Reliability Just Got Smaller

9th May 2013
ES Admin
Connectors must ensure signal integrity even when the environment is far from benign; great forces of shock and vibration, and extremes of temperature may be experienced. Wendy Jane Bourne, Technical & Marketing Engineer with Harwin, explores these strains on high reliability connectors in this article from ES Design magazine.
Size, weight, performance and cost; these are the key determining factors that influence the choice of interconnect system. High-reliability applications such as aircraft, aerospace, robotics, undersea exploration, down-hole drilling, medical, motor sport and robotics make even greater demands.

While certain Hi-Rel connectors used in military applications must endure the horrors and associated physical stresses that face their military counterparts, devices used on commercial aeroplanes are entrusted to carry millions of passengers, so the choice of components used is no less critical — simply put; failure is not an option. As well as the vital systems that keep an aeroplane in the air and in communication with air traffic control, commercial aircraft are increasingly equipped to enhance the passenger experience through a range of sophisticated entertainment systems. Whilst not ‘mission critical’, if the in-flight movie system fails travellers may well be tempted to switch to another carrier, making the systems commercially critical.

In satellites it is the cost of failure that is prohibitive. Even a modest CubeSat costs an estimated $150,000 to make and launch, more sophisticated commercial and defence satellites cost many times that. Even terrestrial applications such as oil and gas exploration cost £1000s per day, so a connector failure in those high vibration/high temperature scenarios is simply not acceptable.

Pitch Perfect

The new Gecko range of 1.25mm pitch Hi-Rel connectors from Harwin has benefited from its track record of manufacturing high-reliability connectors for safety-critical applications, drawing on market feedback over many years to its similarly high-reliability Datamate range. A 2mm pitch cable-to-cable, cable-to-board and board-to-board connector family, Datamate has been specified for use in harsh operating conditions many times, featuring on the Robonaut 2 NASA space robotics program, missile guidance and roadside bomb detection systems, UAVs, auto sport telemetry systems, dialysis and patient monitoring equipment. Datamate's contact design features a stamped, four-fingered, gold-plated beryllium copper clip with highly stressed contact beams. The clips reside in the female half of the connector clasping round pins tightly, ensuring the integrity of electrical connection even under severe conditions. Additions to the Datamate family include miniature, lightweight mixed technology versions offering a multitude of configurations for signal, power and/or coax, Datamate Mix-Tek connectors feature power contacts rated for use at up to 20A; particularly suited to commercial aircraft designs based on ‘everything always on’, that necessitate interconnect systems with a high current carrying capability. Datamate’s signal contacts are rated at up to 3A; coax contacts are rated at 50Ω. The Datamate range also includes REMI shielded versions (Datamate S-Tek) and a variety of latching options for added security.

But inevitably and inexorably, industry is requiring smaller devices. Smaller connectors, yet with the same ability to withstand high shock and vibration, make up a significant part of the Hi-Rel market. UAVs are a case in point. Whether for military or increasingly commercial applications such as agriculture and traffic monitoring, flight time is totally governed by the weight of all components on board. Hence Harwin’s newly-launched, Gecko 1.25mm pitch connector family which suit demanding applications and deliver high performance at commercial price levels.

The low profile G125 series connectors are designed to offer high performance in a miniature package. The 1.25mm pin spacing results in a 35% space saving over other high-performance connectors such as Micro-D and a 45% s reduction in required PCB space over 2mm pitch interconnect systems. The connectors are rated to handle 2A per contact.

Tested and proven to allow high performance in extreme conditions, the G125 family can operate within a wide temperature range (-65 to +150°C) and under extreme vibration (Z axis 100g 6m/s, see table below).

Design Considerations

The performance of miniature connectors under extreme conditions is largely dependent on the contact design. Many styles are used across industry for Hi-Rel applications but Gecko’s high performance is made possible by Harwin’s patented four-finger Copper Alloy contact. The contact, which delivers high performance and extreme reliability, at the 1.25mm pitch level is shown in the image below.

Offering up to 50 contacts per connector and available in dual row cable-to-board and board-to-board configurations, Gecko family connectors include a wealth of features including polarisation points that prevent mis-mating, easy identification of the No 1 position for fast visual inspection and optional latches that allow simple and fast de-latching that requires no special tooling. Cable connectors feature a rear potting wall adding an extra level of strain relief.

G125 connectors are manufactured to withstand high numbers of mating cycles but also feature low insertion and extraction forces. Moldings are manufactured from RoHS-compliant, environmentally friendly materials, eliminating harmful chemicals even before they are added to restricted substances lists. Pre-assembled cable configurations are available in a variety of layouts featuring male and female, single and double ended, in a variety of standard lengths. Board connectors are packaged in tape and reel format.

Addressing cost, it’s fair to say that today, all budgets whether the application is military or commercial, are subject to strict scrutiny. Certainly the days of being able to over-specify a military-style (and military-priced) device for an industrial application are long gone. Gecko addresses this concern, with price-per-contact levels set at industrial levels running at an order of magnitude of military devices.

Many times engineers simply wait (or forget) about connectors until the last minute. The result is that often they 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 and so on — commonly neglecting the more mundane process of connecting board to board, or getting signals to and from their boxes. Yet of course, 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. New breeds of connectors — such as Gecko — deliver the performance and reliability demanded by hi-rel applications, the miniaturisation that is increasingly required, and the cost/performance ratio expected by project teams with tight budgets. Gecko is fully-supported with a range of design tools including Eye Diagrams and CAD Models. Instruction videos are also available.

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