TECHNOLOGY REVIEW
Off-board On demand!
By Alan Jermyn, Avnet Abacus
Good PCB layout requires close attention to ensure that the design meets space and volume constraints, that track lengths are kept short to ensure maximum performance and minimize EMC issues, and to satisfy the need that PCB assembly processes can be performed cost-effectively.
All of the same challenges apply when considering an ‘off -board’ design, but engineers must address other concerns.
While there are obvious exceptions, PCB components tend to be standardised in size, small and lightweight and generally designed for automated PCB assembly processes. Although some off-board components do indeed comply with various standard formats, many do not. Almost all off-board components, by their nature, are bulky and comparatively heavy, and many require secondary manual assembly operations. Lastly, but perhaps most importantly, many of the off-board components will be accessed by the operator or a service engineer, rather than hidden away on a PCB that no one ever touches.
The obvious example of an off-board component is an I/O connector, for instance, a heavy duty circular used in industrial or defence and aerospace applications. These items can be difficult to specify with a myriad of options and suppliers. Often the biggest drivers behind selection are the individual requirements of the application. Does the application require high mating/demating cycles due to its mobile nature, or specific locking mechanisation to withstand extreme levels of vibration and shock, or is the requirement for a fully sealed connection to prevent against the ingress of water, dust or corrosives? Of course in a mission critical military environment
38999 connector - nickel-teflon
these components must also hold military standard approvals and have long life guarantees to prevent costly redesigns.
As well as considering performance requirements in any application, designers will have to think about the application environment and the personnel that will be handling the device. For example, service engineers on a machine shop floor or mass transport service centre will not be working in a clean environment and may not be used to handling sensitive equipment. Power and data connectors may need to be capable of withstanding significant mating and demating by operators who are not ’electronics savvy’ and this must be considered during component selection. As well as connectors, there are other panel mount products such as switches, circuit breakers, fuse holders or indicators, all of which need careful selection as part of the user interface. Particular attention will need to be taken when environmental issues such as moisture or dust ingress are a concern. In this instance IP67, 68 or 69 sealing will be required.
continues > focus magazine - issue 10 7
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