Overlooking a component as seemingly insignificant as a connector can lead to poor designs, faulty products, and high costs, not to mention damage to a company's reputation and profits. However, designers of many electronic systems give little time and consideration to specifying connectors. Many times engineers will simply choose a connector because it was used in previous versions of a product, without examining why the connector was chosen in the first place.
While many design engineers treat the connector like a commodity, it is a crucial--and often vulnerable--link in systems communications. Although responsible for the critical task of transferring electrical signals to other devices, it is exposed to the environment outside the protective chassis or enclosure. For instance, when a standard connector typically found in an office environment is put in the average damp basement, moisture quickly oxidizes and breaks down contacts having low resistance to humidity. In addition, it must guard against unwanted externally generated noise, while acting as a path to ground. Thus, it is appropriate to describe a connector as an "electromechanical" device--the connector functions both in the electrical and physical environments, both of which place very different demands on the connector.
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One size doesn't fit all. Design engineers in different industries (and with different applications) place diverse levels of importance on various attributes. Let's consider four: PC/LAN (local area network), aerospace, medical, and automotive.
The types of connectors used in a PC/LAN vary greatly, depending on where and how the system is to be used. For example, performance-wise, will the system be used as an educational, institutional, or engineering system? Will massive high-speed data and graphics transmission occur, or will small, simple documents travel slowly throughout the system? Operationally, perhaps there will be a need for input/ output connectors that can handle the intensive mating and unmating required by laptops. Here, environmental exposure to heavy lint and dust may be coupled with a need for a small footprint. Regarding cost, low-end desktops will require an economical connector without requiring high cycle life, so why install a connector that will last over 10 years if the system itself will be obsolete in two? Higher-end computer and networking equipment will demand more precise electrical performance, with greater emphasis on longevity, reliability and robustness (see chart).
Military and aerospace interconnections are mission-critical and have no room for error when used by personnel in harm's way. They must operate perfectly under the most stressful conditions. As a result, high-performance connectors have to operate reliably under loads and environmental extremes, with little concern about cost. In aerospace and other vehicles, size and weight may be an issue. Thermal shock, vibration, and electromagnetic pulse are usually factored into the equation as well.
Design concerns for medical interconnects are similar to military/aerospace applications--high reliability, small form-factors, flawless performance, and confidence-over-cost being primary considerations. Oxygen rich operating rooms and hospital areas often contain equipment sensitive to EMI/RFI noise--driving the need for heavily shielded, spark-free materials. In addition, unique environmental factors come into play--many medical sterilizing and processing methods place electronic equipment under extremes of pressure and temperature, which may be repeated over and over.
Automobiles now require a gamut of connector types. Airbag connectors must offer maximum performance and reliability. Radio connectors are less critical, enabling the designer to save a little on cost. Interconnects under the hood experience greater temperature extremes, while any on moving components have to keep contact under loads. Human interfaces, fuel sensors and injectors, smog and ignition systems, and security devices all are connector linked to computers controlling amazingly harsh reactions, sensitive data, and high voltage.
Can you build it (cheaply)? While evaluating connectors, the designer must never lose sight of the manufacturing process. Selecting a low-cost connector will be a costly mistake if the manufacturing process or tooling must be changed to accommodate it. Moreover, when production ramps-up into the thousands of boards per month a single reflow solder process is far more efficient than multiple steps, including wave solder, reflow, and press-fit technologies.
Wire-applied connectors force design engineers to consider the tooling requirements to manufacture the cable, harness, or single lead. Choosing the correct termination equipment relates directly to matching the product's target cost with the desired manufacturing capacity. Designers have to make choices such as: stripping wire to apply contacts or piercing the insulation; how much, if any, EMI/ RFI shielding is needed; and whether strain relief or sealing boots are necessary to prolong connector life.
Do your homework. Designers must keep abreast of new connector technologies. Manufacturers are continually improving their offerings to meet the ever-changing demands of the systems in which they are used. Interestingly, of all components used in computer systems, connectors are the most patented.
Part of a design engineer's job is to understand trade-offs and manage the implications of any choices made. The key to specifying the best connector is to start the process at the beginning of the design cycle. Engineers may want to create a matrix or bar chart of key connector attributes and their relative ranking in importance for the application. Taking this chart to a connector supplier can help ensure the most appropriate and cost-effective connector.
An 8-pack to connector success
When evaluating a connector, there are eight basic questions--the importance of each hinges on the application:
[1] Environmental concerns. Where will your device call home? Variables include temperature extremes, vibration, humidity, dust, and EMI/RFI exposure. Often connectors must meet certification requirements such as UL, or CSA, based on their intended use in a given environment.
[2] Electrical performance. Depending on whether a connector carries signals or power, frequency and voltage vary greatly. Therefore, contact type and plating must be considered. Are you pushing amps, or milliamps? Do you need gold or tin plating? Is your line operating at 60 Hz or 1 GHz?
[3] System protocols. Who's calling the shots? Many times, strict protocols, such as in military, or computer and communications applications, mandate what connectors can be chosen.
[4] Cost. And how deep are their pockets? Under
standing your budget before beginning to specify a connector can save valuable time.
[5] Availability. Are enough around? Even commodities suffer from capacity shortages when demanded by entire industries.
[6] Reliability. Is your system critical, with little or zero tolerance for failure?
[7] Service life. Do you need a connector that lasts two years, or 20?
[8] Manufacturability. Could a choice in your solder attachment or termination process save you money?