De-bouncing keypad and preparation method thereof

Abstract

The present invention discloses a de-bouncing keypad and a preparation method thereof, wherein the keypad is composed of a rubber substrate and a metal contact having three layers of layered structures. A layer of tin alloy or lead alloy is plated on a surface of the metal contact by electroplating or chemical plating. The metal contact plated with the tin alloy or lead alloy has excellent contact bouncing resistance and arc-ablation resistance, and the metal contact is further composited with the rubber to shape and prepare the rubber de-bouncing keypad.

Claims

1. A de-bouncing keypad, comprising: a rubber substrate; and a metal contact, which is a layered complex including a first layer, a second layer, and a third layer, attached with the rubber substrate, wherein the first layer is a rubber layer having a thickness of 0.1-10 mm and contacts the rubber substrate, wherein the second layer is a sheet metal layer having a thickness of 0.1-10 mm and containing magnesium, aluminum, titanium, chromium, manganese, ferrum, cobalt, nickel, copper, zinc, niobium, molybdenum, silver, tin, tantalum or tungsten, and wherein the third layer is a tin alloy plated layer or lead alloy plated layer having a thickness of 0.1-10 m selectively deposited onto the second layer.

2. The de-bouncing keypad according to claim 1, wherein the third layer is electroplated onto the second layer.

3. The de-bouncing keypad according to claim 1, wherein the third layer is chemically deposited onto the second layer.

4. The de-bouncing keypad according to claim 1, wherein the third layer is plated onto one or two sides of the second layer.

5. The de-bouncing keypad according to claim 1, wherein the rubber substrate is a natural rubber, styrene butadiene rubber, butadiene rubber, ethylene propylene rubber, ethylene propylene diene monomer, urethane rubber, methylvinylsiloxane gum or polymethylvinylphenylsiloxane gum.

6. The de-bouncing keypad according to claim 1, wherein the rubber substrate is an ethylene propylene diene monomer, methyl vinyl silicone rubber or polymethylvinylphenylsiloxane gum.

7. The de-bouncing keypad according to claim 1, wherein the first layer is a hydrophobic rubber enabling a water contact angle on a rubber surface to be greater than 65 degrees.

8. The de-bouncing keypad according to claim 7, wherein the hydrophobic rubber is a nonpolar or weak polar rubber.

9. The de-bouncing keypad according to claim 8, wherein the hydrophobic rubber is an ethylene propylene diene monomer, methylvinylsiloxane gum or polymethylvinylphenylsiloxane gum.

10. The de-bouncing keypad according to claim 1, wherein the second layer is a metal sheet having a convex point or a concave point, a metal sheet having a convex line or a concave line, a metal sheet having a convex surface or a concave surface, a metal sheet having a small hole with an area less than 1 mm.sup.2, a metal gauze, metal foams or a metal fiber sintered felt.

11. The de-bouncing keypad according to claim 10, wherein the metal sheet of the second layer is composed of a stainless steel sheet.

12. A de-bouncing keypad, comprising: a rubber substrate; and a metal contact, which is a layered complex including a first layer, a second layer, and a third layer, attached with the rubber substrate, wherein the first layer is a rubber layer having a thickness of 0.1-10 mm; wherein the second layer is a sheet metal layer having a thickness of 0.1-10 mm and containing magnesium, aluminum, titanium, chromium, manganese, ferrum, cobalt, nickel, copper, zinc, niobium, molybdenum, silver, tin, tantalum or tungsten, wherein the second layer is a metal sheet having a convex point or a concave point, a metal sheet having a convex line or a concave line, a metal sheet having a convex surface or a concave surface, a metal sheet having a small hole with an area less than 1 mm.sup.2, a metal gauze, metal foams or a metal fiber sintered felt; and wherein the third layer is a tin alloy plated layer or lead alloy plated layer having a thickness of 0.1-10 m selectively deposited onto the second layer.

13. The de-bouncing keypad according to claim 12, wherein the metal sheet of the second layer is composed of a stainless steel sheet.

14. The de-bouncing keypad according to claim 12, wherein the third layer is electroplated onto the second layer.

15. The de-bouncing keypad according to claim 12, wherein the third layer is chemically deposited onto the second layer.

16. The de-bouncing keypad according to claim 12, wherein the third layer is plated onto one or two sides of the second layer.

17. The de-bouncing keypad according to claim 12, wherein the rubber substrate is a natural rubber, styrene butadiene rubber, butadiene rubber, ethylene propylene rubber, ethylene propylene diene monomer, urethane rubber, methylvinylsiloxane gum or polymethylvinylphenylsiloxane gum.

18. The de-bouncing keypad according to claim 12, wherein the rubber substrate is an ethylene propylene diene monomer, methyl vinyl silicone rubber or polymethylvinylphenylsiloxane gum.

19. The de-bouncing keypad according to claim 12, wherein the first layer is a hydrophobic rubber enabling a water contact angle on a rubber surface to be greater than 65 degrees.

