Abstract:
A blue light emitting element is mounted on a bottom of a case body. A cover member covers the blue light emitting element. Fluorescent material is mixed in the cover member for converting wavelength of light emitted from the blue light emitting element to adjust chromaticity of the light, and luminance reducing material for adjusting the luminance of the light is mixed in the cover member.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a white light emitting device. 
     FIG. 25  is a sectional view of a conventional LED device disclosed in U.S. Pat. No. 6,069,440. The white LED device  70  comprises a substrate  73 , electrodes  71  and  72  secured to the substrate  73  and a blue LED  61  mounted on the substrate  73 . The LED  61  is connected to the electrodes  71  and  72  by lead wires  62 . The LED  61  and electrodes  71 ,  72  are encapsulated with a transparent encapsulating resin  91 . 
   In the resin  91 , fluorescent materials of YAG group are mixed. The fluorescent material comprises phosphor particles  81 . 
   When the current is applied to the blue LED  61  via electrodes  71  and  72 , the LED emits blue light Pb. When a portion of the blue light impinges upon the phosphor particle, the phosphor particle absorbs the blue light and emits yellow light Py. When the yellow light Py and the blue light Pb are combined, white light Pw is created. 
   Furthermore, U.S. Pat. No. 6,319,425 discloses an LED covered by a cap in which fluorescent material is included. 
   Further, U.S. Pat. No. 6,351,069 discloses an LED encapsulated by a transparent resin in which two kinds of phosphor particles are included, thereby producing white light. 
   However, since the LED is a compound semiconductor, there is wide variation in chromaticity and luminance of products. Further, the chromaticity and luminance of the mixed white light Pw also vary widely because of difference of quantity and distribution of the phosphor particles in the encapsulating resin. 
     FIGS. 26 and 27  are graphs showing numeric data widely varied in chromaticity and luminance of LED devices. 
     FIG. 26  is a graph of XYZ chromaticity coordinates showing variation in chromaticity of LED devices by 1 lot mass production. Each black point indicates the chromaticity of an LED device. The variation is in an upward zonal arrangement. Here, the dispersion of the black points in the width direction shown by the letter A means the variation of chromaticity of the blue LED, the dispersion in the longitudinal direction shown by the letter B means the variation of quantity and distribution of the phosphor particles in the encapsulating resin. 
   An LED device having chromaticity which is largely deviated from a central value in  FIG. 26  can not be used as a device for emitting white light. It is frequently desirable that the LED device has chromaticity in a central range shown by hatching where X and Y are in a range of 0.33±0.01. 
   In the graph of  FIG. 27 , the horizontal axis shows luminance and the vertical axis shows the number of LED devices. The luminance variation is distributed in +30% to −40% range from the center of the distribution. However, a desirable range R 2  is about ±20% as shown by arrows in  FIG. 27 . 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a white light emitting device which may correct distributions of the chromaticity and luminance in a desired range. 
   According to the present invention, there is provided a white light emitting device comprising a blue light emitting element, a cover member for covering the blue light emitting element, fluorescent material being mixed in the cover member for converting wavelength of light emitted from the blue light emitting element to adjust chromaticity of the light, and luminance reducing material being mixed in the cover member for adjusting the luminance of the light. 
   The luminance reducing material is pigment or dye for reducing the luminance irrespective of the wavelength of the light emitting from the light emitting element. 
   The cover member is formed with elastomer of silicon group in which the fluorescent material and the luminance reducing material are mixed. 
   The present invention further provides a white light emitting device comprising a case body having a recess forming a reflection face, a blue light emitting element mounted on a bottom of the recess, a cover member including fluorescent material and covering a light emitting face of the case body, fluorescent material being mixed in the cover member for converting wavelength of light emitted from the blue light emitting element to adjust chromaticity of the light, and luminance reducing material being mixed in the cover member for adjusting the luminance of the light. 
   In an aspect of the invention, the white light emitting device further comprises a cover member holding portion formed in the recess of the case body, the cover member being mounted on the cover member holding portion. 
   The recess is formed into a cup shape having an inclination surface open to a light emitting direction, the cover member has an inclined peripheral wall so as to be engaged with the inclination surface. 
