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Cool Tech: Flux Free Soldering

June 24, 2010
EWI has made rapid advances in developing fluxless ultrasonic soldering technology as well as develop a cost-effective Pb-free solder that could potentially help make soldering more environmentally friendly. Conventional soldering be it manual, reflow or wave, requires the use of flux to prevent the formation of surface oxides and to enable wetting of the solder to the base materials.  These fluxes are all very acidic and are difficult to work with and to dispose. In contrast, ultrasonic soldering is a fluxless joining process which consists of introducing high-frequency vibrations through a solder tool into the molten solder and inducing a cavitation action at the tool tip.  By using ultrasonics the oxide layer of the bonding surface is disrupted and removed by cavitation and not by the use of any fluxing agent.

Elimination of flux, leads to many associated benefits during soldering (1) Elimination of corrosion caused by flux entrapment (2) Elimination of hazardous exposure, clean-up issues, and reduction of material costs; (3) Elimination of post-solder cleaning operations and cleaning material costs; (4) Maintaining dielectric constant of solder joints, and (5) Improved wetting inside sharp corners and small crevices. In addition, ultrasonic soldering obviates the use of platings/metallization on difficult-to-wet materials.

EWI has also developed and patented a Pb-free Sn-Al solder, SonicSolderTM designed to work effectively with ultrasonic soldering.  This solder has similar properties as a standard commercially available Pb-free solder like Sn-Ag-Cu but without the presence of the expensive Ag in its composition.  Furthermore, in combination with ultrasonics, this solder enables wetting onto difficult-to-wet materials like glass, ceramics, carbonaceous materials, etc without the need for metallization/platings.  The video below demonstrates wetting of solder onto glass.

Posted by Mark Norfolk

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