Abstract:
A method of manufacturing a light emitting device includes injecting liquid or pasty transparent resin into a sheet forming mold, adding a phosphor to the resin in the mold, centrifugally rotating the mold so as to settle the phosphor included in the resin toward one surface side of the resin, thermally curing the resin so as to form a phosphor sheet, the phosphor sheet including a phosphor layer formed on the one surface side of the resin and a transparent layer formed on an other surface side of the resin, overlaying the phosphor sheet on a light emitting element such that the phosphor layer of the phosphor sheet contacts with a light emitting surface of the light emitting element, mounting the light emitting element with the phosphor sheet overlaid on a board, and flattening a surface of the transparent layer of the phosphor sheet on the light emitting element.

Description:
[0001]    The present application is based on Japanese patent application No. 2016-057609 filed on Mar. 22, 2016, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a method of manufacturing a light emitting device using a phosphor sheet. 
         [0004]    2. Description of the Related Art 
         [0005]    A light emitting device is known in which the phosphor sheet obtained by processing a phosphor containing resin into a sheet is disposed on a light emitting surface of a light emitting element such as a light emitting diode (LED) chip is known. In the light emitting device, a color of a light emitted from the light emitting element and transmitted through the phosphor sheet is mixed with a color of a light emitted from the phosphor in the phosphor sheet so as to produce an emission color of the light emitting device. 
         [0006]    In the above light emitting device, the phosphor is dispersed in a whole thickness direction of the phosphor sheet. Among lights emitted from the light emitting element and passing through the phosphor sheet, with regard to the amount of phosphor-wavelength converted light, light emitted in a direction inclined from immediately above the light emitting element is higher than light emitted immediately above the light emitting element. This is because the light emitted in the inclined direction has longer distance (i.e., optical path) needed for passing through the phosphor sheet than the light emitted immediately above the light emitting element. Thus, a problem on the dispersion of emission chromaticity may arise due to the difference of emission angle. 
         [0007]    To solve the problem, for example, a light emitting device is known which controls the emission chromaticity dispersion caused by the emission angle difference by arranging a phosphor plate which is composed of a base, phosphor and a light scattering material on the light emitting element so as to diffuse the light emitted from the light emitting element by the light scattering material (see e.g. JP-A-2013-153105). 
         [0008]    Also, a two layer structure phosphor sheet is known which is composed of a transparent layer and a high concentrate phosphor layer (see e.g. JP-A-2005-24272). According to the phosphor sheet, the phosphor layer is arranged contacting with or coming close to the light emitting surface of the light emitting element. Thereby, the distance of the light emitted from the light emitting element and passing through the phosphor layer can be nearly equalized at any emission angles so as to prevent the emission chromaticity dispersion caused by the emission angle difference. 
       SUMMARY OF THE INVENTION 
       [0009]    The light emitting device disclosed in JP-A-2013-153105 is constructed such that the light scattering material is contained in the sealing resin. Therefore, the amount of light passing through the phosphor plate may be reduced so as to cause a reduction in brightness of the emission light. On the other hand, the phosphor sheet disclosed in JP-A-2005-24272 needs the transparent layer is manufactured separately from the phosphor layer. Therefore, the manufacturing cost may increase due to the complicated manufacturing process. 
         [0010]    As a modification of the general sealing method in which the light emitting element is sealed with the sealing resin in which phosphor is mixed, it has been proposed that the phosphor in the sealing resin is settled close to the light emitting surface of the light emitting element by controlling the curing temperature of the sealing resin (see e.g., JP-A-2012-9905). However, in the proposed sealing method, it is difficult to provide an equalized curing temperature for the sealing resin which is formed into a thin sheet with a large area. Thus, the phosphor may be settled unevenly such that the phosphor density is dispersed. 
         [0011]    It is an object to the invention to provide a method of manufacturing a light emitting device that prevents a reduction in brightness of the emission light and a dispersion in emission chromaticity due to the emission angle (or optical path) difference while reducing the manufacturing cost and the phosphor density dispersion. 
