Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1998-06-03
2001-07-03
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S327000, C428S328000, C428S332000, C428S339000, C428S341000, C428S546000, C428S626000, C428S929000, C205S109000, C205S154000, C205S194000, C205S196000, C205S220000, C427S058000, C427S430100, C427S435000, C427S405000, C427S409000
Reexamination Certificate
active
06254979
ABSTRACT:
TECHNICAL FIELD
This invention pertains to electrical connectors that provide oxidation resistance and low contact electrical resistance in combination with reduced engage/disengage force requirements.
BACKGROUND OF THE INVENTION
The electrical content of automobiles and other useful articles of manufacture is continually increasing, leading to a corresponding increase in the demand for reliable electrical connectors. In the case of automobile connectors many applications require multi-terminal male/female type connectors. Multi-terminal connectors require appreciable force to engage and disengage the connection and it is, of course, important that such connectors be fully and properly engaged.
Many electrical terminals are made of copper alloys that provide good strength and bulk electrical conductivity properties. However, copper alloy terminals oxidize in air, and the resulting oxidized coatings increase the electrical resistance of the connection. Accordingly, it is a common practice to provide a tin, silver or gold coating to the surface of such copper alloy terminals. These metals provide low electrical contact resistance and oxidation protection to the copper alloy terminal, but tin and silver in particular do not have low coefficients of friction and tend to increase the force required to engage and disengage the connectors. While gold has a relatively low coefficient of friction, it is too expensive for many connector applications.
It would be particularly useful to have a tin or silver coating layer for such copper-based connectors that would retain the low contact resistance of the base metal and yet display a lower coefficient of friction for engaging the terminal pieces. There have been suggestions to incorporate low friction polymer particles such as polyimide, polyamide and polytetrafluoroethylene particles with tin or lead particles to form a mixture that can be applied in suitable fashion to the surface of a copper base terminal alloy stock material. These practices are described, for instance, in Guenin, U.S. Pat. No. 5,028,492, “Composite Coating for Electrical Connectors”; Guenin et al, U.S. 5,141,702, “Method of Making Coated Electrical Connectors”; and Endo et al, U.S. Pat. No. 5,235,743, “Method of Manufacturing a Pair of Terminals Having a Low Friction Material on a Mating Surface to Facilitate Connection of the Terminals”. The preparation of tin, tin alloy or lead alloy particulate mixtures with particles of a suitable polymer requires separate processing operations. Further operations are required to form a cladable layer of the mixture and adhere the cladding material to the copper base terminal alloy. In one embodiment of the Guenin disclosures, it is proposed to co-deposit polymer particles with tin from a tin sulfate electroplating bath so as to provide an electro-deposited tin layer entraining particles of polyimide, polyamide or polytetrafluoroethylene. In these Guenin disclosures, the thickness of the tin matrix with the polymer dispersion is of the order of about one to about three microns, and the diameter of the polymer particles is from about 0.5 to about 3 microns.
As stated, these co-deposition and/or cladding operations are cumbersome and add to the cost of the terminal manufacture. It would be preferable to have a practice that enables a copper alloy terminal stock or a copper alloy terminal to be simply electroplated with tin in a suitable form and a suitable lubricating material applied to the tin that does not reduce the conductivity of the terminal.
SUMMARY OF THE INVENTION
This invention provides electrical conductors based on a core material of suitable bulk conductivity and having a surface layer of tin or, optionally, silver electrodeposited in a suitably coarse grain form so as to accommodate a deposition of very small particles of polytetrafluoroethylene or other suitable low friction insulating polymer particles on and between the grains. The invention involves electroplating a layer of tin or of silver on the base metal surface so that a suitable coarse, grainy electrodeposited layer is formed which is characterized by grains having average dimensions in the range of about 0.5 to 10 micrometers. Preferably, the grain size is about 2 to 5 micrometers in the view provided by a Scanning Electron Micrograph, e.g. A coarse grained electroplated surface of this nature is preferred because it accommodates the deposition of very small particles (for example, micro-sized particles) of polytetrafluoroethylene (PTFE) or other suitable particles having an average dimension in the range of about 0.2 to 0.4 microns. These very small particles of PTFE or the like when applied in a suitable quantity provide individual lubricating particles on and between the grains of the electroplated layer. Under the load applied to the electroplated layer during engagement or disengagement of electrical connectors, the PTFE particles provide sufficient lubricity to accommodate the connect or disconnect step. On the other hand, once the terminals have been brought into full contact, the number of PTFE particles is such that the contact resistance between the engaged terminal pieces is not so high as to adversely affect the electro-connection.
In accordance with the practice of this invention, the electroplated tin or silver matte coating may be applied to the base stock such as a copper alloy from which the terminals or connectors are formed. Alternatively, the terminals can be formed from a suitable alloy, and the electroplating and/or the polymer particle coating accomplished on the shaped terminal piece. Preferably, the quantity of PTFE microparticles that are deposited on the electroplated tin or silver coating is controlled such that the contact resistance of the member with an engaging terminal piece is no greater than about 5 milliohms at the design contact load. In general, a suitable areal density (based on geometric surface area, not actual surface area of the matte plate) of the PTFE particles is in the range of 0.02 gram/m
2
to 0.4 gram/m
2
.
Other advantages and forms of the invention will become more apparent from a detailed description thereof which follows. Reference will be had to the drawings in which:
REFERENCES:
patent: 3494998 (1970-02-01), Anhalt
patent: 4600480 (1986-07-01), Coombes et al.
patent: 5028492 (1991-07-01), Guenin
patent: 5141702 (1992-08-01), Guenin et al.
patent: 5235743 (1993-08-01), Endo et al.
patent: 5477661 (1995-12-01), Gay
patent: 57-152499A (1982-09-01), None
Cheng Yang-Tse
Drew George Albert
Gillispie Bryan A.
Ricketts Mark S.
Suchanek Robert A.
Delphi Technologies Inc.
Jones Richard A.
Rickman Holly
Thibodeau Paul
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