JP2006269544A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device reduced in the size of a light emitting chip while preventing an influence by reflection light. <P>SOLUTION: In LED array chip 26, LED 28 emits light and this light forms an image on a photo conductor 16 via a rod lens array 30. Although part of the light from the LED 28 hits a bonding wire 34, the surface of a wire 34A at the end of the bonding wire 34 is inclined at A° with respect to a plane 36 perpendicular to the central axis CL of the rod lens array 30 (surface 26A of the LED array chip 26), where 0°≤A≤45°, and the light reflected on the bonding wire 34 goes in the direction (direction shown by an arrow B) in which it is not incident into the incidence surface 30A of the rod lens array 30. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light emitting device including a light emitting unit.

  In some light emitting devices, an LED array chip and a substrate are connected by a bonding wire. In such a light emitting device, in order to prevent the influence of reflected light, for example, the bonding portion on the LED array chip may be placed outside the range expected by the optical system (see, for example, Patent Document 1).

However, in this conventional light emitting device, the bonding portion is disposed outside the range expected by the optical system, so that the LED array chip becomes large.
Japanese Patent Laid-Open No. 11-216897

  In view of the above fact, an object of the present invention is to provide a light-emitting device that can reduce the size of a light-emitting chip while preventing the influence of reflected light.

  The light emitting device according to the first aspect of the present invention includes a substrate, a first electrode pad disposed on the substrate, a light emitting chip disposed on the substrate and including a light emitting unit, and the light emitting chip. An optical system that forms an image of the light, a second electrode pad that is disposed on the surface of the light emitting chip and within an aperture angle of the optical system, the first electrode pad, and the second electrode An angle of inclination of a surface of the tip side line portion connected to the pad and extending toward the second electrode pad with respect to a plane perpendicular to the axial direction of the optical system is emitted by the light emitting portion, and the tip side line portion And a bonding wire having an inclination angle in a range in which the reflected light reflected by the surface does not enter the incident surface of the optical system.

  According to the light emitting device of the present invention described in claim 1, the light emitting portion emits light in the light emitting chip, and this light is imaged through the optical system. A part of the light from the light emitting unit hits the bonding wire, but the reflected light travels in a direction not entering the incident surface of the optical system.

  The light emitting device according to a second aspect of the present invention is the light emitting device according to the first aspect, wherein the light emitting portion emits light at an inclination angle with respect to a surface perpendicular to the axial direction of the optical system on the surface of the tip side line portion. The reflected light reflected by the surface of the distal end side line portion has an inclination angle that is smaller than the inclination angle in the range in which the light enters the incident surface of the optical system.

  According to the light emitting device of the present invention described in claim 2, a part of the light from the light emitting portion hits the bonding wire, but the surface of the tip side line portion is inclined with respect to a plane perpendicular to the axial direction of the optical system. Since the angle is set to an inclination angle smaller than the inclination angle in the range in which the reflected light emitted from the light emitting portion and reflected from the surface of the tip side line portion enters the incident surface of the optical system, the reflected light is incident on the incident surface of the optical system. Proceed in the direction not incident on.

  The light emitting device according to a third aspect of the present invention is the light emitting device according to the first or second aspect, wherein an inclination angle A with respect to a surface perpendicular to the axial direction of the optical system on the surface of the tip side line portion is It is characterized by 0 ° ≦ A ≦ 45 °.

  According to the light emitting device of the present invention described in claim 3, the inclination angle A with respect to the surface perpendicular to the axial direction of the optical system on the surface of the tip side line portion is 0 ° ≦ A ≦ 45 °, and the light emission Even if part of the light from the part hits the bonding wire, the reflected light travels in a direction not entering the incident surface of the optical system.

  A light-emitting device according to a fourth aspect of the present invention is the light-emitting array chip according to any one of the first to third aspects, wherein the light-emitting chip includes a plurality of the light-emitting portions, and the light-emitting array. A plurality of chips are alternately arranged on the substrate, and the second electrode pads are disposed at positions adjacent to the light emitting portions of the other light emitting array chips adjacent to each other, and the other light emitting elements adjacent to the bonding wires are disposed. The array chip extends on a side opposite to the light emitting portion.