         [0012]    According to an embodiment of the invention, provided is a method of manufacturing a light emitting element as defined by [1] to [5] below. 
         [0013]    [1] A method of manufacturing a light emitting device, comprising:
       injecting liquid or pasty transparent resin into a sheet forming mold;   adding a phosphor to the resin in the mold;   centrifugally rotating the mold so as to settle the phosphor included in the resin toward one surface side of the resin;   thermally curing the resin with the phosphor settled so as to form a phosphor sheet, the phosphor sheet comprising a phosphor layer formed on the one surface side of the resin and a transparent layer formed on an other surface side of the resin;   overlaying the phosphor sheet on a light emitting element such that the phosphor layer of the phosphor sheet contacts with a light emitting surface of the light emitting element;   mounting the light emitting element with the phosphor sheet overlaid on a board comprising a wiring layer; and   flattening a surface of the transparent layer of the phosphor sheet on the light emitting element.       
 
         [0021]    [2] The method according to [1], wherein the adding of the phosphor comprises adding a first phosphor having a predetermined emission wavelength and a predetermined specific gravity, and a second phosphor having an emission wavelength less than the predetermined wavelength and a specific gravity less than the predetermined specific gravity, and
       wherein the first and second phosphors are simultaneously added to the resin.       
 
         [0023]    [3] The method according to [1], wherein the adding of the phosphor comprises adding a first phosphor having a predetermined emission wavelength and second phosphor having an emission wavelength less than the predetermined wavelength, and
       wherein the second phosphor is added to the resin after the first phosphor is added to the resin.       
 
         [0025]    [4] The method according to [1], wherein the phosphor comprises a phosphor particle that emits a yellowish light, and
       wherein the light emitting element emits a bluish light.       
 
         [0027]    [5] The method according to [2] or [3], wherein the first phosphor comprises a phosphor that emits a reddish light,
       wherein the second phosphor comprises a phosphor that emits a greenish light, and   wherein the light emitting element emits a bluish light.       
 
         [0030]    Effects of the Invention 
         [0031]    According to an embodiment of the invention, a method of manufacturing a light emitting device can be provided that prevents a reduction in brightness of the emission light and a dispersion in emission chromaticity due to the emission angle (optical path) difference while reducing the manufacturing cost and the phosphor density dispersion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    Next, the present invention will be explained in conjunction with appended drawings, wherein: 
           [0033]      FIG. 1  is a schematic drawing of a phosphor settling device according to the first embodiment; 
           [0034]      FIG. 2  is an explanation drawing showing a centrifugal state of a mold shown in  FIG. 1 ; 
           [0035]      FIG. 3  is a block diagram showing the phosphor settling device; 
           [0036]      FIG. 4A  is a cross sectional view showing the method of manufacturing the light emitting device according to the first embodiment; 
           [0037]      FIG. 4B  is the cross sectional view showing the method of manufacturing the light emitting device according to the first embodiment; 
           [0038]      FIG. 4C  is a cross sectional view showing the method of manufacturing the light emitting device according to the first embodiment; 
           [0039]      FIG. 4D  is a cross sectional view showing the method of manufacturing the light emitting device according to the first embodiment; 
           [0040]      FIG. 4E  is a cross sectional view showing the method of manufacturing the light emitting device according to the first embodiment; 
           [0041]      FIG. 5A  is a cross sectional view showing the method of manufacturing the light emitting device according to the second embodiment; 
           [0042]      FIG. 5B  is the cross sectional view showing the method of manufacturing the light emitting device according to the second embodiment; 
           [0043]      FIG. 5C  is a cross sectional view showing the method of manufacturing the light emitting device according to the second embodiment; 
           [0044]      FIG. 5D  is a cross sectional view showing the method of manufacturing the light emitting device according to the second embodiment; 
           [0045]      FIG. 5E  is a cross sectional view showing the method of manufacturing the light emitting device according to the second embodiment; and 
           [0046]      FIG. 5F  is a cross sectional view showing the method of manufacturing the light emitting device according to the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0047]      FIG. 1  is a schematic drawing of a phosphor settling device used in a method of manufacturing a light emitting device according to the first embodiment. The phosphor settling device is provided with a drive part  2  which rotates a rotational axis  1 , a rotating plate  3  which is fixed on the rotational axis  1 , a mold  4  which is hanged on a periphery of the rotating plate  3  through wire  5 , a phosphor supplier  6  (which is provided with a nozzle (not shown)) which is disposed above the mold  4 , and a hose  7  to supply phosphor from a phosphor tank  3 A on the rotating plate  3  to the phosphor supplier  6 . 
