Significance and Use
4.1 This practice was written primarily to guide test participants in establishing, identifying, maintaining, and using suitable environments for conducting high quality neutron tests. Its development was motivated, in large measure, because inadequate controls in the neutron-effects-test process have in some past instances resulted in exposures that have differed by factors of three or more from irradiation specifications. A radiation test environment generally differs from the environment in which the electronics must operate (the operational environment); therefore, a high quality test requires not only the use of a suitable radiation environment, but also control and compensation for contributions to damage that differ from those in the operational environment. In general, the responsibility for identifying suitable test environments to accomplish test objectives lies with the sponsor/user/tester and test specialist part of the team, with the assistance of an independent validator, if available. The responsibility for the establishment and maintenance of suitable environments lies with the facility operator/dosimetrist and test specialist, again with the possible assistance of an independent validator. Additional guidance on the selection of an irradiation facility is provided in Practice F1190.
4.2 This practice identifies the tasks that must be accomplished to ensure a successful high quality test. It is the overall responsibility of the sponsor or user to ensure that all of the required tasks are complete and conditions are met. Other participants provide appropriate documentation to enable the sponsor or user to make that determination.
4.3 The principal determinants of a properly conducted test are: (1) the radiation test environment shall be well characterized, controlled, and correlated with the specified irradiation levels; (2) damage produced in the electronic materials and devices is caused by the desired, specified component of the environment and can be reproduced at any other suitable facility; and (3) the damage corresponding to the specification level derived from radiation environments in which the electronics must operate can be predicted from the damage produced by the test environment. In order to ensure that these requirements are met, system developers, procurers, users, facility operators, and test personnel must collectively meet all of the essential requirements and effectively communicate to each other the tasks that must be accomplished and the conditions that must be met. Criteria for determining and maintaining the suitability of neutron radiation environments for 1-MeV equivalent displacement damage testing of electronics parts are presented in Section 5. Mandatory requirements for test consistency in neutron displacement damage testing of electronic parts are presented in Section 5. Additional background material on neutron testing and important considerations for gamma dose and dose rate effects are presented in (non-mandatory) Appendix X1 and Appendix X2, but compliance is not required.
4.4 Some neutron tests are performed with a specific end application for the electronics in mind. Others are performed merely to ensure that a 1-MeV-equivalent-displacement-damage-specification level is met. The issues and controls presented in this practice are necessary and sufficient to ensure consistency in the latter case. They are necessary but may not be sufficient when the objective is to determine device performance in an operational environment. In either case, a corollary consistency requirement is that test results obtained at a suitable facility can be replicated within suitable precision at any other suitable facility.
4.4.1 An objective of radiation effects testing of electronic devices is often to predict device performance in operational environments from the data that is obtained in the test environments. If the operational and test environments differ materially from each other, then damage equivalence methodologies are required in order to make the required correspondences. This process is shown schematically in Fig. 1. The part of the process (A, in Fig. 1) that establishes the operational neutron environments required to select the appropriate 1-MeV-equivalent specification level, or levels, is beyond the scope of this practice. However, if a neutron spectrum is used to set a 1 MeV equivalent fluence specification level, it is important that the process (B, in Fig. 1) be consistent with this practice. Damage equivalence methodologies must address all of the important contributors to damage in the operational and test environments or the objectives of the test may not be met. In the mixed neutron-gamma radiation fields produced by nuclear reactors, most of the permanent damage in solid-state semiconductor devices results from displacement damage produced by fast neutrons through primary knock-on atoms and their associated damage cascades. The same damage functions must be used by all test participants to ensure damage equivalence. Damage functions for silicon and gallium arsenide are provided in the current edition of Practice E722 (see Note 1). At present, no damage equivalence methodologies for neutron displacement damage have been developed and validated for semiconductors other than silicon and gallium arsenide.
4.4.2 If a 1-MeV equivalent neutron fluence specification, or a neutron spectrum, is provided, the damage equivalence methodology, shown schematically in Fig. 1, is used to ensure that the correct neutron fluence is provided and that the damage in devices placed in the exposure position correlates with the displacement energy from the neutrons at that location.
Scope
1.1 This practice sets forth requirements to ensure consistency in neutron-induced displacement damage testing of silicon and gallium arsenide electronic piece parts. This requires controls on facility, dosimetry, tester, and communications processes that affect the accuracy and reproducibility of these tests. It provides background information on the technical basis for the requirements and additional recommendations on neutron testing.
1.2 Methods are presented for ensuring and validating consistency in neutron displacement damage testing of electronic parts such as integrated circuits, transistors, and diodes. The issues identified and the controls set forth in this practice address the characterization and suitability of the radiation environments. They generally apply to reactor sources, accelerator-based neutron sources, such as 14-MeV DT sources, and 252Cf sources. Facility and environment characteristics that introduce complications or problems are identified, and recommendations are offered to recognize, minimize or eliminate these problems. This practice may be used by facility users, test personnel, facility operators, and independent process validators to determine the suitability of a specific environment within a facility and of the testing process as a whole. Electrical measurements are addressed in other standards, such as Guide F980. Additional information on conducting irradiations can be found in Practices E798 and F1190. This practice also may be of use to test sponsors (organizations that establish test specifications or otherwise have a vested interest in the performance of electronics in neutron environments).
1.3 Methods for the evaluation and control of undesired contributions to damage are discussed in this practice. References to relevant ASTM standards and technical reports are provided. Processes and methods used to arrive at the appropriate test environments and specification levels for electronics systems are beyond the scope of this practice; however, the process for determining the 1-MeV equivalent displacement specifications from operational environment neutron spectra should employ the methods and parameters described herein. Some important considerations and recommendations are addressed in Appendix X1 (Nonmandatory information).
