JP2007268875A - Led print head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide LED arrays for a print head, which prevent an adhesive from overbrimming a seam joint therebetween, and therefore contribute to an improved production yield, and to provide a print head using the LED arrays. <P>SOLUTION: The LED print head is formed by arranging the plurality of LED arrays on a printed wiring board, and bonding lower surfaces of the LED arrays to the printed wiring board via the adhesive. Herein the lower surface of each LED array has a counter-bored hole formed therein to secure a frame portion in which the adhesive is filled, to thereby prevent the adhesive filled inside the frame portion from flowing out of the frame portion. In this manner by uniformly applying the adhesive to the lower surface of each LED array, the adhesive reaches a location immediately below an edge pad, and therefore the strength of a bonding wire is ensured, which leads to prevention of the LED array from cracking. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an LED print head suitable for a printer, such as an exposure light source for a photosensitive drum for a page printer, and a manufacturing method thereof.

  A print head used as an exposure means for an electrophotographic printer or the like has, for example, a structure in which a plurality of LED arrays are attached to the upper surface of a printed board on which a wiring conductor of a predetermined pattern is attached, A predetermined power is applied to each LED element of the LED array based on a print signal from the outside, and the LED elements are selectively made to emit light, and the emitted light is transmitted to an external photosensitive drum through a lens. And a predetermined latent image is formed on the surface of the photosensitive drum, developed, and transferred to a sheet or the like.

  Usually, in order to adhere the LED array to the printed board, a liquid material of an adhesive is applied to a predetermined region on the upper surface of the printed board, and the resin component contained in the adhesive in a state where the LED array is pressed against the applied surface Heat cure and attach.

In conventional LED arrays for printers, as shown in FIGS. 10 and 11, there is no particular attention regarding the shape of the lower surface of the LED array bonded with an adhesive, and it is a simple flat surface and particularly refers to roughness. Was not.
Japanese Patent Laid-Open No. 9-095010

  When fixing the LED array on the printed circuit board with an adhesive, if the amount of this adhesive is large, the weight of the LED array, excess adhesive pushed against the load will be ejected from the joints of the LED arrays due to capillary action, etc. For LED bonds that flow into the upper surface of the LED array and reduce the emission intensity by covering the LED element, or the adhesive changes color due to continued use, and the emission intensity of the LED array partially changes due to the changed adhesive. It flowed into the pad and the attachment of the wire worsened (FIG. 10).

  In order to solve this problem, the amount of the adhesive was reduced to prevent the adhesive from being ejected. However, if the amount was too small, the adhesive did not reach the wire bond pad near the end of the LED array. There is a space between the LED array directly under the pad and the printed circuit board, and the wire bonding ultrasonic waves do not work effectively. In some cases, the LED array breaks at the edge of the adhesive due to the weight of the wire bonding. (FIG. 11).

  Accordingly, the present invention has been made in view of the above, and an object of the present invention is to provide an LED print head capable of uniform light emission and improved in production yield.

  As a result of intensive research, the present inventors have patterned the lower surface of the LED array and provided a frame-like portion on the peripheral edge of the lower surface of the LED array, so that the bond wire does not adhere due to the ejection of the adhesive, and the amount of the adhesive is insufficient. It can be found that the array can be prevented from cracking, thereby increasing the production yield, and as a result, it is possible to obtain an LED print head having high quality and high reliability and low production cost. It came to complete.

  Therefore, the present invention provides an LED print head in which a plurality of LED arrays are arranged on a printed circuit board, and the lower surface of the LED array is bonded to the printed circuit board through an adhesive. A frame-shaped portion is provided along the frame-shaped portion, and a communication groove is formed in the frame-shaped portion to communicate the inside and outside of the frame-shaped portion, and a part of the bonding is led to the outside through the communication groove inside the frame-shaped portion. An LED print head characterized by containing an agent.

  According to the LED print head of the present invention, the frame-shaped portion is provided on the outer periphery of the LED array for the print head, and the adhesive is filled in the frame-shaped portion. It is possible to prevent the adhesive from blowing out and covering the LED elements of the LED array to reduce the light emission intensity. Further, it is possible to prevent the adhesive from flowing into the wire bonding pad to deteriorate the attachment of the wire. In addition, the adhesive is evenly distributed, and the LED array is not broken due to poor adhesion during wire bonding. Thereby, the yield is improved, and a highly reliable LED array can be provided by reducing the cost of the LED head and stabilizing the strength of the bond wire.

