TE - White Papers

Introduction As designers evaluate the capability of a backshell to protect connector-to-wire and -cable terminations, it pays to consider high-quality, economical solutions that can handle multiple challenges. Key functions provided by backshells include strain relief at the back portion of the shell where contacts connect to wires or cable, electromagnetic interference (EMI) shielding, and environmental protection. Material properties of aluminum-alloy or composite-thermoplastic backshells must exhibit rugged, lightweight, and precise-mating features. Physical performance must include the ability to withstand shock, vibration, temperature, and corrosion. Handling these challenges is especially critical when electronic systems are subjected to supersonic speeds and high gravitational (g) forces. That's why TE Connectivity (TE) Micro-D and D-Subminiature backshells for spacecraft applications provide valuable benefits for designers meeting demanding functional, material, and performance requirements where quality and affordability count. Meeting Key Functional Challenges T h e e v o l u t i o n o f D - shaped connectors has g o n e f r o m D - Subminiature (D-Sub) connectors developed in t h e 1 9 5 0 s t o m o r e compact Microminiature- D ( M i c r o - D ) d e s i g n s introduced in the early 1970s to today's high- performance D-sub and Micro-D versions that take advantage of advanced rectangular backshell technology for space-grade applications. Today, rack and panel connectors can utilize highly specialized TE D-Sub backshells for MIL-DTL-24308-compliant mating and Micro-D backshells for MIL-DTL-83513-compliant mating in compact, rectangular form factors. As with standard circular designs, rectangular backshells deliver key functional advantages, which include: * Strain relief that supports cable and wire to help prevent over- bending or flexing. Strain relief can be achieved with a heat- shrink boot, cable clamp, or tie post, depending on customer preferences and testing requirements. Cable clamps help prevent wires from pulling on contacts and general mechanical damage to the termination. Saddle bar cable clamps are integrated into the backshell to simplify installation. However, strain-relief backshells do not provide any EMI or environmental protection and should only be used in clean, dry environments. * Preventing electromagnetic interference (EMI)—also known as radio-frequency interference (RFI) when in the radio frequency spectrum—can affect an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. To help avoid the effects of EMI, electromagnetic c o m p a t i b i l i t y ( E M C ) shielding can be used that employs a properly grounded braided shield or screen terminated to the backshell. To secure the shield/ screen, a Standard Band or Micro-Band can be used, as described below. * Environmental protection incorporated in the strain relief can be as involved as sealing the whole assembly with a heat shrink boot that is itself properly sealed with a potting compound or an adhesive to help prevent water or other fluids from entering wiring. Or it can simply entail providing a protective cover at the rear of a connector that is used as a stand-alone device. * Grounding the system can be achieved by terminating a shield at the backshell. The most basic cable shield termination is comprised of connecting the full circumference of the cable shield to the backshell, which is then connected to the enclosure and ultimately connected to the airframe to help ensure a closed system without a ground loop. Using a backshell for grounding is particularly valuable in situations where grounding is not allowed through a pin. Meeting Material Challenges Backshells in space-rated applications require specialized materials processing and precise mating interfaces. For metallic backshells, the base material and plating must be matched to prevent galvanic corrosion between dissimilar metals. For composite thermoplastic backshells, the nonmetallic material does not corrode, weighs less than metal, and can better withstand harsh environments. Page 1 AEROSPACE, DEFENSE & MARINE / BACKSHELLS IN SPACE FOR MICRO-D AND D-SUB CONNECTORS BACKSHELLS IN SPACE FOR MICRO-D AND D-SUB CONNECTORS by: Carina Logan, Product Manager, Middletown, PA

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