Understand How Superior Contacts Enhance the Performance of Multi-Position Connectors

Connectors are the critical mechanical and electrical link between subsections of a system or between a system and the outside world. Several factors determine the choice of connector type, including electrical and mechanical requirements, industry standards, ease of use and manufacture, the number and type of contacts, mating and unmating scenarios, reliability objectives, and regulatory mandates. Still, the classic D-subminiature (D-sub) connector body has been used for decades and remains the preferred connector for many applications.

While the connector body style and contact arrangement receive much attention, the contacts significantly impact a connector’s electrical and mechanical performance. As designs become increasingly complex and applications become more demanding, designers need to be aware of the latest innovations in contact technology to meet the appropriate standards and requirements, particularly in terms of ruggedness, insertion and retention force, contact resistance, and temperature tolerance.

This article provides a brief overview of connector trends, with an emphasis on the continued role of D-sub connectors. It then introduces advanced contacts from Amphenol Positronic and shows how they can be used to enhance connector performance.

USB, Ethernet, and the importance of D-sub connectors

Despite reduced use of the classic RS-232 interface and the rise of various versions of USB and Ethernet connectors, the classic 9-pin D-sub connector (often called DB-9) and the rest of the broader family of D-sub connectors continue to play an important role in electronic system communication. There are many reasons for this continued use. While USB and Ethernet can meet many interconnection requirements, these two widely used connector types are serial and not multi-line interfaces. They can carry data and power concurrently, but only with severe restrictions on the signal type, voltage and current maximums, and power ratings.

By design, USB and Ethernet cannot handle multiple unrelated signals or varying formats as effectively as an interface with multiple parallel contact paths. An additional yet critical consideration is that standard USB and Ethernet connections were not designed for the level of mechanical and electrical integrity and ruggedness needed in many situations.

For these and other reasons, the D-sub connector is still widely used. The form factor has been around since the 1950s and offers many advantages. It is fully shielded against electromagnetic interference (EMI) and radio frequency interference (RFI), provides a sealed or nearly sealed enclosure, is mechanically rugged, and its mating halves can be locked to each other with small jackscrews. The D-sub connector body, or shell, is offered in at least six standard sizes and provides flexibility in its electrical contact positions and types. In addition to offering connector shells with the same contact type at all positions, “Combo-D” D-subs support a mix of independent signal and power contacts within a single connector shell (Figure 1, top).

Figure 1: The Combo-D subminiature connector style supports many combinations of paths for signals and power (top); D-sub connectors are available in standard shell sizes and contact arrangements (bottom). (Image source: Amphenol Positronic)

A single D-sub can support a variety of standard mix-and-match arrangements (Figure 1, bottom). They are available in two-row versions for standard density and in three-row, high-density versions. There are contacts for signals, power, shields, high voltage, thermocouples, and fiber optics.

Innovations in contact technology

The virtues of the D-sub shell are an important part of the connector story, but the electrical contacts and their attributes are also critical to a successful connector assembly. Over the years, there have been many improvements in contact technology with respect to materials, design, and electrical and mechanical performance.

Among these is Amphenol Positronic’s patented PosiBand contact technology (U.S. Patent 7,115,002). PosiBand takes an innovative approach to contacts that differs from classic designs to provide enhanced performance across many key parameters.

The PosiBand external pressure element design fully separates the mechanical action from the electrical action of the connection (Figure 2). The pressure element performs the mechanical action by applying a force pressing the male pin against the inner female cavity to form a long line of direct electrical contact. The length of the interface line can be varied, allowing designers to optimize the interface resistance of the connection. A solid, unbroken ring at the entry point increases the mechanical robustness of the contact.

Figure 2: PosiBand uses a patented design to separate the mechanical and electrical action of the connection. (Image source: Amphenol Positronic)

The spring clip (Figure 3, left) within the PosiBand is a small but critical part of the assembly and a key contributor to its performance. This spring-tempered beryllium-copper alloy provides a normal force on the male contact, contributing to a rugged and reliable contact pairing (Figure 3, right). At the same time, it offers a lower average insertion force while meeting or exceeding performance requirements.

Figure 3: The PosiBand spring clip (left) provides a normal force across the contact area (right) to maximize the electrical mating-surface contact area. (Image source: Amphenol Positronic)

The PosiBand base contact is made of brass, which has excellent properties for crimping wire onto contacts. It also eliminates the need for annealing of the material, which not only adds to the cost but also is a step that can be done improperly in manufacturing, causing long-term problems.

