Deep ultraviolet LED packaging structure and preparation method thereof

Abstract

The invention provides a deep ultraviolet LED packaging structure and a preparation method thereof, and the packaging structure comprises a three-dimensional ceramic substrate which is provided with a groove, and the groove is provided with a bottom, an inner side wall and an upper surface; the deep ultraviolet LED chip is mounted at the bottom of the groove of the three-dimensional ceramic substrate; the fluororesin is filled in the groove of the three-dimensional ceramic substrate and covers the upper surface and the periphery of the side wall of the deep ultraviolet LED chip, and the fluororesin is carboxylated fluororesin; and the optical lens is mounted on the deep ultraviolet LED chip and the fluororesin, and the edge of the optical lens is fixed on the upper surface or the side wall of the three-dimensional ceramic substrate. The fluororesin and the optical lens are used for assisting in achieving extraction and convergence of photons, the application effect of the device in the fields of ultraviolet inactivation and the like is improved, the reliability of the packaging structure is improved through the adhesion of the fluororesin, the light emitting efficiency is improved, and the cost is reduced at the same time.

Description

Technical Field

[0001] The present invention relates to a deep ultraviolet LED packaging structure and a preparation method thereof, and in particular to a packaging structure and a preparation method thereof for improving the light extraction efficiency of a deep ultraviolet light emitting diode. Background Art

[0002] Nitride deep ultraviolet LED is a solid-state ultraviolet light source based on the principle of semiconductor luminescence. It has the advantages of being green and mercury-free, long life, small size, and easy integration. As a deep ultraviolet solid-state light source that works in an ideal electro-optical conversion mode, deep ultraviolet LED has broad application prospects in replacing traditional mercury lamps and in the fields of ultraviolet inactivation, polymer curing, biochemical detection, non-line-of-sight communication, and special lighting. Unfortunately, the electro-optical conversion efficiency of current nitride deep ultraviolet LEDs is still relatively low, and there are still bottlenecks in application such as low optical power density and high heat generation. Among the reasons that limit the current low light efficiency of deep ultraviolet LEDs, low light extraction efficiency is currently the main factor, which is due to the lateral TM mode-dominated luminescence caused by the inversion of the valence band splitting of the high Al component AlGaN material, and the small total reflection critical angle when light propagates from high refractive index nitride or sapphire to free space. The light polarization modes in deep ultraviolet LED devices include TM mode and TE mode. As the wavelength becomes shorter, especially when the wavelength is shorter than 250nm, the increase in the Al component of the quantum well leads to an increase in the proportion of TM mode emission, that is, the light emitted laterally along the quantum well accounts for a larger proportion, which makes it more difficult for deep ultraviolet light to be emitted from the front of the device.

[0003] Due to the above reasons, the deep ultraviolet LED chip needs to consider the collection of lateral light as much as possible in the packaging structure, so as to greatly improve the light extraction efficiency of the device. However, the current conventional LED packaging technology is mostly to match the refractive index of the part that can emit light from the chip surface or to cooperate with the lens structure to improve the emission of its front photons, which cannot solve the problem of collecting the lateral part of the short-wave deep ultraviolet LED light.

[0004] In addition, in the selection of packaging materials, the resin used in traditional LED packaging has strong absorption of short-wave deep ultraviolet LEDs and cannot meet the extraction requirements of deep ultraviolet light; optical lenses with high transmittance to deep ultraviolet light usually cannot directly form ideal dielectric contact with the chip surface, which causes the lens to be unable to match the medium refractive index of the chip's light-emitting surface, thereby increasing the loss of internal total reflection light.

[0005] In addition, as a UV transparent material, fluororesin has good UV tolerance and high temperature tolerance, and can be used as a filling material in the packaging structure of deep UV LED chips to achieve refractive index matching and enhance light extraction, thus playing an important role in deep UV LED packaging. Summary of the invention

[0006] The purpose of the present invention is to solve the problem of low light extraction efficiency of deep ultraviolet nitride LED chips, provide a specific packaging structure to assist in the extraction and convergence of photons, improve the application effect of the device in the field of ultraviolet inactivation, and improve the reliability of the packaging structure.

