JP2007080643A - Key sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grounding connection capable of contributing to magnification of the degree of freedom for circuit arrangement on a printed circuit board as to a key sheet. <P>SOLUTION: An elastic sheet 15 is provided on the back of a metal frame 14. The elastic sheet 15 has an opening part 19 at the in-plane position of a base sheet 13 on the metal frame 14. The exposed surface part 20 of the metal frame 14 is exposed in the opening part 19. The grounding terminal 21 of the printed circuit board 11 is brought into contact with the exposed surface part 20. Thereby, the key sheet 12 can be grounded and connected to the board circuit of the printed circuit board 11. In this way, the exposed surface part 20 can be formed at any optional position within the surface of the base sheet 13. Therefore, the grounding terminal 21 can be designed so as to be disposed at any optional position on the printed circuit board 11 side, and this key sheet can contribute to magnification of the degree of freedom for the circuit arrangement. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a key sheet for a push button switch in an electronic device such as a mobile phone, a PDA, and a remote controller, and more particularly to an antistatic technique thereof.

In many electronic devices, the superiority of functionality alone is not always sufficient, and the market values have shifted to the advantage of design. One of the appearances of the key sheet is a key sheet that is arranged in a narrow space without separating the key tops like a tile pattern. The key sheet 1 shown in FIGS. 13 to 17 is an example, and a large number of key tops 4 are arranged in a narrow space on an elastic sheet 3 made of a rubber-like elastic body constituting the base sheet 2. The attachment form is unique, and as shown in FIG. 13, for example, it is attached so that a large number of key tops 4 are collectively exposed from the operation opening 7 formed in the housing 6 of the mobile phone 5. That is, the housing 6 of the mobile phone 5 has a feature that the housing 6 does not have a partition bar for partitioning adjacent key tops 4 as in a general mobile phone. Therefore, for the purpose of strengthening the rigidity of the base sheet 2 made of a flexible rubber-like elastic body and preventing the occurrence of distortion, the base sheet 2 is configured to have a metal frame 8 made of a thin metal plate (Patent Document 1). .
JP-A-2005-190849

  By the way, since the key sheet 1 is charged by static electricity, and the device mounted on the printed circuit board may malfunction due to the static electricity, countermeasures are required. Therefore, the present inventor forms an extension portion 9 extending to the outer edge of the base sheet 2 on the metal frame 8, for example, as shown in an enlarged view in FIG. 16, and bends the tip side downward from the outer edge of the base sheet 2. Thus, it has been studied to remove the static electricity by forming the ground connection piece 10 and conductively connecting it to a ground pad (not shown) extending to the end face of the printed board 11 as shown in FIG.

  However, when the ground connection piece 10 is formed on the outer edge of the base sheet 2, the ground pad must be designed to extend to the end face of the printed circuit board 11, and the degree of freedom in circuit arrangement is impaired. There is an inconvenience. Further, since the contact is made with the ground pad on the end face of the printed circuit board 11, there is room for improvement in connection reliability, and in particular, contact failure may occur due to the action of vibration or impact. Further, for example, as shown in FIG. 17, the key sheet 1 is held by being pressed and clamped between the back surface of the housing 6 of the mobile phone 5 and the printed circuit board 11. However, with this, it is difficult to ensure water tightness at the holding portion between the extension 9 and the housing 6. These inconveniences and difficulties are not limited to the key sheet in which the illustrated key tops are arranged in a narrow space, but have a metal frame, the key tops are spaced apart from each other, and are partitioned by a partition bar provided in the housing. The same applies to key sheets.

  The present invention has been obtained through such studies. That is, an object of the key sheet of the present invention is to realize a ground connection that can contribute to an increase in the degree of freedom of circuit arrangement on a printed circuit board. Another object of the present invention is to realize a highly reliable ground connection with a printed circuit board. Furthermore, the object of the present invention is to improve the water tightness in the press holding part between the housing and the printed circuit board.

  And this invention which solves the said subject and achieves this objective is comprised as follows.

  The present invention provides a key sheet provided with a key top on a front surface and a base sheet on which a back surface is placed on a printed circuit board, wherein a thin metal frame is provided on the base sheet, and the printed sheet is positioned in the plane of the base sheet in the metal frame A ground connection portion for ground connection to the substrate is provided.

