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Introduction
This section provides guidance concerning RHA, RHM,
and RHS on system development issues.
These
activities should be initiated as early as possible in the system development
cycle to minimize cost and effort. Moreover, these efforts should be integrated
to the maximum extent practicable in the system’s testability
requirements.
Indeed, if an
aspect of an overall system development activity entails the development and
demonstration of a "new" technology, this development effort should also extend
to qualification, RHA, RHM, and RHS tasks as appropriate.
One example of
such a situation would be the need to develop a radiation hardened cryogenic
microelectronics technology to support a system development. Since the areas of
radiation hardening and testing, reliability testing, process qualification,
etc. are ill-defined for this type of technology, it would be highly desirable
and cost effective to initiate technology qualification, reliability
characterization testing, and RHA efforts in conjunction with the basic
development tasks.
Clearly such a
proactive approach is also appropriate for devices without radiation
requirements. However, the imposition of this additional set of constraints
greatly exacerbates the situation.
Radiation
Hardness Assurance and System Radiation Hardening Considerations
RHA program - The microcircuit RHA program must
include an allocation of radiation design margin in the part acceptance
specification limits which can be combined with other parameter degradation
stresses, such as time and temperature, to assure each system relevant parameter
has tolerable end-of-line (EOL) limits.
As previously
stated, the selection of devices for a particular application requires knowledge
of the radiation response of that device, a description of the environment, an
understanding of the specific device application, and a description of the
system/subsystem where the device will be used.
Electronic
pieceparts are normally obtained for a system through the implementation of a
parts control plan (see the Selection Guidance section) and an integral part of
such a plan is the radiation hardness assurance (RHA) program. The RHA program
refers to all of the methods and procedures which control the acquisition to
specified radiation performance levels. Specific RHA requirements for various
classes of semiconductor suppliers are also discussed in the Selection Guidance
section.
RHA activities
are most apparent during the production phase of a program. However, RHA
considerations (e.g., parts selection, parts control, etc.) should begin during
the initial stage of a program (i.e., concept definition) and pervade all phases
of a program. Such an approach should preclude the need to retrofit radiation
hardening into a system which can be extremely costly. If radiation hardening is
addressed during the initial stages of a systems development the cost of
hardening can be less than 5% of the entire satellite cost.
In addition to
RHA, hardness maintenance and surveillance programs are required to ensure that
the robustness of a system is not compromised during its operational phase due
to incorrect maintenance.
For suppliers
that provide radiation hardened parts, in general all RHA SMDs require devices
to be characterized to indicate device capability (not to system survivability)
using the following MIL-STD-883 Test Methods 1017, 1019, 1020, and 1021; and
ASTM Test Method 1192.
RHA designators
have been developed to allow for the categorization of total ionizing dose
capability levels, as follows:
M = 3 X
103 rad(Si) F = 3 X 105 rad(Si)
D = 1 X
104 rad(Si) G = 5 X 105 rad(Si)
P = 3 X
104 rad(Si) R = 1 X 105
rad(Si)
L = 5 X
104 rad(Si) H = 1 X 106 rad(Si)
For example, if
a part is characterized to 5 X 104 rads(Si) the part would be listed
as a D level part, but if that same part from a different manufacturer shows a
capability to 5 X 105 rads(Si), the part would be listed as an R
level on the same SMD.
The other test
methods are handled within the MIL-PRF-38535, Group E paragraphs in each
detailed specification as required by design or by the purchase order. The
Mil-PRF-38535, Group E Table designates the test method, sample size, identify
specific technology types that allow certain tests to be eliminated or retained
and contain a variety of caveats concerning radiation testing in general.
It should be
noted that the utmost care must be exercised before a specific test is
eliminated. This warning is important since some technologies contain parasitic
structures sensitive to radiation effects that don't affect the primary
structure but are capable of affecting the overall circuit performance. An
example of such a situation would be a combined MOS digital circuit and CCD
device. In general, an MOS digital structure is insensitive to neutron
irradiation, but neutrons can dramatically degrade the operation of a CCD. Thus,
the deletion of neutron testing, which is normally allowed for MOS technology,
would be inappropriate for this case.
By providing a fully
characterized detailed device specification the user knows the device capability
and can make a better judgment on which part best suits his particular
application. However, for the situation where a device without an RHA
specification is used in a situation where radiation hardness is required, as is
often the case, a complete characterization of the device is required for those
applicable environments (e.g., total ionizing dose, SEE, etc.) at the
anticipated radiation levels. Also, any decisions concerning the appropriateness
of the device must include the statistical variations associated with the device
response, anticipated/statistical variations in the operating environment (e.g.,
solar max, solar min, solar flares, etc.) and the actual system parameters
(e.g., shielding, shadowing, end-of-life performance needs, allowable number of
upsets, etc.).
Effects & Environment
Quality System
Selection Guidance
Application Practice
Element Design
System Guidance