Patent Publication Number: US-11640957-B2

Title: Light emitting module

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 16/454,906 filed on Jun. 27, 2019. This application claims priority to Japanese Patent Application No. 2018-123939 filed on Jun. 29, 2018. The entire disclosures of U.S. patent application Ser. No. 16/454,906 and Japanese Patent Application No. 2018-123939 are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a method of manufacturing a light emitting module. 
     BACKGROUND ART 
     Light emitting devices that use light emitting elements such as light emitting diodes, etc., are widely used as a backlight of a liquid crystal display, various types of light sources of a display, etc. As this kind of light emitting device, there has been proposed a structure for which the light emitting element is mounted on a substrate having wiring. For example, Japanese Laid-Open Patent Publication No. 2006-100444 noted hereafter discloses a light emitting device that has wiring on the top surface of a substrate, and has an electrode of the bottom surface of the light emitting element connected to that wiring. 
     SUMMARY 
     In recent years, there has been demand for further miniaturization of light emitting devices. To miniaturize the light emitting device, it is necessary to do placement with high precision when forming wiring. 
     The present invention provides a method of manufacturing a light emitting module for which miniaturization is possible. 
     A light emitting module includes a substrate, a light reflective resin layer, wiring electrodes and a light emitting element. The light reflective resin layer is arranged on the substrate. The wiring electrodes are arranged over the substrate with the light reflective resin layer being interposed between the substrate and the wiring electrodes. The light emitting element has an electrode formation surface including a positive and negative pair of element electrodes, and a light emitting surface on a side opposite to the electrode formation surface. The light emitting element is arranged on top surfaces of the wiring electrodes with the element electrodes facing the top surfaces of the wiring electrodes. 
     According to the method of manufacturing a light emitting module of an embodiment of the present invention, it is possible to realize the light emitting module for which miniaturization is possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic cross section diagram of a light emitting module of an embodiment of the present invention. 
         FIG.  2    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  3    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  4    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  5    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  6    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  7    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  8    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  9    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  10    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  11    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  12    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  13    is a schematic cross section diagram showing a manufacturing step of the light emitting module of an embodiment of the present invention. 
         FIG.  14    is a schematic cross section diagram of the light emitting module of an embodiment of the present invention. 
         FIG.  15    is a schematic cross section diagram of the light emitting module of an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Following, an embodiment of the present invention is explained while referring to drawings as appropriate. However, the embodiment(s) explained hereafter is for putting the technical concept of the present invention into specific form, and unless specifically noted, the present invention is not limited to the items noted hereafter. Also, the size, positional relationship, etc., of the members shown in the drawings may be exaggerated to clarify the explanation. 
     Hereafter, a detailed explanation is given of the present invention based on the drawings. With the explanation hereafter, terms indicating specific directions or positions are used as necessary (for example, “upper,” “lower,” and other terms including these terms), but those terms are used to make it easier to understand the explanation with reference to the drawings, and the technical scope of the present invention is not limited by the meaning of those terms. Also, parts with the same code number appearing in multiple drawings indicate the same or equivalent parts or members. 
     Furthermore, the embodiment shown hereafter shows an example of the light emitting module to put into specific form the technical concept of the present invention, and the present invention is not limited to the item noted hereafter. Also, the dimensions, materials, shape, relative placement, etc., of constituent parts noted hereafter are intended to show an example, and unless specifically noted, do not mean that the scope of the present invention is limited only to those. Also, the contents explained with one embodiment or working example can also be applied to other embodiments or working examples. Also, the size, positional relationship, etc., of members shown in the drawings may be exaggerated to clarify the explanation. 
       FIG.  1    is a schematic cross section diagram of the light emitting module obtained using the manufacturing method of this embodiment. 
     The light emitting module comprises: a substrate  60 ; a light reflective resin layer  50  provided on the top surface of the substrate  60 ; a wiring electrode  40  provided above the substrate  60  with the light reflective resin layer  50  interposed; and a light emitting element  20  mounted on the top surface of the wiring electrode  40 . 
