NASA Technical Reports Server (NTRS) 19990040889: Assurance of COTS Boards for Space Flight. Part 1

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by  NASA Technical Reports Server (NTRS)

//i ¸- . •
Assurance of COTS Boards for Space Flight - Part I
Jeannette Plante, Norm Helmold, Clay Eveland
Swales Aerospace/NASA GSFC Advanced Interconnect Program
5050 Powder Mill Rd
Beltsville, MD 20705
301=595=5500 ph / 301=902=4114 fx
Abstract The lead CUE box designer identified a CompactPCI bus
based system because itprovided several system and
sol, are advantages. Two arrangements were considered
Space Flight hardwareandsoftware designers are
(Figure 1and 2) basedon the use of 6U (6.3"x 9.18") or
increasingly turningto Commercial-Off-the-Shelf
3U (3.94" x 6.30") sized boards.
(COTS) productsinhopes of meeting the demands
imposed onthem byprojects withshort development
There were noboards identified atthe time, withprior
cycle times. The Technology Validation Assurance
flight history soavariety of productswere purchased.
(TVA) team atNASA GSFC hasembarked on applying a
Based on howthey performed individually, together and
method for inserting COTS hardware intothe Spartan25l
afterenvironmental testing, the suite of boards would be
spacecraft. This method includes Procurement, selected. Table 1. listsall of the COTS boards that were
Characterization, Ruggedization/Remediation and
purchased.
Verification Testing process steps which are intended to
increase the user'sconfidence inthehardware'sability to
COTS Assurance Background and Approach
function inthe intended application for the required
duration. As this method isrefined with use, ithasthe
potential forbecoming abenchmark for industry-wide use NASA and the aerospace industry have learned a lot
of COTS inhigh reliability systems. about failure modes inelectronic parts and boards that
result from the stresses of use inflight environments.
Military, NASA and Industry specifications and standards
Introduction and Background
exist which trytoprevent products with flaws, which
cannotindependently survive high and low temperature
The Spartan251 isavehicle which provides experiment extremes, thermal cycling, shock and vibration, vacuum
platforms forinstruments with relatively short(days to and otherenvironmental conditions, from being applied in
weeks) mission lifetimes. The Spartan project isexpected flight hardware. Testing of high reliability parts exercises
to provide experiment platforms which have a fast them using maximum electrical ratings. Qualification
development cycle time (less than 3 years) and a low cost. testing isdone by sampling a production process and is
To meet this challenge the project looked toCOTS considered applicable tosubsequent lots from thatprocess
computer systems primarily as a solution tothe schedule forsome length of time (one ortwo years). The goal isto
challenge. increase system reliability by reducing the number and/or
size of failurecausing flaws and tocharacterize the
Schedule improvements where hoped tobe realized quality of parts produced by a given set of processes.
because so many ofthe development activities would not
be needed: circuit design, breadboarding, troubleshooting, Thesame philosophy can beapplied to evaluating the
parts procurement and board assembly. The software reliability of COTS boards however since COTS products
requiredwas standard. It would also requiredevelopment are not produced with reliability as apriority, the methods
activities and specialized skills tooperate it. are not the same. The processes producing the hardware
are not known tobe controlled orare changed frequently
COTS have as many definitions as there are people to over time (one ortwo years), without notice to the users.
define it. The COTS being implemented by Spartan251 It must beassumed that COTS boards will never beable
are fabricated boards. Some of the boards being used are towithstand flight environments "independently". They
custom designed and fabricated by an outside vendorand are designed and built tooperate inonthe groundand are
they were not considered COTS duringthis assessment. often augmented with heat dissipating mechanisms such
The entire system iscalled the central processing unit as fans and heat sinks to enablethem to survive in a 25°C
electronics (CUE box), and provides command and data environment. Once the fanisremoved, itislikely thatthe
handling forthe spacecraft.
