Real-time monitoring method for temperature of flip-chip packaged GaN-based LED chip

Abstract

This invention provides a method for real-time temperature monitoring of a flip-chip GaN-based LED chip, comprising: fabricating a flip-chip GaN-based LED device; testing the infrared transmittance of a sapphire substrate using an integrating sphere transmission method; and indirectly characterizing YAG:Ce using an infrared camera. 3+ The infrared transmission state of phosphor adhesive was measured; the infrared emissivity of GaN-based LED chips was tested using an integrating sphere reflectometer; the temperature of GaN-based LED chips was tested using indium antimonide infrared transmission at specific spectral wavelengths and the transient thermal resistance method, respectively, verifying the accuracy of the indium antimonide infrared transmission method; the GaN-based LED device was connected to an aging circuit, and the temperature of the GaN-based LED chip was monitored in real time using indium antimonide infrared transmission at specific spectral wavelengths. This invention verifies the infrared transmission state of specific wavelengths of infrared light on sapphire substrates and YAG:Ce... 3+ The transmissivity of the fluorescent adhesive solves the problem that existing technologies cannot monitor the temperature of flip-chip GaN-based LED chips in real time.

Description

Technical Field

[0001] This invention relates to the field of detection technology in the LED semiconductor industry, and in particular to a method for real-time temperature monitoring of flip-chip GaN-based LED chips. Background Technology

[0002] GaN-based LEDs are widely used in aerospace products due to their advantages such as small size, long lifespan, shock resistance, and low power consumption. GaN-based LED chips are typically grown on sapphire substrates. Because sapphire is non-conductive, GaN-based LEDs are mainly packaged using flip-chip technology. The visible light generated by the GaN-based LED chip passes sequentially through the sapphire substrate and phosphor before being displayed. During LED light emission, non-recombination radiation generates a large amount of heat, leading to a significant increase in the internal temperature of the LED device. Therefore, real-time monitoring of the LED chip temperature has become an important research topic. Currently, thermocouple methods, transient thermal resistance methods, and infrared thermal imaging methods are mainly used to monitor LED chip temperature.

[0003] (1) For conventionally packaged LED chips, the thermocouple method can obtain the LED chip temperature by directly contacting the LED chip. However, the flip-chip packaged GaN-based LED chip has a sapphire substrate and phosphor on the top and solder joints and substrate on the bottom. These structures must be destroyed before the thermocouple can directly contact the GaN-based LED chip. In addition, the light generated by the LED chip may be absorbed by the thermocouple and cause the thermocouple temperature to rise. Therefore, the chip temperature measured by the thermocouple will be significantly higher than the chip temperature itself.

[0004] (2) Compared with the thermocouple method, the transient thermal resistance method is a non-destructive testing method that obtains the LED chip temperature through the temperature-sensitive parameters of the LED device; however, the transient thermal resistance method can only give the average temperature of the LED chip and cannot give the temperature distribution of the LED chip.

[0005] (3) Compared to the previous two methods, traditional infrared thermal imaging is also a non-destructive testing method, and it can obtain the temperature distribution of LED devices in a non-contact manner. However, flip-chip GaN-based LED devices have a multi-layer structure, and the sapphire substrate and phosphor on the surface of the LED chip may block the penetration of infrared light. Infrared detectors often only obtain the temperature distribution of the phosphor on the surface of the LED device, and the measured temperature is significantly lower than that of the GaN-based LED chip. In addition, the infrared emissivity of the GaN-based LED chip must be obtained to accurately calculate the LED chip temperature.

