JP2565701B2 - Optical writing head - Google Patents

Description

The present invention relates to an optical writing head used for an LED printer or the like using an electrophotographic method.

[Conventional technology]

FIG. 4 shows a schematic explanatory view of an LED printer using an LED array head.

In the figure, reference numeral 1 is a photosensitive drum whose surface is made of a photoconductive material, and rotates in the direction of the arrow in the figure. This drum 1
Is uniformly charged by the charger 2 and then exposed by the LED array head 3 in accordance with the recorded image information, whereby an electrostatic latent image is formed. This latent image is developed by the developing device 4 to obtain a toner image, and this toner image is transferred to the transfer paper 6 under the action of the transfer device 5. Then, the transfer paper 6 onto which the toner image is transferred is sent to the fixing device 7, where the toner image is fixed on the paper 6. On the other hand, after the transfer, the photosensitive drum 1 is cleaned by the cleaning device 8 and reused.

The LED array head 3 has a large number of LEDs as described later.
(Light emitting diode) LEDs with chips arranged in the print digit direction
The element array includes a self-focusing rod lens array that focuses light emitted from each LED element of the element array and exposes the light onto the photosensitive drum 1.

In the conventional LED array head 3 used in the above-mentioned LED printer, as shown in FIG.
The LED chip 22 is die-bonded on top, and wire bonding is performed corresponding to each light emitting part to energize each LED light emitting part, and at the same time, a bondin wire connected to this LED chip 22 and a ceramic mounting this LED chip 22. A cover glass 26 for protecting the conductor pattern on the substrate 21 is attached to a heat dissipation plate 23 such as aluminum, and the attachment member 25 of the self-focusing rod lens array 24 is supported on the heat dissipation plate 23.
It constituted the D array head.

[Problems to be solved by the invention]

In the above LED array head, when mounting the LED chip on the ceramic substrate, the positioning accuracy such as linearity is required to be about ± 10 μm, and the width of the chip is 0.7.
~ 1mm, width of die bonding pad is 1.2 ~ 1.5m
Since it is quite large (about m), the optical method using a TV camera etc. is inevitable for positioning, not only the efficiency of die bonding of the LED chip decreases, but also the mounting device needs to use an expensive one. was there.

Further, the wire bonding needs to be performed once for each LED light emitting portion (normally 64 LED chips are formed for each LED chip). As an example, a commonly used integration density of 300D
The LED array head for PI (about 12 dots / mm) and A4-letter size requires 2560 wire bonds, and it takes about 40 minutes to 1 hour even if a high-speed wire bonder is used. If even one of the books has a mistake in bonding, the entire LED array head will be defective, so careful attention is required, and the production efficiency is poor and the cost is increased.

Furthermore, the alignment accuracy of the LED chip of the LED array head and the variation in the linearity of the light emitting part in the height direction both require high accuracy of ± 100 μm in the width direction (216 mm for A4 size), so ceramic The warpage and bending of the substrate itself is limited. Therefore, a highly accurate ceramic substrate is required, and it is necessary to sort all the substrates, which makes the substrate expensive.

Further, since the self-focusing type rod lens array is held on the heat dissipation plate to which the ceramic substrate is attached, there is a drawback that errors of these dimensions are accumulated and required accuracy cannot be obtained.
Currently, the positioning accuracy of the self-focusing rod lens array is ± 0.1 mm over the entire length, and it is impossible to confirm the optical mounting position accuracy, and it is necessary to provide the LED array head with a mechanism that enables highly accurate positioning. There is
The cost was also increased in terms of assembly man-hours, manufacturing equipment, number of parts, and the like.

The present invention has been made in view of such problems, and an object of the present invention is to provide a low-priced optical writing head with a simple configuration.

[Means for solving problems]

The optical writing head of the present invention has a light emitting means having a light emitting portion, an electrical conducting means to which the light emitting means is connected, and a fiber plate in which an optical fiber bundle consisting of a plurality of optical fibers is embedded. In the write head led out from the fiber plate, the electric conduction means is a flexible circuit board, the light emitting means is mounted on the circuit board in a flip chip form, and the circuit board and the fiber plate are fixed to each other. It is characterized by being done.

Further, the optical fiber comprises a core, a clad formed on the outer periphery of the core and made of a material having a refractive index lower than that of the core, and a light absorber formed on the outer periphery of the clad. To do.

Furthermore, a transparent member having a high refractive index is interposed between the light emitting unit and the fiber plate.

[Action]

 The above-mentioned means operate as follows.

Since the light emitting means is mounted on the flexible circuit board by the flip chip method, wire bonding is unnecessary.

