Patent Application
20100101927
The present invention relates to a key sheet, a press switch and an electronic device provided with the key sheet, and more particularly to a key sheet improved in heat radiation performance as an element useful for a portable electronic device, a press switch, and an electronic device provided with the key sheet.
In recent years, an electronic device or more specifically a portable electronic device has been needed to be improved in size, thickness and function. Therefore, it is necessary to enhance the density of electronic components to be mounted on a printed-circuit board of the portable electronic device, and to improve the portable electronic device in heat radiation performance.
As shown in
The lower housing 101 has a front member 101a and a rear member 101b. As shown in
More specifically, the flexible electrically-insulating sheet 123 has an area which corresponds to a key contact section 120, and has bores 125 as shown in
Patent document 1: Japanese Patent Laid-Open Publication 2006-310035
In the conventional press switch, the thermally-conductive sheet 123a is in contact with the printed-circuit board 121, and covered with the electrically-conductive film 123b and the key sheet 122. As a result, the conventional electronic device is increasingly reduced in heat radiation performance, and makes it difficult to diffuse heat loss from the electronic circuit 129. Further, the electrically-insulating sheet is generally low in heat conductivity in comparison with the thermally-conductive sheet. As a result, the conventional electronic device is further reduced in heat radiation performance by reason that the electrically-insulating sheet is used in the conventional electronic device.
It is therefore an object of the present invention to provide a key sheet, a press switch and an electronic device, each of which can prevent the housing the button section from being excessively heated by the electronic circuit by controlling and suppressing local elevation of temperature resulting from heat loss from the electronic circuit, and enhance heat radiation performance to effectively diffuse heat loss from the electronic circuit.
The key sheet according to the present invention comprises: a viscoelastic sheet having a viscoelastic property, and having a first surface and a second surface; a button section located on the side of the first surface of the viscoelastic sheet; a thermally-conductive sheet located along the first surface or the second surface of the viscoelastic sheet, the thermally-conductive sheet having a thermal conductivity equal to a specific value; and a contact section projected from the second surface of the viscoelastic sheet, the contact section occupies a position corresponding to the button section.
The key sheet thus constructed is increased in heat radiation performance by reason that the key sheet is in the vicinity of the electronic components mounted on the printed-circuit board, and the thermally-conductive included in the key sheet is close to external air.
In the key sheet according to the present invention, the button section may include a first button section, a second button section, and a third button section which is not on a straight line passing through the first and second button sections, the thermally-conductive sheet is in an area identified by the first to third button sections.
The key sheet thus constructed can suppress local elevation of temperature to even the temperature distribution by reason that the thermally-conductive sheet is in an area identified by the first to third button sections.
In the key sheet according to the present invention, the thermally-conductive sheet may have a first surface and a second surface, the thermally-conductive sheet is located under the condition that the second surface of the thermally-conductive sheet is in contact with the first surface of the viscoelastic sheet.
Under the condition that the second surface of the thermally-conductive sheet is in contact with the first surface of the viscoelastic sheet, the key sheet according to the present invention may further comprise an electrically-insulating cover layer having an insulating property. The electrically-insulating cover layer is in contact with the viscoelastic sheet, and covers a peripheral section of the thermally-conductive sheet.
Under the condition that the second surface of the thermally-conductive sheet is in contact with the first surface of the viscoelastic sheet, in the key sheet according to the present invention, the thermally-conductive sheet may have an opening, the contact section occupies a position of the opening, and is in contact with the first surface of the viscoelastic sheet.
The button section can be illuminated by the LED mounted on the printed-circuit board.
Under the condition that the second surface of the thermally-conductive sheet is in contact with the first surface of the viscoelastic sheet, in the key sheet according to the present invention, the thermally-conductive sheet may have a character-shaped opening.
The button section can be illuminated through the character-shaped opening.
In the key sheet according to the present invention, the thermally-conductive sheet having a first surface and a second surface, the thermally-conductive sheet may be located under the condition that the first surface of the thermally-conductive sheet is in contact with the second surface of the viscoelastic sheet.