Figure1. CUE Configuration A, 6U Boards
Figure 2. CUE Configuration B, 3U Boards
temperature rating given bythe manufacturer the variety of electrical stresses that they may see
will beexceeded, from component self heating. inapplication. Given that the thermal
Certainly the individual parts cannotbetested to environment will have tobe controlled, whether
their electrical limits because they arein a circuit through the use of fans,heatpipes orother
configuration which physically precludes this. methods, and that deriving atest planthat
While we test high reliability partsusing known addresses allpossible sot_ware driven
maximum electrical, thermal andmechanical operational modes isnon-uiviai, the assurance
conditions, we must test COTS boardsina wide engineer will realize thateach COTS boardina
variety of operational modes to expose them to given application should beconsidered unique.
Table 1. COTS Boards Purchased
Board Type Part Number Manufacturer Function
6U Processors CR6400053NBC OR Industrial Computers Compac PCIPentium Board
6Uproce_ors CTM6 OR IndustrialComputers I/OTransition Module
6U Processors ZT5510C4R3P3SIM3 Ziatech CPCI Processor Board
3U Processors CPCI-3603 (103095) Force POWERCORE/CPCI
Processor board
3U Processors CPCI-3740 (104912) Force POWERCORF3CPCI
Processor board (233MHz)
Memory 104949 Force POWERCORF3CPCI memory
board
IPCarriers CPCI-200-FP SBS Greenspring 6U IP Carrier Board
IP Carriers CPCI-IPC Alphi Technology 3U IP Carrier board
IPCarriers CPCI-SIP Alphi Technology 3U IP Carrier board
Analog Input IP-320 Acromag Analog Input
Analog Output IP-220-16 AlphiTechnology 16channel Analog Output
Digital FO IP-UNIDIG-E-48 SBS Greenspring DIGITAL FO
Digital I/O IP-UNIDIG-HV-8I 160 SBS Greenspring DIGITAL I/O
Digital I/O IP-UNIDIG-D SBS Greenspring DIGITAL I/O
Digital I/O IP-OPTO DRIVER SBS Greenspring DIGITAL I/O Optical Driver
Digital I/O IP-445 Acromag 32 Channel, bus isolated
Digital output
Digital I/O IP-440-1 Acromag 32 Channel, bus isolated
Digital I/O +/- 4to +/- 18Vde
Serial I/O SCC-04B Alphi Actis Technolg. Quad RS422 serial interface
Serial FO IP-Serial SBS Greenspring Serial I/O
Serial I/O MP-Serial SBS Greenspring Synch/Asynch Data Corn
Thermistor IF IP-Thermistor SBS Greenspring Thermistor card
Since we cannot control the quality of COTS particularly stressful operations can be
products we need to understand theft limitations minimized or avoided.
and control how they are applied. Sealed
enclosures can provide protection from vacuum At the beginning of the Spartan 251 COTS
effects and may provide astructure in which insertion project afour step process was
mechanisms such as fans or fluid pumps can be proposed to gather information about the
used for thermal management. Mechanical capability of the boards intended for use to
damping should be considered at the board and survive the intended environment and how
box level to reduce vibration and shock effects. ruggedization or failure mitigation approaches
Shielding can be used to limit the total deposited could be validated. This flow is shown in
charge from ionizing radiation. The goal is to Figure 3. Lessons were and are being learned
limit the environment's contribution to flaw along the way that have expanded the original
growth which can result in board or part failure. definitions assigned to each step. The
elaboration described here is intended to describe
The operational modes in which the system is details about the first two process steps and some
used, are as important aconsideration as isthe of the lessons learn during their implementation.
physical environment. The operating system and It is hoped that lessons learned while
the commands used will drive the electronics in implementing the last two,
ways which may be stressful to the electronics Ruggedization/Remediation and Validation, will
when used in specific combinations, repetitively be similarly documented and fed back to
and over time. Consideration must be given to improve the process.
the intended use of the hardware and how
Though the flow chartshows aseries sodesirable, avariety of systems orboards
relationship between Characterization and should beprocured toincrease the chances that
Ruggedization/Remediation we found that itwas the project will havea fullcompliment of boards
very valuable tostartconsidering ruggedization to use when the testing iscompleted. This was
options well aheadoftime, even before the done especially with respect tokey boards such
characterization datawas collected. Ithelped to as the processor andthe IPCarriers.
