Tiny connectors designed to withstand the harsh environment, extreme shock, vibration, pressure, and temperature of deep space and other extreme applications have evolved to mainstream usage.
By Mark A. Madsen
Nano-miniature connectors constitute a family of interconnect devices with center-to-center contact spacing of 0.025-in. Compared to other connector families, they are often the smallest practical connector system for separable interfaces and the smaller sibling of micro-miniature "D-style" connectors that have contact spacing of 0.050 in. Despite their significantly smaller size, nano-miniature connectors are tested per the guidelines of MIL-DTL-83513, which was written for the 0.050-in. micro-miniature connector. Nano-miniature connectors combine their appealing size and weight with desired performance attributes such as low contact resistance, wide operating temperature range, and current capability of 1 A per line, making them truly the smallest and toughest connectors available to designers today.
Design origins
Nano-miniature connectors were originally developed with a visionary eye cast firmly upon the future. The growth of digital electronics created many new challenges for designers and packaging engineers. One such challenge was to find a practical interconnect solution compatible with the continued miniaturization and increased function of silicon chips and the subsequent shrinking of virtually all things electronic. Nano connectors presented a revolutionary, attractive, and viable option for design engineers, by conserving precious board space and delivering MIL-DTL-83513 specifications. As the drive toward miniaturization proliferated to nearly all applications, the need for a variety of nano-sized connectors also grew.
One of the first designs to emerge was the nano-miniature "strip" connector (see Fig. 1). This simplistic design was essentially a low-profile (0.040-in. horizontal configuration) single-row plastic shell that housed the miniature contacts and provided a mating interface. Once engaged, the nano-strip connector relied only upon the friction-coupling forces of the pins and sockets to remain mated. This was acceptable for in-line wire-to-wire termination in a benign environment. When subjected to shock and vibration, however, this coupling method was not rugged enough.
 FIGURE 1. Nano-strip connectors are among the smallest and most compact. Contact spacing down to 0.0125 in. is typical with a single-row configuration. |
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Using lessons learned from the original strip configuration, OEM design engineers helped create the nano-miniature rectangular connector (see Fig. 2). This second-generation nano design, with 0.025-in. contact spacing, featured a simple yet effective lobed polarization scheme and a high-density two-row option with offset pin spacing of 0.0125 in. Additional features included metal shells machined from lightweight aluminum or rugged stainless steel, miniature captivated jackscrews on the plug side, and threaded mounting holes in the receptacle housing. Due in part to jackscrew access and physical geometry, the plug member was chosen to be the wired component and to house the captive jackscrews, while the receptacle side could be configured to provide a board-mount interface.
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Horizontal- and vertical-mount through-hole configurations soon followed and surface mount shortly thereafter. The threaded mid-body mounting holes in the receptacle shell allowed the horizontal configurations to be firmly attached to circuit boards with mounting screws while the vertical-threaded mounting holes allowed for perpendicular orientations to be securely attached as well. The rectangular family of 0.025-in. connectors with its new features and configuration options overcame the limitations previously encountered in shock and vibration environments and rapidly gained acceptance among designers. The once-envisioned nano-miniature connector market had become a reality.
The heart of the nano-miniature connector is the contact system. "Spring-pin" contacts are one type of design. Another popular design uses a spring-socket contact system. In this design, the socket member of the contact pair employs a dimple located inside the tubular contact. When engaged, the socket member creates the desired spring action by forcing the blind bore pin to offset to the far side of the hollow receptacle "tube." The result is a gold-on-gold mating surface area covering approximately 180° of the contact diameter, combined with a desired mating force of no more than 6 oz per contact and resistance of 0.003 to 0.008 W.
Spring-socket contacts are made from pre-plated BeCu alloy formed into a rugged, seamless, blind bore pin and tubular spring-socket contact. These tiny yet rugged pins and sockets can then be crimped to many materials including 30 through 42 AWG insulated discrete wire, tiny rectangular lead frames for circuit board attachment, flexible circuitry including rigid or sculpted flex, and 0.025-in. ribbon-style cable.
Crimping the termination is preferred over soldering to achieve reliable contacts and eliminate solder-related concerns. While the contact systems are designed to optimize electrical performance, the insulator materials and connector housings must bolster the mechanical properties of the connector and accommodate various application geometries.
Material selection is critical due to the nature of nano-connector applications and environments. Materials must be rugged, reliable, lightweight, nonmagnetic, and possess outgassing characteristics of less than 1% total mass loss for most near-Earth and deep-space applications. Materials must also be rugged and versatile enough to withstand the environmental conditions in military and aerospace applications that range from sea level to 70,000 ft in altitude. Furthermore, the materials must resist the extreme shock, vibration, pressure, and subterranean temperatures of down-hole petroleum exploration.
