Ben Oni, Ph.D., NASA MSFC/Tuskegee University

Trent Griffin, Karen Cunningham, Bob Kapustka, and Steve Luna, NASA MSFC, Huntsville, Alabama 35812

Abstract

Various design and manufacturing standards are generally imposed on space flight hardware development processes with the objective to reduce failure risks. In spite of these standards, some chip scale package (CSP) assemblies and discrete components used in power electronics hardware developments still fail in use and require understanding of the failure mechanisms to establish improved confidence in reliability. Failures of space flight inductors and transformers, developed to MIL-STD 981, were studied. The paper characterized the failures in terms of type, cause, method of detection, and frequency of occurrences.

The principal objective for the characterization was to see if there are correlations between the type of failures and the testing and/or analysis that is or is not performed. If it could be determined that the performance of certain tests and/or analyses on power electronics hardware greatly enhance mission success and that the performance of other tests and/or analyses do not, then one would be able to better advise the customer on which test and/or analysis options would give the best value.

Available records, over the last 32 years, of failure data on space flight inductors and transformers were sought from several sources and analyzed. The sources included the Government Industry Data Exchange Program (GIDEP), NASA Reliability Preferred Practices for Design and Test regarding Lessons Learned Information, Magnetics Manufacturers, and Electronic Screening Houses.

The paper also presents the relative importance of the various MIL-STD 981 tests, as perceived by manufacturers of inductors and transformers.

Conclusions

Based on the available GIDEP data used in this analysis, the following conclusions were made:

1. Magnetic components fail more in the open circuit mode than in the short circuit mode.
   
2. More failures result from manufacturing errors than from design or installation errors.
   
3. Advances in manufacturing technology do not show decline in manufacturing related failures with years.
   
4. More components fail the thermal cycle test than other tests.
   
5. About 20% of failures occur in use.
   
6. Failure occurring in use is caused by a number of reasons; however, insulation breakdown and improper solder joints are more prevalent causes.
   
   On the relative importance of MIL-STD 981 tests as perceived by manufacturers of inductors and transformers, the following conclusions were made:
   
7. Tests performed depend on customer applications.
   
8. Irrespective of application, the majority of magnetics manufacturers consider dielectric and electrical tests as highest priority.
   
9. Seal and radiographic tests were generally considered least critical. It is noted, however, that in some applications, these tests may be absolutely necessary.

The full-length paper is posted on the NEPP Web site. Click here to view.