Magnetic solder to reduce porosity of solder joints formed in microgravity

摘要

Solder joints formed in microgravity are inferior to joints formed in Earth gravity. They are mechanically weaker and less electrically conductive due to voids forming in the joints when soldering in microgravity. Surface tension and lack of gravitational buoyancy combine to prevent flux and water vapors from escaping the molten solder in absence of gravity, resulting in more porous solder joints. Additionally, corrosive flux vapor products remain trapped in the voids causing further deterioration.Parabolic aircraft flight microgravity soldering data are presented, to compare the joint porosities of conventional nonmagnetic solders and new magnetic solders, to determine if the magnetic solder, when soldered in the presence of a magnetic field, would reduce porosity of solder joints formed in microgravity. Soldering irons were used to hand-solder resistor leads into PC board though-holes, for nonmagnetic and magnetic solders. Addition of 4 wt% and 6 wt% of iron microparticles to the solder pastes resulted in 24% and 28% reductions in the solder joint average cross-sectional porosity, respectively, relative to average nonmagnetic solder joint porosity. Joint porosity distributions were log-normal, so the Wilcoxon Rank Sum test for statistical significance was used to show these porosity reductions are statistically significant at alpha = 0.05. A fully-developed wire magnetic solder could enable in-space repair of electronics at the component level, giving space mission planners additional flexibility to eliminate some or all spare board-level electronics, and plan instead to perform electronics repairs at the component level. This could then reduce or eliminate required mass of these spare electronics boards.