Connection and connectors

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Connection plays a fundamental role in all electronic systems. It enables the exchange of signals and information, to power them and to connect them with sensors and actuators. Therefore, it is an essential element of the engineering design that should not be underestimated.

Many household appliances contain more than one PCBA, irrespective of their application and manufacturing technology. This implies the need of having to connect them.
There are different types of connectors for PCBA entrusted with different roles to be played on the board and in general in the system of which they are part. The term base connector refers to a multi-component and the application will determine its properties like geometry, sizes, weight and power. Some of the applicative areas need to face problems of SWaP (Size, Weight, and Power) as well as of soundness and reliability; in some cases, it is worth considering the data transmission speed, too. Even if the wireless technology is increasingly spreading, the use of connectors is growing, too. In some applications such as the power transfer, connectors are the only efficacious option.
As connector manufacturers release new products on the market, the choice becomes logically wider and apparently more complex. Connectors are assembled on the PCB with press-fit technology or through soldering and are used to transfer signals from one PCB to the other or to receive them from sensors, to power the circuit and to connect the control to actuators. Connectors provide a user-friendly method of Design for Manufacturing, because boards are assembled individually and connectors can be assembled in the course of the assembly process or afterwards in refinishing operations.

Archer M50 connectors (pitch 1.27 mm), M22 (pitch 2 mm) and M20 (pitch 2.54 mm) by Harwin.

Connectors and applications
They usually work in pair, male and female. The coupling can be a board-to-board, cable- to-board and cable-to-cable connection. The layouts of board-to-board connectors are supplied with connection orientations based on 90-degree increments. Both connectors (male and female) are with vertical orientation. In the right-angle connection, one connector is vertical and one is horizontal, it connects for instance from motherboard to daughterboards. The 180-degree connection is coplanar, both connectors are oriented horizontally, it connects from edge to edge or from edge to cable.
A broad variety of connectors is available for PCB, all designed to satisfy specific application requirements. Some connectors, for instance, are specialized in the resistance to vibrations and to collisions caused by operational factors, their soundness provides stability under stress conditions. Other types of connectors are much more delicate, they are suitable for highly sensitive applications or for mobile devices, others are characterized by standard cheap design for consuming and industrial production.

Different connection solutions on Harting board.

The preliminary condition of each choice is focusing what must be connected: board-to-board, board-to-cable or cable-to-cable; the consideration regarding the environment where it will have to operate and the expected connection frequency is secondary. The response to these questions defines the demanded family of connectors.
A further remark, linked also to previous considerations, concerns the component technology and the assembling process: SMT, PTH and, in its inside, whether to solder or press-fit. If male and female connectors must be used to connect two boards, tolerances become important to assure that PCB are correctly coupled without unduly stressing welding joints. For this reason, many manufacturers of SMD connectors recommend specific geometries for pads on PCB, so that the surface tension of the alloy contributes to the good positioning during remelting. Another important issue from the manufacturing point of view is ensuring that every selected connector is compatible with automated optical inspection (AOI) systems always equipping the production line, to avoid turning to visual inspection.

TE Connectivity designs and manufactures a broad range of electric connectors intended for the data transmission and power supply in various operational environments.

From the electrical point of view
From a purely electric point of view, knowing the currents and the voltages at which we are working defines several component properties. Voltages will influence the material choice, with high voltages a material with high insulation properties is necessary. An alternative approach consists in selecting a connector with broad spacing between terminals, but this can lead to a bigger connector than necessary, which might not be acceptable owing space constraints inside the application. The current defines the features of the contacts on the connector; not only they must be able to manage the current in steady state, but they must be able to cope with any occasional surges. In some cases, more pins can be connected together to support the power supply and earth connections.
If the use of separate connectors for power supply and signals is not possible owing to the narrow space, an alternative approach consists in specifying a type of mixed-technology connector, which integrates more pins intended for power supply and others for signals.
Household appliances are more and more frequently equipped with “smart” devices that need fast and clean signals, also from and to peripheral devices. When the signals’ speed rises, the crosstalk is often a problem for engineers who must include as many performances as possible into the device. The crosstalk occurs where there is an (inductive or capacitive) coupling among the various signal lines, so influencing the integrity of signals themselves. Utmost attention is paid to this problem during the design of the PCB layout, but an unsuitable connector can annul the design validity. Therefore, among the characteristics to be selected for a connector, we should consider anti-crosstalk properties.
Since connectors are often the input or output point for electric signals from a device, they are also potential input and output points for electromagnetic interferences, which can negatively or positively affect the operation of the system itself or of other systems in the proximity. In this case, it is necessary to consider connectors with built-in shielding.
There are particular cases in which grounding, the power supply or a particular signal, such as for instance the enable line, must be coupled before other circuits, the solution is obtained by specifying a connector that has some longer pins than others, so that they are coupled as first and uncoupled as last.

From the mechanical point of view
Connectors can be often subjected to mechanical stresses during their standard operation, especially if the application where they are integrated needs frequent usability and the regular connection/disconnection of cables.
In the applications where the presence of mechanical stresses is probable, it is advisable to select a type of connector that is mechanically fixed to the PCB.
Many connectors integrate functions to improve the mechanical stiffness, including studs and threaded inserts, so permitting their safe fixing.
The connector must be adapted to the environment where it must operate. This means withstanding the operation temperature, including an eventual overtemperature caused by currents. Moreover, there are other factors, such as humidity, which call for a connector suitably protected by seals, anti-dust caps or design solutions against infiltrations.
The number of times when the connector is coupled or uncoupled is another fundamental remark. While several connectors that are integral part of the project are coupled only once, the connectors that are accessible for users might undergo several thousands of coupling cycles, especially in applications like the recharge of portable devices. Therefore, the plating material of contacts, including the plating thickness, must be suitable for the application.