Switch contact element and its preparation method

Abstract

A switch contact element, having a layered structure comprising three layers: the bottom layer is silicone rubber, the middle layer is a continuous base metal sheet layer, and the upper layer is a discontinuous (stripe-shaped, raised-point-shaped or lattice-shaped) precious metal plated layer or a double-metal composite layer of a discontinuous base metal plated layer and a precious metal plated layer. The thickness of the bottom layer is greater than that of the middle layer, the thickness of the middle layer is greater than that of the upper layer, and the thickness of the upper layer meets the conditions that the conductive current is greater than safe current of conductive contacts on a circuit board, and the service life of a switch for the design is ensured.

Claims

1. A switch contact component, wherein the switch contact component is used as a switch conducting contact, capable of connecting two or more conducting contacts switching on a circuit board, being a small cylindrical, elliptical or prismatic disk with a thickness of 0.5-8 mm and a cross sectional area of 0.8-80 mm.sup.2, and being structured in three layer lamination, comprising: an under layer, which is a rubber (1); a continuous base metal sheet, sandwiched as a mid layer (2); and an upper layer, having a pattern selected from striped, convex dotted, and latticed, being either a layer comprising a precious metal plating or a bimetallic composite layer formed by base metal plating (3) and a precious metal plating in which said base metal plating (3) is sandwiched between the mid layer (2) and the precious metal plating (4); wherein a base metal plating material is selected from copper, nickel, titanium, aluminum, zinc or iron, or any alloy of them, or a laminated composite containing any of them or their alloys; wherein a precious metal plating material is selected from gold, silver, ruthenium, rhodium, palladium, osmium, iridium or platinum, or any of their alloys; wherein a width of each stripe in the striped pattern (5) is 0.05-2 mm, the stripes are spaced at intervals of 0.2-2 mm; each interval is smaller than a minimum spacing of two adjacent ones of the two or more conducting contacts on the circuit board; wherein said convex dots of the convex dotted pattern are substantially cylindrical or prism-shaped, and the diameters of their respective top surfaces or circumferences are 0.2-2 mm, and spacing between the adjacent convex dots (6) is 0.05-1 mm, and the spacing between adjacent dots is smaller than a half of a minimum spacing of two adjacent ones of the two or more conducting contacts on the circuit board, to ensure more than two convex dots (6) contact a conducting contact on an other circuit board simultaneously; wherein latticed lines of the latticed pattern (7) are 0.05-2 mm wide, and a void (8) area between adjacent latticed lines is 0.05-5 mm.sup.2; wherein an upper layer thickness satisfies the following condition: in case of stripes, the stripes minimum widththickness>210.sup.4 mm.sup.2; when dots are utilized, the convex dots (6) bottom circumference diameterthickness>110.sup.4 mm.sup.2.

2. According to claim 1, wherein a thickness of the under layer is greater than that of the mid layer; the mid layer thickness is greater than that of the upper layer, and 50 m<the mid layer thickness<1 mm.

3. According to claim 1, wherein the base metal plating (3) is 1.5-10 times as thick as the precious metal plating (4) in the bimetallic composite layer.

4. According to claim 1, wherein said rubber is silicone rubber, said base metal material is stainless steel, and said precious metal material is gold with a purity of higher than 99%.

5. A preparation method for a switch contact component comprising: preparing the switch contact component of claim 1, having the steps of: 1) using a base metal sheet (2) as a substrate, and printing one 2-10 m thick plating mask on an upper surface of the substrate with an ink which is dissolvable with a solvent, an acidic solution or an alkaline solution so that areas not covered with the plating mask are exposed with dense metallic convex dots (6), stripes, or lattices (5) of the substrate upper surface; 2) plating on the areas of the upper surface of the substrate that is not covered with the plating mask, one plating of precious metals (4), or one plating of base metals (3) before the plating of precious metal (4) is applied thereto; 3) removing the plating mask by dissolution using another solvent, another alkaline solution or another acidic solution; 4) bonding an undersurface of the plated sheet with a silicone rubber by thermal vulcanization to form a composite sheet in a thickness of 0.25-5 mm; 5) cutting or punching the composite sheet into cylindrical, elliptical or prismatic disks with cross sectional areas of 0.8-80 mm.sup.2.