  According to the present invention, the ground connection portion of the metal frame is in an in-plane position rather than the outer edge of the base sheet. For this reason, the grounding part on the printed circuit board side, for example, a grounding pad or a grounding terminal can be formed at an in-plane position instead of its end face. Therefore, there is no restriction condition that the ground line has to be wired to the end face of the printed circuit board. Therefore, with the key sheet of the present invention, the degree of freedom of circuit arrangement on the printed circuit board can be expanded.

  In addition, since the ground connection portion contacts at an in-plane position instead of the end face of the printed circuit board, a reliable ground connection can be realized.

  Further, since there is no ground connection portion on the outer edge of the base sheet, a pressing holding portion that presses and holds the key sheet between the housing and the printed circuit board can be secured in the outer edge region of the base sheet. Therefore, the key sheet can be securely attached.

  The base sheet provided in the key sheet of the present invention as described above is, firstly, an elastic sheet in which the base sheet is made of a rubber-like elastic body or a flexible resin film, and the metal frame provided on the surface of the elastic sheet; It can comprise as a form which has. Second, it can be configured as a form having a metal frame having a through hole and a floating support portion made of a rubber-like elastic body that supports the key top in a through hole so as to be capable of being pressed and displaced. And the earth connection part applicable to these base sheets can be comprised as follows.

  The ground connection portion of the first base sheet can be configured as an exposed surface portion of the metal frame exposed from an opening provided in the elastic sheet. The ground connection portion of the second base sheet can be configured as an exposed surface portion of a metal frame facing the printed circuit board. According to these, a reliable ground connection can be realized by bringing the ground terminal mounted so as to protrude from the printed circuit board into contact with the exposed surface portion.

  The ground connection portions of the first and second base sheets can be configured as contact protrusions formed on the metal frame so as to protrude toward the back side. According to this, it is not necessary to prepare the above-mentioned ground terminal and mount it on the printed circuit board. That is, the metal frame can be used for both the rigidity reinforcement of the base sheet and the ground connection to the printed circuit board. Therefore, it is possible to reduce the number of components mounted on the printed circuit board and simplify the mounting process. In addition, since the ground connection portion is a contact protrusion that protrudes from the back surface side, the contact protrusion can be formed by a method that does not cut the metal frame, such as drawing, and watertightness in the metal frame can be ensured. . Further, such contact protrusions can be formed by a simple processing technique such as pressing.

  The ground connection portions of the first and second base sheets can be configured as bent pieces that are formed on the metal frame so as to protrude from the back surface of the base sheet. According to this, like the above-described contact protrusion, the metal frame can be used for both rigidity reinforcement and ground connection, and the number of mounting parts can be reduced and the mounting process can be simplified. Further, the bent piece can be formed by a simple processing technique such as pressing. More specifically, the bent piece can be configured as an elastic bent piece having spring elasticity in the height direction of the gap formed between the metal frame and the printed board. Second, a ground connection through hole is formed in the printed circuit board, and it can be configured to be inserted and connected there. According to these, it is possible to realize a ground connection that is highly resistant to vibration and impact and has high reliability. In addition, according to the first elastic bent piece, since it is possible to connect to the ground by pressing contact by spring elasticity as a normal state, it is possible to realize high connection reliability particularly excellent in vibration resistance and impact resistance.

  The ground connection portions of the first and second base sheets can be configured as conductive elastic connectors having one end in conductive contact with the metal frame and the other end in conductive contact with the ground terminal of the printed circuit board. According to this, since the elastic connector is in conductive contact with the metal frame and the printed circuit board with rubber-like elasticity, a highly reliable ground connection that is resistant to vibration and impact can be realized. Such an elastic connector can be configured as a component separate from the base sheet and fixed to a thin metal plate. Alternatively, the base sheet may be formed of a rubber-like elastic body and may be configured as an integral molded body that becomes a part of the base sheet.

