Connectors are important mechanical and electrical connection devices between various parts of a system or between the system and the external world. The choice of connector type depends on multiple factors, including electrical and mechanical requirements, industry standards, usability and manufacturing, number and type of contacts, mating and non mating situations, reliability goals, and regulatory requirements. However, the classic D-Sub (ultra small D-type) connector body has been in use for decades and is still the preferred connector for many applications.
Although the body style and contact arrangement of connectors have attracted much attention, the contacts themselves have a significant impact on the electrical and mechanical performance of connectors. As designs become increasingly complex and application requirements become higher, designers need to understand the latest innovations in contact technology to meet corresponding standards and requirements, especially in terms of robustness, insertion force and retention force, contact resistance, and temperature tolerance.
This article provides a brief overview of the development trend of connectors, with a focus on the reasons for the continued use of D-sub connectors. Then, the advanced contacts of Amphenol Positronic were introduced, and how to use them to improve the performance of the connector was demonstrated.
USB、 The importance of Ethernet and D-sub connectors
Although the use of traditional RS-232 interfaces has decreased and various versions of USB and Ethernet connectors are emerging, the classic 9-pin D-sub connector (commonly known as DB-9) and other connectors in the wider D-sub connector series still play a crucial role in electronic system communication. There are many reasons for continuous use. Although USB and Ethernet can meet many interconnect requirements, these two widely used connector types are serial interfaces rather than multi wire interfaces. They can simultaneously transmit data and power, but have strict limitations on signal types, maximum voltage and current values, and rated power.
In terms of design, USB and Ethernet cannot effectively handle multiple unrelated signals or different formats like interfaces with multiple parallel contact paths. Another important consideration is that the design of standard USB and Ethernet connections does not meet the required level of mechanical and electrical integrity and robustness in many cases.
Due to these and those reasons, D-sub connectors are still widely used. This type of exterior design appeared as early as the 1950s and has many advantages. It has the function of completely shielding electromagnetic interference (EMI) and radio frequency interference (RFI), providing a sealed or nearly sealed housing, with a sturdy mechanical structure, and its two docking parts can be locked to each other through a small top wire. The D-sub connector body or housing has at least six standard sizes, providing flexible options for electrical contact pin positions and types. In addition to providing connector housings with the same contact type at all pin positions, the "Combo-D" D-sub also supports mixing independent signal and power contacts within a single connector housing (Figure 1, top).
Combo-D ultra small connector style image (click to enlarge)
Figure 1: Combo-D ultra small connector supports multiple signal and power path combinations (as shown in the figure); The D-sub connector adopts standard housing dimensions and contact arrangement (as shown in the figure below). (Image source: Amphenol Positronic)
A single D-sub can support various standard mix and match arrangements (Figure 1, bottom). They offer standard density two row and high-density three row versions, with signal, power, shielding, high voltage, thermocouple, and fiber optic contact options.
Innovation in Contact Technology
The advantage of D-sub casing is an important plot in the connector story, and the electrical contacts and their properties are also the key to the successful assembly of the connector. Over the years, contact technology has made many improvements in materials, design, electrical and mechanical properties.
This includes Amphenol Positronic's patented PosiBand contact technology (US Patent No. 7115002). PosiBand adopts innovative contact design, which is different from traditional design and achieves higher performance in many key parameters.
The PosiBand external pressure element is designed to completely separate the mechanical and electrical actions of the connection (Figure 2). The pressure element applies a force to press the male pin towards the internal cavity, forming a long direct electrical contact line, thus completing the mechanical action. The length of the contact wire can be changed, allowing designers to optimize the interface resistance of the connection. The sturdy and undamaged circular structure at the entrance can enhance the mechanical robustness of the contacts.
Amphenol Positronic PosiBand adopts patented design images (click to enlarge)
Figure 2: PosiBand adopts a patented design that separates the mechanical and electrical actions of the connection. (Image source: Amphenol Positronic)
The spring clip inside PosiBand (Figure 3, left) is a small but critical component in the assembly and a key factor affecting its performance. This resilient beryllium copper alloy sheet can generate normal force on the male contact, thereby achieving firm and reliable contact bonding (Figure 3, right). At the same time, while meeting or exceeding performance requirements, it can also reduce the average insertion force.
Amphenol Positronic PosiBand spring clip (left) provides normal force image in the contact area (right)
Figure 3: PosiBand spring clip (left) provides normal force in the contact area (right) to maximize the contact area of the electrical mating surface. (Image source: Amphenol Positronic)
The PosiBand base contacts are made of brass and have excellent performance in crimping wires onto the contacts. It also eliminates the need for annealing the material, which not only increases costs but can also cause long-term problems if not handled properly during the manufacturing process.
Compared with traditional contact designs, the PosiBand system also increases the contact area between male and female contacts, thereby achieving more reliable electrical integrity. At the micro level, there are more electrical pathways passing through the contact interface. Increasing the contact area reduces the possibility of discontinuity during vibration.
Contrary to intuition, the PosiBand system provides a larger contact area without increasing insertion force; On the contrary, the PosiBand design provides more consistent insertion force, thereby reducing the average insertion force.
Positronic products have entered the Qualified Product List (QPL) of the United States Department of Defense Logistics Agency (DLA), which means they have met the requirements including corresponding product identification, qualification, and periodic validation testing. PosiBand complies with SAE AS3902 and MIL-DTL-24308 specifications, and also meets the higher 40g contact separation test requirements of GSFC S-311-P4/08 and GSFC S-311-P4/10.
Contact size and resistance
PosiBand contacts use standard sizes 20 and 22. The former is applicable to American Wire Gauge (AWG) wires 20, 22, and 24, while the latter is applicable to AWG wires 22, 24, 26, 28, and 30.
The maximum resistance of contact 22 is 0.005 ohms (Ω), while the corresponding resistance of contact 20 is 0.004 ohms. Due to the low contact resistance, I2R loss is small, resulting in low self heating, which provides designers with the opportunity to use contacts 22 and 20 for power supply.
Some engineers do not understand the thermal characteristics of contacts, or only consider this factor in the later stages of designing and selecting connectors. However, heat remains a key factor in evaluating connector and system performance. The temperature rise and current relationship of PosiBand 20 (Figure 4, top) and 22 (Figure 4, bottom) contacts are completely consistent under different contact configurations.