Backplane and enclosure designers beat the heat with new architectures

Feb. 1, 1998
The newest military and aerospace electronic systems are packed with notorious heat-producing components such as the Intel Pentium microprocessor, so packagers now look to optical fiber and other new ways of safeguarding sensitive chips and circuit boards

Backplane and enclosure designers beat the heat with new architectures

The newest military and aerospace electronic systems are packed with notorious heat-producing components such as the Intel Pentium microprocessor, so packagers now look to optical fiber and other new ways of safeguarding sensitive chips and circuit boards

By John Rhea

Electronic enclosures and backplanes, the structures that house and interconnect today`s sophisticated avionics, shipboard munitions guidance, and strategic battle management systems, are under increasing stress as systems designers seek to move and process ever-growing amounts of data, while shielding their systems from ever-increasing amounts of heat, electromagnetic interference, and other potentially hazardous conditions.

It is advances in the integrated circuits and printed circuit boards that lie at the heart of these military and aerospace electronic systems that are driving developments in the backplane and electronic enclosures industry. These sophisticated new integrated circuits are responsible for providing increasingly complex integrated systems with more processing power and improved techniques for distributing that computational power where and when it is needed.

Yet increases in processing power inevitably generate more and more heat at the chip level - and heat is the number-one cause of electronics failures. No designer can take the heat issue lightly. In fact, the chips that are getting warmer to reflect this elevating functionality now come in three types of increasing difficulty for the system designer: "easy to use," "bun warmers," and "bacon sizzlers," quips Barry Isenstein, vice president for advanced technology at Mercury Computer Systems in Chelmsford, Mass.

Still, heat is not the only threat that backplane and enclosure manufacturers seek to mitigate with their products. There is also the problem of electrical power distribution within the avionics and other advanced systems, particularly now that chip makers are switching to the 3.3 volt chips for the new Power PC and Pentium processors, Isenstein points out. As a result, backplane and enclosure designers must tailor their subsystems to these powerful new chips, not merely to the most environmentally vulnerable components to go in the chassis, he adds.

There are basically three ways to remove the heat. Although air cooling is the easiest and cheapest, it presents a big problem for avionics; there is not much air above 10,000 feet, Isenstein says. Systems designers have used a variety of liquid coolants in the past in systems such as the Digital Equipment Corp. VAX 9000 line and the original Cray supercomputers, which actually operated immersed in the equivalent of automotive antifreeze, but that is the approach of last resort. "You never do that if you don`t have to," Isenstein comments. "The [coolant] leak problem is horrendous." The compromise solution, at least at the subsystem level, is conduction cooling.

Cool fiber approach

And then there is the system architecture approach, including the use of optical fiber, to increase the data throughput while reducing some of the heat, weight, power, and volume problems associated with conventional copper cabling as well as the persistent problem of electromagnetic interference (EMI).

Gerald Sauter, an engineer at Lockheed Martin Tactical Defense Systems in Eagan, Minn., says the optimal avionics system architecture for such future systems as the Joint Strike Fighter (JSF) will consist of several interconnected processor units capable of evolutionary growth.

The architecture must meet the demands of future military avionics processing requirements with embedded multiprocessing based on shared memory techniques within a low-cost, flexible, scaleable, modular, and open-standard architecture, Sauter explains. His favored approach uses building blocks that engineers can assemble into various configurations to satisfy requirements for connectivity, performance, and fault tolerance as they change over the lifetime of the system.

The need for multiprocessing (including massively parallel processing) continues to expand almost in lock step with the expansion in functionality. Examples include multi-sensor integration, data fusion, image processing, and automatic target recognition. The idea, according to Sauter, is to move as much sensor processing as possible into modular integrated processing racks.

"We believe that one of the key contributors to affordability over the avionics lifecycle will be the ability to dynamically allocate this pool of processing resources to various tasks as they become critical during a mission," Sauter says. This reduces what he calls "loafing assets," increases fault tolerance, and reduces spares requirements because tasks are not physically dedicated to particular resources.