     The light emitting element  20  has an electrode formation surface  20   a  comprising a positive and negative element electrode  21 , and a light emitting surface on the side opposite the electrode formation surface  20   a . The light emitting element  20  is flip-chip mounted directly or with a bump, etc., interposed so that the element electrode  21  faces opposite the top surface of the wiring electrode  40 . 
     Hereafter, a detailed explanation is given regarding the method of manufacturing a light emitting module based on the schematic cross section diagrams shown in  FIGS.  2  to  12   . 
     (Step for Placing Light Emitting Element  20 ) 
     As shown in  FIG.  2   , the light emitting element  20  is placed on a support member  10 . The light emitting element  20  is placed in a state with the electrode formation surface  20   a  facing upward, and the light emitting surface facing downward. In the light emitting module, it is also possible to place a plurality of the light emitting elements  20  with a designated interval open. In this case, in a step for forming the wiring electrode  40  described later, it is possible to electrically connect the element electrodes  21  of the light emitting elements  20  to each other using the wiring electrodes  40 . 
     The support member  10  is an item for which mounting of the light emitting element  20  is possible. The shape of the support member  10  is not particularly limited, but it is preferable that the top surface be flat. The support member  10  and the light emitting element  20  are stuck together using an adhesive layer  13 . As the adhesive layer  13 , it is possible to use VPA, etc., for example. 
     On the top surface of the support member  10 , a photosensitive resin layer is formed as a peeling layer  11 . The adhesive layer  13  is formed on the top surface of the peeling layer  11  with a protective layer  12  interposed. The peeling layer  11  is an item for separating the light emitting element  20  from the support member  10  later by irradiating light. 
     Next, as shown in  FIG.  3   , the adhesive layer  13  of the region other than the mounting region of the light emitting element is removed by etching. The protective layer  12  has a role of preventing etching of the peeling layer  11 . As the material of the protecting layer  12 , it is preferable to use metal. As the metal of the protective layer  12 , it is possible to use Ti, etc. 
     (Step for Forming Coating Layer  30 ) 
     Next, a coating layer  30  is formed on the support member, surrounding the light emitting element  20 . The coating layer  30  is provided by applying a material of the coating layer  30  on the support member. The application method can be spin coating using a spin coater, discharge using a dispenser, etc., and is not particularly restricted. For the coating layer  30 , it is preferable to use a member configured using an organic substance. By doing this, in the step for removing the coating layer  30  described later, it is possible to easily do removal using etching. As the organic substance, it is possible to use a polyimide, for example. 
     For example, when using resist as the coating layer  30 , as shown in  FIG.  4   , after providing the resist so as to cover the support member  10  and the light emitting element  20 , as shown in  FIG.  4   , exposure is done via a mask M formed in a shape covering above the light emitting element  20 , and by developing, an opening by which the electrode formation surface  20   a  of the light emitting element  20  is exposed is formed as shown in  FIG.  5   . 
     (Step for Forming Wiring Electrode  40 ) 
     Next, the wiring electrode  40  is formed extending from the element electrode  21  of the light emitting element  20  over the coating layer  30 . The wiring electrode is formed by laminating a first metal layer  41  and a second metal layer  42 . 
     In the step for forming the wiring electrode, first, as shown in  FIG.  6   , the first metal layer  41  is formed by sputtering, etc., on approximately the entire surface of the element electrode  21  of the light emitting element  20  and the coating layer  30 . The first metal layer  41  is used as a seed layer when forming the second metal layer  42  using an electrolytic plating method in the step for forming the second metal layer  42  which is post-processing. As the laminated structure of the first metal layer  41 , an example is Al/Ti/Cu, etc., from the support member  10  side. 
     Next, as shown in  FIG.  7   , a resist R is provided on the first metal layer  41 . In the plan view, the resist R is formed to have an opening that includes at least a portion of the element electrode  21 . 
     Next, as shown in  FIG.  8   , inside the opening of the resist R, the second metal layer is formed using the electrolytic plating method. For the second metal layer, the first metal layer is used as the seed layer for electrolytic plating, in other words, as a current path, and is formed by growing plating within the opening of the resist. As the second metal layer, an example includes Cu. 
