Light exposure device, image forming apparatus, light reception device, and image reading apparatus

An LED head includes a base material having one or more wiring pattern formation surfaces and one or more metal wiring patterns formed on the one or more wiring pattern formation surfaces. When the occupancy ratio of the one or more metal wiring patterns in a first region of a substrate is A, and the occupancy ratio of the one or more metal wiring patterns in a second region of the substrate is B, the LED head satisfies 0.75≤A/B≤1 or 0.75≤B/A≤1.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light exposure device that includes a substrate provided with a semiconductor element.

2. Description of the Related Art

In general, a light exposure device including a substrate provided with a light emitting element (for example, a light emitting diode) as a semiconductor element is used in an image forming apparatus, such as a printer, a copy machine, a facsimile machine, and a multi-function machine, which employs an electrophotographic method. For example, the light emitting element is fixed on a base material of the substrate, and a metal wiring pattern (for example, printed wiring, wire bonding pad, etc. on the substrate) electrically connected with the light emitting element is formed on the base material. This light exposure device irradiates light on a surface of a photoreceptor drum in the image forming apparatus and forms an electrostatic latent image, by causing the light emitting element to emit light in accordance with image data (for example, refer to patent reference 1: Japanese Patent Application Publication No. 2009-73041).

SUMMARY OF THE INVENTION

The temperature of the substrate is increased by the light emission of the light emitting element in the above light exposure device, and the base material of the substrate and the metal wiring pattern formed on the base material expands in some cases. In these cases, the substrate tends to warp, depending on wiring pattern structure of the metal wiring pattern on the base material. For example, when the wiring pattern structure (for example, the area of the metal wiring pattern) is asymmetric in a sub-scanning direction of the light exposure device, there is a problem that the substrate tends to warp in the sub-scanning direction due to a rise of the substrate temperature. When the substrate warps in the sub-scanning direction, the position of the light irradiated on the surface of the photoreceptor drum shifts, and the quality of printing by the image forming apparatus decreases.

In order to solve the above problem, a purpose of the present invention is providing a light exposure device that can reduce the warpage of the substrate even when the temperature of the substrate of the light exposure device rises.

Means for Solving the Problem

A light exposure device includes a substrate being longer in a first direction and a plurality of light emitting elements fixed on the substrate. The substrate includes a base material having one or more wiring pattern formation surfaces and one or more metal wiring patterns formed on the one or more wiring pattern formation surfaces. The substrate is divided into two regions by a boundary line which is a center line of the wiring pattern formation surface in a second direction orthogonal to the first direction. One region of the two regions is a first region, and the other region of the two regions is a second region. The light exposure device satisfies 0.75≤A/B≤1 or 0.75≤B/A≤1, where A is a ratio of a sum of one or more areas of the one or more metal wiring patterns in the first region to a sum of one or more areas of the one or more wiring pattern formation surfaces in the first region, and B is a ratio of a sum of one or more areas of the one or more metal wiring patterns in the second region to a sum of one or more areas of the one or more wiring pattern formation surfaces in the second region.

The present invention can provide a light exposure device that can reduce the warpage of the substrate even when the temperature of the substrate of the light exposure device rises.

MODE FOR CARRYING OUT THE INVENTION

First Embodiment

<Configuration of Image Forming Apparatus1>

FIG. 1is a cross-sectional view schematically illustrating a configuration of an image forming apparatus1that includes LED heads13Bk,13Y,13M,13C as light exposure devices according to a first embodiment of the present invention.

The image forming apparatus1is an electrophotographic color printer that employs an electrophotographic method, for example. The image forming apparatus1includes image forming units10Bk,10Y,10M,10C, a transfer unit20, a paper feeding mechanism30(a paper feeding unit), and a fuser40(a fusing unit). Note that the number of image forming units is not limited to four.

The image forming units10Bk,10Y,10M,10C include photoreceptor drums11Bk,11Y,11M,11C as image carriers, charging rollers12Bk,12Y,12M,12C as electric chargers, LED heads13Bk,13Y,13M,13C as light exposure devices, developing rollers14Bk,14Y,14M,14C as developing units (developer carriers), toner supplying rollers15Bk,15Y,15M,15C as developer supplying members, developing blades16Bk,16Y,16M,16C as developer regulating members, and toner cartridges17Bk,17Y,17M,17C as developer storage units, respectively.

The image forming units10Bk,10Y,10M,10C are four image forming units that are independent from each other. The image forming units10Bk,10Y,10M,10C are arranged in a direction (the direction indicated by an arrow e) in which a paper sheet P as a recording medium is conveyed.

The image forming units10Bk,10Y,10M,10C form, on the paper sheet P, images that are black, yellow, magenta, and cyan visible images (for example, toner images as developer images) respectively, by using the electrophotographic method.

In addition to the paper sheet P, an Overhead Projector (OHP) sheet, an envelope, copy paper, specialty paper, etc. may be used as the recording medium.

The charging rollers12Bk,12Y,12M,12C electrically charge uniformly the surfaces of the photoreceptor drums11Bk,11Y,11M,11C, respectively.

The LED heads13Bk,13Y,13M,13C are fixed above the photoreceptor drums11Bk,11Y,11M,11C, so as to face the photoreceptor drums11Bk,11Y,11M,11C, respectively. The LED heads13Bk,13Y,13M,13C perform light exposure. For example, the LED heads13Bk,13Y,13M,13C each cause the LEDs to emit light in accordance with image data, and form electrostatic latent images on the surfaces of the photoreceptor drums11Bk,11Y,11M,11C.

The developing rollers14Bk,14Y,14M,14C supply toner as developer to the photoreceptor drums11Bk,11Y,11M,11C respectively, to form toner images.

The toner supplying rollers15Bk,15Y,15M,15C are pressed against the surfaces of the developing rollers14Bk,14Y,14M,14C, respectively. The toner supplying rollers15Bk,15Y,15M,15C supply the toner stored in the toner cartridges17Bk,17Y,17M,17C to the developing rollers14Bk,14Y,14M,14C, respectively.

The developing blades16Bk,16Y,16M,16C are pressed against the developing rollers14Bk,14Y,14M,14C, respectively. The developing blades16Bk,16Y,16M,16C create thin layers of the toner on the surfaces of the developing rollers14Bk,14Y,14M,14C, respectively.

The transfer unit20is fixed below the photoreceptor drums11Bk,11Y,11M,11C. The transfer unit20includes transfer rollers21Bk,21Y,21M,21C as transfer devices, and a conveyance belt22as a conveyance member. The conveyance belt22is supported in a rotatable manner by rollers, and conveys the paper sheet P in the direction indicated by the arrow e, for example.

