Environmental
particular challenge for optical and optoelectronic parts,
the parts are exposed to high energy protons up to a
certain fluence,” says Pesce.
For SEE testing, energetic ions or high energy protons
are used. These deposit significant charge along their
track when crossing semiconductor devices. This can
induce SEEs ranging from temporary
upsets to potentially destructive events
such as latch-ups, which are similar to
short circuits. Tests are performed at
exposures vastly exceeding that expected
in the mission to detect all possible failure
modes. Testing is performed at EEE part
level. The results of the test are then
assessed in the context of the electronic
circuit and up to system level to assess
mission impacts.
Radiation testing is only one
component of radiation hardening
assurance (RHA). For mission critical
electronic equipment, RHA is an integral
part of the circuit and system design and
engineering. RHA also plays a role in part
selection, design for radiation mitigation,
SEE rates and criticality analyses, and
system integration of radiation effects.
RAD-HARD OR OFF THE SHELF?
There is a trend for space vehicle
developers to use COTS components
instead of radiation hardened ones
because of a reduction in the number of manufacturers
producing radiation-hardened components. COTS
components also often perform better in terms of mass,
size, power and speed.
However, NASA scientists say COTS components can
pose more risk for radiation effects as they are not subject
68 MARCH 2020 \\ AEROSPACETESTINGINTERNATIONAL.COM
“The biggest issue is a lack
of traceability of COTS”
to RHA. While radiation testing may
characterize, it does not guarantee
radiation suitability for a particular
mission or environment. It can also be
difficult to establish whether the quality
of the manufacturing is consistent.
Pesce says, “There could be process
variations, different wafers and masks
used, different manufacturing plants. All
these factors may change the way a
component behaves when exposed to
ionizing radiation. This is called lot-to-lot
variations. Hence, the biggest issue is a
lack of traceability of COTS.”
Johnson, research coordinator at the
88-Inch Cyclotron at the Lawrence
Berkeley National Laboratory in
California says, “With Cold War
components depleted and no longer being
made, there is a lot of interest in COTS
parts for space vehicles. But they do not
hold up as well in heavy ion testing. How
manufacturers and space agencies are
dealing with this is not always clear, but
the need for more testing has clearly increased.”
RINGING THE CHANGES
As the requirements change the vulnerabilities and
testing needs also change. According to Johnson
electronic components are reducing in size, while
complexity is increasing. This is increasing the demand
for higher energies of particle beams to penetrate
thicker silicon overlayers in components. New materials
are also constantly emerging which require evaluation
and assessment.
This means testing facilities are always looking to
develop bigger, better beams. Johnson says, “We bring a
new ion source online around every ten years which will
use higher energy ion sources allowing us to increase
overall beam energies. We are also looking at developing
more precise particle beams, so that very small parts of
components can be irradiated, rather than an entire
circuit board assembly. This could mean far better
diagnostic capability for testers.”
According to Gaza, the increasing complexity of EEE
parts such as microprocessors makes characterization
testing more difficult. He says, “Manufacturers are
often reluctant to share detailed information about
part functionality for radiation testing and
testing black boxes is extremely challenging.
Ultimately, a test aims to correlate
results obtained in an accelerated
environment with performance
in flight. This is impossible
without insight into the
part functionality.” \\
SHIELDING INNOVATION
US researchers at North Carolina State
University have developed a new technique
for shielding electronics from ionizing
radiation in military and space exploration
technology, intended to replace the
aluminum boxing-in method.
The shielding they have created is just
as effective as aluminum, but almost a third
lighter and cheaper.
Oxidized metal powder is mixed into
a polymer, and then incorporated into
a common conformal coating on the
relevant electronics. There is less risk of
electromagnetic interference with metal
oxide powder and it is also less toxic than
the traditional method. The researchers are
hoping for industry interest to help develop
the process further.
5 // Radiation testing at
the Light Ion Facility at
University College
Louvain in Belgium
5
/AEROSPACETESTINGINTERNATIONAL.COM