom support extending between lower portions of the end panels. The supports include a plurality of shallow channels extending laterally therein and spaced regularly therealong to receive edge portions of the substrates. The side rails and bottom supports of the cassette are all formed of plate components that are dimensioned to transmit the maximum amount of the megasonic energy projected into the processing bath, so that the components do not cause sound-shadowing of the substrates supported in the cassette. The side rails and bottom supports are formed of narrow plates having a thickness equal to an integer multiple (i.e., 1, 2, 3, etc.) or an even fractional (i.e., ½, ¼, etc.) number of wavelengths of the ultrasonic energy in the material that comprises the side rails and bottom supports. The wavelength matching dimensions of the structural components couples the sound energy into the quartz to a maximum extent, and it is transmitted through the quartz to the liquid bath as well as to the substrates supported by the structural components. In addition, the narrow plate components may be tilted to be non-horizontal to shed detrimental bubbles that may form in the liquid of the megasonic bath.