JP2002337390A - Optical writing head and its assembling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical writing head in which optical components can be arranged with high accuracy at a relatively low cost by suppressing temperature rise of an LED chip. SOLUTION: A heat sink 42 made of a metallic material is provided beneath an FPC 41 mounting a light emitting element array chip 3. The heat sink 42 is provided, at the opposite ends thereof in the longitudinal direction, with first reference holes and the FPC 41 is provided, at the opposite ends thereof in the longitudinal direction, with second reference holes 40. A continuous copper foil pattern 39 is provided at the edge part of the FPC without being spaced apart therefrom. Edge part of the FPC 41 is abutted against an FPC positioning jig and then the first reference hole is aligned with the second reference hole so that the optical axes of a lens array and the light emitting element array chip 3 on the FPC 41 are aligned with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing head used in an electrophotographic printer or the like and an assembling method thereof, and more particularly, to radiating heat from a light emitting element array chip to a base of a substrate on which the light emitting element array chip is mounted. And a method for assembling the same.

[0002]

2. Description of the Related Art Conventionally, an optical writing head used in an electrophotographic printer or the like has a surface-emitting LED chip mounted on a substrate.
The rod lens arrays are arranged in rows, and the rod lens arrays stacked in one or two rows are arranged at positions opposed to the rows.

FIG. 13 is a sectional view of a conventional optical writing head. In this optical writing head, an LED chip (light emitting element array chip) is provided on a glass epoxy substrate 51.
On the optical axis 52 of the light emitted by the light emitting element of the LED chip 53, a rod lens array 57 is mounted.
A housing (resin cover) 54 fixes the photosensitive drum 55 on the rod lens array 57. Further, the corner around the glass epoxy board 51 is engaged with the tip of the leg of the housing 54. The support 56 has a concave cross-sectional shape, and has a structure in which the housing 54 is inserted into the support 56.

[0004]

In a high-resolution electrophotographic printer, it is necessary to set the accuracy of the imaging position distance of the LED chip in the main scanning direction to 30 μm or less. In order to position the housing, it is required that the housing has significantly improved shape accuracy.

Therefore, the structure of the housing requires a structure for holding the rod lens array, a structure for holding the glass epoxy substrate, and a structure for providing a light shielding function so that external light is not inserted into the head. . Therefore,
Since the shape is complicated, a resin molded product by injection molding is generally used.

Here, a glass epoxy substrate, which is a composite material of a glass fiber mat and an epoxy resin, is usually used as a substrate on which the LED chip is mounted.

The glass epoxy substrate is a material that does not easily conduct heat (heat conductivity is 0.38 W / m · K).
It is difficult to release heat from the ED chip, and since the housing has a sealed structure having a light shielding function as described above, the temperature rise of the LED chip becomes large. LE
The light output of the light emitting element of the D chip has a large temperature dependency,
The light emission amount decreases due to the temperature rise. The light emission amount of the GaAs-based light emitting element is about 0.5 °
% Is known to decrease. A decrease in the amount of emitted light causes a decrease in print density, which is a fatal problem in a printer.

An object of the present invention is to provide an optical writing head capable of suppressing an increase in the temperature of an LED chip, arranging optical components with high precision at a relatively low cost, and a method of assembling the same.

[0009]

According to the present invention, there is provided a light emitting element array chip having a lens array on an optical axis of light emitted by the light emitting element, and further comprising a base material on which a light emitting element array chip is mounted, made of a metal material. In the optical writing head provided with a heat sink, the heat sink includes first reference holes at predetermined intervals in a longitudinal direction of the heat sink, and the substrate is located at the same position as the first reference hole in the longitudinal direction of the substrate. Wherein the first reference hole and the second reference hole are aligned so that the optical axes of the lens array and the light emitting element array chip on the substrate coincide with each other. It is characterized by.

