Rugged connectors are required for applications in a wide variety of settings, from sterile medical facilities to downhole oil and gas rigs. Key considerations for specification include the environment, the function, and the performance requirements.
Rugged Connector Checklist
Rugged connectors must be able to function in environments and under circumstances that would challenge typical connectors. But what exactly makes a connector “rugged”? Environmental challenges that require a more durable component include the following:
- Sudden acceleration and shock loads cause the connector to become disengaged or can cause the contact interface to temporarily separate, interrupting the signal.
- Vibration leads to intermittent contact and fretting corrosion at the contact interface, if the contacts are not stiff enough. With sufficient amplitude, vibration can also cause the connection to become loose or to disengage altogether.
- Excessive heat or cold causes several problems: At high temperatures, metal contacts may lose strength and ductility and experience stress relaxation. Plastic components may creep or distort. Cold temperatures can make materials brittle. Different rates of thermal expansion between components can stress or break seals, which can allow any corrosive gasses or liquids in the environment to attack the contact interface or other connector components.
- Dust and other abrasive elements encourage wear of the plating and can build up at the contact interface, interfering with the electrical path and potentially causing open circuit conditions.
- Corrosive elements such as ammonia (stress-corrosion cracking), sulfur-containing compounds (sulfide stress cracking), and chlorine-containing compounds (stress-corrosion cracking) can attack the copper-based alloys used for the contacts as well as the steel or plastic used in the housings.
- A high number of mating cycles causes wear of plating, the permanent set of contacts if the connector is misaligned while mating, and even low cycle fatigue if the strain is high enough.
- Water often contains dissolved salts that accelerate most forms of corrosion. Many other corrosive or abrasive elements found in the environment will either be dissolved into or carried by water.
- Sterilization of medical components is usually performed in an autoclave using high temperature/high pressure steam, ethylene oxide, nitrogen dioxide, or ozone. If the component has a built-in connector, it must be able to survive this exposure.
A rugged connector may be required simply because it would be inconvenient or expensive to replace. It is much easier to replace a coaxial connector inside a home than 60 meters above the ground on a cell tower. Similarly, connectors on a battlefield, in outer space, downhole, undersea, or in a mine far from populated areas may be impractical or impossible to replace on demand. Connectors used in these environments must be designed to survive far more abuse than their counterparts in more benign locations.
Specification of rugged connectors is often necessary due to the specific application requirements:
- Military connectors are subject to shock, impact, heat, vibration, and abrasive particles. They may also see a high number of mating cycles in harsh environments.
- Aerospace connectors can experience high acceleration, extreme high or low temperatures, vibration, radiation, and extreme low or high pressure. If the connector is going into orbit, the materials used must be radiation-tolerant and should not outgas under vacuum or low pressure. This is particularly important since differential thermal expansion under repeated extreme temperature swings (less than -125°C to greater than +150°C) makes sealing difficult.
- Automotive connectors must survive potential exposure to heat (up to 185°C), vibration (up to 30g depending on location), corrosive gasses, water, and salt, while coping with the challenge of powering more electronic devices and running ever more circuits through the same amount of space. Connectors located in the engine compartment also have the potential to be exposed during routine maintenance to fluids such as ethylene glycol, oils and greases, transmission fluid, etc. EVs and HEVs may have busses operating at 100V – 200V, which means there is the potential to vaporize the contacts via arcing if the connector is disengaged while the circuit is live.
- Downhole oil and gas connectors routinely see high pressures (20,000 psi) and temperatures (175°C – 225°C), shock, and vibration. If seals fail, they could also potentially be exposed to highly corrosive and erosive fluids, so they must be able to survive this exposure until the tool can be pulled out of the ground.
- Mining and off-highway connectors will experience a great deal of shock and vibration. Mining environments are filled with highly abrasive dust and other particulates, especially in salt or coal mines. Those used outside will also see the potential for exposure to water, possibly with dissolved corrosive elements.
- General industrial connectors may need to withstand shock, vibration, heat, fluid exposure, abrasive dust or particles, and exposure to a wide variety of chemicals in manufacturing environments.
- Medical connectors often are required to support hybrid functionality. This means that they need incorporated, separated connection points for electrical signals, power, liquids, gasses, etc. Furthermore, they have the potential to be exposed to medical and bodily fluids and may even need to be able to survive the sterilization process.
- General outdoor connectors must withstand rain, snow, dust, liquid ingress, and any potential corrosive gasses in the atmosphere. Near the ocean this may include salt spray and in agricultural areas ammonia vapors from fertilizer.
- Marine connectors must be sealed to protect against fluid ingress and salt. The housing material must be able to stand up to salt water, salt spray, marine diesel, etc., without corrosion.
Connectors in these environments still must exhibit basic connector functionality, and may even need to contend with additional requirements:
- They need to mate easily and stay mated. Someone may need to plug in or unplug a connector while wearing surgical gloves, work gloves, etc. The mating force must be low enough to meet ergonomic requirements (75N or less mating force in automotive), but the extraction force cannot be so low that it can easily come loose under shock and vibration. This may require some kind of mechanical assist built into the connector housing.
- They must maintain contact force no matter what temperature they experience. This requires good stress relaxation resistance in the contact sockets and good retention of properties at elevated temperatures.
- They need to withstand many mating cycles and tolerate misalignment. This requires high yield strength and fatigue strength in the electrical contacts.
- They may need to handle greater power. Passenger cars in particular have seen a dramatic increase in the number of electrical and electronic features, particularly for infotainment and advanced driver assistance systems (ADAS). These devices require more power to drive them, which means increased voltage and/or current. This trend will only continue to increase when autonomous vehicles enter the roadways, as cars will need ever more sensors (radar, lidar, ultrasound, cameras) and processing units to make sense of all the data.
- They must be EMC-compliant. A greater proliferation of electronic devices and wireless signals provides ever more opportunity for electromagnetic and radio frequency interference. Connectors must be properly grounded, shielded, or bonded so they are immune to external noise and do not become noise sources on their own.
- They need to be designed to allow miniaturization and increased circuit density. Since individual contacts must be made smaller, connectors need to be made from metals with higher conductivity to handle the increased electrical current density; higher strength to withstand the higher stresses necessary to ensure adequate contact force; better formability to fit into tighter spaces; and greater fatigue strength and stress relaxation resistance to maintain good electrical contact over the life of the connector.
- They may need to offer hybrid functionality. This includes hybrids of signal and power, copper and fiber, or some combination of electrical/hydraulic/pneumatic.
- Connector housings will most likely need alignment features such as built-in keys to protect pins and sockets. They may also need to provide sealing, ingress protection, or even hermeticity depending on the severity of the environment and the liquids, gasses, particulates, or chemicals found in it.
With the right combination of materials and design, rugged connectors can withstand whatever demands the end-use application and the surrounding environment throws at them.
Author Mike Gedeon is the engineering manager at Materion.