[0006] In summary, non-destructive infrared thermal imaging holds promise for obtaining the temperature distribution of flip-chip GaN-based LED chips. However, the sapphire substrate and phosphor structures on the LED chip surface significantly affect the infrared light transmittance and also prevent accurate measurement of the infrared emissivity of GaN-based LED chips. Therefore, there is an urgent need to develop an improved infrared thermal imaging method to determine the transmittance of infrared light at specific wavelengths through the sapphire substrate and phosphor, and to accurately measure the infrared emissivity of the LED chip using a non-destructive method, thus solving the problem that traditional methods cannot accurately monitor the temperature of flip-chip GaN-based LED chips in real time. Summary of the Invention

[0007] The purpose of this invention is to provide a method for real-time temperature monitoring of flip-chip GaN-based LED chips, so as to solve the problem that existing technologies cannot monitor the temperature of flip-chip LED chips in real time.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is: to provide a method for real-time temperature monitoring of a flip-chip GaN-based LED chip, comprising the following steps:

[0009] S1. Fabrication of flip-chip packaged GaN-based LED devices;

[0010] S2. Integrating sphere transmission method for testing infrared transmittance of sapphire substrate;

[0011] S3, Indirect characterization of YAG:Ce by infrared camera 3+ Infrared transmission state of fluorescent adhesive;

[0012] S4. Integrating sphere reflectometer method for testing the infrared emissivity of GaN-based LED chips;

[0013] S5. The temperature of GaN-based LED chips was tested using the indium antimonide infrared transmission method and the transient thermal resistance method with specific spectral wavelengths to verify the temperature measurement accuracy of the indium antimonide infrared transmission method.

[0014] S6. GaN-based LED devices are connected to an aging circuit, and the temperature of the GaN-based LED chip is monitored in real time using indium antimonide infrared transmission method with a specific spectral wavelength.

[0015] Furthermore, step S1 includes:

[0016] S11. Deposit N-type and P-type GaN on a sapphire substrate to obtain a GaN-based LED chip;

[0017] S12. The GaN-based LED chip obtained in step S11 is flip-chip packaged onto the upper surface of the substrate using solder balls, and electrode leads are installed on the lower surface of the substrate.

[0018] S13, in Y3Al5O 12Medium-doped Ce 3+ Later obtained YAG:Ce 3+ Fluorescent adhesive is applied to the surface of a flip-chip sapphire substrate and cured by heating; wherein Y3Al5O 12 It is abbreviated as YAG.

[0019] Furthermore, step S2 includes:

[0020] S21, Using an infrared generator to generate wavelengths of 2-20μm and intensity I in Infrared light is used to illuminate a sapphire substrate with uniform thickness.

[0021] S22. After infrared light passes through the sapphire substrate, it undergoes multiple diffuse reflections on the inner surface of the integrating sphere, and finally converges into the infrared sensor to obtain the transmission intensity I of the infrared light. out ;

[0022] S23. Calculate the transmission intensity I when infrared light passes through a sapphire substrate. out and incident intensity I in ratio This ratio ω represents the infrared transmittance of the sapphire substrate;

[0023] S24. Plot the infrared transmittance curve of the sapphire substrate under infrared light irradiation with wavelengths of 2–20 μm. In the wavelength range of 5–20 μm, the infrared light transmittance cannot reach 90%. When the infrared light wavelength drops to 2–5 μm, most of the infrared light penetrates the sapphire substrate, the transmittance reaches 90% and remains constant, and the sapphire substrate appears completely transparent.

[0024] Furthermore, step S3 includes:

[0025] S31. A heating current IH is used to drive the GaN-based LED chip, causing the chip to heat up to a certain temperature and maintain a constant temperature.

[0026] S32. By setting the infrared wavelength range detected by the infrared camera to 2–5 μm, the infrared camera can directly observe the heated GaN-based LED chip, indirectly indicating that YAG:Ce 3+ Fluorescent adhesive does not impede the penetration of 2-5μm infrared light. (YAG:Ce) 3+ The fluorescent adhesive is transparent.

[0027] Furthermore, step S4 includes:

[0028] S41. An infrared generator is used to produce an intensity of L. i(GaN) When infrared light of a specific wavelength is irradiated onto the GaN-based LED device at the bottom of the integrating sphere, part of the infrared light is absorbed and part is reflected.

