From critical military to medical technologies, these seemingly fragile nano devices are proving to be robust and powerful in even the harshest of environments.
BY GREG JONES
Many times, engineers simply wait (or forget) about connectors until the last minute. The result is they often leave themselves with little to no board space (or volume in general) for the connector. Understandably, design teams are more concerned with the more glamorous features of their projects-the processing, imaging, motion, etc.-commonly neglecting the more mundane process of connecting board to board, or getting signals to and from their boxes. Yet every link in the chain is as critical as the next, and a failed connector will knock out a system just as fast as a failed sensor or processor.
Factors that must be considered in connector design include current-carrying capacity, voltage requirements, temperature ratings, available board space, and environmental concerns. Design durability must also be considered: How many times will the connector set be mated and unmated? Who will be handling the connector (lab techs and gloved oil rig workers handle connectors in a much different manner)?
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New applications in diverse fields, such as Unmanned Aerial Vehicles (UAVs) and Cochlear Implants that can bring hearing to the profoundly deaf, require miniature yet very rugged connector systems. This means that the choice of connector is more crucial than ever.
Make way for the mini
New applications in defense, space, medicine, and heavy industries such as oil and gas exploration, are driving the need for miniature connectors that are capable of withstanding the harshest shock, vibration and temperature conditions.
But aren’t smaller connectors-similar in appearance to devices used in portable electronics, such as digital cameras and mobile phones-too delicate to survive these demanding environments? A new generation of products, termed “nano connectors” are proving otherwise.
Some basic physics provide a surprising and yet logical explanation of the durability of these new miniature connectors.
According to Newton’s second law of motion:
So, a lighter connector will actually withstand greater acceleration (in this case, shock) than a heavier one, given equal force and good design.
Nano connectors, which have a performance as defined by MIL-DTL 32139, provide a good example of the levels of performance that can be achieved by a miniaturized connector. Based on a pitch of .025”, these devices are only a quarter of the volume and have 80% less mass than the MIL-DTL-83513 Micro D connectors they supersede (correspondingly smaller and lighter than the D-subminiature Mil C-24308 connectors they were introduced to replace).
The table “Military spec test comparisons” (above) shows the difference in required performance between Micro D (50-mil pitch) and the new nano connectors (25-mil pitch).
Consider the requirements covering shock and vibration, which are considerably higher for the smaller type connector. Nano devices must withstand over three times the shock, yet the permitted discontinuity is much smaller; the vibration spec of the nano allows discontinuities of just one-hundredth the duration of the Micro D.
Crucial contact design
The performance of miniature connectors under extreme conditions is largely dependent on the contact design. Many styles have been put forward, including twist pin, solid pin, pin-in-nest and closed spring pin. All of these can deliver a solution, although with some (notably, the pin-in-nest design), miniaturization is extremely difficult if not impossible. But when developing a contact for nano and other miniature styles, including circulars, Omnetics Corp. designed a split end contact, named Nano Flex Pin, which not only passes reliability tests specified by the military but also delivers significant benefits beyond that for deep space and high temperature applications.
The Nano Flex’s contact is formed from 17,200-ksi beryllium copper, and then plated with gold. Beryllium copper is known for its tensile strength and Brinell hardness, or ‘springiness’. The design of the contact with gap, produced using Air Frame Modeling techniques, ensures that the when the pin is inserted into a socket, the spring force inherent in the beryllium copper ensures that the pin will always remains in contact with the socket.
 Figure 1. Based on a pitch of .025”, nano connectors are only a quarter of the volume and have 80% less mass than the MIL-DTL-83513 Micro D connectors they supersede. |
Given that other pin designs can be used in connectors that meet nano specs, why is this important? Consider the example of a small satellite, typified by the Low Elevation Orbit (LEO) devices that are becoming increasingly popular for achieving greater satellite coverage at lower cost. As LEO satellites orbit the earth, they also spin on their own axis, alternately subjecting sensitive electronics systems to extremes of temperature of +/-200°C. If the contact pin is a solid design (as with twist pins or closed spring pins), then the difference in thermal coefficient of expansion between the pin and the socket means that contact between pin and socket will be periodically lost, as the pin contracts. With the split-end contact’s gapped end pin, the design means that the contact will always be under spring tension, so there will always be contact between pin and socket.
Shock and vibration issues
Now let’s look at the shock and vibration performance. Micro D and nano specifications both allow for some discontinuities: for 100-G shock and 20-G vibration, the acceptable discontinuity is under 10 nanoseconds. For a simple, analog, sine wave-shaped signal, this is perfectly reasonable. Minor discontinuities will not affect performance. But electronic equipment is increasingly reliant on LVDS (low-voltage digital signal) technology, and even a small discontinuity can mean that a signal is lost. Once again, a solid pin of any type is likely to suffer from discontinuities, while nano designs, such as Omnetics’ Flex Pin, will not suffer these discontinuities.
The Nano Flex technology brings one further advantage: The contact is plated only after it is formed. Some processes use pre-plated metal strips, so although the thickness of plating is correct before forming, the plating will be stretched at stress points and bends, with the result being that the plating in these areas will be considerably thinner.
If we compare the measured performance of Omnetics’ Bi-Lobe nano connectors (using the Nano Flex Pin contact, and shown in the opening photo), we see some remarkable differences:
No room for the usual
There is simply no longer the space nor, in the case of satellites, payload available to rely on tried-and-trusted but bulky and heavy MIL-STD 38999 circular style connectors; for similar reasons, traditional rectangular D-subminiature configurations are no longer suitable. Nano connectors, such as Omnetics’ Nano Flex Pin contact technology, are designed to meet these emerging critical design applications.
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Flex Pin is available in a variety of connector formats, including micro strips, latched micro connectors, nano strips, metal nano rectangular, metal and plastic circular, and semi- and full-custom. In addition, Bi-Lobe rectangular connectors are available with backshells and shielded cables for operation in EMI-sensitive environments.
GREG JONES is sales manager for Omnetics Corp. (www.omnetics.com), Minneapolis, MN.
