Research Of Solder Wetting In Aluminum Alloy Ultrasonic Soldering

Aluminum alloy has been widely used in industry due to its excellent performance of heat conduction and conductivity. But the existence of oxide film, which hinders the welding between aluminum alloy, leads to poor weldability. However, the emergence of ultrasonic soldering provides a new solution for the welding of aluminum alloy. The greatest advantage of this technique is that ultrasonic can remove the oxide film without flux in aluminum ultrasonic soldering. The removal of the oxide film has a strong connection with the solder wetting effect, in order to have a better understanding of those factors that have an influence on wetting effect, this thesis conducted the following research: 1. The influence of ultrasonic constraint structure on solder wetting process. 2. The wetting optimal parameters on 1060 aluminum alloy surface during coating process, in which we used pure Sn solder and Sn-9Zn solder respectively. The conclusions developed in this thesis are helpful to understand how parameters influenced the wetting effect and useful for the application of aluminum ultrasonic surface coating technique.In our study we found that, with open constraint structure solder could spread under 9 μm ultrasonic amplitude. However, with "sandwich" structure solder could spread under 5 μm ultrasonic amplitude. The “sandwich” structure could help make the most of the ultrasonic energy, and the reflected wave reinforced the cavitation effect,so in "sandwich" structure liquid solder spread on aluminum alloy surface with smaller ultrasonic amplitude. Through the experiment and the analysis above we verified that the “sandwich” structure had a positive effect on solder spreading.In the wetting process we found that, either for pure Sn solder or Sn-9Zn solder if the ultrasonic amplitude was too small or too large it would both have a negative influence on solder wetting. When the ultrasonic amplitude was too small, there would be residual oxide film preventing wetting process. When the amplitude was too large, the solder splash would increase significantly. At the same time, the ultrasonic time also had a big influence on coating effect. When the time was too short, the interface had some non-wetting zones. When the time was too long, the interface’s structure fluctuation and the amount of solder splash increased evidently. So only using the optical parameters could we gained the ideal wetting result and achieved high strength and thermal reliability coating layer(before and after aging the strength of Sn coating were 33 MPa and 25 MPa respectively while the strength of Sn-9Zn were 35 MPa and 29 MPa). As a result, exploring the wetting’s optical parameters has great significance for the promotion of this technology.