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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

Twin beam contact.

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.

Single Beam

Single beam contact.

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.

Tuning Fork

Tuning fork contact.

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

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.

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