  According to the light emitting device of the present invention described in claim 4, each of the plurality of light emitting portions emits light in the plurality of light emitting array chips, and these lights are imaged through the optical system. A part of the light from the light emitting unit hits the bonding wire connected to the second electrode pad of the adjacent light emitting array chip, but the reflected light travels in a direction not entering the incident surface of the optical system.

  A light-emitting device according to a fifth aspect of the present invention is the light-emitting device according to any one of the first to fourth aspects, wherein the light-emitting chip is a self-scanning LED array chip.

  According to the light emitting device of the present invention described in claim 5, since the light emitting chip is a self-scanning LED array chip and the number of bonding wires is small, the amount of light reflected from the bonding wires is also small.

  A light-emitting device according to a sixth aspect of the present invention is the light-emitting device according to any one of the first to fifth aspects, wherein the bonding wire is bonded to the first electrode pad and then bonded to the second electrode pad. It is characterized by bonding.

  According to the light emitting device of the present invention described in claim 6, since the bonding wire is bonded to the first electrode pad (first bond) and then bonded to the second electrode pad (second bond), the second Since the BALL part cannot be formed on the electrode pad of this electrode and there is no light reflected by the BALL part, the influence of the reflected light by the BALL part is eliminated.

  As described above, according to the light emitting device of the present invention, the light emitting chip can be miniaturized while preventing the influence of reflected light.

  A light emitting device according to a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows an image forming apparatus 10 to which an LED print head 20 as a light emitting device is applied. The image forming apparatus 10 is a so-called tandem image forming apparatus. The image forming apparatus 10 includes an intermediate transfer belt 12 that is stretched substantially horizontally. Under the intermediate transfer belt 12, four image forming portions 14 corresponding to different development colors are arranged. .

  A sheet tray 11 is provided below the image forming unit 14, and a conveyance path 13 extending upward from the sheet feeding side of the sheet tray 11 has a secondary transfer unit 15 in contact with the intermediate transfer belt 12 and a fixing unit. It passes through the portion 17 and reaches the discharge port, and the outside of the discharge port is a discharge tray 19.

  Each image forming unit 14 includes a photoreceptor 16, a charger 18, an LED print head 20 as a light emitting device, a developing device 40, and a cleaner 42.

  The photoconductor 16 has a light receiving surface 16A whose outer peripheral surface is cylindrical, and an electrostatic latent image can be formed on the light receiving surface 16A. The light receiving surface 16A is in contact with the intermediate transfer belt 12 on the downstream side of the developing device 40 in the photosensitive member rotation direction (arrow R direction).

  As shown in FIG. 2, the LED print head 20 as a light emitting device includes a long base member 21, and a lens holder 23 is attached to the base member 21. As shown in FIG. 3, a printed circuit board 22 is attached to the base member 21, and a first bonding pad 24 as a first electrode pad is disposed on the printed circuit board 22, and as a light emitting array chip. LED array chip 26 is arranged. The LED array chip 26 includes a plurality of LEDs 28 as light emitting units arranged one-dimensionally on the surface 26A side along the longitudinal direction of the base member 21 (the direction of arrow M in FIG. 2). The number of pixels corresponding to the number of dots (the number of dots) is provided.

  A circuit for supplying various signals for controlling driving of the LED array chip 26 (each LED 28) is formed on the printed circuit board 22, and image data for one line can be sequentially processed.

  A rod lens array (SLA) 30 serving as a condensing lens (optical system) is provided at a position opposite to the surface 26A of the LED array chip 26 along the same direction as the longitudinal direction of the base member 21 (arrow M direction in FIG. 2). The lens holder 23 is mounted and arranged so that light from the LEDs 28 of the LED array chip 26 is imaged on the photosensitive member 16. A second bonding pad 32 as a second electrode pad is disposed on the surface 26A of the LED array chip 26 and within the range of the opening angle K of the rod lens array 30. The second bonding pad 32 is a thin film formed of Al by sputtering or the like, and has a film thickness of 2 to 3 μm.

