NASA Glenn Research Center's Component Level Electronic Assembly Repair (CLEAR) task is helping to enable future astronauts to repair electronics down to the component level (e.g., resistors, capacitors, and integrated circuits) in spacecraft or future habitats. CLEAR is a supporting task under a project called Supportability, which is part of NASA’s Exploration Technology Development Program. Locally at Glenn, CLEAR is supported by the National Center for Space Exploration Research as well as the ASRC Aerospace Corporation.
Plated-through-the-hole sample configuration used during reduced-gravity testing.
Two resistor lead diameters were used—0.66 and 0.78 mm.
Although CLEAR is looking at all aspects of repair, a key element of the repair process is soldering. From 2000 to 2005, a series of aircraft tests investigated how reduced gravity affected the soldering of small electrical components (see the preceding diagram). This work showed that reduced gravity leads to a significant increase in voids, or porosity, in the joint (ref. 1). These voids (see the following images) come from entrapped vaporized flux, which is part of the soldering process, or water vapor in the circuit board. These gases form bubbles that are driven to the surface by buoyant forces in normal gravity. In reduced gravity they are slowed, becoming trapped and frozen in the final joint. A void in a solder joint can be detrimental to performance, but the use of an externally applied liquid flux and a solid-core solder showed promise as a potential void-mitigation technique (see the table).
Solder was applied to the joint from the top of solder joint as oriented in the images.
This joint shows significant subsurface voids (18.8-percent voiding). Left: Joint after
soldering in reduced gravity. Center: Joint after cross sectioning. Right: Joint after
computer analysis.
|
Test conditiona | OgE | O.10gE |
O.17gE (Moon) |
O.38gE (Mars) | 1gE |
|---|---|---|---|---|---|
| Flux-core solder | |||||
| 11.0±2.38 | 9.27 | 7.75 | 5.41 | 3.21±1.17 | |
| 77 | 11 | 16 | 18 | 102 | |
| Solid solder—liquid fluxb | |||||
| 6.64±1.24 | N/A | 6.44 | 8.53 | 2.75±0.64 | |
| 153 | 7 | 7 | 111 | ||
| aEarth gravity, gE = 9.8 m/sec. | |||||
| bThe solid-solder—liquid-flux data represent a void-mitigation technique (ref. 1). | |||||
Astronaut Suni Williams conducted a similar experiment—the Soldering in Reduced Gravity Experiment (SoRGE)—aboard the International Space Station (ISS), using the soldering kit available on orbit (see the following photograph). The soldered circuit boards were returned to Earth aboard the Space Shuttle Endeavor in August 2007 and are being analyzed at Glenn. SoRGE intends to verify the initial findings from the aircraft studies and to examine several techniques that may mitigate the formation of voids in the solder joints. These results will be used to help guide repair strategies for future long-duration missions.
Suni Williams performs the SoRGE experiment in the ISS Maintenance Work Area
during Expedition 14. The area will be configured similarly for CRE-1 operations.
A follow-on experiment, Component Repair Experiment-1 (CRE-1), is under development by the CLEAR team to demonstrate methods for crewmembers to conduct board-level electronic repairs within a spacecraft. CRE-1 will focus on the physical processes of a manual electronics repair including (1) conformal coating removal, (2) component removal, (3) board cleaning, (4) component soldering, and (5) conformal coating reapplication on a modern circuit card (see the final photograph). Currently, NASA flight crews recover from electronic faults by replacing entire electronic assemblies, or Orbital Replacement Units (ORUs). A faulty ORU is replaced with a spare, and the defective unit is returned to Earth for diagnosis and repair. Because an ORU strategy is more challenging for long-duration missions beyond Earth orbit, component-level repair may be required for future exploration missions.
Test card for the CRE-1 experiment on which crew members
will attempt to remove and replace components (including
conformal coating). The components include both through-the-hole
and surface-mount device technology and both standard and
fine-pitch lead spacing. The board is coated with silicone.
Find out more about this research:
CLEAR Project at Glenn:
http://exploration.grc.nasa.gov/Exploration/Advanced/Capabilities/Clear/
SoRGE:
http://exploration.nasa.gov/programs/station/SoRGE.html
Last updated: October 31, 2008
Responsible NASA Official:
Gynelle.C.Steele@nasa.gov, 216-433-8258
Point of contact for NASA Glenn's Research & Technology reports: Cynthia.L.Dreibelbis@nasa.gov, 216-433-2912
Web page curator: Nancy.L.Obryan@nasa.gov (Wyle Information Systems, Inc.)
