Specifying nanominiature connectors
Making the right choice when failure is not an option
BY BRUCE CUNNINGHAM
AirBorn
Georgetown, TX
http://www.airborn.com
Nanominiature-scale connector systems present unparalleled size and weight advantages in highly critical electronics applications. However, because nanoscale is a relatively new innovation, designers specifying these products must consider environmental, electrical, and mechanical factors in both the manufacturing and the operating environments at the design-in stage.
With densities around 0.635 mm, nanominiature-scale connectors are approximately 30% smaller than their larger relative, the microminiature/micro-D connector. While many connectors may physically fit the application and contain contact systems that appear to work, it is necessary to understand mechanical, thermal, and environmental stresses, and how extremes can impact performance of the interconnection system over time.
Nanominiature connectors are well suited to various applications and conditions.
Nano connectors in harsh conditions
Ruggedized nanominiature connectors are used in a variety of high-reliability applications ranging from deep-space exploration to down-hole logging and drilling operations; from guided munitions to medical instrumentation. Components in these environments typically encounter extreme temperatures, thermal cycling and thermal-vacuum outgassing, high levels of shock/vibration, exposure to corrosive elements, and EMI.
The demands of these applications all require special design features that comprehend the demanding conditions in operating and manufacturing environments the connectors may see. In analyzing the performance of potential types of nanominiature connectors under highly stressful conditions, a designer should consider a variety of mechanical, electrical, and environmental factors, including:
• Hardware to mate and lock the connectors together
• Mounting hardware to minimize solder joint stress
• Type of terminations for PWB or I/O connectors
• Operating and storage temperatures
• Current and voltage levels under all conditions
Additionally, the designer must consider production processing issues that the extremely small connector size may pose, including handling, reparability, solder-pad size and density, and washout/cleanout.
Thermal cycling and prolonged exposure to extreme temperatures�which can range from –50° to 200°C�can be detrimental to nanominiature connectors. Proper contact material selection will help to prevent heat stress relaxation, which can cause intermittence or sustained discontinuity.
Additionally, connector potting material, which will stand up to the temperature extremes, must be specified. The thermal expansion properties of the connector's components must be considered. The shell, dielectric insulator, and retention potting components should be made of materials and constructed in a manner that will not part or separate under multiple thermal cycles.
Though the mass of a nano connector is very small, extreme shock and vibration can play havoc with the integrity of the connector. One must be concerned with contact fretting, which is the abrasive wear-and-tear caused by small repetitive movements of surfaces against each other.
The connector should mount securely to the printed-circuit board with hardware that will transfer stress away from the solder joints, and the mating hardware must securely lock the connectors together. Features and provisions of the fastening design must also be considered, which will lock and hold the connector components together under high G acceleration – which can exceed 20,000 Gs in a guided munitions application, for example.
Depending on the application, whether airborne, ground, or subterranean, or during the manufacturing process itself, the nano connectors are often exposed to the likes of lubricating, cooling or cleaning fluids, and solvents. The designer must select compatible connector component material that is resistant to the degradation effects of exposure to specific fluids and vapors may present.
Along the same lines, in shipboard applications where missiles and guide munitions may experience long-term storage until use, the nanominiature connector must operate in a moisture and salt-laden air environment. Proper material plating, underplating selections, and thicknesses must be considered to prevent the corrosive effects of this kind. Options or provisions for additional sealing or splash-proofing of the connector system should be considered as well.
Because of their minimal size and weight, nanominiature connectors are ideal candidates for satellite and deep space probe applications, where launch costs can exceed more than $10,000 per pound. It is necessary to acknowledge the possibility of contaminate transfer via the effects of thermal vacuum outgassing, which affects the performance of the interconnection system materials and will cause degradation over time.
The electrical environment for the connectors must obviously be considered. The ability to shield individual signals from each other or provisions for providing EMI shielding of the connector system overall may be necessary, depending on the application.
The inherent small size of nanoscale connectors requires proper handling and processing.
Manufacturers must insure lead registration and coplanarity of printed-circuit-board connectors to be maintained during shipping through placement by presenting finished product in a protective and easily accessible format. Nano connectors with standoffs, or clean-out features, are of additional benefit in solder process cleaning, inspection, and repair.
Advertisement
