Patent Publication Number: US-2015076541-A1

Title: Light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-191189, filed Sep. 13, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to light-emitting devices. 
     BACKGROUND 
     The development of a lighting device using a light emitting diode (LED) as a light source is important. For example, a light-emitting device using a combination of a blue LED and a phosphor is small and long-life and is suitable for a light source of a lighting device. However, in this type of light-emitting device, the spectrum of an emitted light changes depending on the optical path length of the LED light that excites the phosphor. As a result, color unevenness that depends on the direction in which the light is emitted develops as result of optical path length differences. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic diagrams depicting a light-emitting device according to an embodiment. 
         FIGS. 2A to 2D  are schematic sectional views, each depicting a process for manufacturing the light-emitting device according to the embodiment. 
         FIGS. 3A and 3B  are schematic diagrams depicting a light-emitting device according to a modified example of the embodiment. 
         FIGS. 4A and 4B  are schematic sectional views, each depicting a light-emitting device according to another modified example of the embodiment. 
         FIGS. 5A and 5B  are schematic sectional views, each depicting a light-emitting device according to still another modified example of the embodiment. 
         FIG. 6  is a schematic sectional view depicting a light-emitting device according to a comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment provides a light-emitting device that can suppress color variation resulting from differences in the direction in which a light is emitted from the light-emitting device. 
     In general, according to one embodiment, a light-emitting device includes a first lead frame, a second lead frame that is electrically insulated from the first lead frame, a light-emitting element mounted on the first lead frame and electrically connected to the first lead frame and the second lead frame, a first frame body portion surrounding the light-emitting element, a resin disposed on the light-emitting element and filling a frame formed by the first frame body portion, and a second body portion surrounding the first frame body portion. The resin contains a phosphor which, when excited by a wavelength of a light emitted by the light-emitting element, emits a light having a wavelength that is different from the wavelength of the light emitted by the light-emitting element, and the second frame body portion has an upper surface at a height above an upper surface of the first frame body portion. 
     Hereinafter, embodiments will be described with reference to the drawings. Identical portions in the drawings are identified with common reference numerals and the detailed descriptions thereof are omitted as appropriate, and only different portions may be described. Incidentally, the drawings are schematic or conceptual diagrams, and the depicted relationships between the thickness and the width of each portion, the size ratio between different portions, etc. are not necessarily identical to the relationship, the size ratio, etc. of an actual device. Moreover, even when the same portion is depicted in different drawing, the dimensions and ratio thereof may be different in different drawings. 
       FIGS. 1A and 1B  are schematic diagrams depicting a light-emitting device  1  according to an embodiment.  FIG. 1A  is a sectional view taken on the line A-A depicted in  FIG. 1B .  FIG. 1B  is a plan view depicting a shape viewed from above. 
     As depicted in  FIG. 1A , the light-emitting device  1  includes a first lead frame (hereinafter, a lead frame  10 ), a second lead frame (hereinafter, a lead frame  20 ), a light-emitting element  30  mounted on the lead frame  10 , and a resin  40  covering the light-emitting element  30 . The lead frame  20  is disposed beside the lead frame  10  in a side by side manner. The lead frame  10  is disposed in a position away from the lead frame  20 , and an insulator  13  is provided between the lead frame  10  and the lead frame  20 . As a result, the lead frame  10  and the lead frame  20  are electrically insulated from each other. 
     The light-emitting element  30  is, for example, a vertical blue LED that passes a drive current between a light-emitting face and a rear face. The light emitting-element  30  is electrically connected to the lead frame  10  and the lead frame  20 . The light-emitting element  30  is mounted in such a way that, for example, the rear face opposite to the light-emitting face is mounted to the lead frame  10 . Then, for example, a metal wire  33  is bonded between an electrode provided in part of the light-emitting face and the lead frame  20  to thereby connect the electrode and the lead frame  20  electrically. 
     Furthermore, as depicted in  FIG. 1B , the light-emitting device  1  includes a first frame body (hereinafter, a frame body  50 ) surrounding the light-emitting element  30  and a second frame body (hereinafter, a frame body  60 ) surrounding the frame body  50 . The frame bodies  50  and  60  are provided in such a way as to lie astride the lead frame  10  and the lead frame  20  and contacting the lead frame  10  and the lead frame  20 . 