  When the first and second base sheets have an attachment structure in which the casing and the printed circuit board are pressed and clamped, the first and second base sheets are provided with elastic outer edges made of rubber-like elastic bodies. Can be configured. Specifically, in the case of the first base sheet, an elastic outer edge can be provided on the outer edge of the elastic sheet. Alternatively, an elastic outer edge surrounding the outer periphery of the metal frame can be provided. In the second base sheet, the elastic outer edge of the rubber-like elastic body can be integrally formed with the metal frame, and the elastic outer edge can be attached to the metal frame using an adhesive or the like. . According to these, it is possible to exhibit high water tightness at the pressing and clamping portion between the housing and the printed circuit board and a reliable holding power of the key sheet.

  According to the key sheet of the present invention, it is possible to contribute to an increase in the degree of freedom of circuit arrangement of the printed circuit board, and it is possible to provide a ground connection portion suitable for it. Therefore, with the key sheet of the present invention, it is possible to realize a ground connection suitable for high-density mounting of a printed circuit board accompanying downsizing of electronic equipment.

  According to the key sheet of the present invention, since a reliable ground connection to the printed circuit board can be realized, the static electricity charged on the key sheet can be surely removed, and the device mounted on the printed circuit board malfunctions due to the static electricity of the key sheet. This can be avoided reliably. In addition, it is possible to prevent dust from adhering due to static electricity and prevent contamination.

  According to the key sheet of the present invention, it is possible to realize high water tightness in the pressing holding portion between the housing and the printed circuit board, and therefore it is possible to prevent damage to the electronic device due to intrusion of rainwater.

  Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings.

First embodiment (FIGS. 1 and 2)
The key sheet 12 of this embodiment includes a key top 4 and a base sheet 13. The base sheet 13 includes a metal frame 14 and an elastic sheet 15.

  The metal frame 14 is formed by drilling a plurality of through holes 16 in a rectangular metal thin plate. The metal frame 14 of the present embodiment is thin and has high rigidity that suppresses the bending of the key sheet 12. Considering this required characteristic and further workability, a simple conductive stainless steel, aluminum, phosphor bronze, magnesium, gold, platinum, copper, or an alloy is used as a material. The metal frame 14 has a thickness of 0.03 mm to 0.3 mm. If it is thinner than 0.03 mm, the key sheet 12 in which the key top 4 is placed in a narrow space cannot exhibit the required rigidity, and it is difficult to form by pressing the “earth connection part” described in the second and subsequent embodiments. Become. On the other hand, if it exceeds 0.3 mm, sufficient rigidity can be exhibited, but it is difficult to achieve differentiation by thinning with market appeal when compared with other key sheets. For example, when the metal frame 14 is replaced with a resin frame made of hard resin, the thickness of the resin frame is about 0.5 mm which is the limit for thinning. However, such a thin resin frame does not provide a practically required rigidity as a narrow key sheet, and must be molded with a thickness exceeding at least 1 mm. However, with this, it is not possible to achieve a thin key sheet 12 with market appeal. On the other hand, with the metal frame 14 of the present embodiment, it is possible to realize the key sheet 12 that achieves both market thinness and surface rigidity.

  The elastic sheet 15 is a molded body of a rubber-like elastic body. As the rubber-like elastic body, synthetic rubber such as silicone rubber and ethylene propylene rubber, natural rubber, and thermoplastic elastomer such as urethane, olefin, and polyester are used. At the time of molding, the metal frame 14 is inserted into the molding die and integrally molded. The elastic sheet 15 is formed with a floating support portion 17 that fills and closes the through hole 16 of the metal frame 14, and the key top 4 is fixed thereto by an adhesive layer. The elastic sheet 14 is formed with an elastic outer edge 18 that protrudes outward from the outer edge of the metal frame 14 so as to surround the outer periphery of the rectangular metal frame 14. As shown in FIG. 2, the elastic outer edge 18 is pressed and clamped between the back surface of the housing 6 and the front surface of the printed circuit board 11, whereby the key sheet 12 is attached to the housing 6. The elastic outer edge 18 is brought into elastic contact with each other by rebound resilience following the surface shape of the back surface of the housing 6 and the surface of the printed circuit board 11. For this reason, high water tightness can be exhibited at the pressing and clamping portion, and the key sheet 12 is securely attached with high holding force.