[0007] The present invention provides the following deep ultraviolet LED packaging structure, comprising: a three-dimensional ceramic substrate, having a groove, wherein the groove has a bottom, an inner side wall and an upper surface; a deep ultraviolet LED chip, mounted on the bottom of the groove of the three-dimensional ceramic substrate; a fluororesin, filled in the groove of the three-dimensional ceramic substrate and covering the upper surface and side wall of the deep ultraviolet LED chip, wherein the fluororesin is a carboxylated fluororesin; the fluororesin located between the deep ultraviolet LED chip and the optical lens has an interface layer thickness, wherein the interface layer thickness is 0.5 to 10 microns; and the optical lens is mounted on the deep ultraviolet LED chip and the fluororesin, and the edge is fixed on the upper surface or the side wall of the three-dimensional ceramic substrate.

[0008] Preferably, the inner side wall of the groove is inclined relative to the bottom of the groove, and the inclination angle is greater than 90°, and the transverse cross-section of the groove is circular or square.

[0009] Preferably, the inner side wall of the groove is inclined at an angle of 120-140° relative to the bottom of the groove.

[0010] Preferably, the inner wall surface of the groove is plated with a metal reflective layer, the metal reflective layer contains one element among aluminum, rhodium and nickel or a metal alloy, and the surface roughness (RMS) of the metal reflective layer is less than 20nm.

[0011] Preferably, the general structural formula of the fluororesin is as follows:

[0012] ,

[0013] The terminal functional group R is -COOH, and the value of n ranges from 100,000 to 500,000; the refractive index of the fluororesin for 250nm ultraviolet light is 1.3 to 1.6.

[0014] Preferably, the deep ultraviolet LED chip is a flip-chip nitride deep ultraviolet LED chip; the fluororesin located between the LED chip and the optical lens has an interface layer thickness, and the interface layer thickness ranges from 0.5 to 10 microns.

[0015] Preferably, at least one of the upper surface of the deep ultraviolet LED chip and the bottom surface of the optical lens is surface modified with a silane coupling agent.

[0016] Preferably, the bottom surface, outer surface and vertex of the optical lens are such that the bottom surface is a plane and the outer surface is a parabolic convex surface; the outer contour of any longitudinal section of the optical lens passing through the vertex conforms to a parabolic curve, and the parabolic curve satisfies y=k*r 2 , the quadratic coefficient k is between 0.4 and 1.2, and r does not exceed half of the side length of the three-dimensional ceramic substrate.

[0017] Preferably, a step is provided on the inner side wall of the groove for supporting the edge of the optical lens.

[0018] The present invention also provides a method for preparing a deep ultraviolet LED packaging structure, and the preparation process is as follows:

[0019] S1. Preparing a three-dimensional ceramic substrate having a groove, the groove having a bottom and an inclined inner side wall;

[0020] S2. depositing a metal reflective layer on the inner sidewall of the three-dimensional ceramic substrate;

[0021] S3. Soldering a deep ultraviolet LED chip on the three-dimensional ceramic substrate;

[0022] S4. Treating the light-emitting surface of the deep ultraviolet LED chip and the bottom surface of the optical lens with a silane coupling agent solvent, and after drying, filling the fluororesin into the three-dimensional ceramic substrate and curing it;

[0023] S5. Heat and soften the fluororesin, and bond the optical lens to the side wall or upper surface of the ceramic substrate with the softened fluororesin under a certain pressure.

[0024] The beneficial effects of the technical solution provided by the embodiment of the present application are:

[0025] 1) Fluororesin has high UV transparency, good UV tolerance and high temperature tolerance, and can be used as a filling material in the packaging structure of deep UV LED chips to achieve refractive index matching and improved light extraction. However, it has weak adhesion to UV chips and optical lenses. If there is no other adhesive material, it is easy for the optical lens to fall off. Therefore, the inventors proposed carboxylating the fluororesin to improve the adhesion of the fluororesin to the UV chips and optical lenses.

[0026] 2) At the same time, the fluororesin forms a thinner optical interface layer between the optical lens and the LED chip. The thinner optical interface layer can significantly increase the total reflection angle of the light on the one hand, and shorten the light path between the LED chip and the optical lens on the other hand, thereby increasing the probability of the light emitted by the LED chip passing through the optical interface layer, thereby improving the light extraction efficiency, and also reducing the usage between the LED chip and the optical lens, thereby reducing the cost of the LED packaging structure.

[0027] 3) The inner wall of the groove of the three-dimensional ceramic substrate is inclined, and the inclination angle between the bottom of the groove and the side wall is preferably 120-140°; in addition, the inner wall surface of the groove is plated with a metal reflective layer, and the roughness (RMS) of the surface of the thin film layer is less than 20nm. Therefore, when the light emitted by the light-emitting layer of the deep ultraviolet LED chip is emitted in the horizontal direction and encounters a side wall with a certain inclination angle during the propagation process, reflection occurs, and the photon propagation path is changed. The light emitted in the horizontal direction can be smoothly refracted / reflected to the light emission direction of the front side of the chip, thereby improving the overall light output efficiency of the chip and suppressing the absorption of photons in the lateral propagation mode of the LED due to traditional packaging structure and packaging materials.