  The first bonding pad 24 and the second bonding pad 32 are connected by a bonding wire 34 made of a gold wire. In this embodiment, the bonding wire 34 is bonded to the first bonding pad 24 (first bond) and then bonded to the second bonding pad 32 (second bond). Bonding is performed by applying a load to the bonding wire 34 after heating the printed circuit board 22 and the LED array chip 26.

  Here, since the bonding wire 34 is bonded to the first bonding pad 24 (first bond) and then bonded to the second bonding pad 32 (second bond), the BALL portion cannot be formed on the second bonding pad 32. Since there is no light reflected by the BALL part, the influence of the reflected light by the BALL part is eliminated.

  A surface 36 perpendicular to the direction of the central axis CL of the rod lens array 30 on the surface of the distal end side line portion 34A of the bonding wire 34 extending toward the second bonding pad 32 (in this embodiment, the same as the surface 26A of the LED array chip 26) The tilt angle A with respect to () is a tilt angle within a range in which the reflected light emitted from the LED 28 and reflected by the surface of the tip side line portion 34A does not enter the incident surface 30A of the rod lens array 30 (the reflected light enters the rod lens array 30). The tilt angle is smaller than the tilt angle in the range incident on the surface 30A). In the present embodiment, the inclination angle A with respect to the surface 36 (surface 26A of the LED array chip 26) perpendicular to the central axis CL direction of the rod lens array 30 on the surface of the distal end side line portion 34A is 0 ° ≦ A ≦ 45 °. It has become. The bonding angle of the bonding wire 34 to the second bonding pad 32 is more easily set to 0 ° ≦ A ≦ 45 ° when the second bond is used than when the first bond is used.

  Here, FIG. 4 and FIG. 5 show the results of simulating the stray light amount that the reflected light reflected from the bonding wire 34 passes through the rod lens array 30 by changing the inclination angle A. FIG. FIG. 4 shows the results for five patterns with different distances L (see FIG. 3) from the light emitting point (LED 28) to wire (bonding wire 34). The horizontal axis is wire angle A (inclination angle A), and the vertical axis Was the amount of stray light. FIG. 5 shows the results for three patterns with different wire diameters (bonding wire 34 diameters). The horizontal axis represents wire angle A (inclination angle A), and the vertical axis represents stray light. As shown in FIGS. 4 and 5, it can be seen that stray light increases rapidly when the wire angle A (inclination angle A) exceeds 45 °.

  That is, if 0 ° ≦ A ≦ 45 ° is set, the distance L (see FIG. 3) from the light emitting point (LED 28) to wire (bonding wire 34) can be set short, or the wire diameter (diameter of bonding wire 34). Even if is set to be somewhat thick, the influence of reflected light can be prevented, and an image having no image streak can be obtained.

  Next, the operation of the LED print head 20 in the first embodiment will be described.

  In the LED array chip 26 shown in FIG. 3, the LEDs 28 emit light, and this light is imaged through the rod lens array 30. A part of the light from the LED 28 strikes the bonding wire 34, but a surface 36 (surface of the LED array chip 26) perpendicular to the central axis CL direction of the rod lens array 30 on the surface of the tip end side line portion 34 </ b> A of the bonding wire 34. Since the tilt angle A with respect to 26A) is 0 ° ≦ A ≦ 45 °, the reflected light travels in a direction not incident on the incident surface 30A of the rod lens array 30 (such as the arrow B direction).

  As described above, even if a part of the second bonding pad 32 and the bonding wire 34 are within the range of the opening angle K of the rod lens array 30, the influence of the reflected light can be prevented, so that the LED array chip 26 can be reduced in size. Can be achieved.