The transfer rollers21Bk,21Y,21M,21C are located to face the photoreceptor drums11Bk,11Y,11M,11C with the conveyance belt22in between. The transfer rollers21Bk,21Y,21M,21C electrically charge the surface of the paper sheet P such that the polarity of the paper sheet is opposite to the polarity of the toner, and transfer the toner images on the photoreceptor drums11Bk,11Y,11M,11C to the paper sheet P, respectively.

The paper feeding mechanism30is located at a lower portion in the image forming apparatus1, for example. The paper feeding mechanism30supplies the paper sheet P toward the conveyance belt22. The paper feeding mechanism30includes a hopping roller31, a registration roller32, a paper sheet containing cassette33as a medium container, and a sheet color measuring unit34.

The sheet color measuring unit34detects the color of the paper sheet P supplied from the paper sheet containing cassette33.

The fuser40is located at a downstream side of the conveyance belt22in the conveyance direction in which the paper sheet P is conveyed. The fuser40includes a heating roller41and a backup roller42. The fuser40fixes the toner transferred on the paper sheet P onto the paper sheet P by applying heat and pressure to the toner.

Further, the image forming apparatus1may include a pinch roller or an ejection roller for ejecting the paper sheet P to the outside of the image forming apparatus1. Further, a paper sheet stacker for stacking the paper sheet P ejected from the inside of the image forming apparatus1may be formed in an upper part of the image forming apparatus1.

<Structure of Light Exposure Device>

The structures of the LED heads13Bk,13Y,13M,13C as the light exposure devices will be described below.

FIG. 2is a perspective view schematically illustrating a structure of a LED head13.FIG. 3is a cross-sectional view along a line C3-C3inFIG. 2. In the present embodiment, the LED heads13Bk,13Y,13M,13C have the same structure as each other, and thus each of the LED heads13Bk,13Y,13M,13C is referred to as “LED head13”. Note that the LED heads13Bk,13Y,13M,13C may have different structures from each other, and at least one of the LED heads13Bk,13Y,13M,13C may have the structure of the LED head13.

The LED head13includes a substrate131, a plurality of light emitting elements132as semiconductor elements, a converging lens133, and a support member134(a lens array holder).

The substrate131is a multi-layer substrate that has a plurality of layers (wiring layers). In other words, the substrate131is an N-layer substrate (N is an even number equal to or greater than 2). In the present embodiment, the substrate131which is a two-layer substrate will be described. However, the substrate131may be formed to have one or more odd-number layers. That is, the substrate131may be an N-layer substrate (N is an integer equal to or greater than 1).

The substrate131includes a base material135(also referred to as “base member”) and one or more metal wiring patterns136(hereafter, metal wiring patterns136). The base material135has one or more wiring pattern formation surfaces135a(hereafter, wiring pattern formation surfaces135a) on which the metal wiring patterns136are formed. Further, the substrate131may be provided with a driver IC (Integrated Circuit) for controlling the plurality of light emitting elements132.

The base material135is a base member of a glass epoxy material, such as Flame Retardant Type 4 (FR-4), for example. Although in the present embodiment the metal wiring patterns136are copper foil patterns made of copper, the material of the metal wiring patterns136is not limited to copper. The thermal expansion coefficient of the base material135is 11 ppm/° C. to 15 ppm/° C. for example, and the thermal expansion coefficient of the metal wiring patterns136is 16 ppm/° C. to 17 ppm/° C. for example.

The length of the base material135in the main scanning direction is 250 mm to 350 mm, for example. In the present embodiment, the length of the base material135in the main scanning direction is 300 mm, and the length of the base material135in the sub-scanning direction is 7 mm. The thickness of the base material135is 0.8 mm to 1.5 mm, for example. In the present embodiment, the thickness of the base material135is 1.0 mm.

Each light emitting element132is an LED chip that irradiates light, for example. In the present embodiment, an LED array chip as a light emitting element array is composed of a plurality of LED chips. The plurality of light emitting elements132are fixed on the substrate131(specifically, the wiring pattern formation surface135a) so as to face the photoreceptor drum (for example, the photoreceptor drum11Bk,11Y,11M, or11C) with the converging lens133in between. In the example illustrated inFIG. 2, the plurality of light emitting elements132are arranged in the main scanning direction. Although in the present embodiment the LED head13has a resolution of 600 dpi, the LED head13may have a resolution other than 600 dpi.

The converging lens133converges the light radiated from each light emitting element132. The converging lens133is supported by the support member134so as to face the photoreceptor drum (for example, the photoreceptor drum11Bk,11Y,11M, or11C). In other words, the converging lens133is disposed between the plurality of light emitting elements132and the photoreceptor drum (for example, the photoreceptor drum11Bk,11Y,11M, or11C). The light converged by the converging lens133is irradiated to an image formation position11aon the surface of the photoreceptor drum. The converging lens133is a rod lens array composed of a plurality of rod lenses, for example.

A distance L1from the light emitting elements132to the converging lens133is equal to a distance L2from the converging lens133to the image formation position11a.

The support member134supports the substrate131and the converging lens133. The support member134is a die-cast product produced by injecting aluminum material into a die, for example.

As illustrated inFIG. 3, a space composed of a first space R1, a second space R2, and a third space R3is formed inside the support member134, for example. The converging lens133is contained in the first space R1that faces the photoreceptor drum (for example, the photoreceptor drum11Bk,11Y,11M, or11C). The second space R2is formed between the substrate131and the converging lens133. The third space R3is wider than the second space R2in the sub-scanning direction. Therefore, a step is formed on an inner surface of the support member134. The substrate131is in contact with a contact surface134aformed by this step.

In order to prevent light and a foreign object from entering into the support member134, a gap between the support member134and the converging lens133is covered by a cover member137, for example. The cover member137is made of silicone material, for example.

Further, the LED head13may include a base member138as a press member for pressing the substrate131onto the contact surface134aof the support member134. The base member138is formed of elastic, flexible material, e.g., a thermoplastic resin. In the present embodiment, a general-purpose engineering plastic consisting of a glass fiber reinforced polyamide is used as the resin. Thus, the heat resistance, load-deflection temperature characteristics, and the like of the base member138can be improved, and the elastic force of the base member138can be stabilized for a long period.

FIG. 4Ais a plan view schematically illustrating a structure of a front side of the substrate131, andFIG. 4Bis a plan view schematically illustrating a structure of a back side of the substrate131.FIG. 5is a cross-sectional view along a line C5-C5inFIG. 4A.

