Systems engineers seek to equip military systems with the latest electronic enclosures, backplanes, and chassis

By Courtney E. Howard

Architecting a system isn't what it used to be. Increased system complexity and system requirements bring new challenges that involve preplanning and innovation, especially when it comes to innovations like rugged enclosure technology, electronic thermal management, and VME chassis systems in rugged military applications such as vetronics.

In the '80s and into the '90s, designers did not really need to worry about the packaging of electronics, recalls Michael R. Humphrey, director of business development at AP Labs Inc. in San Diego. "You could put together a number of boards and didn't have to worry too much until the final stages, when you started to put a wrapper around the whole thing."

"In the past, it could be said that the enclosure was considered to be a non-critical component, in terms of design and lead time by the system designers," says Jim Tierney, vice president of government systems at Carlo Gavazzi Computing Solutions in Brockton, Mass. "Enclosures were viewed more as a commodity item that could be purchased from several suppliers and that baseline designs would meet the requirements. Backplanes were considered a standard component and most systems were of the 19-inch, rack-mount variety. This has changed significantly mainly due to the overall system complexity demanded, specifically in the thermal requirements imposed on the system."

"It was never a major challenge. A lot of packaging was so standardized that you could get to market with a solution quickly," Humphrey explains. "Things have changed considerably, however."

Boards: the few, the small, and the powerful

One major change, and a factor significantly influencing enclosure, backplane, and packaging selection, is the consolidation of boards. Printed circuit boards employed today are remarkably smaller, in size and in number, than in years past.

"Board sets have become less extensive," Humphrey notes. "We are putting so much onto a single-board computer now it's not funny. Three or four board sets and you have a really powerful computer system. We are talking about air-cooled boards in the 60- to 70-Watt range, and multi-core with upwards of 100 Watts."

It is important for a systems engineer to understand what the final configuration needs to look like, Humphrey explains. "You know going in that you have, say, 300 Watts in five or six boards, so you aren't going to escape with just any solution. It is driving designers to look at packaging as a bigger challenge earlier in the development."

In more and more cases, the enclosure/backplane/packaging is the first thing that is considered these days rather than the last, because "performance and power density are higher than ever before and rising quickly," says Rex Harvey, principal engineer at Parker Aerospace, Gas Turbine Fuel Systems Division, Advanced Cooling Systems (ACS) team, in Mentor, Ohio. "Heat and size have to be the first considerations these days, rather than the old process of designing the board and then throwing it over the wall to be packaged and cooled. That approach just does not work with today's performance density demands."

Smaller packages and higher power also breed a greater thermal challenge. "With the latest processors and board sets come greater power consumption and higher heat dissipation," Humphrey notes. "Heat has become the number-one problem."

Thermal management

Systems engineers and systems integrators increasingly are thinking about the enclosure and approaches to thermal management upfront in the process. "Four or five years ago, it was something of an afterthought," recognizes Joe Baddeley, executive vice president of business development and marketing at SprayCool in Liberty Lake, Wash. That is no longer the case. "As people look at making the transition from traditional VME to VPX, for example, they are thinking in terms of what approach is appropriate -- considering, 'Can I get away with simple tooling and letting air cool the components?' -- earlier in the process."

Characteristics that are of most interest early on are thermally related, Harvey acknowledges. "Such things as the temperature limits of the components used and the amount of waste heat that will have to be removed are crucial early design considerations. No matter how elegant a design solution is, it is useless if it will not fit or will burn itself up."

So much of today's selection criteria for an optimal enclosure solution center on thermal performance, Tierney says. "The thermal requirements, more than any other single element, will form the baseline for the design of an enclosure. Depending on the application, size, weight, and power [SWaP] can each have an impact on the approach used to solve the packaging problem, but most often engineers will dedicate a large portion of the design effort to optimizing the thermal efficiency of the system as they become smaller and need to dissipate larger heat loads."

The general shift to smaller designs and electronics footprints, while a boon for military and aerospace applications with strict SWaP requirements, is problematic in two ways. First, reduced size and increased power density drive the need for more-effective thermal management. Second, the cooling solution needs to fit in a smaller space and also not exacerbate power consumption and thermal management challenges. "The continued trend for electronics is more and more power in smaller and smaller boxes; that points to a tough thermal situation," Baddeley says. As a result, system designers and integrators are now considering all the cooling methods and technologies available to them.

Tierney and his colleagues at Carlo Gavazzi are starting to use several cooling techniques in a single enclosure or, more accurately, a hybrid thermal approach; yet, they are also planning ahead to meet future cooling needs. "There is little doubt what the future is bringing: more and more heat coming from smaller and smaller packages," Tierney predicts. "Air cooling will be even longer gone, and conduction cooling will also go by the wayside as liquid cooling becomes the only method of successfully handling the increasing heat loads. This trend is so inevitable that all our IR&D efforts are toward improvements and breakthroughs in the liquid cooling field."