[0029] S42. The reflected infrared light undergoes multiple diffuse reflections on the inner surface of the integrating sphere and is eventually captured by the infrared sensor, outputting the intensity L of the infrared light reflected by the GaN-based LED device. r(GaN) The relevant voltage signal V (GaN) ;

[0030] S43. Replace the GaN-based LED device with a standard reference sample with a reflectivity of 1, using the same wavelength and intensity L. i(ref) The standard reference sample is illuminated with infrared light, and the output is the same as the infrared light intensity L reflected by the standard reference sample. r(ref) The relevant voltage signal V (ref) ;

[0031] S44. Under the premise that the incident infrared light intensity is the same, i.e., L i(ref) =L i(GaN) The ratio of the voltage signal of the GaN-based LED device measured by the infrared sensor to that of the standard reference sample is equal to the ratio of the reflected infrared light intensity of the two, i.e. Since the reflectivity of the standard reference sample is 1, the intensity of infrared light reflected from its surface is L. r(ref) Equal to incident intensity L i(ref) ;

[0032] S45. The formula for calculating the overall infrared emissivity of GaN-based LED devices is derived. The processed voltage signal V is calculated based on the infrared emissivity formula. (GaN) and V (ref) To obtain the overall infrared emissivity of GaN-based LED devices under infrared light irradiation at a specific wavelength;

[0033] S46. Change the parameters of the infrared generator to produce an intensity of L. i(GaN) GaN-based LED devices were sequentially irradiated with infrared light of wavelengths from 2 to 20 μm to obtain the overall infrared emissivity curves of the GaN-based LED devices under irradiation of infrared light from 2 to 20 μm. In this curve, only the overall infrared emissivity of the GaN-based LED devices in the range of 2 to 5 μm can be used as the infrared emissivity of the GaN-based LED chip. The infrared emissivity is a constant value of 0.9 and is not affected by the ambient temperature.

[0034] Furthermore, step S5 includes:

[0035] S51. Test the temperature-sensitive parameter K coefficient of GaN-based LED devices;

[0036] S52. Connect the GaN-based LED device to the transient thermal resistance test circuit. Use the IH heating current to drive the device to raise the temperature of the GaN-based LED chip. After the voltage drop of the chip PN junction measured by the VF voltage sensor stabilizes, use an indium antimonide infrared sensor with a wavelength of 2-5μm to monitor the chip temperature in real time. Then, calibrate according to the constant infrared emissivity of 0.9 to obtain the calibrated temperature of the GaN-based LED chip by indium antimonide infrared transmission method.

[0037] After testing the chip temperature using the S53 indium antimonide infrared transmission method, the IH heating current is quickly switched to the IM test current. At the same time, the VF voltage sensor is used to test the PN junction voltage drop change curve of the GaN-based LED chip. The transient thermal resistance method for GaN-based LED chip temperature is obtained through the K coefficient.

[0038] S54. LED devices were driven using different heating currents IH, and the chip temperature Tr of indium antimonide using infrared transmission method was tested respectively. i Where i = 1, 2, ..., N, N is the heating current and the transient thermal resistance chip temperature Tj. i i = 1, 2, ..., N, where N is the heating current.

[0039] S55. Plot the temperature curves Tr and Tj of the indium antimonide infrared transmission method chip under different heating currents;

[0040] S56. The two curves obtained in step S55 are superimposed, and it is found that the linear correlation and overlap of the two curves are both high. This indicates that the chip temperature tested by the indium antimonide infrared transmission method can accurately reflect the chip temperature tested by the transient thermal resistance method, and the temperature measurement result is not affected by the driving heating current.

[0041] Furthermore, step S51 includes:

[0042] GaN-based LED devices connected to transient thermal resistance testing circuits are placed in a constant temperature oil bath. The oil temperature is adjusted to raise the chip temperature. The PN junction voltage drop-temperature curve of the chip is recorded in real time to determine its temperature sensitivity parameter K coefficient.

