Precision-manufactured pins and sockets designed with both MIL specs and applications in mind provide superior reliability and durability in harsh-environment defense applications. These contacts are critical building blocks for military connectors that must perform under pressure on land, at sea, and in the skies above.
By Steve Smashey, President, and Mike Conte, General Manager, SOS Engineering, Inc. pins and sockets
Contacts are the foundation of connector performance and durability. Connectors used in military, aerospace, defense, and other mission-critical applications require pins and sockets designed to ensure predictable, repeatable, and dependable performance. Whether used in land, sea, or air applications, military and aerospace connectors must be resilient against harsh environment conditions.
Military and Aerospace Specifications
In the 1930s, the United States Department of Defense developed electrical connectors for use in aerospace and other harsh-environment applications. The original Army-Navy (AN) series set the standard for modern military circular connectors and evolved into what are known today as military standard or mil-spec connectors. Many U.S. military standards apply to connectors, ranging from MIL-DTL-5015, which covers heavy-duty circular electrical connectors with soldered or crimped contacts, to MIL-C-83522, which describes the characteristics, performance, and testing criteria for single-terminus fiber optic connectors.
The M39029 (SAE AS39029) specification includes crimp contact requirements designed to ensure durable and consistent signal transmission in demanding operating conditions. Required for use in many military, aerospace, and defense applications, M39029 contacts are available in a variety of options. However, not every M39029 contact is created equal. Application requirements must be taken into account before selecting materials for these pins and sockets because M39029 simply calls for copper alloy contact materials, and there are more than 400 variations of copper alloys, each with different characteristics and capabilities. For example, leaded nickel copper and beryllium copper are ideal for harsh environments due to their inherent durability. Similarly, glass-sealed alloy 52 contacts are often required to reduce thermal expansion in aviation applications as altitudes and temperatures change.
Plating materials and thickness are also vital considerations to ensure performance and long-term durability. Plating materials are chosen for several performance characteristics, including corrosion resistance, electrical conductivity, thermal conductivity, solderability, wear resistance, operational life, and infrared reflectivity. Plating the contacts with a thin layer of gold provides the most valuable benefits. The M39029 specification mandates that gold plating for its exceptional corrosion prevention, enhanced durability and reliability, increased heat protection, diminished fretting degradation, and excellent electrical conductivity.
Selective gold plating plays an important role in reducing connectors costs and achieving durability. Historically, the M39029 specification required 0.000050” of gold plating over the entire outer surface of the contact, but it now allows for selective gold plating as well, which offers significant cost savings for M39029 connectors. Thicker gold plating increases the number of mating cycles by offering improved wear and tear resistance. Gold-plated pins and sockets are also used in many harsh-environment applications to maintain low contact resistance over time, because gold is resistant to oxidation.
Military Aviation Applications
Modern aviation technologies in both the military and commercial markets employ enhanced systems that simplify flight operations and navigation and improve safety and comfort, and nearly all of these advanced aerospace technologies demand specialized connectivity solutions. These systems include AI, which is commonly used in autonomous drone systems, predictive maintenance, advanced navigation, and fuel monitoring systems, cloud-based flight and data management, and sophisticated power generation and distribution. Connectors can be found in every electronic system in an aircraft, from the flight control panels, landing gear, and sensors to the entertainment systems in the cabin and emergency systems.
Connectors must meet several universal performance prerequisites for emerging applications like military and delivery drones, as well as traditional military and commercial aircraft. Next-generation military and aerospace applications require increasingly rugged connectors capable of high-reliability, high-speed data transmission in harsh environments. To meet these design objectives, connectors must employ protection from electromagnetic interference (EMI), shock and vibration, and the elements, as well as the wear-out mechanisms caused by high mating cycles — and all within smaller, lighter-weight, and lower-cost form factors that comply with relevant specifications.
Fiber optic systems are now commonly utilized to meet more advanced military aviation performance demands. Smaller and lighter than traditional copper cables, fiber optic cable assemblies deliver the higher data rates and bandwidths needed for advanced communication protocols and don’t require additional material plating materials like traditional electrical connectors. Fiber optics also offer better tolerances for shock and vibration compared to copper systems and have an inherent immunity to EMI and RFI.
However, traditional copper cable assemblies terminated with circular or rectangular connectors sealed to IP68 must still be utilized in the power electronics within military aviation applications.
