A low color temperature LED light source and a preparation method thereof

Abstract

This invention discloses a low color temperature LED light source, comprising: a packaging substrate; a yellow LED chip and a blue LED chip, fixed to the packaging substrate by a die-bonding layer; a silicone mixture coated on the blue LED chip; the silicone mixture is doped with red phosphor, the peak wavelength range of which is 600nm to 640nm; wherein, both the yellow and blue LED chips are gallium nitride-based LED chips, the peak wavelength range of which is 540nm to 590nm for the yellow LED chip and 440nm to 460nm for the blue LED chip; the color temperature of the low color temperature LED light source is 1600K-2500K, and the color rendering index Ra≥70. By coating the blue LED chip with a silicone mixture doped with red phosphor, a portion of the blue light is converted into red light, thereby mixing to form low color temperature white light. Simultaneously, using only red phosphor effectively avoids the sedimentation and uncontrolled ratio problems that occur when different colored phosphors are mixed and coated, ensuring the long-term stability of the light source's color temperature from a physical structure perspective.

Description

Technical Field

[0001] This invention relates to semiconductor lighting technology, and more particularly to a low color temperature LED light source and its preparation method. Background Technology

[0002] The demand for low color temperature (1600K–2500K) white LED light sources continues to grow in indoor warm lighting, high-end commercial displays, and special lighting scenarios. Currently, the mainstream technical approaches to achieve low color temperature white light mainly include phosphor conversion type and multi-primary color chip mixing type, but both have significant bottlenecks in terms of luminous efficiency, reliability, and cost.

[0003] On the one hand, phosphor conversion solutions require the use of blue LED chips to excite a high-concentration composite system of yellow and red phosphors to achieve a low color temperature. However, the high phosphor load not only exacerbates light scattering, but also causes a significant spectral reabsorption effect due to the overlap of the emission and absorption spectra of yellow and red phosphors, resulting in a decrease in light extraction efficiency. At the same time, the inherent differences in sedimentation rate, thermal stability and light decay characteristics of different phosphor particles can easily cause uneven distribution of coating components, directly causing fluctuations in color temperature consistency between devices, and placing extremely high demands on the uniformity, repeatability and batch stability of the coating process.

[0004] On the other hand, although the multi-color chip mixed light solution avoids phosphor-related process problems by combining GaN-based blue / green light chips with AlGaInP-based red light chips, the electro-optical conversion efficiency of AlGaInP red light chips is highly sensitive to junction temperature. Typically, the luminous efficiency decreases by about 1% for every 1°C increase in temperature. High-specification heat dissipation structures are required to maintain color stability, which increases heat dissipation costs and packaging complexity.

[0005] Another type of low color temperature light source used on a large scale outdoors is the high-pressure sodium lamp (color temperature about 2000K), but its luminous efficacy is low, about 90lm / W, and its color rendering is poor, usually with a color rendering index Ra of less than 30, which cannot truly reflect the color of objects. In addition, the lifespan of high-pressure sodium lamps is short, only about 20,000 hours, which is much shorter than the lifespan of LEDs.

[0006] In summary, there is an urgent need to provide a new LED light source solution that can solve the above problems and achieve a better balance between luminous efficacy, color temperature stability, color rendering, and cost. Summary of the Invention

[0007] Based on this, the present invention provides a low color temperature LED light source with high luminous efficiency, stable color temperature, good color rendering and low cost, and a method for preparing the same.

[0008] In a first aspect, the present invention provides a low color temperature LED light source, comprising: Packaging substrate; Yellow LED chips and blue LED chips are fixed to the packaging substrate by a die bond layer; A silicone mixture is coated onto a blue LED chip; the silicone mixture is doped with red phosphor, the peak wavelength of which is in the range of 600nm to 640nm. Among them, both the yellow LED chip and the blue LED chip are gallium nitride-based LED chips. The peak wavelength range of the yellow LED chip is 540nm~590nm, and the peak wavelength range of the blue LED chip is 440nm~460nm. The color temperature of the low color temperature LED light source is 1600K-2500K, and the color rendering index Ra≥70.

[0009] The low color temperature LED light source provided by this invention involves coating a silicone mixture doped with red phosphor onto a blue LED chip. A portion of the blue light emitted from the blue LED chip is converted to red light by the red phosphor wavelength conversion. The red, blue, and yellow light emitted from yellow LED chips are mixed to form low color temperature white light. By doping the red phosphor into the silicone mixture, which is then precisely coated only on the surface of the blue LED chip, not only is the red and yellow light emitting regions physically separated, but the amount of red phosphor used is also reduced, mitigating the Stokes energy loss caused by the simultaneous excitation of yellow and red phosphors in traditional solutions. Furthermore, using only red phosphor effectively avoids the sedimentation and proportioning problems associated with mixing different colored phosphors, ensuring the long-term stability of the light source's color temperature from a physical structural perspective. In addition, compared to multi-primary-color mixing solutions, this invention avoids the use of AlGaInP red LED chips, improves luminous flux maintenance at high temperatures, and effectively reduces heat dissipation and LED chip costs.

