JP2004006994A - Light-emitting diode array and optical printhead equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical printhead capable of reliably realizing wire bonding and performing high-reliability bonding in a light-emitting diode array of high density of 600 dpi or more. <P>SOLUTION: The light-emitting diode array where a plurality of light-emitting areas 21 and a separate longitudinal electrode 23 connected with the light-emitting areas 21 though an electrode wire 22 are disposed is characterized in that a protective film 25 is formed on the surface of the wire 22 and the surface of an edge section of the electrode 23 and the protective film on a long-side edge of the electrode 23 is removed. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a light emitting diode array and an optical print head including the same.

2. Description of the Related Art Light emitting diode (LED) elements have been widely used as display devices in the past because of their vivid emission, low driving voltage, and easy peripheral circuits.

光 Optical print heads using a light-emitting diode array have been actively studied for the purpose of application to a light source of an optical printer or the like employing an electrophotographic method.

An optical printer using a self-luminous light-emitting diode array as a light source emits each dot of the light-emitting diode array in response to an image signal, and exposes the photosensitive drum with a 1: 1 imaging element such as a distributed index lens. After forming an electrostatic latent image by using a developing device, toner is selectively adhered thereto, and then printing is performed by transferring the toner adhered to plain paper or the like.

A head using a light-emitting diode array can be downsized because (1) there are no moving parts and there are few components, and (2) it is easy to increase the length by connecting an array chip. With features such as.

By the way, in a light emitting diode array having a light emitting region density of, for example, 600 dpi, the pitch of the light emitting region is 42 to 43 μm, and the width of the light emitting region is further shorter than the pitch in consideration of the width of the non-light emitting region between the light emitting regions. . Further, the electrodes on the light emitting region are formed with a width of 42 to 43 μm or less and a pitch of 42 to 43 μm. The wiring electrodes connected to the electrodes on the light emitting region are formed to have a narrow width of 42 to 43 μm or less and a width of 42 to 43 μm or less, and are connected to wide electrodes (pads) for bonding. You. It is necessary to electrically connect the light emitting diode array on which the electrode wiring is formed as described above to, for example, a driving element for driving the light emitting diode array by wire bonding or the like.

(4) Even the stitch bonding which can perform the narrowest bonding at present has a bonding width of 40 μm, and further needs a width of about 20 μm in consideration of the positional accuracy of the bonding apparatus. That is, it is necessary to secure at least about 60 μm as the width of the bonding electrode.

Therefore, in the case of a high-density light emitting diode array of, for example, 600 dpi or more, wire bonding is difficult if the bonding electrodes are arranged in a single row, and the bonding electrode pitch is increased by arranging in a staggered two rows. Nevertheless, the width of the bonding electrode can be as small as only about 60 μm. However, it is becoming extremely difficult to wire the light emitting diode array and the driving element by wire bonding.

As conventional light-emitting diodes (arrays) for this type of optical printer, there are, for example, those disclosed in Patent Documents 1 to 3.

FIG. 4 is a plan view showing a light emitting diode array for an optical printer described in the above document, and FIG. 5 is a sectional view taken along the line A-A 'in FIG.

In these figures, reference numeral 1 denotes a compound semiconductor made of GaP, GaAsP, GaAlAs, GaAs, etc., and a plurality of light emitting regions 11 arranged in a row or in a staggered pattern are formed on the surface thereof by selective diffusion. Reference numerals 2, 3, and 4 denote insulating films made of Si3 N4, SiO2, Al2 O3, and the like, which are sequentially laminated on the surface of the compound semiconductor 1. The insulating films 2, 3, and 4 are provided in a plurality of layers for the purpose of a selective diffusion film in the light emitting region, a protective film on the surface of the compound semiconductor, a pinhole countermeasure film, a wiring reinforcing base film, and a light extraction / brightness adjusting film. Reference numeral 5 denotes an electrode layer made of Al or the like, which is laminated on the insulating films 2 and 3 and has an ohmic contact with the light emitting region 11, for connecting to the light emitting region, for bonding, and for wiring for connecting these. Electrode. Reference numeral 6 denotes a common electrode made of Au or the like provided on the back surface of the compound semiconductor 1.

