The design of a precision bilaminar resonating transducer assembly tool

The performance of bilaminar resonating transducers depends on the thickness and uniformity of the transducer's bond layers. Optimal resonant performance requires a bond thickness between the crystals of ≤5 μm. In addition, a later product assembly step requires precise alignment between each of the transducer components. This article describes a precision tool, designed and built for an industrial sponsor, for assembling these transducers. The tool consists of a screen printer and a press. The screen printer includes a stencil and a powered squeegee cart that rides on a bearing rail. The press contains a bellows that applies pressure, as well as two vacuum heads that hold transducer components in place while pressure is applied. Precision design techniques, such as the use of kinematic couplings and flexures, were used throughout the tool. Bond thicknesses of assembled transducers were evaluated by inspecting each transducer's cross-section with a scanning electron microscope. Preliminary results in indicate that the requirement for a bond thickness of <5 μm was easily achieved; most thicknesses were an optimal 1 μm.