Signal processing circuit substrate used for liquid crystal display unit and method of assembling the same

A signal processing circuit substrate is formed with a through-hole. A device having a variable value and including an value adjustment portion through which the variable value is adjusted is mounted on a first surface of the signal processing circuit substrate. The signal processing circuit substrate includes a flexible arch-shaped member having a height relative to the first surface of the signal processing circuit substrate. The device is electrically and mechanically fixed onto a lower surface of the member in a floating condition above the signal processing circuit substrate such that the value adjustment portion is in alignment with the through-hole so as to allow the value adjustment portion to be adjusted through the through-hole. The member is fixed at opposite edges onto the first surface of the signal processing circuit substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a signal processing circuit substrate used for a liquid crystal display unit, and more particularly to such a signal processing circuit substrate on which a device such as a resistor is mounted.

2. Description of the Related Art

There has been known a signal processing circuit substrate on which a variable resistor is mounted for optimally adjusting a supplied voltage. For instance, such a signal processing circuit substrate is equipped in a liquid crystal panel constituting a liquid crystal display unit used as a display screen of a personal computer.

FIGS. 1A and 1Billustrate a liquid crystal display panel unit including a conventional signal processing circuit substrate.FIG. 1Aincludes a plan view, a bottom view and a side view of the liquid crystal display panel unit, andFIG. 1Bis a cross-sectional view taken along the line1B—1B in FIG.1A.

As illustrated inFIGS. 1A and 1B, a liquid crystal panel unit1has an upper surface la and a lower surface1b. A rectangular liquid crystal panel2and a frame-shaped shield member3covering an outer edge of the liquid crystal panel2are arranged on or above the upper surface1a. First and second signal processing circuit substrates4aand4bare arranged on the lower surface1balong longer and shorter sides, respectively.

As illustrated inFIG. 1B, the shield3is in the form of a frame having a reverse L-shaped cross-section. The shield3covers an entire outer edge of the liquid crystal panel2, and defines an outer wall3aas a sidewall of the liquid crystal panel unit1. As illustrated inFIG. 1A, the shield3is formed with a through-hole5a. As illustrated inFIG. 1B, the through-hole5ais open also to the wall3a.

The first signal processing circuit substrate4ahas an extending portion4A in alignment with the through-hole5a.

A light-guide member7having a multi-layered structure is formed beneath a lower surface of the liquid crystal panel2, as illustrated in FIG.1B. The liquid crystal panel2together with the light-guide member7is assembled into a frame-shaped back light chassis. A light diffusion sheet7aentirely covers the light-guide member7therewith at a lower surface of the light-guide member7. The back-light chassis8has such a size that an outer edge of the liquid crystal panel2is located below the shield3.

There is a space between an outer wall of the back-light chassis8and the wall3aof the shield3below the shield3through which the through-hole5ais formed. A variable resistor6aused for optimally adjusting a supplied voltage is mounted on the extending portion4A in the space, as illustrated in FIG.1B. The variable resistor6ahas a value adjustment portion6bthrough which a resistance of the variable resistor6acan be adjusted. The variable resistor6ais positioned in the space such that the value adjustment portion6bfaces the through-hole5a.

Hence, a resistance of the variable resistor6acan be adjusted by inserting an adjuster such as a screwdriver into the space through the through-hole5a, and rotating the value adjustment portion6bby means of the adjuster. Thus, a supplied voltage can be optimized at the side of the first surface1aof the liquid crystal panel unit1.

It is necessary to adjust a resistance of the variable resistor6ain every liquid crystal panel unit1such that a supplied voltage is an optimal voltage when a direct current is turned into an alternating current in a liquid crystal display unit driven with an alternating current. If the resistance is not properly adjusted, there is likely to occur flicker, burning or sticking, and non-uniformity in display.

FIGS. 2Ato2C illustrate a liquid crystal panel unit including another conventional signal processing circuit substrate.FIG. 2Aincludes a front view, a bottom view and a side view of the liquid crystal panel unit,FIG. 2Bis a cross-sectional view taken along the line2B—2B inFIG. 2A, andFIG. 2Cis an enlarged view of a portion of the liquid crystal panel unit.

As illustrated inFIG. 2B, a liquid crystal panel unit9includes a variable resistor6dwhich is mounted on a first signal processing circuit substrate4c, in place of the variable resistor6a. The variable resistor6dincludes the value adjustment portion6bon a top thereof and an additional value adjustment portion6cat a bottom thereof.