     The frame body  50  is filled with resin  40  which covers the light-emitting element  30 . The resin  40  contains a base material that allows an emitted light of the light-emitting element  30  to pass therethrough and a phosphor  41  that is excited by the emitted light from the light-emitting element  30  and consequently emits a light at a wavelength which is different from the wavelength of the emitted light from the light-emitting element  30 . Incidentally, “allowing a light to pass therethrough” includes not only allowing all of the emitted light of the light-emitting element  30  to pass therethrough but also absorbing part thereof. Thus, the base material need not be completely transparent to light emitted by the light-emitting element  30  and may absorb and/or scatter portions of the light emitted by the light-emitting element  30 . 
     The base material of the resin  40  is, for example, silicone resin and allows a visible light to pass therethrough. The phosphor  41  is, for example, a YAG phosphor and absorbs a blue light emitted from the light-emitting element  30  and emits a yellow light. 
     The frame body  60  is provided outside the frame body  50 . The height of the frame body  60  above each lead frame (lead frames  10  and  20 ) is greater than the height of frame body  50 . For example, a height at which a line LP connecting an inner edge of a top end  60   a  of the frame body  60  to the center of a top face  40   a  of the resin  40  does not intersect the frame body  50 . Moreover, as depicted in  FIG. 1A , the frame body  60  may be connected to the frame body  50  in a lower part  60   b  which may be in contact with the lead frame  10  and the lead frame  20 . 
     The frame bodies  50  and  60  include a component that reflects the emitted lights of the light-emitting element  30  and the phosphor  41 —that is, reflects light at wavelengths of the light emitted by light-emitting element  30  and the phosphor  41 . As the frame bodies  50  and  60 , for example, epoxy resin in which minute particles of titanium oxide are dispersed or silicone white resin is used. In addition, the frame bodies  50  and  60  reflect the emitted light of the light-emitting element  30  and the emitted light of the phosphor  41  contained in the resin  40 . 
     On the other hand, surfaces of the lead frame  10  and the lead frame  20  (e.g., bottom surfaces in  FIG. 1A ) that are opposite to the surface on which the light-emitting element  30  is mounted (upper surfaces in  FIG. 1A ), are exposed. Accordingly, light-emitting device  1  can be mounted on a circuit substrate, for example, by using the exposed surfaces (e.g., bottom surfaces in  FIG. 1A ) of the lead frames  10  and  20  as a bonding pad. 
     Moreover, preferably, the faces of the lead frames  10  and  20  on which the light-emitting element  30  is mounted include a component, for example, silver (Ag), whose degree of reflection of the emitted lights of the light-emitting element  30  and the phosphor  41  is higher than the degree of reflection of a core of each lead frame. 
     Next, with reference to  FIG. 6 , the characteristics of the light-emitting device  1  will be described.  FIG. 6  is a schematic sectional view depicting a light-emitting device  7  according to a comparative example. 
     As depicted in  FIG. 6 , the light-emitting device  7  includes a light-emitting element  30  mounted on a lead frame  10 , a frame body  50  surrounding the light-emitting element  30 , and a resin  40  with which the frame body  50  is filled. However, the light-emitting device  7  does not include an outside frame body  60  surrounding the frame body  50 . 
     Arrows L 1  to L 3  depicted in  FIG. 6  schematically illustrate the light distribution characteristics of the light emitted from the light-emitting device  7 . The length of each arrow represents the ratio of a yellow light in the output from light-emitting device  7 . The longer the arrow in  FIG. 6 , the higher the ratio of the yellow light in the output from light-emitting device  7 . 
     The blue light emitted from the light-emitting element  30  passes through the resin  40  and is emitted from a top face  40   a  to the outside. Part of the blue light is absorbed by a phosphor  41  that is dispersed in the resin  40  and is converted into a yellow light. As a result, the longer the optical path length of a blue light in the resin, the more the light is attenuated by phosphors  41 . Thus, the intensity of the blue light that propagates through the resin  40  in a transverse direction (±X directions, that is the left-right directions in  FIG. 6 ) is reduced. As a result, the ratio of the yellow light in the light L 3  that is emitted sideways (in an oblique direction, rather than perpendicular to top surface  40   a ) becomes higher than the ratio of the yellow light in the light L 1  that is emitted upward (Z direction), and a directional color unevenness develops in the light output from light-emitting device  7 . 