The substrate131is longer in a first direction (also referred to as longer side direction or longitudinal direction). In other words, the substrate131extends in the first direction. The first direction is the main scanning direction, and a second direction (also referred to as shorter side direction or lateral direction) orthogonal to the first direction is the sub-scanning direction.

The substrate131is divided into two regions by a boundary line t which is a center line of the wiring pattern formation surface135ain the second direction. One region of the two regions is a first region A1. The other region of the two regions is a second region B1. The boundary line t is a center line (imaginary line) that passes through the center of the substrate131in the sub-scanning direction.

In the present embodiment, the sum of the areas in the layers from the first layer to the N-th layer in the first region A1and the sum of the areas in the layers from the first layer to the N-th layer in the second regions B1are the same as each other. However, the areas in the layers from the first layer to the N-th layer in the first region A1and the areas in the layers from the first layer to the N-th layer in the second region B1may differ from each other. Further, the area of the first region A1and the area of the second region B1may differ from each other in each layer.

The metal wiring patterns136are formed on the wiring pattern formation surfaces135aof the base material135. In the present embodiment, the wiring pattern formation surface135aon a front side of the base material135in the first region A1is referred to as a wiring pattern formation surface D1; the wiring pattern formation surface135aon the front side of the base material135in the second region B1is referred to as a wiring pattern formation surface D2; the wiring pattern formation surface135aon the back side of the base material135in the first region A1is referred to as a wiring pattern formation surface D3; and the wiring pattern formation surface135aon the back side of the base material135in the second region B1is referred to as a wiring pattern formation surface D4.

The metal wiring patterns136are copper foil patterns formed from a copper foil, for example. However, the metal wiring patterns136may be wiring patterns formed of a material other than copper. For example, the metal wiring patterns136may be formed of a material including at least one of gold, silver, aluminum, nickel, and palladium.

For example, the copper foil patterns are formed by etching a copper foil on a copper-clad laminated plate, forming copper plating, and etching this again. The metal wiring patterns136include the copper foil patterns and copper plating. Further, the metal wiring patterns136include patterns of various shapes, such as a pad-like shapes and a pattern of lines.

In the following, the metal wiring pattern136formed in the first region A1is referred to as a metal wiring pattern136a(first metal wiring pattern), and the metal wiring pattern136formed in the second region B1is referred to as a metal wiring pattern136b(second metal wiring pattern). The metal wiring patterns136aare formed on the wiring pattern formation surfaces D1and D3, and the metal wiring patterns136bare formed on the wiring pattern formation surfaces D2and D4. In the present embodiment, the metal wiring patterns136aand136bare formed of the same material as each other.

The metal wiring patterns136mainly serve a function as lines for supplying the light emitting elements132with an electric current. However, all the metal wiring patterns136are needless to be electrically connected to the light emitting elements132. In the present embodiment, the metal wiring patterns136aand136bon the wiring pattern formation surfaces D1and D2are used as lines for supplying the light emitting elements132with an electric current, and the metal wiring patterns136aand136bon the wiring pattern formation surfaces D3and D4are dummy patterns.

For electrically connecting each of the light emitting elements132with the substrate131, the metal wiring patterns136binclude wiring pattern components each formed like a pad, as illustrated inFIG. 4A, for example. In the present embodiment, the pad-like wiring pattern components concentrate in the second region B1. Hence, in some cases, the occupancy ratio (residual copper ratio) of the metal wiring patterns136ain the first region A1and the occupancy ratio (residual copper ratio) of the metal wiring patterns136bin the second region B1differ from each other.

The occupancy ratio (residual copper ratio) of the metal wiring patterns136is a ratio of the areas of the metal wiring patterns136(for example, the copper foil patterns and the copper plating) to the total area of a certain region. In other words, the occupancy ratio (residual copper ratio) of the metal wiring patterns136is a ratio of the sum of the areas of the metal wiring patterns136in a certain region to the sum of the areas of the wiring pattern formation surfaces135ain the region.

For example, the occupancy ratio (residual copper ratio) of the metal wiring pattern136in the first region A1of the first layer is a ratio of the sum of the area of the metal wiring pattern136aon the wiring pattern formation surface D1to the total area of the wiring pattern formation surface D1. For example, the occupancy ratio of the metal wiring patterns136in the first region A1in the layers from the first layer to the second layer is a ratio of the sum of the areas of the metal wiring patterns136aon the wiring pattern formation surfaces D1and D3to the sum of the areas of the wiring pattern formation surfaces D1and D3.

In the same way, the occupancy ratio (residual copper ratio) of the metal wiring patterns136in the second region B1of the first layer is a ratio of the sum of the areas of the metal wiring patterns136bon the wiring pattern formation surface D2to the total area of the wiring pattern formation surface D2. For example, the occupancy ratio of the metal wiring patterns136in the second region B1in the layers from the first layer to the second layer is a ratio of the sum of the areas of the metal wiring patterns136bon the wiring pattern formation surfaces D2and D4to the sum of the areas of the wiring pattern formation surfaces D2and D4.

When the occupancy ratio of the metal wiring pattern136ain the first region A1of the first layer (i.e., the wiring pattern formation surface D1) is Aa %, and the occupancy ratio of the metal wiring pattern136bin the second region B1of the second layer (i.e., the wiring pattern formation surface D4) is Bb %, the LED head13satisfies 0.75×Bb≤Aa≤Bb or 0.75×Aa≤Bb≤Aa (i.e., 0.75≤Aa/Bb≤1 or 0.75≤Bb/Aa≤1). Accordingly, the warpage of the substrate131can be reduced, and the fluctuation of the radiation position of the light radiated from the plurality of light emitting elements132can be reduced.

Further, when the occupancy ratio of the metal wiring patterns136bin the second region B1of the first layer (i.e., the wiring pattern formation surface D2) is Ba %, and the occupancy ratio of the metal wiring patterns136ain the first region A1of the second layer (i.e., the wiring pattern formation surface D3) is Ab %, the LED head13satisfies 0.75×Ba≤Ab≤Ba or 0.75×Ab≤Ba≤Ab (i.e., 0.75≤Ab/Ba≤1 or 0.75≤Ba/Ab≤1). Accordingly, the warpage of the substrate131can be reduced.