formulate questions aboutwhat the most serious
concerns were andallowed time forplanning. Single assembly lotsand single lot/date codes for
For example, we know that itwas very possible components used to build upthe boards were
that the processor would need an augmented requested. Single lot/date code atthe part level
thermalpathbecause itwas intended to beused was not available atthistime however the
withafan and heatsink. This leadthe industry is startingtorespond tothis need and
mechanical team to startconsidering mechanical individual vendors are specializing in "custom
impacts that heatpipes andother thermal built",ruggedized COTS boards where lot
management augmentations would haveon the control canbe implemented. A single assembly
closely spacedboards and on the CUE box lot was available forthe boards, however the
enclosure. vendor(s) that were amiable to this indicated
increased delivery schedule tomeet this
Procurement requirement aswell as increased cost.
Sequential serial numberswere available.
As notedabove, the boards were selected bythe
projectdesign engineers. The TVA team The user should be aware of the vendor return
became involved prior tothis selection process. policy prior to procurement. Inmost cases where
We first spent time brainstorming ideasabout commercial product isused, flight, spare, and
what type of information may exist thatwould ETU samples are purchased at the same time to
give us insight into theboard and individual part avoid delivery driven schedule delays. This
failure rate. We are accustomed to being able to increases cost risks. Depending onthe vendor's
wimess the production process, facilities and policies, unopened, unused hardware may be
management of companies who make high returnable when characterization testing shows
reliability parts. Due tohigh reliability critical orunavoidable failure modes orother
qualification and screening requirements, these reasons for not using the product. Most of the
manufacturers often keep data formultiple test vendors used onthis project were flexible in
lotsover a long period oftime (3 to 5years) and their return policy since the boards could be
may maintain well documented traceability resold on the commercial market ifthey were
between incoming materials lots and t-mished unopened. Some ofthose that offered areturn
product lots. COTS manufacturers arenot policy gave only account credits which did not
drivenby their main markets to keep these kinds allow the project torecoup funds for returned
of records ortoprovide the manpower required items.
tosupportaNASA vendor survey. They arecost
drivenand will notbe ableto recoup costs A thorough review ofproductspecifications,
requiredtochange theirprocesses toproduce when available, should beperformed duringthe
higher reliability parts forflight use. We decided design cycle. Documentation beyond what is
to askforas much dataand aslittle variabilityas available through the marketing literature is
possible, knowing that itwould be alearning often not available. Critical performance
experience aswe went along abouthow much parameters, not defined bythe manufacturer,
the manufacturers actually document abouttheir may need to be requested. Careful consideration
product. must be given toproduct obsolescence of the
higher level assemblies, as well as critical
It isimpossible toknow with sufficient certainty component(s) (i.e. microprocessor andperipheral
whether ornot aCOTS system will be ableto devices). Significant changes may be made to
withstand the rigors of space flight use before it the product without your knowledge to keep it
ischaracterized through testing. To realize the current with the changing platform environment.
schedule benefits which make the use of COTS
Figure 3. COTS Insertion Process Flow
Procurement
• MfrRedundancy
• Single Lot/Lot Traceability
• ReturnPolicy
• Rztum/Failure Experience
• Drawing Product Specifications
• PartsandMaterials List
• Product Change Notifications
• Product Characterization Data Characterization
• Visual Inspection • Radiation
• Mechanical
• Thermal
• Contamination
• Electrical/SoRware
Ruggedization/Remediation
• Radiation
• Mechanical
• Thermal
• Contamination
• Electrical/Software
_r
I
, Acceptable
'_ for Use
An "as built"partsandmaterials listshould be Finally, the boardsshould be visually inspected
requested from the vendorprior toprocurement. uponreceipt. Oneshould verify that the product
Thepurposeof this istwo-fold. First, potential orderedwas the one shipped and that deviations
contaminates can be identified such as fromexpected configurations are noted. Look
outgassing plastics used forconnector back forobvious flaws such as poor soldering orstress
shells, epoxies, and cleaning solvents. Second, on leads from unsupported parts. Solvent
this allows aparts listreview which highlights residue andcorrosion should benoted. Use this
potential reliability hazards orconcerns. Parts opportunityto trytoidentify as many of the parts
and materials lists were requested from the onthe board aspossible. Some will be easy to
vendors selected forthisproject, however they identify and may even have a lot datecode
were not provided norwere they offered forsale. identified while others will notbe marked atall.
