ISS: Collaborative Research: Acoustic Wave Manipulation of Solder-Joint Defects in Reduced-Gravity Environments

University Of Arizona, Tucson AZ

Investigators

Abstract

The strength of solder joints can be reduced by pores caused by bubbles trapped during the soldering process. Small bubbles are especially likely to be trapped because their buoyancy is relatively weak, especially in reduced-gravity environments; hence, they do not quickly rise to the surface. This research project will explore acoustic waves as a means of quickly expelling small bubbles from molten solder. Acoustic methods have been used successfully in other situations, e.g. to remove bubbles from cell culture media. This project will transplant those methods to molten solder. Experiments in microgravity will allow acoustically driven bubble motion to be isolated from the effects of buoyancy-driven motion. These data will be used to validate simulations of bubble motion and improve future predictions of the same. The results look to speed up soldering operations and reduce the heat energy needed to keep the solder molten. Additional benefits will come from training next-generation aerospace and mechanical engineers. Experiments in space research provide excellent outreach opportunities targeting high-school students. This project aims to develop an acoustics-assisted soldering technique and identify the optimal acoustic parameters (e.g., power, frequency, and activation duration) for effective bubble removal. An acoustic transducer will be used to generate waves within molten solder, actively displacing bubbles. This looks to significantly improve the mechanical strength and thermal/electrical conductivity of soldered joints. Experiments in microgravity aboard the International Space Station (ISS) will eliminate the effects of buoyancy and natural convection. These results will be compared against ground-based experiments, thus decoupling the effects of buoyancy vs. acoustically-driven bubble dynamics. All experiments will be guided by thermal-acoustofluidics simulations, and experimental results will, in turn, be used to validate simulations. This project seeks to expand the application of acoustic manipulation of matter from traditional gels and colloidal materials to molten metals. The knowledge gained from this project intends to benefit manufacturing industries such as automotive, aerospace, and semiconductors, where defects in soldering processes have impeded device performance and jeopardized the longevity of mechanical structures. Beyond benefits on Earth, the microgravity experiments look to also help soldering operations in space, which are important for the emerging industry of space-based manufacturing. Beyond technological benefits, the project will also train students in advanced manufacturing methods and conduct outreach from pre-college to graduate levels. Experiments on the ISS provide an attractive vehicle to communicate the excitement of research, especially to younger students. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.