Further, in the present embodiment, when the occupancy ratio of the metal wiring patterns136ain the first region A1in the layers from the first layer to the second layer is A %, and the occupancy ratio of the metal wiring patterns136bin the second region B1in the layers from the first layer to the second layer is B %, the LED head13satisfies 0.75×B≤A≤B or 0.75×A≤B≤A (i.e., 0.75≤A/B≤1 or 0.75≤B/A≤1). Accordingly, the warpage of the substrate131can be reduced effectively, and the fluctuation of the radiation position of the light radiated from the plurality of light emitting elements132can be reduced effectively.

When the area of the wiring pattern formation surface135a(each of the wiring pattern formation surfaces D1and D3) of each layer in the first region A1and the area of the wiring pattern formation surface135a(each of the wiring pattern formation surfaces D2and D4) of each layer in the second region B1are equal to each other, the relationship between the occupancy ratio of the metal wiring patterns136ain the first region A1and the occupancy ratio of the metal wiring patterns136bin the second region B1can be expressed by the relationship between the areas of the metal wiring patterns136ain the first region A1and the areas of the metal wiring patterns136bin the second region B1.

In this case, when the sum of the area of the metal wiring pattern136ain the first region A1of the first layer (i.e., the wiring pattern formation surface D1) is Aa, and the sum of the area of the metal wiring pattern136bin the second region B1of the second layer (i.e., the wiring pattern formation surface D4) is Bb, the LED head13satisfies 0.75×Bb≤Aa≤Bb or 0.75×Aa≤Bb≤Aa (i.e., 0.75≤Aa/Bb≤1 or 0.75≤Bb/Aa≤1).

In the same way, when the sum of the areas of the metal wiring patterns136bin the second region B1of the first layer (i.e., the wiring pattern formation surface D2) is Ba, and the sum of the areas of the metal wiring patterns136ain the first region A1of the second layer (i.e., the wiring pattern formation surface D3) is Ab, the LED head13satisfies 0.75×Ba≤Ab≤Ba or 0.75×Ab≤Ba≤Ab (i.e., 0.75≤Ab/Ba≤1 or 0.75≤Ba/Ab≤1).

Further, when the total area of the wiring pattern formation surfaces135a(the wiring pattern formation surfaces D1and D3) in the first region A1in the layers from the first layer to the second layer and the total area of the wiring pattern formation surfaces135a(the wiring pattern formation surfaces D2and D4) in the second region B1in the layers from the first layer to the second layer are equal to each other, the relationship between the occupancy ratio of the metal wiring patterns136ain the first region A1in the layers from the first layer to the second layer and the occupancy ratio of the metal wiring patterns136bin the second region B1in the layers from the first layer to the second layer can be expressed by the relationship between the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the second layer and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the second layer.

In this case, when the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the second layer is A, and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the second layer is B, the LED head13satisfies 0.75×B≤A≤B or 0.75×A≤B≤A (i.e., 0.75≤A/B≤1 or 0.75≤B/A≤1).

<Operation of Image Forming Apparatus1>

The operation of the image forming apparatus1will be described below.

When the image formation operation in the image forming apparatus1is started, the paper sheet P in the paper sheet containing cassette33is fed toward the registration roller32by the hopping roller31. Subsequently, the paper sheet P is fed from the registration roller32to the conveyance belt22, and is conveyed to the image forming units (the image forming units10Bk,10Y,10M,10C) as the conveyance belt22rotates.

In the image forming units10Bk,10Y,10M,10C, the surfaces of the photoreceptor drums11Bk,11Y,11M,11C are electrically charged by the charging rollers12Bk,12Y,12M,12C respectively, and electrostatic latent images are formed by the light emission of the LED heads13Bk,13Y,13M,13C.

Thin layers of toner on the developing rollers14Bk,14Y,14M,14C are attracted electrostatically onto the surfaces of the photoreceptor drums11Bk,11Y,11M,11C, respectively. Accordingly, toner images of respective colors based on the electrostatic latent images formed on the photoreceptor drums11Bk,11Y,11M,11C are formed on the photoreceptor drums11Bk,11Y,11M,11C.

The toner images of the respective colors are transferred onto the paper sheet P by the transfer rollers21Bk,21Y,21M,21C. Therefore, a color toner image is formed on the paper sheet P.

After the transfer process, the residual toner on the photoreceptor drums11Bk,11Y,11M,11C can be removed by cleaning devices, for example.

The paper sheet P on which the toner image is formed is sent to the fuser40. In the fuser40, the toner image is fused on the paper sheet P, and a color image is created. The paper sheet P on which the color image is created can be ejected to the paper sheet stacker by the ejection roller and the pinch roller, for example.

The color image is formed on the paper sheet P by the above process.

The effect of the LED head13(for example, the LED heads13Bk,13Y,13M,13C) as the light exposure device according to the first embodiment will be described below.

In general, when an electrostatic latent image is formed by an LED head in an image forming apparatus that employs the electrophotographic method, light emission by LEDs of the LED head causes heat to be generated in the LEDs. The heat is transferred to a substrate of the LED head, and a base material and a metal wiring pattern on the substrate are expanded by the heat in some cases. For example, when the occupancy ratio of the metal wiring patterns136on the base material135in the first region A1differs from the occupancy ratio of the metal wiring patterns136on the base material135in the second region B1, the substrate131tends to warp in the sub-scanning direction.

In an image forming apparatus that uses an LED head of the same size as the LED head13used in the present embodiment, in particular, an LED head that has a resolution of 600 dpi, when a substrate of the LED head greatly warps, a color shift remarkably occurs in the image formation and printing quality significantly reduces. Hence, it is desirable to reduce the warpage of the substrate of the LED head, from the view point of printing quality.

FIG. 6is a table illustrating the amount of warpage of the substrate131in relation to the relationship between the occupancy ratio A % of the metal wiring patterns136ain the first region A1and the occupancy ratio B % of the metal wiring patterns136bin the second region B1when the temperature of the substrate131rises from 25° C. to 70° C. The amount of warpage of the substrate131illustrated inFIG. 6is calculated as described next. the positions (dot positions) of the light radiated from the light emitting elements132when the temperature of the substrate131rises from 25° C. to 70° C., are detected on the basis of the sub-scanning direction (also referred to as Y direction), and a regression line is calculated based on the detected values. On the basis of the calculated regression line (Y=0), the amount of warpage of the substrate131illustrated inFIG. 6is calculated by subtracting the sum of the differences between each detected value on a −Y side and the regression line from the sum of the differences between each detected value on a +Y side and the regression line. The amount of warpage of the substrate131is desirably within 40 μm from the view point of printing quality.