[0028] 4) The outer surface of the light-emitting side of the optical lens is a parabolic convex surface, which can adjust the optical path of the light collected by the bottom surface relative to the traditional one, thereby achieving the purpose of collimating the LED output light. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to make the content of the present invention more clearly understood, the following further describes the purpose and advantages of the present invention according to the specific embodiments of the present invention and in conjunction with the accompanying drawings:

[0030] Figure 1 Schematic diagram of the deep ultraviolet LED packaging structure of the first embodiment of the present invention.

[0031] Figure 2 AE is a schematic diagram of the structure corresponding to each step S1-S5 described in the preparation method of Example 2 of the present invention.

[0032] Figure 3 This is a schematic diagram of the structure at the interface of the bottom surface of the optical lens, the spacing air layer, and the deep ultraviolet LED chip when a traditional optical lens is encapsulated on the top of the deep ultraviolet LED chip.

[0033] Figure 4 This is a schematic structural diagram of the interface between the bottom surface of the optical lens, the fluororesin and the upper surface of the deep ultraviolet LED chip when the optical lens is encapsulated on the upper part of the deep ultraviolet LED chip in Example 1 of the present invention.

[0034] Figure 5 This is a schematic diagram of a packaging structure in which the outer surface of an optical lens according to an embodiment of the present invention is a parabolic convex surface.

[0035] Figure 6 In order to use optical simulation to simulate the emission of light from the inside of the deep ultraviolet LED chip when a traditional optical lens is packaged on the top of the deep ultraviolet LED chip, a TE mode point light source is used to simulate the emission of photons when they pass through the deep ultraviolet LED chip epitaxial structure, sapphire substrate and air layer in sequence.

[0036] Figure 7In order to use optical simulation to simulate the emission of light from the inside of the deep ultraviolet LED chip in the packaging structure of the first embodiment of the present invention, a TE mode point light source is used to simulate the emission of photons when passing through the LED epitaxial structure, sapphire substrate, fluororesin layer and quartz layer in sequence.

[0037] Figure 8 AC is a packaging structure according to the first embodiment of the present invention, the inner wall angle of the groove covered by the reflective layer is 130°, a deep ultraviolet LED chip with a wavelength of 250 nanometers, and a far-field radiation angle distribution test diagram tested under three different lens conditions.

[0038] Explanation of the reference numerals: 1 substrate; 2 inner wall; 3 deep ultraviolet LED chip; 3-1 light emitting surface of the chip; 4, 4-2 fluororesin; 5 optical lens; 6 outer surface of the optical lens; 7 bottom surface of the optical lens. DETAILED DESCRIPTION

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0040] The embodiment of the present application provides a deep ultraviolet LED packaging structure, including: a three-dimensional ceramic substrate, having a groove, wherein the groove has a bottom, an inner wall and an upper surface; a deep ultraviolet LED chip, mounted on the bottom of the groove of the three-dimensional ceramic substrate; a fluororesin, filled in the groove of the three-dimensional ceramic substrate, and covering the upper surface and side walls of the deep ultraviolet LED chip, wherein the fluororesin is a carboxylated fluororesin; an optical lens, mounted on the deep ultraviolet LED chip and the fluororesin, and the edge is fixed on the upper surface or side wall of the three-dimensional ceramic substrate.

[0041] The three-dimensional ceramic substrate is the main bearing structure of the package. The deep ultraviolet LED chip can be welded on the three-dimensional ceramic substrate through a solid crystal process to form a reliable connection. The three-dimensional ceramic substrate has a groove to form a dam structure, and the groove has a bottom, an inner side wall and an upper surface. The inner side wall of the groove is inclined relative to the bottom of the groove, and the inclination angle is greater than 90°, so that the bottom opening of the groove is small and the upper opening of the groove is large. According to the processing technology of the dam structure, the groove is circular or square along the transverse section, and the depth of the groove is higher than the height of the deep ultraviolet chip.

[0042] Preferably, the inner side wall of the groove is inclined at an angle of 120-140° relative to the bottom of the groove.

