In the world of military, defense, and aeronautics, many electronic systems are designed to excel in some of the harshest environments imaginable. Deep-sea systems must endure high-pressure and corrosive salt water while systems on land bear high-vibration, gritty, and hot conditions such that is found on a battlefield. So true of aerospace systems, withstanding repeated take-offs and landings and constant in-flight vibration. Think too of the unrelenting temperature fluctuations that spacecraft sustain during their time exploring the vastness of space. The idea of designing truly extreme “rugged & reliable” electronic components has been relentlessly pursued by engineers and manufacturers alike for decades.
The term “rugged & reliable” is a common phrase used in countless marketing pieces within the electronic component industry. That distinction is also applied specifically to connectors, one of the core components of many electronic systems. Because no easily-referenced grading system exists to distinguish truly rugged & reliable connectors from commercial-grade connectors only claiming to be, engineers must see through the marketing hype to determine a connector’s true nature. After all, the definition of rugged & reliable depends chiefly on the context of the product’s final application and the severity of its usage.
Connector features such as mating cycles, mounting & mating hardware, shielding, backshells, insulator materials, and latching are all important factors to delivering rugged & reliable performance. But much like the transmission in Oshkosh Defense’s Joint Light Tactical Vehicle (JLTV), a connector’s dependability begins where the pins and sockets meet: the contact system. This is especially critical in the micro-miniature connectors of today, where implementing the same traits of ruggedness & reliability that larger connectors may exhibit prove extremely challenging to replicate at microscopic levels.
The contact types typically employed in high-end, rugged & reliable connectors are: pin-and-socket contacts, twist-pin contacts, and hyperboloid contacts.
Pin-and-socket contacts, as this illustration shows, are cylindrical contacts where either the pin or the socket relies on a spring to force the mating element into a position of positive contact. These springs wipe the mating surfaces and maintain contact pressure.
Twist pin contacts are made from a bundle of spring cable arc welded at its end, crimped to a sleeve, and bulged out to create a similar spring element as shown here.
Hyperboloid contacts are essentially the reverse approach to a twist pin, by creating a similar spring mesh but on the socket side of the contact as shown in the image on the left.
What is the common theme among these contact types: multiple points-of-contact! If there was a single attribute that best differentiates truly rugged & reliable from commercial-grade connectors, my vote would be multiple points-of-contact. There are other important distinguishing factors, but having only a singular or even two points-of-contact creates potential for intermittent and inconsistent pin and socket contact under high-vibration or high g-force scenarios. One brief moment of de-mating at the contact level can have devastating effects.
In addition to multiple points-of-contact, ruggedness & reliability is also achieved through other key attributes; the first being contact engagement. Contact engagement is the length of contact made between the pin and socket. A general rule-of-thumb for rugged & reliable performance is a minimum contact engagement of 1.5 times the diameter of the pin.
Another central attribute is contact normal force. With either the pin or the socket acting as a spring member, the amount of force that each ‘tine’ of the spring contact makes to the mating contact is critical to maintaining solid contact in high-vibration environments. The normal force must be maintained sufficiently over the life of the connector, so employing an excellent base material for the spring member of the contact is critical. Greater contact force offers the added benefit of minimizing air gaps between the two mating faces, resulting in reduced electrical resistance. Contact geometry plays an important role in maintaining good contact force as well. Two flat surfaces butting against each other distribute forces evenly across the surface, lowering the contact force. Conversely, a rounded surface contacting a flat surface concentrates the contact force into a smaller area, resulting in a higher contact normal force. Optimizing contact geometry to optimize contact normal force is an astounding feat of engineering given the micro-miniature size of contact systems today.
Finally, Contact base materials play a central role in delivering proper contact normal force through spring performance. Base materials carry significance too in terms of electrical and thermal conductivity, ease of fabrication and material costs. Beryllium Copper (BeCu), is the base material-of-choice for spring member contacts in ultra-high reliability connectors. This is attributable to high-yield strength and high hardness but with added formability and spring stability. Berryllium’s has very high fatigue resistance, a critical facet of high-endurance components, especially under cyclic loads. Phosphor Bronze or Brass is often the material-of-choice for non-spring contact members such as pins. Contact plating, or metal used to coat the base material at the mating face, is classically gold due to its resistance to corrosion, thus sustaining consistent electrical conductivity. Gold also provides a very durable connection provided a 50 μin coating thickness is used. Commercial grade connectors often reduce their thicknesses to 30 μin or less.
While it may be tempting to design in a commercial grade connector to keep costs down, in the micro-miniature connector world, designing in these critical factors at the microscopic level of contacts used today and more importantly, consistently producing these contacts with such features, is a technological marvel. And it’s what separates truly rugged and reliable connectors and suppliers from the crowded commercial grade pack.