JPH044335Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a key unit used in electronic equipment such as a microwave oven, and particularly to a so-called membrane key unit that utilizes the bending deformation of a film.

[Conventional technology]

Conventional examples of this type of key unit are shown in FIGS. 4 and 5.

FIG. 4 is a longitudinal cross-sectional view of the main part of the key unit, in which a pair of upper and lower contact sheets 2 and 3 are overlapped in the figure with one insulating sheet 1 in between.
The character sheet 4 is stacked on the contact arrangement portion 2a side of the upper contact sheet 2, while the lower contact sheet 3
A reinforcing plate 5 made of an iron plate or the like is stacked on the side of the contact arrangement portion 3a.

FIG. 5 is a plan view of the surface of the lower contact sheet 3 viewed from the upper contact sheet 2 side, and on the contact sheet 3 there are a plurality of electrical circuit patterns 6 _G made of silver paste, carbon paste, etc. , 6 _A , 6 _B
is printed, while the cable part 3 of the contact sheet 3
In b, the electrical circuit patterns 6 _G , 6 _A and 6 _B are covered with an insulating tape 7 . Upper contact sheet 2
also has almost the same configuration as the lower contact sheet 3,
The insulating tapes 7 and 8 pasted on each contact sheet 2 and 3 insulate the upper and lower contact sheets 2 and 3 and the adjacent electrical circuit patterns in each contact sheet 2 and 3, preventing foreign matter from entering between these. This prevents short connections.

Among the electrical circuit patterns 6 _G , 6 _A , and 6 _B , the electrical circuit patterns 6 _A and 6 _B constitute a part of the keypad matrix, respectively, and are LSIs whose voltage changes as shown by symbols A and B in FIG. 6, respectively. While the key reading signal from the contact sheet 3 is applied, the electric circuit pattern 6 _G arranged so as to surround the outer periphery of the contact sheet 3 functions as a ground pattern, and is designated by the symbol G in FIG.
As shown in , the voltage is maintained at approximately 0V.

In addition, this type of key unit uses a signal transmission system in which a voltage of approximately -15V is normally applied to the circuit patterns _6A and _6B , and increases to approximately 0V only when a signal is input. For example, the circuit pattern 6 _A and the circuit pattern 6 _G which is always kept at 0V
(ground pattern), there is normally a potential difference of about 15V.

The key unit having the above configuration is installed in a device such as a microwave oven.
A microwave oven has also been manufactured in which the cable parts 2b, 3b are located below the microwave oven body, and the cable parts 2b, 3b are exposed downward from the microwave oven main body. In this case, the upper edges of the insulating tapes 7 and 8 extend vertically to the cable portion 2.
Each electric circuit pattern 6 _G arranged in parallel on b, 3b,
It intersects 6 _A and 6 _B and is located almost horizontally.

[The problem that the idea attempts to solve]

However, as mentioned above, especially in a device having a structure in which the cable portion of the key unit is exposed downward, there is a problem in that short circuits are likely to occur in the electrical circuit pattern. In other words, when wiping dirt off the front panel of a microwave oven using a solution such as water or detergent, the solution that flows down the front panel will also adhere to the cable of the key unit and flow down. If there is even a slight gap between the upper edges of the insulating tapes 7 and 8, the insulating tapes penetrate into the gap and remain. As a result, the adhesive force at the upper edges of the insulating tapes 7, 8 decreases, the gap widens, and the amount and length of penetration along the upper edges of the insulating tapes 7, 8 gradually increases. The circuit also wraps around from _the front panel side to the printed side of the circuit pattern, and as _shown in _FIG . This results in a situation where the solution L that bridges the patterns 6 _G , 6 _A , and 6 _B remains for a long time.

As mentioned above, in the above electric circuit pattern, there is usually a potential difference of about 15V between the electric circuit pattern 6 _A and the electric circuit pattern 6 _G (ground pattern), so the above-mentioned intrusion solution L is applied to these electric circuits. When the patterns 6 _A and 6 _G are bridged, a current flows between the two electric circuit patterns 6 _A and 6 _G via this solution L.
At this time, among the materials of the electrical circuit pattern, silver is easily ionized positively under the above-mentioned electrical conditions, so at this time, the solution L bridging between the electrical circuit patterns 6 _A and 6 _G is
This silver ion Ag ⁺ becomes easier to move inside. That is,
In the relationship of the potential difference between the electric circuit patterns 6 _A and 6 _G , the silver ions Ag ⁺ move from the electric circuit pattern 6 _G toward the electric circuit pattern 6 _A side.