[0010] As an alternative solution for the low color temperature LED light source of the present invention, the coating thickness of the silicone mixture on the blue LED chip is 0.2mm to 0.5mm; the mass ratio of red phosphor in the silicone mixture is 0.5wt% to 5wt%, and the red phosphor is a nitride matrix red phosphor.

[0011] As a preferred option among the above-mentioned alternatives, the chemical formula of the nitride-based red phosphor is (Ca... 1- x Sr x AlSiN3:Eu 2+ , where 0≤x≤1.

[0012] As an alternative solution for the low color temperature LED light source of the present invention, the red phosphor is composed of a first red phosphor and a second red phosphor, wherein the peak wavelength range of the first red phosphor is 600nm to 614nm and the peak wavelength range of the second red phosphor is 615nm to 640nm.

[0013] The low color temperature LED light source provided by this invention can more flexibly optimize the spectral composition of the light source by adjusting the peak wavelength of the yellow LED chip, the peak wavelength of the blue LED chip, the peak wavelength of the red phosphor, the doping concentration of the red phosphor, and the coating thickness of the silicone mixture, so as to achieve the target color temperature and color coordinates and achieve a color rendering index ≥70, thus achieving a good color rendering effect.

[0014] As an optional embodiment of the low color temperature LED light source of the present invention, each blue LED chip is surrounded by a dam, and the cavity formed by the dam is in a plane parallel to the encapsulation substrate. The silicone mixture is disposed in the cavity and covers the surface of the blue LED chip. The inner dimension L1 of the dam in the length direction is 110% to 130% of the length L2 of the blue LED chip, and the inner dimension W1 of the dam in the width direction is 110% to 130% of the width W2 of the blue LED chip. The height H of the dam is greater than the sum of the thickness of the blue LED chip and the thickness of the die-bonding layer, and the range of H is 0.4 mm to 0.7 mm. The material of the dam is a white colloid.

[0015] As an alternative solution for the low color temperature LED light source of the present invention, a white adhesive layer is provided in the area of ​​the packaging substrate not covered by the yellow LED chip and the blue LED chip. The height of the white adhesive layer is less than the sum of the thickness of the yellow LED chip and the thickness of the die bonding layer, and less than the sum of the thickness of the blue LED chip and the thickness of the die bonding layer.

[0016] As an optional solution for the low color temperature LED light source of the present invention, the low color temperature LED light source further includes: A primary optical lens is used to seal yellow and blue LED chips; the exit surface of the primary optical lens can be spherical, freeform, or planar. Leads connect the yellow LED chip and the blue LED chip to the circuitry of the packaging substrate.

[0017] Secondly, the present invention also provides a method for preparing a low color temperature LED light source, which includes the following steps: Provide packaging substrate; The yellow LED chip and the blue LED chip are fixed onto the packaging substrate through the die bonding process; Through wire bonding technology, electrical interconnection between yellow LED chips, blue LED chips and packaging substrate is achieved using leads; A silicone mixture doped with red phosphor is coated on the surface of a blue LED chip; A primary optical lens is fabricated using dispensing or molding processes, and then the yellow and blue LED chips are packaged to complete the fabrication of a low color temperature LED light source.

[0018] As an optional embodiment of the preparation method of the present invention, before coating the silicone mixture doped with red phosphor, the method further includes the step of coating a white adhesive layer on the area of ​​the encapsulation substrate not covered by the yellow LED chip and the blue LED chip; or, by using a dispensing process, a dam is prepared around the blue LED chip using white adhesive, which confines the subsequently applied silicone mixture within the containment cavity formed by the dam.

[0019] Thirdly, the present invention also provides a method for compensating for color coordinate drift of a low color temperature LED light source, comprising: Set the preset color coordinate target for low color temperature LED light source; By pre-setting the color coordinates of the low color temperature LED light source, the target color coordinates (X2, Y2) of the emitted light from the blue LED chip after wavelength conversion by red phosphor and modulation by a primary optical lens are determined. Based on the target color coordinates (X2, Y2), the initial color coordinates (X1, Y1) that the emitted light of the blue LED chip needs to reach after wavelength conversion by red phosphor are determined through reverse iterative experiments before the optical lens is prepared. Based on the initial color coordinates (X1, Y1), the concentration of red phosphor in the silicone mixture is adjusted so that the color coordinates of the low color temperature LED light source reach the preset target.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, some of which will become clear as the description proceeds, and others will be learned by practicing the invention. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a cross-sectional schematic diagram of the low color temperature LED light source in Embodiment 1 of this application.

[0023] Figure 2 This is a top view of the low color temperature LED light source in Embodiment 1 of this application.