[0043] The metal reflective layer is plated on the inner wall surface of the groove. When the light emitted by the light-emitting layer of the deep ultraviolet LED chip is emitted in the horizontal direction and encounters the inner wall of the groove with a certain inclination angle during the propagation process, it is reflected by the metal reflective layer, and the photon propagation path is changed. The specific angle can smoothly refract / reflect the light emitted in the horizontal direction to the light emitting direction of the chip front side, thereby improving the overall light output efficiency of the chip and suppressing the absorption of photons in the LED lateral propagation mode due to traditional packaging structure and packaging materials.

[0044] The metal reflective layer includes one of aluminum, rhodium, and nickel or a metal alloy, and the surface roughness (RMS) of the metal reflective layer is less than 20 nm, and the surface roughness is low to form a smooth reflective surface, which can improve the optical reflectivity. The metal reflective layer is, for example, an aluminum metal layer or a rhodium metal layer.

[0045] Fluororesin is filled in the groove of the three-dimensional ceramic substrate and covers the upper surface and sidewalls of the deep ultraviolet LED chip. The fluororesin tightly fills the gap between the surface of the deep ultraviolet LED chip and the optical lens, and forms a tight fit with the light-emitting surface of the deep ultraviolet LED chip and the bottom surface of the optical lens. Fluororesin has a refractive index value of 1..3 to 1.6 (for 250nm ultraviolet light), which is higher than the refractive index of air. It can increase the total reflection angle of light emitted from the inside of the chip, inhibit the total internal reflection loss caused by the sudden change of refractive index on the light-emitting path, so that the light emitted by the LED avoids encountering a low refractive index air or vacuum layer to produce a large total internal reflection loss when passing through the high refractive index sapphire substrate or AlGaN material interface, that is, by matching the refractive index of the medium on the light-emitting path, the light-emitting efficiency of the deep ultraviolet LED is improved.

[0046] The fluororesin filler is mainly a resin composed of fluorine-carbon atoms, which has good ultraviolet transmittance, ultraviolet tolerance and high temperature tolerance. The general structural formula of the fluororesin is as follows:

[0047] ,

[0048] The terminal functional group R is -COOH. The terminal functional group R of the fluororesin can make the fluororesin have adhesion, which is used to help improve the adhesion between the fluororesin and the chip surface and the bottom surface of the optical lens, thereby avoiding the optical lens from falling off and improving the reliability of the packaging structure.

[0049] Furthermore, since the fluororesin increases adhesion, the amount used between the deep ultraviolet LED chip and the optical lens can be reduced, thereby reducing the physical thickness of the fluororesin between the deep ultraviolet LED chip and the optical lens, forming a thinner optical interface layer. The thinner optical interface layer can significantly increase the total reflection angle of the light on the one hand, and shorten the optical path of the light between the deep ultraviolet LED chip and the optical lens on the other hand, thereby increasing the probability of the light emitted by the deep ultraviolet LED chip passing through the optical interface layer, thereby improving the light extraction efficiency.

[0050] At the same time, since the fluororesin increases the adhesion, the usage between the deep ultraviolet LED chip and the optical lens can be reduced, and the cost of the LED packaging structure can also be reduced.

[0051] The fluororesin can be directly filled into the groove of the dam-type three-dimensional ceramic substrate through one of the deposition processes such as dispensing, spraying, continuous dipping, spin coating or physical evaporation, and completely wrap the upper surface and side wall of the welded and fixed deep ultraviolet LED chip.

[0052] Preferably, the fluororesin forms a thinner optical interface layer between the optical lens and the LED chip. The thinner optical interface layer can significantly increase the total reflection angle of the light on the one hand, and shorten the light path between the LED chip and the optical lens on the other hand, thereby increasing the probability of the light emitted by the LED chip passing through the optical interface layer, thereby improving the light extraction efficiency, and at the same time, the amount of the LED chip and the optical lens can be reduced, thereby reducing the cost of the LED packaging structure. The improvement of the adhesion of the fluororesin can also effectively promote the optical lens to be stably fixed on the fluororesin.

[0053] Preferably, the thickness of the fluororesin forming a thinner optical interface layer between the optical lens and the LED chip is between 0.5 and 10 microns. Since the surface of the sapphire substrate is not absolutely smooth and has a certain degree of roughness, with a maximum roughness of 0.5 microns as the limit, the thickness of the fluororesin must at least exceed the maximum roughness of the sapphire substrate surface of the deep ultraviolet chip, so that the fluororesin can cover the deep ultraviolet LED chip and prevent water vapor erosion. In addition, the present invention proposes that the optical lens can be installed and adhered to the fluororesin by hot pressing, thereby achieving a thinner thickness of the fluororesin between the LED chip and the optical lens, not exceeding 10 microns.