The shield3is not formed with a through-hole such as the through-hole5a, but the first signal processing circuit substrate4cis formed with a through-hole5b. The variable resistor6dis mounted on the first signal processing circuit substrate4csuch that the additional value adjustment portion6cis located within the through-hole5b.

The other structures of the liquid crystal panel unit9are the same as the structures of the liquid crystal panel unit1illustrated inFIGS. 1A and 1B.

Hence, a resistance of the variable resistor6dcan be adjusted by inserting an adjuster such as a screwdriver into the space through the through-hole5b, and rotating the value adjustment portion6cby means of the adjuster. Thus, a supplied voltage can be optimized at the side of a second surface9bof the liquid crystal panel unit9.

The above-mentioned liquid crystal panel units1and9are designed to have a small frame and a small thickness in order to be thin and have a broad display area in response to requirements of a small size, a light weight and small power consumption in a personal computer. For instance, the liquid crystal display units1and9are designed to have a thickness in the range of 6 to 8 mm, and have an effective pixel area occupying about 90% of an area of the panel.

In addition, the liquid crystal panel units1and9have to be designed such that the value adjustment portions6band6care exposed through the through-holes5aand5b, respectively, because the variable resistors6aand6dare adjusted with an operator observing a display screen after the first signal processing circuit substrates4aand4chave been mounted on the liquid crystal panel2.

The variable resistor6awhich is adjusted at the side of the first surface1aof the liquid crystal panel unit1has a height of about 1 mm, and is lower than the variable resistor6dwhich is adjusted at the side of the second surface9aof the liquid crystal panel unit9and has a height of about 1.5 mm. Accordingly, the variable resistor6ais more appropriate for reduction in a height of a liquid crystal panel unit. However, as illustrated inFIG. 1B, it is necessary to form the through-hole5athroughout the shield3.

In the liquid crystal display panel9, a space between the liquid crystal panel2and the light-guide member7is smaller than 1.5 mm at a central area of the first signal processing circuit substrate4c. Hence, the variable resistor6ccannot be positioned in the central area of the first signal processing circuit substrate4c, and accordingly, has to be positioned in a marginal area of the first signal processing circuit substrate4cin which a sufficiently broad space can be ensured.

In addition, it is unavoidable that the shield3formed with the through-hole5awould have a reduced mechanical strength.

Furthermore, if the variable resistor is mounted on the signal processing circuit substrate in a marginal area thereof, the back-light chassis8has to be formed thin in order to ensure a sufficient space for mounting the variable resistor therein in a limited space inside the shield3. As a result, it is unavoidable that a mechanical strength of the back-light chassis8is reduced. This is quite severe condition for the shield3which is formed as narrow as possible in order to form an effective pixel area as wide as possible.

A space between the first signal processing circuit substrate4a,4cand the light guide7is almost in its limit. If the space were formed greater, the liquid crystal panel2has to be formed thinner, resulting in that it would be impossible to ensure requisite functions of the liquid crystal panel2. Hence, it is quite difficult to form the space greater.

Since the value adjustment portion6cof the variable resistor6dis exposed through the through-hole5bformed through the signal processing circuit substrate4c, an adjuster such as a screwdriver could be readily engaged to the value adjustment portion6c. On the other hand, since the value adjustment portion6bof the variable resistor6ais much spaced away from the through-hole5a, an operator has to look for the value adjustment portion6bwith an adjuster after inserting the adjuster through the through-hole5a. As a result, an operator may damage the variable resistor6awith the adjuster.

Thus, in the above-mentioned conventional liquid crystal panel units1and9, the variable resistors6aand6dhave to be positioned in a limited area, and the variable resistors6aand6dmay be damaged in assembling the liquid crystal panel units1and9, due to reduction in a mechanical strength.

In the above-mentioned liquid crystal panel units1and9, the variable resistors6aand6dare explained as examples, but the same problems as mentioned above are caused when other devices such as a capacitor are to be mounted on a signal processing circuit substrate.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems in the conventional signal processing circuit substrates, it is an object of the present invention to provide a signal processing circuit substrate which is capable of positioning a device without limitation with respect to an area in which the device is to be mounted, and avoiding reduction in a mechanical strength of a device to thereby avoid the device from being damaged in assembling.

In one aspect of the present invention, there is provided a signal processing circuit substrate used for a liquid crystal display unit, a device being mounted on a first surface of the signal processing circuit substrate, the device having a variable value and including an value adjustment portion through which the variable value is adjusted, the signal processing circuit substrate including a mounting member to which the device is electrically and mechanically connected such that the value adjustment portion faces a through-hole formed throughout the signal processing circuit substrate, the mounting member being fixed at opposite thereof onto the first surface of the signal processing circuit substrate.

