Imagine a geological research station operating in the frigid Arctic valley, a space shuttle propelling through Earth’s atmosphere to deep space or a long-haul transportation truck driving through the Sonoran Desert. The electronics embedded in those systems must face and survive extremely harsh conditions.
Exposure to extreme temperatures, high humidity, vibration, dust, electromagnetic interference (EMI) and corrosive substances challenges the reliability, longevity and performance of electronic components.
Engineers designing ruggedized electronics for harsh environments must ensure the operating temperatures are within the specifications for the components and that they are resilient to factors such as water ingress, condensation, shocks, vibrations and corrosion. To overcome these challenges, you must carefully select materials, employ robust design techniques and conduct rigorous testing.
Selecting Material
One of the key considerations for designing ruggedized electronics is the selection of materials. In harsh conditions, the printed circuit board (PCB) substrate must be able to withstand thermal, mechanical and chemical stresses. PCBs using ceramic are more resilient in extreme temperatures and offer better thermal conductivity. Polymide, with superior thermal and mechanical properties, is suitable for aerospace and military applications.
Conformal coatings create polymeric films that protect PCBs from moisture, dust, chemicals, dirt, abrasion and mechanical stress. Acrylic, silicone, parylene and urethane are commonly used as conformal coatings. Acrylic coatings, which offer moderate protection, are easy to apply and remove. In high-temperature environments, silicone is suitable for its thermal and moisture resistance. Polyurethane prevents damage from chemicals and abrasion, while parylene is a good light-weight option.
Enclosure materials are also vital as they protect the electronics from physical and environmental damage. Durable and corrosion-resistant options include aluminum, stainless steel, polycarbonate and fiberglass reinforced plastic (FRP).
Considerations for Connectors
Connector design is constantly evolving to facilitate reliable operation in increasingly harsh environments. For example, connectors used in agricultural farms are exposed to dirt, heat and subsequently high-pressure washdown systems, which collectively could lead to a mechanical failure.
Harsh environment connectors ideally provide metallic sealing, along with an electrical connection achieved by soldering the connector directly to the board or through a cable connection.
The impact of various factors, including temperature, solvents, icing, salt exposure, moisture, corrosion and fungus, is a crucial consideration in connector selection. Suboptimal connectors compromise the integrity, performance and durability of the applications.
In environments where electromagnetic interference is common, connectors must shield components from EMI radiation. Radiation can be emitted from a device, affecting adjoining devices, or vice versa. Connectors, fitted with conductive gaskets and plated metal shells, ensure optimum EMI performance in harsh environments. Termination style also affects performance and longevity.
Intrinsic Safety Consideration
Intrinsically safe embedded electronics are resilient to multiple failure conditions. Design considerations include shielding the electric circuit to protect against ignition and restricting the energy discharged if a component or wiring fails.
Batteries should be sufficiently robust and have minimal electrolyte leakage to protect against severe short-circuit environments. The stored energy in energy-storing components, such as capacitors, inductors and ferrite beads, must be restricted so that there is insufficient energy to ignite an explosive atmosphere. Energy-storing components are vulnerable to compliance with spark-ignition parameters. Encapsulation can be used to shield circuits against any chance of spark ignition.
Thermal Considerations
While active and passive cooling are inherent design considerations for integrated circuits (ICs), it’s not practical in many ruggedized applications, including transportation, aerospace, industrial and mining. The operating temperature of around 125° Celsius is quite common inside an automotive hood. Jet propulsion systems are another example where temperature can soar to hundreds of degrees Celsius. The geothermal gradient of deep wells exposes ICs used in the downhole oil and gas applications to increasingly high temperatures of over 200°C while operating at peak capability. Failures in systems operating at such high temperatures lead to costly rig downtime.
Thermal issues crop up in electronics when exposed to extreme temperature conditions, affecting durability and performance. ICs designed for an industrial ecosystem characterized by extreme operating conditions must withstand thermal exposures ranging from -40°C to 200°C.
Thermal shutdowns used in voltage regulators and power ICs can prevent thermal faults. Implementing super-low thermal impedance packages can help to transfer heat away from the device. Using aluminum heat pipes or heat sink casings creates a lower thermal impedance path to air, thus reducing operating temperature.
Testing and Validation
The intended lifespan of electronics used in industrial PLCs, sensors, actuators and motors extends to decades. Adequate testing and validation are integral to system design, ensuring reliable operation for decades.
Environmental testing exposes devices to temperature cycles involving alternating high and low temperatures. The robustness of the devices is validated by exposing them to high-humidity conditions and by simulating various stress conditions.
Vibration in electronic equipment is a significant contributor to system failure and other operational issues. In many industrial and military verticals, vibration isolation is a crucial part of a product’s design. While modeling and analysis can help determine potential vibration levels, testing is needed to ensure reliability in harsh conditions. Advanced stress testing techniques, such as highly accelerated life tests (HALT) and highly accelerated stress tests (HASS), are often required to detect potential vibration issues that may occur during a military-grade product’s 30-year lifespan. These methods stress products beyond their specifications to identify both operational and destructive limits.
Conclusion
Designing ruggedized electronics for harsh environments is essential to cater to the needs of various industries, including automotive, industrial, oil and gas and aerospace. Every use case has its unique challenges. Along with implementing robust design techniques, you need reliable components and connectors designed specifically for harsh conditions. TTI is committed to partnering with engineers in their relentless journey of building ruggedized electronics.
Sravani Bhattacharjee has worked as a tech leader at Cisco, Honeywell and other companies where she delivered many successful innovations to the market. As the principal of Irecamedia, she collaborates with Industrial IoT innovators to create compelling vision, strategy and content that drives awareness and business decisions.
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