[0054] More preferably, the thickness of the optical interface layer is at least 1 micron, so that the fluororesin can have a good sealing effect on the deep ultraviolet LED chip, and prevent water vapor from entering the deep ultraviolet LED chip through gaps caused by uneven distribution of the fluororesin interface layer due to being too thin, causing the LED chip to become damp and fail.

[0055] The deep ultraviolet LED chip is usually a flip-chip nitride deep ultraviolet LED chip, which emits light in the deep ultraviolet band (200-280nm). The flip-chip nitride deep ultraviolet LED chip specifically includes a sapphire substrate, a semiconductor light-emitting stack made of aluminum indium gallium nitride elements supported by the sapphire substrate, and an N-electrode and a P-electrode pad. During installation, the N-electrode and the P-electrode pad can be welded to the bottom of the groove of the ceramic substrate through a die bonding process to form a reliable connection.

[0056] When the inverted nitride deep ultraviolet LED chip is mounted at the bottom of the groove of the ceramic substrate, the sapphire substrate provides the light-emitting surface of the deep ultraviolet LED chip, the fluororesin covers the light-emitting surface of the sapphire substrate, and the fluororesin serves as an interface layer between the deep ultraviolet LED chip and the optical lens, allowing light emitted from the deep ultraviolet LED chip to pass through the fluororesin and reach the interior of the optical lens, and then radiate out through the outer surface of the optical lens.

[0057] The optical lens can be made of transparent quartz material, and the optical lens has a bottom surface and an outer surface, wherein the bottom surface is a plane and the outer surface is an arc-shaped surface. The bottom surface of the optical lens is directly opposite to the deep ultraviolet LED chip, and when the light emitted by the deep ultraviolet LED chip passes through the fluororesin, it can enter the optical lens through the bottom surface, and then radiate out through the outer surface of the optical lens; at the same time, the light emitted by the deep ultraviolet LED chip and reflected by the inner wall of the groove can also be converged and emitted through the optical lens, thereby improving the proportion of forward light emission and meeting the needs of various application scenarios of deep ultraviolet LEDs, such as sterilization.

[0058] Preferably, the optical lens can be a traditional spherical optical lens. To achieve higher photon efficiency extraction, the optical lens can also be a conical optical lens, that is, the outer contour of any longitudinal section of the optical lens passing through the vertex conforms to a parabola. The outer surface of the parabola design can adjust the optical path of the light from all directions collected by the bottom surface and converge in the forward direction, thereby achieving the purpose of collimating the LED output light. More preferably, the parabola of the longitudinal section satisfies y=k*r 2 The quadratic coefficient k is between 0.4 and 1.2. A too low k value causes the optical lens to be close to a plane mirror, resulting in a poor optical convergence effect. A too high k value causes the optical path in the optical lens to be too long, resulting in light loss. r does not exceed half of the side length of the three-dimensional ceramic substrate.

[0059] Preferably, at least one of the upper surface of the deep ultraviolet LED chip and the bottom surface of the optical lens is modified with a silane coupling agent, which can change the polarity of the upper surface of the deep ultraviolet LED chip and the bottom surface of the optical lens, and further enhance the adhesion effect between the fluororesin and the optical lens and the deep ultraviolet LED chip. The silane coupling agent can have a very thin thickness, such as a single molecular layer or multiple molecular layers, such as between 0.1 and 10 nm, such as 1 nm, 2 nm, 3 nm, 5 nm, 7 nm or 10 nm.

[0060] Preferably, a step into which the optical lens can be embedded is reserved on the inner wall of the groove for installing the optical lens structure, and the step is conducive to the fluororesin covering the outer edge wall of the optical lens after the hot pressing step, so as to facilitate fixation.

[0061] The present invention also provides a method for preparing a deep ultraviolet LED packaging structure, and the preparation process is as follows:

[0062] S1. Preparing a three-dimensional ceramic substrate having a groove, the groove having a bottom and an inclined inner side wall;

[0063] S2. depositing a metal reflective layer on the inner sidewall of the three-dimensional ceramic substrate;

[0064] S3. Soldering a deep ultraviolet LED chip on the three-dimensional ceramic substrate;

[0065] S4. Treating the light-emitting surface of the deep ultraviolet LED chip and the bottom surface of the optical lens with a silane coupling agent solvent, and after drying, filling the fluororesin into the three-dimensional ceramic substrate and curing it;

[0066] S5. Heat and soften the fluororesin, and bond the optical lens to the side wall or upper surface of the ceramic substrate with the softened fluororesin under a certain pressure.