[0024] Figure 3 This is a chromaticity diagram of the light emitted by the yellow LED chip in Embodiment 1 of this application.

[0025] Figure 4 This is a chromaticity diagram of the blue LED chip emitted from Embodiment 1 of this application.

[0026] Figure 5 This is the chromaticity diagram of the low color temperature LED light source in Embodiment 1 of this application.

[0027] Figure 6 This is the spectrum of the low color temperature LED light source in Embodiment 1 of this application.

[0028] Figure 7 This is a cross-sectional schematic diagram of the low color temperature LED light source in Embodiment 2 of this application.

[0029] Figure 8 This is a top view of the low color temperature LED light source in Embodiment 2 of this application.

[0030] Figure 9 This is a chromaticity diagram of the light emitted by the yellow LED chip in Embodiment 2 of this application.

[0031] Figure 10 This is a chromaticity diagram of the blue LED chip emitted from the chip in Embodiment 2 of this application.

[0032] Figure 11 This is the chromaticity diagram of the low color temperature LED light source in Embodiment 2 of this application.

[0033] Figure 12 This is the spectrum of the low color temperature LED light source in Embodiment 2 of this application.

[0034] Figure 13 This is a cross-sectional schematic diagram of the low color temperature LED light source in Embodiment 3 of this application.

[0035] Figure 14 This is a top view of the low color temperature LED light source in Embodiment 3 of this application.

[0036] Figure 15 This is a chromaticity diagram of the light emitted by the yellow LED chip in Embodiment 3 of this application.

[0037] Figure 16 This is a chromaticity diagram of the blue LED chip emitted from the chip in Embodiment 3 of this application.

[0038] Figure 17 This is the chromaticity diagram of the low color temperature LED light source in Embodiment 3 of this application.

[0039] Figure 18 This is the spectrum of the low color temperature LED light source in Embodiment 3 of this application.

[0040] In the figure: 11-packaging substrate, 12-yellow LED chip, 13-blue LED chip, 14-silicone mixture, 15-die bonding layer, 16-lead wire, 17-primary optical lens; 28-dam; 38-white adhesive layer. Detailed Implementation

[0041] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. However, the following embodiments are only illustrative, and the scope of protection of the present invention is not limited to these embodiments.

[0042] This application provides a low color temperature LED light source, including: Packaging substrate 11; Yellow LED chip 12 and blue LED chip 13 are fixed to the packaging substrate 11 by die bonding layer 15; A silicone mixture 14 is coated onto a blue LED chip 13. The silicone mixture 14 is doped with red phosphor, the peak wavelength of which is in the range of 600nm to 640nm. It should be noted that a portion of the blue light emitted by the blue LED chip is converted to red light by the red phosphor. The red phosphor is only distributed on the surface of the blue LED chip, achieving physical separation between the red and yellow light emitting areas, thus reducing the amount of red phosphor used. Using only red phosphor reduces the Stokes energy loss caused by the simultaneous excitation of yellow and red phosphors in traditional solutions, and also avoids the sedimentation and uncontrolled ratio problems when different colored phosphors are mixed and coated, ensuring the long-term stability of the light source's color temperature from a physical structure perspective. Furthermore, compared to multi-primary-color mixing solutions, it avoids the use of AlGaInP red LED chips, improves the luminous flux maintenance rate at high temperatures, and effectively reduces heat dissipation costs and LED chip costs. Among them, both the yellow LED chip 12 and the blue LED chip 13 are gallium nitride-based LED chips. The peak wavelength range of the yellow LED chip 12 is 540nm to 590nm, and the peak wavelength range of the blue LED chip 13 is 440nm to 460nm. The color temperature of the low color temperature LED light source is 1600K-2500K, and the color rendering index Ra≥70. It should be noted that by changing the peak wavelengths of the yellow LED chip, the blue LED chip, and the red phosphor, the spectral composition of the light source can be optimized more flexibly to achieve the target color temperature and color coordinates, and to achieve a color rendering index ≥70.

[0043] In some embodiments, the coating thickness of the silicone mixture 14 on the blue LED chip 13 is 0.2 nm to 0.5 mm; the mass percentage of red phosphor in the silicone mixture is 0.5 wt% to 5 wt%, and the red phosphor is a nitride-based red phosphor. It should be noted that by changing the coating thickness of the silicone mixture and the doping concentration of the red phosphor, the proportion of red light components in the light source can be adjusted, allowing for more flexible optimization of the spectral composition of the light source to achieve the target color temperature and color coordinates, and to realize a color rendering index ≥ 70.

[0044] In some embodiments, the chemical formula of the nitride-based red phosphor is (Ca... 1-x Srx AlSiN3:Eu 2+ Where 0 ≤ x ≤ 1. It should be noted that red phosphors containing Ca and Sr can balance red light color coordinates and high light conversion efficiency.