         [0048]    The rotating plate  3  is rotated by receiving driving force from the drive part  2  through the rotational axis  1  in a predetermined rotating frequency. 
         [0049]    The mold  4  is connected with one end of plural wires  5  (three wires in the present embodiment) of which the other end are connected to a hanging member (not shown) of the rotating plate  3 , and supported by the hanging member of the rotating plate  3  so as to swing freely. That is, the mold  4  is swung for substantial horizontal direction by receiving centrifugal force and rising from the vertical direction when the mold  4  is rotated by rotating the rotating plate  3 . 
         [0050]    Also, a transparent resin  8  having fluidity such as liquid or paste is injected into the mold  4 , and the transparent resin  8  is held so as to be in the form of a sheet. 
         [0051]    The phosphor supplier  6  is supported by a supporting member  4 A such as metallic wire so as to set and remove freely. And the phosphor supplier  6  jets evenly, for example, a yellow phosphor (or yellowish phosphor)  9  which is supplied in the phosphor tank  3 A on a whole surface of the transparent resin  8  from above the mold  4 . 
         [0052]      FIG. 2  shows a state of the mold  4  in centrifugal rotating. When the rotating plate  3  stands, as shown by a dot-line shown in  FIG. 2 , the mold  4  is hanged in the vertical direction caused by the gravity. However, when the rotating plate  3  is rotated, the mold  4  swings toward the arrow direction by the centrifugal force, and rotates in the substantial horizontal direction by about 90° from the vertical direction. When the transparent resin  8  and the yellow phosphor  9  are injected into the mold  4  in stopping the rotating plate  3 , and then the rotating plate  3  is rotated with the predetermined rotating frequency, the yellow phosphor  9  on the surface side of the transparent resin  8  can be settled toward a mold  4  bottom surface side. 
         [0053]      FIG. 3  is a block diagram showing the phosphor settling device. As shown in  FIG. 3 , the phosphor settling device is provided with a control part  10  to output a driving signal for a drive part  2  which drives the rotational axis  1 , and an input part  11  which outputs a control condition to the control part  10  by inputting the predetermined rotating frequency, and setting rotational time etc. The control part  10  monitors a driving state of the drive part  2  and controls the drive part  2  so as to keep the predetermined rotating frequency set previously. 
         [0054]    Next, the method of manufacturing the light emitting device according to the first embodiment will be explained below. 
         [0055]    (Phosphor Settling Process) 
         [0056]    The transparent resin  8  having fluidity such as liquid or paste is injected into the mold  4  of the phosphor settling device shown in  FIG. 1 . In this case, for example, silicon resin or epoxy resin is used as the transparent resin  8 . 
         [0057]    Next, the yellow phosphor  9  is supplied from the phosphor tank  3 A of the phosphor settling device to the phosphor supplier  6  through the hose  7 , and is jet evenly on the whole surface of the transparent resin  8  from above the mold  4 . For example, YAG phosphor (Y 3 Al 5 O 12 :Ce) is used as the yellow phosphor  9 . 
         [0058]    After adding the yellow phosphor  9  into the transparent resin  8 , the rotating plate  3  is rotated with the predetermined rotating frequency which is input from the input part  11 . 
