Soldering in Reduced Gravity Experiment, SDTO 17003-U (SoRGE) - 07.29.14
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The Soldering in Reduced Gravity Experiment (SoRGE) will examine solder joints created in microgravity. Recent simulated microgravity (aboard the KC-135 and C-9B reduced gravity aircraft) testing has shown that, on average, solder joints produced in microgravity (space) exhibit approximately 3-times more voids (defects) compared with those produced in normal gravity (Earth). Without gravity, gas bubbles (from solder flux or water vapor) form pores or void defects in solder joints and can reduce their strength. For SoRGE operations, crewmembers will be soldering small electronic components using the ISS soldering iron to validate the results observed in C-9B aircraft testing, including potential mitigation techniques for reducing solder joint voids.
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ZIN Technologies Incorporated, Cleveland, OH, United States
National Center for Space Exploration Research, Cleveland, OH, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
September 2006 - April 2007
Previous ISS Missions
SoRGE is a new investigation for ISS research.
- Testing of soldering in simulated microgravity (aboard the reduced gravity aircraft) and microgravity showed significant increases in void defect formation within the solder joint. Such defects can reduce solder joint strength and thus long-term reliability. For future long-duration space missions where soldering may be required for electronics repair, techniques for mitigating void formations must be established.
- SoRGE will verify the findings from the aircraft studies and will also examine several techniques which may mitigate the formation of voids in the solder joints.
- SoRGE test kits are comprised of a series of small circuit cards, with small electrical components attached to the surface. These components, which were brought to the ISS on STS-115/12A, will be soldered in microgravity and then returned to Earth. Upon return, the solder joints will be examined to determine the amount of voids in each joint. The results of this research will be used to help guide potential repair strategies for future long-duration space missions.
Current electronics maintenance procedures aboard the International Space Station (ISS) call for the replacement of failed hardware instead of repair. This strategy relies on re-supply flights from Earth to provide the replacement units. Since this logistical support may not be easily available for future exploration missions beyond low Earth orbit, repairing electronics at the lowest component level will potentially ease the logistical burden by minimizing the upmass and volume of required spares.
Soldering in Reduced Gravity Experiment (SoRGE) involves soldering small electronic components in reduced gravity aboard the ISS. SoRGE uses the soldering kit currently aboard the ISS and seeks to quantitatively examine the effects of microgravity on the soldering process. This experiment is the next step in a systematic study of soldering in microgravity, following normal gravity studies and reduced gravity studies aboard NASA's reduced gravity aircraft.
Earlier studies showed two primary differences between joints produced in normal gravity and microgravity, including external geometric differences, and a greatly increased amount of voids in the simulated microgravity samples (about three times the normal Earth gravity in reduced gravity). The changes in geometric shape are due to the dominance of surface tension in microgravity, where body forces are not acting on the mass of molten solder. The increase in void fraction during microgravity is due to the lack of buoyant forces on flux and water vapor that are present in the molten solder and are inherent to the soldering process. These entrapped gasses, the presence of which is due to the need for flux in the soldering process, and from water vapor evolving from the circuit board itself during the soldering process, are normally transported to the joint surface and eliminated while the joint is molten during normal gravity soldering operations.
The amount of porosity in soldered samples is anticipated to be even greater when conducted in the microgravity environment of the ISS when compared with the aircraft results. This is because the "noisy" acceleration environment aboard the aircraft (from atmospheric turbulence, airframe vibrations, etc.) is believed to have provided some residual buoyant forces that may have helped drive out some of the bubbles, prior to the solidification of the joint. Strategies for mitigating the formation of voids in the solder joint will also be tested during SoRGE. Certain techniques showed considerable promise during extensive ground and aircraft testing, but must be proven in the true microgravity environment of the ISS before use during future long-duration space exploration missions.
After flight operations aboard the ISS, the samples (as well as the video recording of the soldering operations) returned to the investigators for analysis using both non-destructive CT-scanning techniques using X-ray, and industry-standard internal metallographic examination methods.
The current strategy for electronics maintenance aboard the ISS calls for replacement of Orbital Replacement Units (ORU's) and relies on re-supply flights from Earth to provide the replacement units. This logistical support may not be easily available for future exploration missions beyond low earth orbit. Repairing electronics at the lowest component level could ease the logistical burden by minimizing the upmass and volume of required spares. Before such a strategy can be adopted, data must be gathered about the practicality of performing such repairs in microgravity. This includes understanding how the physical processes (such as soldering) are affected by the microgravity environment. SoRGE is the next step in understanding the role that reduced gravity plays in the repair of electronic components.
Through better understanding of the inherent physics, the study of soldering in space could lead to better soldering techniques on Earth.
SoRGE is being conducted in the ISS Maintenance Work Area (MWA), which serves to contain any contaminants created during the soldering procedure. The soldering iron (already on board the ISS), uses a rechargeable battery and can heat up to 315.6 degrees C (600 degrees F). The ISS video camera will be positioned to captue video of the soldering of the SoRGE samples. After soldering is complete, the samples and video will be stowed on the ISS and returned to Earth for detailed examination and analysis.
For SoRGE operations crewmembers will setup the MWA, the SoRGE hardware will be placed inside the MWA, and the ISS video camera will be positioned to capture video of the solder operations. Crewmembers will then solder one circuit board with 32 solder joints. There are 3 different types of test kits (12 kits total) provided with the experiment; each test kit contains a different type of solder and/or flux. Upon completion of a kit, the crewmember may continue to another kit or continue at a later time. Concluding the investigation the crewmember will clean up and stow the MWA. Results of this experiment will be used to guide soldering techniques for future space missions.
Ground Based Results Publications
Pettegrew RD, Struk PM, Watson JK, Haylett DR, Downs RS. Gravitational Effects on Solder Joints. Welding Journal. 2003; 82(10): 44-48.
Easton JW, Struk PM, Rotella A. Imaging and Analysis of Void-Defects in Solder Joints Formed in Reduced Gravity Using High-Resolution Computed Tomography. 46th Aerospace Sciences Meeting and Exhibit, Reno, NV; 2008
Advanced Capabilities Project Office - Component-Level Electronics-Assembly Repair
Researchers conducting solder testing aboard the reduced gravity research aircraft. Image courtesy of NASA.
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Side-view of a solder joint before (left) and after metallographic sectioning (right). The right image shows significant void defect formation within this solder joint produced on the reduced gravity research aircraft. Image courtesy of NASA.
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Soldering operations on reduced gravity research aircraft similar to those to be conducted aboard the ISS. Image courtesy of NASA.
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NASA Image - ISS015E06769: Astronaut Suni Williams performs the Soldering in Reduced Gravity Experiment (SoRGE) in the Maintenance Work Area (MWA). SoRGE will examine how the microgravity environment affects soldering joints.
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NASA Image - ISS015E06764: This image shows the samples that were used during the SoRGE investigation. SoRGE will examine how the microgravity environment affects soldering joints.
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