Here, in the case of a high-density light-emitting diode array of, for example, 600 dpi or more, the following problems occur in the method of performing wire bonding directly to the bonding electrode on the upper surface of each light-emitting diode array.

In other words, if the electrode width of the wiring connected to the bonding electrode and the distance between adjacent wirings are made extremely small in order to increase the wiring density, the wiring electrodes will be deformed by the external force applied during the array cleaning process and the head assembly process. In such a case, the deformed wiring electrode easily comes into contact with the adjacent wiring, so that it is necessary to further thicken the protective film formed on each wiring electrode to prevent corrosion and the like. For example, in a light emitting diode array of about 300 dpi, the formation of a protective film using an inorganic film (SiO 2, SiN, etc.) of about 0.2 μm is sufficient. However, since a sufficient protection function cannot be obtained, it has been attempted to use a polyimide-based material as the insulating film 4.

FIGS. 6 to 8 are diagrams for explaining wire bonding to a light-emitting diode array using, for example, a polyimide-based material as the insulating film 4.

As shown in FIG. 6, when, for example, a polyimide-based material is used as the insulating film 4, a polyimide-based thick film solution is spun on the electrode layer 5 to form the insulating film 4 serving as a protective film. The upper portion is patterned by etching to provide a through hole 4a for wiring connection. The wiring connection through hole 4 a is opened, for example, as shown by a hatched portion in FIG. 7, and a wide connection region 5 a is formed on the electrode layer 5.

Then, as shown in FIG. 8, the connection region 5a of the electrode layer 5 is ball-bonded by using a capillary 12 with a bonding wire 13 made of, for example, a gold wire. Are respectively connected by bonding wires 13. Alternatively, the output terminals of the drive elements may be first ball-bonded with the bonding wires 13, and then the output terminals of the ball-bonded drive elements and the connection regions 5 a may be connected with the bonding wires 13. In this case, since there is no ball portion on the connection region 5a where the second bonding is to be performed, it is necessary to bond the bonding wire 13 so as to rub it while crushing it.
Japanese Utility Model Publication No. 7-36754 JP-A-5-347430 JP-A-5-155063

However, as shown in FIG. 6, in the case of protection with a polyimide-based thick film (1 to 2 μm), such a thick film exists on the connection region, so that the bonding wire is not appropriately broken during bonding and the connection is insufficient. Is a problem. In particular, when a bonding wire is bonded on the connection region by second bonding, the thick film on the connection region may obstruct the height direction and the connection may be incomplete. In the worst case, the capillary may not be connected. In some cases, the bonding itself could not be performed due to collision with the thick film. In addition, if the bonding strength is insufficient, the probability of occurrence of disconnection or the like due to a difference in thermal expansion between different metals (usually Αl / Au) in the bonding portion or a change with time increases.

The above is the case of ball bonding, but there is a similar problem with stitch bonding that enables high-density connection.

An object of the present invention is to solve the above-described conventional problems. For example, when high resolution of 600 dpi or more is required and high-density connection by wire bonding is required, wire bonding can be reliably realized. It is an object of the present invention to provide a light emitting diode array capable of performing high bonding and an optical print head including the same.

A light-emitting diode array according to the present invention is a light-emitting diode array in which a plurality of light-emitting regions and a vertically long individual electrode connected to the light-emitting region via an electrode wiring are arranged. A protective film is formed on a surface of the electrode wiring and a surface of an edge portion of the individual electrode, and the protective film on a long side edge of the individual electrode is removed.

The light-emitting diode array of the present invention, as described in claim 2, a plurality of aligned light-emitting regions, and vertically elongated individual electrodes connected to the light-emitting region via electrode wiring and arranged in a staggered manner, In a light-emitting diode array having a plurality of rows, a protective film is formed on the surface of the electrode wiring so as to protect the electrode wiring which is passed between the individual electrodes in the staggered first row and is wired to the individual electrodes in the second staggered row. And forming a protective film on the surface of the edge portion of the individual electrode in a state where most of the individual electrode is exposed, and that the protective film on the long side edge of the individual electrode is removed. Features.

