Flux-less direct soldering of aluminum by ultrasonic surface activation

Abstract

Effective flux-less soldering of aluminum has been realized in a process that combines ultrasonic abrasive activation of aluminum surface and subsequent reflowing. In this method, a sheet of solder sprinkled with a controlled amount of fine alumina powder is placed against aluminum surface and subjected to in-plane ultrasonic vibration under low clamping pressure (20MPa) at room temperature for a short duration (∼1s). This disrupts the oxide on the aluminum surface and purges oxygen from the solder-aluminum interface. Subsequent reflow melts the solder on the activated aluminum surface, forming a metallurgically bonded aluminum-solder joint upon cooling. No pre-treatment of aluminum surface or atmosphere control is required. Optimally joined Aluminum 1100-SN100C joints were free of defects at interface and showed joint strengths (45–48MPa) that are comparable with that of Sn-base solder joints.