The present invention further comprises a lens array on the optical axis of light emitted by the light emitting element of the light emitting element array chip,
Further, in an optical writing head including a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted, the heat sink includes first reference holes at both longitudinal ends of the heat sink, and the substrate includes: A second reference hole is provided at both ends in the longitudinal direction of the substrate, and a metal pattern at a predetermined interval is provided at an edge portion of the substrate, and an optical axis of the lens array and the light emitting element array chip on the substrate is aligned. The first reference hole and the second reference hole are aligned so as to coincide with each other.

The present invention further comprises a lens array on the optical axis of light emitted by the light emitting element of the light emitting element array chip,
Further, in an optical writing head including a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted, the heat sink includes first reference holes at both longitudinal ends of the heat sink, and the substrate includes: A second reference hole is provided at both ends in the longitudinal direction of the substrate, and a metal pattern that is continuous without being separated from an edge of the substrate is provided, and light between the lens array and the light emitting element array chip on the substrate is provided. The first so that the axes coincide
The reference hole and the second reference hole are aligned.

The present invention also includes a lens array on the optical axis of light emitted by the light emitting element of the light emitting element array chip,
Further, in the method for assembling an optical writing head including a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted, a first reference hole is provided at predetermined intervals in a longitudinal direction of the heat sink, A second reference hole is provided at the same position as the first reference hole in the direction, and the first reference hole and the second reference hole are aligned so that the optical axes of the lens array and the light emitting element array chip on the substrate coincide with each other.
And the reference hole is aligned.

The present invention also provides a lens array on the optical axis of light emitted by the light emitting element of the light emitting element array chip,
Further, in the method for assembling an optical writing head including a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted, a first reference hole is provided at both ends in a longitudinal direction of the heat sink. A second reference hole is provided at both ends of the substrate, and a metal pattern at a predetermined interval is provided at an edge of the substrate, and the optical axes of the lens array and the light emitting element array chip on the substrate are aligned with each other. The first reference hole and the second reference hole are aligned.

The present invention further comprises a lens array on the optical axis of light emitted by the light emitting element of the light emitting element array chip,
Further, in the method for assembling an optical writing head including a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted, a first reference hole is provided at both ends in a longitudinal direction of the heat sink. A second reference hole is provided at each end of the substrate, and a continuous metal pattern is provided at the edge of the substrate without being separated from the substrate, so that the optical axes of the lens array and the light emitting element array chip on the substrate coincide with each other. And positioning the first reference hole and the second reference hole.

[0015]

Next, a first embodiment of the present invention will be described with reference to the drawings.

According to the present invention, in order to avoid the problem that the temperature of the light emitting element rises and the amount of emitted light decreases and the print density of the printer decreases, a metal material is used as the base of the substrate on which the light emitting element array chip is mounted. This is to release the temperature.

FIG. 1 shows a first example of the optical writing head of the present invention.
FIG. 3 is a side view in a direction perpendicular to the main scanning direction, showing the embodiment.

FPC (Flexible Print)
d Circuit: One end of a flexible substrate (1) is attached to a heat sink (metal block) 2 and bonded. The light emitting element array chip 3 is die-bonded thereon, and the wiring on the FPC 1 and the electrode pad of the light emitting element on the light emitting element array chip 3 are connected by wire bonding using the wire 4. Thereafter, the heat sink 2 is attached to the support 5 by means such as bolts 6. The drive circuit board 8 of the light emitting element array chip 3 is mounted on the support 5 in advance. The wiring between the FPC 1 and the drive circuit board 8 is connected by connecting a connector terminal 9 provided at the other end of the FPC 1 to the drive circuit board 8 with a connector 10.
The lens array 7 is fixed on the optical axis of the light emitting element array chip 3 by the support 5.

Since the structure of the heat sink 2 to which the FPC 1 is bonded may be, for example, a simple rectangular shape, a metal material suitable for cutting and polishing can be used for the heat sink 2.

In the first embodiment, since a metal material can be applied to the heat sink 2 and the support 5,
Less susceptible to performance changes due to temperature changes around the head.