The limitations of traditional thermal management methods, coupled with increased power density and heat dissipation, are contributing to an up tick in mil-aero systems designers looking at liquid cooling, whether liquid flow-through or direct spray. "Customers come to us already with an understanding that 3U boxes over 250 to 300 Watts and 6U boxes over 500 to 600 Watts probably need liquid cooling as the baseline," Baddeley explains. "That is certainly a new paradigm. There is a greater understanding and acceptance for where liquid cooling not only makes sense, but may be the only viable solution."

Traditional thermal-management methods, such as air cooling, are starting to lose favor among engineers not only due to increased heat dissipation, but also for environmental reasons.

"Powdery sand is an issue overseas," Baddeley says. "You have two choices: conduction-cooled or spray-cooled boxes that are completely environmentally isolated. It's not just about power and thermal issues; it is about survivability in general of air-cooled cards."

Environment is essential

Systems engineers should first consider the environments in which an electronics system will be deployed, Humphrey recommends. "The environmentals we are being faced with are extreme. If you take vehicles--everything from a HMMWV [Humvee] to a Bradley, Striker, or larger platform--every one of those beasts has its own shock and vibe characteristic." AP Labs engineers have dealt with shock and vibe from military wheeled vehicles for undisclosed contract work. "It's nasty -- inconsistent, with big swings and lots of shock," he describes.

Temperature is another environmental factor affecting electronics on land, sea, and in the air. Vetronics often have to start up in the morning when the temperature is well below zero. Avionics in an unmanned aerial vehicle (UAV), for example, also need to work effectively and reliably in areas with little, dense, and very cold air. "In the past five years, we've seen huge minus temperature numbers, and silicon doesn't like working in that environment from a temperature standpoint," Humphrey says.

A bulk of SprayCool's most recent contract wins center around airborne applications, specifically UAVs. SprayCool chassis enabled Northrop Grumman engineers to install their high-end signals intelligence payload in unpressurized and uncontrolled environments, such as pods on the U-2 and unpressurized bays within the Global Hawk and Predator aircraft under the Air Force's Airborne Signals Intelligence Payload (ASIP) program.

You have got to take into account the environmentals, insists Humphrey. "Is it going in a nice warm tank, shipboard, a man-occupied fuselage, or a UAV? It is important. All have different specs and quirks. The packaging has to be driven by what environment this entity is going to see."

In more and more instances today, a single system will be placed in a variety of platforms and environments. Systems engineers, and consequently enclosure/backplane/packaging vendors, are then faced with the challenge of combining land, sea, and air requirements into a single processing box to be employed in several different platforms.

"Key to meeting the harsh environmental demands of a mil-aero application is to select a proven, modular design concept that has been tested to mil standards, such as MIL-STD 810, 901, 461, 167, and 704," says Shan Morgan, senior vice president of systems sales at Elma Electronic in Fremont, Calif. "Whether the application calls for a convection-, conduction-, or liquid-cooled solution, by selecting a modular platform that has been demonstrated to meet the shock, vibration, and EMC needs of the application, the focus can shift to addressing more specific needs, such as: temperature extremes, altitude, power input source, I/O access, weight, and overall size/configuration."

Morgan admits that a system's thermal demands become a major design driver when considering the extremes in operating temperature and high-altitude environments typically encountered in mil-aero applications. "Perhaps the single most import consideration in selecting the optimal enclosure for mil-aero applications," Morgan continues, "is to work with a packaging partner that has extensive experience meeting the needs of this demanding market."

Undersea server

Crystal Group Inc. in Hiawatha, Iowa, won a contract from Technology Systems Inc. (TSI) in Brunswick, Maine, to design and build a waterproof server for video-capture applications. The system delivered by Crystal Group engineers is being used on small RIBs (rigid inflatable boats) to serve U.S. Coast Guard and Drug Enforcement Administration (DEA) needs.

"The environment is extremely harsh with substantial shock and vibration requirements as well as exposure to salt water," describes Jim Shaw, vice president of engineering at Crystal Group.

The power on the small boats is typically characterized by spikes, so Crystal Group engineers also needed to design an 11- to 32-volt DC (VDC) power supply with a 10-second hold up, Shaw explains. "We were able to create an IP68-rated (Ingress Protection rating) enclosure for these types of applications," he says. "Crystal Group is seeing a great deal of interest in this type of product."

Modernization drives customization

Makers of electronics enclosures, backplanes, and packaging are seeing a flurry of activity in modernization programs. Upgrading current force platforms with the latest electronics technologies -- smaller boards, more powerful processors, new form factors and I/O, and more -- is a priority and a challenge.

When it comes to upgrading current-force platforms, "We feel the need for speed," says Shaw, noting a constant push to get quality product to the warfighter faster. Rather than focusing on any one particular technology, Crystal Group personnel have been working on their internal processes to deliver needed solutions as quickly as possible. The company's engineers delivered to two undisclosed prime contractors a tactical computing module for a military vehicular application.

