The present invention relates to metallic terminals for electrically connecting pin terminals with another circuit member. More particularly, it relates to a new and improved pin-receiving contact structure including resiliently supported contact beams which provide a pin-receiving contact section characterized by high normal forces and a significantly increased elastic deflection range.
Electrically mateable connectors including mateable pin and receptacle contact terminals are widely used in a variety of forms throughout the electronics field for electrically connecting two or more circuit members to each other. Illustrative interconnect applications employing mating pin and receptacle contacts include board-to-board, wire-to-board, cable or FFC-to-board, cable-to-cable, discrete wire-to-discrete wire, discrete wire-to-FFC or cable, component-to-component, and component to board connections.
Recent developments in the field of electronics, and electrical devices and appliances in general, now require electrical interconnection manufacturers to provide compact, more miniaturized connectors having higher circuit densities. Present-day design requirements for miniaturized connectors are testing the limits of a manufacturer's ability to mold plastics and stamp and form metals. In addition to the design pressure for miniaturization, the marketplace now demands high quality connection products having extended use lives to be provided with zero defects on a just-in-time delivery schedule. As a result, the connection manufacturer must consider manufacturability issues in designing products.
New products must now be designed so that they may be reliably manufactured at the lowest limits of manufacturing tolerances and, if certain aspects of a design cannot be held to a desired tolerance, then other aspects of the design must accommodate these production realities. Price competition in this market is intense.
These modern design pressures are especially applicable to mating pin and receptacle terminals and connectors. As used herein what is meant by a miniaturized pin-receiving contact is a receptacle contact designed to mate with a rectangular or round pin terminal having a width or diameter of less than about 0.030 inches (e.g. less than 1.0 mm). The pin-receiving contact section may include contact beams having a beam length of less than about 0.120 inches (e.g. less than about 4 mm) and having a beam width of less than about 0.050 inches (e.g. less than about 1 mm).
In addition to these stringent size limitations, miniature connectors are now required for mating with high density multicircuit pin arrays wherein the centerline spacing between adjacent pins is extremely small, i.e. less than about 0.100 inches and often as low as 0.050 inches. Moreover, each pin-receiving contact, even in view of its miniature size and spacing requirements, may now be required to exert normal mating contact forces of greater than 50 grams per contact and preferably at least about 75 to 100 grams per contact. Each contact may also be required to withstand repeated mating and unmating operations without yielding or losing normal contact loads over time. Finally, each contact in addition to providing high contact forces may also be required to be compliant to manufacturing tolerances and mating pin misalignments.
Prior art miniature pin-receiving contacts are known and commercially important examples are shown in FIGS. 1-3, prior art, of the attached Drawings. FIG. 1 shows a conventional miniature pin-receiving contact commonly referred to as a tuning fork type contact. This prior art contact generally comprises a planar stamped metallic contact including a base portion and a pair of parallel, spaced cantilevered spring arms extending from the base. Pin-receiving contact surfaces are defined on the opposing inner facing surfaces of each beam adjacent their free ends to define an early entry pin-receiving contact. Early entry contacts are desirable to provide longer wipe of the female contacts against the pin surfaces during insertion of the pin for improved contact reliability.
Tuning fork contacts of the type shown in FIG. 1, are adapted to receive square or rectangular pins only and therefore may not be used with round pins. Although the tuning fork contacts may provide a desirably high spring rate per beam, the elastic deflection range of the contact is undesirably low. For this reason, the tuning fork contact is very sensitive to mating misalignments. Even minor offsets in pin placement during mating may cause displacement of a contact beam exceeding its elastic deflection range, thereby causing yield in the beams introducing a new permanent set in the terminal which results in lower normal contact forces.
In an effort to improve the compliance of the contact to overstressing and misalignments, thinner metal stock has been used to improve the elastic deflection range of the contact beams. This change however reduces the effective spring rate of each beam which compromises the normal mating contact load of the tuning fork against the pin. To improve the spring rate and elastic deflection range of the tuning forks, manufactures have stamped the terminals from higher grade stock such as beryllium copper and specially heat-treated or tempered beryllium copper stock. These higher grade sheet metal stocks are generally seven times more expensive than lower grade phosphor bronze stocks and, if additional heat treating steps are required, the cost may be increased even further. Often, even after changing to higher grade stocks, the resulting contact still may not provide desired spring rate and elastic deflection range to meet modern design criteria and larger contact sizes and spacing must be used.
A second conventional type of miniature pin-receiving contact, known as a dual cantilevered spring arm type, is shown in FIG. 2. This prior art contact is capable of electrically mating with rectangular or round pins and is also of an early entry type. The contact is generally characterized by low or moderate normal contact force loads and by a medium elastic deflection range. Although this pin-receiving contact structure is versatile and useful and exhibits a larger elastic deflection range than a tuning fork-type contact, the elastic deflection range is still too small for many modern design requirements. As was the case with the tuning fork, efforts to improve the elastic deflection range of the dual cantilever beam type contacts have included stamping from thinner gauge stock, which compromises the spring rates achievable for each beam, or moving to higher quality stocks which drastically increases the cost of each contact.
Still another prior art miniature pin-receiving contact is shown in FIG. 3. This contact may be referred to as a dual supported beam contact. The dual supported beam contact shown is a relatively late-entry pin-receiving contact as compared with the two early entry contact structures mentioned above. The FIG. 3 contact is generally characterized by high contact forces and very low elastic deflection range. The dual supported beam is relatively easily overstressed and is very sensitive to mating pin misalignments. Efforts to improve the elastic deflection range of the contact to provide a more compliant pin-receiving terminal have included changing to beryllium copper sheet stock with a very large increase in expense and only minor expansion of the elastic deflection range.
In order to remedy the deficiencies of the prior art pin-receiving contacts, it is an object of the present invention to provide a new and improved pin-receiving electrical contact characterized by high normal contact forces and exhibiting a significantly improved elastic deflection range.