[0043] Furthermore, step S6 includes:

[0044] The GaN-based LED device leads were connected to an aging circuit. An indium antimonide infrared sensor with a wavelength of 2–5 μm was used to monitor the temperature of the GaN-based LED chip in real time. The infrared emissivity of 0.9 measured in the 2–5 μm range was used to calibrate the temperature of the GaN-based LED chip monitored by the indium antimonide infrared sensor in real time using the integrating sphere reflectometer method.

[0045] The beneficial effects of the real-time temperature monitoring method for flip-chip GaN-based LED chips provided by this invention are:

[0046] 1) Traditional thermocouple methods require direct contact between the thermocouple and the LED chip to obtain the chip's temperature. This invention achieves accurate temperature testing of GaN-based LED chips without damaging the phosphor and sapphire substrate on the LED chip surface, making it a non-destructive testing method. Traditional transient thermal resistance methods are cumbersome and cannot monitor the temperature of flip-chip GaN-based LED chips in real time during the aging process. This invention eliminates the need for wiring the flip-chip GaN-based LED device, enabling real-time monitoring of the LED chip's temperature during aging without affecting the aging circuitry, resulting in a simpler and more accurate temperature measurement process.

[0047] 2) Traditional infrared methods can only test the surface temperature distribution of devices. To address this issue, this invention systematically studies the application of infrared light with wavelengths of 2–20 μm in YAG:Ce 3+ The transmittance of phosphor and sapphire substrates was measured to verify the transmittance of infrared light with wavelengths of 2–5 μm in these two semiconductor materials. Furthermore, 2–5 μm infrared light was selected to test the infrared emissivity of GaN-based LED chips, calibrating the LED chip temperature measured by the infrared detector. This overcomes the limitation of traditional infrared methods in obtaining the internal chip temperature of GaN-based LED devices, enabling real-time monitoring of flip-chip LED temperature.

[0048] 3) Infrared light of 2–5 μm can penetrate YAG:Ce 3+ For fluorescent adhesives and sapphire substrates, the influence of these two semiconductor materials on the infrared emissivity of the LED chip does not need to be considered. Therefore, for GaN-based LED devices using these two semiconductor materials for flip-chip packaging, the chip temperature of the LED device can be directly monitored using this invention, and the measured temperature can be calibrated according to the infrared emissivity of 0.9. For non-GaN-based LED chips using these two semiconductor materials for flip-chip packaging, the temperature of non-GaN-based LED chips can be monitored in real time simply by testing the constant infrared emissivity of the LED chip in the 2-5 μm range using the integrating sphere reflectometer method and calibrating the LED chip temperature measured by the infrared detector. For LED chips using other types of fluorescent adhesives and substrates for flip-chip packaging, as long as the infrared wavelength range that can penetrate the fluorescent adhesive and substrate is determined, the constant infrared emissivity of the LED chip within this infrared wavelength range can be tested using the integrating sphere reflectometer method and the infrared detector temperature calibrated, allowing for real-time monitoring of the LED chip temperature. Attached Figure Description

[0049] The invention will be further described below with reference to the accompanying drawings:

[0050] Figure 1 This is a flowchart illustrating a preferred embodiment of the real-time temperature monitoring method for a flip-chip packaged GaN-based LED chip according to the present invention.

[0051] Figure 2This is a schematic diagram illustrating the fabrication of a GaN-based LED chip on a sapphire substrate according to a preferred embodiment of the present invention.

[0052] Figure 3 This is a schematic diagram of a GaN-based LED chip flip-chip package according to a preferred embodiment of the present invention;

[0053] Figure 4 In a preferred embodiment of the present invention, a GaN-based LED chip is flip-chip packaged and then coated and cured with YAG:Ce on a sapphire substrate. 3+ A schematic diagram of fluorescent adhesive;

[0054] Figure 5 This is a schematic diagram of an integrating sphere used to test the infrared transmittance of a sapphire substrate according to a preferred embodiment of the present invention.

