Ultrasonic soldering uses either ultrasonically coupled heated solder iron tips (0.5—10 mm) or ultrasonically coupled solder baths. In these devices, piezoelectric crystals are used to generate high frequency (20—60 kHz) acoustic waves in molten solder layers or batch, to mechanically disrupt oxides that form on the molten solder surfaces. The tips for ultrasonic soldering irons are also coupled to a heating element while the piezoelectric crystal is thermally isolated, in order to prevent degradation of the piezoelectric element. Ultrasonic soldering iron tips can heat (up to 450 °C) while mechanically oscillating at 20—60 kHz. This soldering tip can melt solder filler metals as acoustic vibrations are induced in the molten solder pool. The vibration and cavitation in the molten solder then permits solders to wet and adhere to many metal surfaces.

The acoustic energy created by the solder tip or ultrasonic solder pot works via cavitation of the molten solder which mechanically disrupts oxide layers on the solder layers themselves and on metal surfaces being joined.

Cavitation in the molten solder pool can be very effective in disrupting the oxides on many metals, however, it is not effective when soldering to ceramics and glass since they themselves are oxides or other non-metal compound that cannot be disrupted since they are the base materials. In the cases of soldering direct to glasses and ceramics, ultrasonic soldering filler metals need to be modified with active elements such as In, Ti, Hf, Zr and rare earth elements (Ce, La, and Lu). Solders when alloyed with these elements are called active solders since they directly act on the glass/ceramic surfaces to create a bond.