[0045] In some embodiments, the red phosphor is composed of a first red phosphor and a second red phosphor. The peak wavelength range of the first red phosphor is 600 nm to 614 nm, and the peak wavelength range of the second red phosphor is 615 nm to 640 nm. It should be noted that by changing the proportions of the two red phosphors, the color coordinates of the red light in the light source can be flexibly adjusted to achieve the target color temperature and color coordinates of the light source, and to achieve a color rendering index ≥ 70.

[0046] In some embodiments, each blue LED chip 13 is surrounded by a dam 28, and the cavity formed by the dam 28 lies in a plane parallel to the encapsulation substrate 11. A silicone compound 14 is disposed within the cavity and covers the surface of the blue LED chip 13. The inner dimension L1 of the dam 28 in the length direction is 110% to 130% of the length L2 of the blue LED chip 13, and the inner dimension W1 of the dam 28 in the width direction is 110% to 130% of the width W2 of the blue LED chip 13. The height H of the dam 28 is greater than the sum of the thickness of the blue LED chip 13 and the thickness of the die-attach layer 15, and H ranges from 0.4 mm to 0.7 mm. The material of the dam 28 is a white colloid. It should be noted that the dam design facilitates the coating of the silicone compound doped with red phosphor onto the surface of the blue LED chip, and the coating process of the silicone compound can be achieved through a dispensing process.

[0047] In some embodiments, a white adhesive layer 38 is provided on the area of ​​the packaging substrate 11 not covered by the yellow LED chip 12 and the blue LED chip 13. The height of the white adhesive layer 38 is less than the sum of the thickness of the yellow LED chip 12 and the thickness of the die-bonding layer 15, and also less than the sum of the thickness of the blue LED chip 13 and the thickness of the die-bonding layer 15. It should be noted that providing the white adhesive layer can increase the secondary light extraction efficiency, that is, the secondary extraction of back-reflected / scattered light.

[0048] In some embodiments, the low color temperature LED light source further includes: A primary optical lens 17 seals the yellow LED chip 12 and the blue LED chip 13; the exit surface of the primary optical lens 17 is a spherical surface, a freeform surface, or a plane; it should be noted that the setting of the primary optical lens can provide physical protection for the LED chip and the gold wire, improve the light extraction efficiency, and realize the control of the light output pattern; Lead 16 connects the yellow LED chip 12 and the blue LED chip 13 to the packaging substrate 11 via the lead 16.

[0049] This application also provides a method for preparing a low color temperature LED light source, which includes the following steps: Provide packaging substrate 11; The yellow LED chip 12 and the blue LED chip 13 are fixed onto the packaging substrate 11 by the die bonding process. Electrical interconnection between the yellow LED chip 12, the blue LED chip 13 and the packaging substrate 11 is achieved by using wire bonding technology and lead wire 16. A silicone mixture 14 doped with red phosphor is coated on the surface of the blue LED chip 13; An optical lens 17 is fabricated using dispensing or molding processes to encapsulate the yellow LED chip 12 and the blue LED chip 13, thus completing the fabrication of the low color temperature LED light source.

[0050] In some embodiments, before coating the silicone mixture 14 doped with red phosphor, the method further includes the steps of: coating a white adhesive layer 38 on the area of ​​the encapsulation substrate 11 not covered by the yellow LED chip 12 and the blue LED chip 13; or, using a dispensing process, a dam 28 is prepared around the blue LED chip 13 with white adhesive to confine the subsequently applied silicone mixture 14 within the containment cavity formed by the dam 28.

[0051] Furthermore, it should be noted that the light source structure of the embodiments of this application adopts integrated packaging. If the yellow LED chip and the blue LED chip coated with silicone mixture are packaged separately, they should also be within the scope of protection of this invention.

[0052] The applicant discovered in their research that when using the aforementioned low color temperature LED light source technology, if the exit surface of the primary optical lens is not planar—for example, if the exit surface is spherical or freeform—the lens encapsulation causes a shift in the color coordinates of the emitted light from the blue LED chip after wavelength conversion by the red phosphor and modulation by the primary optical lens. Specifically, this manifests as an increase in the blue light component and a rise in color temperature in the emitted light. The reason for this was found to be that some of the blue light, which should have undergone multiple reflections and been excited to produce red light in the silicone mixture doped with red phosphor, was directly extracted to the outside due to the high light extraction efficiency of the non-planar primary optical lens. Therefore, it is necessary to adjust the color coordinates of the emitted light from the blue LED chip after wavelength conversion by the red phosphor before forming the non-planar primary optical lens, so that the low color temperature LED light source can still achieve the required color coordinates even after the lens encapsulation causes a shift.