  Hereinafter, an LED print head according to the present invention and a printer equipped with the LED print head will be described in detail with reference to the drawings. The following embodiments are illustrative, and the present invention is not limited to these embodiments.

(Embodiment 1)
FIG. 1 shows the configuration of a multi-photosensitive drum type printer 1. The printer 1 includes, for example, four photosensitive drums 1a to 4a, developing devices 1b to 4b provided around the photosensitive drums 1a to 4a, and upper portions of the photosensitive drums 1a to 4a. LED print heads 1c to 4c as writing optical systems, a transfer belt 2 onto which latent images formed on the respective photosensitive drums 1a to 4a are sequentially transferred, and a registration roller for conveying recording paper onto the transfer belt 2 A pair 3 and a fixing roller pair 4 that receives the copied recording paper from the transfer belt 2 and performs fixing processing are provided.

  The LED print heads 1c to 4c as writing optical systems form latent images on the corresponding photosensitive drums 1a to 4a, and the latent images are copied onto the recording paper fed from the pair of registration rollers 3, The copied recording paper is sent to the fixing roller pair 4 where fixing processing is performed.

  As shown in FIGS. 2 and 3, the LED print heads 1 c to 4 c operate the light emission of the printed circuit board 8, the plurality of LED arrays 9 arranged on the printed circuit board 8, and the LED elements 10 on the LED array 9. A driving IC. The LED array 9 includes a plurality of LED elements 10 attached to the printed circuit board 8, and a frame-shaped portion 11 having a certain height provided on the opposite side of the LED element 10 side. And an adhesive layer 12 filled inside the frame-like portion 11.

  The LED array 9 for LED print heads applies a predetermined power to each LED element 10 based on a print signal from the outside, and selectively causes the LED elements 10 to emit light individually. For example, when A4 size printing is performed, 40 5.4 mm LED arrays 9 are mounted on the printed circuit board 8, and 5,120 LED elements 10 are mounted on the 600 dpi LED print heads 1c to 4c. .

  4 is a top view showing an embodiment of the LED array 9 used in the print heads 1c to 4c, FIG. 5 is a longitudinal sectional view showing a cross section in the longitudinal direction of the LED array 9, and FIG. It is the cross-sectional view which showed the cross section of the transversal direction of 9. Hereafter, each component of the LED array 9 for print heads of this invention is demonstrated in detail for every component.

(Frame part 11)
5 and 6 show the cross-sectional shape of the LED array 9. On the lower surface of the LED array 9, a spot face is formed inside the patterned frame-like portion 11 by photoetching or the like. The adhesive is filled in the area where the spot face is formed. Since the region exists inside the frame-shaped portion 11, the frame-shaped portion 11 prevents the adhesive from flowing out even when the adhesive is too much when the print head LED array 9 is bonded to the printed circuit board 8. be able to. Further, the provision of the frame-like portion 11 makes it possible to apply the adhesive uniformly, thereby preventing the occurrence of a portion with too little adhesive. As shown in FIGS. 4 and 5, the cross-sectional shape of the frame-shaped portion 11 may be a rectangular shape in the long-side portion and the short-side portion of the LED array, or the frame in the short-side portion of the LED array. The cross-sectional shape of the LED-shaped portion 11 is an inverted trapezoidal shape that widens as the distance from the lower surface of the base of the LED array 9 increases, and the cross-sectional shape of the frame-shaped portion 11 in the longitudinal direction of the LED array decreases It may be. Moreover, the cross-sectional shape of the frame-shaped part 11 in the part of the transversal direction of a LED array and the part of a longitudinal direction may be an inverted trapezoid shape which spreads as it leaves | separates from the said lower surface. It is preferable that the cross-sectional shape of the frame-shaped part 11 in the short-side portion of the LED array is an inverted trapezoidal shape that spreads away from the lower surface. Although the short-side portions of the frame-shaped portion 11 are arranged so as to be adjacent to each other, by making the cross-sectional shape of the frame-shaped portion 11 in the short-side portion of the LED array as described above, This is because the adhesive can be prevented from reaching the upper surface of the adjacent LED array 9.
Moreover, it is preferable that the height of the frame-shaped part 11 exists in the range of 0.002 mm-0.1 mm. This is because when the height of the frame-shaped part 11 exceeds 0.1 mm, the amount of adhesive necessary for bonding increases, and the drying time of the adhesive is longer than necessary, and 0.002 mm. This is because it is not possible to prevent the adhesive from flowing out. The height of the frame portion 11 is more preferably in the range of 0.002 mm to 0.1 mm.