Military Shipboard Systems
Some military ships, including aircraft carriers, cruisers, and amphibious assault ships are now being tasked with service for up to 50 years, which requires all enabling systems and components to be designed for extended operating lives. Much like military planes and drones, military ships feature complex systems capable of supporting a wide range of functionalities. From high-speed, high-bandwidth navigation and communication networks to high-power electrical systems, connectivity is vital to sustaining ship-wide operations.
Marine connectors must be resistant to moisture, shock, vibration, EMI, and extreme temperatures, and even salt spray and fog, as salt can quickly corrode metal, and salt on contacts can create shorts in the system. Military-grade marine connectors exposed to the elements should be equipped with hermetic glass seals qualified to MIL-DTL-38999 (EN3645) for resistance to 48 (Class N) or 500 (Class Y) hours of salt spray fluids to protect the contacts within. Plastic housings are commonly used for their intrinsic resistance to salt corrosion.
Fiber optics are increasingly being deployed in marine applications to better support the vast shipboard communication networks. MIL-PRF-28876 is a universal standard for circular fiber optic connectors in shipboard applications. These connectors must deliver low optical insertion loss, high reliability and repeatability, and effective strain relief in marine applications. Fiber optic systems support 1,000 times the bandwidth over 100 times the distance, compared to copper wire. So, in large ships running miles of cable, fiber only experiences 3% signal degradation over distances greater than 100 meters, compared to copper’s 94% loss of signal. In addition, fiber optics aren’t affected by salt and have a longer shelf life than copper systems — up to 50 years versus an average of just five years. Due to the expected longevity of many military ships, copper wire and connectors must be designed for simplified retrofitting and upgrading to extend system life and reduce cost of ownership. As a result, fiber is the natural choice for many military marine data applications.
Military Soldier Systems
Soldiers in the field require many of the same attributes as aviation equipment. C4ISR systems (command, control, communications, computers, intelligence, surveillance, and reconnaissance systems) must be small, lightweight, and above all else, consistent in the field. From military-grade electronics and handheld radios to advanced 3-D imaging headsets, reliable connectors equipped with durable, high-performance pins and sockets are a primary design consideration. Standard MIL-DTL-5015 circular power connectors utilize stamped and formed contacts to reduce weight compared to machined parts. Smaller, 26-gauge contacts are often implemented in these connectors, as they offer size and weight reductions while still meeting power or signal requirements. These connectors must also deliver IP68 or better waterproof performance and rugged resistance to contaminants including sand, dirt, and mud, as well as shock and vibration.
Just as important is ease of use. Circular connectors must enable quick connections and disconnections with structures designed for low insertion force and quick locking. Pins and sockets must support this design objective while maintaining high conductivity performance throughout the numerous mating cycles in harsh conditions. Field repair is also of the upmost importance. If damaged, contacts must be easy to replace. Crimp contacts are best for field repair.
Fiber optics have also seen some penetration into C4ISR systems due to their small size, light weight, and high data transmission rates.
Military Ground Vehicles
From Jeeps, Humvees, and trucks to tanks and armored vehicles, ground vehicles require resilient connectors to withstand severe environmental conditions like extreme temperatures, shock and vibration, moisture, dirt, and mud. Circular and rectangular connectors are commonly used to meet the specific needs of the military vehicle industry. Like soldier systems, military ground vehicles use circular connectors for quick-connect vehicle applications and load them with pins and sockets designed to handle numerous mating cycles without losing signal integrity.
Rectangular connectors are also available in a wide range of materials, housing styles and configurations, and contact manufacturing and termination options. MIL-DTL-24308 D-Sub and MIL-DTL-83513 miniature D-Sub connectors are just two types of high-density, rectangular I/O connectors commonly used to deliver high-reliability performance in rugged, harsh-environment designs.
Designing and manufacturing connectors with predictable and repeatable performance characteristics is particularly challenging when they also have to operate in harsh-environment conditions and satisfy stringent specifications. There are many factors to consider when designing connectors for military applications, but electrical contacts play an especially vital role in the integrity and reliability of signal transmissions.
Pins and sockets thoughtfully designed and precision manufactured by well-experienced, industry-proven suppliers are at the heart of all the highest-reliability and highest-performance military connector products. In mission-critical military applications, contact failures can spell disaster, cause costly damage to equipment, and even lead to loss of life. Application requirements, such as environmental conditions, mechanical performance, electrical performance, and physical size constraints determine the selection of pin, socket, and plating materials, as well as termination techniques. Whether operating in military aviation, marine equipment, soldier systems, or ground vehicle applications, only the highest quality connector contacts can deliver the high operational integrity, reliability, and durability required for the job.