Since the optical writing head shown in FIG. 1 is used for a high-resolution electrophotographic printer, the deviation of the light emitting element array chip 3 is set to ± 30 μm or less in a direction orthogonal to the main scanning direction. It is necessary to position the lens array 7 and the light emitting element array chip 3 on the FPC 1 with high precision so that the optical axes thereof coincide with each other. Therefore, in the first embodiment, the positioning of the FPC 1 and the heat sink 2 is not performed. This is an important point.

In the first embodiment, the positioning of the FPC 1 and the heat sink 2 is performed, for example, by providing reference holes at predetermined intervals at the same location on both sides and matching the reference holes.

FIG. 2 is a view showing a state in which the FPC is attached to the heat sink. 2A is a plan view, and FIG. 2B is a cross-sectional view taken along line AA in FIG. 2A. FIG. 3 is a perspective view showing an example of a method for positioning the FPC and the heat sink.

As shown in FIG. 2, a wiring pattern 12 is formed on the FPC 1, and a connector terminal 9 for coupling with the connector 10 is provided at an end of the wiring pattern 12.
Are formed. On the wiring pattern 12 in the longitudinal direction of the FPC 1, the light emitting element array chips 3 are formed in a staggered arrangement in the main scanning direction. Outside the wiring pattern 12 in a direction orthogonal to the longitudinal direction of the FPC 1, reference holes 11a for positioning with the heat sink 2 are provided at predetermined intervals.

Reference holes 11a are provided at predetermined intervals in the longitudinal direction of the FPC 1 and, as shown in FIG.
Is attached to the heat sink 2, the reference pin 14 is inserted into the reference hole 11b provided on the heat sink 2 at the same interval as the reference hole 11a of the FPC 1, and the reference pin 14 is inserted into the reference hole 11a of the FPC 1. The FPC 1 is attached to the heat sink 2.

The distance between the reference holes 11a and 11b must be within 30 mm in order to make the mounting accuracy of the light emitting element array chip ± 30 μm or less in the direction perpendicular to the main scanning direction. The reference hole 11a provided in the heat sink 2 is generally a circular depression, but may have any shape.

FIG. 4 is a schematic sectional view of a jig, an FPC, and a heat sink showing another example of the positioning method.

In FIG. 4, after the reference pin 15 provided on the jig 18 is inserted into the reference hole 15a of the heat sink 2 to perform positioning, the reference pin 15 is inserted into the reference hole of the FPC 1, and the FPC 1 is mounted. The FPC 1 is attached to the intermediate plate 17 of the jig 18 via the rubber 16, and the intermediate plate 17 is lowered to bring the FPC 1 and the heat sink 2 into close contact.

The FPC 1 is attached to the heat sink 2 by the above-described positioning method, and is placed in an oven at 150 ° C. while the FPC 1 and the heat sink 2 are in close contact with each other. The adhesive is melted and solidified, and FPC1
And the heat sink 2 are bonded and fixed.

FIG. 5 is a sectional view showing the structure of the FPC. As shown in FIG. 5, the base film (25 μm thick)
m) Below the adhesive 21, there is an adhesive 20, which bonds the heat sink 2 to the FPC 1. Copper foil (thickness 18 μm) 22
The adhesive (thickness 25 μm) 23 on the top is for bonding a coverlay film (thickness 25 μm) 24 for protecting the copper foil 22.

FIG. 6 shows an optical writing head according to the first embodiment. FIG. 6 is a cross-sectional view in a direction orthogonal to the main scanning direction of the optical writing head. On FPC1,
The light emitting element array chip 3 is mounted, and the lens array 7 is fixed on the optical axis 26 of the light emitted by the light emitting element array chip 3 by the resin cover 28 via the silicon filler 27, and is mounted on the lens array 7. Is provided with a photosensitive drum 25. Further, a space is provided on the heat sink 2 outside the edge of the FPC 1, and the FPC 1
Has a structure not in contact with the resin cover 28.

