GB2285339A

GB2285339A - Membrane switch and method for making membrane switch

Info

Publication number: GB2285339A
Application number: GB9326562A
Authority: GB
Inventors: Bright Huang
Original assignee: Silitek Corp
Current assignee: Silitek Corp
Priority date: 1993-12-30
Filing date: 1993-12-30
Publication date: 1995-07-05
Also published as: DE4400098A1; CA2120393A1; CA2120393C; GB9326562D0

Description

2285339 MEMBRANE SWITCH AND METHOD FOR MAKING MEMBRANE SWITCH This

invention relates to membrane switches and to methods of making membrane switches.

The pace of our modern life goes very fast, the simplification, high performance have become the goal of design. In light of this, the multilayer membrane switch can not meet the requirements for modern life.

Many skilled in the art has made many efforts to modify or change the design of the conventional membrane swich.

Referring to Figure 3, a conventional membrane switch used in keyboard of a computer. In this membrane switch assembly, there are three layer of sheet 3a, 4a and Sa wherein the upper sheet 3a and lower sheet Sa are distributed with electrical wires. The middle sheet 4a is used to separate the upper and lower sheet 3a, Sa from contacting with each other. There are a plurality of holes disposed at the middle sheet 4a to facilitate an electrical contact between the upper and lower sheet 3a, Sa.

The upper sheet 3a in Figure 3 is viewed from rear side. The signal generated by this membrane is done by an electrical contact between the wires of X and Y axis. From Figure 1, the signal generated from la of X-axis and 2a of Y-axis can be found in Table shown in Figure 2. If we hope to input "A", then the keytop with respect to YO and X2 shall be pressed. When the keytop is pressed, an "A" will is be generated through an encoder. In normal condition, the la of X-axis and 2a of Y-axis are separated from each other. In light of this, the wires of la in X-axis are disposed in an individual sheet, the wires of 2a in Y-axis are disposed in another individual sheet. An isolated sheet is disposed therebetween. A plurality of holes 41 are disposed on said isolated sheet with respect to each intersection of X-axis and Y-axis. When the rubber block 6a is depressed, an electrical contact will be constructed between the wire la of X-axis and 2a of Y-axis, as shown in Figure 4.

The steps of manufacturing a conventional membrane are described detailed below. Taking a first sheet 3a for distributing wire la for X-axis. A silver net 32a will be printed to the sheet 3a via a clear glue foil 31a. Each intersection points will be coated with carbon powder 33a to increase the durability of the membrane switch. Then an isolate sheet 4a having a plurality of holes 41 with respect to each keys 1S attached to the upper side of said first sheet 3a. Afterward, a third layer Sa of wires 2a is attached to the upper side of the isolated sheet 4a. The third sheet 5a is identical with the first sheet 3a, it comprises a clear glue foil 5 la, a silver net 52a and a coated carbon powder 53a. Then, a conventional membrane switch is made.

In the conventional art, the membrane switch assembly comprises three individual sheets and each of them needs an individual design. Accordingly, the cost is high and the steps are complicated. The present cost for making a conventional membrane switch assembly takes twentyeight to thirty New Taiwan dollars. Although there are coated carbon powder 33a, 53a disposed at each intersection point to increase the durability, the space between the first sheet 3a and the third sheet Sa provided by the middle sheet 4a become smaller and smaller because the deformation of the clear glue foil 31a and Sla. At last, no space will be found between intersection points and the membrane switch assembly become useless. In average, each intersection point can be depressed for 10M (ten million) to 20M times.

From above description, the shortcomingfor a conventional membrane switch assembly can be concluded with the following.

1. There are three individual sheets are used to make a membrane switch assembly. The electrical wires for X-axis and Y-"is are distributed into two different sheet and an isolated sheet is disposed therebetween. Besides, the silver net shall be disposed to the sheet by means of a clear glue foil and coated with carbon powder at each intersection point. The cost is high and the steps is complicated.

2. The silver net provides an excellent conducting capability, the signal is strong and clear. on the other hand, the extension of silver is excellent. Besides, within 20 millimetres (20 mm), the electrical resistance is zero (0). But the silver costs high, the longer the wire, the higher the cost.

3. Although there are coated carbon powder disposed at each intersection point to increase the durability, the space between the first sheet 3a and the third sheet provided by the middle sheet become smaller and smaller because the deformation of the clear glue foil. At last, no space will be found between intersection points and the membrane switch assembly become useless. In average, each intersection point can be depressed for 10M (ten million) to 20M times.

This invention provides a method for making a membrane switch assembly, which integrates the conducting wire of X-axis and of Yaxis are integrated into a single membrane, comprising the steps of 1) printing silver net onto a base membrane to form a plurality of loop; 2) applying layer of anti-oxidant to said silver net; 3) applying layer of isolating treatment layer to said anti-oxidant layer; and 4) applying carbon treatment layer to said isolating treatment layer.

