Abstract:
Rotary electrical signal generator includes fixed electric contacts and slider contacts which engage the fixed contacts. To enhance the abrasion resistance and the corrosion resistance, the surface of printed electrodes is coated with an amorphous Ni-P plated layer containing from 15 to 25 atom % of P.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an electric contactor device including fixed electric contacts and a movable electric contact which is disposed for abutment against the fixed contacts. In particular, while not limited thereto, the invention relates to an electric signal generator including fixed electric contacts formed on a printed circuit board and an electric slider contact carried by a rotor and disposed for abutment against the fixed electric contacts. 
     Such an electric signal generator may be utilized as a throttle opening sensor which is connected to a throttle valve of an engine, one example of which is disclosed in U.S. Pat. No. 4,345,240 issued to Hiroyuki Amano et al. The throttle opening sensor includes a plurality of split electrodes formed on a printed electrical circuit board and an electrically conductive slider having a plurality of radially extending legs which fixedly carry contact members disposed for contact with the plurality of split electrodes. The electrically conductive slider is secured to a shaft which is in turn fixedly mounted on the rotatable shaft of a throttle valve. The potential of the slider is maintained at a ground potential while the split electrodes assume the ground potential only when they are engaged by contact members on the slider. In this manner, the output is in the form of a bi-level signal, and the combination of outputs from the split electrodes constitute together a code corresponding to the opening of the throttle valve. 
     Generally, the throttle opening sensor is mounted on an engine or is disposed very close to the engine, and thus is subject to heat radiation therefrom to raise its temperature. The plurality of split electrodes formed on a printed electrical circuit board comprises a conductor on the circuit board formed by a copper foil, which is then plated with nickel, and the nickel plating is in turn plated with gold or palladium. The nickel plating has a relatively high level of abrasion resistance but exhibits a relatively low level of corrosion resistance and a relatively high contact resistance, which is the reason to provide the gold or palladium plating or coating thereon. As is well recognized, a gold plating exhibits an increased corrosion resistance and a reduced contact resistance, but since it has a low level of abration resistance, it is applied as a relatively thick coating. Because both gold and palladium are relatively expensive, the described throttle opening sensor requires an increased cost for the materials. 
     SUMMARY OF THE INVENTION 
     It is a first object of the invention to increase the corrosion resistance and the abrasion resistance of fixed electric contacts and a movable electric contact, which is disposed for abutment against the fixed contacts, of an electric contactor device which may be used in a throttle opening sensor. A second object is to reduce the cost required for the materials. 
     The above objects are achieved in accordance with the invention by coating the surface of the electric contacts, including both the fixed and the movable contacts, with an amorphous plating containing abrasion resistant conductor metal element. In a preferred embodiment of the invention, the surface is coated with nickel-phosphorus amorphous plating. Grain boundaries are reduced or substantially absent in an amorphous plating containing conductor metal element, and thus stand in the way to the growth of a corrosion process, whereby the amorphous plating exhibits an increased corrosion resistance. Since the plating essentially comprises nickel, it exhibits a high abrasion resistance and can be inexpensively applied. 
     Other objects and features of the invention will become apparent from the following description of an embodiment thereof with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view, partly broken away, of a preferred embodiment of the invention; 
     FIG. 2 is a cross section taken along the line II--II shown in FIG. 1; 
     FIG. 3a is an enlarged cross section of part of a printed circuit board shown in FIG. 1 during a masking step; 
     FIG. 3b is an enlarged cross section of part of the printed circuit board shown in FIG. 1 during a plating step; 
     FIG. 3c is an enlarged cross section of part of the printed circuit board shown in FIG. 1; and 
     FIG. 4 is a perspective view of the rotatable arm and the contacts carried thereby. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, which illustrate a throttle opening sensor according to a preferred embodiment of the invention, there is shown a base 1 in which an annular boss 1a is formed. The boss 1a is formed with a bore through which a rotatable shaft 7 extends. A printed circuit board 4 is secured to the internal surface of the base 1, and fixedly carries a plurality of split electrodes 6 (6 1 , 6 2 , 6 3 , 6 4 ) and their connected printed electrode leads 16 (16 1  to 16 4 ). At its one end, the rotatable shaft 7 fixedly carries a rotatable arm 3 while its other end is coupled to a rotating shaft of a throttle valve, not shown. 
     Split electrodes 6 2 , 6 3  on the printed circuit board 4 are shown in an enlarged cross section of FIG. 3c. It is to be noted that each of the split electrodes 6 comprises a layer of copper foil 6a which is contiguous with an associated printed electrode lead 16, and an amorphous nickel-phosphorus plated layer 6b which covers the surface of the layer 6a. 
     The rotatable arm 3 has secured thereto an electrically conductive slider having a plurality of radially extending legs 2 which fixedly carry contact members disposed for contact with the plurality of split electrodes 6, the legs 2 being disposed so as to be located opposite to the plane of the circuit board 4. 