The reason why a space is provided outside the edge portion of the FPC 1 so that the FPC 1 does not contact the resin cover 28 is that there is a difference in the thickness of the FPC 1 between the portion where the FPC 1 has a pattern and the portion where the FPC 1 does not have a pattern. So resin cover 2
This is because, when the resin cover 8 is attached, the resin cover 28 itself undulates in the scanning direction, the distance between the light emitting element array chip 3 and the lens array 7 varies, and the resolution becomes uneven.

As described above, in the first embodiment, the light emitting element array chip can be positioned with high accuracy. However, the mounting accuracy of the light emitting element array chip is ± 30 μm or less in the direction orthogonal to the main scanning direction. To do this, the interval between the reference holes of the FPC must be within 30 mm. For example, in the case of the A3 size, 12 (350/30) reference holes are required, and the reference holes of the FPC are also required. Is outside the area of the wiring pattern 12 of the FPC as shown in FIG.

Further, since the space is provided outside the edge portion of the FPC 1, the width of the optical writing head in the direction orthogonal to the main scanning direction is increased.

Next, a second embodiment of the present invention will be described with reference to the drawings.

The second embodiment has the same structure as that of the first embodiment shown in FIG.
The FPC is provided only at both ends in the longitudinal direction of the PC, thereby reducing the number of reference holes and eliminating the space for the reference holes of the FPC which is required in the first embodiment.
The width in the direction orthogonal to the longitudinal direction of the above is reduced.

FIG. 7 is a view showing a state in which the FPC according to the second embodiment is attached to a heat sink. FIG.
7A is a plan view, and FIG. 7B is a plan view of FIG.
It is sectional drawing which followed the -B line. FPC 31 shown in FIG.
The reference holes 30 are provided at both ends outside the pattern area in the longitudinal direction of the FPC 31 for positioning.
A copper foil pattern 29, which is a metal pattern having a width of about 0.5 mm, is provided at a predetermined interval at the edge portion 31. Similarly, the heat sink 32 is also provided with reference holes at both ends in the longitudinal direction.

The copper foil pattern 29 is provided between the reference holes provided at both ends of the FPC 31 in the longitudinal direction.
The heat sink 32 is used as a positioning reference for preventing the positioning accuracy of the edge of the FPC 31 from being degraded due to the deflection of the edge when the edge of the FPC 31 is abutted against a jig for positioning the FPC. is there.

In the second embodiment, the positioning of the FPC and the heat sink is performed as follows.

FIG. 8 shows a jig and an F showing an example of a positioning method.
It is a schematic cross section of a PC and a heat sink. The jig 33 for positioning the FPC is provided with a guide groove 38 for aligning the heat sink 32 with the heat sink 32 by abutting the edge of the FPC 31 against the jig.

First, the reference pin 34 provided on the jig 33 for positioning the FPC is inserted into the reference hole 34 a of the heat sink 32.
After the positioning, the reference pin 34 provided on the jig 33 is inserted into the reference hole of the FPC 31 at the position of the top dead center of the intermediate plate 36 (the point where the intermediate plate 36 rises most). Then, the FPC 31 is attached to the intermediate plate 36 of the jig 33 via the rubber 35.

Next, by lowering the jig 33,
The heat sink mating surface 37 is inserted into the jig 33 so that both positioning alignments are achieved.

Next, the intermediate plate 36 is lowered, and FP
C31 is brought into close contact with the heat sink 32 with a uniform surface pressure.

Next, the FPC 31 and the heat sink 32 fixed to the jig 33 are inserted into the heating furnace in this state, and are bonded and fixed by the thermosetting adhesive of the FPC 31.

Finally, the heat sink 32 to which the FPC 31 is adhered is taken out of the jig 33.

As described above, in the FPC according to the second embodiment, the reference holes are provided at both ends outside the pattern area in the longitudinal direction of the FPC for positioning.
When the edge portion of the FPC is applied to the jig to perform the butt positioning, a copper foil pattern is provided at a predetermined interval on the butt edge of the FPC with the jig in order to prevent a decrease in the positioning accuracy due to twisting of the edge portion of the FPC. It is provided in.