   In another aspect of the invention, the white light emitting device further comprises a shoulder formed in the recess of the case body for holding the cover member. 
   The blue light emitting element is mounted on the bottom of the recess by face down bonding. 
   The blue light emitting element is mounted on a substrate by face down bonding to form a light emitting unit, and the substrate is mounted on the bottom of the recess. 
   The blue light emitting element is an LED of InGaN group. 
   The fluorescent material is a fluorescent material of YAG group. 
   The luminance reducing material is a pigment of black. 
   The present invention also provides a white light emitting device comprising, a case body having a recess forming a reflection face, a blue light emitting element mounted on a bottom of the recess, a cover member including fluorescent material and covering a light emitting face of the case body, the case body comprising a pair of metal cores which are opposed to each other interposing an insulation member, the surface of each of the metal cores being coated with a metal plating having high reflectance, fluorescent material for converting wavelength of light emitted from the blue light emitting element to adjust chromaticity of the light, and luminance reducing material for adjusting the luminance of the light being mixed in the cover member. 
   The metal case is made of a magnesium alloy, the surface of the metal core is coated with silver plating. 
   The cover member has arms, the arms are engaged with grooves formed in the case body. 
   A projection is formed on the arm of the cover member, the projection is engaged with an engaging hole formed in the groove of the case body. 
   The cover member is provided by separating from a cover member assembly comprising a plurality of cover members which are connected by arms. 
   These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view of a white light emitting device according to a first embodiment of the present invention; 
       FIG. 2  is a perspective view of the white light emitting device in which a cover member in  FIG. 1  is removed; 
       FIG. 3  is a sectional view of the white light emitting device taken along a line III—III of  FIG. 1 ; 
       FIG. 4  is a perspective view of a light emitting unit; 
       FIG. 5  is a sectional view showing a white light emitting device according to a second embodiment of the present invention; 
       FIG. 6  is a perspective view showing a white light emitting device according to a third embodiment of the present invention; 
       FIG. 7  is a perspective view of the white light emitting device as viewed from a reverse side thereof; 
       FIG. 8  is a sectional view taken along a line VIII—VIII of  FIG. 6 ; 
       FIG. 9  is a flowchart showing the steps for manufacturing the third embodiment; 
       FIGS. 10 ,  11 ,  12 ,  13   a  and  13   b  are perspective views for explaining a method for manufacturing a light emitting element unit assembly; 
       FIG. 14  is a perspective view of a metal core assembly; 
       FIGS. 15 ,  16 ,  17  and  18  are perspective views for explaining a method for manufacturing a light emitting device; 
       FIG. 19  is a perspective view showing a method for combining a light emitting element unit and a cover member; 
       FIG. 20  is a plan view showing a white light emitting device according to a fourth embodiment of the present invention; 
       FIG. 21  is a sectional view of the device taken along a line A—A of  FIG. 20 ; 
       FIGS. 22   a  to  22   c  are perspective views for explaining a method of manufacturing a white light emitting device of a fourth embodiment; 
       FIG. 23  is a plan view of a white light emitting device according to a fifth embodiment of the present invention; 
       FIG. 24  is a sectional view of the device taken along a line B—B of  FIG. 23 ; 
       FIG. 25  is a sectional view of a conventional LED device disclosed in U.S. Pat. No. 6,069,440; and 
       FIGS. 26 and 27  are graphs showing dispersion in chromaticity and luminance of LED devices. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is a perspective view of a white light emitting device according to a first embodiment of the present invention,  FIG. 2  is a perspective view of the white light emitting device in which a cover member in  FIG. 1  is removed,  FIG. 3  is a sectional view of the white light emitting device taken along a line III—III of  FIG. 1 , and  FIG. 4  is a perspective view of a light emitting element unit. 
   Referring to  FIGS. 1 to 3 , a white light emitting LED device  10  comprises a cubic case  1  made of moldable metal having a high heat conductivity such as Mg group and formed by injection molding, and having a recess  1   c  of an inverted truncated cone and having an inclined inside wall  1   k . The case  1  comprises a pair of first and second half metal cores  3   a  and  3   b , interposing an insulation layer  2  which is made of resin and charged in a slit  1   g . The inside wall of the recess  1   c  and an upper surface  1   a  of the case  1   c  are processed into a light reflection surface by silver plating. 