This invention also provides a membrane switch fabricated by the above method.

This invention also provides a membrane switch comprising:

base membrane; plurality of loops on said base membrane, formed by printing a silver net onto said base membrane; a layer of anti-oxidant disposed on said silver net; an isolating treatment layer disposed on said anti-oxidant layer; and a carbon treatment layer disposed on said isolating treatment layer.

Embodiments of this invention provide a novel wire distribution method which facilitates a limited jumping length of electrical wires for X-axis and Y-axis in a single sheet.

The computer has become a necessity of our modern life. It provides us countless convenience. We -can find it at railway station, airport and bank. Almost everyone has a personal computer to serve his daily life. In light of this, the keyboard plays more important role in computer. Hence, af ter considerable design effort, embodiments of this invention provides a newly developed method for making membrane switch which provides a durable membrane switch assembly.

1 1 Embodiments of this invention provide a method for making membrane switch which facilitates a simply distributed jump line with limited length to control the resistance of a loop.

Embodiments of this invention - use carbon as the jump line to decrease the cost of making the membrane switch and increase the durability of the membrdne switch assembly.

The invention will now be described by way of example with reference to the accompanying drawings, throughout which like parts are referred to by like references, and in which:

Figure 1 is a circuitry of a conventional keyboard; Figure 2 is an arrangement of a circuitry with respect to a keyboard; Figure 3 disassembled view for a conventional membrane switch which includes three individual sheets; Figure 4 is a cross sectional view of a conventional keyswitch showing the actuation of it; Figure 5 is a clear glue foil; Figure 6 is a sketch view of a silver net; Figure 7 is a layer of anti-oxidant and a membrane switch assembly coated with said anti-oxidant layer; Figure 8 is a layer of isolation and a membrane switch assembly coated with said isolation layer; Figure 9 is a layer of carbon powder and a membrane switch assembly coated with said carbon powder layer; Figure 10 is sketch view showing a keyswitch is triggered; 5- Figure 11 is a perspective view showing a keyswitch made according to an embodiment of this invention; and Figure 12 is a cross sectional view showing the keyswitch as triggered.

Referring to Figures 5, 6, 7, 8 and 9, the conducting wire la of X-axis and 2a of Y-axis are integrated into a single membrane. Because of limited space in a single membrane, each loop can not be made by a single wire, hence a plurality of jumping wire is used to save more space. By this arrangement, there are five to six jumping wires located in a single loop. The carbon material is used to make the jumping wire because it is very cheap. But the resistance of the carbon wire are slightly high as compared with silver line. Normally, the resistance of carbon wire are 100 ohms/ mm. In application, the resistancein 20 millimetres - shall not exceed 100 ohms, otherwise incorrect signal will be generated. In light of this, in the actual design of this invention, the jumping line in a single loop will not exceed six lines. For example, we take six individual carbon lines, each has a length of 20 milli metres. Then the total ohms is 6 x 100 = 600 ohms. When this ohms values is added with the resistance of silver line, the total ohms will not exceed the requirements for generating a proper signaL By this arrangement, the conducting wire la of X-axis and 2a of Y-axis are integrated into a single membrane.

The configuration of the membrane made according to this embodiment will be described below.

Referring to Figure 5, a clear glue foil 1 is printed with silver line 2 according to predetermined arrangement, as shown in Figure 6. This silver line 2 includes keyswitch connecting point 21 and jumping line connection 22. The silver line 2 is an ideal material for conducting wire and it has an excellent capability of extension. On the other hand, the silver line 2 is coated with a layer of anti-oxidant is 3 to prevent the silver from oxidation, as shown in Figure 7. But the keyswitch connecting point 21 and jumping line connection 22 are not coated with this layer of anti-oxidant 3. This layer of anti-oxidant 3 is served as an isolation layer. But the isolating effect of this layer of anti-oxidant is not perfect. Hence a further isolating layer 4 is coated to the carbon jumping wire 51, as shown in Figure 8.

After these three steps is completed, a carbon treatment layer 5 is coated to the keyswitch connecting point 21 and jumping line connection 22 and the carbon jumping wire 51, as shown in Figure 9. By this arrangement, a carbon jumping wire 51 and carbon keyswitch connecting point 52 is formed. Since the carbon line has a larger resistance, hence a checking silver point 23 is disposed in every 20 millimetre length and this is finished with printing the silver line 2. Besides, a checking point 53 is disposed at the carbon treatment layer 5 to check the resistance of the carbon wire. By this arrangement, we reach an excellent layout of conducting wire.