With this copper foil pattern, the strength of the edge portion of the FPC can be improved, and the bonding accuracy of the FPC can be improved by reducing the deviation of the edge portion when the FPC is abutted against a jig. In the second embodiment, the multiple reference holes provided in the first embodiment can be omitted. Therefore, in the second embodiment, the width in the direction orthogonal to the longitudinal direction of the FPC can be narrowed, and therefore, compared to the first embodiment, the width is orthogonal to the main scanning direction of the optical writing head. The width in the direction of movement can be reduced. Further, the number of steps for manufacturing the reference hole can be reduced.

Next, a third embodiment of the present invention will be described with reference to the drawings.

The third embodiment is different from the second embodiment in that the copper foil pattern is provided at a predetermined interval on the edge of the FPC, but the copper foil pattern is provided on the edge of the FPC in the longitudinal direction of the FPC. Are provided continuously without being separated from each other. The third embodiment is different from the third embodiment in that a copper foil pattern is continuously provided in an edge portion of the FPC in the longitudinal direction of the FPC.
The configuration is the same as that of the second embodiment, and the method of positioning the FPC and the heat sink is the same as that of the second embodiment.

FIG. 9 is a view showing a state in which the FPC according to the third embodiment is attached to a heat sink. FIG.
9A is a plan view, and FIG. 9B is a plan view of FIG.
It is sectional drawing which followed the -C line. In the FPC shown in FIG. 9, reference holes 40 are provided at both ends outside the pattern area in the longitudinal direction of the FPC 41 for positioning, and a copper foil pattern 39 having a width of about 0.5 mm is formed on the edge of the FPC 41. This portion is provided continuously without being separated in the longitudinal direction of the FPC 41. Similarly, the heat sink 42 is provided with reference holes at both ends in the longitudinal direction.

The FPC 41 is formed by the copper foil pattern 39.
Since the thickness of the edge portion is also uniformed, it can be used as a height reference plane when a resin cover holding the lens array is mounted, and the total width of the head can be reduced.

FIG. 10 shows an optical writing head according to the third embodiment. FIG. 10 is a cross-sectional view in a direction orthogonal to the main scanning direction of the optical writing head. FPC41
The light emitting element array chip 3 is mounted thereon, and the lens array 47 is fixed on the optical axis 43 of light emitted by the light emitting element array chip 3 by the resin cover 44 via the silicone filler 46. A photosensitive drum 45 is provided on 47. Further, the tip of the leg of the resin cover 44 is joined to the copper foil pattern at the edge of the FPC 41.

As described above, in the FPC according to the third embodiment, the reference holes are provided at both ends outside the pattern area in the longitudinal direction of the FPC for positioning.
When the edge portion of the FPC is applied to the jig for butt positioning, the copper foil pattern is not separated from the butt edge of the FPC with the jig to prevent a decrease in the positioning accuracy due to the deflection of the edge portion of the FPC. Are provided continuously.

With this copper foil pattern, the strength of the edge portion of the FPC can be improved, and the bonding accuracy of the FPC can be improved only by reducing the deflection of the edge portion when the FPC is abutted against the jig. However, as described above, the tip of the leg of the resin cover is joined to the copper foil pattern so that the resin cover overlaps the FPC.
Because there is no need to take space outside the edge of the PC,
In the third embodiment, as in the second embodiment, the width of the optical writing head in the direction orthogonal to the main scanning direction can be reduced.

Further, a copper foil pattern is continuously provided on the edge portion of the FPC without being separated in the longitudinal direction of the FPC, and the thickness of the copper foil pattern is constant. Height reference plane.

In the second and third embodiments,
As shown in FIGS. 7 and 9, the copper foil patterns are provided on both edges in the direction perpendicular to the longitudinal direction of the FPC, but the copper foil patterns are provided only on one The positioning of the heat sink may be used as a reference for one side. As shown in FIGS. 7 and 9, reference holes are provided at both ends in the longitudinal direction of the FPC to perform positioning at both ends. However, reference holes are provided at only one end, and positioning is performed at only one side. You may go.