"Crystal Group was able to design, develop, build, test, and deliver the 3 GHz Core 2 Duo modules in six weeks," Shaw continues. "We have set up a pilot line cell in the plant that caters to these types of programs. The pilot line takes a huge chunk of time out of the schedule because we devote these resources to a single project."

Systems engineers and systems integrators leading modernization efforts are faced not only with a need for a more powerful thermal management, but also with the constraints of a pre-existing space. "There are a lot boxes out there today that operate with a very simple cooling system: a fan that is either off or on," Baddeley says. "The issue now is that when they upgrade the electronics, the simple fan is not good enough.

"They have a platform. It has a box on it. They are going through an upgrade cycle, but they find that the new box has twice the power level of the old box," Baddeley continues, profiling a typical customer today. "They need to fit all the new power in the same space with thermal management."

Humphrey is witnessing much the same at AP Labs. "Customers are coming to us and saying, 'I have a 14x9x23 space and that's all I have got; the cold plate is here, air comes in from here, here is my spec., here is my solution,'" he explains. "We are seeing that more and more."

Size is always a consideration when designing for mil-aero applications, but space constraints are especially critical when it comes to retrofitting -- adding new technologies and functionality to older systems.

"One of the important characteristics to be considered at the very start is the overall physical envelope in which the equipment is being installed," Harvey explains. "Such things as backplane sizes and thicknesses become critical in advanced mil-aero applications because package size is usually so very limited." He cites as an example retrofits into ATR spaces, which limit backplane thicknesses and placement, especially if special latches and/or insertion/extraction devices are needed to meet shock and vibe requirements or if optical interfaces are to be used requiring turn radius allowances.

Officials at Raytheon Co. in Waltham, Mass., contracted Elma Electronics engineers to develop and deliver a customized VME64x chassis for the Patriot missile system upgrade program.

Raytheon won an award of up to $3.3 billion to provide the United Arab Emirates with Patriot Config-3 capabilities, its most advanced Patriot system, and Patriot GEM-T missiles. For its part, Elma Electronics personnel combined custom parts from three of the company's U.S. divisions--a backplane and rear transmission modules (RTMs) from Elma Bustronic, a front panel and ejectors from the Components division, and the assembled enclosure from the System Platform division -- in a 9U chassis. The unit also boasts a 15-slot custom VME64x design using the company's 12R2 modular rugged system platform, as well as a custom I/O solution with special RTMs, a custom power supply, and a custom alarm board enabling fans to run only in certain temperature conditions.

Increasing mil-aero modernization activity, and the extreme requirements that accompany these projects, will drive non-standard packaging for the replacement market, Humphrey predicts. "The future market is current force, and we are talking about massive requirements for upgrades in current vehicles or current designs of vehicles in manufacture," he says. "This will drive custom packaging solutions."

Enveloping vetronics

Modernization of electronics systems in existing platforms, especially current-force combat vehicles, calls for enclosures, backplanes, packaging, and even cooling that are unique to each specific application.

When it comes to updating ground vehicles, "there's a lot of interest in low-cost, smaller solutions," Baddeley observes. "They have an existing space with an old box, now they want more computing requirements, but they can't grow that box. If the heat goes up, the box stays the same. They don't want to pay a lot of money for it, and they cannot cool it through conventional means."

Harvey credits specifications, such as the VITA 46/48/58 family, for offering "the ability to provide the needed functional density while retrofitting into existing ATR [air transport racks] and the smaller odd spaces that are available in modern ruggedized vehicles of all types. Depending upon the requirements, these specifications allow bare boards or rugged enclosed modules capable of two-level maintenance. They incorporate the VPX fabric interface that can supply over 800 Watts per 6U module. Obviously, power levels this high require very careful thermal considerations. More and more, liquid cooling is being called for as the only possible cooling method capable of removing that much heat from such a small package."

For high performance, high heat density applications, such as military vetronics upgrades, Parker Aerospace's ACS team designed the F-2 chassis. The rugged, modular electronics enclosure is designed to house VITA 48.2, 48.3, or 48.4 modules and to convert conduction-cooled slots to liquid-cooled slots. "This is becoming more important as applications waver near the edge of conduction cooling capability," Harvey explains. "Technology refresh upgrades can push these marginal conduction applications over to liquid cooling. The F-2 chassis alleviates the need to replace the entire chassis when this changeover in cooling methods is required."

Success in custom solutions

It would seem that the future, as it relates to enclosures, backplanes, and electronics packaging, is decidedly custom, and unique to each specific application. "The world of a standardized box is going to be poorly served," Humphrey predicts. "Opportunities exist at the engineering/design packaging stage where there's an embedded computer application to be created and the space it has got to fit in doesn't fit any IEEE and VITA document known to man--that's the opportunity."

Morgan agrees, stating: "With the increased complexity of electronics packaging, we expect to see the trend of more customization to continue. The impetus will be on providing solutions versus offering products."