Modern electrical engineering is subject to one trend more than ever: miniaturization. Assemblies and their components must not only become increasingly powerful, but also increasingly smaller. Yet they are often used in harsh real-world conditions. Components, including connectors, are therefore becoming increasingly delicate while withstanding the same level of stress. A high-quality connector, however, not only withstands this stress just as well as its older and larger counterpart, but even better. The reason for this lies in advancements in material composition and product design, such as in the geometry of the insulating body (Fig. 1).

 A variety of factors affect the durability of a connector. One of these is the contact surface. This plays a key role in determining the connector’s service life, which is typically measured in mating cycles. During field use, the connector is subjected to certain micro-movements. These lead to surface abrasion and, consequently, to oxidation (Fig. 2).

The contacts of a connector are stamped or turned. However, during stamping, an uneven, sharp-edged surface forms on the underside of the stamped strip that is visible under a microscope. Conventional systems make contact at this stamped edge, which results in increased surface abrasion and thus higher contact resistance. This can be avoided by bending the spring tulip 90 degrees in a so-called stamping-bending process, so that it contacts the blade contact with its smooth, rolled surface (Fig. 3).
 
However, it is not only the design of the spring strip but also that of the blade strip that is crucial for the connector’s longevity. This is because the blade strip must also be cleanly punched and further processed to avoid defective, sharp geometries.

In contrast, connectors with a so-called “gender-neutral” contact system are even more robust. The key feature here is that the contact geometries of the two connector halves—the plug and the socket—are identical. Both therefore feature both a spring and a blade. This ensures that each pin is contacted by two springs, while the plug and socket are interlocked and cannot separate from one another. While a double-sided spring strip always ensures at least one contact point under mechanical stress, the interlocking geometries in gender-neutral contact systems ensure that signal transmission always occurs via two contact points. This high level of redundancy thus enables maximum contact reliability (Fig. 5).

  In this process, the press-fit pin has a larger diagonal dimension than the diameter of the PCB hole. The connector pin is flexible in the press-fit zone so that the PCB is not deformed by the physical forces during the press-fit process. Deformation is therefore limited to the press-fit zone (Fig. 8). A cold weld forms between the contact pin and the metallized PCB hole: a gas-tight, corrosion-resistant, low-resistance, and electrically conductive mechanical connection that is also suitable for potting. It is also specified in DIN EN 60352-5 and maintains reliable contact even under very high mechanical and thermal stresses, such as vibration, bending, and extreme temperature changes, and can even withstand shock loads of up to 200g.
 
Due to its outstanding robustness and a failure-in-transit (FIT) rate ten times lower than that of automated soldered connectors, press-fit technology is frequently used in high-security applications where signal transmission must not be interrupted under any circumstances, such as in airbag systems or ABS and ESP modules.

 The insulation body geometry of a connector also helps protect the contacts from damage during operation or installation. It should be designed so that the vulnerable contacts are shielded inside the connector.

 Lead-in chamfers can also prevent damage during assembly. They help compensate for any misalignment of the circuit boards in any direction during mating. With the aid of an additional catch area, the two connector halves can be mated without damage even in the event of a center or angular misalignment (Fig. 10).

Some connectors also feature board locks. These are metal brackets attached to the insulator and soldered to the printed circuit board (Fig. 11). This provides additional stability—even under adverse conditions such as vibration and shock.

The tolerance range of a connector plays a crucial role in assessing its robustness. If the connector cannot compensate for given tolerances, mechanical movements will lead to wear or even damage to the connection. During installation, insertion chamfers help ensure that the male and female connectors can be mated without damage. However, micro-movements must also be accommodated when the connector is mated. This is achieved through the geometry of the contacts and insulating bodies. If a connector has a floating function, it can compensate for up to ±0.4 mm even during operation. This function is becoming increasingly important, as it plays a crucial role when a printed circuit board is populated with multiple connectors. In the field, however, stresses arise not only in the x and y directions but also in the z direction (Fig. 12).

 There are various testing methods available to thoroughly evaluate the durability characteristics of connectors. These methods involve measuring variables such as dielectric strength and contact resistance both before and after a stress test, as well as visually inspecting the condition of the contacts. For example, the effects of 500 mating cycles on dielectric strength can be assessed, or a climatic test can determine whether several hours at -55°C followed by 125°C have a negative impact on the contact resistance of the connector. In the temperature shock test, the connector must withstand rapid cycling between these extreme temperatures 100 times for 30 minutes each. Furthermore, the center and angular misalignment during mating, as well as the tolerance range in the mated state, should not only be verified theoretically on the CAD model but also extensively tested in practice, with the load-bearing capacity confirmed empirically. It is equally important that various tests critical to the contact surface be performed in combination to simulate real-world conditions. For example, mating cycle and corrosive gas tests could be conducted in combination to ensure that the connector’s performance in terms of contact resistance and dielectric strength has not deteriorated and that the contacts have not been damaged (Fig. 14).