[0055] Figure 6 Infrared transmittance curve of sapphire substrate under infrared light irradiation with wavelengths of 2-20 μm, which is a preferred embodiment of the present invention;

[0056] Figure 7 Indirect characterization of YAG:Ce by an infrared camera according to a preferred embodiment of the present invention 3+ A schematic diagram of the transparent state of fluorescent adhesive;

[0057] Figure 8 This is a schematic diagram illustrating the infrared emissivity test of a GaN-based LED chip using an integrating sphere reflectometer method according to a preferred embodiment of the present invention.

[0058] Figure 9 The infrared emissivity curve of the GaN-based LED device under infrared light irradiation with wavelengths of 2-20 μm is shown in the preferred embodiment of the present invention.

[0059] Figure 10 This is a schematic diagram illustrating the temperature-sensitive parameter K coefficient of a GaN-based LED device according to a preferred embodiment of the present invention.

[0060] Figure 11 Schematic diagrams of temperature testing of GaN-based LED chips using indium antimonide infrared transmission method and transient thermal resistance method with wavelengths of 2-5 μm, respectively, in a preferred embodiment of the present invention.

[0061] Figure 12 This is a superimposed graph of chip temperature curves tested by indium antimonide infrared transmission method and transient thermal resistance method with wavelengths of 2-5 μm under different heating currents, which is a preferred embodiment of the present invention.

[0062] Figure 13 This is a schematic diagram illustrating the temperature test of a GaN-based LED chip connected to an aging circuit using an indium antimonide infrared transmission method with a wavelength of 2–5 μm, according to a preferred embodiment of the present invention. Detailed Implementation

[0063] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the real-time temperature monitoring method for flip-chip packaged GaN-based LED chips proposed in this invention. The advantages and features of this invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise ratios, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0064] This invention solves the problem of existing technologies being unable to monitor the temperature of flip-chip LEDs in real time. The real-time temperature monitoring method for flip-chip packaged GaN-based LED chips of this invention includes: fabricating flip-chip packaged GaN-based LED devices; testing the infrared transmittance of a sapphire substrate using an integrating sphere transmission method; and indirectly characterizing YAG:Ce using an infrared camera. 3+ The infrared transmission state of the fluorescent adhesive; the infrared emissivity of the GaN-based LED chip was tested using the integrating sphere reflectometer method; the temperature of the GaN-based LED chip was tested using the indium antimonide infrared transmission method with specific spectral wavelengths and the transient thermal resistance method, respectively, to verify the temperature measurement accuracy of the indium antimonide infrared transmission method; the GaN-based LED device was connected to an aging circuit, and the temperature of the GaN-based LED chip was monitored in real time using the indium antimonide infrared transmission method with specific spectral wavelengths.

[0065] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0066] Figure 1 This is a flowchart illustrating a preferred embodiment of the real-time temperature monitoring method for flip-chip packaged GaN-based LED chips according to the present invention.

[0067] See Figure 1 The real-time temperature monitoring method for flip-chip packaged GaN-based LED chips according to embodiments of the present invention includes the following steps:

[0068] S1, fabricating flip-chip packaged GaN-based LED devices;

[0069] S11, such as Figure 2 First, N-type and P-type GaN are deposited on a sapphire substrate 112 to obtain a GaN-based LED chip 111;

[0070] S12, as Figure 3 The sapphire substrate 112 containing the GaN-based LED chip 111 is flipped, and the GaN-based LED chip 111 is flip-chip packaged onto the upper surface of the substrate 115 using solder balls 113; the positive electrode 116 and the negative electrode 117 of the electrode leads are installed on the lower surface of the substrate 115.

[0071] S13, as Figure 4 In the Y3Al5O garnet structure 12 (YAG) doped with Ce 3+ Later obtained YAG:Ce 3+Phosphor adhesive 114 is then coated onto the surface of the flip-chip packaged sapphire substrate 112. The YAG:CeO2 is then heated by increasing the temperature of the heating element 118. 3+ Fluorescent adhesive 114 is cured and molded;

[0072] S14. Based on the structure and fabrication process of GaN-based LED devices, the working principles of visible and infrared light within them can be analyzed, providing insights for real-time monitoring of GaN-based LED chip temperature.

