Patent Publication Number: US-2022231205-A1

Title: Ultraviolet light emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-004905 filed on Jan. 15, 2021. 
     TECHNICAL FIELD 
     The technical field of the present specification relates to an ultraviolet light emitting device including an ultraviolet light emitting element. 
     BACKGROUND ART 
     In a light emitting device which emits visible light, a semiconductor light emitting element mounted on a substrate is sealed with a resin. The sealing resin is, for example, a silicone resin or an epoxy resin. A refractive index of these resins is greater than a refractive index of the atmosphere. Therefore, reflection at an interface between the semiconductor light emitting element and the sealing resin is prevented. That is, light extraction efficiency is high. 
     In recent years, a light emitting device using an ultraviolet light emitting element has been researched and developed. Ultraviolet light degenerates the silicone resin and the epoxy resin. The resin cured or deteriorated by the ultraviolet light causes cracks. Therefore, an ultraviolet light emitting device which does not use a silicone resin or an epoxy resin has been developed. For example, JP-A-2007-311707 discloses a technique of using a fluororesin as a refractive index difference alleviating substance  20  directly above an ultraviolet light emitting element (paragraph [0025] in JP-A-2007-311707). Accordingly, the difference in refractive index between the ultraviolet light emitting element having a refractive index of about 1.7 and the atmosphere having a refractive index of 1 is alleviated. 
     Some ultraviolet light emitting devices cover a periphery of the ultraviolet light emitting element with a resin film. The resin film is flexible and deforms according to an outer shape of the ultraviolet light emitting element. In this case, a gap is generated between the ultraviolet light emitting element and the resin film There is air in this gap. Since the difference in refractive index between the ultraviolet light emitting element and air is large, a critical angle for total internal reflection is small. That is, the light emitted from the ultraviolet light emitting element is likely to cause total internal reflection at a boundary with air. 
     The light extraction efficiency of this ultraviolet light emitting device tends to be low. Therefore, even when the resin film is used, it is preferable to alleviate the difference in refractive index to improve the light extraction efficiency. 
     SUMMARY OF INVENTION 
     An object of the present specification is to provide an ultraviolet light emitting device covered with a resin film and having high light extraction efficiency. 
     An ultraviolet light emitting device according to a first aspect includes: a substrate; an ultraviolet light emitting element; a bonding layer; a fluororesin film; and a fluorocarbon compound. The substrate includes a mounting surface mounting the ultraviolet light emitting element. The ultraviolet light emitting element has a first surface having an electrode, a second surface opposite to the first surface, and a side surface. The bonding layer bonds the electrode on the first surface of the ultraviolet light emitting element and a part of the mounting surface of the substrate. The fluororesin film is a flexible material configured to transmit ultraviolet light. The substrate and the fluororesin film are disposed in a state where the ultraviolet light emitting element is sandwiched therebetween. The fluorocarbon compound is a liquid at normal temperature and pressure. The fluorocarbon compound fills a gap between the side surface of the ultraviolet light emitting element and the fluororesin film in a state of being in contact with the side surface and the fluororesin film. 
     In this ultraviolet light emitting device, the gap between the side surface of the ultraviolet light emitting element and the resin film is filled with the fluorocarbon compound. Therefore, the side surface of the ultraviolet light emitting element is not in contact with air. Therefore, there is no concern that the light emitted from the ultraviolet light emitting element is reflected at an interface between the ultraviolet light emitting element and air. Therefore, this ultraviolet light emitting device has high output. 
     In the present specification, it is possible to provide an ultraviolet light emitting device covered with a resin film and having high light extraction efficiency. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a light emitting device  100  according to a first embodiment. 
         FIG. 2  is a diagram (part  1 ) illustrating a method for producing the light emitting device  100  according to the first embodiment. 
         FIG. 3  is a diagram (part  2 ) illustrating the method for producing the light emitting device  100  according to the first embodiment. 