For instance, the mounting member may be comprised of a flexible printed circuit.

It is preferable that the mounting member is composed of flexible material, and the device is supported by the mounting member in a floating condition above the signal processing circuit substrate.

It is preferable that the mounting member is fixed at one corner thereof onto the first surface of the signal processing circuit substrate and fixed together with terminals of the device at three corners thereof onto the first surface of the signal processing circuit substrate.

It is preferable that the device is mounted on the mounting member such that the value adjustment portion does not project beyond a second surface of the signal processing circuit substrate.

It is preferable that the through-hole has such an area that an adjuster used for adjusting the value adjustment portion can move sufficiently to be engaged with the value adjustment portion through the through-hole.

It is preferable that the area is equal to a sum of a first area actually occupied by the device and a second area in which the device is allowed to move.

The signal processing circuit substrate may further include a plate for reinforcing the mounting member which plate absorbs a compressive force exerted on the mounting member when the value adjustment portion is adjusted.

It is preferable that the plate is fixed onto the mounting member at the opposite side of the device.

The signal processing circuit substrate may further include a plurality of reinforcing pads which fix the mounting member onto the first surface of the signal processing circuit substrate.

It is preferable that the signal processing circuit substrate includes at least two reinforcing pads which are located on a diagonal line passing through a center of the mounting member.

It is preferable that the mounting member is formed with a device for preventing the mounting member from being wrongly fixed onto the signal processing circuit substrate.

It is preferable that the device is comprised of three holes which are located in no rotational symmetry about a center of the mounting member.

It is preferable that the device is comprised of three projections which are located in no rotational symmetry about a center of the mounting member.

It is preferable that the means is comprised of three marks which are located in no rotational symmetry about a center of the mounting member.

It is preferable that the mounting member is fixed onto the first surface of the signal processing circuit substrate by any one or more of soldering, application of an adhesive, screwing and welding.

For instance, the device may be a resistor, a capacitor or a laser trimming resistor.

There is further provided a signal processing circuit substrate used for a liquid crystal display unit, a device being mounted on a first surface of the signal processing circuit substrate, the device having a variable value and including an value adjustment portion through which the variable value is adjusted, the signal processing circuit substrate being formed with a through-hole, the signal processing circuit substrate including a flexible arch-shaped member having a height relative to the first surface of the signal processing circuit substrate, the device being electrically and mechanically fixed onto a lower surface of the member in a floating condition above the signal processing circuit substrate such that the value adjustment portion is in alignment with the through-hole so as to allow the value adjustment portion to be adjusted through the through-hole, the member being fixed at opposite edges onto the first surface of the signal processing circuit substrate.

For instance, the member may be comprised of a flexible printed circuit.

It is preferable that the member is fixed at one corner thereof onto the first surface of the signal processing circuit substrate and fixed together with terminals of the device at three corners thereof onto the first surface of the signal processing circuit substrate.

It is preferable that the device is mounted on the member such that the value adjustment portion does not project beyond a second surface of the signal processing circuit substrate.

It is preferable that the through-hole has such an area that an adjuster used for adjusting the value adjustment portion can move sufficiently to be engaged with the value adjustment portion through the through-hole.

It is preferable that the area is equal to a sum of a first area actually occupied by the device and a second area in which the device is allowed to move.

The signal processing circuit substrate may further include a plate for reinforcing the member which plate absorbs a compressive force exerted on the member when the value adjustment portion is adjusted.

It is preferable that the plate is fixed onto the member at the opposite side of the device.

The signal processing circuit substrate may further include a plurality of reinforcing pads which fix the member onto the first surface of the signal processing circuit substrate.

It is preferable that the signal processing circuit substrate includes at least two reinforcing pads which are located on a diagonal line passing through a center of the member.

It is preferable that the reinforcing pads are located adjacent to a bending of the member.

It is preferable that the signal processing circuit substrate includes four reinforcing pads located in a rotational symmetry about a center of the member and adjacent to a bending of the member.

It is preferable that the member is formed with means for preventing the member from being wrongly fixed onto the signal processing circuit substrate.

It is preferable that the means is comprised of three holes which are located in no rotational symmetry about a center of the member.

It is preferable that the means is comprised of three projections which are located in no rotational symmetry about a center of the member.

It is preferable that the means is comprised of three marks which are located in no rotational symmetry about a center of the member.

