The failure mechanisms of electrical connectors have become more complex, as connector technology has evolved and downsized into fine pitch packages for high speed applications. These mechanisms can be obvious to the naked eye, as well as subtle, requiring extensive testing. For instance, electrical connectors that are subjected to frequent vibrations can induce micro-displacements, causing fretting fatigue of the contacts and a reduced life expectancy. When misalignment between an electrical connector's pin and socket members exists during insertion or withdrawal, mechanical damage can occur, causing pin/socket deformations, which can result in an increase in contact resistance to total failure.

 

Connector designers have employed a number of ways to increase the reliability of a connection system, such as including robust connector shells, socket retainers, contact wipers, contact lubricants, spring loading of contacts, and alternate contact configurations (e.g., butt-style), to name a few. One recent solution to avoiding connector failures is to incorporate a multi-beam, wave-spring, floating mechanism within the connector socket to give a small amount of play between pin and socket contact members. An example of such a connector is produced by Molex and called the Coeur CST High-Current Interconnect System which achieves low mating forces, prevents potential damage to socket contacts, and limits increases in contact resistance due to high contact beam deflection.

 

Back to the Basics: Contact Resistance and Contact Force

The quality of an electrical connection system depends on several factors, including contact resistance, contact force, contact material, and resistance to contact surface layer degradation. Contact resistance is one of the most important factors in establishing a reliable electrical connection. The higher the contact resistance, the greater the quantity of heat released by the contact. If contact temperature increases above the design limit, the contact will deteriorate -- soften, melt, and ultimately fail.

 

Contact resistance is also influenced by the quality of the contact surface layer. Manufacturing variations and machining tolerances can create imperfections on the contact's surface layer, creating a rough or uneven texture. Because of these imperfections, the true contact area is much smaller and localized than the apparent surface area of the contact. Hence, current conduction at the contact interface is limited to very small contact spots or constrictions (commonly called a-spots). Thus, constriction resistance forces a deviation of the lines of current as they travel across randomly located contact spots of the surface layer. In addition, surface films create layers of oxidation on the contact surface and can introduce a film resistance that can increase the overall contact resistance; increased contact resistance will produce more heat and more oxidation, accelerating contact deterioration.

 

Low contact resistance generally depends on maintaining contact force. Contact force creates the contact interface by deforming of the contact-to-contact mating area to create the a-spots. While the contact force provides the initial mating force, it also provides the frictional force to keep the contacts mated. Contact force can be reduced over time due to stress relaxation of the connection system, the physical nature of contact materials, or working temperature, which ultimately can increase contact resistance, heating, and connector failures.

 

Solving Pin and Socket Misalignment Problems

Pin and socket connection problems are often mechanical in nature. Mechanical stresses, such as high insertion or withdrawal forces, cause connection system failures and shorten the lifespan of the contact members. Misalignment of pin to sockets can cause contact overstress, impacting contact resistance, or causing pin damage, leading to connector failures.

 

It is difficult to have perfect pin-to-socket alignment (e.g., angle of engagement to accumulated tolerances) when mating two rigid PCBs, especially when high density of pin-and-socket connectors must mate at the same time. Bus bar joints and/or connectors need to maintain a low resistance while providing high mechanical strength, as well as resistance to oxidation, stress relaxation, and thermal expansion.

 

To accommodate pin to socket connector misalignment, the Coeur CST High-Current Interconnect System employs a float design where the entire core socket assembly can move within an outer housing. The float technology provides up to 1.00mm of axial float, which moderates any misalignment of the male pin to the female socket during connector mating. This solution is ideal for applications where the need for float is critical, such as power distribution mechanical packaging.

 

 

Preventing Voltage Drops in Electrical Connectors

In theory, we like to think connectors are a zero-resistance circuit component, but in reality all connectors have a resistance at the contact interface. What happens when the resistance is excessive? Two things generally can occur: the connector will be a load and drop a voltage, potentially causing circuit malfunctions, intermittent or inconsistent equipment operation, and for low voltage systems such as programmable logic devices or some of the newest microcontrollers that operate as low as 1.2V, the voltage drop can cause logic circuits to experience false triggering.

 

The other issue that comes up with connector voltage drops is that they manifest themselves as power dissipation in the form of heat (I2R losses). Basically, voltage drops negatively impact power efficiency. And power efficiency is critical to cost management, especially for large installations that consume lots of power such as data centers, server farms, and colocation facilities. Another problem that can arise is that a hot connector is effectively derated due to the heat build up, which is another way voltage drops can impact connector reliability.

 

To address this problem, the Coeur CST High-Current Interconnect System is designed with multiple contact beams per socket. This serves to ensure a low contact resistance, thereby maintaining low voltage drop across the connection, and a reduction in I2R losses and improvements to power efficiency.

 

The Impact of Contact Materials and Plating

Contact materials also affect the quality of the electrical contact. Some materials inherently have low contact resistance, such as silver and gold. But gold is expensive and silver does not have good mechanical endurance. Copper has good electrical conductivity but tarnishes and pits under an arc. Brass (copper-and-zinc alloy) is cost-effective and very easily machined. Yet brass experiences frictional wear and oxidizes at ambient temperature, which increases its contact resistance. Under an arc, brass pits, which allows in-depth oxidization. Silver-nickel alloys are often used because they combine the low contact resistance of silver with the durable mechanical properties of nickel.