In the key sheet according to the present invention, the thermally-conductive sheet has an opening, the contact section may occupy a position of the opening, and may be in contact with the second surface of the viscoelastic sheet.
The key sheet according to the present invention may further comprise an electrically-insulating cover layer having an insulating property, the electrically-insulating cover layer is in contact with the viscoelastic sheet, and covers a peripheral section of the thermally-conductive sheet. The electrically-insulating cover layer may have a white or glossy-colored upper section. The electrically-insulating cover layer may be white or glossy.
In the key sheet according to the present invention, the electrically-insulating cover layer may have a visible light reflective property.
The key sheet thus constructed can guide visible light to a specific section in the housing to illuminate the button sections through the electrically-insulating cover layer without irregular color. In this case, the electrically-insulating cover layer may have a white or glossy-colored upper section. The electrically-insulating cover layer may be white or glossy.
In the key sheet according to the present invention, the thermally-conductive sheet may be constituted by a sheet made of graphite.
The press switch comprises: a printed-circuit board provided with an electronic circuit, the printed-circuit board having a first surface and a second surface; a switch section located on the first surface of the printed-circuit board, the switch section having a push point to change the connection state of the electronic circuit, and a key sheet defined in claim 1, and located in relation to the push point.
The press switch thus constructed can suppress local elevation of temperature to even the temperature distribution by reason that the thermally-conductive sheet is in an area identified by the first to third button sections.
In the press switch according to the present invention, the thermally-conductive sheet may be constituted by a sheet made of electrically-conductive material, and the printed-circuit board may have an electrically-conductive layer electrically connected to the thermally-conductive sheet.
The electronic device according to the present invention comprises the above press switch.
The electronic device thus constructed can suppress local elevation of temperature to even the temperature distribution by reason that the thermally-conductive sheet is in an area identified by the first to third button sections by reason that the heat radiation performance is increased by reason that the key sheet is in the vicinity of the electronic components mounted on the printed-circuit board, and the thermally-conductive included in the key sheet is close to external air.
The term “thermally-conductive sheet” is intended to indicate a sheet larger in thermal conductivity than the electrically-insulating cover layer and other members.
The following description is directed to specific values of thermal conductivity of the thermal conductive sheet. For example, the thermally-conductive sheet may be made of graphite, and may be set to 700 (W/(m·K)) in thermal conductivity on the surface of the thermally-conductive sheet (in X-Y direction) under the condition that the thermally-conductive sheet made of graphite is 100 μm in thickness (in Z-direction). The thermally-conductive sheet may be set to 850 (W/(m·K)) in thermal conductivity in any direction on the surface (in X-Y direction) under the condition that the thermally-conductive sheet made of graphite is 70 μm in thickness (in Z-direction). The thermally-conductive sheet made of graphite may be set to 1600 (W/(m·K)) in thermal conductivity in any direction on the surface (in X-Y direction) under the condition that the thermally-conductive sheet made of graphite is 25 μm in thickness (in Z-direction).
The thermally-conductive sheet may be made of aluminum, and may be set to 237 (W/(m·K)) in thermal conductivity on the surface of the thermally-conductive sheet (in X-Y direction). The thermally-conductive sheet may be made of copper, and may be set to 398 (W/(m·K)) in thermal conductivity on the surface of the thermally-conductive sheet (in X-Y direction).
The present invention is to provide a key sheet, a press switch, and an electronic device improved in heat radiation performance can effectively diffuse heat loss from an electronic circuit and the like.
a) and 12(b) are cross sectional views showing press switches of the electronic device according to the second embodiment of the present invention.
