It can be argued that small form factor design trends are paradoxical. As form factor size decreases, functionality requirements increase; as processing power requirements heighten, lower power consumption and thermal output is expected. Add to that the requirement for ruggedness to accommodate for the shock, vibration, humidity, and temperature extremes and variance inherent in mobile and outdoor applications, and designers are faced with a very complex soup.

Figure 1. The PC/104 embedded computing format has no backplane, instead allowing modules to stack together like building blocks. Many applications in defense and transportation still incorporate legacy devices that require an ISA-BUS interface.
Mobility and environmental extremes are critical considerations for rugged board design in military, transportation, industrial and surveillance applications, to name a few. And with today’s emphasis on SWaP(-C) in embedded system design, it’s critical for embedded designers to follow industry standards, and equally critical for industry standards to continue evolving to maintain relevance.

Selecting the Right Form Factor

Embedded Board eXpandable (EBX) and PC/104 are good format options for designs that can handle slightly larger Single Board Computer (SBC) form factors. With just 46 square inches of surface area (8" × 5.75"), EBX balances size and functionality with a bolt-down SBC format supporting rugged embedded designs with higher-performance Central Processing Units (CPUs), such as those using multi-core technology for networking, digital signal processing (DSP), and graphicsheavy applications, and generous onboard Input/Output (I/O) functions to support everything from large data exchange to video. The PC/104 embedded computing format has no backplane, allowing modules to stack together like building blocks more rugged than typical bus connections in PCs (such as PCI or PCI Express slot cards).

PC/104 delivers high performance combined with low power, stackable configurations and adherence to MIL-STD, and it meets key industrial and transportation standards for electromagnetic interface/compatibility (EMI/EMC), e.g. EN50121, EN50155, EN610000-x, etc. The ability to build stacks of PC/104 modules creates opportunities for developing a diversity of complex, often mobile, applications that range across industrial, transportation, and defense environments where PC/104’s robust and reliable capabilities are required. In addition, PC/104’s transition into vision and visual security monitoring systems is benefitted by PCI Express, as it has the capacity to directly meet the bandwidth needed to support multiple data streams (Figure 1).

Though the number of stacks included in PC/104 systems has been decreasing, the form factor continues its warm relationship with industries requiring rugged applications with high resistance to shock and vibration. In defense and transportation, legacy devices and ISA-BUS interface requirements are still plentiful. With high-speed serial I/O interfaces, such as PCI Express, supported in current PC/104-based standards, PC/104 boards are keeping pace with the movement toward consolidating workload on expansion modules, requiring fewer layers to fulfill application requirements.

The ability to withstand temperature extremes often associated with remote environments still allows PC/104 to excel in off-grid computing (e.g., defense apps). Stackable, mix-and-match modularity and the intrinsically rugged design of PC/104 is ideal for many of today’s technology upgrade programs looking for Commercial Off-the-Shelf (COTS) options — especially those that value SWaP(-C). In addition to ruggedness, users of PC/104 have come to expect long lifecycle support. When considering shrinking DoD budgets, the robustness, longevity and compatibility of the PC/104 ecosystem ensure strong system support and minimized costs.

Figure 2. A design using the COM Express form factor provides off-the-shelf functionality and an easy upgrade path by putting the customization on the baseboard, thereby creating more flexibility with the module without sacrificing performance.
While PC/104 allows flexibility by combining cards to meet application requirements, the PC/104 format becomes less attractive when very high computing speed and network throughput is required — situations where VPX or CompactPCI (cPCI) formats are better suited. In cases where an application design requires very specific I/O or physical size/shape restrictions, then a Computer-on-Module (COM) approach would provide better results.

COMs are complete embedded computers built on a single circuit board for use in small or specialized applications requiring low power consumption or small physical size. Though they are compact (ETX/XTX at 114mm x 95mm and COM Express at 125mm x 95mm to 84mm x 55mm) and highly integrated, COMs can accommodate complex CPUs (Figure 2).