     Next, as shown in  FIG.  9   , when the resist is removed, the second metal layer appears as a portion of the wiring electrode. 
     Subsequently, as shown in  FIG.  10   , a portion of the second metal layer is removed by etching to make a thin film of the second metal layer, and also, the first metal layer of the region in which the second metal layer is not formed is removed. By doing this, the wiring electrode made by lamination of the first metal layer  41  and the second metal layer  42  is formed extending from the element electrode  21  of the light emitting element  20  over the coating layer  30 . 
     In this way, with the wiring electrode, to form on the element electrode  21  of the light emitting element  20 , even if position skew of the light emitting element  20  occurs in the step of placing the light emitting element  20 , it is possible to adjust the position for providing the wiring electrode  40 . By doing this, compared to when placing the light emitting element on the wiring electrode on the substrate, it is possible to suppress connection failure due to position skew of the element electrode  21  of the light emitting element  20  and the wiring electrode  40 . 
     (Step for Forming Light Reflective Resin Layer  50 ) 
     Next, as shown in  FIG.  11   , the light reflective resin layer  50  is formed on the wiring electrode and the coating layer  30 . As the light reflective resin layer  50 , for example, it is possible to use an item for which titanium oxide and silicone resin are mixed. The light reflective resin layer  50  is formed using a method such as transfer molding, compressing molding, potting, printing, spraying, etc., for example. Also, the light reflective resin layer  50  may also be formed by sticking on the wiring electrode and the coating layer  30  a sheet comprising a material for which titanium oxide and silicone resin are mixed. 
     (Step for Joining Substrate  60 ) 
     Next, as shown in  FIG.  12   , the separately prepared substrate  60  is joined on top of the light reflective resin layer  50 . It is possible to use glass, ceramic, etc., for the substrate  60 . 
     (Step for Removing Support Member  10 ) 
     Next, as shown in  FIG.  13   , the support member is removed using a laser lift-off method. In specific terms, by irradiating laser of a wavelength that is transmitted through the support member on the peeling layer  11  from the support member side, the light emitting element  20  and the support member  10  are separated. 
     (Step for Removing Coating Layer  30 ) 
     Next, as shown in  FIG.  1   , the coating layer  30  is removed. Removal of the coating layer  30  can be done using dry etching, etc. By removing the coating layer  30  together with the peeling layer  11 , the protective layer  12 , and the adhesive layer  13 , the wiring electrode  40  and the light reflective resin layer are exposed surrounding the light emitting element  20 . 
     Working in this way, it is possible to obtain a light emitting module  100 . With the light emitting module  100 , the top surface of the wiring electrode  40 , and the top surface of the light reflective resin layer  50  provided surrounding the wiring electrode  40  are formed on the same plane. 
     Following, each constituent element of the light emitting module is explained. 
     (Substrate  60 ) 
     As long as the substrate  60  is an item for which the light reflective resin layer  50  can be formed on the top surface, the shape is not particularly limited, but it is preferable that the top surface be flat. It is possible to use an item with insulating properties for the substrate  60 , and it is preferable to use glass, ceramic, etc., for example. 
     (Light Reflective Resin Layer  50 ) 
     The light reflective resin layer  50  is placed on the top surface of the substrate  60 . By providing the light reflective resin layer  50  between the light emitting element  20  and the substrate, it is possible to reflect the light facing from the light emitting element  20  to the substrate  60  side to the light guide plate side. 
     The light reflective resin layer  50  has a reflection rate of 60% or greater with respect to the light emitted from the light emitting element  20 , and preferably has a reflection rate of 90% or greater. The light reflective resin layer is preferably a resin that contains a white pigment, etc. Silicone resin that contains titanium oxide is particularly preferable. By doing this, it is possible to make the light emitting module inexpensive by using a large amount of a raw material that is inexpensive such as titanium oxide as the material used in relatively large amounts to cover one surface of the substrate  60 . 