         FIG. 4  is a diagram (part  3 ) illustrating the method for producing the light emitting device  100  according to the first embodiment. 
         FIG. 5  is a schematic configuration diagram of a light emitting device  200  according to a modification of the first embodiment. 
         FIG. 6  is a schematic configuration diagram of a light emitting device  300  according to a modification of the first embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, specific embodiments will be described with reference to the drawings, taking an ultraviolet light emitting device as an example. However, the technique of the present specification is not limited to the embodiments. A structure different from that of the embodiments may be included. The thickness ratio of each layer in each figure is conceptually shown, and does not indicate the actual thickness ratio. 
     First Embodiment 
     1. Light Emitting Device 
       FIG. 1  is a schematic configuration diagram of a light emitting device  100  according to a first embodiment. As illustrated in  FIG. 1 , the light emitting device  100  includes a substrate  110 , an ultraviolet light emitting element  120 , a bonding layer  130 , a fluororesin film  140 , an adhesive layer  150 , a fluorocarbon compound  160 , and an air layer  170 . The light emitting device  100  is an ultraviolet light emitting device which emits ultraviolet light. 
     The substrate  110  is a substrate mounting an ultraviolet light emitting element  120 . The substrate  110  has a mounting surface  110   a . The mounting surface  110   a  is a surface mounting the ultraviolet light emitting element  120 . The substrate  110  includes a base material  111 , circuit patterns  112  and  113 , and a through hole  114 . The circuit pattern  112  is a pattern on a mounting surface  110   a  side in the substrate  110 . The circuit pattern  113  is a pattern on a side opposite to the mounting surface  110   a  side in the substrate  110 . The through hole  114  electrically connects the circuit pattern  112  and the circuit pattern  113 . The through hole  114  is filled with a metal. The mounting surface  110   a  is a surface of the circuit pattern  112 . 
     The ultraviolet light emitting element  120  is a semiconductor light emitting element which emits ultraviolet light. An emission wavelength of the ultraviolet light emitting element  120  is, for example, 200 nm or more and 320 nm or less. The ultraviolet light emitting element  120  is mounted on the substrate  110  via the bonding layer  130 . The ultraviolet light emitting element  120  has a first surface  120   a , a second surface  120   b , and a side surface  120   c . The first surface  120   a  has an electrode. The first surface  120   a  faces the mounting surface  110   a  of the substrate  110 . The second surface  120   b  is a surface opposite to the first surface  120   a . The second surface  120   b  is a light extraction surface which extracts light to the outside of the ultraviolet light emitting element  120 . The second surface  120   b  faces the fluororesin film  140 . The side surface  120   c  is a surface other than the first surface  120   a  and the second surface  120   b.    
     The bonding layer  130  is a layer mounting the ultraviolet light emitting element  120  on the substrate  110 . The bonding layer  130  bonds the electrode on the first surface  120   a  of the ultraviolet light emitting element  120  and the circuit pattern  112  of the mounting surface  110   a  of the substrate  110 . The material of the bonding layer  130  is, for example, an Au—Sn solder. 
     The fluororesin film  140  is a translucent fluororesin film for suitably extracting ultraviolet light emitted from the ultraviolet light emitting element  120  to the outside. The fluororesin film  140 , of course, transmits ultraviolet light. The fluororesin film  140  is a flexible material which can be bent. The fluororesin film  140  is adhered to the substrate  110  in a bent state. The fluororesin film  140  is, for example, FEP. The fluororesin film  140  has a refractive index higher than the refractive index of the atmosphere. The refractive index of the fluororesin film  140  is, for example, 1.2 or more and 1.6 or less. 
     The fluororesin film  140  has a ceiling surface  141 , a side wall surface  142 , and a flat surface  143  on a substrate  110  side. The ceiling surface  141  faces the second surface  120   b  of the ultraviolet light emitting element  120 . The side wall surface  142  faces the side surface  120   c  of the ultraviolet light emitting element  120 . The flat surface  143  is in contact with the adhesive layer  150 . The flat surface  143  is adhered to the substrate  110  via the adhesive layer  150 . 
