Ultrasonic soldering

Ultrasonic soldering is a flux-less soldering process that uses ultrasonic energy, without the need for chemicals to solder materials, such as glass, ceramics, and composites, hard to solder metals and other sensitive components which cannot be soldered using conventional means. Ultrasonic (U/S) soldering, as a flux-less soldering process, is finding growing application in soldering of metals and ceramics from solar photovoltaics and medical shape memory alloys to specialized electronic and sensor packages. U/S soldering has been reported since 1955 as a method to solder aluminum and other metals without the use of flux.

Ultrasonic soldering is a distinctly different process than ultrasonic welding. Ultrasonic welding uses ultrasonic energy to join parts without adding any kind of filler material while ordinary soldering uses external heating to melt filler metal materials, namely solders, to form a joint. Ultrasonic soldering can be done with either a specialized soldering iron or a specialized solder pot. In either case the process can be automated for large-scale production or can be done by hand for prototyping or repair work. Initially, U/S soldering was aimed at joining aluminum and other metals; however, with the emergence of active solders, a much wider range of metals, ceramics and glass can now be soldered.

Ultrasonic soldering uses either ultrasonically coupled heated solder iron tips (0.5 – 10 mm) or ultrasonically coupled solder baths as mentioned above. 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 U/S soldering irons are also coupled to a heating element while the piezoelectric crystal is thermally isolated, not to degrade 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.

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Wikipedia