     (Wiring Electrode  40 ) 
     The wiring electrode  40  is electrically connected to the element electrode  21  of the light emitting element  20 . By providing the wiring electrode  40 , it is possible to electrically connect a plurality of the light emitting elements  20  to each other, for example, and possible to easily form the necessary circuits for local dimming, etc. 
     As the material of the wiring electrode  40 , a material with low electrical resistance is preferable, with examples including items that contain at least one item selected from the group comprising Cu, Au, and Al. Among these, it is preferable to use Cu. Also, for the wiring electrode  40 , it is preferable to be configured using a material for which the surface of the substrate side has a high light reflection rate with respect to the light from the light emitting element  20 , and examples include items that contain at least one item selected from the group comprising Al, Ag, Pt, and Rh. Among these, it is preferable to use Al, Ag, or an alloy containing these metals with a high light reflection rate with respect to the light from the light emitting element  20 . In particular, Al is preferable because it is reflective with respect to light from the light emitting element  20 , and also has excellent electrical conductivity which is necessary as a wiring circuit. The thickness of the wiring electrode  40  is not particularly limited, but for example is 0.1 μm to 5 μm. 
     (Light Emitting Element  20 ) 
     The light emitting element  20  has the pair of electrodes provided on the same surface side. For the light emitting element  20 , it is possible to use an already known semiconductor light emitting element configured from a nitride semiconductor, etc. Also, for the light emitting element  20 , it is possible to select an item with any wavelength to obtain a desired light emission color. 
     As the light emitting element  20 , it is possible to use light emitting diodes of various light emission wavelengths. Also, to obtain the desired light emission color, it is also possible to combine with a phosphor described later. In particular, to obtain white emitted light, it is preferable to combine a nitride semiconductor light emitting element that emits blue light with a phosphor that absorbs blue light and emits yellow light, green light, or red light. 
     (Light Reflective Member  70 ) 
     As shown in  FIG.  14   , the light emitting module  100  may have the light reflective member  70  be provided on the light reflective resin layer and the wiring electrode  40 , and surrounding the light emitting element  20 . By covering the electrode formation surface  20   a  of the light emitting element  20  and the side surface using the light reflective member  70 , the light utilization efficiency is improved. Also, since it is possible to place the light reflective member  70  between mutually adjacent light emitting elements  20 , when light is emitted selectively for a portion of the light emitting elements among the plurality of light emitting elements, it is possible to suppress leakage of light from the light emitting region to the non-light emitting region. 
     As shown in  FIG.  15   , it is also possible to further provide a light transmissive member  80  and a wavelength conversion member  90  above the light emitting element  20 . 
     (Light Transmissive Member  80 ) 
     The light transmissive member  80  is preferably provided between the light emitting element  20  and the wavelength conversion member  90  described later. By doing this, it is possible to make the light emitted from the light emitting element  20  incident on the wavelength conversion member  90  with good efficiency. As the light transmissive member  80 , it is possible to use transparent resin, glass, etc. As the transparent resin, it is preferable to use silicone resin, etc., from the perspective of durability, ease of molding, etc. 
     (Wavelength Conversion Member  90 ) 
     The wavelength conversion member  90  is placed on the top surface of the light transmissive member  80 . The wavelength conversion member  90  contains phosphor that is able to absorb light from the light emitting element  20  and to emit light of other wavelengths. By doing this, the light emitting module  100  can emit to outside a mixed light of the light from the light emitting element  20  and the light that underwent wavelength conversion by the wavelength conversion member  90 , such as white light, for example. By selecting the type of the light emitting element  20  and the type of the phosphor, it is possible to suitably adjust the color of the emitted light. 
     As shown in  FIG.  15   , in the light emitting module  100 , one light transmissive member  80  and wavelength conversion member  90  are provided with respect to a plurality of the light emitting elements  20 . By doing this, it is possible to configure the light emitting module  100  that is capable of large area planar light emission. The light transmissive member  80  and the wavelength conversion member  90  may also be provided for each light emitting element  20 .