According to a third aspect of the present invention, there is provided the light emitting diode array, wherein the plurality of aligned light emitting regions are connected to the light emitting regions via an electrode wiring, and are adjacent to each other in the same direction as the alignment direction of the light emitting regions. A light-emitting diode array comprising at least two or more rows of individual electrodes arranged in a line, wherein a protective film is provided between the surface of the electrode wiring except at least the individual electrode portion and the row of the individual electrodes. .

In the light emitting diode array according to the present invention, a thin film covering the light emitting region is formed separately from the protective film to prevent corrosion of the individual electrodes.

An optical print head according to the present invention includes a light emitting diode array, a driving element for driving the array, and a thin metal wire electrically connecting the array and the driving element by bonding. In the optical print head provided, the light emitting diode array is used as the light emitting diode array.

An optical print head according to the present invention includes a light emitting diode array, a driving element for driving the array, and a thin metal wire electrically connecting the array and the driving element by bonding. In the optical print head, wherein the first bonding of the thin metal wire is performed on the driving element side and the second bonding is performed on the light emitting diode array side, the light emitting diode array is used as the light emitting diode array. Features.

The light-emitting diode array and the optical print head according to the present invention can provide a highly reliable optical print in a high-density light-emitting diode array of, for example, 600 dpi or more, while protecting the surface of the electrode wiring and performing reliable bonding. A head can be realized.

FIG. 1 is a plan view showing the structure of a light emitting diode array according to an embodiment of the present invention. This light emitting diode array has a dot density equivalent to 600 dpi.

FIG. 2 is a cross-sectional view of the light-emitting diode array of FIG. 1 taken along the line AA ', and FIG. 3 is a cross-sectional view of the light-emitting diode array of FIG.

In these figures, reference numeral 20 denotes a light-emitting diode array in which a plurality of light-emitting diodes constituting the light-emitting region 21 are integrated, and the main material is a compound semiconductor made of GaP, GaAsP, GaAlAs, GaAs, or the like. A plurality of light emitting regions 21 arranged in a line are formed on the surface of the light emitting diode array 20 by selective diffusion, and these are arranged linearly at a pitch of 600 dpi (about 42 to 43 μm). When the light emitting regions 21 are assembled as an optical printer head, they are arranged at equal intervals (42.3 μm) and with good linearity even at the joint portion of the light emitting diode array.

An electrode wiring 22 made of Al or the like in ohmic contact is connected to the light emitting region 21, and the other end of the electrode wiring 22 is arranged in two rows in a zigzag pattern as electrode wiring pads 23 of individual electrodes (anode electrodes). You. The electrode wiring pads 23 are for wire bonding. For example, the width is 60 μm and the length is 120 μm. The electrode wiring pads 23 are vertically long. Edges of each electrode wiring pad 23 are removed. The electrode wiring 22 portion of the pad 23 is formed to be wide 23a. The staggered first row of electrode wiring pads 23 and the staggered second row of electrode wiring pads 23 have, for example, a staggered step of 40.5 μm in the horizontal direction and 135 μm in the vertical direction.

As shown in FIG. 3, a common electrode (cathode electrode) 24 made of Au or the like is formed on the entire back surface of the light emitting diode array 20.

In such a light emitting diode array 20, a thick surface protection film 25 made of a polyimide material is formed on the surface of the electrode wiring 22 excluding the light emitting region 21 and the electrode wiring pad 23. The hatched portion in FIG. 1 shows the region where the surface protection film 25 is formed. As shown in the hatched portion, the surface protection film is formed so as to cover only the surface portion of the electrode wiring 22 which has been thinned for high-density wiring. The film 25 is formed, and the surface protection film 25 is not coated on other regions, especially on the respective electrode wiring pads 23. That is, in the conventional general wiring rule, the surface of the electrode wiring and the edge portion of the electrode wiring pad are protected by the protective film for corrosion prevention or the like, but in the present embodiment, the general wiring rule is reserved. The electrode wiring pad 23 is not protected by a thick film, and the surface protection film 25 is formed only on the surface of the electrode wiring 22 which is ultra-fine for high-density wiring.

The electrode wiring pad 23 on which the surface protection film 25 is not coated is reliably connected to an output terminal (not shown) of the driving element by wire bonding without being affected by the thick film at the edge portion and is electrically connected. .