[0053] Based on this, embodiments of this application also provide a method for compensating for color coordinate drift of a low color temperature LED light source, including: Set the preset color coordinate target for low color temperature LED light source; By presetting the color coordinates of the low color temperature LED light source, the target color coordinates (X2, Y2) of the emitted light from the blue LED chip 13 after wavelength conversion by red phosphor and modulation by the primary optical lens 17 are determined. Based on the target color coordinates (X2, Y2), the initial color coordinates (X1, Y1) to be reached by the emitted light of the blue LED chip 13 after wavelength conversion by the red phosphor are determined before the optical lens 17 is fabricated. Based on the required initial color coordinates (X1, Y1), the concentration of red phosphor and the proportion of red phosphor at different wavelengths in the silicone mixture 14 are adjusted to ensure that the emitted light from the blue LED chip 13, after wavelength conversion by the red phosphor, reaches the required initial color coordinates (X1, Y1), thus achieving the preset target color coordinates for the low color temperature LED light source. It should be noted that the required initial color coordinates (X1, Y1) can be obtained through inverse iterative experiments or optical simulation models. This method allows for accurate control of the color temperature and color coordinates of light sources with different packaging structures.

[0054] Furthermore, the compensation method for color coordinate drift of low color temperature LED light source provided in this application embodiment is also applicable to other similar color coordinate drift scenarios caused by changes in refractive index distribution in the optical path, such as filling a transparent optical medium layer between a phosphor conversion LED (such as a phosphor red LED) with a planar light-emitting structure and a secondary optical lens.

[0055] The following are some embodiments of this application, and the embodiments of the present invention will further describe the technical solution of the present invention in detail. Example 1

[0056] This embodiment provides a low color temperature LED light source, such as... Figure 1 As shown, the package includes a packaging substrate 11, on which a yellow LED chip 12 and a blue LED chip 13 are fixed by a die-bonding layer 15. The surface of the blue LED chip 13 is coated with a silicone mixture 14, which is doped with red phosphor. The yellow LED chip 12 and the blue LED chip 13 are connected to electrodes on the packaging substrate 11 via leads 16 to achieve electrical interconnection. The packaging substrate 11 also has a primary optical lens 17, which seals the yellow LED chip 12 and the blue LED chip 13.

[0057] Among them, the yellow LED chip 12 is a vertically structured gallium nitride-based LED chip with a peak wavelength of 555nm and a photoelectric conversion efficiency of 31%. The blue LED chip 13 is also a vertically structured gallium nitride-based LED chip with a peak wavelength of 455nm and a photoelectric conversion efficiency of 60%. The packaging substrate 11 is a ceramic substrate, the leads 16 are gold wires, and the exit surface of the primary optical lens 17 is planar. Figure 2As shown, there are two yellow LED chips 12 and two blue LED chips 13. The four LED chips are arranged in a square array, with the two yellow LED chips 12 and the two blue LED chips 13 occupying two sets of diagonal positions of the square respectively.

[0058] Specifically, the silicone mixture 14 forms a single-layer thin film on the surface of the blue LED chip 13, with a film thickness h1 = 0.2 mm. The red phosphor is composed of a first red phosphor and a second red phosphor, with the first red phosphor having a peak wavelength of 614 nm and the second red phosphor having a peak wavelength of 628 nm. The first red phosphor accounts for 0.555 wt% of the mass of the silicone mixture, and the second red phosphor accounts for 0.445 wt% of the mass of the silicone mixture. The silicone mixture 14 also includes transparent silicone, in which the red phosphor is doped. The chemical formula of the red phosphor is (Ca... 1-x Sr x AlSiN3:Eu 2 + , where 0≤x≤1.

[0059] In this embodiment, when the low color temperature LED light source is working, the chromaticity diagram of the yellow light emitted by the yellow LED chip 12 is as follows: Figure 3 As shown. A portion of the blue light emitted by the blue LED chip 13 is converted into red light by red phosphor wavelength conversion. The chromaticity diagram of the light resulting from the mixture of the converted red light and the unconverted blue light is shown below. Figure 4 As shown. The converted red light, unconverted blue light, and yellow light are mixed to form low color temperature white light. The color temperature of the low color temperature white light is 2400K, and the color rendering index Ra is 75. The chromaticity diagram of the low color temperature white light is shown below. Figure 5 As shown, the spectrum is as follows Figure 6 As shown.

[0060] This embodiment also provides a method for preparing the low color temperature LED light source, including the following steps: Step S1: Provide a ceramic substrate as a packaging substrate 11.

[0061] Step S2: Fix the yellow LED chip 12 and the blue LED chip 13 onto the ceramic substrate using a die bonding process.

[0062] Step S3: Through wire bonding process, the yellow LED chip 12, the blue LED chip 13 and the packaging substrate 11 are electrically interconnected using the lead wire 16.

[0063] Step S4: Coat the surface of the blue LED chip 13 with a silicone mixture 14 doped with red phosphor.