When aproblem was found with aspecific part Use thisinformation to createa partmapfor
duringtesting, the manufacturer was ableto futurereference (An example isshown inFigure
provide partspecific information. 4).
The user should request to be made aware of Itisimportantat this stage tobe surethat all
productchanges that would affect their design. storage and handling areas where these boards
Engineering changes may ormay not be will be kept,must beelectrostatic discharge
adequately reflected bythe documentation. It (ESD) controlled. Packing materials must be
may be the case as well, that documentation such controlled aswell. Itmight be prudentas well at
as circuit orlayout drawings must be requested this pointto set up a controlled
orpurchased separately. Change notifications
(controlled) were notavailable tothe project system forstocking the COTS hardware. Ifthe
because itwas not considered avolume
testing goes well and some "gems" areidentified,
customer. A case of out-of-date documentation
otherprojects will beanxious to absorb the
was found fortwo boardtypes. Oneset of
spares.
documentation didnot match the revision letter
printedon the boardandthe otherboard
Characterization
contained an un-insulated jumper wire that was
notpartof the documented configuration.
The boardsmust be characterized inorderto
The user should obtain allcharacterization data understand the ability of the "as received" units
available from the manufacturer. Depending on towithstand the intended application and
avendor'sparticipation in"high reliability" environment and to understand the engineering
markets, they may ormay not maintain quality challenges associated with providing risk
orreliability data. Some manufacturers perform mitigation paths for the hardware.
acceptance testing and some that ruggedize their Characterization involves understanding their
products forharshenvironments have performance with respect to ionizing radiation,
qualification datatoprove the effectiveness of mechanical shock, vibration and temperature.
their approaches. Many manufactures of COTS Assessments must also be made with respect to
electronics do neitherand do nothave temperature ratingsof the boards, increases in
performance dataavailable. No vendors ambient temperatures due to self heating, sources
provided existing characterization dataforthe of contamination, concerns with respect to use in
boards bought forSpartan251. vacuum, and electrical performance such as
power consumption and timing considerations.
As COTS f'mdincreasing use on flight hardware,
historical datawill begin to accumulate. At this Since COTS hardware isnormally designed for
time thisisalready occurring and itisprudentto terrestrial applications which maintain
contact NASA and military organization that temperatures around 25°C 4-15°C (although
may have use the products you are considering, "ruggedized" boards and individual parts may
to learnabouttheir experiences. Itisimportant have much wider temperature ratings) their
to remember though thatmost COTSproducts ability towithstand the vacuum, thermal,
mechanical and radiation environment are
are not controlled forquality ordesigned for
unknown until the board istested.
reliability and cannotbe qualified by similarity.
Characterization testing then must be considered
tobe destructive and extra boards must be
Figure 4. Part Map
procured for it. The project referred to these must represent the application that the parts will
destruct units as Martyr boards. be used in, to the greatest extent possible.
Radiation Characterization The proton testing consists of high fluence and
low fluence testing. High fluence proton testing
provides data on component susceptibility, rate
The first step is to perform asusceptibility
prediction data and total accumulated dose.
assessment of the radiation environment. Based
High fluence testing is destructive. For the
on the mission launch date, duration and orbit,
Spartan project, 63 MeV incident protons were
the radiation environment can be defined. This
used with a fluence of 3.8E10 protons/cm 2.