It is preferable that the member is fixed onto the first surface of the signal processing circuit substrate by any one or more of soldering, application of an adhesive, screwing and welding.

In another aspect of the present invention, there is provided a method of fabricating a signal processing circuit substrate used for a liquid crystal display unit, a device being mounted on a first surface of the signal processing circuit substrate, the device having a variable value and including an value adjustment portion through which the variable value is adjusted, the method including the steps of (a) mounting the device onto an upper surface of a flexible member such that the value adjustment portion upwardly faces, (b) bending the flexible member at first lines thereof towards the lower surface, (c) bending the flexible member at second lines towards the upper surface, the second lines being located between the device and the first lines, and (d) fixing the flexible member at its opposite ends onto the first surface of the signal processing circuit substrate such that the value adjustment portion is exposed through a through-hole formed through the signal processing circuit substrate.

The method may further include the step of (e) fixing a reinforcing plate onto a lower surface of the flexible member, the step (e) being carried out before the step (d).

It is preferable that the flexible member is fixed at one corner thereof onto the first surface of the signal processing circuit substrate and fixed together with terminals of the device at three corners thereof onto the first surface of the signal processing circuit substrate in the step (d).

It is preferable that the flexible member is fixed onto the first surface of the signal processing circuit substrate such that the value adjustment portion does not project beyond a second surface of the signal processing circuit substrate.

The method may further include the step of (f) fixing the flexible member onto the first surface of the signal processing circuit substrate with a plurality of reinforcing pads.

It is preferable that at least two reinforcing pads are located on a diagonal line passing through a center of the member, in the step (f).

It is preferable that four reinforcing pads are located in a rotational symmetry about a center of the member and adjacent to a bending of the flexible member, in the step (f).

There is further provided a method of fabricating a signal processing circuit substrate used for a liquid crystal display unit, a device being mounted on a first surface of the signal processing circuit substrate, the device having a variable value and including an value adjustment portion through which the variable value is adjusted, the method including the steps of (a) patterning a flexible printed circuit sheet into patterns which will make flexible printed circuits, (b) covering the flexible printed circuit sheet with an electrical insulator, (c) mounting the device on a second surface of the flexible printed circuit sheet, (d) cutting the flexible printed circuit sheet into flexible printed circuits, (e) downwardly bending the flexible printed circuit sheet at first lines across the device, (f) upwardly bending the flexible printed circuit sheet at second lines across the device, the second lines being located between the device and the first lines, and (g) fixing the flexible printed circuit sheet onto the first surface of the signal processing circuit substrate such that the value adjustment portion of the device is in alignment with a through-hole formed throughout the signal processing circuit substrate.

The method may further include the step of (h) adhering a reinforcing plate on a first surface of the flexible printed circuit sheet across a width of the flexible printed circuit sheet, the step (h) being carried out prior to the step (d).

The method may further include the step of (i) forming marks located in no rotational symmetry about a center of the printed circuit sheet.

It is preferable that the marks are comprised of holes, and the step (i) is carried out concurrently with the step (d).

It is preferable that the flexible printed circuit is fixed onto the first surface of the signal processing circuit substrate such that the value adjustment portion does not project beyond a second surface of the signal processing circuit substrate.

The method may further include the step of fixing the flexible printed circuit onto the first surface of the signal processing circuit substrate with a plurality of reinforcing pads.

It is preferable that at least two reinforcing pads are located on a diagonal line passing through a center of the flexible printed circuit.

It is preferable that four reinforcing pads are located in a rotational symmetry about a center of the flexible printed circuit and adjacent to the second lines of the flexible printed circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments in accordance with the present invention will be explained hereinbelow with reference to drawings.

FIG. 3includes a front view, a bottom view and a side view of a liquid crystal panel unit including a signal processing circuit substrate in accordance with a preferred embodiment of the present invention.

As illustrated, a liquid crystal panel unit10includes a rectangular liquid crystal panel11and a frame-shaped shield member12covering an outer edge of the liquid crystal panel11, both on an upper surface10a, and first and second signal processing circuit substrates13and14on a lower surface10b.

The liquid crystal panel unit10is designed to be thin and to have a wide display area in response to requirements of a small size, a light weight and small power consumption in a personal computer in which a liquid crystal display unit is used. For instance, the liquid crystal panel unit10has a thickness of about 4 to 8 mm, and has an effective pixel area which occupies about 90% of a panel.