"Additionally, these modular racks enable the affordable insertion of new technology resulting in an architecture that is both scaleable and adaptable," Sauter continues. "However, the key to implementing this type of architecture is the use of a high-bandwidth and low-latency interconnect between all processing resources within the avionics system."

Lockheed Martin`s approach, which it is developing under the Naval Air Systems Command (NavAir) Optical Backplane Interconnect System program, is an array of fiber optic connections based on the SEM-E printed circuit card form factor and backplane data bus that makes the maximum possible use of commercial off-the-shelf (COTS) technology.

The Optical Backplane Interconnect System program to date has demonstrated the use of a self-contained, replaceable, repairable optical backplane and the use of commercial optical ferrules for connection from the module to the optical backplane. Operational systems are expected to include two to 16 racks with as many as 64 modules per rack.

Competing optical technologies

The competing technologies include single optical fibers in a switchboard layout, integrated optical waveguides from polymers, embedded optical fibers touted on the electrical backplane, and multi-channel optical media strips encased in a rugged housing. Within a tactical aircraft, for example, the distances between racks are expected to be less than 100 meters where optical fiber should support gigabit data rates.

Although single-channel optical transmitters and receivers are generally available in military-grade packages, they tend to be expensive and do not always provide the necessary bandwidth. NavAir experts are looking at multi-channel vertical cavity surface emitting laser arrays and comparable photodiode arrays for future systems to push the bandwidth. NavAir officials plan a flight test for this year using the Navy`s F/A-18E/F aircraft.

Fiber optic local area networks (LANs) within aircraft are not new. Engineers at Boeing-McDonnell Douglas in St. Louis pioneered their use in the 1970s with a non-flight-critical application in the AV-8B Improved Harrier jump jet to demonstrate feasibility, including installation and maintenance procedures. They have also been considered for "fly-by-light" control systems on the U.S. Air Force F-22 advanced tactical jet fighter and for commercial jet airliners from the European consortium Airbus Industrie, but engineers tend to regulate them to secondary uses such as in-flight entertainment systems.

Now, however, as military aircraft undergo service life extension, the inherent advantages of fiber optics make this the technology of choice. The obvious benefits of immunity to EMI and significantly greater bandwidth than their copper-wire cousins make the optical fiber decision a "no brainer" in the words of Sam Densler, manager of a program to upgrade the Joint Surveillance Target Attack Radar System aircraft - better known as Joint STARS - from Northrop Grumman Corp. in Melbourne, Fla.

Northrop Grumman designers received two contracts totaling $132 million from the Air Force last spring to upgrade the Joint STARS computers with COTS equivalents and thus take advantage of the high processing power available from state-of-the art digital signal processors. Replacing copper cables with their fiber optic equivalents was not even in the original statement of work, adds, Alan Metzger, Northrop Grumman`s chief engineer on the project. But company experts proposed - and Air Force leaders agreed - that as long as they had to rip out the original cabling, this was an opportunity to create an infrastructure to meet future needs.

Densler and Metzger estimate that the LAN replacement represents about $6 million out of the total Joint STARS upgrade project. Instead of copper cables, with a bandwidth limit of about 10 megabits per second, Northrop Grumman designers are using multi-mode and single mode fibers with an initial data rate of 100 megabits per second half duplex and 160 megabits full duplex, and with growth capability to the gigabit range.

As part of the system architecture change, Northrop Grumman designers are moving away from the traditional databus structure to cross bar switching. The LAN will support Fibre Channel or asynchronous transfer mode - better known as ATM - and accommodate the latest SHARC digital signal processors (DSPs) from Analog Devices in Norwood, Mass., and the next generation PowerPC microprocessors. The new fiber optic system links the processors (three, including one hot spare, a reduction from the five processors needed in the original configuration) to the operator stations. Engineers designed in patch panels for flexibility.

For the future, this gives the Air Force a multimedia capability, including imagery, video and image exploitation, that would not have been possible with copper, Densler explains. Joint STARS was ideal for this demonstration, he adds, because the Boeing 707 aircraft represents a relatively benign environment for COTS components and subsystems.