  An opening 19 as shown in FIG. 2 is formed in the elastic outer edge 18, whereby an exposed surface portion 20 as an “earth connection portion” is formed in the metal frame 14. The opening 19 has a tapered surface with a small opening area from the opening end side to the exposed surface portion 20. The first reason is to prevent the elastic sheet 15 from peeling off by leaving as much contact area as possible with the metal frame 14. Second, when the key sheet 12 is placed on the printed board 11, the ground terminal 21 mounted on the printed board 11 fits into the opening 19, and the key sheet 12 is attached to a predetermined position on the printed board 11. This is to guide. The key sheet 12 is grounded to the printed circuit board 11 when the tip of the ground terminal 21 abuts through the opening 19.

  As described above, in the key sheet 12, the exposed surface portion 20 as the “earth connection portion” of the metal frame 14 exists at an in-plane position instead of the outer edge of the base sheet 2. For this reason, the mounting position of the ground terminal 21 on the printed circuit board 11 can be arranged in the plane of the printed circuit board 11, and the degree of freedom of circuit arrangement on the printed circuit board 11 can be expanded. In the background art, there is a restriction that the ground line extends to the outer edge of the printed circuit board 11 and the ground pad must be provided on the end surface of the printed circuit board 11. However, with the key sheet 12 of this embodiment, such a restriction is eliminated. Further, the ground terminal 21 is abutted against and brought into contact with the metal frame 14 at an in-plane position of the base sheet 2 and the printed board 11. For this reason, a reliable ground connection can be realized.

Second Embodiment [FIGS. 3 and 4]
A feature of the key sheet 22 of the present embodiment is a configuration of an “earth connection portion”. The rest of the configuration and the actions and effects resulting therefrom are the same as those of the key sheet 12 of the first embodiment.

  The “earth connection portion” of the present embodiment is formed as a semicircular contact protrusion 23 that protrudes toward the back side of the metal frame 14. The contact protrusion 23 can be formed by a simple processing technique such as pressing. On the other hand, the elastic sheet 15 is formed with a recess 24 for exposing the semicircular contact protrusion 23. Therefore, the key sheet 22 is grounded and connected to the printed circuit board 11 when the contact protrusion 23 abuts against the ground pad 25 of the printed circuit board 11 through the recess 24.

  In the key sheet 22 as described above, the use of the ground terminal 21 shown in the first embodiment can be eliminated. That is, the metal frame 14 can be used not only for reinforcing the rigidity of the base sheet 2 but also for ground connection to the printed circuit board 11. For this reason, it is possible to reduce the mounting parts of the printed board 11 and simplify the mounting process.

  Further, since the contact protrusion 23 can be formed without cutting the metal frame 14, water tightness can be secured to the metal frame 14. Therefore, the key sheet 22 can realize high waterproofness in combination with the compact pressing and clamping at the elastic outer edge 18.

Third Embodiment (FIGS. 5 and 6)
A feature of the key sheet 26 of the present embodiment is a configuration of an “earth connection portion”. The rest of the configuration and the actions and effects resulting therefrom are the same as those of the key sheet 12 of the first embodiment.

  The “ground connection portion” of the present embodiment is formed as an elastic bent piece 27 that is bent so as to protrude toward the back side of the metal frame 14 and has spring elasticity. The elastic bent piece 27 can be formed by a simple processing technique such as pressing. On the other hand, the elastic sheet 15 is formed with a recess 29 for exposing the contact portion 28 having a V-shaped cross section in the elastic bent piece 27. Therefore, the key sheet 26 is grounded to the printed circuit board 11 when the contact portion 28 of the elastic bent piece 27 abuts against the ground pad 25 through the recess 29.

  Such an elastic bent piece 27 of the present embodiment can be grounded and connected to the ground pad 25 in a normal state by pressing by spring elasticity, so that it is possible to realize high connection reliability that is particularly excellent in vibration resistance and impact resistance.

  Similarly to the second embodiment, the use of the ground terminal 21 can be abolished, and the metal frame 14 can be used not only for reinforcing the rigidity of the base sheet 2 but also for ground connection to the printed circuit board 11. Therefore, it is possible to reduce the number of mounting parts of the printed board 11 and simplify the mounting process.

  The elastic bent piece 27 is formed with a flat base end portion 30 continuous with the contact portion 28 having a V-shaped cross section. Elastic grooves 15 are filled in the grooves on both sides of the base end 30 and hardened. In this way, watertightness is secured around the elastic bent piece 27. Therefore, the key sheet 26 can realize high waterproofness in combination with the compact pressing between the elastic outer edges 18.