     On the other hand, in the light-emitting device  1  according to the embodiment, the frame body  60  provided outside the frame body  50  surrounding the light-emitting element  30  reflects the light L 3  that is emitted sideways in an oblique direction. Then, the light reflected by the frame body  60  is mixed into the lights L 1  and L 2  that are emitted in the Z direction. As a result, in the light-emitting device  1 , color unevenness that depends on the direction in which the light is emitted can be suppressed. 
     Also, by simply blocking the light L 3  that is emitted in a transverse direction with the frame body  60 , color unevenness can be reduced. That is, the frame body  60  may absorb the blue light emitted from the light-emitting element and the yellow light emitted from the phosphor  41 . Specifically, as the frame body  60 , black resin containing carbon particles, for example, may be used. 
     Furthermore, the height H of the frame body  60  depicted in  FIG. 1A  is set with consideration given to an emission angle of the light L 3  in which the ratio of the yellow light is high. For example, an upper limit of the angle θ between the top face  40   a  of the resin  40  and the straight line LP is limited by the mounting conditions or the light distribution angle. On the other hand, a lower limit of θ is set in accordance with an acceptable range of color unevenness. 
     Next, with reference to  FIGS. 2A to 2D , a method for producing the light-emitting device  1  according to an embodiment will be described.  FIGS. 2A to 2D  are schematic sectional views, each depicting a process of production of the light-emitting device  1  according to the embodiment. 
     As depicted in  FIG. 2A , a resin frame  17  is formed on a metal plate  15 . The metal plate  15  is, for example, a copper plate having a punched lead pattern. The top face of the metal plate  15  is preferably plated with a component, for example, silver (Ag), which has a high reflectivity for the emitted lights of a light-emitting element  30  and a phosphor  41 . Moreover, the metal plate  15  includes an insulator  13  that provides isolation between a lead frame  10  and a lead frame  20 . 
     The resin frame  17  is formed by using, for example, epoxy resin in which powder of titanium oxide is dispersed or silicone in such a way as to include a frame body  50  and a projection  65  that will be divided into frame bodies  60 . 
     Next, as depicted in  FIG. 2B , a light-emitting element  30  is mounted in a portion of the metal plate  15 , the portion surrounded with the frame body  50 . The light-emitting element  30  is firmly fixed to a portion to be processed into the lead frame  10  with a conductive paste, for example, sandwiched between the light-emitting element  30  and the portion. Then, a metal wire  33  is bonded to an electrode provided on a light-emitting face (top face) of the light-emitting element  30  and a portion to be processed into the lead frame  20 . 
     Next, as depicted in  FIG. 2C , the portion surrounded with the frame body  50  is filled with resin  40 , whereby the light-emitting element  30  is encapsulated therein. The resin  40  is injected into each portion by using a potting method, for example, and is then hardened. Filling of the resin  40  may be performed in such a way that the resin  40  and the top face of the frame body  50  are on the same level or may be performed in such a way that a portion of resin  40  is higher than the top face of the frame body  50 . Alternatively, filling of the resin  40  may be performed in such a way that the top face  40   a  of the resin  40  becomes lower than the top face of the frame body  50 . 
     Next, as depicted in  FIG. 2D , the resin frame  17  and the metal plate  15  are divided at the center of the projection  65 , whereby the light-emitting device  1  is completed. The resin frame  17  and the metal plate  15  are cut by using a dicing blade, for example. By using the above-described method, a small and low-cost light-emitting device can be formed. 
     Next, with reference to  FIGS. 3A to 5B , light-emitting devices  2  to  6  according to modified examples of the embodiment will be described. It should be noted that these examples are typical examples and the disclosure is not limited thereto. 
       FIGS. 3A and 3B  are schematic diagrams depicting the light-emitting device  2  according to a modified example.  FIG. 3A  is a sectional view taken on the line B-B depicted in  FIG. 3B .  FIG. 3B  is a plan view depicting a shape viewed from above. 
     As depicted in  FIG. 3A , the light-emitting device  2  includes a lead frame  10 , a lead frame  20 , a light-emitting element  30  mounted on the lead frame  10 , and a resin  40  covering the light-emitting element  30 . The frame body  50  is filled with the resin  40 . 
     In addition, on the outside of the frame body  50 , a frame body  61  is provided. An inner surface  61   a  of the frame body  61  has a shape spreading in the direction (Z direction) in which a light is emitted. The inner surface  61   a  is, for example, a paraboloid and reflects obliquely emitted light from resin  40  toward the Z direction. As depicted in  FIG. 3B , the frame body  61  can be formed into a circle. 
