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Why can ultrasonic soldering be performed without soldering flux?
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Ultrasonic soldering does not require flux because the process uses high-intensity ultrasonic vibrations to perform the necessary surface cleaning.1
In standard soldering, flux is required to remove oxide films and prevent reoxidation to ensure proper wetting of the surfaces. However, in ultrasonic soldering, the vibrations effectively break down and remove these oxide layers—even on difficult materials like aluminum—directly at the site of the joint. By creating an extremely clean surface free from oxidation through mechanical action, the need for chemical flux to prepare the metal is eliminated.231