Test and Measurement
Environmental protection for electronic assemblies
A product development team’s worst nightmare — designing a brilliant product only for it to fail at the environmental testing or qualification phase. Protecting an electronic assembly from its environment throughout the product’s lifetime is not always an easy task, so what can design engineers do for the best chance of success? Here Paul Whitehead, strategic accounts manager at adhesives specialist Intertronics, explains how to approach the environmental protection of an electronic product
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anufacturers typically protect electronic assemblies from dust, debris, moisture, pressure, extreme temperature, impact,
vibration, and chemicals. It is best to consider these factors, among others, at the design stage, to ensure that your product is more likely to pass testing first time. Furthermore, it is important to consider any sector specific requirements. For example, military applications require Mil-Spec testing, and wearable devices may need to comply with ISO 10993 or skin sensitivity requirements. In industries where intellectual property is important, encapsulation or potting can help prevent competitors from reverse engineering your product. The characteristics of this material will be important, such as cured hardness for vibration protection, and thermal expansion properties.
Primary and secondary protection There are two approaches to environmental protection, primary and secondary. Primary protection can be an enclosure (sealed or gasketed), overmoulding, or complete potting. Secondary protection involves adding layers of polymeric materials by encapsulation or conformal coating. The level of protection depends on design; for example, if housed in a sealed box which offers primary protection, then additional protection or conformal coating may not be needed. However, if the electronics will be in an open top enclosure, potting/total encapsulation might be more suitable. We recently worked with sustainable fishing start-up SNTech to design a new version of its flagship product — a sophisticated kit of ten LED lights that fits onto fishing gear to enable more precise fishing. The new version, which is now commercially available, can survive the high pressures of deep-sea fishing and is suitable for being submerged up to 1,000 metres.
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Light colour and intensity were critical to functionality, so we recommended an optically clear potting compound for the device top, and a cheaper non-optically clear potting compound for the bottom. We also supported process development, ensuring materials were used effectively and bubbles weren’t introduced during the process.
Materials for environmental protection
Common chemistries for the environmental protection of electronic assemblies are polyurethanes (PUs), epoxies, silicones, acrylates and modified acrylates, acrylated urethanes, and fluorochemicals. An experienced adhesives partner can support you through the specification process, advising you on which chemistry will best meet your requirements. For example, for high thermal conductivity, extended pot life at room temperature and suitable rheology to fill gaps, we may recommend Polytec TC 437, which is a two-part thermally conductive epoxy.
Curing
Curing mechanisms include chemical (mixing two parts together), heat, light, or a combination. If multiple chemistries
Components in Electronics
would meet your functional requirements, process and cure are the next important considerations, including the costs and process resources needed for application and curing. Two-part materials may need mixing equipment, and thermal or light curing products will need ovens and lamps. Think about capital costs, and running, maintenance and training overheads for additional equipment; this may be offsetable against productivity benefits.
We recently worked with Nottingham Trent University’s Advanced Textile Research Group on the encapsulation of electronic yarn, where the team selected a UV curing resin because it is solvent free, gives process time improvements, and avoids potential damage to components from process heat. Another interesting example comes from a customer who manufactures electronic tracking devices that need to survive extremely aggressive testing, exemplified by a ten-minute battering with a sledgehammer. We found its original inexpensive polyester potting compound had uneven cure, leading to exothermic hot spots and shrinkage, causing component damage, and that it was not sufficiently shockproof. Our team recommended IRS 3071 flame retardant polyurethane potting compound, which is
waterproof, impact and thermally resistant, electrically transmissive, and easy to process.
Applying the material
Another important consideration is production volume — high volumes benefit from an automatable material, while low volumes are more suited to manual production. Conformal coatings, encapsulants, and potting compounds can be applied by spraying, dispensing, or metering, mixing, and dispensing — which can be manual or automated. Equipment choice depends on accuracy and repeatability requirements, and whether the materials are single part, or multi- part requiring mixing.
Materials can be supplied in bulk containers, aerosol cans, pre-filled dispensing cartridges or syringes, twin-pack sachets or bags, and so on. For low volumes of two- part potting compounds, purchasing in a twin-pack bag offers processing advantages. Alternatively, at higher volumes, a metering, mixing and dispensing machine may make financial sense.
At Intertronics, we can help your product pass environmental testing and qualification. For more information, visit:
https://www.intertronics.co.uk.
www.cieonline.co.uk
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