  Next, a second embodiment of the light emitting device will be described with reference to FIGS. In addition, about the same member as 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 6, LED array chips 27 as a plurality of light emitting array chips are alternately arranged in two rows on the printed circuit board 22 such that end portions in the longitudinal direction partially overlap. In the present embodiment, a self-scanning LED (SLED: Self-scanning LED) array chip is used as the LED array chip 27. Since the SLED array can selectively emit light by using two signal lines at the on / off timing of the switch, the data line can be shared and the wiring can be simplified. As the SLED array, for example, one disclosed in JP-A-8-216448 can be applied.

  Each LED array chip 27 has a plurality of LEDs 28 arranged in the longitudinal direction, and a transfer thyristor 29 for sequentially lighting the LEDs 28 serially. Near the both ends of the LED array chip 27 in the arrangement direction of the LEDs 28, second bonding pads 32 as second electrode pads are arranged, and the first bonding pads 24 on the printed circuit board 22 and the first bonding pads 24 on the LED array chip 27 are arranged. Two bonding pads 32 are connected by a bonding wire 34.

  In this self-scanning LED, the number of second bonding pads 32 serving as electrodes can be significantly reduced as compared with the conventional LED chip. For this reason, the second bonding pads 32 can be concentrated on the end of the LED array chip 27 in the arrangement direction of the LEDs 28, and the chip size can be reduced, so that the number of chips taken from one wafer is greatly increased. Thus, the cost per chip can be reduced. Further, since the number of bonding wires 34 is reduced corresponding to the number of second bonding pads 32, the amount of light reflected from the bonding wires 34 is also reduced.

  However, since there is no LED 28 at the position where the second bonding pad 32 is disposed, the LED array chip 27 is used to perform exposure without a gap in a direction perpendicular to the moving direction of the photosensitive member 16 (see FIG. 1). It is necessary to arrange the portion where the second bonding pad 32 is disposed so as to overlap the LED 28 of the adjacent LED array chip 27. For this reason, the second bonding pad 32 is disposed at a position close to the LED 28 of the other adjacent LED array chip 27, and as shown in FIG. 7, the second bonding pad 32 is connected to the LED array chip 27. The surface 27A is disposed within the range of the opening angle K of the rod lens array 30. The bonding wire 34 extends to the opposite side of the LED 28 of the other adjacent LED array chip 27.

  Note that the light collection performance deteriorates as the LEDs 28 deviate from the central axis CL of the rod lens array 30 (lens density unevenness occurs), and such a shift leads to image disturbance. Needs to be as small as possible, and is preferably 0.2 mm or less.

  Also in the present embodiment, as in the first embodiment, the bonding wire 34 is bonded to the first bonding pad 24 (first bond) and then bonded to the second bonding pad 32 (second bond). A surface 36 perpendicular to the central axis CL direction of the rod lens array 30 on the surface of the distal end side line portion 34A of the bonding wire 34 extending toward the second bonding pad 32 (in this embodiment, the same as the surface 27A of the LED array chip 27) ) Is 0 ° ≦ A ≦ 45 °.

  Next, the operation of the LED print head 20 in the second embodiment will be described.

  Each of the plurality of LEDs 28 (see FIG. 6) in the plurality of LED array chips 27 emits light, and these lights are imaged through the rod lens array 30. A part of the light from the LED 28 strikes a bonding wire 34 connected to the second bonding pad 32 of the adjacent LED array chip 27, but the bonding wire 34 extends to the opposite side of the LED 28 and extends to the bonding wire. Since the inclination angle A with respect to the surface 36 (surface 27A of the LED array chip 27) perpendicular to the central axis CL direction of the rod lens array 30 on the surface of the front end side line portion 34A of 34 is 0 ° ≦ A ≦ 45 °, reflection The light travels in a direction not incident on the incident surface 30A of the rod lens array 30 (such as the arrow B direction).

  In order to confirm the operation of the above embodiment, a comparative experiment between an LED print head according to an example shown below (hereinafter simply referred to as an example) and an LED print head according to a comparative example (hereinafter simply referred to as a comparative example) is performed. went.

  The example has the same configuration as that of the second embodiment, and the surface 36 (surface 27A of the LED array chip 27) perpendicular to the central axis CL direction of the rod lens array 30 on the surface of the distal end side line portion 34A of the bonding wire 34. ) Was set to A = 35 °. The comparative example has the same configuration as the example except that the inclination angle A is set to A = 55 °.

