Early Environmental Screening of Spacecraft Electronic Units using Pre-Unit-Level Thermal Testing

Thermal test requirements for United States military spacecraft electronic units are specified in MIL-STD-1540. One of the primary objectives of this testing is to provide an effective stress screening environment for the detection of latent defects in flight hardware. Ideally, stress screening should be accomplished at the earliest test opportunity because late detection of design and workmanship defects can have a significant impact on hardware delivery schedules and program costs. Environmental testing standards, such as MIL-STD- 1540, address screening at the unit level with the specification of test conditions typically more severe than what is expected in flight. When stress screening of electronic units is performed at a pre-unit level of assembly (e.g., printed wire board or slice), the test hardware can be screened more efficiently by detecting defects early, thereby increasing overall test effectiveness. In the latest revision of MIL-STD-1540, pre-unit-level thermal testing of electronic units is an option to the baseline test approach and may result in the relaxation of unit-level thermal test requirements. This paper discusses the implications of pre-unit-level thermal testing of electronic units and how these tests can be designed to effectively meet test objectives.