20. The de-bouncing keypad according to claim 19, wherein the hydrophobic rubber is a nonpolar or weak polar rubber.

21. The de-bouncing keypad according to claim 20, wherein the hydrophobic rubber is an ethylene propylene diene monomer, methylvinylsiloxane gum or polymethylvinylphenylsiloxane gum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a structural schematic diagram of a de-bouncing keypad according to the present invention; in the figure: 1 refers to rubber layer; 2 refers to sheet metal layer; 3 refers to tin alloy or lead alloy plated layer; 4 refers to rubber substrate; and a metal contact is composed of 1, 2 and 3;

(2) FIG. 2 is a schematic diagram of a de-bouncing keypad switch; in the figure: 1 refers to rubber layer; 2 refers to sheet metal layer; 3 refers to tin alloy or lead alloy plated layer; 4 refers to rubber substrate; 5 refers to gold-plated contact on printed circuit board; and 6 refers to printed circuit board;

(3) FIG. 3 is a test pattern of bouncing on an ordinary nickel-plated keypad according to the present invention; and

(4) FIG. 4 is a test pattern of bouncing on a tin-plated keypad according to the present invention.

DETAILED DESCRIPTION

Embodiment 1

(5) FIGS. 1 to 2 are structural schematic diagrams of the present invention, illustrating a rubber layer 1, a sheet metal layer 2, a tin alloy or lead alloy coated layer 3, a rubber substrate 4, a convex point or line or concave point or line 10, as well as a gold-plated contact 5 on a printed circuit board and the printed circuit board 6. As shown in FIGS. 3 to 4, a bouncing trace appears on a test pattern of bouncing on an ordinary nickel-plated keypad, while no keypad bouncing appears on a tin-plated keypad of the present invention.

(6) The sheet metal layer was prepared by stainless steel (model number is 304; and national grade No. is 0Cr18Ni9) having a thickness of 0.1 mm. The stainless steel was rolled into a sheet having fine ripples by a mechanical method, wherein a peak height of the ripples was 0.1 mm and a peak spacing was 0.2 mm. Then a basic cleaning liquid having a pH value around 9 was used to clean and deoil the sheet, then the sheet was washed by water, and further cleaned and deoiled by industrial alcohol, and blow-dried by cold air. Other methods can also be used for cleaning, deoiling and activating.

(7) Polymethylvinylphenylsiloxane gum (for example, Elastosil R 401/60 produced by Wacker Chemie AG), vinyl tris-tert-butyl peroxy silane (VTPS) and dicumyl peroxide (DCP) were uniformly mixed by an open mill. The content of the VTPS in a rubber compound was 1%, and the content of the DCP in the rubber compound was 0.5%. VTPS was a coupling agent containing a peroxide component, which not only can crosslink silicone rubber containing vinyl but also can promote the bonding between the silicone rubber containing vinyl with metals (such as nickel, carbon steel, stainless steel, copper, or the like).

(8) Heat vulcanization adhesion and heat vulcanization shaping were performed between the stainless steel sheet having fine rippers and the foregoing rubber compound under 165 C., wherein a curing time was 12 min, to form a layered composite sheet of stainless steel and silicone rubber having a thickness of 1.0 mm. A surface of a mold cavity of a mold for preparing the composite sheet had a Teflo coating. The existence of the Teflo coating prevented the rubber compound from being adhered to the mold during heat vulcanization. The composite sheet was punched into a small wafer having a diameter of 5 mm. The small wafer was cleaned by basic cleaning liquid, washed by water, then put into 10% dilute sulfuric acid for activation for 1 min, and then cleaned, and drained off.

(9) Preparing a chemical plating bath having following compositions:

(10) 8 g/L stannous chloride dihydrate, 75 g/L trisodium citrate dihydrate, 20 g/L disodium edetate dihydrate, 10 g/L sodium acetate, 0.5 g/L benzene sulfonic acid, 0.2 g/L sodium saccharin, 8 g/L titanium trichloride, and proper aqueous ammonia were added to make the pH within 8.0-9.0. The chemical plating bath was in a ready-to-use form. Titanium trichloride may be resolved by deionized water or diluted hydrochloric acid, and not added into the plating bath earlier.

(11) 500 small wavers above were put into 300 mL plating bath above under a temperature of 80 C. and stirred continuously, taken out after 60 min, rinsed by distilled water or deionized water, drained off, and blow-dried by cold air, or put into a 70 C. constant temperature drying oven to dry, thus obtaining small wafers with a metal surface plated with a tin layer.

(12) The small wafer containing the tin layer of the silicone rubber layer was used as a contact to perform heat vulcanization adhesion and heat vulcanization shaping with the silicone rubber, to form a rubber keypad containing the contact, as shown in FIG. 1. Heat vulcanization adhesion was performed between a silicone rubber face in the small wafer and other silicone rubber, wherein one face with a metal plated layer faced outwards, so that the metal plated layer may be contacted with other contact such as a gold-plated contact on a printed circuit board (PCB) to form an access, as shown in FIG. 2. When the contact in this keypad is contacted with other contact (such as the gold-plated contact on the PCB), a contact bouncing phenomenon will not occur substantially, or a bouncing time thereof is approaching to zero. Therefore, the keypad is a de-bouncing keypad. Our test showed that the switching times were more than 100,000 times when a current between the contacts was 50 mA, the resistance between the contacts was not increased substantially, and the switching-on performance of the contact was excellent. When the current between the contacts was 300 mA and the switching times were 30,000 times, the contact resistance between the contacts was not increased substantially and maintained within 1 ohm. Relatively, a contact bouncing phenomenon would occur when the keypad containing a stainless steel contact not plated with a tin layer was contacted with the gold-plated contact on the PCB, wherein the average bouncing time was about 10 ms; when the current between the contacts was 300 mA and the switching times were about 3000 times, the resistance between the contacts was increased remarkably, and raised to 10 ohm above.

