JPH0725060A - Optical printing head and manufacture thereof - Google Patents

Abstract

PURPOSE:To enhance the productivity and reliability of an optical printing head by a method wherein wire bonding is eliminated in a process for arranging and packaging a light-emitting diode array chip on a light transmittable board. CONSTITUTION:A plurality of electroconductor film 22 for circuit are arranged on the surface of a light transmittable board 21. On the light emitting surface side of a light emitting diode array chip 23, which is formed by integrating a plurality of light emitting diodes 24 in tandem, the metallic bumps 26 for the electrode terminals of the light-emitting diode are arranged. The light emitting diode array chip 23 is die-bonded onto the board 21 by turning facedown or under the condition that its light-emitting surface faces to the surface of the board and the metallic bumps 26 come into contact with the metal plating layer 27 of conductor film 22. The metallic bump 26 has the Young's modulus, which is higher than that of the metal plating layer 27. In addition, the film thickness of the metal plating layer 27 is larger than the fluctuating dimension of the height of the metallic bump 26.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical print head which is incorporated in an electrophotographic printer, a digital copying machine or the like to convert an electric signal of one-dimensional image information into a one-dimensional optical image and a manufacturing method thereof. It is a thing.

[0002]

2. Description of the Related Art An optical print head suitable as a writing means of a non-impact printer is applied to electrophotographic printers, digital copying machines and the like. In the electrophotographic printer, one modulated laser beam is applied to a rotary polygon mirror to be deflected, and the obtained deflected light is applied to an electrophotographic photosensitive member, or a plurality of light emitting diode arrays are radiated. For example, there is a system in which light from a book is focused by a SELFOC lens array and is applied to an electrophotographic photosensitive member. The latter has been applied to high-speed printers, personal facsimiles, etc. because it can write in parallel, can write in parallel, and can design the optical system in a small size.

As an optical system attached to an optical print head using a light emitting diode array, there are a converging rod lens array which is an equal-magnification optical lens, an optical fiber array substrate (JP-A-55-98879), and the like. The latter is also relatively inexpensive because the printer can be made compact.

A typical conventional optical print head will be described with reference to FIGS. 9 and 10. A plurality of die-bonded substrates are formed on an insulating substrate 1 through a circuit conductor film 2 and a die-bonding conductive resin layer 3. The light emitting diode array chips 4 are arranged in a straight line. Each light emitting diode array chip 4 has a plurality of light emitting diodes 5 monolithically formed on a single crystal semiconductor substrate and its electrode terminals 6. A driving IC 7 is die-bonded on the insulating substrate 1 similarly to the light emitting diode array chip 4, and the respective electrode terminals 6 and 8 are wire-bonded to each other by a metal wire 9. The output light of the light emitting diode 5 is taken out through the converging rod lens array 10 and forms an image at a focal point 11. Reference numeral 12 indicates a chassis.

The information signal input through the external terminal 13 is transmitted to the driving IC 7 through the circuit conductor film 2 and the metal wire 9, and the driving IC 7 performs serial / parallel conversion of this information signal to correct the emission intensity. The light emitting diode 5 of the light emitting diode array chip 4
Then, the signal is transmitted again through the metal wire 9. The light emitting diode array chip 4 causes the light emitting diode 5 to emit light with a radiation intensity proportional to the transmitted signal current.

FIG. 11 shows the configuration of an optical printer using such an optical print head. The photoconductor drum 14 includes an organic photoconductor (O) on a cylindrical conductor made of aluminum or the like.
It has a photoconductive material layer such as PC) or an amorphous silicon photoconductor and rotates in the direction of the arrow. The charger 15 uniformly charges the surface of the photoconductor drum 14 at several hundreds of volts. The optical print head 16 shown in FIGS. 9 and 10 is arranged so that its focal point is located on the surface of the photosensitive drum 14. The optical signal radiated from the light emitting diode 5 through the rod lens array 10 forms an image on the surface of the photoconductor drum 14 to form a one-dimensional electrostatic latent image. The electrostatic latent image is toner-developed by the developing device 17, and the obtained toner image is transferred to the transfer paper 19 by the transfer device 18. 20 indicates a cleaner.

Here, the conventional method for manufacturing the optical print head 16 will be described. First, the light emitting diode 5 and its electrode terminal 6 are monolithically formed in a single crystal III-V group semiconductor substrate (wafer). The wafer is cut and separated into units of the light emitting diode array chip 4. On the other hand, a conductive resin layer 3 is applied and formed on a predetermined circuit conductor film 2 on the surface of the insulating substrate 1, and a plurality of light emitting diode array chips 4 are linearly arranged on the conductive resin layer 3. Similarly, the driving IC 7 is also mounted on the circuit conductor film 2 via the conductive resin layer 3. After that, both resin layers 3 and 3 are cured at a temperature of about 150 ° C. and die-bonded. Next,
An optical print head 16 completed by wire bonding using a gold wire or an aluminum wire between both electrode terminals 6 and 8.
The focusing rod lens array 10 together with the chassis 12
Built in.