[0067] In step S1, the three-dimensional ceramic substrate is prepared, and the inclination angle of the inner wall of the dam is determined as needed. In order to achieve the best chip light output and far-field focusing effect, the inclination angle of the three-dimensional ceramic substrate in the LED irradiation direction is preferably 120-140 degrees.

[0068] In step S2, a metal reflective layer with a smooth surface is deposited on the inner wall of the groove of the ceramic substrate or prepared by precision machining. The metal material includes but is not limited to metal film layers or metal alloy film layers such as aluminum, rhodium, and nickel. The roughness (RMS) of the film layer surface is less than 20nm to reduce the disordered light scattering loss caused by the surface roughness.

[0069] In a preferred embodiment, the metal film in step S2 is deposited by physical evaporation, and the deposited film thickness is 100 to 1000 nm. A low-cost aluminum metal film is preferred, which can achieve a reflectivity of more than 85% in the deep ultraviolet band. The subsequent filling of fluororesin can effectively protect the aluminum metal film from oxidation or corrosion.

[0070] In step S3, the deep ultraviolet LED chip may be soldered on the ceramic substrate by a solder paste soldering process.

[0071] In step S4, the fluororesin is filled in the dam and solidified by using one of the deposition processes such as dispensing, spraying, continuous dipping, spin coating or physical evaporation, wherein the dispensing process is preferably used to drop the fluororesin solution in the dam, and the temperature is slowly increased from low temperature to high temperature in a vacuum drying oven, the heating rate is about 10 degrees / hour, and the maximum temperature does not exceed 250 degrees. The solid content of the fluororesin solution is 1% to 20%.

[0072] In step S5, the ceramic substrate is heated to soften the fluororesin, and the optical lens is bonded to the surface of the ceramic substrate by the softened fluororesin under a certain pressure, and the step on the inner wall of the reserved groove is used to place the optical lens. The pressure of a single chip is not less than 0.2N, and the heating process is preferably carried out in a vacuum oven, and the heating temperature must exceed the glass transition temperature of the selected fluororesin, and the typical temperature range is 120 to 270°C.

[0073] The optical lens is bonded to the surface of the ceramic substrate by fluororesin through a heating and pressurizing process. The introduced pressure can make the light-emitting surface of the chip tightly bonded with the bottom surface of the optical lens, and avoid bubbles and other situations that may affect the propagation of light.

[0074] The packaging structure of the present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. The accompanying drawings of the present invention are only for illustration to make it easier to understand the present invention.

[0075] Embodiment 1

[0076] Please refer to Figure 1 , Figure 1A deep ultraviolet LED packaging structure provided by an embodiment of the present application includes a three-dimensional ceramic substrate 1 with a groove, which is in a square shape, such as a common 3535 ceramic substrate, and the inner side wall of the groove contains a metal reflective layer 2; the inclination angle between the inner side wall of the groove and the bottom of the groove is defined as θ, and the deep ultraviolet LED chip 3 has a chip light-emitting surface 3-1; the metal material of the metal reflective layer 2 is aluminum, and the roughness (RMS) of the surface of the film layer is about 10nm; the ultraviolet LED chip is welded to the center of the bottom of the groove of the ceramic substrate. Fluororesin 4 is filled in the three-dimensional ceramic substrate 1 including the groove, and the optical lens 5 is installed on the fluororesin 4 and the deep ultraviolet LED chip 3, and the edge is installed on the step on the inner side wall of the three-dimensional ceramic substrate 1. Due to the presence of the metal reflective layer, part of the light propagated laterally by the deep ultraviolet LED chip can be refracted to the light-emitting direction of the front of the LED through the reflective surface in the packaging dam.

[0077] The deep ultraviolet LED chip 3 is a nitride flip-chip light-emitting LED chip.

[0078] The general structural formula of the fluororesin is as follows:

[0079] ,

[0080] The terminal functional group R is -COOH, the n value is about 200,000, and the refractive index value is close to 1.4. The fluororesin 4 is bonded between the bottom surface of the optical lens 5 and the upper surface of the deep ultraviolet LED chip 3 for emitting light.

[0081] Embodiment 2

[0082] A method for manufacturing a deep ultraviolet LED packaging structure according to embodiment 1 is provided, such as Figure 2 As shown in AE, the production steps are as follows:

[0083] S1. Prepare a three-dimensional ceramic substrate 1 with a groove, and determine the inclination angle of the inner wall of the groove as needed. In order to achieve the best chip light output and far-field focusing effect, the inclination angle of the three-dimensional ceramic substrate in the LED irradiation direction is preferably 120-140°.

