A technology company developed an edge device tailored for monitoring various facets of agricultural equipment, from fuel consumption to engine management. They selected a robust off-the-shelf enclosure and subjected the enclosure to rigorous outdoor testing, confident that it was fit-for-purpose after being exposed to harsh weather elements.
As the device was deployed in the field, a problem emerged. The supposedly robust enclosures faltered. Initially, the failure was attributed to UV exposure. However, after closer inspection the real problem was revealed – diesel splashes. The device was installed in the proximity of a fuel cap. Despite its high rating and considerable cost, the plastic polymer suffered from exposure to diesel, which resulted in cracks in the enclosure.
Design decisions about the robustness of electronic enclosures often focus solely on weather conditions, leading to the perception that off-the-shelf IP-rated enclosures are adequate. The tendency to go for IP67 or IP68 casings further exacerbates the problem. No, or little, consideration is given to dust, vibration, temperature variation, and exposure to UV or chemicals.
The deployment of IoT devices has grown exponentially and is expected to continue growing. IoT and remote devices are increasingly deployed in challenging environments like mining, transport, marine, and agriculture. It is paramount for these devices to endure harsh conditions to ensure both data continuity and reliable control.
IoT edge devices typically include sensing capabilities, a controller (a microcontroller or small compute module), and a communication module. The design of IoT edge devices requires an integrated approach between electronic, mechanical and enclosure design. Robust electronic design is essential to handle physical, EMI, and power challenges, especially for remote or mobile applications. Mechanical design considerations for the PCB and wiring should include heat, vibration, and corrosion. Added to this, the casing or enclosure of the device needs to be robust enough to protect and prevent the electronics and mechanics from failure in extreme environments.
Very often, chemical resistance is the culprit in severely damaging enclosures. In the transport industry, diesel and cleaning agents are known for weakening enclosures. In any environment, petroleum-based fuels, cleaning agents or greases can weaken polymer along stress concentrations. This failure mode is regularly overlooked.
With regards to IP ratings, IP67 and IP68 are designed for underwater purposes, which poses challenges. While the benefit is easy testing – just hold it under water to check for leaks – the requirement for complete sealing becomes problematic during temperature fluctuations. This issue intensifies with larger enclosures, leading to water ingress over time, due to condensation. Experience indicates that even custom-designed enclosures with these IP ratings can experience water-related failures in as little as two weeks, making it a major concern for IoT and remote devices.
Another significant problem for edge devices is insects. Despite receiving minimal attention, insects can quickly damage or disrupt the functioning of electronic devices. The mitigation of insect-related issues demands specialised design considerations.
Solutions for creating rugged enclosures
The lifecycle of robust edge devices starts with design. All aspects, including electronic components, packaging, shipping, installation, and servicing needs to be considered at the design stage to ensure that an edge device can operate in the environment it is intended for.
Designing for IP67 or IP68 ratings typically increases cost from a sealing and connector aspect, but may also set up the product to fail as explained earlier. Designing only for IP65 or IP66 is mostly not sufficient, as the ingress rating is not high enough.
A solution is opting for IP69K. The automotive industry developed IP69K as a non-submersible rating with the intention to withstand washdown from high-pressure washers. If the energy from the water can be effectively managed within a good design, the enclosure, and the peripherals, like connectors, do not need higher IP ratings. Therefore, more affordable component choices can be made.
Next, material choice is critical, with the favouring of low-volume or high-volume plastic manufacturing methods over exotic materials or aluminium, which are not feasible. Injection-moulded parts in suitable materials would often be the most cost-effective option. The benefit of IP69K is that it will not be an ordeal to fit injection-moulded parts to its rating, as opposed to IP67 or IP68.
Heat management is a special consideration when high processing power is required by edge devices. Examples are the Jetson Nano or Xavier, or similar SoM devices where heat needs to be actively removed from the enclosure. The use of fans is a certain failure point, and forcing air over the electronics is a guarantee that there will be contamination. It is at this point where the enclosure designer and the PCB designer need to work closely together, as the heat management starts at the PCB, but does not end at the heatsink. Here, aluminium enclosures are beneficial if careful design is implemented for the heat path.
Potting of electronics is an option with simple PCB designs, but has its own challenges. Proper potting materials should be used. Hard thermoset materials that exhibit high shrinkage, or materials with chemicals which have the potential to damage the PCB, must be avoided. There are still products going to market where silicone is used as either a sealant for the enclosure or worse, as potting material. Silicone sealer uses acetic acid as the curing agent which destroys tracks on PCBs.
The most expensive component of IoT or remote devices is installation and servicing. The cost of replacement or repair and the loss of data due to field failure far exceeds the win on the BoM choices on the robustness of the product.
At SKEG the recommended approach is one that involves the concurrent design of the PCB, internals, and the enclosure, allowing these challenges from the project’s inception to be addressed. Typically, the environment in which enclosures will operate will be reviewed, but the solutions toolbox has matured to a point where we can design for the IP specification, address heat management, and select materials that will work in almost any extreme environment. These solutions can be manufactured in low volume, and when quantities justify it, scale to higher volume processes, retaining all design attributes. To ensure compliance and a robust product extensive testing is performed inhouse.
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