Electronic device

According to one embodiment, an L-shaped printed circuit board is connected to the periphery of a film sensor at a plurality of connection portions. Long holes are each formed in the periphery of a film sensor at the center of a portion of the film sensor located between a corresponding pair of adjacent connection portions.

FIELD

Embodiments described herein relate generally to an electronic device with a touch panel, and more particularly, to an electronic device, such as a personal digital assistant (PDA) or a personal computer that is provided with a built-in touch sensor formed of a film (hereinafter referred to as a “film sensor”).

BACKGROUND

Jpn. Pat. Appln. KOKAI Publication No. 2008-234470 (Patent Document 1) discloses a tough panel in which ends of the lines of a pair of insulating-film side electrodes are connected to ends of insulating-substrate side lines by a conductive adhesive. The touch panel has a slit near a corner of the insulating film and near a connecting portion that electrically connects ends of the insulating-film side wiring and the insulating-substrate side wiring.

The slit of the insulating film prevents stress concentration in the above connection portions, when the touch panel is heated to cause deformation of the insulating film and the insulating substrate due to the difference in coefficient of thermal expansion between the film and the substrate. Namely, the slit functions to absorb deformation of the insulating film to thereby prevent stress concentration in the connection portions. As a result, detachment of the connection portions due to the stress caused by thermal expansion is prevented.

However, since the insulating film expands in all planar directions, stress occurs in, for example, connection portions between the insulating film and another substrate and between the above-mentioned lines. Namely, stress occurs in the two connection portions serving as the insulating film connection portions, whereby the above-mentioned detachment problem occurs. In particular, in the case of a large touch panel, the deformation amount of the insulating film relative to the substrate increases, which means that the problem of detachment between the insulating film and the substrate inevitably becomes conspicuous.

DETAILED DESCRIPTION

In general, according to one embodiment, a printed circuit board4is attached to the film sensor2at a plurality of attachment portions3. Holes2aare formed in the film sensor2between adjacent ones of the attachment portions3.

FIG. 1shows an outward appearance of a personal digital assistant (PDA)10as one example of an electronic device according to the embodiment.

As shown inFIG. 1, the PDA10includes a display15that contains a touch sensor (film sensor) in the form of a film. The display15provides various operation screens to a user, and functions as a user interface for enabling the user to select an item displayed on a selected screen by touching the item by, for example, a finger12or using a touch pen (not shown). The film sensor provided on the surface of the display15will be described later.

FIG. 2is a block diagram illustrating the configuration of the PDA10.

As shown inFIG. 2, the PDA10comprises a CPU14for controlling the devices incorporated in the PDA10, a display15with a film sensor described later, a memory16, such as a flash memory, for temporarily storing data, a communication unit17functioning as a connection interface to be connected to, for example, the Internet, and a recording medium18, such as an HDD or a flash memory, which has a greater memory capacity than the memory16.

The CPU14loads, in the memory16, various applications, such as an operating system (OS) and a display control application100stored in the recording medium18, thereby controlling the whole operation of the PDA10in accordance with commands supplied via the film sensor of the display15.

As shown inFIG. 3, the display control application100comprises a detection control unit101, a display selection unit102, an execution unit103and a storing unit104. The detection control unit101is connected to the film sensor described later, and detects whether a finger12of the user or a touch pen touches an item displayed on the screen of the display15. When text data is selected on the display15, the display selection unit102, for example, highlights the selected text data. The execution unit103copies, detects, pastes, cuts or searches for the selected text data. When the execution unit103searches for the selected text data, it searches a built-in dictionary or searches the Internet via the communication unit17. The storing unit104stores a display menu and/or item data (an item “copy,” an item “delete,” an item “paste,” an item “cut,” an item “search,” etc.).

FIG. 4is an exploded perspective view illustrating a sensor assembly20incorporated in the display15. The sensor assembly20comprises a film sensor2provided on the surface of the display15, a printed circuit board4attached to the reverse side of the film sensor2, a spacer6and a fixing frame8.

The film sensor2has a structure in which XY patterns (not shown) in a matrix are formed on a rectangular vinyl film, and the ends of the patterns are lead to the edges of the film. A piezo film sensor, for example, is known as the film sensor2. The film sensor2is formed of, for example, a polyethylene-based film material.

The printed circuit board4is L-shaped and provided along a pair of short and long sides of the film sensor2. The circuit board4has a circuit pattern (not shown) on a surface thereof that faces the XY patterns of the film sensor2, and has an IC chip (not shown) mounted on the other surface. The printed circuit board4is formed of glass epoxy.

When attaching the printed circuit board4to the film sensor2, the former is adhered to the sides of the latter so that the circuit pattern of the former is connected to the XY patterns of the latter via a conductive adhesive. As a result, the IC chip on the printed circuit board4is electrically connected to the XY patterns.

The spacer6is also L-shaped, and is provided along the other sides of the film sensor2. The fixing frame8is formed rectangular to cover the reverse sides of the printed circuit board4and the spacer6.

Namely, the sensor assembly20has a structure in which the fixing frame8is adhered to the reverse surface of the periphery of the film sensor2, with the printed circuit board4and the spacer6interposed therebetween.

The spacer6is provided to eliminate the step that is formed between the film sensor2and the printed circuit board4when these two elements are adhered to each other.