As illustrated inFIG. 6, when the ratio R (i.e., A/B or B/A) between the occupancy ratio A % of the metal wiring patterns136ain the first region A1and the occupancy ratio B % of the metal wiring patterns136bin the second region B1satisfies 0.9≤R≤1 (i.e., 0.9≤A/B≤1 or 0.9≤B/A≤1), the amount of warpage of the substrate131is 10 μm. When the ratio R satisfies 0.75≤R≤1 (i.e., 0.75≤A/B≤1 or 0.75≤B/A≤1), the amount of warpage of the substrate131is 30 μm. When the ratio R satisfies 0.70≤R≤1 (i.e., 0.70≤A/B≤1 or 0.70≤B/A≤1), the amount of warpage of the substrate131is 40 μm.

The result illustrated inFIG. 6indicates that, when the ratio R satisfies 0.70≤R<0.75, there is not a sufficient margin from a threshold value of color shift generation, and thus it is desirable that the ratio R satisfies 0.75≤R≤1. Further, when the ratio R satisfies 0.9≤R≤1, there is more sufficient margin from the threshold value of color shift generation, and the printing quality of the image forming apparatus1can be increased.

As described above, when the occupancy ratio of the metal wiring patterns136ain the first region A1is A %, and the occupancy ratio of the metal wiring patterns136bin the second region B1is B %, the LED head13according to the first embodiment satisfies 0.75×B≤A≤B or 0.75×A≤B≤A (i.e., 0.75≤A/B≤1 or 0.75≤B/A≤1). Therefore, it is possible to provide the LED head13capable of reducing the warpage of the substrate131can be provided even when the temperature of the substrate131rises. In particular, the LED head13can make it difficult for the substrate131to warp in the sub-scanning direction.

As described above, the LED head13according to the first embodiment can suppress the amount of warpage of the substrate131in the sub-scanning direction within 30 μm. Accordingly, when the electrostatic latent image is formed on the photoreceptor drum in the image forming apparatus1, the positional shift of the electrostatic latent image formed on the photoreceptor drum can be prevented, and high quality printing can be performed, for example.

Further, when the relationship between the occupancy ratio A % of the metal wiring patterns136ain the first region A1and the occupancy ratio B % of the metal wiring patterns136bin the second region B1satisfies 0.9×B≤A≤B or 0.9×A≤B≤A (i.e., 0.9≤A/B≤1 or 0.9≤B/A≤1), the printing quality of the image forming apparatus1can be further increased.

Further, even when the external environment of the image forming apparatus1changes, in particular even when the air temperature rises, warpage of the substrate131in the sub-scanning direction is unlikely to occur, and the printing quality of the image forming apparatus1can be increased.

First Variant Example of First Embodiment

FIGS. 7A and 7Bare plan views schematically illustrating the structure of a substrate131aof an LED head as a light exposure device according to a first variant example of the first embodiment. Specifically,FIG. 7Ais a plan view schematically illustrating the structure of a front side of the substrate131a, andFIG. 7Bis a plan view schematically illustrating the structure of a back side of the substrate131a.FIG. 8is a cross-sectional view along a line C8-C8inFIG. 7A.

The structure of the metal wiring patterns136aand136bof the substrate131ais applicable to the substrate131of the LED head13according to the first embodiment. That is, the structure of the metal wiring patterns136aand136bof the substrate131ais applicable to at least one of the layers (wiring layers) of the substrate131of the LED head13according to the first embodiment.

The metal wiring pattern136aon the wiring pattern formation surface D1is formed in a reflectively inverted wiring pattern (wiring pattern structure) of the metal wiring pattern136bon the wiring pattern formation surface D4. In other words, the metal wiring pattern136aon the wiring pattern formation surface D1and the metal wiring pattern136bon the wiring pattern formation surface D4are reflectively symmetrical (line symmetry) to each other. In the same way, the metal wiring patterns136bon the wiring pattern formation surface D2are formed in reflectively inverted wiring patterns of the metal wiring patterns136aon the wiring pattern formation surface D3. In other words, the metal wiring patterns136bon the wiring pattern formation surface D2and the metal wiring patterns136aon the wiring pattern formation surface D3are reflectively symmetrical (line symmetry) to each other.

That is, the metal wiring patterns136of the first layer are formed in reflectively inverted wiring patterns of the metal wiring patterns136of the second layer. In other words, the metal wiring patterns136of the first layer and the metal wiring patterns136of the second layer are reflectively symmetrical to each other. Thus, when the occupancy ratio of the metal wiring patterns136ain the first region A1in the layers from the first layer to the second layer is A %, and the occupancy ratio of the metal wiring patterns136bin the second region B1in the layers from the first layer to the second layer is B %, the LED head according to the first variant example of the first embodiment satisfies A=B. However, the occupancy ratio of the metal wiring patterns136ain the first region A1and the occupancy ratio of the metal wiring patterns136bin the second region B1are needless to be strictly the same as each other. Thus, the LED head according to the first variant example of the first embodiment satisfies 0.75×B≤A≤B or 0.75×A≤B≤A (i.e., 0.75≤A/B≤1 or 0.75≤B/A≤1) in the same way as the first embodiment.

In other words, when the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the second layer is A, and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the second layer is B, the LED head according to the first variant example of the first embodiment satisfies A=B. In this case, the amount of the metal wiring patterns136ain the first region A1in the layers from the first layer to the second layer and the amount of the metal wiring patterns136bin the second region B1in the layers from the first layer to the second layer are desirably equal to each other. However, the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the second layer and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the second layer are needless to be strictly equal to each other.

The LED head according to the first variant example of the first embodiment has the same effect as the LED head13described in the first embodiment. Further, the warpage of the substrate131acan be prevented more effectively by satisfying the relationship of A=B as described above. Accordingly, the printing quality in the image forming apparatus1can be increased.

Second Variant Example of First Embodiment

FIG. 9is a plan view schematically illustrating the structure of a substrate131bof an LED head as a light exposure device according to a second variant example of the first embodiment. The structure of the metal wiring patterns136aand136bof the substrate131bis applicable to the substrate131of the LED head13according to the first embodiment. That is, the structure of the metal wiring patterns136aand136bof the substrate131bis applicable to at least one of the layers (wiring layers) of the substrate131of the LED head13according to the first embodiment.

In at least one of the first region A1and the second region B1, a plurality of metal wiring patterns are arranged in the main scanning direction, and the plurality of metal wiring patterns are formed in a divided manner from each other. In other words, in at least one of the first region A1and the second region B1, the metal wiring patterns are formed intermittently in the main scanning direction. In the example illustrated inFIG. 9, a plurality of metal wiring patterns136bare arranged in the main scanning direction, and the plurality of metal wiring patterns136bare formed in a divided manner from each other in the second region B1of the substrate131b.