The shield12is in the form of a frame having a L-shaped cross-section, and is composed of a metal plate. The shield12includes a standing wall12asurrounding the liquid crystal panel11and defining a sidewall of the liquid crystal panel unit10.

A variable resistor15is mounted on the first signal processing circuit substrate13through a flexible printed circuit16. The variable resistor15includes a resistance adjustment portion15a(see FIG.5B). By rotating the resistance adjustment portion15awith an adjuster such as a screwdriver, a resistance of the variable resistor15can be adjusted for optimally adjusting a supplied voltage. As mentioned later, the variable resistor15is mounted on the first signal processing circuit substrate13such that the resistance adjustment portion15bis exposed through a through-hole31(seeFIG. 5B) formed throughout the first signal processing circuit substrate13.

FIG. 4is an exploded perspective view of a liquid crystal module including the liquid crystal panel illustrated in FIG.3.

As illustrated inFIG. 4, a liquid crystal module17is comprised of the above-mentioned liquid crystal unit10, the above-mentioned shield12, and a back-light unit18. The liquid crystal panel unit10is integrally sandwiched between the shield12and the back-light unit18.

The first signal processing circuit substrate (source substrate)13is attached to the liquid crystal panel11at a longer side, and the second signal processing circuit substrate (gate substrate)14is attached to the liquid crystal panel11at a shorter side. A plurality of tape carrier packages (TCP)19each constituting a driver integrated circuit is attached to the first signal processing circuit substrates13at its longer side, and a plurality of tape carrier packages (TCP)20each constituting a driver integrated circuit is attached to the second signal processing circuit substrates14at its longer side.

The first and second signal processing circuit substrates13and14are connected to the liquid crystal panel11through the tape carrier packages19and20, respectively. The first and second signal processing circuit substrates13and14can be folded onto the liquid crystal panel11through the tape carrier packages19and20, respectively.

The back-light unit18is comprised of a light-guide plate22, a plurality of light diffusion sheets23and a back-light mold24, and is rectangular in shape. The back-light unit18includes a lamp (not illustrated) at a lower end of the light-guide plate22, and a lamp cable25extends from the lower end of the light-guide plate22. The lamp cable25has a connector25aat a distal end thereof. The light-guide plate22and the light diffusion sheet23are layered one on another, and integrally fixed to each other at their outer edges through the back-light mold24.

The shield12covering the back-light mold24therewith defines an outer edge of the liquid crystal module17. The light-guide plate22has a thickness gradually increasing from an upper end to a lower end. Hence, there is formed a small space between an upper portion of the light-guide plate22and the first signal processing circuit substrate13. The space is constant by virtue of a thickness of the back-light mold24entering an upper portion of the space.

The tape carrier packages19have distal ends which are arranged in a curve along an outer edge of the back-light mold24, and which are electrically connected to a thin film transistor (TFT) substrate of the liquid crystal panel11.

FIGS. 5Ato5C illustrate a part of the first signal processing circuit substrate13on which a variable resistor is mounted.FIG. 5Ais a plan view,FIG. 5Bis a cross-sectional view taken along the line5B—5B inFIG. 5A, andFIG. 5Cis a bottom view of the first signal processing circuit substrate13.

As illustrated inFIGS. 5A and 5B, a variable resistor15is mounted on a first surface13aof the first signal processing circuit substrate13, and the first signal processing circuit substrate13is formed with a rectangular through-hole31in alignment with the variable resistor15.

As mentioned earlier, the variable resistor15includes the resistance adjustment portion15. The rectangular through-hole31is designed to have such a smallest area that an adjuster used for adjusting the value adjustment portion15can move sufficiently to be engaged with the value adjustment portion15through the through-hole31, in order to prevent the variable resistor15from being damaged during adjusted with an adjuster such as a screwdriver and from making contact with the first signal processing circuit substrate13.

For instance, the rectangular through-hole31has an area equal to a sum of an area actually occupied by the variable resistor15and an area in which the variable resistor15ais allowed to move.

As illustrated inFIG. 5B, the variable resistor15is mounted not directly on the first signal processing circuit substrate13, but through the flexible printed circuit16such that the variable resistor15is in a floating condition relative to the first signal processing circuit substrate13. The flexible printed circuit16has flexibility to a stress applied thereto, and hence, absorbs such a stress therein. The variable resistor15is mounted on the flexible printed circuit16such that the resistance adjustment portion15ais exposed through the through-hole31, as illustrated inFIGS. 5B and 5C.