definition should provide the severity of the
Low fluence testing is performed on the flight
proton, gamma ray and heavy ion environment units and is not destructive, however the board is
that will allow proper determination of the considered to have accumulated total dose. Low
fluence to use during Single Event Effect (SEE)
fluence testing provides data which gives a
testing. SEE testing will show if charged
reasonable confidence that the flight boards have
panicle impacts will cause the electronics to
a radiation susceptibility that is similar to that
temporarily (upset) or permanently fail (latchup,
shown during the high fluence testing.
lock'up, etc.). The environment definition should
also describe the total accumulated (electron)
Mechanical Characterization
dose expected so that the board's ability to
withstand deposited charge can be evaluated
and/or shielding can be designed. Total Ionizing Mechanical characterization of the Spartan CUE
Dose isnot an issue for short duration missions Box and its COTS electronics boards was done
in low earth orbits. The radiation assessment using both structural analysis and mechanical
done for the Spartan 251 mission showed that the vibration testing. Resonance frequencies of
primary radiation environment risk was due to vibration, random vibration, steady state and
protons. Wansient loading and thermal loading (simulating
Space Shuttle launch and landing conditions) are
Following environment definition, application applied in the testing of these items. Excessive
and mission-specific radiation test procedures deformation, excessive mechanical cycling of the
must be prepared. The test procedure must be boards and failure of the solder joints are the
based on the conditions of the application and critical reliability concerns. This is especially
should simulate in-flight usage of the COTS the case for the Spartan 251 project because most
hardware. COTS hardware cannot be "qualified" of the components on the COTS boards are
as a technology like electronic parts are. They surface mounted. The boards need to survive
must be validated on a lot-by-lot basis so testing one shuttle flight.
Qualification andacceptance vibration levels clearance between them. A random vibration
were defined for the CUE Box. The analysis was plannedfor the 6U IPCarrierusing
qualification level isused on the Martyrboards the FEM,which includes edge constraints that
andthe acceptance level isused on the flight estimate the fixity that the actual boardwill have
boards. The boardswill beheld inthe CUE box inthe CUE box. This analysis should provide a
along their side edges, along the bottom edges good ideaofwhere toexpect the maximum
and atthe toptwo comers of each board. Wedge= displacement of the board under random
lock type cardretainers normally used inspace vibration loading.
flight boxes cannotbe used because only 0.10
inches of edge space areavailable for securing Arandom vibrationtest can then be performed
the boardsinthe box. A less robust, onthe 6U IPCarrierwith an accelerometer
commercially available, edge restrainer was attached to the location that the FEM analysis
baselined foruse. predicts maximum displacement will occur.
The displacement data will be used forthe
The PC boardsshould have resonance following two purposes: to verify whether ornot
frequencies of vibration that aresufficiently the two boardswill contact during vibration and
different than those of the CUE box inwhich to update the FEM. The edge conditions
they are secured so that the resonance simulated inthe FEM will be modified so that
frequencies of the boards and box do notcouple. the FEM randomanalysis results match the
If they docouple, excessive mechanical randomtest results. Sine sweep test data
excitation could occur and cause board failure. obtained duringthe test isalso used inthe
StructuralFinite Element Models (FEMs) oftbe adjusUnent of the edge restraintsimulation.
boards are developed and used inall ofthe
structuralanalyses involving the boards and the Thermal Characterization
CUE box. Modal testing of each COTS board,
using free-free edge conditions isused toprovide
Thermal characterization isperformed toget an
datathatcan beused to adjustthe FEMs sothat
understanding of the thermal effects onthe
they accurately representthe boardundertest.
components and materials due to: self-heating
by the electronic components and the ambient
Three-axis randomvibration testing isused to
temperature, the availability of thermal paths and
characterize the integrity of each COTS board
and each module attached tothe Carrierboards. the lack of convective cooling in vacuum and
zero G. Theoretical and empirical analysis must
These tests are performed in atest fixture
be done toestablish the thermal conditions that
designed tosecure the boards using the same
will be seen by the boards in flight configuration,
hardware and configuration that will be used in
invacuum. Worst case power dissipation's
the CUE Box application. Board preparation
should be used for the analysis to simplify
steps include: staking the components, soldering
obtaining the power data.
