Precision machined tight-tolerance connector designs with military pedigrees are preferred for I/O interfaces in mission-critical military and aerospace electronics, such as cockpit avionics systems. End-user customers in mil/aero-grade environments have little patience for cheaper, lesser caliber interconnects that can adversely impact system life-spans and performance, even though they may reduce the initial purchase price of the system.
Durability, sealing, and size are important considerations for ruggedized mil/aero applications, but the list doesn’t stop there. Ruggedization, as a design practice, is applied to every aspect of an interconnect, ranging from environmental sealing to robust resistance to vibration and shock. Six crucial connector considerations for ruggedized mil/aero applications include mating cycles, coupling style, EMC shielding, shock and vibration, ruggedized mounting/electrical connections, and the right partner. Avnet’s qualified mil connector Value Add Center prides itself on quality, efficiency, and flexibility, as well as meeting our customer’s mission critical and business needs.
Mating cycles vary considerably from application to application. Mating cycle benchmarks are born out of military specification norms and are typically de-rated from the mating pair’s actual capabilities. Some systems require interconnects to be mated for testing and acceptance but, once engaged on the platform, are only unmated and mated again due to an issue or an upgrade.
Interconnects can be optimized for tens of mates to tens of thousands of mates. Material selection, finish, surface roughness, the contact system, and lubrication all play a significant role in the number of mating cycles an interconnect can reliably perform.
Interconnect coupling systems facilitate mating and unmating processes. Simple threaded coupling systems are generally adequate for converting torque into axial displacement, but often require multiple rotations of the coupling nut to fully engage the connectors. Multi-start threaded coupling systems can reduce the number of rotations required to fully engage connectors, and thus enable quicker mating and unmating. One shortcoming of threaded coupling systems is that there is often no clear indication that the connectors have been fully mated.
Electromagnetic compatibility (EMC) shielding protects a signal from outside electromagnetic energy that can disrupt the signal and prevents emissions from the signal itself from interfering with external electronics. EMC shielding can control both electromagnetic interference (EMI) and radio frequency interference (RFI)..
Effective shielding in electrical wire interconnect systems depends on connector component selection, conductive plating, wire and cable shielding, individual and overall cable shield grounding, the use of conductive gaskets or fittings, and more. Because the entire transmission path — including cabling, connectors, printed circuit board (PCB) sockets, input/output (I/O) ports, etc. — is vulnerable, it is important to view EMC shielding in terms of a “follow-the-wire” approach to interconnect design.
All mechanical systems experience shock and vibration at some point in their existence. Depending on the application, sometimes the shock and vibration associated with shipping and handling can be greater than that of the intended platform; so, all environments must be carefully considered.
Shock is typically associated with rapid acceleration or deceleration. Shock also causes mechanical components to oscillate at their natural frequency and typically results in a short duration of sinusoidal vibration.
Vibration is the continuous input of oscillating mechanical energy. It can be sinusoidal, such as that generated by the rotation of a motor that isn’t perfectly balanced.
Weld- and solder-mount I/O receptacles can contribute to ruggedization, especially in tightly-sealed systems. For general environmental applications, designers tend to select single-hole jam-nut mounted receptacles over multiple-hole box- or wall-mount receptacles due to ease of assembly and superior sealing. Simply put, the more holes you introduce into your box or panel, the greater the odds of suffering an environmental leak.
One of the challenges for I/O connector-to-board terminations is maintaining the electrical “goodness” of the signal. In high-speed systems that have little or no budget for signal degradation, designers sometimes opt for the shortest and most direct board termination. These junctures can be ruggedized by selecting PCB-mount connectors that incorporate auxiliary mounting posts (i.e., threaded attachments) or extremely rugged eye-of-the-needle (i.e., compliant pin) PC-tail terminations. When opting for ribbon wire or flex for final termination to the board, care must be given to ensure that impedance-matching and shielding is maintained from the I/O all the way to the board.