The variable resistor15is fixed at its surface15bopposite to the resistance adjustment portion15a, centrally onto the flexible printed circuit16which is broader than the surface15bof the variable resistor15. For instance, the variable resistor15may be soldered to the flexible printed circuit16through a pad or pads.

The flexible printed circuit16is fixedly soldered at four corners thereof onto the first surface13aof the first signal processing circuit substrate13through solders32ato32dsuch that the flexible printed circuit16entirely covers the rectangular through-hole31therewith.

The variable resistor15has three connection terminals15c. These connection terminals15care soldered together with the flexible printed circuit16onto the first signal processing circuit substrate13through the solders32ato32c.

The solders32aand32dare equally spaced away from a center of a shorter side of the flexible printed circuit16, and the solders32band32care equally spaced away from a center of another shorter side of the flexible printed circuit16. That is, the flexible printed circuit16are fixed onto the first surface13aof the first signal processing circuit substrate13through the four solders32ato32dwhich are located in symmetry about a center of the flexible printed circuit16.

When the flexible printed circuit16is fixed onto the first signal processing circuit substrate13through the solders32ato32d, the flexible printed circuit16is formed such that the resistance adjustment portion15adoes not project beyond a lower surface of the first signal processing circuit substrate13.

Thus, the flexible printed circuit16formed in a curve supports the variable resistor15in a floating condition relative to the first signal processing circuit substrate13such that the resistance adjustment portion15ais exposed through the rectangular through-hole31and that the resistance adjustment portion15adoes not project beyond the first signal processing circuit substrate13.

The flexible printed circuit16is comprised of a thin plate which can be readily bent. Since the flexible printed circuit16can be formed in a single step, the number of steps for assembling the liquid crystal panel unit10can be reduced.

Thus, the flexible printed circuit16connects the variable resistor15not only electrically but also mechanically to the first signal processing circuit substrate13, and defines a height of the variable resistor15relative to the first signal processing circuit substrate13, and can reduce a thickness of the liquid crystal panel unit10including the first signal processing circuit substrate13.

As illustrated inFIGS. 5A and 5B, a reinforcing plate33is fixed to the flexible printed circuit16in alignment with the variable resistor15at the opposite side of the variable resistor15. The reinforcing plate33is composed of the same material as a material of which the first signal processing circuit substrate13is composed, and has an area which is broader than the surface15bof the variable resistor15, but does not extend beyond the flexible printed circuit16.

The reinforcing plate33absorbs a rotational compressive force exerted on the flexible printed circuit16when the resistance adjustment portion15ais adjusted, to thereby prevent the flexible printed circuit16from being damaged.

For instance, the reinforcing plate33may be composed of glass and epoxy resin, polyethylene terephthalate (PET) or acrylic resin.

Reinforcing pads34aand34bfix the flexible printed circuit16onto the first signal processing circuit substrate13at two corners of the first signal processing circuit substrate13on a diagonal line passing through a center of the first signal processing circuit substrate13. The reinforcing pads34aand34bprevents the flexible printed circuit16from peeling off the first signal processing circuit substrate13, and absorbs a rotational force exerted on the flexible printed circuit16when the resistance adjustment portion15bis adjusted.

The reinforcing pads34aand34bmay be fixed onto the first signal processing circuit substrate13, for instance, by soldering, application of an adhesive, welding or screwing alone or in combination.

The flexible printed circuit16is designed to have three holes35located in no rotational symmetry about a center of the flexible printed circuit16for preventing the flexible printed circuit16from being wrongly positioned relative to the first signal processing circuit substrate13.

Since the flexible printed circuit16is symmetrical in a length-wise direction, the flexible printed circuit16might be positioned oppositely in a length-wise direction. However, by checking a positional relation among the holes35, it would be possible to prevent the flexible printed circuit16from being wrongly positioned, when the flexible printed circuit16is fixed onto the first signal processing circuit substrate13.

The flexible printed circuit16may be designed to include a reference mark or a projection such as a hook, in place of the holes35.

FIGS. 6A and 6Bare cross-sectional views of the flexible printed circuit16, illustrating respective steps of a method of mounting the variable resistor on the first signal processing circuit substrate13.

FIG. 6Aillustrates the flexible printed circuit16. First, as illustrated inFIG. 6B, the reinforcing plate33is fixed onto a lower surface of the flexible printed circuit16.

Then, as illustrated inFIG. 6C, the variable resistor15is mounted on an upper surface of the flexible printed circuit16such that the resistance adjustment portion15bfaces upwardly.

Then, as illustrated inFIG. 6D, the flexible printed circuit16is downwardly bent at first lines16ain the vicinity of opposite ends.