[0008]

However, with such a structure, it is necessary to wire bond the electrode terminals 6 of the individual light emitting diodes 5 one by one. As an example,
In an optical print head (A4 size) having a light emitting diode resolution of 400 dpi, 3,456 wire bonds are required on the light emitting diode array chip 4 side alone, and about 4,000 wire bonds are required when the driving IC 7 side is included. Therefore, even if a high-speed wire bonder is used, a time of 30 minutes to 1 hour is spent for wire bonding, which is a major factor that hinders improvement in productivity and yield.

Further, the height of the light emitting diode array chip 4 mounted on the insulating substrate 1 tends to vary depending on the layer thickness and position of the conductive resin layer 3 for die bonding, which is
By shifting the focus position of the converging rod lens array 10,
There is also a problem that the light emission output and the resolution are lowered.

[0010]

In order to solve the above-mentioned problems, the present invention provides a transparent substrate having a plurality of circuit conductive films arranged on the surface thereof, and a plurality of light emitting diodes arranged in a straight line. And a light emitting diode array chip in which metal bumps as electrode terminals of each light emitting diode are arranged on the light emitting surface side, and the light emitting diode array chip has its light emitting surface on the surface of the transparent substrate. An optical print head characterized in that the metal bump is in contact with a metal plating layer of the circuit conductor film, and the metal bump has a higher Young's modulus than the metal plating layer. Provided.

Further, a light-transmissive substrate having a plurality of circuit conductor films arranged on its surface and a plurality of linearly arranged light emitting diodes are integrated to form metal bumps as electrode terminals of each light emitting diode. A light emitting diode array chip arranged on a surface on the light emitting surface side, the light emitting diode array chip is die-bonded with its light emitting surface facing the surface of the transparent substrate, and the metal bumps are on the circuit conductor film. In contact with at least the metal plating layer formed at a position facing the metal bump, and the metal plating layer has a layer thickness larger than the height variation of the metal bump and smaller than the height of the metal bump. An optical print head is provided.

Further, metal bumps, which are electrode terminals, are arranged on the light emitting surface side of the light emitting diode array chip.
Stacking the metal plating layer of the conductor film for a circuit arranged on the surface of the transparent substrate at a predetermined position, pressing the light emitting diode array chip to the transparent substrate side for temporary fixing, A step of releasing pressure, a step of heating the metal bump and the metal plating layer on the conductor film for a circuit to a temperature between the melting point of the former and the melting point of the latter to perform final fixing, and a light emitting diode A method for manufacturing an optical print head, comprising: a step of injecting a translucent insulating resin into a gap between an array chip and a translucent substrate; and a step of curing the translucent insulating resin. .

[0013]

According to the present invention, the light emitting diode array chip is die-bonded in a face-down posture with its light emitting surface facing the surface of the transparent substrate, and the electrode terminals of the light emitting diode are for circuits on the surface of the transparent substrate. Bonded directly to the conductor film. Therefore, the conventional wire bond is not necessary, and the bonding corresponding to the wire bond is achieved at the same time as the die bonding, and the bonding at a plurality of points is achieved all at once.

Further, since the bonding is achieved by pressing the metal bump strongly against the metal plating layer, even if there is a variation in the layer thickness of the conductive resin layer for die bonding, it can be made uniform during die bonding. it can.

Further, by setting the Young's modulus of the metal bump higher than the Young's modulus of the metal plating layer, or by setting the layer thickness of the metal plating layer larger than the height variation of the metal bump, It is possible to ensure the important temporary fixing performed prior to the fixing process.

[0016]

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

As shown in FIG. 1, the transparent substrate 21 has a plurality of circuit conductive films 22 arranged on the surface thereof. The light emitting diode array chip 23 monolithically integrates a plurality of linearly arranged light emitting diodes 24. The metal bumps 26 provided as electrode terminals on the electrode lead portions 25 of each light emitting diode 24 have a light emitting surface side. Are arranged on the surface of. The light emitting diode array chip 23 is die-bonded such that its light emitting surface faces the surface of the transparent substrate 21 in a face-down posture. The metal bumps 26 are in contact with the metal plating layer 27 of the circuit conductor film 22. The conductor film 22 for a circuit has a metal bump 2 in its entire length.
The metal plating layer 27 is provided only on the surface portion with which 6 abuts. In addition, the light-transmissive substrate 21 may be transparent at least in a region serving as an optical path. 28 is a translucent insulating resin layer, 2
Reference numeral 9 is a conductive resin layer, 30 is a chip back surface electrode, and 31 is a driving IC.