  The LED 28 of Example and Comparative Example was caused to emit light, and the light after passing through the rod lens array 30 was photographed through the CCD. The experimental results are shown in FIG. In the comparative example, stray light is generated as shown in FIG. 8B, whereas in the example, it is confirmed that stray light is not generated as shown in FIG. 8A. did it.

1 is a schematic configuration diagram illustrating a configuration of an image forming apparatus to which an LED print head according to a first embodiment of the present invention is applied. 1 is a perspective view showing an LED print head according to a first embodiment of the present invention. It is an end view which shows the LED print head etc. which concern on the 1st Embodiment of this invention. (It is a figure corresponded to the 3-3 line end surface of FIG. 2.) It is a graph which shows the result of having simulated the difference in the amount of stray light by inclination angle A. FIG. (Shows five patterns with different distances from the light emitting point to wire.) It is a graph which shows the result of having simulated the difference in the amount of stray light by inclination angle A. FIG. (Shows three patterns with different wire diameters.) It is a layout diagram showing the layout and the like of LED array chips on a printed circuit board in the second embodiment of the present invention. It is an end elevation which shows the LED print head which concerns on the 2nd Embodiment of this invention. (It is a figure equivalent to the 7-7 line | wire end surface of FIG. 6.) It is a photograph which shows the result of an experiment example. FIG. 8A shows the case of the embodiment. FIG. 8B shows the case of the comparative example.

Explanation of symbols

20 LED print head (light emitting device)
22 Printed circuit board (board)
24 First bonding pad (first electrode pad)
26 LED array chip (light emitting array chip (light emitting chip))
26A LED array chip surface (light emitting chip surface)
27 LED array chip (light emitting array chip (light emitting chip))
27A LED array chip surface (light emitting chip surface)
28 LED (light emitting part)
30 Rod lens array (optical system)
30A Incident surface 32 Second bonding pad (second electrode pad)
34 Bonding wire 34A Tip side line portion 36 Surface perpendicular to the central axis direction of the rod lens array (surface perpendicular to the axial direction of the optical system)
A Inclination angle K Aperture angle

Claims (6)

A substrate,
A first electrode pad disposed on the substrate;
A light emitting chip disposed on the substrate and including a light emitting unit;
An optical system for imaging light from the light emitting chip;
A second electrode pad disposed on the surface of the light emitting chip and within an aperture angle of the optical system;
An inclination angle with respect to a plane perpendicular to the axial direction of the optical system on the surface of the distal end side line portion that connects the first electrode pad and the second electrode pad and extends toward the second electrode pad. A bonding wire having an inclination angle in a range in which reflected light emitted from the light emitting part and reflected by the surface of the tip side line part is not incident on the incident surface of the optical system;
A light emitting device comprising:   Reflected light that is emitted from the light emitting part and reflected from the surface of the tip side line part is incident on the entrance surface of the optical system at an inclination angle with respect to a surface perpendicular to the axial direction of the optical system on the surface of the tip side line part. The light-emitting device according to claim 1, wherein the inclination angle is smaller than the inclination angle within a range to be applied.   3. The light emitting device according to claim 1, wherein an inclination angle A with respect to a surface perpendicular to the axial direction of the optical system on the surface of the tip side line portion is 0 ° ≦ A ≦ 45 °. .   The light emitting chip is a light emitting array chip having a plurality of light emitting units, and a plurality of the light emitting array chips are alternately arranged on the substrate, and the second electrode pads are adjacent to the other light emitting array chips. 4. The light emitting unit according to claim 1, wherein the bonding wire extends to a side opposite to the light emitting unit of the other light emitting array chip adjacent to the light emitting unit. The light emitting device according to 1.   The light emitting device according to claim 1, wherein the light emitting chip is a self-scanning LED array chip.   6. The light emitting device according to claim 1, wherein the bonding wire is bonded to the first electrode pad and then bonded to the second electrode pad. 6.

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