6. A preparation method for a switch contact component comprising: preparing the switch contact component of claim 1, having the steps of: 1) using a base metal sheet (2) as a substrate, and on an undersurface of the substrate bonding, a silicone rubber by thermal vulcanization to form a composite sheet with a thickness of 0.25-5 mm; 2) printing one 2-10 m thick plating mask on a bottom side of the base metal sheet, with an ink which is dissolvable in a solvent, an acidic solution or an alkaline solution so that areas of the substrate not covered by the plating mask is exposed with metallic convex dots (6), stripes or lattices (5); 3) plating, on areas of the substrate not covered by the plating mask, one plating of precious metal (4), or applying one plating of base metals (3) before the plating of precious metal (4) is applied on the base metal plating (3); 4) removing the plating mask by dissolution; 5) cutting or punching the plated composite sheet into cylindrical, elliptical or prismatic disks with cross sectional areas of 0.8-80 mm.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a top view of the structure of this invention

(2) FIG. 2 is a top view of another structure of this invention

(3) FIG. 3 is a top view of the third structure of this invention

(4) FIG. 4 is a schematic drawing for the longitudinal section structure of FIG. 1

(5) FIG. 5 is a schematic drawing for the transverse section structure of FIG. 1

(6) Elements in the figures are: 1. silicone rubber; 2. base metal sheet layer; 3. base metal plating; 4. precious metal plating; 5. stripe; 6. convex dots; 7. lines; 8. voids

DETAIL DESCRIPTION OF EMBODIMENTS

(7) The detail description of this invention is given below in light of the attached figures and examples.

Practical Example No. 1

(8) The switch contact component as shown in FIGS. 1, 4, and 5, is a small elliptic columnar granule with a three layer laminated structure, with a thickness of 3 mm and a cross sectional area of 8 mm.sup.2.

(9) The under layer is a silicone rubber layer 1; the continuous base metal copper sheet layer 2 is sandwiched as a mid layer; and the upper layer is a bimetallic layer of striped base metal nickel plating 3 and precious metal gold plating 4. The stripe 5 is 1 mm wide and the spacing between the adjacent stripes 5 is 1.5 mm, and the thickness of the base metal plating 3 of the composite layer is 3 times the thickness of the precious metal plating 4.

(10) The said nickel base metal plating 3 is between the base metal sheet 2 and the precious metal gold plating 4.

(11) The upper layer thickness meets the following condition: the stripe's minimum widththickness>110.sup.3 mm.sup.2

(12) The under layer thickness is greater than the mid-layer; the mid-layer thickness is greater than that of the upper layer, and 0.5 mm<mid-layer thickness<1 mm

Practical Example No. 2

(13) A square stainless steel sheet (the material is, for example, SS304) with a side length of 100 mm and a thickness of 0.05 mm, is cleaned with an alkaline detergent, treated with 5% dilute hydrochloric acid for 3 minutes to remove the oxides on the stainless steel surface, and then rinsed with de-ionized water. After drying, one side of the sheet (the undersurface) is coated with a rubber-metal adhesive (such as Megum 3270), and then the coated undersurface is bonded with silicone rubber (such as KE 951) by thermal vulcanization to form a 1.0 mm thick stainless steel-silicone rubber laminated composite sheet. On the stainless steel surface of this composite sheet, a partial coating of 6 micron thick ink, which is dissolvable in an organic solvent but not dissolvable in an acidic or alkaline solution, is printed, leaving latticed voids (7; 8) with the lattice line (7) 1 mm wide, and the void area (8) between the latticed lines 1 mm.sup.2. The ink, as the plating mask, makes the areas of the composite sheet not covered with the plating mask become latticed (7; 8) grid to expose the stainless steel surface; on the areas of stainless steel sheet not covered with the plating mask, one plating of 5 micron thick nickel is plated by electroplating before a plating of gold with a thickness of 1 micron and a purity of greater than 99% is applied; then an organic solvent is used to wash out the plating mask; this nickel-plated and gold-plated composite sheet is punched into small cylindrical granules with a diameter of 5 mm. These small cylindrical granules, as contact components for pairing with the contacts in PCBs, are used to make the silicone rubber keypads. These switches so structured have good mechanical strength, long service life, and good dust and oil stain resistance.