Since the military adopted the policy ofpurchasing commercial-off-the-shelf(COTS) products whenever possible,military program managers have beenable to acquire COTS VMEbus productsfor use in benign environments. However,COTS VMEbus boards are not typicallydesigned for use in the extreme environ-ments encountered in most militaryapplications. This has forced militaryprogram managers to request ruggedizedversions of some COTS VMEbus boards,and that sometimes means a completeredesign of the board. In this articleRobert provides a list of design rulesthat can be used to guide an engineerin designing reasonably priced COTSVMEbus boards with ruggedization inmind. By following these design rules,the COTS board can be designed tosatisfy a wide range of ruggedizationrequirements without major designchanges.

Since the early 1980s when the mili-tary instituted its policy of usingCOTs products whenever possible,

VMEbus has been a solid choice because:

� the VMEbus standard is one of themost open, reliable and scalable busarchitectural standards

� the products introduced for VMEbusprovide continuously climbing perfor-mance and upward compatibility

� the VMEbus electrical and mechanicaldesign rules make it “ready to harden”and therefore conducive to ruggedization

In short, VMEbus provides an idealCOTS platform for military systems.

The use of COTS VMEbus boards pro-vide the military with several advantages,compared to custom designs, including:

� lower cost� a shorter time of procurement� greater software support� a future roadmap of upgraded products

However, COTS boards are typically notdesigned to withstand the harsh deploy-ment environments characteristic of most

military applications. As a result, manymilitary program managers have chosento stay with proven military-grade compo-nents and boards despite:

� higher costs� lower availability� technological obsolescence

Using COTS boards in extended environmentsTypically, ruggedization of a COTS singleboard computer (SBC) for use in harshenvironments involves the substitution ofwide temperature range components.However, simply replacing componentswith MIL grade parts is not usually suffi-cient to ruggedize the entire board. In fact,many components are not even availableas MIL grade components — especiallystate-of-the art VLSI components andprocessor chips.

Even if wide temperature range compo-nents can be found, the board must still beenvironmentally tested, and the board’slogic might even need to be redesigned towork reliably, because of the wider timingtolerances that are characteristic of widetemperature range components.

Thus the ruggedization of a COTS SBCcan raise the cost of the board consider-ably, and can complicate the manufactur-ing process. Ruggedized COTS boardsmust also undergo time-consuming retest-ing and requalification and (if substitutecomponents must be used for those notavailable in wide temperature versions)software might need to be ported andrequalified. All of this obviates the advan-tages that motivated the adoption of theCOTS board in the first place.

The challenge for VMEbus board vendorsThe challenge for VMEbus board vendorsis to design ruggedizable COTS productsthat can easily be equipped to tolerate awider temperature range (as well as phys-ical abuse) without any redesign, and withminimal cost and time penalties.

This challenge can only be met by incor-porating ruggedization as a design objec-tive for COTS boards. Hardening andendurance considerations must be “builtinto” the product design process and the

manufacturing process by the developmentof (and strict adherence to) formalizeddesign rules. These design rules constrain:

� the functional specifications� the choice of components� the circuit design� the logic simulation� the printed circuit board component

placement and routing� the testing and verification� the software integration� the manufacturing test procedures

Thus, the rules impact virtually everyaspect of the board’s design and manufac-ture, ranging from architectural specifica-tion to post-manufacture testing. Forexample, the rules for the design and ver-ification phase cover:

� Architecture� Design� Implementation� Thermal management� Testing� Shock and vibration� Validation and verification� Component selection� Component end-of-life management� Low temperature extension� High temperature extension

Architecture rulesThe architecture should be based uponsynchronous buses (such as the PCIbusand the PowerPC Bus) to provide a fast,efficient interconnect between all onboardcomponents, while minimizing noise andcrosstalk problems on the board.

EDAC memory should be used to protectthe program and data integrity at run time— especially when a board is used inharsh EMC or radiation environments.

Exception cycles (such as retry cycles)should be used to provide an additionallevel of security, and hardware and soft-ware features should be provided to man-age the recovery process transparently tothe application software.