Fourth Embodiment (FIGS. 7 and 8)
A feature of the key sheet 31 of the present embodiment is a configuration of an “earth connection portion”. The remaining structure, operation and effect are the same as those of the key sheet 26 of the third embodiment and the key sheet 12 of the first embodiment.

  The “earth connection part” of the present embodiment is a bent piece 32 that is bent and protrudes so as to protrude toward the back side of the metal frame 14. The bent piece 32 can be formed by a simple processing technique such as pressing. The tip of the bent piece 32 is inserted into a ground connection through hole 33 formed in the printed circuit board 11 and fixed. Therefore, the key sheet 31 is restrained by the through hole 33 at the tip of the bent piece 32, so that it is possible to realize ground connection with the printed board 11 that is resistant to vibration and impact and has high reliability.

  As in the third embodiment, in the key sheet 31 of the present embodiment, the elastic sheet 15 is filled and cured in the grooves on both sides of the bent piece 32, so that watertightness is secured in the periphery thereof. Yes. Therefore, the key sheet 31 can realize high waterproofness in combination with the compact pressing and clamping at the elastic outer edge 18.

Fifth embodiment (FIGS. 9 and 10)
A feature of the key sheet 34 of the present embodiment is that a conductive elastic connector 35 is provided as an “earth connection portion”. The remaining configuration, actions and effects are the same as those of the key sheet 12 of the first embodiment.

  The elastic connector 35 has a cylindrical shape and is a molded body integrated with the elastic sheet 15. That is, the elastic connector 35 is previously molded from conductive rubber, and is inserted into a molding die together with the metal frame 14 when the elastic sheet 15 is molded, and is integrally molded. The upper end surface of the elastic connector 35 is in contact with the metal frame 14, and the key sheet 34 can be grounded to the printed circuit board 11 by bringing the lower end surface into contact with the ground pad 25. Since the elastic connector 35 comes into contact with the metal frame 14 and the ground pad 25 with rubber-like elasticity, it is possible to realize a highly reliable ground connection that is resistant to vibration and impact.

  It should be noted that a housing hole may be formed in advance in the elastic sheet 15, and a pre-formed elastic connector 35 may be inserted into the elastic sheet 15 and fixed by adhesion or the like. In addition, the magnetic conductive medium is mixed in the molding material of the elastic sheet 15, and the magnetic conductive medium is oriented in the thickness direction by applying a magnetic field in the molding die to the position where the elastic connector 35 is formed. It is also possible to form an anisotropic conductive elastic connector as an integral molded body.

Sixth Embodiment [FIGS. 11 and 12]
The base sheet 37 of the key sheet 36 according to the present embodiment has a metal frame 38 as a base. A plurality of through holes 16 are formed in the metal frame 38, and a floating support portion 17 made of a rubber-like elastic body that elastically supports the key top 4 so as to close the through holes 16 is formed. An elastic outer edge 39 made of a rubber-like elastic body is attached to the front and back surfaces of the outer edge of the metal frame 38.

  The “earth connection portion” in the present embodiment is the back surface of the metal frame 38 inside the elastic outer edge 39. As described above, also in the key sheet 36 of the present embodiment, the in-plane position of the metal frame 38 inside the elastic outer edge 39 can be used as a contact point of the ground terminal 21 of the printed circuit board 11. There is an advantage that the degree of freedom of arrangement can be expanded. In addition, since the ground terminal 21 is brought into contact with and contacted with the metal frame 38, a reliable ground connection can be realized. Further, since the elastic outer edge 39 is adhered, the key sheet 36 can be reliably held by the housing 6 and the printed board 11.

  In this embodiment, the elastic outer edge 39 is attached, but it may be integrally formed with the metal frame 38. Further, although it is fixed to the hole wall of the through hole 16, the floating support portion 17 may be formed so as to cover the front and back surfaces of the metal frame 38 around the hole edge of the through hole 16.

Modifications of Embodiments In the above embodiments, the key sheets 12, 22, 26, 31, 34, and 36 in which the adjacent key tops 4 are arranged in a narrow space are illustrated. However, it can also be applied to a key sheet in which the key tops 4 are spaced apart.