     The ends of the printed electrode leads 16 are connected to lead wires 15 (15 1  to 15 4 ). At any point within a predetermined range of angle of rotation for the rotatable shaft 7, a given one of the plurality of the legs is maintained in contact with a given one, 6 1 , of the plurality of split electrode 6. As mentioned previously, the split electrode 6 1  is contiguous with the printed electrode lead 16 1  which is connected to the lead wire 15 1 , to which the ground potential or a constant positive potential is applied. Accordingly, the ground potential or the constant positive potential is applied to all of the legs 2. The ground potential or the positive potential is applied to any of the remaining split electrodes (6 2 , 6 3 , . . . ) only when it is engaged by the leg 2, and a combination of potentials on the lead wires 15 2 , 15 3  and 15 4  represents a throttle opening. 
     A casing 8 is fixedly connected to the base 1 so that the combination of the casing 8 and the base 1 encloses a space in which the printed circuit board 4 and the rotatable arm 3 are received. The lead wires 15 are secured to a lead wire support member 9 which is secured to the base 1. 
     Referring to FIGS. 3a, 3b and 3c, a method of manufacturing the split electrodes 6 will be described. Initially referring to FIG. 3a, the printed circuit board 4 comprises a board of synthetic resin such as epoxy resin, on the surface of which is bonded the copper foil 6a. A screen printing plate 20 having openings formed therein except for the locations of the split electrodes 6 and their contiguous printed electrode leads 16 is placed on top of the surface of the copper foil 6a. Synthetic resin 11, which serves as a mask or a plating resist subsequently, is then screen printed onto the copper foil 6a through the plate 20. 
     As shown in FIG. 3b, an amorphous nickel-phosphorus layer 6b is applied to the copper foil 6a on the printed circuit board 4 in regions where it is exposed, by employing an amorphous plating process. The synthetic resin 11 is then removed, and an etching process is used to remove the copper foil 6a in regions where it has previously been masked by the synthetic resin 11, as shown in FIG. 3c. 
     The amorphous plating process described above employs an electroless plating bath disclosed in pending U.S. patent application Ser. No. 736,859 filed May 23, 1985, now U.S. Pat. No. 4,636,255, by Jho Tsuda and assigned to the assignee of the present application. The electroless plating bath is an aqueous solution comprising nickel ions, a nickel ion reducing agent, a pH adjuster, a pH buffer, a nickel ion sequestering agent, a reduced amount of stress reducing agent and phosphorus deposition promoter. The phosphorus deposition promoter includes a first and a second promoter. The first phosphorus deposition promoter comprises trisodium N-(2-hydroxyethyl)ethylenediamine-N,N&#39;,N&#39;-triacetate (C 10  H 15  N 2  Na 3  O 7 ). ##STR1## The second phosphorus deposition promoter comprises one or more salts chosen from sulfates such as ammonium sulfate, lithium sulfate, potassium sulfate, sodium sulfate or the like. The first phosphorus deposition promoter may be employed alone, or the first and the second phosphorus deposition promoter may be used in combination. However, the second phosphorus deposition promoter cannot be used alone. The second phosphorus deposition promoter is effective only when it is used in combination with the first phosphorus deposition promoter. 
     The electroless plating bath including at least the first phosphorus deposition promoter enables the deposition of phosphorus to a medium level by adjusting the amount of the first phosphorus deposition promoter added. Trisodium N-(2-hydroxyethyl)-ethylenediamine-N,N&#39;,N&#39;-triacetate C 10  H 15  N 2  Na 3  O 7 ) has a high sequestering capacity and adjusts the isolated nickel ions in the bath to a preferred condition, thus substantially improving the stability of the bath, the deposition rate and the uniformity of a film deposited. The second phosphorus deposition promoter may be added in an amount as required, and through an adjustment of the amount of addition of such promoter, an amorphous nickel-phosphorus alloy film 6b containing from 15 to 25 atom % of phosphorus can be deposited on the copper foil 6a in a relatively facilitated and stable manner. 
     An amorphous nickel-phosphorus alloy film 6b containing from 15 to 25 atom % of phosphorus exhibits excellent corrosion and abrasion resistances and non-magnetic properties. Accordingly, during an etching process which removes the synthetic mask 11 as well as the copper foil 6a in its regions located below the mask 11 after the application of the amorphous coating, an etching solution containing ferric chloride, for example, may be used, and the amorphous film 6b serves as an etch resist. Accordingly, the use of a separate resist film can be dispensed with. 
     In the preferred embodiment of the invention, the split electrodes 6 have the amorphous nickel-phosphorus alloy plated layer 6b containing from 15 to 25 atom % of phosphorus on its surface, and exhibit a high abrasion and corrosion resistance. The oxidation of the split electrodes 6 can be avoided up to relatively high temperature if the temperature of these electrodes rises due to heat radiation from the associated engine or by Joule heat caused by a contact resistance between the slider contacts and the split electrodes 6. Accordingly, a current of a relatively high magnitude can be used to flow through the split electrodes 6. 
     While the invention has been described above in connection with a particular embodiment thereof, it should be understood that a number of changes, modifications and substitutions will readily occur to those skilled in the art in the light of above teachings. By way of example, the copper foil 6a may be replaced by other metal layers which are used in a printed circuit arrangement. The slider may also comprise an amorphous plating. It is also possible to form the amorphous layer 6b by plasma chemical vapor deposition or sputtering process. Accordingly, the scope of the invention is not limited to the specific embodiment shown and described, but should be solely defined by the appended claims.