Design rulesComputer aided design (CAD) toolsshould be used to simulate the dynamicbehavior of all logic on the board. Bothmin/max and worst case simulation should

Designing VMEbus COTS boardsfor ruggedizationBy Robert Negre

be used to determine the timing marginsfor each technology used on the board.Component behavioral models should bebased on the minimum and maximumjunction temperatures over an extremeambient temperature range, including:

� a negative range of – 40°C to 0°C� a positive range of +70°C to 105°C

Implementation rulesPrinted circuit boards should employground and Vcc layers, to reduce groundbounce and improve signal integrity. Thenew 5-row VMEbus connectors (withadditional GND and Vcc pins) should alsobe used to further improve these factors.

Analog electrical simulation should done(based on the physical routing of thetraces on the printed circuit board) todetect any threats to signal integrity,including potential crosstalk and propa-gation/reflection problems. Fast-edge dri-ver models should be used to simulatelow temperature effects, which might alsothreaten signal integrity.

Thermal management rulesLow and high ambient temperaturerequirements should be defined in theboard’s functional specification. Potentialhot spots on the board should be identifiedwith thermal simulation tools. Placementof components on the board should takeinto account:

� each component’s power dissipation� each component’s impact on airflow

speed, whether forced or natural con-vection

� each component’s contribution of heatto the thermal conduction layer withinthe board

The overall temperature of the boardshould be monitored with thermal sensorsthat measure the temperature of the airflowing past it.

The temperature of the processor chipshould be monitored with a dedicatedthermal sensor to track the processor’sjunction temperature, thus allowing foroptimum power management.

Testing rulesThe test specifications should ensure thatthe board’s test coverage will be as com-prehensive as possible, throughout themanufacturing process.

Extensive “Built In Test” software shouldbe provided to simplify the first-linemaintenance on a deployed system.

Shock and vibration rulesTo strengthen the board, the front panel

should be secured at multiple points, andheat sinks should be secured to the printedcircuit board.

Where extreme shock and vibration toler-ance is required, the board should bedesigned to permit the add-on of a“Ruggedizer” shell, to increase the rigid-ity of the board.

All boards should be shock and vibrationqualified, with documented test reports.

Validation and verification rulesFollowing prototyping, each board prod-uct must be fully qualified prior to releasefor manufacture. Board features subject toqualification include:

� performance benchmarking� driver support for VxWorks/tornado,

LynxOS, and AIX� built-in self test firmware� operating-system-level test software� documentation� determination of the computed MTBF� electromagnetic compatibility

(radiated EMI)� determination of the operational

temperature range

The validation of the board should be con-ditional on it being fabricated by a con-tract manufacturer with adequate qualitysafeguards, such IPC 610 Class 2 or 3.

Manufacturing test should be performedon each board.

Extended R Class (ruggedized) boardsshould each be tested from –40° C to+85° C.

Component selection rulesComponents should be selected from astandard component database. To beincluded in this database a componentmust meet requirements for:

� quality� accessibility (many sources => highly

accessible)� market acceptance and trends� long term visibility, meaning that the

supplier(s) should allow users visibil-ity into their future plans for support-ing the component, including a possi-ble replacement part if the componentis discontinued

� long term reliability, meaning thatthere will be sufficient market demandfor the component to make continuedsupport economically viable

Analog components (such as oscillatorsand phase-locked loop devices) are typi-cally not available in Mil-Spec versions,but industrial grade components can and

should be used.

The TTL glue logic should be provided by3.3 volt chips, which are qualified to oper-ate from –40° C to +85°C.

Component end-of-lifemanagement rulesComponent end-of-life (EOL) shouldmonitored, and updates made continu-ously to the component databases, withthe goal of providing long term support ofboards for up to 20 years.

In addition to continuous surveying of themarket, EOL management should elimi-nate the potential problems of obsoles-cence by:

� finding compatible second-source com-ponents when possible

� finding functionally equivalent com-ponents when second-source compo-nents are not available

� stocking an adequate number of com-ponents to ensure continued supply tothe critical programs

Low temperature extension rulesLow temperature device performanceshould be determined for each individualtechnology, including:

� CMOS digital silicon� analog devices� low-voltage TTL� large-scale VLSI� ASICs� memories

Although commercial-grade componentsare not generally qualified below zero,digital CMOS components offer excellentswitching characteristics because theirset up times and their transition timesbecome shorter at low temperatures. Forexample, low voltage (3.3v) TTL is com-pliant at –40 °C.