   Referring to  FIG. 4 , a light emitting element unit  5  comprises a blue LED  6  of InGaN group, a substrate  7  made of ceramics and having upper electrodes  7   a  and  7   b  and lower electrodes  7   c  and  7   d . The upper and lower electrodes  7   a  and  7   c , and the upper and lower electrodes  7   b  and  7   d  are electrically connected with each other by a pair of through-holes  7   e , thereby forming a pair of wiring patterns. A pair of bumps  6   a  ( FIG. 3 ) are secured to a pair of electrodes (not shown) on the underside of the LED  6 . The blue LED  6  as a light emitting element is mounted on the upper electrodes  7   a ,  7   b  through bumps  6   a  by face down bonding. The underside of the LED  6  is encapsulated by a resin  8  to protect the bumps  6   a . Further, the LED  6  is encapsulated by a resin  9 . The light emitting element unit  5  is mounted on the bottom of the recess  1   c  by soldering the lower electrodes  7   c ,  7   d  to the metal cores  3   a ,  3   b.    
   A cover member  11  made of transparent resin such as elastomer of silicon group has an outside shape so as to engage with the inclined wall  1   k  of the empty recess  1   c , and is spaced from the bottom of recess  1   c . If required, the cover member  11  is secured to the recess  1   c  by caulking or an adhesive. In the cover member  11 , YAG phosphor particles  12  and a luminance reducing material particles  13  such as pigment and dye particles  7   f  are mixed. The phosphor particle  12  and the pigment particle  13  are selected so that the chromaticity and luminance of the light emitted from the LED  6  are corrected to desired values. 
   As the phosphor particle is selected from fluorescent materials of YAG group where the ratio of Ga to Gd is variously changed. 
   As the luminance reducing material, pigments of black group in which graphite and carbon or red, green and blue pigments are mixed are used. 
   In operation, when the current is applied to the metal cores  3   a  and  3   b , the current is applied to the blue LED  6  via the electrodes  7   a ,  7   b ,  7   c ,  7   d  and bumps  6   a . Thus the LED  6  is excited to emit blue light. When a part of the blue light impinges upon the phosphor particle  12 , the blue light is absorbed in the phosphor particle  12  and the particle emits yellow light. When the yellow light and the blue light which does not impinge upon the phosphor particle are mixed, white light produces. Further, the chromaticity and luminance of the white light are corrected to desired chromaticity and luminance by the phosphor particles  12  and pigment particles  13 . 
   Since the case  1  is made of a metal having a high heat conductivity, the case is superior in heat radiation. Therefore, the LED device can effectively be used for a light emitting device in which the case temperature rises highly because of a large current. 
   There is provided the cover member  11  in which the phosphor particles  12  and the luminance reducing particles  13  are mixed. A white light emitting device  1  satisfies both of the chromaticity and luminance in a desired range, thereby reducing the variation in characteristics. Since the luminance reducing member is used, initial luminance can be set to a large value, so that the luminance is adjusted by reducing the luminance. Therefore, luminance can be adjusted in a wide range. 
   Since the cover member  11  is made of the elastomer of silicon group, the phosphor particles  12  and the luminance reducing particles  13  are uniformly distributed in the cover member without depositing and biasing. Therefore, the LED device emits light uniform in chromaticity and luminance. 
     FIG. 5  is a sectional view showing a white light emitting device according to a second embodiment of the present invention. The white light emitting device  20  has the case  1  same as that of the first embodiment. A cover plate  14  made of glass or transparent solid plastic such as acrylic resin and silicon is secured to the upper surface  1   a  to press the cover member  11  against the inside wall of the recess  1   c . Other parts are identified by the same reference numerals as  FIG. 3 . 
   Since the cover member  11  is held by the cover plate  14 , it is not necessary to adhere the cover member  11  to the wall of the recess  1   k.    
     FIG. 6  is a perspective view showing a white light emitting device according to a third embodiment of the present invention.  FIG. 7  is a perspective view of the white light emitting device as viewed from a reverse side thereof,  FIG. 8  is a sectional view taken along a line VIII—VIII of  FIG. 6 . 