     The adhesive layer  150  adheres the substrate  110  and the fluororesin film  140 . The substrate  110  and the fluororesin film  140  are disposed in a state where the ultraviolet light emitting element  120  is sandwiched therebetween. The adhesive layer  150  bonds the substrate  110  and the fluororesin film  140  in this state. The adhesive layer  150  adheres the mounting surface  110   a  of the substrate  110  and the fluororesin film  140 . The adhesive layer  150  is not present between the second surface  120   b  of the ultraviolet light emitting element  120  and the fluororesin film  140 . 
     The fluorocarbon compound  160  is located between the ultraviolet light emitting element  120  and the fluororesin film  140 . 
     The air layer  170  is a closed space located between the substrate  110  and the ultraviolet light emitting element  120 . The air layer  170  is filled with a gas. The gas is, for example, atmosphere. The air layer  170  is located between the mounting surface  110   a  of the substrate  110  and the first surface  120   a  of the ultraviolet light emitting element  120 . There is no air layer either between the second surface  120   b  of the ultraviolet light emitting element  120  and the fluororesin film  140  or between the side surface  120   c  of the ultraviolet light emitting element  120  and the fluororesin film  140 . 
     2. Fluorocarbon Compound 
     2-1. Region of Fluorocarbon Compound 
     The fluorocarbon compound  160  is a polymer having a CF bond. The fluorocarbon compound  160  is a liquid at normal temperature and pressure. The number of carbon atoms in the fluorocarbon compound  160  is 1.9 times or less the number of fluorine atoms in the fluorocarbon compound  160 . The fluorocarbon compound  160  is, for example, perfluoropolyether (PFPE). The fluorocarbon compound  160  may have a refractive index greater than that of the atmosphere, and equal to or less than that of the ultraviolet light emitting element  120 . The refractive index of the fluorocarbon compound  160  is, for example, 1.2 or more and 1.6 or less. 
     As illustrated in  FIG. 1 , the fluorocarbon compound  160  fills a gap either between the second surface  120   b  of the ultraviolet light emitting element  120  and the fluororesin film  140  or between the side surface  120   c  of the ultraviolet light emitting element  120  and the fluororesin film  140  in a state where the second surface  120   b  and the side surface  120   c  of the ultraviolet light emitting element  120  are in contact with the fluororesin film  140 . 
     The fluorocarbon compound  160  has an upper surface portion  161  and a side surface portion  162 . The upper surface portion  161  and the side surface portion  162  are connected to each other. The upper surface portion  161  faces the second surface  120   b  of the ultraviolet light emitting element  120 . The side surface portion  162  faces the side surface  120   c  of the ultraviolet light emitting element  120 . 
     The upper surface portion  161  is a region sandwiched between the second surface  120   b  of the ultraviolet light emitting element  120  and the ceiling surface  141  of the fluororesin film  140 . The upper surface portion  161  has a rectangular parallelepiped shape. Vertical and horizontal lengths of the rectangular parallelepiped shape are equal to vertical and horizontal lengths of the ultraviolet light emitting element  120 . 
     The side surface portion  162  is a region surrounded by the side surface  120   c  of the ultraviolet light emitting element  120 , the side wall surface  142  of the fluororesin film  140 , and the mounting surface  110   a  of the substrate  110 . The side surface portion  162  is in contact with the side surface  120   c  of the ultraviolet light emitting element  120 , the side wall surface  142  of the fluororesin film  140 , and the mounting surface  110   a  of the substrate  110 . The side surface portion  162  surrounds a periphery of the ultraviolet light emitting element  120 . The side surface portion  162  has an annular shape. 
     A thickness of the side surface portion  162  of the fluorocarbon compound  160  in contact with the side surface  120   c  of the ultraviolet light emitting element  120  decreases as a distance from the mounting surface  110   a  of the substrate  110  increases. 