Each of the metal wiring patterns136bcan be used for different purposes from each other, such as electric power supply and data transmission. In other words, the plurality of metal wiring patterns136bare divided from each other, and thus can transmit signals that differ from each other. Further, the LED head according to the second variant example of the first embodiment has the same effect as the LED head13described in the first embodiment.

Third Variant Example of First Embodiment

FIG. 10is a plan view schematically illustrating the structure of a substrate131cof an LED head as a light exposure device according to a third variant example of the first embodiment. The structure of the metal wiring patterns136aand136bof the substrate131cis applicable to the substrate131of the LED head13according to the first embodiment. That is, the structure of the metal wiring patterns136aand136bof the substrate131cis applicable to at least one of the layers (wiring layers) of the substrate131of the LED head13according to the first embodiment.

In the substrate131c, at least one of the metal wiring patterns136aand136bis formed continuously in the main scanning direction. In other words, in at least one of the first region A1and the second region B1, the metal wiring pattern is formed continuously in the main scanning direction. Accordingly, even when the moisture of the base material135fluctuates (moisture removal or moisture absorption), the warpage of the substrate131cin the sub-scanning direction can be reduced. In the example illustrated inFIG. 10, both of the metal wiring patterns136aand136bare formed continuously in the main scanning direction. Accordingly, the warpage of the substrate131cin the sub-scanning direction can be effectively reduced as compared with a substrate on which one of the metal wiring patterns136aand136bis formed continuously in the main scanning direction.

The metal wiring patterns136aand136bformed continuously in the main scanning direction can be used as power supply lines or ground connection lines, for example. Further, the LED head according to the third variant example of the first embodiment has the same effect as the LED head13described in the first embodiment.

Second Embodiment

FIGS. 11A to 11Dare plan views schematically illustrating the structure of a substrate231of an LED head as a light exposure device according to a second embodiment of the present invention. Specifically,FIG. 11Ais a plan view schematically illustrating the structure of a first layer of the substrate231(the structure of a front side of the substrate231) of the LED head according to the second embodiment;FIG. 11Bis a plan view schematically illustrating the structure of a second layer of the substrate231(the structure as seen from the front side of the substrate231);FIG. 11Cis a plan view schematically illustrating the structure of a third layer of the substrate231(the structure as seen from a back side of the substrate231); andFIG. 11Dis a plan view schematically illustrating the structure of a fourth layer of the substrate231(the structure of the back side of the substrate231).FIG. 12is a cross-sectional view along a line C12-C12inFIG. 11A.

The LED head according to the second embodiment differs from the LED head13according to the first embodiment in that the LED head according to the second embodiment includes the substrate231of a four-layer substrate, and is the same as the LED head13in other points. Specifically, the substrate231of the LED head according to the second embodiment differs from the substrate131of the LED head13in that the substrate231includes the second layer (wiring pattern formation surfaces D5and D6) and the third layer (wiring pattern formation surfaces D7and D8) which are intermediate layers. The LED head according to the second embodiment is applicable to the image forming apparatus1, in place of the LED head13according to the first embodiment.

In the following, the second embodiment will be described by using the same reference signs as the elements described in the first embodiment for the elements that are the same as or corresponding to the elements described in the first embodiment.

The substrate231is longer in the first direction. In other words, the substrate231extends in the first direction. The first direction is the main scanning direction, and the second direction orthogonal to the first direction is the sub-scanning direction.

In the present embodiment, the wiring pattern formation surface135aon the first layer (the front side of the base material135) in the first region A1is referred to as wiring pattern formation surface D1; the wiring pattern formation surface135aon the first layer in the second region B1is referred to as wiring pattern formation surface D2; the wiring pattern formation surface135aon the fourth layer (the back side of the base material135) in the first region A1is referred to as wiring pattern formation surface D3; and the wiring pattern formation surface135aon the fourth layer in the second region B1is referred to as wiring pattern formation surface D4.

Further, in the present embodiment, the wiring pattern formation surface on the second layer in the first region A1is referred to as wiring pattern formation surface D5; the wiring pattern formation surface on the second layer in the second region B1is referred to as wiring pattern formation surface D6; the wiring pattern formation surface on the third layer in the first region A1is referred to as wiring pattern formation surface D7; and the wiring pattern formation surface on the third layer in the second region B1is referred to as wiring pattern formation surface D8.

the one or more metal wiring patterns136a(hereafter, metal wiring patterns136a) are formed on the wiring pattern formation surfaces D1, D3, D5, and D7, and the one or more metal wiring patterns136b(hereafter, metal wiring patterns136b) are formed on the wiring pattern formation surfaces D2, D4, D6, and D8.

The formation method and the material of the metal wiring patterns136aand136bare the same as those in the first embodiment.

In the present embodiment, the metal wiring patterns136aand136bon the first layer and the fourth layer (the wiring pattern formation surfaces D1, D2, D3, and D4) can be used as electrical wiring, for example. In this case, the metal wiring patterns136aand136bon the second layer and the third layer (the wiring pattern formation surfaces D5, D6, D7, and D8) are dummy patterns.

In the present embodiment, the occupancy ratio (residual copper ratio) of the metal wiring patterns136in the first region A1in the layers from the first layer to the fourth layer is a ratio of the areas of the metal wiring patterns136ato the total area of the wiring pattern formation surfaces D1, D3, D5, and D7. Likewise, the occupancy ratio (residual copper ratio) of the metal wiring patterns136in the second region B1in the layers from the first layer to the fourth layer is a ratio of the areas of the metal wiring patterns136bto the total area of the wiring pattern formation surfaces D2, D4, D6, and D8.

In the same way as the first embodiment, the occupancy ratio of the metal wiring patterns136in each region of each layer is expressed by a ratio of the areas of the metal wiring patterns136to the area of each wiring pattern formation surface D1, D2, D3, D4, D5, D6, D7, or D8.

When the occupancy ratio of the metal wiring pattern136ain the first region A1of the first layer (i.e., the wiring pattern formation surface D1) is Aa %, and the occupancy ratio of the metal wiring pattern136bin the second region B1of the second layer (i.e., the wiring pattern formation surface D6) is Bb %, the LED head according to the second embodiment satisfies 0.75×Bb≤Aa≤Bb or 0.75×Aa≤Bb≤Aa (i.e., 0.75≤Aa/Bb≤1 or 0.75≤Bb/Aa≤1). Accordingly, the warpage of the substrate231can be reduced.