After the membrane switch assembly is completed, this assembly can be applied to the keyboard. As shown in Figure 10, 11, and 12, when the rubber block 6 having a carbon connect 61 at bottom of the a keyswitch is lowered, it will construct a electrical contact with the carbon connecting point 53. Hence, a conducting loop of wire la of X-axis and wire 2a of Y-axis is constructed. Then a signal will be generated and an IC will pick up this signal. By this arrangement, the clear glue foil 1 will not pressed. By using the carbon connecting point 53 and rubber block 6, this membrane keyswitch assembly can be pressed from at least 30M to 50M times. With the method provided by this embodiment, only one sheet of membrane is used together with silver net 2, anti-oxidant layer, isolating treatment layer 4, carbon treatment layer 5. Two sheet of membrane is omitted. The conducting wire la of X-axis and 2a of Y-axis are integrated into a single membrane.

Besides, the length of the wine is largely decreased and a plurality of carbon wire are used as jumping wire to decrease the amount of silver line. Hence, the cost of this membrane switch assembly is lowered to fourteen to sixteen (14-16) New Taiwan dollars.

The present. embodiment can be concluded with the following advantages.

1. The conducting wire la of X-axis and 2a of Y-axis are integrated into a single membrane. Two sheet of membrane is omitted. Besides, only taking four steps, 1) printing silver net; 2) applying layer of anti-oxidant; 3) applying layer of isolating treatment layer; and 4) applying carbon treatment layer, to make this membrane switch assembly. It saves times and lowers the cost.

2. Because of limited space in a single membrane, each loop can not be made by a single wire, hence a plurality of jumping wire is used to save more space.

By this arrangement, there are five to six jumping wires located in a single loop. The carbon material is used to make the jumping wire because it is very cheap.

3. The embodiment takes a very strict quality control to provide an excellent quality. A checking silver point is disposed in every 20 millimetre length and this is finished with printing the silver line. Besides, a checking point is disposed at the carbon treatment layer to check the resistance of the carbon wire. By this arrangement, we reach an excellent layout of conducting wire.

4. When the rubber block having a carbon connect at bottom of the a keyswitch is lowered, it will construct a electrical contact with the carbon connecting point. Hence, a conducting loop of wire of X-axis and wire of Y-axis is constructed. By using the carbon connecting point and rubber block, this membrane keyswitch assembly can be pressed from at least 30M to SOM times.

5. The length of the wine is largely decreased and a plurality of carbon wire are used as jumping wire to decrease the amount of silver line. Hence, the cost of this membrane switch assembly is lowered to fourteen to sixteen (14- 16) New Taiwan dollars.

8 therefore, embodiments of the invention or special technique for making membrane switch which facilitates a simply distributed jump line with limited legnth to control the resistance of a loop. By this arrangement, the membrane switch can be manufactured by a single layer of sheet and provides a durable and high performance membrane switch.

In summary Drovide a method

Although the present invention has been described in connection with Preferred embodiment thereof, many other variations and modifications will now become apparent to those skilled in the art without departing from the scope of the invention. It is preferred, therefore, that the present invention not be limited by the specific disclosure herein, but only by the appended claims.

Claims

CLAIMS:

1. A method for making a membrane switch assembly, which integrates the conducting wire of X-axis and of Y-axis are integrated into a single membrane, comprising the steps of 1) printing silver net onto a base membrane to form a plurality of loop; 2) applying layer of anti-oxidant to said silver net; 3) applying layer of isolating treatment layer to said anti-oxidant layer; and 4) applying carbon treatment layer to said isolating treatment layer.

2. A method as recited in claim 1, wherein each single loop comprises a plurality of jumping wires having a length not more than 20 millimetres, the number of jumping wires in each loop shall no more than six.

3. A method as recited in claim 2, wherein said jumping lines are made from carbon.

4. A method as recitedin claim2, wherein the resistanceof the jumping wirewill not exceed one hundred (100) ohms within 20 millimetres.

5. A method as recited in claim 1, wherein a plurality of connecting points are formed at said silver net.

6. A method as recited in claim 5, wherein said connecting points are not coated with anti-oxidant.

7. A method as recited in claim 2 wherein a plurality of checking points are formed on said jumping wire in every 20 millimetres, said checking points are formed simultaneously with said silver net, a connecting point with length of millimetres is formed also at said carbon treatment layer to monitor the resistance not more than one hundred (100) ohms.

8. A membrane switch fabricated by a method according to any one of the preceding claims.

A membrane switch comprising:

base membrane; plurality of loops on said base membrane, formed by printing a silver net onto said base membrane; a layer of anti-oxidant disposed on said silver net; an isolating treatment layer disposed on said anti-oxidant layer; and a carbon treatment layer disposed on said isolating treatment layer.

10. A method for making a membrane switch assembly, the method being substantially as hereinbefore described with reference to the accompanying Figures 5 to 12.

11. A membrane switch substantially as hereinbefore described with reference to the accompanying Figures 5 to 12.

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