     The ceiling surface  141  of the fluororesin film  140  faces the second surface  120   b  of the ultraviolet light emitting element  120  in a state where the upper surface portion  161  of the fluorocarbon compound  160  is sandwiched therebetween. The side wall surface  142  of the fluororesin film  140  faces the side surface  120   c  of the ultraviolet light emitting element  120  in a state where the side surface portion  162  of the fluorocarbon compound  160  is sandwiched therebetween. 
     The fluorocarbon compound  160  does not fill a gap between the mounting surface  110   a  of the substrate  110  and the first surface  120   a  of the ultraviolet light emitting element  120 . 
     2-2. Effect of Fluorocarbon Compound 
     The fluorocarbon compound  160  covers the second surface  120   b  and the side surface  120   c  of the ultraviolet light emitting element  120 . The refractive index of the fluorocarbon compound  160  is greater than the refractive index of the atmosphere and equal to or less than the refractive index of the ultraviolet light emitting element  120 . Therefore, the light to be emitted from the second surface  120   b  and the side surface  120   c  of the ultraviolet light emitting element  120  is less likely to be totally reflected at a boundary surface with the fluorocarbon compound  160 . That is, the light extraction efficiency on the second surface  120   b  and the side surface  120   c  of the ultraviolet light emitting element  120  is high. 
     3. Refractive Index 
     The ultraviolet light emitting element  120  has a refractive index of about 1.7. The fluorocarbon compound  160  has a refractive index of about 1.2 or more and 1.6 or less. The fluororesin film  140  has a refractive index of about 1.2 or more and 1.6 or less. The atmosphere has a refractive index of 1. The refractive index of the fluorocarbon compound  160  is preferably greater than the refractive index of the fluororesin film  140 . The ultraviolet light emitting element  120 , the fluorocarbon compound  160 , and the fluororesin film  140  have a higher refractive index in this order. In this case, total reflection is less likely to occur at the boundary between the materials. 
     In the first embodiment, the second surface  120   b  and the side surface  120   c  of the ultraviolet light emitting element  120  are not in contact with the air layer  170 . As described above, the refractive index of the ultraviolet light emitting element  120  is sufficiently greater than the refractive index of the air layer  170 . Since in the ultraviolet light emitting element  120 , the second surface  120   b  and the side surface  120   c  from which the light is extracted to the outside are not in contact with the air layer  170  having a lower refractive index, the light from the ultraviolet light emitting element  120  is likely to be emitted to the outside of the element. Therefore, the light extraction efficiency of the light emitting device  100  is high. 
     3. Production Method 
     3-1. Element Mounting Step 
     As illustrated in  FIG. 2 , the ultraviolet light emitting element  120  is mounted on the mounting surface  110   a  of the substrate  110 . A solder is placed on the mounting surface  110   a  of the substrate  110 . The ultraviolet light emitting element  120  is placed on the solder such that the electrode on the first surface  120   a  of the ultraviolet light emitting element  120  is in contact with the solder. Then, the ultraviolet light emitting element  120  is mounted on the substrate  110  by, for example, reflow. 
     3-2. Fluorocarbon Compound Supply Step 
     As illustrated in  FIG. 3 , the fluorocarbon compound  160  is supplied to the second surface  120   b  and the side surface  120   c  of the ultraviolet light emitting element  120 . At this stage, the fluorocarbon compound  160  is not in contact with the side surface  120   c  of the ultraviolet light emitting element  120 . 
     3-3. Adhering Step 
     As illustrated in  FIG. 4 , the adhesive layer  150  is coated onto the mounting surface  110   a  of the substrate  110 . Thereafter, the fluororesin film  140  is bent and adhered to the mounting surface  110   a  of the substrate  110 . Accordingly, the light emitting device  100  is produced. 