Moreover, since a plurality of optical fiber bundles are directly embedded in the fiber plate, the number of parts can be reduced and the mechanism can be simplified.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, 11 is a fiber plate made of glass or the like, and a two-layer FPC 12 made of a polyimide 12c on which a desired fine conductor pattern 12a, 12b is formed is provided on the surface 11a by a copper foil. There is. This conductive pattern 12a
The LED chip 13 has solder bumps 12a on its top so that its light emitting portion 13a faces the FPC 12. Further, the back electrode 13b of the LED chip 13 is electrically connected to the ground pattern 20 of the FPC 19 by the silver paste 14. The FPC 19 has a structure in which a conductive pattern 20 of a copper foil is formed on a polyimide 21 like the FPC 12. In order to prevent a short circuit between the FPC 19 and the FPC 12, an insulating layer 2 made of polyimide is further formed on the upper surface of the FPC 12.
Two are provided. The light emitting portion 13a of the LED chip 13 has a diameter described later through a transparent synthetic resin 15 having a high refractive index.
One end 16a of a fiber bundle 16 having a structure in which a large number of optical fibers 17 of 10 to 25 μm are assembled is close to each other while being embedded in the fiber plate 11. As shown in FIG. 2, the above-mentioned optical fiber 17 is formed by a core 17a made of garam having a high refractive index, a clad 17b made of glass having a low refractive index and formed on the outer periphery of the core 17a, and an outer periphery of the clad 17b. It has a three-layer structure including an absorber 17c made of carbon or the like.

In the LED array head configured as described above, as shown in FIG. 1, the light emitted from the light emitting portion 13a of the LED chip 13 enters from the one end 16a of the fiber bundle 16 through the transparent synthetic resin 15. Then, it is transmitted through the fiber bundle 16 with high efficiency, and is radiated from the other end portion 16b to the surface of the exposed object 18 such as the photosensitive drum.

Next, a method of manufacturing the LED array head of this embodiment will be described.

First, as shown in FIG. 3, the first and second conductive patterns 12a and 12b of the two-layer FPC 12 are simultaneously formed on one piece of polyimide, and the contacts are exposed by etching. Cut into 2 pieces. Then, two sheets are superposed on each other and further polyimide for the insulating layer 22 is superposed on each other and then welded by a large current pulse to manufacture an FPC 12 having a two-layer conductive pattern. Next, the conductive pattern 12a of this FPC 12 and the LED array 13
And are connected by TAB (Tape Automated Bonding) method. Next, the fiber plate 11 in which the fiber bundle 16 is embedded and the FPC 12 are bonded and fixed. At this time, the synthetic resin 15 is inserted between the light emitting portion 13a of the LED array 13 and the fiber bundle 16. Finally the back electrode 1 of the LED array 13
Apply silver paste 14 to 3b and bake at about 150 ℃ to make FPC19
Then, the LED array head of this embodiment is completed.

The present invention is not limited to the above embodiment, and various modifications can be made.

〔The invention's effect〕

In the present invention, the following effects are provided by configuring the optical writing head as described above.

The flip-chip mounting of the light emitting means eliminates the need for a bonding wire, which improves the yield, significantly shortens the bonding time, improves the production efficiency, and reduces the cost. Furthermore, expensive mounting equipment is not required. Since the conventional pad width for bonding is not required, the size of the optical writing head can be reduced.

By mounting the light emitting means on the flexible circuit board, the mounting work can be facilitated and the yield as the optical writing head can be improved. Further, due to the flexibility, a cable or the like to be connected to the optical writing head can also be used as a flexible circuit board, and the production efficiency of the device is improved.

Since the optical fiber does not have a focus unlike the self-focusing type rod lens array, the distance between the light emitting portion of the light emitting means and the object to be exposed can be reduced, and the device can be downsized. Then, the optical fiber is used as a core, a clad,
With the three-layer structure with the light absorber, the light emitted from the light emitting portion is transmitted to the exposed object with high efficiency in the optical fiber and is irradiated to the object to be exposed, so that the power supplied to the light emitting means can be reduced. Therefore, the life of the light emitting means is extended.

Further, by interposing a transparent member having a high refractive index between the light emitting section and the fiber plate, it is possible to suppress light scattering and to more efficiently irradiate the exposed object with the light emitted from the light emitting section.

[Brief description of drawings]

FIG. 1 is a structural sectional view of an LED array head showing an embodiment of the present invention, FIG. 2 is a sectional view of the same optical fiber, FIG. 3 is a plan view of an FPC, and FIG. 4 is a configuration of an ordinary LED printer. FIG. 5 is a schematic configuration diagram illustrating FIG. 5, and FIG. 5 is a structural cross-sectional view of a conventional LED array head. 11 …… Fiber plate 12 …… FPC 13 …… LED chip 13a …… Light emitting part 16 …… Fiber bundle 17 …… Optical fiber

Claims (3)

(57) [Claims] 1. A light emitting means having a light emitting portion, an electrical conducting means to which the light emitting means is connected, and a fiber plate in which an optical fiber bundle composed of a plurality of optical fibers is embedded. In the optical writing head derived from the above, the electrical conduction means is a flexible circuit board, the light emitting means is mounted on the circuit board in a flip-chip form, and the circuit board and the fiber plate are fixed to each other. An optical writing head characterized by that. 2. The optical fiber comprises a core, a clad formed on the outer periphery of the core and made of a material having a refractive index lower than that of the core, and a light absorber formed on the outer periphery of the clad. The optical writing head according to claim 1, wherein: 3. The optical writing head according to claim 1, wherein a transparent member having a high refractive index is interposed between the light emitting portion and the fiber plate.