[0064] Step S5: A primary optical lens 17 with a planar exit surface is formed using a molding process, with a planar thickness h2=1mm; the primary optical lens 17 is then baked and cured, and the yellow LED chip 12 and blue LED chip 13 are packaged to complete the fabrication of the low color temperature LED light source. Example 2

[0065] This embodiment provides a low color temperature LED light source, such as... Figure 7 As shown, the package includes a packaging substrate 11, with a yellow LED chip 12 and a blue LED chip 13 fixed to the packaging substrate 11 by a die-bonding layer 15. A dam 28 is provided around the blue LED chip 13, and a silicone mixture 14 is confined within the cavity formed by the dam 28 and covers the surface of the blue LED chip 13. The silicone mixture 14 is doped with red phosphor. The yellow LED chip 12 and the blue LED chip 13 are electrically interconnected with electrodes on the packaging substrate 11 via leads 16. A primary optical lens 17 is also provided on the packaging substrate 11, which seals the yellow LED chip 12 and the blue LED chip 13.

[0066] Among them, the yellow LED chip 12 is a vertically structured gallium nitride-based LED chip with a peak wavelength of 565nm and a photoelectric conversion efficiency of 29%. The blue LED chip 13 is also a vertically structured gallium nitride-based LED chip with a peak wavelength of 455nm and a photoelectric conversion efficiency of 60%. The packaging substrate 11 is a ceramic substrate, the leads 16 are gold wires, and the exit surface of the primary optical lens 17 is curved (the primary optical lens 17 is hemispherical). Figure 8 As shown, there are two yellow LED chips 12 and two blue LED chips 13. The four LED chips are arranged in a square array, with the two yellow LED chips 12 and the two blue LED chips 13 occupying two sets of diagonal positions of the square respectively.

[0067] Specifically, the containment cavity formed by the dam 28 is in a plane parallel to each chip on the packaging substrate 11. The inner dimension L1=1mm in the length direction of the dam 28 is 125% of the length L2=0.8mm of the blue LED chip 13, and the inner dimension W1=1mm in the width direction of the dam 28 is 125% of the width W2=0.8mm of the blue LED chip 13. The height H of the dam 28 is greater than the sum of the thickness of the blue LED chip 13 and the thickness of the die-bonding layer 15, and H is 0.4mm. The material of the dam 28 is a white colloid, and the thickness B of the dam is 0.1mm.

[0068] Specifically, the thickness of the silicone mixture 14 on the surface of the blue LED chip 23 is h1 = 0.2 mm. The red phosphor is composed of a first red phosphor and a second red phosphor, with the first red phosphor having a peak wavelength of 608 nm and the second red phosphor having a peak wavelength of 615 nm. The first red phosphor accounts for 0.757 wt% of the mass of the silicone mixture, and the second red phosphor accounts for 0.443 wt% of the mass of the silicone mixture. The silicone mixture 14 also includes transparent silicone, in which the red phosphor is doped. The chemical formula of the red phosphor is (Ca... 1-x Sr x AlSiN3:Eu 2+ , where 0≤x≤1.

[0069] In this embodiment, when the low color temperature LED light source is working, the chromaticity diagram of the yellow light emitted by the yellow LED chip 12 is as follows: Figure 9 As shown. A portion of the blue light emitted by the blue LED chip 13 is converted into red light by red phosphor wavelength conversion. The chromaticity diagram of the light resulting from the mixture of the converted red light and the unconverted blue light is shown below. Figure 10 As shown. The converted red light, unconverted blue light, and yellow light are mixed to form low color temperature white light. The color temperature of the low color temperature white light is 2000K, and the color rendering index Ra is 70. The chromaticity diagram of the low color temperature white light is shown below. Figure 11 As shown, the spectrum is as follows Figure 12 As shown.

[0070] This embodiment also provides a method for preparing the low color temperature LED light source, including the following steps: Step S1: Provide a ceramic substrate as a packaging substrate 11.

[0071] Step S2: Fix the yellow LED chip 12 and the blue LED chip 13 onto the ceramic substrate using a die bonding process.

[0072] Step S3: Through wire bonding process, the yellow LED chip 12, the blue LED chip 13 and the packaging substrate 11 are electrically interconnected using the lead wire 16.

[0073] Step S4: Apply white adhesive around the blue LED chip 13 using a dispensing process to form a dam 28.

[0074] Step S5: Using a dispensing process, a silicone mixture 14 doped with red phosphor is coated on the surface of the blue LED chip 13. The silicone mixture 14 is confined within the containment cavity formed by the dam 28.

[0075] Step S6: A primary optical lens 17 with a curved exit surface is formed by molding process. The primary optical lens 17 is hemispherical with a maximum height h2=2.5mm. The primary optical lens 17 is then baked and cured. The yellow LED chip 12 and blue LED chip 13 are then packaged to complete the preparation of the low color temperature LED light source.

