FEATURE HAZARDOUS AREA EQUIPMENT
John Johnson, NPI Director, Chemigraphic
perform reliably in a variety of challenging circumstances. However, this requirement inevitably adds a layer of complexity to the manufacturing process. Just as mobile phones do not react well to being dropped in a pool or sink, harsh outdoor elements can have a big impact on how products function and behave. However, there are a whole class of products that are designed specifically to operate in actively hazardous environments, conforming to regulations and standards such as Intrinsically Safe (IS). From underwater locations and explosive atmospheres, to areas at risk from severe weather conditions or contamination of various substances such as carbon dust, these products are purpose-built to thrive in these conditions, requiring techniques and processes from EMS experts during the design and manufacture stages.
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MANUFACTURING ELECTRONIC PRODUCTS FOR UNDERWATER ENVIRONMENTS There are a number of circumstances that require electronic products to function and perform in sub-sea condition. These range from oil and gas research facilities, to marine industry operations and rovers or maintenance machinery. Many of these products will be operated and controlled remotely, so it is vital that their electronic functions are robust and hardy enough to withstand the sub-sea conditions. There are a number of physical challenges involved in manufacturing products for underwater environments, such as erosion caused by salt and force of the water. Salt in particular is extremely corrosive and can literally eat through metal components and casings if the correct protective measures are not taken. In order to combat this particular threat, specialist coatings and sacrificial layers can be applied to the product structures and to the circuitry inside by EMS teams, protecting them from salt and other corrosive substances. Conformal coatings act as a protective varnish for circuit components and casings,
18 JUNE 2018 | ELECTRICAL ENGINEERING
lectronic products are becoming more and more prevalent in all walks of life, and as such, are often required to
HARSH BUT FAIR
and as technology has developed, coatings can be applied via robotic, automated processes to increase cost-effectiveness and consistency. Encapsulation of circuitry provides an extra level of protection for the components, effectively closing them off from external elements. This approach is extremely effective in underwater locations where there are multiple barriers to product functionality.
PROTECTION FROM CONTAMINATES AND EXPLOSIVE ATMOSPHERES Products which are designed for use in high risk areas, such as those that are contaminated with toxic substances or carbon dust, have to be manufactured in a way that ensures they can withstand contact with these particles. The first consideration is to ensure that all ‘critical parts’ are correct to specification. These include circuitry, which in theory could lead to an over-current fault condition, which could then overheat and cause a fire and an explosion. This means it is critical to vet and validate each supplier robustly, meaning sources are reputable and batch traceability is ensured. Good inwards inspection criteria must ensure each part is received and correct to specification, conducting enhanced checks and measurements rather than just visual confirmation. Batch segregation may be necessary for mixed stock. The EMS will then need to employ systems
with sufficient material control governance to ensure that only the correct parts are fitted into the correct locations. This can be challenging when the vast majority of small footprint SMT components do not have markings and are visually identical. In addition, the volumes in consideration are vast - a kit of parts for a sophisticated PCB might run to 500-600 distinct lines. Part of the solution is to optimise the use of barcoding and intelligent materials trace, such as RFID enabling and automated kitting - measures which remove opportunities for human error. The next consideration is to check and provide evidence that the correct parts are
fitted. Manual inspection processes are again subject to an element of human error and are not sustainable in a higher volume environment, meaning automated optical inspection becomes mandatory.
DEALING WITH HIGH-SHOCK ENVIRONMENTS Acceleration forces in rocket-propelled devices obviously require careful component selection in order to be sufficiently robust to survive take-off. This particularly applies to devices with motion potential such as gyroscopes, valves and actuators. The EMS partner needs to ensure optimal assembly integrity starting from bare PCB rigidity, where thickness and copper weight need to be balanced against payload constraints. There may be a requirement for additional bracing such as bonded layers, struts and multiple restraint points to provide further strengthening. Due to the extreme temperatures and hostile
conditions involved, solder integrity becomes critical and the base process needs to be robust and repeatable. Automation is a great way to enforce consistency, but the process is only as good as the knowledge and expertise of the engineering teams who establish the operating criteria of the machines.
ACCOUNTABILITY AND DOCUMENTATION With any manufacturing process, keeping thorough records of activity undertaken and results achieved is vital. However, this element is particularly critical when it comes to developing products for harsh and hazardous environments. As so many complex conditions and procedures are involved, it is essential that every step is prepared, researched and accounted for, with documentation and certification available and presented to customers at every opportunity. This allows for continuous control and traceable processes that create evidence of compliance to industry standards and regulatory requirements.
Chemigraphic
www.chemigraphic.co.uk
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