Rugged Nano-D Connectors Deliver Mission-Critical Gigabit Connectivity in Challenging Environments

Nanominiature connectors provide a robust path for electromagnetic signals in applications where reliability in rugged environments is essential and where space and weight budgets are tight. They are integral to industrial robotics, autonomous systems and unmanned aerial vehicles (UAVs), avionics, aerospace systems, military and defense equipment, satellites, and deep space vehicles.

Engineers designing equipment for these applications must understand nanominiature, or nano-D, connectors to make the most of their high reliability and high bandwidth connectivity. This article discusses the construction of nano-D connectors, their electrical performance, and the implementation options available to meet application requirements from rugged environments to space constraints to mission-critical bandwidth.

Connector construction

Given the challenging application environments for aerospace, military, and industrial connectors and the need for high reliability, it’s no surprise that nano-D connectors for these industries must comply with the United States military specification MIL-DTL-32139. The specification standardizes aspects of these connectors, which have D-shaped male and female halves, each of which is terminated to a printed circuit board (PCB) or in a cable assembly.

MIL-DTL-32139 standardizes nano-D connectors’ contact spacing at 0.025 in. (0.64 mm) center-to-center. It also defines a standard female socket geometry that lacks the aligning spring common in larger D-shaped connectors. Instead, manufacturers put spring elements in the mating pin to account for misalignment and add tolerance for vibration.

High-speed nano-D BiLobe connectors (Figure 1) from Omnetics Connector Corporation are examples of MIL-DTL-32139-compliant designs.

Figure 1: High-speed nano-D BiLobe connectors are 0.450 to 0.650 in. wide by 0.125 to 0.165 in. tall and comply with MIL-DTL-32139. (Image source: Omnetics Connector Corporation)

These connectors use a Flex Pin design consisting of two long spring beams or tines stamped from beryllium copper. The tines are formed with two radii for a compound beam geometry. This allows them to compress smoothly toward each other when they are inserted into a socket with a typical mating force of 2.5 oz (0.71 g) per contact, well below the 5.0 oz maximum permitted by the MIL standard.

The resulting spring force maintains contact between the gold-plated, coined edges of the tines and the gold-plated inner surface of the socket for a low-resistance electrical connection. When compressed by insertion, the ends of the tines touch. The mutual support helps the connection withstand vibration and shock.

During insertion, the tines’ coined edges also create a wiping action along the internal surface of the socket, removing contaminants and oxides to ensure a low contact resistance of 71 mΩ, as evidenced by a maximum voltage drop of 71 mV with a 1 A test current (Figure 2).

Figure 2: BiLobe connectors have Flex Pins with two compound beryllium copper spring beams that maintain contact with the socket wall. (Image source: Omnetics Connector Corporation)

Bumping up bandwidth

This low contact resistance helps high-speed nano-D BiLobe connectors safely carry up to 1 A per contact and support bandwidths up to 20 Gbps per differential pair. The connectors have a controlled 100 Ω ±5 Ω impedance that facilitates data protocols such as USB 3.0, 10 Gb Ethernet, the serial communication Camera Link protocol, and Peripheral Component Interconnect Express (PCIe) with minimal signal reflection, loss, or noise.

To further match impedance and optimize performance, BiLobe connectors are available in high-density (HS2) and high-performance (HS3) variants, which separate positive, negative, and drain pins among available contacts (Figure 3).

Figure 3: BiLobe connectors are available in (a) high density (HS2) and (b) high performance (HS3) pinout variants. (Image source: Omnetics Connector Corporation)

A 30 AWG cable optimized for 100 Ω impedance has insulated conductors with diameters of around 0.035 in., too large to allow every contact to be wired when contacts are spaced only 0.025 in. apart. Compact HS2 layouts allow for the maximum number of differential pairs, leaving only one empty contact between them.

The close spacing of conductors in HS2 variants of BiLobe connectors results in an approximate impedance range of 70 to 105 Ω. Insertion loss can be as much as -6 dB at 5 GHz and above. HS2 variant connectors have bandwidths ranging from 10 to 15 Gbps, depending on the PCB mounting type and jumper length, although 20 Gbps can be achieved with a vertically oriented surface-mount unit connected with a 6 in. jumper.

Putting more space between conductors in HS3 variants of the connectors reduces the number of differential pairs available; only two-thirds as many pairs can fit in the same connector with HS3 pinouts. However, the spacing allows HS3 variants to achieve 100 Ω ±5 Ω impedance and minimizes insertion loss. The resulting bandwidth ranges from 16 to 20 Gbps.

Configuring reliable connections

While connector configuration options such as cable length or PCB orientation have a slight effect on performance, engineers need options that will work for space-limited applications where PCB layout and cable routes are strictly constrained. High-speed nano-D BiLobe connectors have several configuration options.

The male BiLobe connectors are supplied on RoHS (2015/863/EU)-compliant jumper cables 6 to 108 in. long. Each conductor is a 30 AWG silver-plated copper wire twisted from seven strands of 38 AWG wire. Clad in white and blue fluoropolymer insulation, each differential pair is wrapped in a polyimide aluminum shield and a fluoropolymer jacket.

Female connectors are PCB-mounted with liquid crystal polymer (LCP) or polyetheretherketone (PEEK) insulators and an epoxy encapsulant. They are usually secured to the PCB with surface-mount technology.

Horizontally mounted female connectors have a mating motion parallel to the plane of the board and are dubbed AA in Omnetics’ part-numbering system. The female AA connector has two rows of sockets on one side and corresponding solder-coated terminations that extend horizontally from the other side, turning 90° toward the plane of the PCB. These terminations are spaced to connect to solder pads on the PCB via automated surface-mount processes. Horizontally mounted connectors enable more compact assemblies, but the proximity of contacts to other conductors and soldered connections can inhibit impedance matching and increase insertion loss.

For applications with stringent performance requirements, a vertical configuration, dubbed VV in Omnetics’ nomenclature, is preferred. The VV configuration also has solder-clad terminations extending opposite the connector’s sockets, but these emerge at right angles to the connector housing, parallel to the PCB plane when the housing is placed vertically.

In addition to AA and VV configurations, high-speed nano-D BiLobe connectors are available with latching and panel-mount housings. All configurations have the option of a passivated 300 series stainless steel shell or a 6061 aluminum shell with an electroless nickel coating at least 500 µin. thick.

These robust shells give BiLobe connectors the durability for over 2,000 mate-unmate cycles at temperatures from -55°C to +125°C, with +260°C capability available upon request. They have a dielectric withstanding voltage (DWV) of 250 VAC RMS at sea level and an insulation resistance of 5,000 MΩ at 100 VDC. They also meet NASA outgassing requirements for space hardware with under 1.0% total mass loss (TML) and 0.1% volatile condensable material (VCM).

The connectors also withstand mechanical shocks up to 100 times the force of gravity (g) and vibrations up to 20 g while maintaining signal integrity. In specialized ballistic applications, shocks of 10,000 g have been tolerated. Under these extreme conditions, the connectors experience less than 10 seconds of signal discontinuity.

Conclusion

High-speed nano-D BiLobe connectors combine a miniaturized, ruggedized design that withstands shock and vibration, tolerates a wide temperature range, and lasts thousands of mating cycles with carefully managed impedance for reliable, high-bandwidth digital transmission. The connectors bring gigabit-speed connectivity to space missions, avionics, UAVs, and other applications where reliability and performance are both mission-critical.