[0076] Since the exit surface of the primary optical lens in this embodiment is curved, there is a color coordinate drift problem. This embodiment also provides a method for compensating for the color coordinate drift of a low color temperature LED light source, including: (1) Set the preset target color coordinates of the low color temperature LED light source.

[0077] (2) By using the preset target color coordinates of the low color temperature LED light source, the target color coordinates of the emitted light of the blue LED chip 13 after wavelength conversion by red phosphor and modulation by the primary optical lens 17 are determined (X2=0.5715, Y2=0.3450).

[0078] (3) Based on the target color coordinates (X2=0.5715, Y2=0.3450), the initial color coordinates (X1=0.5944, Y1=0.3622) of the emitted light of the blue LED chip 13 after wavelength conversion by red phosphor were determined by reverse iterative experiment before the optical lens 17 was prepared.

[0079] (4) Based on the initial color coordinates (X1=0.5944, Y1=0.3622), adjust the mass concentration of red phosphor in the silicone mixture 14 to 1.2wt% so that the color coordinates of the low color temperature LED light source reach the preset target. Example 3

[0080] This embodiment provides a low color temperature LED light source, such as... Figure 13 As shown, the package includes a packaging substrate 11, on which a yellow LED chip 12 and a blue LED chip 13 are fixed by a die-bonding layer 15. The surface of the blue LED chip 13 is coated with a silicone mixture 14, which is doped with red phosphor. The yellow LED chip 12 and the blue LED chip 13 are electrically interconnected with electrodes on the packaging substrate 11 via leads 16. A primary optical lens 17 is also provided on the packaging substrate 11 to seal the yellow LED chip 12 and the blue LED chip 13. A white adhesive layer 38 is provided on the area of ​​the packaging substrate 11 not covered by the yellow LED chip 12 and the blue LED chip 13. The height of the white adhesive layer 38 is less than the sum of the thickness of the yellow LED chip 12 and the thickness of the die-bonding layer 15, and less than the sum of the thickness of the blue LED chip 13 and the thickness of the die-bonding layer 15.

[0081] Among them, the yellow LED chip 12 is a vertically structured gallium nitride-based LED chip with a peak wavelength of 555nm and a photoelectric conversion efficiency of 31%. The blue LED chip 13 is also a vertically structured gallium nitride-based LED chip with a peak wavelength of 455nm and a photoelectric conversion efficiency of 60%. The packaging substrate 11 is a ceramic substrate, the leads 16 are gold wires, and the exit surface of the primary optical lens 17 is planar. Figure 14 As shown, there is one yellow LED chip 12 and three blue LED chips 13, and the four LED chips are arranged in a square array.

[0082] Specifically, the silicone mixture 14 forms a single-layer thin film on the surface of the blue LED chip 13, with a film thickness h1 = 0.2 mm. The red phosphor is composed of a first red phosphor and a second red phosphor, with the first red phosphor having a peak wavelength of 608 nm and the second red phosphor having a peak wavelength of 631 nm. The first red phosphor accounts for 0.244 wt% of the mass of the silicone mixture, and the second red phosphor accounts for 0.756 wt% of the mass of the silicone mixture. The silicone mixture 14 also includes transparent silicone, in which the red phosphor is doped. The chemical formula of the red phosphor is (Ca... 1-x Sr x AlSiN3:Eu 2 + , where 0≤x≤1.

[0083] In this embodiment, when the low color temperature LED light source is working, the chromaticity diagram of the yellow light emitted by the yellow LED chip 12 is as follows: Figure 15 As shown. A portion of the blue light emitted by the blue LED chip 13 is converted into red light by red phosphor wavelength conversion. The chromaticity diagram of the light resulting from the mixture of the converted red light and the unconverted blue light is shown below. Figure 16 As shown. The converted red light, unconverted blue light, and yellow light are mixed to form low color temperature white light. The color temperature of the low color temperature white light is 1700K, and the color rendering index Ra is 72. The chromaticity diagram of the low color temperature white light is shown below. Figure 17 As shown, the spectrum is as follows Figure 18 As shown.

[0084] This embodiment also provides a method for preparing the low color temperature LED light source, including the following steps: Step S1: Provide a ceramic substrate as a packaging substrate 11.

[0085] Step S2: Fix the yellow LED chip 12 and the blue LED chip 13 onto the ceramic substrate using a die bonding process.

[0086] Step S3: Through wire bonding process, the yellow LED chip 12, the blue LED chip 13 and the packaging substrate 11 are electrically interconnected using the lead wire 16.

[0087] Step S4: Apply a white adhesive layer 38 to the area of ​​the packaging substrate 11 that is not covered by the yellow LED chip 12 and the blue LED chip 13. The thickness of the white adhesive layer 38 is 0.15 mm.

[0088] Step S5: Coat the surface of the blue LED chip 13 with a silicone mixture 14 doped with red phosphor.