The preferred embodiments of the present invention will be described hereinafter with reference to accompanying drawings.
a) is a perspective view showing a key sheet for press switches of the electronic device according to the first embodiment, while
As shown in
As shown in
As shown in
As shown in
The electrically-insulating sheet 13 is constituted by a sheet made of electrically-insulating resin such as for example polyethylene terephthalate (PET), and an adhesive layer or an electrically-insulating adhesive layer (not shown). Further, the electrically-insulating cover layer 15 is also constituted by a sheet made of electrically-insulating resin such as for example polyethylene terephthalate (PET).
When the click section 13a (pressure point) is pressed, the press switch 10 of the electronic circuit assumes a conduction state by reason that the first contact section 11a is electrically connected to the second contact section 11b. The click section 13a of the electrically-insulating sheet 13 on the printed circuit board 11 is constituted as a circular portion projected on the operation side of the electronic device 1, and distant from the printed circuit board 11.
Additionally, the click section 13a may not assume a convex shape when the click section 13a is not in the pushed state (a state in which the electronic device is not operated through the press switch). The click section 13a and the center section 12c may assume a predetermined position when the click section 13a is in a released state.
Further, the electrically-insulating sheet 13 may have a restorative force necessary to assume an original position. On the other hand, a member constituted as a contact section or a member to be electrically connected to the member has a restorative force necessary to assume an original position. Therefore, the click section 13a has flexibility to allow the center section 12c of the third contact section 12 to be changed in response to a force from the button section 16a.
More specifically, as shown in
As shown in
The third contact section 12 allows the center section 12c to function as a movable contact point. When the button section 16a is pushed down by the user, the third contact section 12 sags downwards in the center in response to a force from the button section 16a of the key sheet 16 through the click section 13a of the electrically-insulating sheet 13 to assume a state in which the first contact section 11a is electrically connected to the second contact section 11b through the third contact section 12.
When, on the other hand, the force for pushing the button section 16a of the key sheet 16 is released, the third contact section 12 assumes a state in which the first contact section 11a is not electrically connected to the second contact section 11b, and restores to its original state.
The electrically-insulating sheet 13 is adhered to and retained by the printed-circuit board 11 as an insulation protection layer, while the third contact section 12 is adhered to the electrically-insulating sheet 13.
The electrically-insulating cover layer 15 is adhered to the thermally-conductive sheet 14 as an insulation protection layer. The thermally-conductive sheet 14 is located throughout all parts of the body. The upper surface and the peripheral portion of the thermally-conductive sheet 14 are covered with the electrically-insulating sheet 15. It is preferable that the peripheral portion of the thermally-conductive sheet 14 be electrically insulated by the electrically-insulating sheet 15.
In this embodiment, the third contact section 12 is retained and adhered by an adhesive layer (not shown) to the click section 13a of the electrically-insulating sheet 13 under the condition that the lower portions of the third contact section 12 are positioned and electrically connected to the second contact sections 11b on the printed-circuit board 11.
The key sheet 16 is located along one side of the electrically-insulating sheet 13, while the printed-circuit board 11 is located along the other side of the electrically-insulating sheet 13. The button sections 16a operatively arranged on the key sheet 16 are exposed as keys through openings of the housing member 17a on the side to be operated. On the other hand, the contact sections 16d from the lower side of the key sheets 16 are respectively in contact with the click section 13a of the electrically-insulating sheet 13.
As shown in
In the electronic device 1, a plurality of electronic components (not shown) are mounted on the printed-circuit board 11 as a control circuit for communications and input/output control and accommodated in the lower housing 17. When the electronic device 1 is running, heat generating components 19 such as power amplifiers and the like mounted on the printed-circuit board 11 generates heat loss in the lower housing 17. As a result, the heat generating components 19 and its surrounding components are heated, and produce an increase in temperature the inside of the lower housing 17.
In this state, heat loss from the printed-circuit board 11 is diffused through the thermally-conductive sheet 14 formed along the viscoelastic sheet 16b of the key sheet 16 (in a spreading direction). As a result, the printed-circuit board 11 can suppress local elevation of temperature of the button sections 16a and the housing member 17a in the vicinity of the heat generating components 19 of the electronic device 1.