   Referring to  FIGS. 6 and 7 , the white light emitting device  30  comprises a case  21  having a cubic shape. The case  21  comprises a pair of metal cores  23   a  and  23   b  made of metal having a high heat conductivity, and a combining resin  24  of heat resistivity. The combining resin  24  is mounted on a step  21   f  of the case  21  to form an upper shape of the case, charged in a slit  21   g  between the metal cores  23   a  and  23   b , and in grooves  23   c  and  23   d  formed in the side wall and the underside of the metal cores  23   a  and  23   b , thereby combining the metal cores. 
   The undersides of the metal cores  23   a  and  23   b  form a pair of electrodes  25  and  26 . A recess  21   c  is formed in the metal cores  23   a  and  23   b . The inside wall of the recess  21   c  and the surfaces of the metal cores  23   a  and  23   b  are processed into light reflection surfaces by silver plating. A shoulder  21   e  is formed in an upper portion of the recess  21   c , and a cover member  32  is mounted on the shoulder. Other parts are the same as the first embodiment and identified by the same reference numerals as the first embodiment. 
     FIG. 9  is a flowchart showing the steps for manufacturing the third embodiment, and  FIGS. 10˜18  are perspective views showing the steps, whereby a plurality of light emitting element devices are manufactured at the same time. 
   At a step S 1 , a substrate assembly for a light emitting element unit is manufactured. 
     FIG. 10  is a perspective view of a substrate assembly  107 . 
   The substrate assembly  107  is divided into nine areas  24  for nine LED devices by dicing lines  26  and  27 . On the upper surface and the underside of a substrate material, four sets of electrodes  107   b  are secured. 
   In each area, a pair of through-holes  107   c  are formed to electrically connect the upper and lower electrodes  107   b.    
   At a step S 2 , the blue LED  6  is mounted on the upper electrodes  107   b  through bumps (not shown) as shown in  FIG. 11 . Further, at a step S 3 , the underside of the LED  6  is encapsulated by the resin  8  and encapsulating resin  9  to form a light emitting element unit assembly  105  as shown in  FIG. 12 . 
   Next, at a step S 4 , the light emitting element unit assembly  105  is cut off along the dicing lines  26  and  27  to produce the light emitting element unit  5  from the assembly  105  as shown in  FIG. 13   b.    
   The chromaticity and luminance of each of the produced lighting element units are measured. The measured units are classified into ranks dependent on the result of the measurement. 
   Next, at a step S 5 , a metal core assembly is manufactured. As shown in  FIG. 14 , a metal core assembly  123  is formed by injection molding and divided into nine areas  30  for nine units  5  by dicing lines  31  and  32 . A cylindrical portion  123   b  having recess  21   c  is formed in each area  30  at a central portion. Three slits  123   g  are formed in parallel to the lines  32  except a peripheral frame  123   a.    
   Further, three grooves  123   c  are formed. 
   At a step S 6 , a resin is charged in a recess within the peripheral frame  123   a , slits  123   g  and grooves  123   c  to form a resin layer  104  as shown in  FIG. 15 . Thus, a case assembly  121  is produced. 
   Next, at a step S 7 , light emitting element units  5  belonging to the same class are mounted on bottoms  21   d  of recesses  21   c  as shown in  FIG. 16 . 
   At a step S 8 , cover members  32  belonging to the same rank are secured to the inside wall of the recesses  21   c , respectively, to form a light emitting element device assembly  130  as shown in  FIG. 17 . 
   At a step S 9 , the assembly  130  is cut off along the dicing lines  31  and  32  to separate the independent light emitting device  30  as shown in  FIG. 18 . 
   Finally, at a step S 10 , the test of the product is carried out. 
     FIG. 19  is a perspective view showing a method for combining a blue light emitting element unit and a cover member. 
   A method for combining the blue light emitting element  6  and the cover member  32  is described hereinafter with reference to  FIG. 19 . 
   The blue LED  6  in the unit  5  is measured about the chromaticity and the luminance by an LED tester, and measured LEDs are classified into classes, for example classes a, b, c, in accordance with the measured characteristics. 