Crosstalk and reflection problems can arisewith the propagation of the faster signaltransitions seen at low temperatures. Thesepotential problems should be identifiedearly with signal integrity analysis tools.

Key components (such as analog devices,PLL and oscillators) should be selectedfrom industrial range devices, to guaran-tee to that they will operate at tempera-tures down to –40°C.

Complex CMOS VLSI chips should bescreened for compliance to –40°C, andASICs should be qualified for low tem-perature operation. During board manu-facture, each SBC should be comprehen-sively tested, to ensure compliance withextended environmental requirements.

High temperature extension rulesEven when the ambient air temperatureflowing over the board is within specifica-tions, care must be taken to ensure that thejunction temperature of each componenton the board is kept below its specifiedmaximum.

Harsh environments generally require tol-erance of a maximum ambient temperaturein the 70°C to 85°C range. These limitsnormally can be supported by low powercommercial silicon components, providedthat the relevant design rules are applied.

For example, hot components should belocated near the edge of the board, tofacilitate thermal extraction. Also, no highdissipation chips should be located undermezzanine boards, or on the underside ofthe board.

Where necessary, the clock frequency ofdigital CMOS chips should be lowered, inorder to raise the chip’s maximum permis-sible junction temperature. For example, aCMOS microprocessor with a maximumjunction temperature of 65°C at 466 MHzcan be reliably operated at a junction tem-perature of 85°C when the clock fre-quency is reduced to 450 MHz.

Harsh environment technology:The RuggedizerFor the harshest environments, VMEbusboards require further stiffening and tem-perature tolerance. This requirement, (com-

bined with the comprehensive list of designrules given above) was the driving forcebehind Cetia’s Ruggedizer technology.

The Ruggedizer is a board-size, convec-tion-cooled aluminum heat sink thatis affixed to the face of Cetia COTSVMEbus boards to extend their thermaland mechanical operating ranges.

The Ruggedizer is created using apatented 3-dimensional laser scanningtechnique, which produces a precise 3Dprofile of the component heights on theface of each board. This profile allows themachining of a board-size heat sink thatexactly matches the component profile,with extremely tight mechanical toler-ances. When this heat sink is then affixedto the face of the board, it evenly distrib-utes and dissipates the heat generated bythe components on the board, thus allow-ing the board to operate at a much higherambient temperature than would other-wise be possible — up to 75°C or 85°C,depending on the board’s total powerdissipation.

Acting as an heat distributor, it conductsheat from the hottest areas of the boardto cooler areas, thus lowering the tem-peratures of the hottest components,so they remain well within their stan-dard operating range. The MTBF of theboard is greatly increased because thehottest components work at a lowertemperature.

Because the Ruggedizer physically inter-faces to the upper surface of each com-ponent on the board, it also acts as amechanical stabilizer for the components,increasing their resistance to shock andvibration.

A Ruggedizer heat sink can be createdand added to a COTS board, even if theoriginal functional specification for thatboard did not call for ruggedization. Thisprovides a quick and inexpensive way toconvert a COTS board into a ruggedizedboard.

The Ruggedizer can also be easilyremoved from the board to permit repairswith techniques identical to the repair ofany standard COTS board. Remountingsimply requires that a new thermal film beinserted between the board and the inner(machined) face of the Ruggedizer.

Ruggedization classesCetia offers 3 classes of COTS SBCs forharsh environments:

� S Class is the standard commercialVMEbus range.

� W Class is an extension of the S Class operating temperature range.

� R Class (which is convectivelycooled and requires the Ruggedizer)is the ruggedized version of theW Class.