(4) A part of the surface protective film 25 is disposed as a protective film 25a in a space between the first staggered electrode wiring pads 23 and the second staggered electrode wiring pads 23. The protective film 25a functions so as to prevent the thin metal wire 27 for wire bonding connected to the staggered first-row electrode wiring pads 23 from contacting the adjacent staggered second-row electrode wiring pads 23. .

Hereinafter, a method for manufacturing the light-emitting diode array 20 and a method for using the same in an optical print head will be described.

The light-emitting diode array 20 is made of a compound semiconductor made of GaP, GaAsP, GaAlAs, GaAs, or the like. , And the other end of the electrode wiring 22 is arranged in two lines in a staggered manner as electrode wiring pads 23 of individual electrodes (anode electrodes).

(3) As shown in FIG. 3, a common electrode (cathode electrode) 24 made of Au or the like is formed on the back surface of the individual light emitting element 20.

In this state, a polyimide-based thick film solution is spun on the surface of the light emitting diode array 20 including the electrode wiring 22 and the electrode wiring pad 23 to form a surface protection film 25 having a thickness of about 1 μm.

Then, etching is performed using a mask pattern (resist) having a shape shown by hatching in FIG. 1, and the resist is further removed, so that a polyimide-based material is formed only on the surface of the electrode wiring 22 except for the light emitting region 21 and the electrode wiring pad 23. A thick surface protection film 25 made of the above material is formed.

Thereby, as shown by the hatched portion in FIG. 1, the surface protection film 25 is formed so as to cover only the surface portion of the electrode wiring 22 which has been thinned for high-density wiring. The surface protective film 25 is not coated. Also, the surface protection film 25 is not formed on the surface of the light emitting region 21.

The thick surface protection film 25 is required to protect the thinned electrode wiring 22 for high-density wiring. In particular, the thick surface protection film 25 passes between the electrode wiring pads 23 in the staggered first row. This is for protection of the electrode wiring 22 that is wired to the electrode wiring pads 23 in the staggered second column. That is, if the thin wiring portion of the high-density wiring can be protected, the object can be achieved. 25 is not coated.

Next, the electrode wiring pads 23 serving as individual electrodes and the output terminals of the driving elements (not shown) are electrically connected to each other by thin metal wires (bonding wires) 27 such as gold wires by a wire bonding method. Since the surface protection film (thick film) 25 does not exist on the entire surface of the connection region including the edge portion on the electrode wiring pad 23, the first bonding is performed on the drive element side, and then the second bonding is performed on the electrode wiring pad 23. And bonding the thin metal wire 27 to the connection region by performing the above-described process, the thick film on the connection region does not obstruct the height direction and the connection is not incomplete, and a sufficient bonding strength is obtained. And a highly reliable optical print head can be realized.

Since the surface protective film 25 is not coated on the electrode wiring pad 23, protection such as corrosion prevention on the surface of the electrode wiring pad 23 cannot be achieved. However, the electrode wiring pad 23 has, for example, a width of 60 μm and a length of 120 μm, and has an area that is too large to be compared with the width of the high-density wiring electrode 22 (the minimum part is about several μm). Even if a certain degree of corrosion progresses on the surface of the pad 23, there is basically no problem.

However, in order to prevent corrosion of the electrode wiring pad 23, a method of (1) applying a varnish or the like on the electrode wiring pad 23 or (2) forming a thin film for corrosion prevention can be adopted. In this way, corrosion on the electrode wiring pads 23 can be prevented, and reliability can be further improved. In the present embodiment, the method (2) of forming a thin film for preventing corrosion is adopted. 2 and 3 show a corrosion prevention film 26 formed for this purpose. In this case, the formation of the corrosion prevention coating 26 is different from the thick surface protection film 25 made of a polyimide-based material described above, and is merely a thin film for preventing corrosion. Therefore, silicon nitride (Si3 N4), silicon oxide It is sufficient to form a thin inorganic film by (SiO2) or the like. Further, such an inorganic film made of silicon nitride or silicon oxide needs to cover the light emitting region 21 for another purpose such as a light extraction / brightness adjustment film. In the present embodiment, the nitride film serves both of the two purposes. A film was formed with silicon.