[0089] Step S6: A primary optical lens 17 with a planar exit surface is formed using a molding process, with a planar thickness h2=1mm; the primary optical lens 17 is then baked and cured, and the yellow LED chip 12 and blue LED chip 13 are packaged to complete the preparation of the low color temperature LED light source.

[0090] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0091] The above descriptions are merely embodiments of this application, which enable those skilled in the art to understand and implement this application. Various modifications to the embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Claims

1. A low color temperature LED light source, characterized in that, include: Packaging substrate; Yellow LED chips and blue LED chips are fixed to the packaging substrate by a die-bonding layer; A silicone mixture is coated onto the blue LED chip; the silicone mixture is doped with red phosphor, the peak wavelength of which is in the range of 600nm to 640nm. The yellow LED chip and the blue LED chip are both gallium nitride-based LED chips. The peak wavelength range of the yellow LED chip is 540nm to 590nm, and the peak wavelength range of the blue LED chip is 440nm to 460nm. The color temperature of the low color temperature LED light source is 1600K-2500K, and the color rendering index Ra≥70.

2. The low color temperature LED light source according to claim 1, characterized in that: The coating thickness of the silicone mixture on the blue LED chip is 0.2 mm to 0.5 mm; the mass percentage of the red phosphor in the silicone mixture is 0.5 wt% to 5 wt%, and the red phosphor is a nitride-based red phosphor.

3. The low color temperature LED light source according to claim 2, characterized in that: The chemical formula of the nitride matrix red fluorescent powder is (Ca 1-x Sr x )AlSiN3:Eu 2+ , wherein 0≤x≤1.

4. The low color temperature LED light source according to claim 1, characterized in that: The red phosphor is composed of a first red phosphor and a second red phosphor. The peak wavelength range of the first red phosphor is 600nm to 614nm, and the peak wavelength range of the second red phosphor is 615nm to 640nm.

5. The low color temperature LED light source according to claim 1, characterized in that: Each blue LED chip is surrounded by a dam, and the cavity formed by the dam is in a plane parallel to the encapsulation substrate. The silicone mixture is disposed in the cavity and covers the surface of the blue LED chip. The inner dimension L1 of the dam in the length direction is 110% to 130% of the length L2 of the blue LED chip, and the inner dimension W1 of the dam in the width direction is 110% to 130% of the width W2 of the blue LED chip. The height H of the dam is greater than the sum of the thickness of the blue LED chip and the thickness of the die-bonding layer, and the range of H is 0.4 mm to 0.7 mm. The material of the dam is a white colloid.

6. The low color temperature LED light source according to claim 1, characterized in that: A white adhesive layer is provided on the area of ​​the packaging substrate not covered by the yellow LED chip and the blue LED chip. The height of the white adhesive layer is less than the sum of the thickness of the yellow LED chip and the thickness of the die-bonding layer, and also less than the sum of the thickness of the blue LED chip and the thickness of the die-bonding layer.

7. The low color temperature LED light source according to claim 1, characterized in that, The low color temperature LED light source also includes: A primary optical lens is used to seal the yellow LED chip and the blue LED chip; the exit surface of the primary optical lens is a spherical surface, a freeform surface, or a plane. The yellow LED chip and the blue LED chip are connected to the circuit of the packaging substrate via leads.

8. A method for fabricating a low color temperature LED light source, used to fabricate a low color temperature LED light source as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Provide packaging substrate; The yellow LED chip and the blue LED chip are fixed onto the packaging substrate by the die bonding process; The yellow LED chip, blue LED chip and the packaging substrate are electrically interconnected by wire bonding process using leads; A silicone mixture doped with red phosphor is coated on the surface of the blue LED chip; An optical lens is prepared using dispensing or molding processes, and the yellow LED chip and blue LED chip are then packaged to complete the preparation of the low color temperature LED light source.

9. The preparation method according to claim 8, characterized in that, Before coating the silicone mixture doped with red phosphor, the process includes the following steps: coating a white adhesive layer on the area of ​​the encapsulation substrate not covered by the yellow LED chip and the blue LED chip; or, using a dispensing process, using white adhesive to create a dam around the blue LED chip, confining the subsequently applied silicone mixture within the containment cavity formed by the dam.

10. A method for compensating for color coordinate drift in a low color temperature LED light source, characterized in that, The method includes: Set the preset color coordinate target for low color temperature LED light source; By pre-setting the color coordinates of the low color temperature LED light source, the target color coordinates (X2, Y2) of the emitted light from the blue LED chip after wavelength conversion by red phosphor and modulation by a primary optical lens are determined. Based on the target color coordinates (X2, Y2), through reverse iterative experiments, the initial color coordinates (X1, Y1) that the emitted light of the blue LED chip needs to reach after wavelength conversion by red phosphor is determined. Based on the initial color coordinates (X1, Y1), the concentration of red phosphor in the silicone mixture is adjusted so that the color coordinates of the low color temperature LED light source reach the preset target.

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