In the third embodiment, the FPC
Although the resin cover overlaps the FPC by joining the tip of the resin cover to the copper foil pattern at the edge, the pattern is also insulated on a normal glass epoxy board by insulating coating on the glass epoxy board. It is also possible for the resin covers to overlap.

In the first, second, and third embodiments, a rod lens array or a resin erecting equal-magnification lens array can be used as the lens array. FIG. 11 is a cutaway perspective view showing an example of the configuration of the rod lens array. The rod lens array is configured by arranging rod lenses 48 whose refractive index decreases from the central axis toward the periphery in one or two rows, and can form an erect equal-magnification image. FIG. 12 is a perspective view showing an example of the configuration of a resin erecting equal-magnification lens array. The resin erecting equal-magnification lens array is formed by stacking two or more lens array plates 50 each having the monocular lens 49 arranged in one or two rows, and can form an erecting equal-magnification image. The monocular lens 49 has the same focal length and aperture, and is convex on one side or convex on both sides.

[0059]

As described above, the present invention provides an FPC
And the reference hole is provided in the same position of the heat sink,
The FPC, that is, the light emitting element array chip can be positioned with high accuracy with respect to the heat sink.

Further, according to the present invention, since the reference holes are provided at both ends in the longitudinal direction of the FPC and the heat sink, and the copper foil patterns are provided at predetermined intervals at the edges of the FPC, the copper foil patterns are used. By reducing the deflection of the edge portion when the FPC is abutted against the jig, the bonding accuracy of the FPC can be improved, so that the width in the direction orthogonal to the longitudinal direction of the FPC can be reduced. Therefore, the width of the optical writing head can be reduced. Further, the number of steps for manufacturing the reference hole can be reduced.

Further, according to the present invention, since the resin cover can be overlapped on the copper foil pattern by continuously providing the copper foil pattern at the edge of the FPC, the width of the optical writing head can be further reduced. As well as
Since the thickness of the copper foil pattern is constant, the upper surface of the FPC can be used as a height reference surface for the resin cover device.

[Brief description of the drawings]

FIG. 1 is a side view in a direction perpendicular to the main scanning direction, showing a first embodiment of an optical writing head according to the present invention.

FIG. 2 is a diagram showing a state in which an FPC is attached to a heat sink.

FIG. 3 is a perspective view showing an example of a method for positioning an FPC and a heat sink.

FIG. 4 is a schematic cross-sectional view of a jig, an FPC, and a heat sink showing another example of a positioning method.

FIG. 5 is a cross-sectional view illustrating a structure of an FPC.

FIG. 6 is a sectional view of the optical writing head according to the first embodiment in a direction orthogonal to the main scanning direction.

FIG. 7 is a partial plan view of an FPC according to a second embodiment.

FIG. 8 is a schematic cross-sectional view of a jig, an FPC, and a heat sink showing an example of a positioning method according to a second embodiment.

FIG. 9 is a partial plan view of an FPC according to a third embodiment.

FIG. 10 is a cross-sectional view of the optical writing head according to a third embodiment in a direction orthogonal to the main scanning direction.

FIG. 11 is a cutaway perspective view showing an example of the configuration of a rod lens array.

FIG. 12 is a perspective view showing an example of a configuration of a resin erecting equal-magnification lens array.

FIG. 13 is a sectional view of a conventional optical writing head.