As described above, the optical print head according to the embodiment has the surface of the thick film made of a polyimide-based material only on the surface of the electrode wiring 22 except for the light emitting region 21 of the light emitting diode array and the electrode wiring pad 23 (individual electrode). Since the protective film 25 is formed, a protective film having a sufficient thickness accompanying the high-density wiring is formed on the surface of the electrode wiring 22 to effectively protect the electrode wiring 22 (by the external force of the electrode wiring 22). Deformation and short-circuit accidents caused by the deformation), and there is no obstruction of the thick film in the height direction on the surface protection film 25 when the electrode wiring pad 23 and the driving element are wire-bonded. A sufficient bonding strength can be obtained, and a highly reliable optical print head can be realized.

た め Since only the shape of the mask for forming the surface protective film needs to be changed, there is no special member or an increase in the number of manufacturing steps as compared with the conventional example, and there is an excellent effect that it can be easily and immediately implemented.

Therefore, in the structure of the present light-emitting diode array, a high-density optical print head of 600 dpi or more is possible because an arrangement structure in which the electrode wiring pads can be sufficiently connected by the current wire bonding technology can be obtained.

In the light emitting diode array of the present embodiment, the surface protection film 25 is formed so as to cover the surface portion of the electrode wiring 22, but at least the surface of the electrode wiring 22 excluding the electrode wiring pad (individual electrode) 23 portion. Any structure may be used as long as the structure includes the surface protection film 25. In short, it is sufficient that a connection region having a sufficient width capable of bonding is secured. For example, as shown in FIG. 1, the electrode wiring 22 portion of the electrode wiring pads 23 on the drive element side in two rows in a staggered manner is formed to have a wide width 23 a for reinforcing the electrode wiring 22. Up to the surface protection film 25.

Further, in the present embodiment, the surface protection film 25 is formed on the surface of the electrode wiring 22 except for the electrode wiring pad (individual electrode) 23 portion. Of course, the same effects as in the present embodiment can be obtained in the following cases.

Basically, it is only necessary that the thick film of the surface protection film 25 be formed on the electrode wiring pad (individual electrode) 23 without any hindrance to bonding. That is, since the width of the electrode wiring pad 23 tends to become narrower as the density of the optical print head becomes higher (higher resolution), the edge located in the width direction of the electrode wiring pad 23 (the arrangement direction of the electrode wiring pad 23). When the surface protection film 25 is formed on the surface, the wire bonding is hindered as described above. Therefore, it is not preferable to form the surface protection film 25 on the edge of the electrode wiring pad 23 in the width direction of the electrode wiring pad 23. However, the length of the electrode wiring pad 23 can be set relatively freely regardless of the high density (high resolution) of the optical print head. Therefore, if the electrode wiring pad 23 is formed to be vertically long and the length does not hinder the wire bonding as described above, the length direction of the electrode wiring pad 23 (the arrangement direction of the electrode wiring pad 23) The surface protective film 25b may be formed only at the edge (short side edge) of the direction (perpendicular to the direction), for example, at the position shown in FIG.

That is, as in the conventional case, the surface protection film 25 is formed so as to expose most of the surface of the electrode wiring pad 23 and cover only the edge portion of the electrode wiring pad 23. If the electrode wiring pad 23 is vertically long, Then, the surface protection film 25 in the width direction (on the long side edge) of the electrode wiring pad 23 is removed, and the surface protection film 25 is left so as to leave only the surface protection film 25 in the length direction (on the short side edge) of the electrode wiring pad 23. The film 25b can be formed. As described above, if the surface protection film 25b is formed on each of the electrode wiring pads 23 only at the edge in the length direction (short side edge), particularly at the edge having a planar overlap with the thin metal wire 27, of the surface thereof. Similarly to the above-described protective film 25a, when the thin metal wire 27 to be wire-bonded hangs down along the length direction of the electrode wiring pad 23, a part of the hanging thin metal wire 27 is supported by the protective film 25b. The contact (short circuit) between the electrode wiring pad 27 and the adjacent electrode wiring pad 23 can be prevented beforehand.

The surface protective film is generally made of polyimide, but may be any film as long as it does not crack even if it becomes a thick film of about 1 μm or more, for example, a compound obtained by adding an organic binder to a silicon compound. May be.

