Issue link: https://te.mouser.com/i/1477778
Backshells in either material are available in solder cup, pre-wired, and printed circuit board (PCB) versions. * Aluminum backshells are made from lightweight, rugged, machined aluminum alloy and employ stainless-steel accessory hardware. Plating is typically done with electroless nickel, which provides a low-resistance, conductive finish appropriate for non- environmental applications. Gold plating offers excellent resistance to space corrosion and radiation. Because cadmium plating sublimates in a vacuum, it is not acceptable in applications where outgassing is a concern. * Composite thermoplastic backshells are made from chemical- resistant composite thermoplastic materials that significantly reduces interconnect system weight and handles SO 2 fog better than metallic. Because composite housings are transparent to EMI, electroless nickel plating is used for EMI shielding. * Precision mating helps ensure the electrical integrity of an interconnect by eliminating discontinuity in diameters between pairs. Precision-machined backshells not only enable accurate mating between interfaces, but also strong mating retention force. For easy installation over terminated wires, split-shell backshells can fit over the connector without a ferromagnetic clip c o m p o n e n t a n d employ screw locks t o c o u p l e connectors. (One- piece backshells, in contrast, must be p l a c e d o n t h e w i r e b u n d l e b e f o r e w i r e - t o - c o n n e c t o r terminations are completed.) Backshells requiring a platform for banding straps can utilize a low-profile Micro-Band that accommodates narrow, space-saving band widths. Meeting Performance Challenges During launch, flight, and orbit, backshells used in interconnects aboard spacecraft are subjected to extreme conditions requiring critical performance features that include: * Shock and vibration protection: Specific backshell features play a critical role in maintaining electrical continuity by reducing stress and strain during violent shaking and extreme g-forces. TE D-Sub and Micro-D backshell features are designed to meet customer requirements suitable to the application, not generic specifications. For example, where EMI shielding is required, the designer can use Micro-Band termination for that purpose, plus enjoy a measure of protection against inadvertent removal due to vibration and shock. A self-coupling locking nut on the band improves mechanical protection against loosening under vibration. Light-duty strain relief can be achieved by incorporating tie posts into banded backshells. Tie posts are optional in banded Micro-D backshells because wires are typically potted in place and the shield braid adds sufficient strain relief. Potting itself provides some strain relief as the epoxy resin or other material used to fill the space in the rear of a connector will harden into a solid, offering a degree of holding force to support the contacts in the housing. Cable entry points are also vulnerable to vibration. Elliptical-shaped cable entries can be employed to reduce contact angles to minimize areas of wear compared to round cable entries. However, uneven force around bands in elliptical-shaped cable entries causes problems as the larger radius has a tendency to allow braiding to pull out. Proper processing can mitigate this problem, but this type of entry is not recommended in high-vibration conditions. * Temperature tolerance: Whether at very high peak temperatures, low troughs, or cycling between high and low temperatures, extreme heat and cold stress materials—metal, glass, and polymers—causing cracking and fatigue, as well as distorting assemblies and rupturing seals due to different coefficients of thermal expansion. Generally, TE backshells are certified to the MIL-STD-883 temperature cycling test range of -55°C to +125°C. However, specialized materials and platings are available to handle the cryogenic cold of space and for higher- temperature electronics (Figure 1). Figure 1: Temperature Ranges for Various Backshell Platings Aenean vulputate eleifend tellus. Aenean leo ligula, porttitor eu, consequat vitae, eleifend ac, enim. Aliquam lorem ante, dapibus in, viverra quis, feugiat a, tellus. Phasellus viverra nulla ut metus varius laoreet. Quisque rutrum. Aenean imperdiet. Etiam ultricies nisi vel augue. Curabitur ullamcorper ultricies nisi. Nam eget dui. Etiam rhoncus. Maecenas tempus, tellus eget condimentum rhoncus, sem quam semper libero, sit amet adipiscing sem neque sed ipsum. Nam quam nunc, blandit vel, luctus pulvinar, hendrerit id, lorem. Maecenas nec odio et ante tincidunt tempus. Donec vitae sapien ut libero venenatis faucibus. Nullam quis ante. Etiam sit amet orci eget eros faucibus tincidunt. Duis leo. Sed fringilla mauris sit amet nibh. Donec sodales sagittis magna. Sed consequat, leo eget bibendum sodales, augue velit cursus nunc, quis gravida magna mi a libero. Plating °C °F Cadmium QQ-P-416, Type II, Class 3 over Electroless Nickel -65 to +175 -85 to +347 Electroless Nickel, AMS-C-26074, Class 4, Grade B -65 to +200 -85 to +392 Zinc Nickel Passivate over Electroless Nickel -65 to +200 -85 to +392 Zinc Cobalt over Electroless Nickel -65 to +200 -85 to +392 Unplated, Shot Blast for Non-Reflective Finish -65 to +175 -85 to +347 Passivate, per QQ-P-35 or MI-S-5002 -65 to +200 -85 to +392 Electroplated Gold per MIL-G-45204 Type II, Grade C -65 to +200 -85 to +392 Page 2 AEROSPACE, DEFENSE & MARINE / BACKSHELLS IN SPACE FOR MICRO-D AND D-SUB CONNECTORS