         [0059]    When the rotating plate  3  begins to rotate, the mold  4  hanged in the vertical direction also rotates with the rotating plate  3 . When the mold  4  rotates, the mold  4  swings gradually for the allow direction by the centrifugal force, and the mold  4  rotates in substantial horizontal direction while the position of the mold  4  keeps in rotating by 90° if the rotating frequency of the rotating plate  3  reaches the predetermined rotating frequency (for example, 1000 rpm) (a state shown by the full line in  FIG. 2 ). And the phosphor supplier  6  supported by the supporting member  4 A so as to set and remove freely follows the movement of the mold  4 . 
         [0060]    In this case, the yellow phosphor  9  on the surface side of the transparent resin  8  begins to settle toward the mold  4  bottom surface side.  FIG. 4A  shows settling the yellow phosphor  9 . After the predetermined rotating time (for example, 5 minutes) which is input from the input part  11  passes, all yellow phosphor  9  is settled in the mold  4  bottom surface side of the transparent resin  8 . 
         [0061]    (Heating Process) 
         [0062]    When the yellow phosphor  9  is settled in the mold  4  bottom surface side of the transparent resin  8 , the mold  4  is released from the phosphor settling device, and the transparent resin  8  is cured, for example, under the condition at a temperature of 150° C. for 1 hour in a furnace (not shown). Hereby, the phosphor sheet  12  is obtained. Meanwhile, the transparent resin  8  may be heated immediately or heated while the transparent resin  8  is centrifugal separated after arranging a heating mechanism in the phosphor settling device shown in  FIG. 1  and settling the phosphor. These manufacturing methods can reduce manufacturing cost. 
         [0063]      FIG. 4B  shows the phosphor sheet  12  which is the transparent resin  8  cured by the heating process released from the mold  4 . The yellow phosphor  9  contained in the transparent resin  8  is dispersed evenly with high concentration in a bottom surface  12 B side transparent resin  8  by settling for the bottom surface  12 B side by the centrifugal force in the phosphor settling process, and the phosphor layer  8 B is formed by the above method. Meanwhile, the yellow phosphor  9  is disappeared in the upper surface  12 A side transparent resin  8 , thus a transparent layer  8 A is formed. By this way, a phosphor sheet  12  which is separated with the transparent layer  8 A and the phosphor layer  8 B is formed. After the phosphor sheet  12  is released from the mold  4 , the phosphor sheet  12  is cut out so as to adjust the size of the light emitting surface of the light emitting element described below. 
         [0064]    (Light Emitting Device Fabricating Process) 
         [0065]    Next, as shown in  FIG. 4C , a light emitting element  13  is prepared by the other method. And the phosphor sheet  12  is overlaid on the light emitting element  13  such that the bottom surface  12 B of the phosphor sheet  12  obtained by the heating process contacts on the light emitting surface of the light emitting element  13   
         [0066]    The light emitting element is provided with a board and a crystal layer containing a light emitting layer (not shown each other). The light emitting element is a flip-chip light emitting element of which an electrode (not shown) faces bottom (an opposite side of the phosphor sheet  12  side). For example, the light emitting element is an LED chip or a laser diode chip and emits blue light (or bluish light) from the phosphor sheet  12  side surface as the light emitting surface. 
         [0067]    Next, as shown in  FIG. 4D , the upper surface  12 A side of the phosphor sheet  12  is removed with a predetermined thickness and the upper surface  12 A is smoothed such that the thickness of the phosphor sheet  12  is even. 
         [0068]    After smoothing the upper surface  12 A of the phosphor sheet  12 , as shown in  FIG. 4E , the light emitting element  13  is mounted on the board  14  by connecting a wiring pattern of the board  14  obtained by the other process with the electrode of the light emitting element  13  through a conductive bump. The board  14  is, for example, a wiring board having the wiring pattern on the surface or is a lead frame inserted board. 