In the conventional press switch disclosed in the patent document 1, a thermally-conductive sheet in contact with the printed-circuit board is covered with an electrically-conductive film and a key sheet, and away from external air. As a result, it is difficult to effectively diffuse heat loss from the heat-generating electronic component 19. The heat radiation performance is decreased. On the other hand, the heat radiation performance of the electronic device 1 is increased by reason that the thermally-conductive sheet 14 included in the key sheet 16 is close to external air in the press switch 10 according to the first embodiment.
The thermally-conductive sheet 14 is improved in radiation effect under the condition that, for example, the thermally-conductive sheet 14 is made of graphite, and 700 or more (W/(m·K)) in thermal conductivity in the direction of the thermally-conductive sheet 14. As a result, thermally-conductive sheet 14 can be reduced in thickness to 100 μm or less. Therefore, the key sheet 16 is reduced in thickness. The electronic device 1 can be further reduced in thickness by comprising a press switch 10 reduced in thickness.
The computer simulation has been executed under the condition that the housing member 17a on the side to be operated is 0.9 millimeters in thickness and 0.3 (W/(m·K)) in thermal conductivity, the printed-circuit board 11 is 0.5 millimeters in thickness and 35 (W/(m·K)) in thermal conductivity, the viscoelastic sheet 16b is 0.5 millimeters in thickness (the height of the viscoelastic sheet 16b above the lower end of the projection 16c is 0.1 millimeters) and 0.2 (W/(m·K)) in thermal conductivity, the heat-generating electronic component 19 is 1.0 millimeters in thickness and 1 (W/(m·K)) in thermal conductivity, the thermally-conductive sheet 14 is constituted by a sheet made of graphite, the electrically-insulating sheet 13 is 0.1 millimeters in thickness and 700 (W/(m·K)) in thermal conductivity (in a direction along its surface), and the printed-circuit board 11 has a section corresponding to the button sections 16a, the section is covered with the electrically-insulating sheet 13.
From this computer simulation, it will be understood that, in the electronic device 1 according to the first embodiment, the temperature of the housing member 17a is equalized within the section covered with the electrically-insulating sheet 13, and kept below the designated level. Further, from
On the other hand,
In this case, the temperature distribution of the electronic device shown in
From a result obtained from a computer simulation on the first embodiment shown in
The button sections 16a of the key sheet 16 can be illuminated with light from light emitting diodes 18 mounted on the printed-circuit board 11 through openings of the thermally-conductive sheet 14. The button section 16a of the key sheet 16 can be illuminated with light from the light emitting diode 18 mounted on the printed-circuit board 11 through character-shaped openings of the thermally-conductive sheet 14.
In this embodiment, the electrically-insulating cover layer 15 or the viscoelastic sheet 16b has a notched section corresponding to a contact section (not shown), the thermally-conductive sheet 14 is exposed and electrically connected to the grounded pattern of the printed-circuit board 11 through conductive layer and metal spring. Therefore, the thermally-conductive sheet 14 electrically connected to the grounded pattern of the printed-circuit board 11 can prevent the electronic device 1 from functioning improperly by preventing static electrical charge from flowing into each contact section.
The electronic device can be improved without being increased in the number of assembling process by reason that the key sheet 16 includes a thermally-conductive sheet 14 provided along the viscoelastic sheet 16b, the thermally-conductive sheet 14 is stacked when the key sheet 16 is mounted on the electronic device.
Even if the thermally-conductive sheet made of graphite is reduced in thickness, the thermally-conductive sheet reduced in thickness can be enhanced in thermal conductivity on the basis of conventionally-known technique for enhancing the thermal conductivity of the thermally-conductive sheet made of graphite and reduced in thickness.
As another example, the thermally-conductive sheet may be made of aluminum, and set to 237 (W/(m·K)) in thermal conductivity in a direction based on the surface of the thermally-conductive sheet (in X-Y direction). The thermally-conductive sheet may be made of copper, and set to 398 (W/(m·K)) in thermal conductivity in a direction based on the surface of the thermally-conductive sheet (in X-Y direction).