  In all of the above embodiments, the exposed surface portion 20 as the “earth connection portion”, the contact protrusion 23, the elastic bent piece 27, the bent piece 32, and the elastic connector 35 are provided in one place on the metal frame 14. However, it may be provided at a plurality of locations, and may be formed anywhere so as to correspond to the ground connection location on the printed circuit board 11 side as long as the formation position is within the plane of the metal frame 14.

  The metal frame 14 of the first to fifth embodiments is exemplified by a rectangular annular outer frame portion and an inner frame portion that partitions the inside of the outer frame portion into a grid shape. However, a metal frame having only the inner frame portion without the outer frame portion may be used. Further, a plurality of metal frames may be provided at different positions on one base sheet.

FIG. 3 is a plan view of a key sheet according to the first embodiment. FIG. 2 is an enlarged cross-sectional view of a main part showing a mounting state of the key sheet of FIG. The principal part expansion perspective view of the key sheet by 2nd Embodiment. FIG. 4 is an enlarged cross-sectional view of a main part showing a mounting state of the key sheet of FIG. The principal part expansion perspective view of the key sheet by 3rd Embodiment. FIG. 7 is an enlarged cross-sectional view of a main part showing a mounting state of the key sheet of FIG. The principal part expansion perspective view of the key sheet by 4th Embodiment. FIG. 8 is an enlarged cross-sectional view of a main part showing a mounting state of the key sheet of FIG. The principal part expansion perspective view of the key sheet by a 5th embodiment. FIG. 10 is an enlarged cross-sectional view showing a main part of the key sheet shown in FIG. FIG. 10 is a plan view of a key sheet according to a sixth embodiment. FIG. 12 is an enlarged cross-sectional view of a main part showing a mounting state of the key sheet of FIG. The external appearance perspective view of a mobile telephone provided with the key sheet by a prior art example. The top view of the key sheet | seat by one prior art example. FIG. 14 is a sectional view taken along line SA-SA in FIG. FIG. 14 is an enlarged perspective view of the SB portion in FIG. Sectional drawing which shows the use condition of the key sheet | seat shown in FIG.

Explanation of symbols

1 Key sheet
2 Base sheet
3 Elastic sheet
4 Key top
5 Mobile phone
6 Enclosure
7 Operation opening
8 Metal frame
9 Extension
10 Ground connection piece
11 Printed circuit board
12 Key sheet (first embodiment)
13 Base sheet
14 Metal frame
15 Elastic sheet
16 Through hole
17 Floating support
18 Elastic outer edge
19 opening
20 Exposed surface (ground connection)
21 Ground terminal
22 Key sheet (second embodiment)
23 Contact protrusion (ground connection)
24 recess
25 Grounding pad
26 Key sheet (Third embodiment)
27 Elastic bent piece (bent piece, ground connection)
28 Contact
29 Recess
30 Base end
31 Key sheet (4th embodiment)
32 Curved piece (ground connection)
33 Through hole
34 Key sheet (fifth embodiment)
35 Elastic connector (ground connection)
36 Key sheet (6th embodiment)
37 Base sheet
38 metal frame
39 Elastic outer edge

Claims (5)

In the key sheet provided with a base sheet on which the key top is provided on the front surface and the back surface is placed on the printed circuit board,
A key sheet characterized in that a metal frame is provided on the base sheet, and an earth connection portion for ground connection to the printed circuit board is provided at an in-plane position of the base sheet in the metal frame. The base sheet has an elastic sheet and the metal frame provided on the surface of the elastic sheet,
2. The key sheet according to claim 1, wherein the ground connection part is an exposed surface part of the metal frame exposed from an opening provided in the elastic sheet.   2. The key sheet according to claim 1, which is a contact protrusion formed on the metal frame so that the ground connection portion protrudes from the back surface of the base sheet.   2. The key sheet according to claim 1, wherein the key sheet is a bent piece formed on the metal frame so that the ground connection portion protrudes from the back surface of the base sheet.   2. The key sheet according to claim 1, wherein the ground connection portion is an elastic connector having one end in conductive contact with the metal frame and the other end in conductive contact with the ground terminal of the printed circuit board.

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