Nano-strip
Nano-miniature strip-style connectors are among the smallest in terms of overall size and profile. This connector style is based on a single row of 0.025-in. pitch contacts housed within a low-profile, molded liquid-crystal polymer (LCP) or polyphenylene sulphide (PPS) insulator, and typically configured for wire-to-wire, or wire-to-board termination options.
The strip design lacks a rugged built-in polarization scheme and provisions for circuit-board attachment. The strip connector typically uses a guide-pin polarization approach that, while considered effective, reduces the number of available working contacts. Efforts to polarize the strip configuration without reducing active pin count, adding a latching mechanism, or introducing threaded mounting holes for circuit-board attachment, result in a larger shell size and/or increased profile, which can nullify the criteria for which the connector was originally selected.
D-style rectangular
Nano-miniature rectangular connectors are the most popular and widely used style of nano connector. The two-lobed polarization scheme is machined into the rectangular connector shell, negating the need for guide pins without increasing the package size. This polarization method is standard on all molded plastic or machined metal rectangular shells, both in one- and two-row connector styles. Single-row pin counts range from 5 to 51, while two-row designs offer higher density and normally use pin counts from 9 to 65. Even as pin counts increase, the design remains compact: the highest density 65-pin connector is 1 in. across and 0.126 in. tall.
 FIGURE 3. Nano coax connectors are frequently used in communication systems onboard space applications. |
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The rectangular configuration quickly became the nano connector of choice among designers faced with input/output challenges. Acceptance into a broad range of applications resulted in many innovative rectangular design derivatives. Examples of successful application-driven derivatives include highly specialized filtered versions, environmentally sealed versions, DSCC certifications, adaptations for termination to all types of miniature flex circuitry, and glass-to-metal sealed hermetic versions. Blind-mate board-to-board versions, along with panel-mount styles and even solder-up versions, allow the end user to terminate the connectors in-house.
Circular
As nano-connectors evolved, a 0.025-in. splash-proof circular design emerged. Nano circulars offer pin counts of 7, 19, and 44 positions, housed within a threaded coupling-style plug, which mates to a panel-mount-style receptacle for use in wire-to-wire and wire-to-panel applications. The nano-circular family is further distinguished from larger existing circular connectors by using gold-plated, lightweight aluminum shells and the same rugged, high-reliability, pin-and-spring socket contact system found in the nano-strip and rectangular styles. Recent developments in nano-circulars include environmentally sealed versions that offer the choice of quick-disconnect- or threaded-coupling-style plugs and flush- or panel-mount-style receptacles.
Nano-coaxial system
Nano-coaxial 50-W connectors are the final element in rugged nano-miniature connectors (see Fig. 3). This style offers designers the flexibility to choose from up to nine nano-coaxial contacts terminated with RG-178 coaxial cable, and five signal contacts terminated with 30 AWG or smaller discrete wire, integrated within a "nano-sized" rectangular connector shell. This mixed-signal coaxial system is compatible with frequencies up to 20 GHz and comes in wire-to-wire or wire-to-board configurations. Designers who do not require mixed-signal capability can specify connectors with coaxial contacts only.
The trend toward commercial off-the-shelf (COTS) components has had a positive impact on nano connectors and will ultimately increase the size of the nano-connector market. A consortium consisting of top designers from each of the leading nano-connector manufacturers has pooled ideas and experiences to jointly create a viable COTS nano connector. Combining the effective lobed polarization scheme with stamped-and-formed contacts and increased hardware size has resulted in the newest family of lower-cost, reduced-performance, intermateable nano connectors. The emerging COTS nano connector will offer new capabilities in applications in which size, weight, and component cost are critical parameters. The COTS connector is not designed for high reliability, ruggedness, and extreme temperature capabilities, but addresses the less restrictive design parameters and lower performance requirements of commercial applications and military-grade equipment.
The continuing push toward system miniaturization has truly revolutionized the connector industry while obliterating many existing paradigms. Increased acceptance by designers encompassing a wider industry range of applications, coupled with electronic systems that continue to decrease in size and weight while increasing in functionality, indicates that the future of nano connectors will continue to be very active. What had originally been developed as an immediate-need solution, has evolved into the latest link in the miniaturization chain of interconnect devices. When system designers require a highly reliable, rugged, nano-miniature style connector, the variety of choices has never been greater.
Mark A. Madsen is senior product specialist at Tyco Electronics, 3101 Fulling Mill Road, Middletown, PA 17057. Tel: (800) 242-6266; Email: mark.madsen@tycoelectronics.com.