Backplane developments

The backplane business, a segment of the overall connector business, is evolving. Ken Fleck, a market analyst based in Santa Ana, Calif., estimates it at around $1.5 billion (a little more than half of that in North America) out of the global connector business of about $27 billion.

One trend that officials of Teradyne Connection Systems Division in Nashua, N.H., identify is the move away from in-house "captive" production to greater reliance on merchant market suppliers, paralleling a similar trend throughout the electronic component industry. With the increasing tempo of technology, end users can get better, more economical products from outside vendors.

And, as with the rest of the electronics business, growing commercial markets are driving the technology. Telecommunications component vendors, in particular, sell high-reliability products in sufficient volumes and at attractive enough prices to make these solutions attractive for military systems designers as COTS items. Teradyne leaders, who entered the commercial backplane market in 1984 with their High Density Plus line, have seen their commercial sales soar over the past 13 years from 30 percent to more than 80 percent of their $250 million annual volume.

Using this commercial business as a base, Teradyne officials are forming working relationships with their customers at the initial stages of a product life cycle. As equipment makers outsource more of this work, they must get more involved with higher levels of systems-integration issues than they did only a few years ago. Vendors today have to tackle such technical issues as how many circuit boards they need to interconnect, how many interconnections are necessary per slot, and how much power they need to distribute. These are issues that ultimately determine costs and the critical time-to-market concerns in competitive commercial industries.

Roger Stevenson, manager of business development at Hybricon Corp. of Ayer, Mass., a manufacturer of VME64 extension backplanes, in fact, sees the second-level subcontractors on major aerospace programs as the focal point of the market. In effect, Hybricon officials sell to the companies that sell to the prime aerospace contractors. This results in backplanes that are known quantities to their users. "It`s a lot of generic boxes, and the Navy loves `em," Stevenson notes.

Hybricon engineers supplied the extension enclosures for shipboard tactical computers, and now are parlaying that technology for backplanes and enclosures for the international space station. Stevenson also maintains that the VME business is moving from supporting the conventional 5 volt devices to 3.3 volt chips, which he expects to be mandatory within a year. The pin density is increasing, and other refinements are necessary to keep pace with user demands.

At Vero Electronics of Wallingford, Conn., product manager John Bratton stresses an integrated packaging approach in a sort of mix-and-match combination of COTS racks, subracks and enclosures, power supplies, multilayer backplanes, and thermal management. He agrees on the need to accommodate 3.3 volt devices and warns about potential hot spots in an aircraft. Vero Electronics is a subsidiary of the England-based Vero Group.

Bratton says the U.S. Navy is the service that most readily has accepted COTS backplanes with the Army following closely behind. In submarines and main battle tanks, for example, systems integrators found it possible to redesign the systems to protect the electronics. Air Force officials have been more cautious in its approach, he adds, but the Joint Strike Fighter is VME-compatible and represents a "clean sheet" approach.

Dawn VME Products of Fremont, Calif., has worked with Sun Microsystems of Mountain View, Calif., on VME-compatible subsystems for commercial market and now provides custom design capabilities for military and commercial systems designers. Bill Reilly, director of sales and marketing at Dawn, says he sees opportunities for VME64 extension hardware in the high-performance military systems, including classified programs. For military customers, he estimates that COTS solutions can save at least 20 percent depending on quantity.

"There has been some movement in COTS," Reilly notes, "but there`s room for improvement." The problem stems from the red tape necessary to implement COTS in the older programs, he adds.

Kevin Rowan, vice president for sales and marketing at Lockhart Industries, a rugged enclosures firm based in Paramount, Calif., stresses the need for cooling at the card level. What is needed, he says, is a rugged, zero-leak quick-disconnect liquid coolant.

High densities of electronics are driving this requirement, Rowan maintains, and there is the continuing requirement for EMI protection. In electronic systems that generate extreme amounts of heat, liquid cooling can be four or five times as efficient as air, he adds. He also expects the SEM-E form factor to continue in use.