     4. Effect of First Embodiment 
     The fluorocarbon compound  160  covers the second surface  120   b  and the side surface  120   c  of the ultraviolet light emitting element  120 . Therefore, the light to be emitted to the outside from the second surface  120   b  and the side surface  120   c  of the ultraviolet light emitting element  120  is less likely to be totally reflected at the boundary surface with the fluorocarbon compound  160 . That is, the light extraction efficiency on the second surface  120   b  and the side surface  120   c  of the ultraviolet light emitting element  120  is high. 
     5. Modifications 
     5-1. Fluorocarbon Compound 
       FIG. 5  is a schematic configuration diagram of a light emitting device  200  according to a modification of the first embodiment. The light emitting device  200  includes the substrate  110 , the ultraviolet light emitting element  120 , the bonding layer  130 , a fluororesin film  240 , the adhesive layer  150 , a fluorocarbon compound  260 , and the air layer  170 . 
     The fluororesin film  240  has a ceiling surface  241 , an inclined surface  242 , and a flat surface  243  on the substrate  110  side. The ceiling surface  241  of the fluororesin film  240  is in contact with the second surface  120   b  of the ultraviolet light emitting element  120 , and is not in contact with the fluorocarbon compound  260 . That is, there is no gap between the ceiling surface  241  of the fluororesin film  240  and the second surface  120   b  of the ultraviolet light emitting element  120 , and the fluorocarbon compound  260  filling the gap is not present. 
     Even in this case, the light from the ultraviolet light emitting element  120  is suitably incident on the fluororesin film  240 . That is, the light is suitably extracted from the ultraviolet light emitting element  120 . 
     In order to produce the light emitting device  200 , a force for pressing the fluororesin film  140  against the ultraviolet light emitting element  120  may be increased. 
     5-2. Air Layer 
       FIG. 6  is a schematic configuration diagram of a light emitting device  300  according to a modification of the first embodiment. The light emitting device  300  includes the substrate  110 , the ultraviolet light emitting element  120 , the bonding layer  130 , the fluororesin film  140 , the adhesive layer  150 , and a fluorocarbon compound  360 . 
     The light emitting device  300  does not have an air layer between the mounting surface  110   a  of the substrate  110  and the first surface  120   a  of the ultraviolet light emitting element  120 . Instead, the fluorocarbon compound  360  fills the gap between the mounting surface  110   a  of the substrate  110  and the first surface  120   a  of the ultraviolet light emitting element  120 . 
     Even in this case, the light from the ultraviolet light emitting element  120  is transmitted through the fluorocarbon compound  360  and then suitably incident on the fluororesin film  140 . That is, the light is suitably extracted from the ultraviolet light emitting element  120 . 
     In order to produce the light emitting device  300 , the amount of the fluorocarbon compound  360  supplied to the second surface  120   b  of the ultraviolet light emitting element  120  may be increased. The fluorocarbon compound  360  may spill out from the second surface  120   b  of the ultraviolet light emitting element  120  and spread to some extent to the mounting surface  110   a  of the substrate  110 . Alternatively, the fluorocarbon compound  360  may be separately supplied to the periphery of the bonding layer  130  by underfill. 
     5-3. Filler 
     The fluorocarbon compound  160  may contain a filler which transmits ultraviolet light. The material of the filler is, for example, fluorine powder or silica. The filler may have a refractive index about the same as the refractive index of the fluorocarbon compound  160 . The refractive index of the filler is, for example, 1.2 or more and 1.6 or less. The filler has a particle diameter of, for example, 20 nm or more and 50 μm or less. An abundance ratio of the filler in the fluorocarbon compound  160  is, for example, 0.1 wt % or more and 50 wt % or less. 
     When the filler is a material which does not contain fluorine, such as silica, the filler may absorb ultraviolet light. In this case, the particle diameter of the filler may be smaller than a peak value of the emission wavelength of the ultraviolet light emitting element  120 . The filler has a particle diameter of, for example, 20 nm or more and 100 nm or less. 