Company Telephone websiteAP Labs 619-546-8626 www.aplabs.com Aydin Displays 215-657-8600 www.aydin.comBI RA Systems, Inc. 505-881-8887 www.bira.comBill West Inc. 203-261-6027 www.bwi.comCarlo Gavazzi, Inc. Mupac Business Unit 800-926-8722 www.carlogavazzi.comCETIA, Inc. 617-494-0987 www.cetia.comCondor Engineering 805-965-8000 www.condoreng.com DY 4 Systems 613-599-9191 www.dy4.comDynatem, Inc. 800-543-3830 www.dynatem.comElma Electronic, Inc. 510-656-3400 www.elma.comForce Computers, Inc. 408-369-6000 www.forcecomputers.comHewlett Packard 800-637-7740Matrix Corporation 800-848-2330 www.matrix.com Mektron Systems Ltd 44 1252 629937 www.mektron.co.ukPEP Modular Computers 412-921-3322 www.pep.comPrimagraphics 44 1763 852222 www.primago.co.ukRadstone Technology Corporation 800-368-2738 www.radstone.comSBS Technologies, Inc. 877-727-2374 www.sbs.comSchaefer 508-881-7330 www.schaeferpower.comSCI Systems, Inc. 205-882-4569 www.asp-vme.comStorage Concepts, Inc. 800-525-9217 www.storcon.com Synergy Microsystems, Inc. 619-452-0020 www.synergymicro.comThemis Computer 510-252-0870 www.themis.com Tricom Technology 727-895-2481 www.tricomtech.comTriple E Corporation 978-453-0600 www.tripleease.comVISTA Controls Corporation 805-257-4430 www.vistacc.com

Figure 1 shows the characteristics foreach class.

Cetia’s PowerEngine6 boardFigure 2 shows the PowerEngine6, a next-generation, dual-processor, PowerPC 750single board computer that has been de-signed using the rules in this article, to pro-vide a versatile, low cost, COTS VMEbusboard that can also be manufactured ina full ruggedized military version. (SeeFigure 3) The processor clock on the com-mercial version of the board runs at 450MHz, while the clock on the Mil-Spec ver-sion runs at 350 MHz clock.

The PowerEngine6 features a new host-bridge processor (codeveloped by Cetiaand IBM) that allows for exceptional busspeed. The architecture of this chip

increases the speed of the of the onboardPowerPC bus, and allows faster accessover the PCI 64 bus and the VMEbus.

The high component density allows thisboard to provide two processors (withtheir corresponding caches) in a single6U VMEbus slot. The low-power dissi-pation of the PowerEngine6 (combinedwith Cetia’s conduction-cooledRuggedizer technology) allows theboard to be used in severe environ-ments.

The PowerEngine6 is currently available

in 3 versions, to allow its use in a widerange of thermal environments:

� S (Commercial: 0° C to + 55° C)� W (Extended temperature:

–20° C through +65° C)� R (Fully ruggedized, with

conductive cooling: –40°C through +85 °C)

Rugged COTS with all the benefitsBy adhering to the abovedesign rules (and by keepingin mind the need to ruggedizefrom design through manufac-turing) it is possible to pro-duce COTS boards that can bemanufactured in versions suit-able for harsh environmentswithout sacrificing the bene-fits of standard commercial

products. In addition, the production ofhigh quality boards using high reliabilitycomponents reduces the overall manufac-turing costs and the time-to-market, thusproviding the vendor with a competitiveadvantage in the eyes of the user.

Robert Negre joinedCetia in 1987 asCetia’s computerarchitecture servicemanager and today isthe vice president ofR&D. He completedhis graduate studies atthe Ecole Superieure

d’Electricite, Paris, France, in 1980 and hashad articles published in VITA(OBS), RTS,RTC and COTS journal. Robert has anextensive background in single board com-puter architectures, PowerPC microproces-sors, VMEbus technology and COTS forDefense and Aerospace.

Figure 2

Figure 3

SBC Class S W R RConvective ConductiveRuggedizer Ruggedizer

Temperature 0 to + 55°C –20 to + 65°C –40 to +75°C –40 to +85°CAirflow:1.2 m/sec Airflow:1.2 m/sec Airflow: 1.5m/sec conductive enclosure

Sine vibration 20/500Hz: 2g 20/500Hz: 2g Same as W Class + Same as W Class operating range 5/20Hz: 1.25mm 5/20Hz: 1.25mm 50/170Hz: 2.5g 50/170Hz: 2.5g

170/2KHz: 2g 170/2KHz: 2g

Random 10/2000Hz: 10/2000Hz: 10/2000Hz: 10/2000Hz:operating range from 0.01 to 5*10–5 g/Hz from 0.01 to 5*10–5 g/Hz from 0.04 to 0.02 g/Hz from 0.01 to 0.02 g/Hz

Shock 10g/16ms 10g/16ms 40g/20ms 40g/20msoperating range 100g/6ms(*) 100g/6ms(*)

Figure 1