Defining and Selecting Module Connectors

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When designing any electronic system the modules connectors will have a significant impact upon the system reliability.

The system could be designed for a traditional high reliability application like railway, aerospace, medical, military or maybe an emerging one like high frequency trading.

Perhaps the first and simplest approach is to group the connectors in the functional types Power, Control, Data and Clocks etc. as each of these will be addressed in a different manner.

For instance it is possible to have prime and redundant power connectors, but if your system has a large number of data interfaces then it is not possible to have prime and redundant connectors for each input. This may lead to the need for system level redundancy in the worse case.

Regardless of the connector function we need to consider the following aspects

• Pin Derating, maximum reliability of a component is achieved by reducing the electrical stress placed upon it. There are many different standards for this (ESA, NASA, US Military etc) however; the basic idea is to reduce the voltage and current applied to the pins.

• Connector pin out, can a power pin short to a ground pin which will effect the overall power distribution system. It is therefore a good idea to ensure separation of power and ground separating them correctly. If necessary you can use unused pins to add isolation.

• Use of different connector types, styles and keying to prevent incorrect mating of connectors when the system is assembled. An incorrect assembly and power application could result in many hours of design analysis to prove no parts have been subject to electrical overstress.

• Number of mating cycles, the number of times the modules are mated / de-mated from the system has to be recorded. For this reason many designers use connector savers which can be connected to the system and reduce the number of mating cycles.

• Suitability for the job at hand for example if your system uses high speed serial links to communicate then your connector requirements will be very different from a power interface or low speed interface.

• Environmental and Dynamic considerations, many high reliability systems see extremes of temperature, vibration and shock. Can the connector system survive the demands and still stay connected.

Once you have determined your connector philosophy the next stage is ensuring you have a reliable system is in ensuring you cannot propagate a fault outside of your unit should a failure within occur.

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