     The shape of the frame body provided outside the frame body  50  is not limited to the above example and may be any shape, and the planar shape (the shape when viewed from above, as in  FIG. 3B ) thereof may be a rectangular, circular, or oval shape. Moreover, the frame body  50  may also have any shape, and the planar shape thereof is not limited to a rectangular shape depicted in  FIGS. 1A and 1B  and  FIGS. 3A and 3B . 
       FIG. 4A  is a schematic sectional view depicting light-emitting device  3 . As depicted in  FIG. 4A , the light-emitting device  3  includes a lead frame  10 , a lead frame  20 , a light-emitting element  30  mounted on the lead frame  10 , and a resin  40  covering the light-emitting element  30 . The frame body  50  is filled with the resin  40 . 
     On the outside of the frame body  50 , a frame body  63  is provided. An inner surface  63   a  of the frame body  63  has an inclination spreading in the direction (e.g., the Z direction of  FIG. 4A ) in which a light is emitted, and which reflects upward light that is emitted from the resin  40  sideways (in an oblique direction to the upper surface of resin  40 ). That is, frame body  63  has an inner surface  63   a  that is outwardly angled (inclined) rather than perpendicular to the upper surface of resin  40 . 
       FIG. 4B  is a schematic sectional view depicting light-emitting device  4 . As depicted in  FIG. 4B , the light-emitting device  4  includes a lead frame  10 , a lead frame  20 , a light-emitting element  30  mounted on the lead frame  10 , and a resin  40  covering the light-emitting element  30 . The frame body  50  is filled with the resin  40 . In addition, on the outside of the frame body  50 , a frame body  60  is provided. 
     The light-emitting element  30  includes a p-electrode and an n-electrode on a rear face opposite to a light-emitting face. In addition, the light-emitting element  30  is mounted by flip-chip bonding in such a way as to lie astride the lead frames  10  and  20 . The light-emitting elements  30  described in other embodiments may be replaced with the light-emitting element  30  depicted in  FIG. 4B . That is, for example, rather than using a bonding wire as depicted in  FIG. 1A , flip-chip bonding may be incorporated to make an electrical connection to lead frame  20  of light-emitting device  1 . Similar modifications can be incorporated into light-emitting device  2 , light emitting device  3 , light-emitting device  5  (described below), and light-emitting device  6  (described below) or other embodiments of the present disclosure. 
       FIG. 5A  is a schematic sectional view depicting the light-emitting device  5 . As depicted in  FIG. 5A , the light-emitting device  5  includes a lead frame  10 , a lead frame  20 , a light-emitting element  30  mounted on the lead frame  10 , and a resin  40  covering the light-emitting element  30 . The frame body  50  is filled with the resin  40 . 
     On the outside of the frame body  50 , a frame body  67  is provided. Portions of the frame body  67 , the portions in contact with the lead frames  10  and  20 , are formed in positions away from the frame body  50 . That is, frame body  67  is spaced from frame body  50 . In this example, a gap is formed between inner surface  67   a  of frame body  67  and frame body  50 . In this example, an inner surface  67   a  of the frame body  67  is formed to be perpendicular to the lead frames  10  and  20 , but the shape is not limited thereto. For example, similar to as depicted in  FIGS. 3A and 3B  and  FIG. 4A , the inner surface  67   a  may have a shape for reflecting light in a direction (Z direction) toward which a light is to be emitted from light-emitting element  5 . 
       FIG. 5B  is a schematic sectional view depicting the light-emitting device  6 . As depicted in  FIG. 5B , the light-emitting device  6  includes a lead frame  10 , a lead frame  20 , a light-emitting element  30  mounted on the lead frame  10 , and a resin  40  covering the light-emitting element  30 . 
     In this example, a frame body  70  is provided on the lead frames  10  and  20 , and the frame body  70  is filled with the resin  40 . The frame body  70  includes an outer portion  71  and an inner portion  73  provided inside the outer portion  71  in step-like form—that is, outer portion  71  and inner portion  73  have different upper surface heights. 
     The outer portion  71  is formed to be higher than (have an upper surface height that is greater than) the inner portion  73 . An inner surface  71   a  of the outer portion  71  may have a shape reflecting obliquely emitted light from resin  40  in the direction (Z direction) in which light is to be emitted from light emitting device  6 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.