If such a phenomenon is repeated over a long period of time, the electrical circuit patterns _6A and _6G will eventually be short-circuited by the silver, causing an error in the signal reading operation of the key unit.

In the above configuration example, the circuit pattern _6A and the circuit pattern _6B are both maintained at about -15V in a normal state with no signal input, and normally no potential difference occurs between them, as shown in FIG. A-B
As shown in , since the potential difference that occurs for a short time when a signal is input is AC-like, the phenomenon that causes the movement of silver ions Ag ⁺ as described above does not occur, but between the circuit patterns 6 _B and 6 _G Then, a similar mechanism causes a short circuit between the electrical circuit patterns.

In order to prevent this phenomenon, if we try to prevent the solution from adhering to the key unit or from penetrating into the key unit itself, the prevention structure will become complicated and the cost will increase significantly, so there is no practical countermeasure. It cannot be.

The present invention has been devised in consideration of the above conventional problems, and its purpose is to provide a key unit that can reliably prevent short-circuit accidents between electrical circuit patterns caused by adhesion of solution.

[Means to solve the problem]

In order to achieve the above object, the key unit of the present invention is such that the cable part of the contact sheet, in which the terminal ends of a plurality of electrical circuit patterns are arranged in parallel, is covered with insulating tape except for the end regions, and each electrical circuit pattern is In the key unit assembled so that the edge of the insulating tape intersecting with the contact sheet is located approximately horizontally, the edge of the insulating tape The insulating tape is characterized in that a bridging prevention means for preventing it from remaining along the insulating tape is provided near the edge of the insulating tape.

[Effect]

In the above, near the edge of the insulating tape,
For example, a waterproof resist ink applied to cover this edge to prevent solution from entering the edge, or an insulating tape that crosses the edge and penetrates at a position between each circuit pattern. A bridging prevention means is further provided, such as by providing an aperture to prevent bridging. For this reason, the solution that adheres to the surface of the contact sheet and flows down, for example when the waterproof resist ink described above is provided, flows down beyond the waterproof resist ink without touching the edges of the insulating sheet. Therefore, short circuits between the electrical circuit patterns due to the adhesion of the solution are prevented. Also,
For example, if the above opening is provided, even if the solution remains along the edge of the insulating tape,
This residual solution becomes separated at the position of the opening and does not create a bridge between the electrical circuit patterns, so that, similarly to the above, short circuits between the electrical circuit patterns due to adhesion of the solution are prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a vertical cross-sectional view showing the main parts of the key unit of this embodiment, and is
A pair of contact sheets 12 and 13 are stacked so as to face each other. The character sheet 14 is stacked on the surface (upper surface in the figure) of the contact arrangement section 12a of the outer contact sheet 12 located on the upper side in the figure, while the back surface of the contact arrangement section 13a of the inner contact sheet 13 A reinforcing plate 15 is superimposed on the bottom surface (in the figure).

FIG. 2 is a plan view of the inner contact sheet 13 viewed from the outer contact sheet 12 side, and the contact placement portion 13a of the contact sheet 13 is coated with a material such as silver paste or carbon paste. A plurality of electrical circuit patterns 16 _G , 16 _A , 16 _B are printed. Further, the inner contact sheet 13 is provided with a cable portion 13b that is connected to the contact arrangement portion 13a and has a narrow shape.
Above are the electric circuit patterns 16 _G , 16 _A , 16 _B.
In order to electrically connect the cable to the outside, the terminal ends of each of the electrical circuit patterns 16 _G , 16 _A , and 16 _B are formed in a shape that extends parallel to each other at a predetermined pitch to the terminal end of the cable section 13b. .

Most of the area of the cable portion 13b except for both ends is covered with an insulating tape 17. Then, waterproof resist ink 19 is applied to the contact arrangement part 13a and the cable part 1 so as to cover the edge of the insulating tape 17 on the contact arrangement part 13a side.
It is applied to cover the boundary area with 3b.

As the resist ink 19, polyester ink is suitable due to printability, viscosity, waterproof properties, etc., but UV type, epoxy type, etc. can also be used.

On the other hand, the outer contact sheet 12 also has substantially the same structure as the inner contact sheet 13, and the first
As shown in the figure, the cable portion 12b
There is an insulating tape 18 covering the electric circuit pattern 16.
is pasted, and waterproof resist ink 20 is applied to the boundary area between the contact placement part 12a and the cable part 12b so as to cover the edge of the insulating tape 18 on the contact placement part 12a side. There is.