Joseph Schooley Jr., senior applications engineer at Malco Inc. in Colmar, Pa., sees the enclosures and backplane business as a "job shop" to customize these components for the major primes. Colmar designers produces standard VME backplanes and custom integrated subsystems containing custom backplanes, various power and cooling options, interwiring and cabling, and I/O options. The company also works on military and telecommunications applications.

Leaders at I-Bus, a Maxwell Technologies company in San Diego, have built a base with their Thresher Pentium Pro-based board for applications using 32-bit operating systems like Windows NT. They are now launching a dual Pentium II board, designated the Nautilus. Pam Miller, director of marketing, explains that her company also has an Ultra2 Wide SCSI interface to support high-end applications that is targeted for imaging and data processing.

Click here to enlarge image

Rugged enclosures are an increasingly popular way to use commercial-grade components in rugged environments. Pictured above is the Verak enclosure, which screens components from radio frequency interference, from Vero Electronics Inc. of Wallingford, Conn.

Click here to enlarge image
Click here to enlarge image
Click here to enlarge image
Click here to enlarge image
Click here to enlarge image

VME computer enclosures and backplanes such as those pictured above from Dawn VME are becoming ever-more standardized to facilitate modular designs, yet are starting to offer increasing amounts of throughput. VME backplane data buses are approaching bandwidth of 320 megabytes per second with the coming VME 320 standard.

Whatever happened to Tempest?

The days of full-Tempest specifications to maintain information security in military systems are dwindling down to a precious few, and the reason is commercial off-the-shelf (COTS) technology, say experts who are in a position to know.

Tempest refers to metal shielding around computers, monitors, and peripherals to contain stray electronic signals. Sophisticated surveillance equipment is capable of intercepting static electronic signals emitted from computers to capture sensitive data.

"Tempest dried up at the time of COTS two or three years ago," comments John Bratton, product manager at Vero Electronics in Wallingford, Conn. Some classified programs retain the requirement, but most program managers have found that they can meet data-security requirements without the complication of using Tempest gear.

Ted Brewster, director of marketing and sales at Carlo Gavazzi Inc. in Brockton, Mass., says the decision comes down to some simple arithmetic: "You can make your computer Tempest, but that costs a fortune. Or you can build a fence around the building and cut the price in half."

However, Tempest-level shielding has not completely gone away, Brewster adds. The Milstar satellite network needs it, and military officials must maintain tight security for e-mail and targeting for the Tomahawk cruise missile.

But for most applications, a commercial chassis can do the job - at substantially lower cost than Tempest-qualified equipment. Brewster cites the example of a power supply designed for the full military environment that used to cost $10,000. Using best commercial practices, that power supply now costs $1,000.

What used to be the rigid Tempest specification is now divided into two levels of security, Brewster explains: "red," which still meets the full Tempest cryptographic requirements, and "black," which must meet only standard Federal Communications Commission limitations on electromagnetic radiation. - J.R.

Who`s who in backplanes and enclosures

AP Labs

San Diego / 619/546-8626

Bustronic Corp.

Fremont, Calif. / 510/490-7388

C&R Systems

Hamilton, Ohio / 513-860-1544

Carlo Gavazzi

Brockton, Mass. / 508/588-6110

Dawn VME Products

Fremont, Calif. / 510-657-4444

Elma Electronic Inc.

Fremont, Calif. / 510/656-5829

Hybricon Corp.

Ayer, Mass. / 508/772-5422


division of Maxwell Laboratories

San Diego / 619/974-8400

Kingston Technology Co.

Fountain Valley, Calif. / 714/435-2615

Lockhart Industries

Paramount, Calif. / 562/663-2499

Malco Inc.

Colmar, Pa. / 215/997-8454

Teradyne Connection Systems Division

Nashua, N.H. / 603/791-3000

Vero Electronics Inc.

Wallingford, Conn. / 203/949-1100

Voice your opinion!

To join the conversation, and become an exclusive member of Military Aerospace, create an account today!