The optical print head thus constructed is incorporated in the chassis 33 together with the converging rod lens array 32, as shown in FIG. 34 is an external terminal, 3
Reference numeral 5 denotes a photosensitive drum.

The information signal voltage input to the external terminal 34 is input to the driving IC 31 through the circuit conductor film 22, the metal plating layer 27 and the metal bumps 26. Here, output correction to the light emitting diode array chip 23 is performed by parallel / serial conversion by a shift register, voltage / current conversion, and the like. Then, the signal current to each light emitting diode 24 is input again to the electrode lead portion 25 of the light emitting diode array chip 23 through the circuit conductor film 22, and each light emitting diode 24 has the light emission intensity corresponding to the input signal current. Emits light.

The method of manufacturing the optical print head having the above structure is as follows. First, single crystal III-
A plurality of light emitting diodes 2 are provided on a group V semiconductor substrate (wafer).
4 and its electrode lead portion 25 are built in. In this example, one light-emitting diode with emission wavelengths of 660 nm and 740 nm is used.
It was built in at 6 dots / mm. Next, the metal bumps 26 are formed on the electrode lead portions 25. The metal bump 26 may be formed by plating gold, indium, solder, or the like, or may be formed by fusing a metal thin wire such as a gold wire into a spherical shape by heat energy and ultrasonic energy. In this example, a gold wire having a wire diameter of about 25 μm is fused into a spherical shape of several μm to 50 μm.
m projections were formed for the metal bumps. After that, the wafer is cut and separated into units of the light emitting diode array chip 23 by a high precision dicing technique.

On the other hand, a plurality of circuit conductor films 22 are formed on the surface of the transparent substrate 21. The circuit conductor film 22 is formed into a predetermined pattern film by printing a gold thick film paste and curing it, followed by patterning by photolithography and etching. Of the circuit conductive film 22, the electrode lead portion 2 of the light emitting diode array chip 23.
The metal plating layer 27 is formed in the portion facing 5 In this example, an electrolytic plating method was applied to form a nickel plating layer having a layer thickness of about 1 μm, and then a solder plating layer having a layer thickness of about 10 μm was formed.

Next, as shown in FIG. 3A, the light emitting diode array chip 23 is arranged at a predetermined position on the transparent substrate 21. Although only three metal bumps 26 are shown for each light emitting diode array chip 26 in FIG. 3, 64 light emitting diodes are actually integrated for each light emitting diode array chip 23. Therefore, there are 64 metal bumps 26.

Next, as shown in FIG. 3B, a pressing tool 37 is used to apply a pressure in the vertical direction from the back surface side of the light emitting diode array chip 23 aligned on the front surface of the transparent substrate 21. Press. By this pressure, the metal bump 2
6 and the metal plating layer 27 elastically deform. Thereafter, the pressure is released, but the light emitting diode array chip 23 is temporarily fixed on the surface of the transparent substrate 21 by this step.

The Young's modulus of the metal bump 26 is set to be larger than that of the metal plating layer 27. By selecting the material in such a relationship, the metal plating layer 27 undergoes large elastic deformation before the metal bumps 26, and the metal bumps 26 are embedded in the metal plating layer 27. Following this, the metal bumps 26 are elastically deformed and leveled, so that height variations are corrected. The metal bump 26 is temporarily fixed to the metal plating layer 27 by such a mechanism.

The thickness of the metal plating layer 27 is set to the metal bump 26.
By setting it to be larger than the height variation dimension after the elastic deformation, all the metal bumps 26 can be reliably embedded in all the metal plating layers 27, and a sufficient temporary fixing effect can be obtained.

The metal plating layer 27 has a layer thickness of the metal bump 2
The height is set to be smaller than the height of 6 after the elastic deformation. If the layer thickness of the metal plating layer 27 is equal to or greater than the height of the metal bump 26, the metal bump 26 will be
There is a risk that the plating layer material such as solder will come into contact with the electrode lead portion 25 formed on the light emitting diode array chip 23, because it will be completely buried inside. Since the electrode lead portion 25 is usually made of a metal whose main component is aluminum,
It easily corrodes against solder and reduces reliability. Therefore, the layer thickness of the metal plating layer 27 such as solder is set to the metal bump 26.
By making the height smaller than that after elastic deformation, contact between the electrode lead portion 25 and the metal plating layer 27 is avoided.