         [0069]    Finally, a circular wall portion  15  is formed on the board  14  so as to surround the light emitting element  13  and the phosphor sheet  12 . And thus, the light emitting device  16  is manufactured. The wall portion  15  is made of resin such as silicon resin containing white paint such as Titanium oxide. 
         [0070]    For the light emitting device  16  manufactured by the above method, when the blue light is emitted from the light emitting element  13 , the yellow light is emitted from the yellow phosphor  9  by exciting the yellow phosphor  9  by part of the blue light in the phosphor layer  8 B which is formed evenly with high concentration at the bottom surface  12 B side of the phosphor sheet  12 . Thus, a white light which is the mixed light of a blue light emitted from the light emitting element  13  through the upper surface  12 A of the phosphor sheet  12  and the yellow light emitted from the yellow phosphor  9  is emitted. In this case, since the distance of the blue light emitted from the light emitting element and passing through the phosphor layer  8 B is nearly equal even by either emission angle, the proportion of wavelength conversion substantially has no difference and emission chromaticity dispersion caused by the emission angle difference can be controlled. 
       Second Embodiment 
       [0071]      FIGS. 5A to 5F  are explanation diagrams showing a light emitting device according to the second embodiment. A method of manufacturing the light emitting device according to the present embodiment is different in using a red phosphor (or reddish phosphor) and a green phosphor (or greenish phosphor) instead of the yellow phosphor used in the first embodiment. Since the heating process and the fabricating process of the light emitting device are followed by the first embodiment, a phosphor settling process will be mainly explained below. 
         [0072]    First, the transparent resin  8  having fluidity such as liquid or paste is injected into the mold  4  of the phosphor settling device shown in  FIG. 1 , and then the red phosphor  9  is supplied from the phosphor tank  3 A of the phosphor settling device to the phosphor supplier  6  through the hose  7 , and is jet evenly on the whole surface of the transparent resin  8  from above the mold  4 . For example, KSF phosphor (K 2 SiF 6 :Mn) is used as the red phosphor  17 . 
         [0073]    Next, the rotating plate  3  is rotated with the predetermined rotating frequency which is input from the input part  11 . When the rotating plate  3  is rotated, as shown in  FIG. 5A , the red phosphor  17  on the surface side of the transparent resin  8  begins to settle toward the mold  4  bottom surface side. After the predetermined rotating time which is input from the input part  11  passes, all red phosphor  17  is settled in the mold  4  bottom surface side of the transparent resin  8 . 
         [0074]    Next, the rotating plate  3  stops rotating, and then the green phosphor  18  is supplied from the phosphor tank  3 A for the green phosphor which is changed with the phosphor tank  3 A for the red phosphor to the phosphor supplier  6  through the hose  7 , and the green phosphor  18  is jet evenly on the whole surface of the transparent resin  8  from above the mold  4 . For example, β SiAlON phosphor ((Si, Al) 6 (O, N) 8 :Eu) is used as the green phosphor  18 . 
         [0075]    Next, the rotating plate  3  is rotated with the predetermined rotating frequency which is input from the input part  11 . When the rotating plate  3  is rotated, as shown in  FIG. 5B , the green phosphor  18  on the surface side of the transparent resin  8  begins to settle toward the mold  4  bottom surface side. After the predetermined rotating time which is input from the input part  11  passes, all green phosphor  18  is settled on the settled red phosphor  17  of the transparent resin  8 . 
         [0076]    After the phosphor settling process is finished, as with the first embodiment, the heating process and the fabricating process of the light emitting device are carried out (as shown in  FIGS. 5C to 5F ), the light emitting device  16  is manufactured. 