[0073] When the GaN-based LED chip 111 is in operation, because the underside of the chip consists of opaque solder balls 113 and a substrate 115, the visible light generated by the chip itself can only pass through the sapphire substrate 112 and YAG:Ce 3+ Phosphor 114 transmits outwards; this visible light passes through the sapphire substrate 112 to reach YAG:Ce 3+ After fluorescent adhesive 114, YAG:Ce 3+ Fluorescent adhesive 114 causes a portion of the visible light to be converted, while the remaining visible light passes directly through YAG:Ce. 3+ Phosphor 114 produces a specific mixed light when two types of visible light are mixed; however, since visible light is not directly related to the temperature of LED chips, it is impossible to reflect the temperature of GaN-based LED chips through these visible lights.

[0074] When the GaN-based LED chip 111 is in operation, the heated chip itself will radiate infrared light; infrared light within a specific wavelength range can completely penetrate the sapphire substrate 112 and YAG:Ce 3+ The fluorescent adhesive 114 is transported outwards, and the YAG:Ce ratio is... 3+ The fluorescent adhesive 114 does not convert infrared light; by collecting and analyzing this infrared light with an infrared detector and combining it with the blackbody radiation law, the temperature of the LED chip can be indirectly tested.

[0075] When GaN-based LED devices are irradiated with infrared light, infrared light within a specific wavelength range can completely penetrate the sapphire substrate 112 and YAG:Ce. 3+ The fluorescent adhesive 114 is reflected by the opaque GaN-based LED chip 111. The intensity of the reflected infrared light is closely related to the infrared emissivity of the LED chip. By determining a constant infrared emissivity of the LED chip, the temperature of the LED chip measured by the infrared detector can be calibrated, thereby improving the accuracy of temperature measurement.

[0076] In summary, to accurately test the temperature of the GaN-based LED chip 111, it is necessary to ensure the stability of the sapphire substrate 112 and the YAG:Ce base under infrared light irradiation within a specific wavelength range. 3+ The fluorescent adhesive 114 has a sufficiently high infrared transmittance, and the GaN-based LED chip 111 also needs to have a constant infrared emissivity.

[0077] S2, Integrating sphere transmission method for testing infrared transmittance of sapphire substrate;

[0078] S21. Since the sapphire substrate has a simple structure and uniform thickness, actively irradiating the sapphire substrate with infrared light of a specific intensity and testing its transmission intensity is the most direct and effective method to obtain the transmittance of the sapphire substrate.

[0079] S22, as Figure 5 A sapphire substrate 112 of uniform thickness is placed at the bottom of an integrating sphere 122, and an infrared generator 121 is used to generate an infrared generator with a wavelength of 2-20 μm and an intensity of I. in Infrared light is emitted and irradiates the sapphire substrate 112. After passing through the sapphire substrate 112, the infrared light undergoes multiple diffuse reflections on the inner surface of the integrating sphere 122, and finally converges into the infrared sensor 123 to obtain the transmission intensity I of the infrared light. out ;

[0080] S23, Calculate the transmission intensity I when infrared light passes through the sapphire substrate 112. out and incident intensity I in ratio This ratio ω represents the infrared transmittance of the sapphire substrate 112;

[0081] Figure 6 Infrared transmittance curve of sapphire substrate under infrared light irradiation with wavelengths of 2-20 μm, which is a preferred embodiment of the present invention;

[0082] S24, as shown Figure 6 Infrared transmittance curves of sapphire substrates under infrared light irradiation with wavelengths of 2–20 μm were plotted.