As shown in
As shown in
More specifically, as shown in
The third contact section 12 sags downwards in the center in response to a force from the button section 26a of the key sheet 26 through the click section 13a of the electrically-insulating sheet 13 to assume a state in which the first contact section 11a is electrically connected to the second contact section 11b through the third contact section 12. When, on the other hand, the force from the button section 26a of the key sheet 26 through the click section 13a of the electrically-insulating sheet 13 is released from the third contact section 12, the third contact section 12 is away from the first contact section 11a to assume a state in which the first contact section 11a is not electrically connected to the second contact section 11b through the third contact section 12.
More specifically, as shown in
On the other hand, the key sheet 26 includes a thermally-conductive sheet 24 and an electrically-insulating cover layer 25 on the opposite side of the button sections 26a. Here, the thermally-conductive sheet 24 is larger in thermal conductivity the electrically-insulating cover layer 25 of the key sheet 26 and the printed-circuit board 11, and may be made of, for example, graphite or metal. The electrically-insulating cover layer 25 may be made of, for example, resin such as for example polyethylene terephthalate.
Here, each of the thermally-conductive sheet 24 and the electrically-insulating cover layer 25 has, for example, a circular-shaped opening based on the profile shape of the contact section 26d of the key sheet 26. As shown in
As shown in
As shown in
From the foregoing description, it will be understood that the key sheet according to the second embodiment of the present invention can effectively diffuse heat loss from the printed-circuit board 11 to prevent local elevation of temperature by reason that the heat loss from the printed-circuit board 11 is diffused through the thermally-conductive sheet 24 located along the viscoelastic sheet 26b.
Further, the button sections 26a of the key sheet 26 can be evenly illuminated with light from the light emitting diode mounted on the printed-circuit board 11 through an opening of the contact section of the thermally-conductive sheet 24.
In the second embodiment, the button section 26a of the key sheet 26 can be evenly illuminated with light from the light emitting diode mounted on the printed-circuit board 11 through an opening for the contact section 26d by reason that part or all of the electrically-insulating cover layer 25.
As shown in 12(b), the electrically-insulating cover layer 25 may be constituted by a transparent sheet. The electrically-insulating sheet 27 may be constituted by a white or glossy sheet. Additionally, the electrically-insulating sheet 27 may be constituted by a white or glossy sheet made of resin such as for example polyethylene terephthalate, and may have openings based on the profile shape of the contact sections 26d of the key sheet 26.
In the key sheet thus constructed, the opening of the electrically-insulating sheet 27 is larger in size than that of the transparent electrically-insulating sheet, and smaller in size than or equal to that of the thermally-conductive sheet. As a result, the passage of light from the LED 18 mounted on the printed-circuit board 11 to the button section 26a of the key sheet 26 can be increased in comparison with the construction shown in
In the second embodiment, the thermally-conductive sheet 24 is electrically connected to the grounded pattern of the printed-circuit board 11 through conductive layer and metal spring. As a result, the thermally-conductive sheet 14 electrically connected to the grounded pattern of the printed-circuit board 11 can prevent the electronic device 1 from functioning improperly by preventing static electrical charge from flowing into each contact section.
From the foregoing description, it will be understood that the electronic device according to the second embodiment of the present invention can be improved without being increased in the number of assembling processes by reason that the key sheet 26 is constituted by a layered sheet including a thermally-conductive sheet 24 located along the viscoelastic sheet 26b.
From the foregoing description, it will be understood that the key sheet according to the present invention can effectively diffuse heat loss from heat-generating electronic components to prevent local elevation of temperature by reason that the heat loss from heat-generating electronic components is diffused through the thermally-conductive sheet located along the viscoelastic sheet, and useful for a small and thin-model electronic device to be frequently carried and touched with one's hand.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/051901 | 2/5/2007 | WO | 00 | 8/4/2009 |