 

Contact plating is also part of the quality equation, so to speak. Tin needs a very high contact force to remove accumulated surface oxides  on the contact surface layer. The downside of high contact mating forces impacts durability and the life expectancy of the contact. Gold plating, albeit more costly, tends to be free of oxides, and thus low contact mating forces are permissible. The Coeur CST High-Current Interconnect System utilizes a combination of contact materials to enhance conductivity while maintaining durability.

 

Flexible Design for High-Current Applications

The Coeur CST High-Current Interconnect System delivers up to 200A through 3 diameter sizes (8.00mm, 6.00mm and 3.40mm) and offers a wide range of configurations to connect PCBs, busbars, and cables. CST connectors offer a flexible design to meet a wide range of high-current applications. The connectors feature a low profile, where the male pin does not protrude above the socket housing when mated by a top entry, to save space above the PCB or busbar.  A common contact design in all CST sockets is utilized regardless of form factor sizes. They have fully shrouded female and male contacts, making them touch safe. Options include mate-first-last-break option, positive latching, panel-mounting (vertical, right-angle, PCB, and busbar mounting header). Coeur CST applications include data center solutions, including circuit breakers, data storage, instrumentation, PDUs, routers, servers, switches, UPS/battery storage, and more.

 

For more Information about the Coeur CST High-Current Interconnect System:

element14 Commmunity Discussion: What Do You Think About This Product: Coeur CST High-Current Interconnect System

DataSheet

Features, Applications and Sizes

 

How To Build a Coeur CST High Current Interconnect System

Once you determine the pitch, mounting style, and maximum current per contact, select from the list below:

 

Contact Pin

 

Screw-In Mounted

Coeur CST High-Current Male Screw-Mounted Pin, 6.00mm Diameter, 25.50mm Length, 140A, 600V Click to Learn More

Coeur CST High-Current Male Screw-Mounted Pin, 8.00mm Diameter, 26.15mm Length, 200A, 600V Click to Learn More

 

Press-Fit

Coeur CST High-Current Male Press-Fit Pin, 3.40mm Diameter, 26.00mm Length, 75A, 600V Click to Learn More

Coeur CST High-Current Male Press-Fit Pin, 6.00mm Diameter, 26.00mm Length, 140A, 600V Click to Learn More

Coeur CST High-Current Male Press-Fit Pin, 8.00mm Diameter, 26.00mm Length, 200A, 600V Click to Learn More

 

Surface-Mounted

Coeur CST High-Current Male Surface Mount Pin, 3.40mm Diameter, 20.00mm Length, 75A, 600V Click to Learn More

Coeur CST High-Current Male Surface Mount Pin, 3.40mm Diameter, 14.00mm Length, 75A, 600V Click to Learn More

Coeur CST High-Current Male Surface Mount Pin, 6.00mm Diameter, 20.00mm Length, 140A, 600V Click to Learn More

Coeur CST High-Current Male Surface Mount Pin, 6.00mm Diameter, 31.75mm Length, 140A, 600V Click to Learn More

 

Socket

 

Press Fit

Coeur CST High-Current Female Press-Fit Socket, 3.40mm Diameter, with 1.00mm Float, 75A, 600V Click to Learn More

Coeur CST High-Current Female Press-Fit Socket, 6.00mm Diameter, with 1.00mm Float, 140A, 600V Click to Learn More

Coeur CST High-Current Female Press-Fit Socket, 6.00mm Diameter, 140A, 600V Click to Learn More

Coeur CST High-Current Female Socket, 8.00mm Diameter, with 1.00mm Float, PressFit, 200A, 600V Click to Learn More

Coeur CST High-Current Female Socket, 8.00mm Diameter, Press-Fit, 200A, 600V Click to Learn More

 

Surface Mounted

Coeur CST High-Current Female Surface Mount Socket, 3.40mm Diameter, 75A, 600V Click to Learn More

Coeur CST High-Current Female Surface Mount Socket, 3.40mm Diameter, with 1.00mm Float, 75A, 600V Click to Learn More

Coeur CST High-Current Female Surface Mount Socket, 6.00mm Diameter, 140A, 600V Click to Learn More

Coeur CST High-Current Female Surface Mount Socket, 6.00mm Dia., with 1.00mm Float, 5.17mm Height, 140A, 600V Click to Learn More

Coeur CST High-Current Female Socket, 8.00mm Diameter, Surface Mount, 200A, 600V Click to Learn More

Coeur CST High-Current Female Socket, 8.00mm Diameter, with 1.00mm Float, Surface Mount, 200A, 600V Click to Learn More

 

Crimp

 

Coeur CST High-Current Female Crimp Socket for 1/0 AWG Click to Learn More  or Part Detail

 

Housing

 

Coeur CST High-Current Female Crimp Housing Click to Learn More or Part Detail

Coeur CST High-Current Female Terminal Retention Housing Click to Learn More or Part Detail

Coeur CST High-Current Male Header, 2 Circuits, Screw Attach Click to Learn More or Part Detail