In the military, defense, and aerospace industries, many electronic systems are designed with the harshest possible operating environments in mind. For example, deep-sea electronic systems must withstand high pressure and corrosive saltwater, while terrestrial systems may have to endure battlefield conditions, including mud, dust, high vibration, and high temperatures. The same applies to aerospace systems, which must withstand multiple takeoffs and landings, continuous flight vibrations, and the extreme temperature fluctuations experienced by spacecraft exploring vast spaces. Designing truly robust and reliable electronic components has always been a relentless pursuit for engineers and manufacturers.
Ruggedness and reliability are common terms in the electronics components industry, frequently used to describe the characteristics of connectors, which serve as core components in many electronic systems. Because there are no readily available, reliable rating systems, true commercial-grade ruggedness and reliability are not easily confirmed. Therefore, engineers must investigate the true characteristics behind the numerous advertisements and promotions in the market. Ultimately, ruggedness and reliability depend primarily on the product's final application and testing.
Connector characteristics, such as engagement cycle, mounting and mating hardware, shielding, back shell, insulating materials, and locking mechanisms, are all important factors in achieving robust and reliable performance. However, just like the drivetrain in the Oshkosh Joint Light Tactical Vehicle (JLTV), connector reliability begins where the pins and sockets make contact: the contact system.
Contact systems are particularly important in modern miniature military connectors because the same robustness and reliability found in larger connectors can be replicated and achieved in miniature connectors. Three common contact types used in high-end, robust, and reliable connectors are pin and socket, twisted pin, and hyperboloid connections.
The pin-to-socket contact is a cylindrical contact between the pin and the socket that relies on spring force to engage in the correct contact position. This spring force also wears down the contact surface and maintains contact pressure.
Figure 1: Pin and socket connection
A twisted-pin connection is made by welding a bundle of elastic wire to the end, curling it into a sleeve, and having a protrusion that creates a spring section.
Figure 2: Twisted pin connection
Hyperboloid contact is essentially the reverse of torsion pin contact because they have similar spring units/grids, but the contact point is at the socket instead of the pin.
Figure 3: Hyperboloid Connection
What these three contact technologies have in common is that each can achieve multiple contact points. If the engineering community were to determine the best way to ensure robustness and reliability, it would almost certainly be multiple contact points. While there are certainly other important methods, such as single contact points, or even only two contact points, under high vibration or high gravity conditions, it is possible for the pin and socket to break or make unstable contact. Such temporary disengagement can sometimes have serious destructive effects.
Several other properties also contribute to the robustness and reliability of connectors; the first is contact area. Contact area refers to the length of the contact area between the pin and the socket. For robust and reliable performance, a general rule of thumb is that the minimum contact area should be 1.5 times the pin diameter.
Figure 4: Contact quantity (left) and contact force (right)
Another key attribute is contact normal force. When connector pins or sockets act as spring components, maintaining continuous contact with each spring contact is crucial in high-vibration environments. Contact normal force must be adequately guaranteed throughout the connector's lifespan; therefore, using a robust base material is essential for the spring components of robust, high-reliability contacts. Greater contact force also minimizes the air gap between the two mating surfaces, thereby reducing resistance. Contact shape design also plays a significant role in maintaining good contact force. Two contacting planes distribute the force evenly across the surface, reducing contact force, while a circular surface in contact with a plane concentrates the contact force into a smaller area, resulting in a higher contact normal force. Considering the miniaturization of today's contact systems, optimizing contact geometry to achieve optimal contact normal force is a remarkable achievement.
The contact substrate plays a crucial role in achieving appropriate contact normal force and is also important in terms of electrical and thermal conductivity, ease of manufacturing, and material cost. Beryllium copper (BECU), with its unique yield strength, high hardness, formability, spring stability, and exceptional fatigue resistance, has become the fundamental material for spring contacts in ultra-high reliability connectors and is a key component for high-durability parts, especially under cyclic loads. Phosphor bronze or brass is often the preferred material for non-spring contact components, such as pins. Contact plating, used to coat the mating surfaces with the metal of the substrate, helps maintain stable conductivity due to its high corrosion resistance; gold is a classic example. A 50μm gold plating thickness can also provide a very durable connection. Commercial-grade connectors typically reduce the gold plating thickness to 30μm or less.
Figure 5: AirBorn's Versi series open pin connectors have sockets with four redundant contacts to enhance reliability in critical applications; compliant with mil-dtl-83513 requirements.
While using commercial-grade connectors can reduce costs in demanding, high-reliability applications, it is best to use connectors with more robust and reliable properties, including multiple contact points, high contact engagement, high contact normal force, and substrates with superior performance characteristics. With the increasing prevalence of miniature connectors, it is also crucial to obtain robust and reliable connectors from trusted, experienced suppliers. Designing key robustness and reliability factors into miniature connectors is a technological marvel, and these characteristics are precisely what distinguish truly robust and reliable connectors and connector suppliers from commercial-grade components.
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