  Further, the width of the frame portion 11 may be in any range, but is preferably in the range of 0.02 mm to 0.1 mm. This is because if the width of the frame-shaped portion 11 is 0.02 mm or less, the frame-shaped portion 11 is structurally fragile and may be broken when the LED array is pressed. In addition, the upper limit value of the width of the frame-like portion 11 is determined in consideration of the horizontal width of the LED array, but the upper limit value is preferably 50% or less of the half length of the horizontal width of the LED array, More preferably, it is 20% or less.

  The constituent material of the frame portion 11 may be the same as or different from the material of the LED array 9, but is preferably the same as the material of the LED array 9. A preferred material constituting the frame portion 11 is gallium arsenide. This material is preferable because anisotropic etching can be performed. By using a material capable of such anisotropic etching and etching it, the cross-sectional shape of the frame-like portion 11 in the short direction portion of the LED array 9 can be changed to an inverted trapezoidal shape. The cross-sectional shape of the frame-like portion 11 in the longitudinal direction portion can be a trapezoid.

  Moreover, it is preferable that the frame-shaped part 11 has the communication groove 15 at least in part. This is because the adhesive flows smoothly by providing the communication groove 15 in at least a part of the frame-like portion 11. When there is no communication groove 15, a gas layer such as air between the frame-shaped portion 11 and the adhesive acts as a resistance, and the adhesive cannot be diffused into the frame-shaped portion 11 in a short time. On the other hand, by providing the communication groove 15, the gas such as air is released from the communication groove 15, and this does not become a resistance, so that the adhesive can be diffused into the frame-shaped portion 11 in a short time. The communication groove 15 is preferably provided in a longitudinal direction portion of the frame-like portion 11. This is because when the communication groove 15 is provided in the short-side portion of the frame-shaped part 11, the adhesive flows out of the communication groove 15 and is likely to reach the upper surface of the adjacent LED array 9, When provided in the longitudinal direction portion, the adhesive flows out from the lateral direction of the LED array 9 as shown in FIG. 2, but the LED array is not arranged adjacent to the longitudinal direction portion. This is because there is a low possibility that the adhesive covers.

  The adhesive liquid material is applied to a predetermined area on the upper surface of the printed circuit board on which the wiring conductor is attached, that is, an area where the LED array 9 is attached using a conventionally known printing technique or a dispenser. A plurality of LED arrays 9 obtained as described above are arranged in a line on the adhesive application surface, and heat is applied to the anisotropic conductive adhesive in a state where each LED array 9 is pressed to the printed circuit board 8 side, The LED array 9 is attached to the upper surface of the printed circuit board 8 by thermally curing the resin in the adhesive.

(Printed circuit board 8)
Subsequently, the printed circuit board 8 to which the LED elements are attached will be described. The printed circuit board 8 may be made of any material, but is preferably made of an electrically insulating material such as glass epoxy resin. A plurality of wiring conductors, a plurality of LED arrays 9 and the like are supported on the upper surface of the printed board 8.

(LED element 10)
Next, the LED element 10 disposed on the printed board 8 and irradiating the photoreceptors 1a to 4a will be described. As shown in FIG. 3, the LED elements 10 are linearly arranged on the upper surface of the LED array 9. The LED element 10 has a large number of terminal electrodes that are individually connected to each other, and a predetermined power is applied to each of the LED elements 10 through the terminal electrodes to selectively select the large number of LED elements 10 individually. To emit light. The light emitted from the LED element 10 is applied to the external photosensitive drums 1a to 4a through the lenses 1d to 4d, whereby a predetermined latent image is formed on the surfaces of the photosensitive drums 1a to 4a.

  Here, the wavelength of the light emitted by the LED element 10 may be in any range. The wavelength of the LED is determined by the characteristics of the photosensitive drum. When an α-Si drum is used as the photosensitive drum, the LED element 10 having a wavelength of 685 ± 10 nm is used.

