Contact design is critical to the performance of any connector — especially for devices that must function in harsh environments where extremes of temperature, shock, and vibration are to be encountered. Yet there are many different contact styles, and each supplier will claim an advantage. This article aims to set out clearly and concisely the merits and drawbacks of each of the main styles.
Twin beam contacts have two spring fingers on opposing sides. The mating pin is normally square, but twin beam contacts can also be used with circular (round pin) or rectangular (blade terminal) contacts. The twin beam contact provides two points of contact to the pin, ensuring electrical continuity. This design offers good performance levels for industrial and commercial connectors. It performs well in conditions of vibration and shock, particularly if the direction of vibration is considered.
The disadvantages of this design are that if made in phosphor bronze, the upper operating temperature is limited to 105 °C. Also, if the mating pin is oversized or misaligned, it can result in the twin beam contacts suffering permanent (an irreversible deformation of the shape) set with the risk of discontinuity.
Typical applications include automotive units, consumer electronics, white goods electronics, industrial electronics, medical electronics, and military equipment in a benign environment.
With this design, there is only one point of contact on each of the male and female connectors. The separate mating contacts are designed to connect using a sliding motion; the design can be hermaphroditic, i.e. both mating parts have the same shape. The designation of plug and socket is determined by the molded shape of the housing in which the single beam contact is contained.
Single beam contacts are most commonly found on fine pitch connectors of 1.00-mm pitch or smaller, which is enabled by the thin contact design. The advantages of this design include low cost as a result of the stamping process, and a low, or zero insertion force (ZIF). A disadvantage is a low resistance to vibration and shock, which is dependent on molding design.
Typical applications include consumer electronics, industrial electronics, test equipment, medical electronics, and office equipment.
The similarity in appearance to a musical tuning fork gives rise to the name. This flat, stamped component has two contacts on opposing sides that provide a rigid shape to accept the mating pin. The mating pin is normally square, and on PC/104-compatible connectors, the square handle of the tuning fork becomes the PC tail of the connector stacked above. The advantage of using such a design is the low cost due to the pressed metal manufacturing process.
The disadvantage is that a mating pin must be within tolerance since there is only a small movement of the tuning fork contacts on insertion of the pin. An oversized mating pin would result in a permanent set with a risk of discontinuity. Also, the low spring tension makes this design unsuitable for applications in environments of extreme vibration or shock.
Typical applications are industrial control systems, servers, communications devices, test equipment, automotive systems, data loggers, vending machines, medical instruments, PCI bus adapters, and bridges.
Circular Stamped Contact Clip
This is a stamped beryllium copper contact strip, with multiple spring fingers, formed into a circle. Devices can have three, four, or six spring fingers. The mating pin is circular, allowing multiple points of surface contact. These contacts are commonly used on high-reliability connection systems and individual PCB sockets. The main advantage is that the point of contact is always maintained; this is essential for continuous signal transmission. The clip performs extremely well in conditions of vibration and shock. This design provides high durability at low cost. The operating temperature is in line with MIL-Spec parameters of -55 °C to 125 °C. The clip can be inserted into a variety of shells, making the contact very versatile.
The disadvantage is the limitation on current-handling; therefore, they are not suitable for high-current applications.
Typically, circular stamped contact clips are used across a wide spectrum of applications, particularly when high reliability and low cost are required. These include military equipment, civil and military avionics, critical medical, high-performance industrial, and precision test instruments.
Circular Turned Multi-Fingered Contact
This contact is machined in beryllium copper with the spring fingers (also known as tines) being an integral part of the contact, rather than a subcomponent. The mating pin is circular to ensure contact is made with all of the tines. This one-part design overcomes the current-carrying limitation of the circular stamped contact clip, while at the same time maintaining signal continuity during conditions of vibration at a smaller size.
This style of contact is used in a wide variety of high-reliability applications where small size and light weight are pre-requisites such as UAVs, military portable equipment, and avionics.
Individual spring contacts (also known as shield fingers or grounding contacts) are a simple folded metal strip design that can be mated with a variety of flat surfaces. The design is used to connect PCBs to other boards or components, to pass signals and current, or to the chassis for grounding. The advantage is that they offer a low cost of ownership — they are both low-cost to purchase and low-cost to assemble onto a PCB. They are usually supplied on tape-and-reel packaging, thus enabling use of advanced manufacturing processes such as pick-and-place machines.
A disadvantage is a risk of over-compression that can result in permanent set, although there are some designs that have a “positive stop” to prevent this.
Typical applications include wearables, mobile devices, and antennas.
Spring Loaded Contact
This design comprises a plunger, spring, and barrel. The plunger is held under pressure by the spring contained in the barrel. The mating part is usually a fixed flat surface either as part of a connector or as an individual PCB pad. This design is used when rapid mating and un-mating of the connector is required in applications where there is a risk of variation in the closing mating dimension. It can also be used in “blind mate” applications where the engagement of the connectors cannot be seen, and precise alignment cannot be achieved. The spring loaded contact is also commonly used as a probe on automatic test equipment. Devices have high durability, with the number of operational cycles being 10,000 or more. These features come with a cost that is noticeably higher than that of the spring contact.
This is an arrangement of twisted wires to form a hyperbola shape between the two ends of a socket. The mating round pin, when inserted, stretches the wires, putting tension on the pin and creating a good electrical contact. The main disadvantage is the particularly high cost of the contact design.
This design offers high durability and is used in applications where shock and vibration are expected such as military, avionic, railway, and other rugged applications.
Contact performance varies considerably due to the contact design, as discussed above, and the manufacturer. Great care and consideration should therefore be paid to the selection of technology and supplier, especially if the connector is to be used in harsh and challenging environments. The customer should ensure that they have a full understanding of their performance and environmental criteria, which can also help connector manufacturers guide them to the most suitable connection technology.
This article was written by Scott Flower, Product Strategy Manager – High-Reliability Connectors at Harwin, Salem, NH. For more information, Click Here .