1. Connector characteristics

When describing and selecting connectors, we come across many different standards, technical characteristics, properties and concepts. Let’s briefly look at some of them, with some examples.

1.1 Standards

Because of the diversity of these standards, it is worth saying a few words about them, a bit beyond the heading.

Some of the standards for connectors are specific to the location and conditions of use, as aerospace (civil/military), automotive (cargo/personal, engine/road, safety/entertainment), medical equipment….e.g.: devices in explosive environments are covered by ATEX and IECEx standards, railway applications are covered by ECTBX.E235076.

Standards prescribe not only the compliance of components and equipment with the given conditions, but also the manufacturing conditions, end-of-production testing steps, tools and documentation of the entire manufacturing process.

Various data transmission standards can be considered application specific, which may specify signal transmission rate, throughput, impedance…, but do not necessarily define the physical appearance of the connectors. An example is USB. The USB connector, which has since undergone several improvements, was born at the beginning of USB signal transmission. Today there are many applications of this connector that do not correspond to its original function and USB signal transmission is also running on other connectors. Some others are ETHERNET/RJ45, RS232/9p D-Sub, RS485/25p D-Sub, IEEE-1394/Firewire. The standardization of high-speed signaling (PCIxx, VITAxx, etc.) has resulted in different connector designs from different manufacturers, but there are also manufacturer collaborations to reduce development costs and the time-to-market.

The other part of the standards is specific to connectors – irrespective of their application. One well-known example is DIN 41612 (IEC/EN 60603-2), which is mainly used as connectors for backpanel rack systems (e.g. VMEbus). Supplemented by a lettering (e.g. DIN 41612 C) it defines several connector configurations in three performance levels (class 1, 2 and 3),. It’s important to mention that the specification defines the contact surface and the quality – not the external dimensions and fixing points of the connector. Some other known examples of connectors defined by the standard are DIN41652/D-Sub and DIN41622/knife-edge connectors.

Another category is MIL-DTL-XXXXX standards. Between the two world wars, the US Department of Defense and some military companies agreed with Cannon (now ITT Cannon) to develop a standard covering their requirements (this became MIL-DTL-5015) and then to develop a connector to fulfill them. After the Second World War, changes in requirements and advances in electronics and materials technology necessitated and enabled the development of new standards (MIL-DTL-38999 Series I, II and III, MIL-DTL-26482 Series I and II, MIL-DTL-83723…..) and new connectors. These standards specify both compliance with environmental conditions (material, temperature, sealing, shock and impact resistance, EMI…) and connector dimensions.  MIL standards also specify the properties of the contacts to be used in these connectors (MIL-C- 39029) and the tools to support their use (MIL-DTL-22520), as well as the different contact layouts (layouts: MIL-STD-1554, and-1651). MIL standards now also regulate connectors for military navigation (MIL-DTL-288240) and military communications (MIL-DTL-55116 and -55181). Another group of MIL standards regulate the military applicability of connectors designed for civilian use (e.g. D-Sub MIL-DTL-24308, micro-D-Sub MIL-DTL-83513, nano-D-Sub mil-dtl-32139).

The degrees of protection against dust and moisture (IPXX) and the methods of measurement are described in IEC 60529, the classification of mechanical resistance (impact resistance) (IKXX) is defined in IEC 62262:2002 and IEC 61373 / EN 50155.

1.2 Immunity

Traditionally, protection has been understood to mean protection against dust and moisture (IPXX), but the term impact resistance (IKXX), used for enclosures and switches, has also been applied to connectors. A special case of protection is hermetic sealing.

1.3 Ambient temperature

Storage temperature range – compliance with this is rarely a problem.
Operating temperature range – this is about the operational limits of the connectors, but: see current carrying capacity.

1.4 Load performance

Contact – contact or contact-to-housing breakdown voltage, possibly also air gap and creepage current path to be considered.
The current carrying capacity of connectors/contacts is usually given at room temperature, but this value is temperature dependent – this is described in the derating diagram.
Depending on the load capacity, we can talk about low current (~several times up to 100mA), high current (from a few A up to several times 100A), high voltage (~n*kV) or high frequency (~n*GHz) contacts or connectors.

1.5 Transmissible frequency

Usually specified for high frequency connectors (e.g. 1Mhz).

1.6 Transmission speed

Characteristic of connectors used for data transmission (e.g. 112 GBPS)

1.7 Connection (in medical, industrial applications there are connectors for air, liquid, but for now let’s stay at electrical and optical signal transmission)

PCB connectors: TH, Press-fit or SMT
Wired connectors: solder, screw, crimp, IDC, wire-wrap, spring-clamp
Optical connectors: glass or plastic are used as light conductor

1.8 Attachment of pairs of connectors to each other

Bayonet, screw, push-pull, stirrup, lever, magnetic, breakaway, or without any of these.

1.9 Fixing of connectors

PCB connectors are either fixed to the PCB with signal contacts only, or (especially for SMT connectors) with a separate TH foot, and/or possibly with screws.
On the mounting board, the connectors are fixed from the front or rear with a screw, flange or snap-in method.

1.10 Manufacturing technology of contacts

Turned, hyperboloid, RadSok, stamped, hybrid.

1.11 Material and surface finish of terminals

The basic material of the contacts is a copper alloy whereas the surface finish is usually made of precious metals or a combination of precious metals and sometimes tin, depending on the signal to be transferred and the expected lifetime.
The material and surface finish of the connector body and the connector housing are dependent mainly on the intended application environment.

1.12 External form

This characteristic is usually indicated on wire terminals and their counterparts – usually round or rectangular designators are used. The connectors we call round are indeed round, but those we call rectangular are in fact sometimes of triangular shape. Cube shaped connectors were also used in the past – they were popular as sensor- and valve connectors. Today, round (e.g. M12) sensor- and valve connectors are mostly in use.

The appearance of both PCB and wired connectors can also be affected while talking about hybrid connectors. We can distinguish two types of hybrid connectors:

• those with several types of contacts in one connector body
• those with several plastic carriers for different contacts in one connector housing.

The latter are mostly user-specific modular connectors.