Further, when the occupancy ratio of the metal wiring patterns136bin the second region B1of the first layer (i.e., the wiring pattern formation surface D2) is Ba %, and the occupancy ratio of the metal wiring patterns136ain the first region A1of the second layer (i.e., the wiring pattern formation surface D5) is Ab %, the LED head according to the second embodiment satisfies 0.75×Ba≤Ab≤Ba or 0.75×Ab≤Ba≤Ab (i.e., 0.75≤Ab/Ba≤1 or 0.75≤Ba/Ab≤1). Accordingly, the warpage of the substrate231can be reduced.

Further, when the occupancy ratio of the metal wiring pattern136ain the first region A1of the third layer (i.e., the wiring pattern formation surface D7) is Ac %, and the occupancy ratio of the metal wiring pattern136bin the second region B1of the fourth layer (i.e., the wiring pattern formation surface D4) is Bd %, the LED head according to the second embodiment satisfies 0.75×Bd≤Ac≤Bd or 0.75×Ac≤Bd≤Ac (i.e., 0.75≤Ac/Bd≤1 or 0.75≤Bd/Ac≤1). Accordingly, the warpage of the substrate231can be reduced.

Further, when the occupancy ratio of the metal wiring pattern136bin the second region B1of the third layer (i.e., the wiring pattern formation surface D8) is Bc %, and the occupancy ratio of the metal wiring pattern136ain the first region A1of the fourth layer (i.e., the wiring pattern formation surface D3) is Ad %, the LED head according to the second embodiment satisfies 0.75×Bc≤Ad≤Bc or 0.75×Ad≤Bc≤Ad (i.e., 0.75≤Ad/Bc≤1 or 0.75≤Bc/Ad≤1). Accordingly, the warpage of the substrate231can be reduced.

Further, in the same way as the first embodiment, when the occupancy ratio of the metal wiring patterns136ain the first region A1in the layers from the first layer to the fourth layer is A %, and the occupancy ratio of the metal wiring patterns136bin the second region B1in the layers from the first layer to the fourth layer is B %, the LED head according to the second embodiment satisfies 0.75×B≤A≤B or 0.75×A≤B≤A (i.e., 0.75≤A/B≤1 or 0.75≤B/A≤1). Accordingly, the warpage of the substrate231can be reduced effectively, and the fluctuation of the irradiation position of the light irradiated from the plurality of light emitting elements132can be reduced effectively.

In the same way as the first embodiment, when the total area of the wiring pattern formation surfaces in the first region A1in the layers from the first layer to the fourth layer (the wiring pattern formation surfaces D1, D3, D5, and D7) and the total area of the wiring pattern formation surfaces in the second region B1in the layers from the first layer to the fourth layer (the wiring pattern formation surfaces D2, D4, D6, and D8) are equal to each other, the relationship between the occupancy ratio of the metal wiring patterns136ain the first region A1in the layers from the first layer to the fourth layer and the occupancy ratio of the metal wiring patterns136bin the second region B1in the layers from the first layer to the fourth layer can be expressed by the relationship between the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the fourth layer and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the fourth layer.

In this case, when the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the fourth layer is A, and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the fourth layer is B, the LED head according to the second embodiment satisfies 0.75≤A/B≤1 or 0.75≤B/A≤1.

The LED head according to the second embodiment has the same effect as the LED head13described in the first embodiment. Further, the LED head according to the second embodiment includes the one or more intermediate layers, and thus can make it easy to set the occupancy ratio of the metal wiring patterns136, as compared with an LED head that does not include the one or more intermediate layers.

Although the substrate231of four-layer substrate has boon described in the present embodiment, the substrate231may be formed to have even-number layers which are equal to or more than six layers. In other words, the substrate231may be an N-layer substrate (N is an even number equal to or greater than 6). Further, the substrate231may be formed to have odd-number layers which are equal to or more than three layers. In other words, the substrate231may be an N-layer substrate (N is an integer equal to or greater than 3).

Variant Example of Second Embodiment

FIGS. 13A to 13Dare plan views schematically illustrating the structure of a substrate231aof the LED head as the light exposure device according to a variant example of the second embodiment.FIG. 14is a cross-sectional view along a line C14-C14inFIG. 13A.

The substrate231aof an LED head according to the variant example of the second embodiment differs from the substrate231of the LED head according to the second embodiment (FIG. 11B) in the structure of the metal wiring patterns136in the second layer (FIG. 13B), and are the same as the substrate231of the LED head according to the second embodiment in other points. The LED head according to the variant example of the second embodiment is applicable to the image forming apparatus1, in place of the LED head13according to the first embodiment.

The metal wiring pattern136aon the wiring pattern formation surface D1is formed in a reflectively inverted wiring pattern of the metal wiring pattern136bon the wiring pattern formation surface D6. In other words, the metal wiring pattern136aon the wiring pattern formation surface D1and the metal wiring pattern136bon the wiring pattern formation surface D6are reflectively symmetrical to each other.

In the same way, the metal wiring patterns136bon the wiring pattern formation surface D2are formed in reflectively inverted wiring patterns of the metal wiring patterns136aon the wiring pattern formation surface D5. In other words, the metal wiring patterns136bon the wiring pattern formation surface D2and the metal wiring patterns136aon the wiring pattern formation surface D5are reflectively symmetrical to each other.

In the same way, the metal wiring pattern136aon the wiring pattern formation surface D7is formed in a reflectively inverted wiring pattern of the metal wiring pattern136bon the wiring pattern formation surface D4. In other words, the metal wiring pattern136aon the wiring pattern formation surface D7and the metal wiring pattern136bon the wiring pattern formation surface D4are reflectively symmetrical to each other.

In the same way, the metal wiring pattern136bon the wiring pattern formation surface D8is formed in a reflectively inverted wiring pattern of the metal wiring pattern136aon the wiring pattern formation surface D3. In other words, the metal wiring pattern136bon the wiring pattern formation surface D8and the metal wiring pattern136aon the wiring pattern formation surface D3are reflectively symmetrical to each other.

That is, the metal wiring patterns136of the first layer are formed in reflectively inverted wiring patterns of the metal wiring patterns136of the second layer, and the metal wiring patterns136of the third layer are formed in reflectively inverted wiring patterns of the metal wiring patterns136of the fourth layer. In other words, the metal wiring patterns136of the first layer and the metal wiring patterns136of the second layer are reflectively symmetrical to each other, and the metal wiring patterns136of the third layer and the metal wiring patterns136of the fourth layer are reflectively symmetrical to each other.