[Explanation of symbols]

 1, 31, 41 FPC 2, 32, 42 heat sink 3 light emitting element array chip 4 wire 5, 56 support 6 bolt 7, 47 lens array 8 drive circuit board 9 connector terminal 10 connector 11a, 11b, 15a, 30, 34a, 40 Reference Hole 12 Wiring Pattern 14, 15, 34 Reference Pin 16, 35 Rubber 17, 36 Intermediate Plate 18, 33 Jig 20, 23 Adhesive 21 Base Film 22 Copper Foil 24 Coverlay Film 25, 45, 55 Photosensitive Drum 26 , 43, 52 Optical axis 27, 46 Silicon filler 28, 44 Resin cover 29, 39 Copper foil pattern 37 Heat sink mating surface 38 Guide groove 48 Rod lens 49 Monocular lens 50 Lens array plate 51 Glass epoxy board 53 LED chip 54 Housing 57 Rod lens array

Claims (8)

[Claims] 1. An optical writing head comprising: a lens array on an optical axis of light emitted by a light emitting element of a light emitting element array chip; and a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted. The heat sink includes first reference holes at predetermined intervals in the longitudinal direction of the heat sink, and the substrate includes second reference holes at the same position as the first reference holes in the longitudinal direction of the substrate. An optical writing head, wherein the first reference hole and the second reference hole are aligned so that the optical axes of the lens array and the light emitting element array chip on the substrate coincide with each other. 2. An optical writing head comprising: a lens array on an optical axis of light emitted by a light emitting element of a light emitting element array chip; and a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted. The heat sink has first reference holes at both ends in the longitudinal direction of the heat sink, and the substrate has second reference holes at both ends in the longitudinal direction of the substrate, and has an edge at the edge of the substrate. The first reference hole and the second reference hole are provided so as to have a metal pattern at a predetermined interval, and to align the optical axis of the lens array with the light emitting element array chip on the substrate. An optical writing head, characterized in that: 3. An optical writing head comprising: a lens array on an optical axis of light emitted by a light emitting element of a light emitting element array chip; and a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted. The heat sink has first reference holes at both ends in the longitudinal direction of the heat sink, and the substrate has second reference holes at both ends in the longitudinal direction of the substrate, and has an edge at the edge of the substrate. The first reference hole and the second reference hole are provided so as to have a continuous metal pattern without being separated from each other so that the optical axes of the lens array and the light emitting element array chip on the substrate coincide with each other.
An optical writing head, wherein the reference hole is aligned with the reference hole. 4. An optical writing head according to claim 1, wherein said lens array is a rod lens array or a resin erecting equal-magnification lens array. 5. An optical writing head comprising: a lens array on an optical axis of light emitted by a light emitting element of a light emitting element array chip; and a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted. In the assembling method, a first reference hole is provided at a predetermined interval in a longitudinal direction of the heat sink, a second reference hole is provided at the same position as the first reference hole in a longitudinal direction of the substrate, and the lens array is provided. A method of assembling an optical writing head, comprising: positioning the first reference hole and the second reference hole such that an optical axis of the light-emitting element array chip on the substrate is aligned. 6. An optical writing head comprising: a lens array on an optical axis of light emitted by a light emitting element of a light emitting element array chip; and a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted. In the assembling method, a first reference hole is provided at both ends in a longitudinal direction of the heat sink, a second reference hole is provided at both ends in a longitudinal direction of the substrate, and a metal having a predetermined interval is provided at an edge of the substrate. An optical writing head, wherein a pattern is provided and the first reference hole and the second reference hole are aligned so that the optical axes of the lens array and the light emitting element array chip on the substrate coincide with each other. How to assemble. 7. An optical writing head comprising: a lens array on an optical axis of light emitted by a light emitting element of a light emitting element array chip; and a heat sink made of a metal material on a base of a substrate on which the light emitting element array chip is mounted. In the assembling method, a first reference hole is provided at both ends in a longitudinal direction of the heat sink, and a second reference hole is provided at both ends in a longitudinal direction of the substrate, and the second reference hole is continuous without being separated from an edge of the substrate. Wherein the first reference hole and the second reference hole are aligned so that the optical axes of the lens array and the light emitting element array chip on the substrate coincide with each other. How to assemble the write head. 8. The method for assembling an optical writing head according to claim 5, wherein said lens array is a rod lens array or a resin erecting equal-magnification lens array.