In this example, since the height variation of the metal bumps 26 made of gold after being pressed could be suppressed to less than 3 μm, the thickness of the metal plating layer 27 made of solder was 3 μm to 3 μm.
An appropriate value was 0 μm. Especially, the layer thickness is 10 μm to 2
When selected in the range of 0 μm, favorable results were obtained in terms of both stability in temporary fixing and reliability in main fixing.

Similarly, the second and third light emitting diode array chips are sequentially arranged, and the light emitting diode array chips 23 are arranged in a number corresponding to the optical recording width of the optical print head by sequentially applying pressure (FIG. 3c). In this example, 54 chips were arranged on a straight line to manufacture a contact type optical print head of A4 size 16 dot / mm.

FIG. 3 shows a light emitting diode array chip 23.
Although only shown, the same metal bump as described above is formed on the driving IC 31. Then, the semiconductor chips after cutting and dividing are arranged in a predetermined position and temporarily fixed by pressurization.

Next, the light emitting diode array chip 23
The transparent substrate 21 on which the driving IC 31 is temporarily fixed is placed in a high temperature atmosphere. At this time, the temperature is set between the melting point of the metal bump 26 and the melting point of the metal plating layer 27. In this example, the temperature is set to 185 ° C to 220 ° C. As a result, only the solder plating layer having a low melting point was melted, and the surface tension of the solder plating layer blew up onto the surface of the gold bump, and an ideal solder connection effect could be obtained (d in FIG. 3).

Next, the light emitting diode array chip 23
A transparent insulating resin layer 28 is formed by filling each gap between the driving IC 31 and the transparent substrate 21. As this material, a UV-curable translucent insulating resin is used. After the filling, ultraviolet rays are irradiated from the chip non-mounting surface of the transparent substrate 21 to cure (e in FIG. 3).

Although an ultraviolet curable resin is used in this example, a thermosetting type resin may be used. Also, a heat / ultraviolet combined type resin may be used. Light emitting diode array chip 23
Is filled with a translucent insulating resin, but the driving IC3
1 does not have to be translucent.

After this, the light emitting diode array chip 2
An epoxy-based conductive resin layer 29 for electrically connecting the back electrode 30 of No. 3 and the predetermined circuit conductor film 22 is formed.

Epoxy conductive resin is applied and the temperature is 130 ° C.
Cure at a temperature of ~ 150 ° C for about 1 hour (f in Figure 3).

Since the structure and manufacturing method are as described above, it is not necessary to set the two steps of the die bonding step and the wire bonding step, and electrical connection and mechanical connection can be obtained at the same time. In addition, since electrical connection can be achieved at a large number of points between the light emitting diode array chip and the driving IC, it is possible to obtain a highly reliable optical print head that is highly productive. The integrated circuit that drives the light emitting diode array chip is temporarily fixed at the same time as the light emitting diode array chip, fully cured, and filled with translucent insulating resin.
It is possible to cure the translucent insulating resin, apply the conductive resin, and cure the conductive resin, thereby further improving the productivity.

The optical print head of the embodiment shown in FIG. 4 uses the optical fiber array substrate 38. Reference numeral 39 denotes an optical fiber bundle. The optical fiber array substrate 38 has a structure as shown in FIGS. 40 indicates a base glass. The optical fibers forming the optical fiber bundle 39 have a clad 42 having a small refractive index around the core 41 as shown in FIG. 7 in order to remove light having an angle larger than the incident angle corresponding to the numerical aperture (NA). The light absorber layer 43 is provided around it. Core diameter is 12 and numerical aperture is 0.
9 optical fibers were used. Each core 41 has a clad 42 having a thickness of about 2 μm and a light absorber layer 43 having a thickness of about 2 μm.
Are covered. A plurality of such optical fibers are combined to form an optical fiber bundle 39, and the optical fiber bundle 39 is arranged between two base glasses 40 and 40 having a thermal expansion coefficient substantially equal to that of the optical fibers, and heating / heating is performed. Apply pressure to melt and integrate. For this reason, the optical fiber bundle, which was initially circular, is deformed into a pentagonal or hexagonal cross-sectional shape. This is cut out to an appropriate thickness, and the exposed end surface of the optical fiber is optically polished to a mirror surface to obtain an optical fiber array substrate 38. The circuit conductor film 22 is formed on the optical fiber array substrate in the same manner as in the above embodiment. At this time, the light emitting diode 24 of the light emitting diode array chip 23 is formed so as to face the end face of the optical fiber bundle 39. The metal plating layer and the metal bump are formed in the same manner as in the above-mentioned embodiment.