In the present embodiment, a film made of a silicon nitride film (corrosion preventing film 26) is formed to prevent corrosion of the individual electrodes. Since the purpose of this thin film is to serve also as an antireflection film in the light emitting region, a silicon nitride film is used. However, a silicon oxide film can also be used to protect the surface of the thin film. However, since the silicon nitride film has a larger refractive index than the silicon oxide film and a large antireflection effect, and further has high hydrophobicity and high reliability, it is appropriate to use the silicon nitride film.

Also, in the present embodiment, an array corresponding to 600 dpi has been described, but the present invention is naturally applicable to an array having a higher density, for example, 1200 dpi.

{Furthermore, in the present embodiment, ball bonding for bonding different metals (usually $ 1 / Au) has been described, but the same effect can be obtained with stitch bonding that enables high-density connection.

The optical print head according to the embodiment may have any configuration as long as it has the above-described structure. The manufacturing process, the type of the substrate, the number and size of the electrodes and the like, and the rows in a staggered arrangement. The arrangement state including the number is not limited to the above embodiment.

The present invention is applicable to high-density arrays such as 600 dpi and 1200 dpi. The present invention is applicable to an optical print head having such an array.

It is a top view showing the structure of the light emitting diode array concerning the embodiment to which the present invention is applied. FIG. 2 is a sectional view taken along the line AA ′ in FIG. 1. FIG. 2 is a sectional view taken along the line BB ′ in FIG. 1. FIG. 9 is a plan view showing a conventional light emitting diode array for an optical printer. FIG. 5 is a sectional view taken along the line A-A ′ in FIG. 4. FIG. 9 is a cross-sectional view illustrating wire bonding of a conventional light emitting diode array. FIG. 9 is a plan view for explaining wire bonding of a conventional light emitting diode array. FIG. 9 is a cross-sectional view illustrating wire bonding of a conventional light emitting diode array.

Explanation of reference numerals

Reference Signs List 20 light-emitting diode array 21 light-emitting area 22 electrode wiring 23 electrode wiring pad (individual electrode)
24 Common electrode (cathode electrode)
25 Surface protection film 26 Corrosion prevention film

Claims (6)

In a light-emitting diode array in which a plurality of light-emitting regions and a vertically long individual electrode connected to the light-emitting region via an electrode wiring are arranged, the surface of the electrode wiring and the surface of an edge portion of the individual electrode are protected. A light emitting diode array, wherein a film is formed and a protective film on a long side edge of the individual electrode is removed. In a light-emitting diode array in which a plurality of aligned light-emitting regions and a plurality of vertically elongated individual electrodes connected to the light-emitting regions via electrode wiring and arranged in a staggered manner are arranged in a plurality of rows, A protective film is formed on the surface of the electrode wiring so as to protect the electrode wiring wired to the individual electrodes in the staggered second row passing between the individual electrodes, and in a state where most of the individual electrodes are exposed. A light emitting diode array, wherein a protective film is formed on a surface of an edge portion of the individual electrode, and the protective film on a long side edge of the individual electrode is removed. A light-emitting diode array comprising a plurality of aligned light-emitting regions and at least two or more rows of individual electrodes connected to the light-emitting regions via electrode wirings and aligned adjacent to the light-emitting regions in the same direction as the light-emitting regions. 3. The light-emitting diode array according to claim 1, further comprising a protective film between a surface of the electrode wiring excluding at least the individual electrode portion and a row of the individual electrodes. 4. The light-emitting diode array according to claim 1, wherein a thin film covering the light-emitting region is formed separately from the protection film to prevent corrosion of the individual electrodes. 5. An optical printhead comprising a light emitting diode array, a driving element for driving the array, and a thin metal wire for electrically connecting the array and the driving element by bonding, wherein the light emitting diode array is used as the light emitting diode array. An optical print head using the light-emitting diode array according to any one of the above. A light emitting diode array, a driving element for driving the array, and a thin metal wire for electrically connecting the array and the driving element by bonding; a first bonding of the thin metal wire is performed on the driving element side; 5. An optical print head in which the second bonding is performed on the light emitting diode array side, wherein the light emitting diode array according to claim 1 is used as the light emitting diode array.

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