     The filler is suitable for adjusting a static viscosity and a kinematic viscosity of the fluorocarbon compound  160 . That is, the kinematic viscosity is preferably low so as to facilitate dropping. It is preferable to use a value of the static viscosity such that the side surface portion  162  maintains a suitable shape after the fluorocarbon compound  160  drips on the side surface  120   c  of the ultraviolet light emitting element  120 . 
     5-4. Ceiling Surface 
     The ceiling surface  141  is a plane parallel to the mounting surface  110   a  of the substrate  110 . However, the ceiling surface  141  may not be parallel to the mounting surface  110   a  of the substrate  110 . The ceiling surface  141  may be a curved surface. 
     5-5. Adhesive Surface 
     The fluororesin film  140  may have an adhesive surface coated with an adhesive on the substrate  110  side. In this case, the adhesive on the adhesive surface is disposed between fluororesin film  140  and fluorocarbon compound  160 . The area where the adhesive on the adhesive surface comes into contact with the fluorocarbon compound  160  is large. 
     Therefore, as illustrated in  FIG. 1 , it is preferable that the adhesive is present only on the mounting surface  110   a  of the substrate  110 . 
     5-6. Combination 
     The above modifications may be freely combined. 
     APPENDIX 
     An ultraviolet light emitting device according to a first aspect includes: a substrate; an ultraviolet light emitting element; a bonding layer; a fluororesin film; and a fluorocarbon compound. The substrate includes a mounting surface mounting the ultraviolet light emitting element. The ultraviolet light emitting element has a first surface having an electrode, a second surface opposite to the first surface, and a side surface. The bonding layer bonds the electrode on the first surface of the ultraviolet light emitting element and a part of the mounting surface of the substrate. The fluororesin film is a flexible material configured to transmit ultraviolet light. The substrate and the fluororesin film are disposed in a state where the ultraviolet light emitting element is sandwiched therebetween. The fluorocarbon compound is a liquid at normal temperature and pressure. The fluorocarbon compound fills a gap between the side surface of the ultraviolet light emitting element and the fluororesin film in a state of being in contact with the side surface and the fluororesin film. 
     In the ultraviolet light emitting device according to a second aspect, the fluorocarbon compound includes a side surface portion facing the side surface of the ultraviolet light emitting element. The fluororesin film includes a side wall surface on a substrate side. The side wall surface of the fluororesin film faces the side surface of the ultraviolet light emitting element in a state where the side surface portion of the fluorocarbon compound is sandwiched therebetween. 
     In the ultraviolet light emitting device according to a third aspect, a thickness of the side surface portion of the fluorocarbon compound is smaller as a distance from the mounting surface of the substrate increases. 
     In the ultraviolet light emitting device according to a fourth aspect, the fluorocarbon compound includes an upper surface portion facing the second surface of the ultraviolet light emitting element. The fluororesin film includes a ceiling surface on the substrate side. The ceiling surface of the fluororesin film faces the second surface of the ultraviolet light emitting element in a state where the upper surface portion of the fluorocarbon compound is sandwiched therebetween. 
     In the ultraviolet light emitting device according to a fifth aspect, the fluororesin film includes a ceiling surface on the substrate side. The ceiling surface of the fluororesin film is in contact with the second surface of the ultraviolet light emitting element. 
     In the ultraviolet light emitting device according to a sixth aspect, the fluorocarbon compound fills a gap between the mounting surface of the substrate and the first surface of the ultraviolet light emitting element. 
     In the ultraviolet light emitting device according to a seventh aspect, the fluorocarbon compound does not fill a gap between the mounting surface of the substrate and the first surface of the ultraviolet light emitting element. 
     In the ultraviolet light emitting device according to an eighth aspect, the fluorocarbon compound contains a filler configured to transmit ultraviolet light. The filler has a refractive index of 1.2 or more and 1.6 or less. 
     The ultraviolet light emitting device according to a ninth aspect further includes an adhesive layer. The adhesive layer adheres the mounting surface of the substrate and the fluororesin film, and is not present between the second surface of the ultraviolet light emitting element and the fluororesin film.