The LED element 10 is manufactured by a known semiconductor manufacturing technique. Specifically, when manufacturing a GaAsP-based LED array, for example, a wafer made of GaAs is first heated in a furnace to a high temperature and an appropriate amount of AsH ₃ (arsine), PH ₃ (phosphine), and Ga (gallium) is used. A single crystal of n-type semiconductor GaAsP (gallium-arsenic-phosphorus) is grown on the surface of the wafer by contacting the gas containing it, and then a windowed film of Si ₃ N ₄ (silicon nitride) is coated on the surface of the GaAsP single crystal. A semiconductor wafer having a pn junction is formed by exposing a Zn (zinc) gas to the window and diffusing Zn into a part of the n-type semiconductor GaAsP single crystal to form a p-type semiconductor. Is manufactured by dicing a large number of LED elements 10 into a group of LED elements 10 and cutting out a large number of LED arrays from a single semiconductor wafer. It is. As another semiconductor manufacturing method, a MOCVD method is used to grow a crystal having a required wavelength by introducing AsH ₃ , trimethylgallium, and trimethylaluminum into a GaAs substrate or Si substrate in the form of gas, and photoetching is performed. There is a method of manufacturing by performing individual light emitter separation.

(Photosensitive drums 1a to 4a)
The photosensitive drums 1a to 4a in the printer apparatus will be described. The photosensitive drums 1a to 4a can form a latent image with light from the print head for writing, and can print on a recording sheet with the formed latent image. The photosensitive drums 1a to 4a are arranged on the LED array of the print head so as to be separated from the print head by a predetermined distance and substantially parallel to the print head.

  Each of the photosensitive drums 1a to 4a has a structure in which a photoconductive layer made of an inorganic semiconductor such as amorphous silicon or an organic semiconductor is attached to the outer surface of a cylindrical base made of aluminum metal or the like. When the photoconductive layer is rotated around an axis by a motor or the like (not shown) and the photoconductive layer is irradiated with light from the print head, the specific resistance of the photoconductive layer is drastically reduced to form a predetermined latent image on the photoconductive layer. Form. The latent images formed on the photosensitive drums 1a to 4a are converted into a toner image through a development process, and a predetermined image is recorded by transferring and fixing the toner image on a recording sheet.

(LED array manufacturing method)
Below, the preferable manufacturing method of the LED array of this invention is demonstrated. In the said manufacturing method, the frame-shaped part 11 is provided in the lower surface peripheral part of an LED array by patterning on the lower surface of an LED array through the following (1)-(4) processes sequentially. Further, a notch may be provided in a part of the frame-like portion in order to guide the excess adhesive in a desired direction. In the manufacturing method, patterning may be performed by providing a pattern of the frame portion from the beginning on a photomask used for photoetching. Below, the process in the manufacturing method of the LED array of this invention is demonstrated.

  (1) When the upper surface of the substrate of the LED array is patterned first, the upper surface of the substrate is covered with a protective tape or the like, and if necessary, back grinding is performed here so as to obtain a desired thickness.

  (2) A resist is applied to the lower surface in a state where the upper surface of the substrate is protected, and patterning is performed by a photoetching technique so that a frame-shaped portion is formed on the peripheral edge of the array. The alignment at this time can be performed by using an infrared scope or the like and matching the pattern provided on the upper surface.

When the frame-like portion is formed on the base of the LED array composed of gallium arsenide, wet etching using an etchant such as H ₂ SO ₄ : H ₂ O ₂ : H ₂ O system or CCl ₂ F ₂ is used. A dry etch using gas is used. In the formation of the LED array, by selecting the direction in which the LED elements are arranged to be the [110] direction, a portion orthogonal to the LED element array direction when wet etching is performed in the H ₂ SO ₄ : H ₂ O ₂ : H ₂ O system The frame-shaped part is an inverted trapezoid that makes it more difficult for the adhesive to flow, and the part parallel to the LED element array direction (the part in the longitudinal direction of the LED array) is extra. A trapezoidal shape that makes it easier to guide the adhesive can be obtained. The inverted trapezoidal shape refers to a shape that becomes wider as the distance from the substrate of the LED array increases, and the trapezoidal shape refers to a shape that decreases in width as the distance from the substrate increases. Further, when a silicon substrate is used as the base of the LED array 9, it is preferable to use an etching solution such as an HF: HNO ₃ : H ₂ O system or a KOH aqueous solution.

  (3) After forming the pattern on the lower surface of the LED array, the protective film on the upper surface is removed and dicing is performed. At this time, since the pattern is formed on the lower surface, it is effective for dicing from the lower surface. Dicing from the lower surface can solve the problem that the bottom of the LED array protrudes together with scribing from the upper surface and dicing with a thinner blade, making it difficult to arrange them at equal pitches.

  (4) It is also possible to pattern the LED array 9 on the upper surface side by first forming a frame-like pattern on the lower surface. In that case, there is a possibility that the lower surface is further etched in the etching process in the middle, but since the etching is performed uniformly over the entire surface, it is not necessary to protect the lower surface each time.