The PosiBand system also increases the interface area between male and female contacts, compared to traditional contact designs, for more reliable electrical integrity. On a micro level, there are a greater number of electrical paths through the contact interface. The increased contact area reduces the likelihood of discontinuity during vibration.

Counterintuitively, the greater contact area offered by the PosiBand system does not increase insertion forces; on the contrary, the PosiBand design provides a more consistent insertion-force value, which results in a lower average insertion force.

Positronic products are part of the U.S. Defense Logistics Agency (DLA) Qualified Products List (QPL), which means they have met requirements that include appropriate product identification, qualification, and periodic verification testing. PosiBand is qualified under SAE AS3902 and MIL-DTL-24308 specifications and is also qualified to the higher 40 gram (g) contact-separation test requirement of GSFC S-311-P4/08 and GSFC S-311-P4/10.

Contact size and resistance

PosiBand contacts are available in standard sizes of 20 and 22. The former is designed for American Wire Gauge (AWG) 20, 22, and 24 wires, while the latter is designed for AWG 22, 24, 26, 28, and 30 wires.

The maximum resistance of size 22 contacts is 0.005 ohms (Ω), while the corresponding figure for size 20 contacts is 0.004 Ω. This low contact resistance, and subsequent low self-heating due to the resulting minimal I²R losses, offers designers opportunities to use size 22 and size 20 contacts for power.

The thermal characteristics of contacts are a factor that some engineers are either unaware of or only take into consideration late in the design and connector-selection process. Nonetheless, thermals are a critical factor when evaluating connector and system performance. The PosiBand size 20 (Figure 4, top) and size 22 (Figure 4, bottom) contacts are fully characterized for temperature rise versus current for various contact configurations.

Figure 4: Shown is the temperature rise versus rated current for size 20 (top) and size 22 (bottom) PosiBand contacts in various configurations. (Image source: Amphenol Positronic)

The maximum current permitted is limited by the maximum temperature that the connection and contact can tolerate.

PosiBand products for real-world applications

For designers assembling their own cabling and connectors, PosiBand contacts are available as individual items. For example, the FC6020D2-14 (Figure 5) is a size 20, copper alloy, machined socket contact that is crimped to the wire termination.

Figure 5: The FC6020D2-14 is a size 20, copper alloy, machined socket contact that is crimped to the wire termination. (Image source: Amphenol Positronic)

This nickel-plated copper contact is coated with 1.27 micrometers (µm) of gold to ensure low resistance and reliable continuity. For these crimped (non-soldered) connections, Amphenol Positronic offers a specific crimping tool to ensure the connections meet precise specifications for consistency and reliability.

For designers looking for off-the-shelf solutions, fully assembled connectors, such as the MACH-D Series MCD15M51R700K/AA-15 (Figure 6, left) and CBC7W2S110000 (Figure 6, right), are available as standard items for some of the more common configurations. The MCD15M51R700K/AA-15 is a 15 position, stainless steel, D-sub plug connector (male pins) with identical size 20 contacts rated at 17 amperes (A). It is intended for right-angle circuit-board soldering. In addition to the right-angle board-mount terminations, it is offered with crimp, solder cup, and press-fit termination options.

Figure 6: The MCD15M51R700K/AA-15 (left) is a 15 position, D-sub plug connector (male pins) with size 20 contacts; the CBC7W2S110000 (right) is a 7 position combo receptacle connector with female contacts, featuring five size 20 PosiBand signal contacts and two MC/FC 4012D power contacts. (Image source: Amphenol Positronic)

In contrast, the CBC7W2S110000 is a 7 position D-sub combo receptacle connector with female sockets. This connector features five size 20 PosiBand signal contacts plus two MC/FC 4012D 100 A power connectors (coaxial-cable contacts are also available). Its shell is zinc-plated steel with a chromate seal for electrical and environmental integrity.

Conclusion

The classic multi-position parallel connectors of the D-sub family are the preferred connector for many applications. They offer designers multiple physical-size options and flexibility in contact number and arrangement. Amphenol Positronic’s innovative PosiBand signal contacts, combined with their D-sub connector shells, support enhanced reliability and performance.