Embodiment 2

(13) The sheet metal used was the same as that in embodiment 1, but the sheet metal was processed by chemical plating to plate a layer of nickel having a thickness of 2.5 m on a stainless steel sheet having fine ripples. One object of nickel plating was to reduce the resistance on the surface of the sheet metal (because the electric conductivity of the nickel was greater than that of the stainless steel), and the other object was to adhere the stainless steel and a tin alloy plated layer more firmly. Then the sheet metal treated in this manner was composited with silicone rubber, then punched into small wafers, plated with a tin alloy by chemical plating, and finally prepared into a de-bouncing and arc-ablation resistant keypad.

Embodiment 3

(14) Like embodiment 1, the small wafer containing silicone rubber and stainless steel layer was prepared, then a layer of nickel having a thickness of 2.5 m was plated on the small wafer, and then a tin alloy layer having a thickness of 2.5-5.0 m was plated on a metal surface of the small waver as shown in embodiment 1, and this plated object was used as metal contact, and then a de-bouncing arc-ablation resistant keypad was prepared.

Embodiment 4

(15) All the processes were similar to the embodiments 1, 2 or 3, but the compositions of the chemical plating bath used were different. The compositions of the plating bath adopted in the embodiment were as follows: 15 g/L stannous chloride dihydrate, 0.3 g/L lead chloride, 75 g/L trisodium citrate dihydrate, 25/L disodium edetate dihydrate, 15 g/L nitrilotriacetic acid, 2 g/L sodium saccharin, 8 g/L titanium trichloride, and proper aqueous ammonia or 10% acetic acid are added to make the pH within 6.0-7.5. The temperature of the chemical plating was set as 60 C., and the time was set as 1 h.

(16) The plated layer obtained using the plating bath above was a tin lead alloy plated layer. The plated layer was more stable during storage and use, and tin whisker will not grow. The keypad having such a plated layer had no contact bouncing.

Embodiment 5

(17) Like embodiment 1, a s stainless steel sheet having fine rippers and silicone rubber were prepared into a layered composite sheet of stainless steel and silicone rubber having a thickness of 1.0 mm. 10% dilute sulfuric acid solution was used to clean the composite sheet for 3 min. Then a tin alloy plated layer having a thickness of 2.5-5.0 m was electroplated on the sheet. The plating bath and conditions used were as follows:

(18) 50 g/L stannous mono-sulphate, 90 g/L sulfuric acid and 0.4 g/L benzalacetone. The temperature of the plating bath was controlled to be 15 C. around, and the density of a cathode current was 1.0 A/dm.sup.2.

(19) In the plating bath, benzalacetone was a brightener. The sulfuric acid has such effects of reducing the activity of stannous ions, preventing the stannous ions from hydrolysis, improving the electrical conductivity of the plating bath and the efficiency of an anode current, etc. when the sulfuric acid was insufficient, the stannous ions were easily oxidized into quadrivalent tin.

(20) Then the sheet plated with tin alloy was punched into small wavers having a diameter of 5 mm. The small wafer was used as a metal contact to perform heat vulcanization adhesion and heat vulcanization shaping with silicone rubber, to form a rubber keypad having a contact. The keypad prepared also had excellent de-bouncing effect and arc-ablation resistance.

Embodiment 6

(21) A 400-mesh stainless steel plain net (the model of the stainless steel was 304) was used to replace the stainless steel sheet having fine ripples in embodiment 1, and the contact prepared using the process in embodiment 1 also had preferable de-bouncing effect and preferable arc-ablation resistance.

(22) A mesh of the 400-mesh stainless steel net was very small, and the silicone rubber will not penetrate through the mesh of the stainless steel net when molding the stainless steel net with the silicone rubber. If a stainless steel net with a small mesh number, for instance, a stainless steel net with a mesh below 80, was selected, a technical problem that the silicone rubber penetrated through the mesh of the stainless steel net during molding will occur. Therefore, a stainless steel net with a larger mesh number needs to be adopted for preparing a switch contact having a plated layer.

Embodiment 7

(23) A rubber keypad containing a contact plated with a tin layer was prepared like embodiments 1, 2, 3, 5 or 6. The rubber keypad was processed using a basic lead solution to replace partial tin in the tin coated layer on the surface of the contact with lead, thus forming a paper-thin tin lead alloy on the surface of the plated layer of the contact. In this way, whisker will not grow in the plated layer of the contact in the rubber keypad while the rubber keypad has de-bouncing function and arc-ablation resistance.