As shown inFIG. 1, the PDA10constructed as above contains all devices in its rectangular housing. Therefore, when the PDA10is turned on, the temperature in the housing increases with time. In particular, the backlight of the liquid crystal display (LCD), for example, is considered a main heat source.

When the PDA10is heated, the film sensor2and the printed circuit board4of the sensor assembly20are also heated, whereby they are thermally expanded to their respective degrees corresponding to their respective thermal expansion coefficients. Since the film sensor2and the printed circuit board4are electrically connected at several connection portions via the conductive adhesive as mentioned above, stress will concentrate on the connection portions due to the difference between the thermal expansion coefficients, whereby the connected portions may well be detached.

More specifically, as shown inFIG. 6, the L-shaped printed circuit board4of the embodiment is electrically connected to the film sensor2at a plurality of connection portions via a conductive adhesive3. The connection portions will now be denoted by reference number3. The connection portions3are predetermined in accordance with the circuit pattern of the printed circuit board4.

The film sensor2of the embodiment is formed of a vinyl film, and the printed circuit board4of the embodiment is formed of glass epoxy. Thus, the film sensor2and the printed circuit board4connected to each other at the connection portions3are formed of materials having different coefficients of thermal expansion.

Accordingly when the two members are simultaneously heated to a certain temperature, a different may occur in the amount of deformation between the members due to the different coefficients of thermal expansion. In the combination of the materials employed in the embodiment (i.e., the combination of vinyl and glass epoxy), when they are heated under the same conditions, the film sensor is thermally expanded by a greater ratio than the printed circuit board4.

Namely, in this case, the film sensor2is thermally expanded more greatly than the printed circuit board4between adjacent ones of the connection portions3arranged along the printed circuit board4. Accordingly, stress concentrates in the connection portions3. When the on and off operations of the PDA10are repeated to thereby repeat thermal expansion and contraction, the above-mentioned stress concentration causes shearing force to be exerted on the connection portions3, with the result that the connection portions3will be detached at worst.

To avoid this, a plurality of long holes2a(seeFIG. 5) for leaking the above-mentioned stress are formed in the peripheral portion of the film sensor2. As shown inFIG. 7, the long holes2aare formed so that when the printed circuit board4is attached to a peripheral portion of the film sensor2, each of the long holes is positioned at substantially the center of the corresponding adjacent connection portions3.

Further, the length of each long hole2a(which is elongated along the width of the printed circuit board4) is designed to a value that enables deformation of the film sensor2to be sufficiently absorbed when a tensile force or a compression force is exerted on the film sensor2between the corresponding adjacent connection portions3. More specifically, the long holes2aare at least set longer than the diameter of the connection portions3.

The long holes2amay have any arbitrary shape. However, it is desirable that the periphery of each hole is curved so as not to be sheared when the film sensor2is deformed as a result of stress concentration.

Referring now toFIG. 8, a more detailed description will be given of the function of the long holes2aof the film sensor2.

FIG. 8is a sectional view illustrating a state in which the L-shaped printed circuit board4of glass epoxy is connected to a peripheral portion of the film sensor2of vinyl via the conductive adhesive3at a plurality of connection portions.

When the sensor assembly20constructed as above is heated, the film sensor2greater in coefficient of thermal expansion than the printed circuit board4is more greatly expanded and deformed than the printed circuit board4. At this time, attention will now be paid to the portions of the two members2and4located between a certain pair of adjacent connection portions3. A compression force is exerted on the film sensor2between the certain pair of adjacent connection portions3in the directions indicated by arrows a.

When no long holes2aare formed in the film sensor2unlike the embodiment, the above-mentioned compression force causes stress in the two connection portions3. In contrast, the embodiment employs a long hole2aformed between the two connection portions3. In this case, the long hole2ais deformed to absorb the compression force to narrow the width of the long hole2a, whereby no stress occurs in the two connection portions3.

On the other hand, when the sensor assembly20is cooled from this state, the film sensor2and the printed circuit board4both contract. Contraction of the film sensor2having a relatively high coefficient of contraction can be compensated for if the long holes2aare widened, with the result that no stress occurs in the two connection portions3.

As described above, in the embodiment, since the above-mentioned long holes2aare formed in the peripheral portion of the film sensor2adhered to the printed circuit board4, stress concentration in the connection portions3due to thermal expansion can be prevented, thereby enabling the connection state of the film sensor2and the printed circuit board4to be maintained in good condition. In particular, in the embodiment, the connection state of the film sensor2and the printed circuit board4can be improved and the additional cost can be suppressed simply by forming a plurality of long holes2ain the peripheral portion of the film sensor2.

FIG. 9shows a first modification of the embodiment.

In this modification, two long holes2aare formed between each pair of adjacent connection portions3provided along the peripheral portion of the film sensor2. Thus, when the distance between each pair of adjacent connection portions3is long, two or more long holes may be formed between them.

FIG. 10shows a second modification of the embodiment, in which notches2bare formed in place of the long holes2a. Thus, the means for avoiding stress concentration due to thermal expansion are not limited to holes.

Further, although the above-described embodiments and modifications employ one or more long holes2a(or one or more notches2b) are formed between every pair of adjacent connection portions3, the invention is not limited to this. If the distance between each pair of adjacent connection portions3is short, no long holes2a(no notches2b) may be formed between them.