The key unit having the above structure is installed, for example, in a microwave oven. In this case, the character sheet 14 superimposed on the outer contact sheet 12 is exposed on the front operation section of the microwave oven main body. In some cases, this assembly positions the cable portions 12b and 13b of the key unit on the lower side, and in this case, conventionally,
As mentioned above, the wiping solution used to remove dirt, such as water and detergent, remains along the upper edge of the insulating tape covering the cable section, resulting in short circuits between the circuit patterns. Ta.

However, in the configuration of the above embodiment,
Since the upper edges of the insulating tapes 17 and 18 are respectively covered with waterproof resist inks 19 and 20 as a bridging prevention means, it is difficult for the solution to enter and remain along the upper edges of the tapes as in the conventional case. Things will disappear. As a result, it is possible to avoid the occurrence of a short circuit caused by movement of silver ions Ag ⁺ due to bridging of the solution between the electrical circuit patterns 16 _G , 16 _A and 16 _B , which has conventionally occurred. Further, in the above, it is possible to prevent short circuits with a simple structure of applying waterproof resist ink 19, 20 to cover the edges of insulating tapes 17, 18,
It can be manufactured at extremely low cost.

Next, another embodiment of the present invention will be described with reference to FIG.

In this embodiment, as shown in FIG.
The circuit pattern 16 G ′, on the edge of the insulating tape 17 ′ that covers the circuit patterns 16 _G ′, 16 _A ′, 16 _B ′ on the cable portion 13 b ′ of the contact sheet 13 _′ ,
_16A ', a bridging prevention opening 21 is formed as a bridging prevention means that penetrates the contact sheet 13'. As a result, adjacent electric circuit patterns 16
The solution entering between _G ' and _16A ' is separated into the circuit pattern _16G ' side and the circuit pattern _16A ' side.

In this case, for example, the solution L' that has entered from the circuit pattern 16 _G ' (ground pattern) side is prevented from flowing into the circuit pattern 16 _A ' side by the opening 21, so that the solution L' enters the circuit pattern 16 _G ', 16 Bridging caused by the solution _L ' is prevented not only between the circuit patterns _16G ' and _16B ', but also between the circuit patterns 16G' and 16B', thereby preventing a short circuit between them. Although this opening 21 itself is a factor that allows solution to enter, the opening 21
The presence of the solution that has entered the circuit pattern 16 is connected to the solution L' on _{the G} ' (ground pattern) side and the circuit pattern 16.
There is no problem because the solution is reliably separated from the solution L'' on the _A ' side.Also, if a large amount of solution enters, filling the entire opening 21, the circuit patterns _16G ' and _16A ' will be temporarily disconnected. Although it is bridged by the solution, there is no problem because the solution is also separated by the opening 21 within a short time.

[Effect of idea]

As described above, in the key unit of the present invention, the cable portion of the contact sheet in which the terminal ends of a plurality of electrical circuit patterns are arranged in parallel is covered with insulating tape except for the end region, and the In the key unit assembled so that the edge of the insulating tape is located approximately horizontally, the solution attached to the surface of the contact sheet and flowing down is placed along the edge of the insulating tape so that the solution that adheres to the surface of the contact sheet and flows down bridges each electrical circuit pattern. A bridging prevention means for preventing the insulating tape from remaining is provided near the edge of the insulating tape.

This prevents the solution from remaining along the edges of the insulating tape and bridging the circuit patterns, thereby preventing short circuits between the circuit patterns caused by the adhesion of the solution. play.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of the main part showing one embodiment of the present invention, Fig. 2 is a plan view of the lower contact sheet, and Fig. 3
The figure is a plan view of main parts showing another embodiment of the present invention.
5 is a plan view of the lower contact sheet, and FIG. 6 is a waveform diagram showing the voltage applied to the electric circuit pattern and the potential difference between the patterns. 11 is an insulating sheet, 12 is an outer contact sheet,
12b is a cable part, 13 is an inner contact sheet,
13b is a cable part, 14 is a character sheet, 15 is a reinforcing plate, 16, 16A, 16B, 16G are electrical circuit patterns, 17, 18 are insulating tapes, 19, 20 are waterproof resist ink (bridging prevention means), 21 is a This is a bridging prevention opening (bridging prevention means).

Claims (1)

[Claims for Utility Model Registration] A cable portion of a contact sheet in which the terminal ends of a plurality of electrical circuit patterns are arranged in parallel is covered with insulating tape except for the end regions, and the insulating tape intersects with each electrical circuit pattern. In a key unit assembled so that the edge is located approximately horizontally, the solution that adheres to the surface of the contact sheet and flows down remains along the edge of the insulating tape so as to bridge between each electrical circuit pattern. A key unit characterized in that a bridging prevention means for preventing this is provided near an edge of the insulating tape.