Then, as illustrated inFIG. 6E, the flexible printed circuit16is upwardly bent at second lines16bin the vicinity of the variable resistor15such that opposite ends of the flexible printed circuit16is located almost the same level as or slightly lower than the resistance adjustment portion15a.

Then, as illustrated inFIG. 6F, the flexible printed circuit16is fixed at the opposite ends thereof onto the first surface13aof the first signal processing circuit substrate13through the solders32ato32csuch that the resistance adjustment portion15ais exposed through the through-hole31and does not project beyond the surface13bof the first signal processing circuit substrate13.

FIGS. 7Ato7E are plan views of the flexible printed circuit16, illustrating respective steps of a method of mounting the variable resistor15on the first signal processing circuit substrate13.

First, as illustrated inFIG. 7A, a flexible printed circuit sheet36is patterned to define a copper pattern36awhich will make the flexible printed circuit16, and then, is covered with polyimide except areas where three pads for mounting the variable resistor15on the first signal processing circuit substrate13are located, and the solders32ato32dand the reinforcing pads34aand34bare located.

Then, as illustrated inFIG. 7B, the reinforcing plate33is adhered to a lower surface of the flexible printed circuit sheet36across a width of the flexible printed circuit sheet36.

Then, as illustrated inFIG. 7C, the variable resistors15are fixed onto an upper surface of the flexible printed circuit sheet36, for instance, by soldering.

Then, the flexible printed circuit sheet36is cut into the flexible printed circuits16. At the same time, each of the flexible printed circuits16is formed with the holes35.

Then, as illustrated inFIG. 7D, each of the flexible printed circuits16is downwardly bent at the first lines16a, as having been explained with reference to FIG.6D.

Then, as illustrated inFIG. 7E, each of the flexible printed circuits16is upwardly bent at the second lines16b, as having been explained with reference to FIG.6E.

Then, each of the flexible printed circuits16is fixed at their opposite ends onto the first signal processing circuit substrate13.

As mentioned so far, the flexible printed circuit16is fixed on the first signal processing circuit substrate13such that the resistance adjustment portion15aof the variable resistor15is exposed through the rectangular through-hole31when observed from the lower surface13bof the first signal processing circuit substrate13. Hence, an operator could readily insert an adjuster such as a screwdriver through the through-hole31from the lower surface13b, and adjust the resistance adjustment portion15a. Accordingly, an operator could adjust a resistance of the variable resistor15by rotating the resistance adjustment portion15ato optimally adjust a supplied voltage as looking at a display screen of the liquid crystal module17.

For instance, the flexible printed circuit16is comprised preferably of the following components, taking into consideration that the flexible printed circuit16preferably has a thickness and is composed of a material such that the flexible printed circuit16can be folded by a short length and can be resistive to a stress exerted thereon when the variable resistor15is adjusted:about 18 micrometers of a silver foil;about 12.5 micrometers of a base film;about 12.5 micrometers of a cover film; andabout 0.3 mm of a reinforcing plate.

Since the flexible printed circuit16is flexible enough to absorb a stress exerted thereon when the variable resistor15is adjusted, it would be possible to prevent such a stress from being applied directly to the back-light unit18. As a result, it would be possible to prevent the variable resistor15from being damaged, and further prevent degradation in display quality in a liquid crystal display unit including the signal processing circuit substrate in accordance with the embodiment.

A variable resistor including a resistance adjustment portion at one of its upper and lower surfaces is generally lower in height than a variable resistor including a resistor adjustment portion at its upper and lower surfaces. In accordance with the embodiment, it would be possible to use the former, ensuring reduction in a thickness of a liquid crystal panel including the signal processing circuit substrate in accordance with the embodiment.

Since the variable resistor15is mounted on the first signal processing circuit substrate13through the flexible printed circuit16fixed to the first signal processing circuit substrate13through the solders32ato32d, a stress exerted on the variable resistor15is leveled by the flexibility of the flexible printed circuit16, preventing the variable resistor15from being damaged and the flexible printed circuit from being torn off.

In accordance with the embodiment, if the first signal processing circuit substrate13were varied in design, it would not be necessary to prepare a variable resistor conforming to the varied signal processing circuit substrate. Merely by varying the copper pattern36aof the flexible printed circuit sheet36, the variable resistor15can be mounted on the varied signal processing circuit substrate. Thus, the signal processing circuit substrate13could have enhanced designability.

