Page 7 - 2021 Connectivity Components: Everything but the Connectors eBook

A Look at Connector Shells Materials and Plating Robert S. Grzib, Marketing Manager, CDM Electronics
A connector’s main shell houses a preconfigured insulator that holds electrical contacts. Shells generally conform to industry-standard configurations to optimize consistency of form, fit, and function with standard, DIN, mil-spec, or microminiature/nanominiature circular connectors.
A prime example of the benefits of shell standardization relates to the sub-series within MIL-DTL-38999 or MIL- DTL-55181 connectors. By maintaining common dimensional attributes, materials, finishes, and coupling styles, design engineers are assured that the specified connectors’ intermateability, and compatibility of materials and plating, meet or exceed the performance requirements for mission-critical applications.
Apart from maintaining standardized physical attributes, shells support additional electrical options and alternative ground paths. Such paths include shell-to-shell, ground contact/grounding finger-to-shell, or shield-to-shell. Metallic inserts also provide electrical continuity between the shell and contacts. Similarly, shells may be employed to enhance environmental sealing, including protection from electromagnetic interferences. Sealing methodologies are usually a function of the coupling design and insulator type than of the shell itself.
Shell design, material, and plating are dictated by intended termination type and application. All shells have a mating surface comprising a coupling mount method (e.g., threaded, bayonet, or push-pull). Mounting methods are typically application-driven and determined by commercial or military standards.
Base material options
Metals and alloys are the predominant materials specified for shell structure. Metals are widely used because they tend to have the lowest cost, and meet the broadest range of military and commercial specifications.
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» Brass is the most corrosion-resistant material with a galvanic potential close to the coating. Some forms of brass are notably RoHS non-compliant.
• Brassisthemostcorrosion-resistantmetalwithagalvanicpotentialcloseto the coating. This ensures that, even when exposed, the current density and voltage available for corrosion is insufficient to start a corrosion reaction. Note that not all forms of brass are RoHS-compliant.
• Aluminum is commonly used and often coated with chromium or nickel to optimize corrosion-resistance. Corrosion can occur in any areas where the aluminum is exposed.
• Stainless steel offers enhanced chemical resistance and significant levels of passivation protection from standard environmental corrosion. There are several grades of stainless steel with various compositions, making it an optimum material for machining or welding.
• Alternative metals are utilized for highly specific applications and include space-grade aluminum, carbon steel (extra hard for hermetic applications), and titanium.
• Composites are manufactured materials which deliver exceptional corrosion resistance, vibration dampening, weight reduction, and overall durability. These materials contain fibers — primarily glass — and are impregnated within a plastic resin. They are lightweight and can be produced at lower costs when manufactured in high volumes. Manufacturers may also plate composites to augment surface hardness and conductivity. Their applications include harsh environments where resistance to high temperatures, outgassing, corrosive fluids,