   On the other hand, the cover members  32  are also classified into classes A, B and C so that the combinations a and A, b and B, c and C perform to emit desirable white lights. The combined sets are mounted in the case  21 . Thus, white light emitting devices  30  are produced. 
   In accordance with the third embodiment, since the shoulder  21   e  is formed in the recess  21   c , the cover member  32  can easily be set in the recess. On the inside wall of the recess  21   c , the vertical wall  21   m  is formed, and the side wall  32   a  of the cover member  32  is accordingly vertical. Therefore, when the cover member is set in the recess  21   c , it is not necessary to judge the distinction of both sides of the cover member. 
     FIG. 20  is a plan view showing a white light emitting device according to a fourth embodiment of the present invention,  FIG. 21  is a sectional view of the device taken along a line A—A of  FIG. 21 . The white light emitting device  40  comprises a case  31  comprising a pair of metal cores  33   a  and  33   b  and a slit  33   c  between the metal cores  33   a  and  33   b . The device  40  is characterized in that four grooves  31   a  are formed in the upper surfaces of the metal cores  33   a ,  33   b  radially extending from the recess  21   c . On the other hand, four arms  42   a  are radially extending from a cover member  42 , corresponding to the grooves  31   a . The arms  42   a  are engaged in the grooves  31   a  and secured thereto. 
   Since the method for manufacturing the white light emitting device of the fourth embodiment is substantially same as that of the third embodiment, only different method is described hereinafter. 
     FIGS. 22   a˜   22   c  are perspective views showing steps for manufacturing a light emitting device assembly. Referring to  FIG. 22   a , nine cover members  42  are assembled by connecting arms  42   a  of each cover member  42 , thereby forming a cover member assembly  142 . 
   On the other hand, in a case assembly  131  as shown in  FIG. 22   b , nine recesses  21   c , grooves  131   a  and slits  133   c  are formed. The light emitting element unit  5  is mounted in each recess  21   c.    
   As shown in  FIG. 22   c , the cover member assembly  142  is mounted on the case assembly  131 . Thus a light emitting device assembly  140  is formed. 
   In accordance with the fourth embodiment, a plurality of cover members  42  having the same characteristics are assembled. Therefore, light emitting devices of same characteristics can be produced. Further, constructing steps are reduced. 
     FIG. 23  is a plan view of a white light emitting device according to a fifth embodiment of the present invention,  FIG. 24  is a sectional view of the device taken along a line B—B of  FIG. 23 . The white light emitting device  50  comprises a case  41  comprising a pair of metal cores  43   a  and  43   b  and a slit  43   c  between the metal cores  43   a  and  43   b . In the white light emitting device  50 , four grooves  41   a  are formed in the upper surfaces of the metal cores  43   a ,  43   b , radially extending from the recess  21   c . In one of the grooves  41   a , an engaging hole  41   j  is formed in the bottom of the groove. On the other hand, four arms  51   a  are radially extending from a cover member  51  and a projection  51   c  is formed on the underside of the arm  51   a  corresponding to the hole  41   j  of the groove  41   a . The arms  51   a  are engaged in the grooves  41   a  and the projection  51   c  is engaged with hole  41   j  and secured thereto. 
   In accordance with the fifth embodiment, the cover member  51  is strongly fixed to the case  41  by the engagement of the projection  51   c  with the hole  41   j.    
   In accordance with the present invention, there is provided the cover member in which the phosphor particles and the luminance reducing particles are mixed. Therefore the white light emitting device produces white light which satisfies both of the chromaticity and luminance in a desired range by selecting the amount of the phosphor and luminance reducing particles, thereby reducing the dispersion in characteristics. 
   Since the luminance reducing member is used, initial luminance can be set to a large value, so that the luminance is adjusted by reducing the luminance. Therefore, luminance can be adjusted in a wide range. 
   Since the cover member is made of the elastomer of silicon group, the phosphor particles and the luminance reducing particles are uniformly distributed in the cover member without depositing and biasing. Therefore, the LED device emits light uniform in chromaticity and luminance. 
   While the invention has been described in conjunction with preferred specific embodiment thereof, it will be understood that this description is intended to illustrate and not limit the scope of the invention, which is defined by the following claims.