Thus, when the occupancy ratio of the metal wiring patterns136ain the first region A1in the layers from the first layer to the fourth layer is A %, and the occupancy ratio of the metal wiring patterns136bin the second region B1in the layers from the first layer to the fourth layer is B %, the LED head according to the variant example of the second embodiment satisfies A=B. However, the occupancy ratio of the metal wiring patterns136ain the first region A1and the occupancy ratio of the metal wiring patterns136bin the second region B1are needless to be strictly the same as each other. Thus, in the same way as the second embodiment, the LED head according to the variant example of the second embodiment satisfies 0.75×B≤A≤B or 0.75×A≤B≤A (i.e., 0.75≤A/B≤1 or 0.75≤B/A≤1).

In other words, when the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the fourth layer is A, and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the fourth layer is B, the LED head according to the variant example of the second embodiment satisfies A=B. In this case, the amount of the metal wiring patterns136ain the first region A1in the layers from the first layer to the fourth layer and the amount of the metal wiring patterns136bin the second region B1in the layers from the first layer to the fourth layer are desirably equal to each other. However, the sum of the areas of the metal wiring patterns136ain the first region A1and the sum of the areas of the metal wiring patterns136bin the second region B1are needless to be strictly equal to each other.

The LED head according to the variant example of the second embodiment has the same effect as the LED head described in the second embodiment. Further, the warpage of the substrate231acan be prevented more effectively by satisfying the relationship of A=B as described above. Accordingly, the printing quality in the image forming apparatus1can be increased.

Although the first embodiment (including each variant example) has described the substrate131of two-layer substrate, and the second embodiment (including the variant example) has described the substrate231of four-layer substrate, the substrate applied to the LED head described in the first or second embodiment may be an N-layer substrate including a first layer to an N-th layer (N is an integer equal to or greater than 1). That is, the N-th layer includes at least one layer (wiring layer). This N-layer substrate includes the wiring pattern formation surface135ain each layer. In this case, when the occupancy ratio of the one or more metal wiring patterns136a(hereafter, metal wiring patterns136a) in the first region A1in the layers from the first layer to the N-th layer (N is an integer equal to or greater than 1) is An %, and the occupancy ratio of the one or more metal wiring patterns136b(hereafter, metal wiring patterns136b) in the second region B1in the layers from the first layer to the N-th layer is Bn %, this LED head satisfies 0.75×Bn≤An≤Bn or 0.75×An≤Bn≤An (i.e., 0.75≤An/Bn≤1 or 0.75≤Bn/An≤1).

When the total area of the one or more wiring pattern formation surfaces135a(hereafter, wiring pattern formation surfaces135a) in the first region A1in the layers from the first layer to the N-th layer (N is an integer equal to or greater than 1) and the total area of the wiring pattern formation surfaces135ain the second region B1in the layers from the first layer to the N-th layer are equal to each other, the relationship between the occupancy ratio of the metal wiring patterns136ain the first region A1in the layers from the first layer to the N-th layer and the occupancy ratio of the metal wiring patterns136bin the second region B1in the layers from the first layer to the N-th layer can be expressed by the relationship between the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the N-th layer and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the N-th layer. In this case, when the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the N-th layer is An, and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the N-th layer is Bn, this LED head satisfies 0.75≤An/Bn≤1 or 0.75≤Bn/An≤1.

Further, the sum of the areas of the metal wiring patterns136ain the first region A1in the layers from the first layer to the N-th layer and the sum of the areas of the metal wiring patterns136bin the second region B1in the layers from the first layer to the N-th layer are desirably equal to each other. Further, the amount of the metal wiring patterns136ain the first region A1in the layers from the first layer to the N-th layer and the amount of the metal wiring patterns136bin the second region B1in the layers from the first layer to the N-th layer are desirably equal to each other.

Further, when the substrate applied to the LED head described in the first or second embodiment is an N-layer substrate including even-number layers in the layers from a first layer to an N-th layer (N is an even number equal to or greater than 2), the substrate applied to the LED head described in the first or second embodiment is desirable to be formed such that the reflectively inverted wiring patterns of the metal wiring patterns in each layer in the layers from the first layer to the N/2-th layer are identical with the metal wiring patterns of the remaining layers (the layers other than the first layer to the N/2-th layer).

With the structure described above, the LED head that includes the substrate including the first layer to the N-th layer (N is an integer equal to or greater than 1) has the same effect as described in the first and second embodiments (including each variant example).

Third Embodiment

Other usage of the LED head (including each variant example) described in the first and second embodiments will be described below.

<Configuration of Image Scanner3>

FIG. 15is a perspective view schematically illustrating an image scanner3as an image reading apparatus according to a third embodiment of the present invention.

As illustrated inFIG. 15, the image scanner3as the image reading apparatus includes a housing301, a document table302for putting a document, and a cover303(a document table cover) for covering the document put on the document table302from above. A contact image sensor head304as a light reception device, guides305a,305b, a stepping motor306, a drive belt307, a control circuit308, and a flexible flat cable309are disposed inside the housing301.

The contact image sensor head304includes a light source (for example, a light emitting diode as a light emitting element) that radiates light, and a substrate304a. One of the substrates described in the first and second embodiments (including each variant example of the first and second embodiments) is employed as the substrate304a. Light reception elements (for example, photo diodes) as semiconductor elements for detecting light are fixed on this substrate304a, in place of the light emitting elements (for example, the light emitting elements132described in the first and second embodiments). The light reception elements detect reflected light from a medium put on the document table302. That is, the light source of the contact image sensor head304radiates light, and the light reception elements of the contact image sensor head304detect the reflected light from the medium put on the document table302. The contact image sensor head304can read an image of the medium put on the document table302on the basis of the detected reflected light.

The contact image sensor head304is supported in a straightly movable manner along the paired guides305a,305bfixed to the housing301. In order to slide the contact image sensor head304in the sub-scanning direction along the guides305a,305b, the contact image sensor head304engages with the drive belt307engaging with the stepping motor306. The control circuit300for controlling the contact image sensor head304is connected to the contact image sensor head304via the flexible flat cable309.

The image scanner3according to the third embodiment uses the LED head described in the first and second embodiments (including each variant example), and thus has the same effect as described in the first and second embodiments (including the effect of each variant example) even when the temperature of the substrate304arises. Accordingly, the image reading quality of the image scanner3according to the third embodiment can be increased.

The feature of each embodiment and the feature of each variant example described above can be combined properly with each other.

DESCRIPTION OF REFERENCE CHARACTERS