  As described above, when the lower surface of the LED array is a simple flat surface, when the amount of adhesive used for fixing to the printed circuit board is large, the adhesive sprays from the joint between the LED arrays and flows into the upper surface of the LED array to emit light. Or flow into the wire bonding pad 16. On the other hand, when the adhesive is small, there is a problem that the bond wire is not attached or the LED array is broken at the end of the adhesive due to the weight of the wire bonding.

However, according to the present invention, the adhesive is prevented from being ejected from the joint between the LED arrays by patterning so that the outer peripheral portion of the lower surface of the LED array is left like a frame-like portion, and the adhesive is uniform. As a result of the wide spread, the adhesive agent is rotated to a position just below the wire bonding pad 16 at the end, and the LED array is not broken by the wire bonding, and the ultrasonic wave is effectively used to enable a connection with sufficient strength. In addition, a pattern that opens a part of the frame-like portion so as to guide the excess adhesive in the preferred direction is used, and when gallium arsenide is used for the substrate, the LED array indicates the [110] direction of the substrate. If the direction is specified, for example, an anisotropic etching solution such as H ₂ SO ₄ : H ₂ O ₂ : H ₂ O system is used, so that it is more difficult for the adhesive to flow in a portion orthogonal to the LED element array direction. In the inverted trapezoidal shape, the trapezoidal shape that makes it easier to induce excess adhesive in the parallel part can be achieved. Furthermore, the die mounting process is more stable by adhering the area of the frame-like portion so that the adhesive covers the upper portion of the upper surface of the wire bonding pad 16 without leaving any excess, and variations in the amount of adhesive and weight can be absorbed. . As a result, the quality of the LED head is improved and the yield can be improved to supply a lower cost LED head.

  The present invention is not limited to the above-described embodiment, and various modifications and improvements can be made without departing from the gist of the present invention. For example, the above-described embodiment may be applied to an LED print head. Although described as an example, the present invention can be applied to other print heads such as an EL head, a plasma dot head, a liquid crystal shutter head, a fluorescent head, and a PLZT.

  The LED print head of the present invention according to the present invention is used for exposure means such as an optical printer, a facsimile machine, and a copying machine, that is, a print head for printing.

1 is a schematic diagram of a printer. It is a top view when the LED array of this invention is die-mounted on a printed circuit board. It is sectional drawing when the LED array of this invention is die-mounted on a printed circuit board. It is a top view of the LED array lower surface which concerns on one embodiment of this invention. It is sectional drawing of the long side of the LED array which concerns on one embodiment of this invention. It is sectional drawing of the short side of the LED array which concerns on one embodiment of this invention. It is a top view of the LED array lower surface which concerns on another embodiment of this invention. It is sectional drawing by the side of the long side of the LED array which concerns on another embodiment of this invention. It is sectional drawing of the short side of the LED array which concerns on another embodiment of this invention. It is a principal part cross-sectional schematic which shows the ejection of the adhesive agent in the conventional LED array. It is a principal part cross-section schematic which shows the crack in the conventional LED array.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum type printer 1a-4a Photosensitive drum 1b-4b Developing device 1c-4c LED print head 2 Transfer belt 3 Registration roller pair 4 Fixing roller pair 8 Printed circuit board 9 LED array 10 LED element 11 Frame-shaped part 12 Adhesion Agent layer 15 Communication groove 16 Wire bond pad

Claims (5)

In an LED print head in which a plurality of LED arrays are arranged on a printed circuit board, and the lower surface of the LED array is bonded onto the printed circuit board through an adhesive,
A frame-shaped portion is provided along the outer periphery of the lower surface of the LED array, and a communication groove is formed in the frame-shaped portion so as to communicate with the inside and outside of the LED array. An LED print head characterized in that it contains the adhesive that has been led out.   The LED print head according to claim 1, wherein a communication groove for guiding an adhesive outflow direction is provided in a part of the frame-shaped portion.   The cross-sectional shape of the frame-shaped portion of the LED array in the short direction is an inverted trapezoidal shape that spreads away from the lower surface of the base of the LED array, and the cross-sectional shape of the frame-shaped portion of the LED array in the longitudinal direction is the cross-sectional shape 3. The LED print head according to claim 1, wherein the LED print head has a trapezoidal shape that becomes narrower as the distance from the lower surface increases.   The LED print head according to any one of claims 1 to 3, wherein the frame-like portion is arranged outside a region immediately below a wire bonding pad arranged on the LED array. The LED print head according to claim 1, wherein the LED array includes gallium arsenide.

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