Rugged development requires†integration of design and test from start to finish
In 1972, Dave Packard of Hewlett-Packard said, “There is only one road to reliability. Build it, test it, and fix the things that go wrong. Repeat the process until the desired reliability is achieved.” Few areas of hardware engineering require more testing than the development of rugged industrial products. In order to develop a truly rugged solution that meets required international standards, government regulations, general environmental specifications, and customer-specific performance requirements, designers must incorporate rugged design methodology into every aspect of the development process. This means following a rigid validation and verification testing process that is as much a part of the development cycle as the product design itself.
The term ruggedized often refers to commercial-grade designs that are screened at high temperatures with high yield fallout. However, ruggedization of existing mechanics isn’t enough to meet the requirements of industrial applications 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. For truly rugged electronics, boards and systems are best designed for harsh environments from the ground up, with special attention and care given to component selection; circuit design; printed circuit board (PCB) thickness, layout, and materials; thermal solutions; enclosure design; and manufacturing process. Just as important to the development cycle is testing of the design in order to validate choices and guarantee required performance levels and solution durability in a variety of simulated environmental conditions. Robust test methods ensure optimal product design phases in order to meet a product’s stringent requirements, such as -40 °C to +85 °C operating temperature range, MIL-STD, shock and vibration, and long-term 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.
With rugged, in-vehicle applications, vibration control is critical for performing functions like capturing video or securing targets. Some rugged boards offer a thicker PCB fabrication to add rigidity so that 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, as heat is a common unwanted byproduct of processing power.
Selecting the right form factor for rugged designs
Rugged boards come in many form factors, so starting with the right one is key in being able to deliver customer-specific requirements. Let’s take a quick look at industry-standard single board computers (SBCs) and computers-on-module (COMs).
Embedded Board eXpandable (EBX) and PC/104 are good format options for designs that can handle slightly larger SBC form factors. With just 46 square inches of surface area (8 inches by 5.75 inches), 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 multicore technology for networking, digital signal processing (DSP), and graphics-heavy applications; EBX also sports generous onboard I/O functions to support everything from large data exchange to video. The PC/104 embedded computing format has no backplane, instead 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; it also 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 create 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. (Figure 1.)
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 size, weight, power, and cost (SWaP-C). In addition to ruggedness, users of PC/104 have come to expect long life cycle support. When considering shrinking DoD budgets, the robustness, longevity, and compatibility of the PC/104 ecosystem ensure strong system support and minimized costs.
In cases where an application design requires very specific I/O or physical size/shape restrictions, then a 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. With the COM approach, all generic PC functions are readily available in an off-the-shelf foundation module, enabling 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 enables 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. The modular processing block enables the designer to create a price and value advantage without getting locked into a single vendor for board creation. As 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. (Figure 2.)
Rugged design validation
Guaranteeing the customer experience means not only satisfying regulatory requirements (EMC/safety/environmental testing), but also hewing to availability and durability requirements. Strength and Highly Accelerated Life Test (HALT) are used to simulate product aging to find design limits and maximum operating range by testing for issues such as displacement due to tolerances. This entire process enables hidden product defects to be exposed and addressed early in the development cycle.
Rugged designs are subjected to extensive voltage and temperature margin tests during the new-product development process, then are validated using HALT, shock and vibration testing, and voltage margining.
The HALT process consists of progressively increased extremes of temperature (both high and low), rapid thermal transition, six-axis vibration and – finally – combined temperature and vibration stress. Failures and the physical damage found at the destruct limits provide data, which is used to improve the ruggedness of the product design.
Rugged board products are generally shock and vibration tested to meet the MIL-STD-202G standard. This includes subjecting the product to multiple 50 G shocks and 11.95 Grms of random vibration between 100 Hz and 1,000 Hz along each axis.
Additionally, voltage and temperature margin testing is used during the product development process to subject the product to temperatures well outside the intended operating temperature range (-40°C to +85°C for extreme rugged products). The product is simultaneously subjected to minimum and maximum rated voltages (±5 percent). This process verifies products are functional and stable over combined extremes of both temperature and voltage, and ensures wide design margins resulting in long-term reliability under all specified operating conditions.
Fulfilling extreme expectations
Industrial computers are used in myriad rugged applications. They are subjected to frequent vibrations aboard vehicles, are found in factories with high temperature and humidity, are deployed in deserts or high mountains with temperature differences of as hot as 90 degrees Celsius, or are designed into guided missiles as flight controllers. To provide customers with highly reliable industrial-grade products that conform to catalog specifications and rugged application environments, solution providers must put as many resources – time, money, and human – into testing as they do into design. Just as rugged products are expected to perform when taken to extremes, a comprehensive rugged hardware-development process with equal emphasis on design and test processes must mirror those extremes.
ADLINK Technology (408) 360-0200