With the COM approach, all generic PC functions are readily available in an off-the-shelf foundation module, allowing system developers to focus on their core competencies and the unique functions of their systems. A custom designed carrier board complements the COM with additional functionality that is required for specific applications. The carrier board provides all the interface connectors for peripherals, such as storage, Ethernet, keyboard/mouse and display. This modularity allows the designer to upgrade the COM on the carrier board without changing any other board design features, and also allows more customization of peripherals as dictated by a specific application.

The COM Express form factor offers flexibility in the development and advancement of ultra-rugged embedded applications for a wide range of industries. By using the modular processing block, the designer creates a price and value advantage; he/she isn’t locked into a single vendor for board creation and can customize based on pricing and performance requirements. Because it is easily swapped from a carrier board and comes in one of the smallest form factors, COM Express is ideal for long-life embedded applications with a critical development cycle, as well as more progressive applications that require frequent processor upgrades without affecting other application design elements.

Rugged Design for Harsh Environments

Figure 3. Rugged military systems using small form factor COTS design and industry standards, such as the high-performance embedded computing (HPEC) platform built around VITA75 shown above, are required to meet the requirements for SWaP(-C).
Rugged solutions are most often housed outdoors or in moving vehicles, where exposure to a variety of climates dictates the need to operate in extended temperatures and to power up in any extreme. The easiest initial step is to select a rugged board or system that is designed for harsh environments from the ground up. To support the extremes of shock, vibration, humidity, and temperature, care is given to component selection, circuit design, printed circuit board (PCB) layout and materials, thermal solutions, enclosure design, and manufacturing process. Robust test methods, including Highly Accelerated Life Testing (HALT), ensure optimal product design phases in order to meet a product’s stringent requirements, such as -40°C to +85°C operating temperature range, MILSTD, shock and vibration, and longterm reliability.

Conformal coating can also reduce degradation from exposure to outside elements. A variety of conformal coating materials (such as acrylic, polyurethane, epoxy, and silicone) and application methods (such as brushing, spraying, and dipping) are currently used to protect against moisture, dust, chemicals, and temperature extremes that can potentially damage electronics. The correct coating or application method varies depending on established standard operating conditions for an application. With transportation applications, different coatings may be selected based on a primary need for moisture resistance versus abrasion resistance versus temperature stability.

Maintaining Performance While Mobile

With rugged, in-vehicle applications, vibration control is critical for performing functions like capturing video or securing targets. Some rugged SBCs offer a thicker PCB fabrication to add rigidity so the board can withstand higher levels of vibration strain. The thicker PCB offers stability to the overall surface area, protecting electronic components from damage due to vibration.

The thicker PCB also offers the ability to use more copper between layers for thermal considerations. Heat is a common unwanted by-product of processing power. In addition to cooling fans and large heat sinks, which may not always be possible for compact, mobile transportation designs, PCBs with adequate amounts of integrated copper facilitate heat conduction away from temperature- sensitive electronic components to prevent performance degradation.

Focus On The Military

Nowhere is the concept of SWaP (-C) more emphasized than in the defense market. And yet the demand for highperformance embedded computers has never been greater. The changing face of military engagements, fewer troops on the ground, more use of reconnaissance gathered via UAVs, real-time feeds to ground mobile operations and the emergence of network-centric warfare are driving what needs to be created to support today’s warfighter.

At their core, today’s battlefield engagements depend on access to and the ability to share complex, real-time data with the battlefield commanders, and an ability to push select information all the way down to the front-line warfighter. As the defense market demand increases for better SWaP with every increasing level of performance, solution providers must respond with smallform- factor, high-performance, rugged, embedded computing designs based on open standards.

For instance, VITA75 — which defines specific box sizes, connector content and placement, and multiple types of cooling — is one example of a standard that will enable this type of high-value, no lock-in solution. By electing to build solutions based on industry standards, this provides choice to the defense market customer. Now selection and evolution of a solution can be based on a value/cost return analysis rather than being hardwired into a proprietary solution (Figure 3).

Leveraging COTS Technology

There is innovation required to provide more processing in smaller, lighter, and more power-efficient form factors while also adhering to industry-accepted standards. The industry’s focus should be on leveraging COTS technology to bring that innovation to markets that need rugged solutions.

This article was written by Jeff Munch, CTO, ADLINK Technology (San Jose, CA). For more information, Click Here .