The operation of the optical print head thus constructed is basically the same as that of the above-described embodiment. The light emitted from the light emitting diode enters from the end face of the optical fiber. Only light that is incident at an angle smaller than the angle corresponding to the numerical aperture of the fiber is repeatedly completely reflected inside the core of the fiber and is emitted from the other end of the fiber.

As shown in FIG. 8, the other end of the optical fiber of the optical fiber array substrate 38 is arranged in proximity to the photoconductor drum 35, and the predetermined position of the photoconductor drum 35 is irradiated with light. Light incident at an angle larger than the angle corresponding to the numerical aperture is absorbed by the light absorber layer 43 of each optical fiber.

Here, as the photosensitive drum 35, a photosensitive belt formed by forming a transparent electrode on a translucent belt and then applying a photosensitive member thereto can be used. In this case, the optical fiber array substrate 35 can be brought into close contact with the surface of the photosensitive belt on which the photosensitive member is not applied, and such a configuration is advantageous in terms of resolution and the like.

In the optical print head thus obtained, when the recording medium is illuminated by using the same light emitting diode as in the conventional optical print head using the SELFOC lens array, an optical signal of about 4 to 8 times is obtained. I was able to get

[0041]

As described above, according to the present invention, the wire connection is not required for the electrical connection from the electrode terminals of the light emitting diode array chip to the driving IC, so that the productivity, reliability and yield of the optical print head can be improved. Both can be greatly improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical print head according to an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a printer to which the optical print head according to the embodiment of the invention is applied.

FIG. 3 is a manufacturing process diagram of an optical print head according to an embodiment of the present invention.

FIG. 4 is a side view of an optical print head according to another embodiment of the present invention.

FIG. 5 is an explanatory diagram of an optical fiber array substrate.

FIG. 6 is an explanatory diagram of an optical fiber array substrate.

FIG. 7 is an explanatory diagram of an optical fiber array substrate.

FIG. 8 is a cross-sectional view of a main part of a printer to which an optical print head according to another embodiment of the present invention is applied.

FIG. 9 is a cross-sectional view of a conventional optical printhead.

FIG. 10 is a vertical cross-sectional view of a conventional optical print head.

FIG. 11 is a configuration diagram of an optical printer.

[Explanation of symbols]

 21 Translucent Substrate 22 Circuit Conductor Film 23 Light Emitting Diode Array Chip 24 Light Emitting Diode 25 Electrode Lead 26 Metal Bump 27 Metal Plating Layer

Claims (5)

[Claims] 1. A light transmissive substrate having a plurality of circuit conductive films arranged on the surface thereof and a plurality of light emitting diodes arranged in a straight line are integrated to form a metal bump as an electrode terminal of each light emitting diode. The light emitting diode array chip is arranged on the surface of the light emitting surface, and the light emitting diode array chip is die-bonded with its light emitting surface facing the surface of the transparent substrate, and the metal bumps are on the circuit conductor film. Of at least the metal plating layer formed at a position facing the metal bump, and the metal bump has a Young's modulus higher than that of the metal plating layer. 2. A light-transmitting substrate having a plurality of circuit conductor films arranged on the surface thereof, and a plurality of light emitting diodes arranged in a straight line, and metal bumps serving as electrode terminals of each light emitting diode. The light emitting diode array chip is arranged on the surface of the light emitting surface, and the light emitting diode array chip is die-bonded with its light emitting surface facing the surface of the transparent substrate, and the metal bumps are on the circuit conductor film. At least in contact with a metal plating layer formed at a position facing the metal bump, and the metal plating layer has a layer thickness larger than the height variation dimension of the metal bump and smaller than the height of the metal bump. Optical print head characterized by 3. The optical print head according to claim 1, wherein the metal bump is made of gold and the metal plating layer is made of solder. 4. The metal bump is made of non-eutectic solder, and the metal plating layer is made of eutectic solder.
Alternatively, the optical print head according to claim 2. 5. A metal bump, which is an electrode terminal arranged on the light emitting surface side of the light emitting diode array chip, is provided at a predetermined position of the metal plating layer of the circuit conductive film arranged on the surface of the transparent substrate. A step of stacking, a step of temporarily pressing the light emitting diode array chip toward the transparent substrate side, a step of releasing the pressure, the metal bump and the metal plating layer on the circuit conductive film. Is heated to a temperature between the melting point of the former and the melting point of the latter to perform permanent fixing, and a step of injecting a translucent insulating resin into the gap between the light emitting diode array chip and the translucent substrate, And a step of curing the light-insulating resin.