[0084] S2. A metal reflective layer 2 with a smooth surface is deposited on the inner side wall of the groove of the three-dimensional ceramic substrate 1 or prepared by precision machining. The metal material is aluminum, and the roughness (RMS) of the surface of the thin film layer is about 10 nm.

[0085] S3. Soldering a deep ultraviolet LED chip 3 on the three-dimensional ceramic substrate 1, the ultraviolet LED chip 3 has a light emission wavelength of 200 to 280 nm.

[0086] S4. Use the dispensing deposition process to fill the dam with fluororesin 4 and solidify it, slowly increase the temperature from low temperature to high temperature in a vacuum drying oven, with a heating rate of about 10°C / hour, maintain it at 250 degrees for 2 hours, and then cool it to room temperature. The solid content of the fluororesin solution (the solvent is perfluoroalkane) used is 10% (mass content).

[0087] S5. Soften the fluororesin 4 on the three-dimensional ceramic substrate 1 under heating, select a parabolic optical lens, and bond the optical lens 5 to the surface of the ceramic substrate by the softened fluororesin 4 under a certain pressure, and use the reserved step of the optical lens 5 for positioning and installation. The heating is carried out in a vacuum oven at a temperature of 250°C and a pressure of 0.3N for a single chip.

[0088] After hot pressing, a thin optical interface layer can be formed between the fluororesin 4 and the optical lens 5. The thin optical interface layer can significantly increase the total reflection angle of the light, thereby increasing the probability of the light emitted by the LED chip passing through the optical interface layer, thereby improving the light extraction efficiency and reducing the cost of the LED packaging structure. After hot pressing, the thickness of the fluororesin at the interface of the interface layer is about 5 microns.

[0089] like Figure 3 As shown, the outer surface of the light-emitting side of the optical lens 5 is a parabolic convex surface, which can adjust the optical path of the light collected by the bottom surface, thereby achieving the purpose of collimating the LED output light.

[0090] like Figure 4 As shown, it is a traditional packaging structure, the optical lens is directly packaged on the upper part of the deep ultraviolet LED chip, and fluororesin is not used. The structure of the three layers at the interface of the optical lens bottom surface 7, the spacer air layer 4-1, and the deep ultraviolet LED chip upper surface 3-1 is schematically shown. Among them, n1, na, and n2 are the refractive indices of the LED light-emitting side material (such as LED sapphire substrate), air or vacuum, and quartz, respectively, and usually n1>n2>na. When the light emitted by the deep ultraviolet LED chip propagates to the emission surface, it encounters an air layer with a lower refractive index (na). Due to the large refractive index difference (n1>na), the light is emitted by the inner surface of the LED light-emitting side and is totally reflected, and the critical angle of total reflection (C1) is small, which seriously limits the effective emission and extraction of photons.

[0091] like Figure 5As shown, the packaging structure of the present invention uses fluororesin 4 to bond the quartz lens 5 and the upper surface of the deep ultraviolet LED chip, and forms an extremely thin interface layer after hot pressing. Since the refractive index (nr) of the fluororesin is greater than the refractive index of air (na) and close to the refractive index (n2) of quartz, this makes an extremely thin interface layer, and when the thickness of the fluororesin reaches a thickness of several microns, the fluororesin has an equivalent refractive index ni, ni is between n2 and n1, n1>ni>n2. The interface layer acts as a transition medium layer and can significantly increase the critical angle C2 of total internal reflection when the light is emitted from the LED light-emitting surface, thereby reducing the light loss caused by total internal reflection and improving the light-emitting efficiency of the deep ultraviolet LED.

[0092] like Figure 6 As shown in the figure, the traditional packaging structure is installed with a 250nm deep ultraviolet LED chip, and the light is emitted from the inside of the LED when there is no fluorine resin bonding to form an interface layer. It can be seen from the figure that when the photons pass through the LED epitaxial structure, sapphire substrate and air layer in turn, due to the existence of the air layer, the critical angle of total reflection is only 33°, which greatly limits the effective emission of photons. The calculated light extraction efficiency is only 4.0%.

[0093] like Figure 7 As shown, the packaging structure of the present invention is installed with a 250nm deep ultraviolet LED chip. After the fluororesin interface layer of the present invention is used, when photons pass through the LED epitaxial structure, sapphire substrate, fluororesin interface layer and quartz layer in sequence, due to the existence of interface matching refractive index, the total reflection critical angle of the LED light-emitting layer surface increases to 50°, which greatly improves the effective emission of photons, and the calculated light extraction efficiency is 9.2%. Compared with the traditional case without an interface layer, the light extraction efficiency is more than doubled.