         [0077]    For the light emitting device  16  manufactured by the above method, when the blue light is emitted from the light emitting element  13 , the red light is emitted from the red phosphor  17  by exciting the red phosphor  17  by part of the blue light in the phosphor layer  8 B which is formed evenly with high concentration at the bottom surface  12 B side of the phosphor sheet  12 , and the green light is emitted from the green phosphor  18  by exciting the green phosphor  18  by part of the blue light. Thus, a white light which is the mixed light of the blue light emitted from the light emitting element  13  through the upper surface  12 A of the phosphor sheet  12 , the red light emitted from the red phosphor  17 , and the green light emitted from the green phosphor  18  is emitted. In this case, since the distance of the blue light emitted from the light emitting element and passing through the phosphor layer  8 B is nearly equal even by either emission angle, the proportion of wavelength conversion substantially has no difference and the emission chromaticity dispersion caused by the emission angle difference can be controlled. 
         [0078]    Also, as with the present embodiment, when the red phosphor  17  whose emission wavelength is in long wavelength side and the green phosphor  18  whose emission wavelength is in short wavelength side are settled in the transparent resin  8 , if the phosphor whose emission wavelength is in the long wavelength side is disposed nearer to the emitting surface side than the phosphor whose wavelength is in the short wavelength side, since the light emitted from the phosphor whose emission wavelength is in the short wavelength side excites the phosphor whose emission wavelength is in the long wavelength side, color balance becomes unbalance. Thus, it is preferable to settle the phosphor whose emission wavelength is in the short wavelength side after settling the phosphor whose emission wavelength is in the long wavelength side in the transparent resin  8 . 
         [0079]    Also, in the case that settles the phosphor whose emission wavelength is in the long wavelength side and the phosphor whose emission wavelength is in the short wavelength side in the transparent resin  8 , if a specific gravity of the phosphor whose emission wavelength is in the short wavelength side is less than a specific gravity of the phosphor whose emission wavelength is in the long wavelength side, the phosphor whose emission wavelength is in the long wavelength side and the phosphor whose emission wavelength is in the short wavelength side may be settled at the same time. In this case, since the settling speed of the phosphor whose emission wavelength is in the long wavelength side is faster than the settling speed of phosphor whose emission wavelength is in the short wavelength side, the phosphor whose emission wavelength is in the short wavelength side is disposed on the phosphor whose emission wavelength is in the long wavelength side. 
         [0080]    Meanwhile, in the first and second embodiments, although the phosphor settling device has a structure to rotate the mold hanged in the vertical direction. However, it is not limited thereto. The phosphor settling device may have the structure which can keep the transparent resin  8  in the form of a sheet and apply the centrifugal force in the sheet vertical direction by rotating such as a structure which rotates the mold disposed in an outer circumference surface of a drum or an inner circumference surface of a cylindrical drum. 
         [0081]    [Advantageous Effects of the Embodiments] 
         [0082]    According to the present embodiments, by centrifugal rotating the transparent resin  8  containing the phosphor and settling the phosphor in the transparent resin  8 , since the transparent resin  8  has two layer structure having the transparent layer  8 A and the phosphor layer  8 B, and the phosphor sheet  12  is formed by thermal curing the two layer structure, the dispersion by the concentration of the phosphor layer  8 B can be controlled and forming the transparent layer  8 A by the other process is not necessary. Thus, the manufacturing cost can be reduced. Also, since the thin phosphor layer  8 B is formed on the light emitting surface of the light emitting element  13 , the distance of the light emitted from the light emitting element  13  and passing through the phosphor layer  8 B is nearly equal even by either emission angle, the emission chromaticity dispersion caused by the emission angle difference can be controlled. Also, since it is not needed to contain a light scattering material in the phosphor layer  8 B, the emission light fails to be dark. 
         [0083]    Although the embodiments of the invention have been described, the invention is not to be limited to the embodiments. Further, the various kinds of modifications can be implemented without departing from the gist of the invention. 
         [0084]    Although the embodiments of the invention have been described, the invention according to claims is not to be limited to the embodiments. Further, it should be noted that all combinations of the features described in the embodiments are not necessary to solve the problem of the invention.