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  A brief introduction to connector housing
bown£º3298time date£º2011-4-13
A brief introduction to connector housing
From Internet, auther unknown
Requirements for a Connector Housing
The housing performs four functions:
A  electrically isolates the contacts
B  holds the contacts in geometric position for mating and dimensional stability
C  provides mechanical protection of, and support for, the contacts
D  shields the contacts from the operating environment to reduce corrosion susceptibility.
The last function, environmental shielding, depends on the design of the housing, in particular on how"closed" the housing structure is so that it can restrict access of the environment to the contact interface.Such shielding is a critical design factor in connectors that are to be used in severe environments.
The other functions depend on various properties of the polymer from which the housing is made.Examples include surface and volume resistivity, creep strength, mold shrinkage and flexural strength,for example. As mentioned previously, contact springs are characterized by a broad variety of designs and a limited number of materials. Connector housings, in contrast, cover a wide range of materials while housing designs share many common features and requirements. The range in materials results from the wide variety of requirements a housing material must meet not only in the connector application environment, but, arguably more so, in the manufacturing and assembly process. In many cases it is assembly processing, in particular surface mount requirements, which limit the options of housing material selection.
The electrical requirements of a connector housing are, in general, readily satisfied by most engineering polymers. Polymers vary primarily in the stability of electrical properties with respect to environmental exposures. This stability depends on polymer structure. An additional electrical characteristic of polymers, which is of increasing importance, is the dielectric constant. The dielectric constant is primarily of interest in connectors intended for high frequency/speed applications.
Two different types of mechanical requirements are listed above, dimensional stability and mechanical support. Dimensional stability depends, in large measure, on the sensitivity of the polymer to processing variations, for example mold shrinkage, both in magnitude and directionality. This sensitivity depends on the polymer structure. Dimensional stability is important in many aspects of connector functionality. Two major examples of such requirements are maintaining the footprint of the connector for mounting the connector to printed wiring boards and maintaining contact spacing for proper mating of the connector.
Examples of mechanical protection and support include lead in ramps to facilitate mating, anti
overstress features and the retention of the contact in the housing. Mechanical protection and support functions also depend on polymer structure, in this case on the potential for reduction of the polymers intrinsic properties due to structural degradation, primarily during processing, but also due to thermal and creep effects.
Thermal effects are arguably more important during assembly operations, in particular soldering. The most critical soldering application may be surface mounting of the connector to a printed wiring board.
Clearly polymer structure is critical to connector housing function. The discussion begins with the mechanical properties of polymers and how polymer structure influences the magnitude and stability of those properties.
(To be continued)