[0094] like Figure 8 As shown, the far-field radiation angle distribution of a deep ultraviolet LED package device with a wavelength of 250nm using two typical optical lenses is shown, and compared with the luminescence without a lens and with a fluororesin filler. It can be seen from the figure that when the inclination angle of the inner wall reflector of the fixed groove is 130°, the far-field radiation intensity of the LED is significantly improved after the introduction of the optical lens, and the convergence effect is best when the optical lens is the outer surface of the parabola, and the quadratic coefficient k = 0.8, and the light output improvement of the conventional spherical lens is second.

[0095] The above embodiments are only used to further illustrate a deep ultraviolet LED packaging structure with enhanced light output and a manufacturing method thereof of the present invention, but the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A deep ultraviolet LED packaging structure, characterized in that: include: A three-dimensional ceramic substrate having a groove, wherein the groove has a bottom, an inner side wall and an upper surface; A deep ultraviolet LED chip is mounted at the bottom of the groove of the three-dimensional ceramic substrate; A fluororesin is filled in the groove of the three-dimensional ceramic substrate and covers the upper surface and sidewalls of the deep ultraviolet LED chip, wherein the fluororesin is a carboxylated fluororesin; The optical lens is mounted on the deep ultraviolet LED chip and the fluororesin, and the edge is fixed on the upper surface or the side wall of the three-dimensional ceramic substrate.

2. A deep ultraviolet LED packaging structure according to claim 1, characterized in that: The inner side wall of the groove is inclined relative to the bottom of the groove, and the inclination angle is greater than 90°. The transverse cross-section of the groove is circular or square.

3. A deep ultraviolet LED packaging structure according to claim 2, characterized in that: The inner side wall of the groove is inclined at an angle of 120 to 140 degrees relative to the bottom of the groove.

4. A deep ultraviolet LED packaging structure according to claim 1, characterized in that: The inner wall surface of the groove is plated with a metal reflective layer, the metal reflective layer contains one element among aluminum, rhodium and nickel or a metal alloy, and the surface roughness (RMS) of the metal reflective layer is less than 20nm.

5. The deep ultraviolet LED packaging structure according to claim 1, characterized in that: The general structural formula of the fluororesin is as follows: ， The terminal functional group R is -COOH, and the value of n ranges from 100,000 to 500,000; the refractive index of the fluororesin for 250nm ultraviolet light is 1.3 to 1.

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6. A deep ultraviolet LED packaging structure according to claim 1, characterized in that: The deep ultraviolet LED chip is a flip-chip nitride deep ultraviolet LED chip; the fluororesin located between the deep ultraviolet LED chip and the optical lens has an interface layer thickness of 0.5 to 10 microns.

7. The deep ultraviolet LED packaging structure according to claim 1, characterized in that: At least one of the upper surface of the deep ultraviolet LED chip and the bottom surface of the optical lens is surface-modified with a silane coupling agent.

8. The deep ultraviolet LED packaging structure according to claim 1, characterized in that: The bottom surface, outer surface and vertex of the optical lens, the bottom surface is a plane, the outer surface is a parabolic convex surface; the outer contour of any longitudinal section of the optical lens passing through the vertex conforms to the parabola, and the parabola satisfies y=k*r 2 , the quadratic coefficient k is between 0.4 and 1.2, and r does not exceed half of the side length of the three-dimensional ceramic substrate.

9. The deep ultraviolet LED packaging structure according to claim 1, characterized in that: A step is arranged on the inner side wall of the groove for supporting the edge of the optical lens.

10. A method for preparing a deep ultraviolet LED packaging structure, the preparation process is as follows: S1. Preparing a three-dimensional ceramic substrate having a groove, the groove having a bottom and an inclined inner side wall; S2. depositing a metal reflective layer on the inner sidewall of the three-dimensional ceramic substrate; S3. Soldering a deep ultraviolet LED chip on the three-dimensional ceramic substrate; S4. Treating the light-emitting surface of the deep ultraviolet LED chip and the bottom surface of the optical lens with a silane coupling agent solvent, and after drying, filling the fluororesin into the three-dimensional ceramic substrate and curing it; S5. Heat and soften the fluororesin, and bond the optical lens to the side wall or upper surface of the ceramic substrate with the softened fluororesin under a certain pressure.

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