insocketed parts, conformal coating ofthe entire
board(except at specified masked off areas) and
Since the design margins, electrical and thermal
installation of connectors as applicable. The
are not known for COTS boards, itisimportant
staking, soldering and conformal coating steps
to measure these conditions for the boards
will be duplicated forthe flight boards. Care
received. Infrared Imaging can be used to
must be takenwhen applying solder, coating and
measure radiated emissions from hot objects
staking materials so that the temperature ratings
such asthe parts on theboard. These radiated
of the components are not exceeded.
emissions, which are visible inthe infrared
A full boardeleclrical functional test should be frequency range, can be translated to temperature
provided the emissivity of the material isknown.
performed duringand after each axis of testing.
Extreme caremust be taken when collecting this
Careful visual inspections must bemade to
data toavoid stray sources of reflected emissions
validate that solderjoints are not damaged.
and to isolate the subject from cooling
Photographs should betaken forthis purpose.
mechanisms (such asmoving air) that will not be
available inthe flight application. An
Maximum displacement of the 6U IPCarrier
understanding of how the camera works and its
boards was aconcern. On the 8-slot backplane
limitations with respect toaccuracy and fidelity,
chosen forthe CUE box, two IP Carrier boards
will be inadjacent slots with only 0.1 inches
Tbermocoupwleesrealsoputin place to trackthe Summary
accuracy of the temperatures calculated fromthe IR data.
The delta between these two forms of temperaturedata By using this methodology for purchasing and
varied between 0.35°C and3.83°C (averages foreach characterizing COTS boards, aproject should be ableto
board). The temperatures measured were inthe range of understandthe most critical vulnerabilities of the system
23°C (ambient temperature) to 62.9°C. Comparisons inthe space environment and will be able tocreate a
between the temperatures measured andthe partratings ruggedization and/or riskreduction planthat addresses
(at leastthose which could be identified) indicated that these quantified concerns. Theoretical and empirical
there was probably littleto no thermal margin at60°C methods canbeused to simulate environments without
ambient temperature (the project's maximum operating sacrificing hardware. Since qualification testing has
temperature requirement). The thermal margins were limited application inthe case of COTS, itisimportant to
based onthe additionof 27°C tothe measurements taken
get data forthe flight units in the configuration inwhich
at23°C ambient Figure 6shows the IRimaging set-up. they will beused.
Thermal modeling can beused topredict orreveal
thermal problem areas invacuum (or inasealed
enclosure) that could notbe measured duringtesting. The Thiswork was done undercontract toNASA GSFCfor
results of these models may be selection anddesign ofan the NASA Advanced Interconnect Program and the
alternate enclosure oradditional thermal management Spartan 25I program. Work which wasperformed on the
assemblies. Additional thermocouple measurements may Spartan 251 COTS task which contributed significantly to
be required afterthe results of the thermal modeling are thispaper was done by Dr. Michele Gates, Greg Martins,
obtained. The thermal dataindicated aneedforadditional Dr. Henning Leidecker, Don Deibler andBeverly Settles.
thermalmanagement atthe boardand/or partlevel. The Their contributions are appreciated
thermocouple and IRdata was provided tothe thermal
engineering groupto both validate their models ofthe
thermal system and to help them begin todesign
ruggedization hardware.
Contamination
Since COTS boards aregenerally not designed foruse in
applications that are extremely sensitive to contamination,
the COTS hardwaremust be reviewed and tested for
sources of contamination and moisture. The first place to
collect this data is fromthe manufacturerwhere itmay or
may not beavailable. Ifthe materials cannotbe
adequately documented inthisway, testing isrequired.
Firstthe boards should be baked out inan oven atthe
highest temperature allowed by the manufacturer's
ratings. This should be done foras long asthe schedule
will allow (one totwo weeks formaximum temperatures
of 50°(3). An instrumented outgassing testthen should be
runon the bakedout board to verify that the
contamination level isacceptable. Following bake outs,
the boards should beconformally coated inaccordance
withNASA standardprocedures. Extreme careshould be
taken to avoid exposing components to temperatures
beyond their rating.