The reinforcing plate33enhances adjustability of the resistance adjustment portion15a, and prevents the flexible printed circuit16from being damaged. When adjusted, a stress including a compressive force and a rotational moment unavoidably exerts on the variable resistor15. The reinforcing plate33uniformly distributes such a stress.

The reinforcing pads34aand34bprevents the flexible printed circuit16from being peeled off the signal processing circuit substrate13, and further distributes a compressive force and a rotational force exerted on the flexible printed circuit16when the resistance adjustment portion15ais rotated by a screwdriver.

Since the resistance adjustment portion15aenters the through-hole31, a part of a height of the variable resistor15is absorbed into a thickness of the signal processing circuit substrate13, ensuring reduction in a height of the variable resistor15when mounted on the signal processing circuit substrate13.

A final bar to reduction in a thickness of a liquid crystal panel was a variable resistor. Since the above-mentioned embodiment can reduce a height of a variable resistor, it would be possible to reduce a thickness of a liquid crystal panel.

In addition, since the variable resistor15does not project beyond the signal processing circuit substrate13, it would be possible to prevent the variable resistor15from being damaged due to collision with another parts and from being short-circuited due to electrical contact with another parts.

Furthermore, since the variable resistor15is supported by the flexible printed circuit16in a floating condition relative to the signal processing circuit substrate13, it is not necessary to form a mount on the signal processing circuit substrate for supporting the variable resistor15therewith. This ensures the signal processing circuit substrate to be flat without a projection.

FIG. 8is a plan view of a signal processing circuit substrate on which a variable resistor is mounted through another flexible printed circuit37.

As illustrated inFIG. 8, the copper pattern36ainto which the flexible printed circuit sheet36is patterned is comprised of an electrical mount portion38aand a mechanical mount portion38b. The electrical mount portion38ais designed to meet a function of electrical connection, and the mechanical mount portion38bis designed to meet a function of mechanical connection. The electrical mount portion38amerely presents electrical conductivity, and the mechanical mount portion38bhas a broader area than an area of the electrical mount portion38aso as to provide a strength against rotational and compressive forces.

It is not always necessary to form the reinforcing pads34aand34bin the flexible printed circuit37illustrated inFIG. 8, however, mechanical connection could be enhanced by forming the reinforcing pads34aand34b.

FIG. 9Ais a plan view of a signal processing circuit substrate on which a variable resistor is mounted through still another flexible printed circuit39.

In comparison with the flexible printed circuit16illustrated inFIGS. 5Ato5C, the reinforcing pads34aand34bare positioned in a different location. In the flexible printed circuit39, the reinforcing pads34aand34bare positioned between first lines33aand the opposite ends of the flexible printed circuit39and just adjacent to the first lines33a. Herein, the first lines33aare similar to the first lines16aillustrated inFIG. 6Dat which the flexible printed circuit39is downwardly bent.

The flexible printed circuit39could be prevented from peeling off the first signal processing circuit substrate13due to the reinforcing pads34aand34bmore certainly than the flexible printed circuit33, and could have a greater strength against rotational and compressive forces than the flexible printed circuit33illustrated inFIGS. 5Ato5C.

In addition, an area occupied by the reinforcing pads34aand34billustrated inFIG. 9Aremain the same as an area occupied by the reinforcing pads34aand34billustrated inFIGS. 5Ato5C.

FIG. 9Bis a plan view of a signal processing circuit substrate on which a variable resistor is mounted through yet another flexible printed circuit40.

The illustrated flexible printed circuit40has four reinforcing pads34a,34b,34cand34dlocated in symmetry about a center of the variable resistor15. In the flexible printed circuit40, the reinforcing pads34ato34dare positioned between first lines40aand the opposite ends of the flexible printed circuit40and just adjacent to the first lines40a. Herein, the first lines40aare similar to the first lines16aillustrated inFIG. 6Dat which the flexible printed circuit40is downwardly bent.

The flexible printed circuit40could be prevented from peeling off the first signal processing circuit substrate13due to the reinforcing pads34ato34dmore certainly than the flexible printed circuit39illustrated inFIG. 9A, and could have a greater strength against rotational and compressive forces than the flexible printed circuit39illustrated in FIG.9A.

In the above-mentioned embodiments, the variable resistor15is explained as a device to be mounted on the signal processing circuit substrate13. However, the above-mentioned embodiments can be applied to other devices having a similar structure to the variable resistor15, such as a variable capacitor or a laser trimming resistor.

The entire disclosure of Japanese Patent Application No. 2000-64532 filed on Mar. 9, 2000 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.