[0083] When the infrared wavelength is between 8 and 20 μm, the infrared transmittance of the sapphire substrate is 0%, and the sapphire substrate is opaque. Infrared light in the range of 8 to 20 μm is partially reflected on the surface of the sapphire substrate, and partially absorbed by the sapphire substrate, causing the sapphire substrate to heat up.

[0084] When the infrared wavelength drops to 5-8 μm, the infrared transmittance of the sapphire substrate begins to increase, and the sapphire substrate begins to appear translucent. Infrared light in the 5-8 μm range can penetrate the sapphire substrate, while the remaining part is reflected on the surface of the sapphire substrate or absorbed by the sapphire substrate, causing the sapphire substrate to heat up.

[0085] When the infrared wavelength drops to 2–5 μm ( Figure 6In region 124), the transmittance of the sapphire substrate reaches 90% and remains constant, making the sapphire substrate completely transparent; most of the infrared light in the 2-5μm range penetrates the sapphire substrate, and a very small portion is reflected on the surface of the sapphire substrate or absorbed by the sapphire substrate.

[0086] S3. An infrared camera was used to observe the GaN-based LED chip in a heated state under the driving current, indirectly characterizing YAG:Ce. 3+ Infrared transmission state of fluorescent adhesive;

[0087] S31, due to YAG:Ce 3+ The fluorescent adhesive 114 exhibits a hemispherical shape with uneven thickness. If the method in step S2 is used to measure YAG:Ce... 3+ The transmittance of fluorescent adhesive 114 will vary with the YAG:Ce content. 3+ The thickness of fluorescent adhesive 114 fluctuates, therefore YAG:Ce can only be observed indirectly using an infrared camera. 3+ Infrared transmission state of fluorescent adhesive 114;

[0088] S32, such as Figure 7 A T3ster heating current IH 131 is used to connect the positive terminal 116 and the negative terminal 117 of the LED. The 2A heating current IH 131 drives the GaN-based LED chip 111, causing the chip to heat up and maintain a constant temperature. The GaN-based LED chip 111, at its high temperature, can emit more infrared light in a radiative form, resulting in a greater contrast difference compared to other packaged structures and more obvious observation results. During this upward emission of infrared light, it passes sequentially through the sapphire substrate 112 and the YAG:Ce... 3+ The fluorescent adhesive 114 finally reaches the infrared camera 132;

[0089] S33, According to the analysis in step S24, the transmittance of infrared light with wavelengths of 2 to 5 μm in the sapphire substrate 112 is 90%, therefore the sapphire substrate 112 will not block the penetration of infrared light with wavelengths of 2 to 5 μm.

[0090] S34, such as Figure 7 The infrared wavelength range detected by the infrared camera 132 is set to 2–5 μm. The GaN-based LED chip 111 is observed using the infrared camera 132. The infrared camera 132 can directly observe the heated GaN-based LED chip 111, indirectly indicating that the YAG:Ce 3+ Fluorescent adhesive 114 does not hinder the penetration of 2-5μm infrared light. (YAG:Ce) 3+ Fluorescent adhesive 114 is transparent;

[0091] S4. Under infrared light irradiation with wavelengths of 2–20 μm, the infrared emissivity of the GaN-based LED chip was tested using the integrating sphere reflectometer method.

[0092] S41, as Figure 8 An infrared generator 121 at the top of the integrating sphere 122 generates an intensity of L. i(GaN) Infrared light of a specific wavelength is irradiated onto the GaN-based LED device at the bottom of the integrating sphere 112. Part of the infrared light is absorbed, and part is reflected. The reflected infrared light undergoes multiple diffuse reflections on the inner surface of the integrating sphere 122 before being captured by the infrared sensor 123, which outputs the intensity L of the reflected infrared light from the GaN-based LED device. r(GaN) The relevant voltage signal V (GaN) The baffle 142 is to prevent the infrared light generated by the infrared generator 121 from shining directly on the infrared sensor 123, so as to prevent it from affecting the accuracy of the test.

[0093] S42, replace the GaN-based LED device at the bottom of the integrating sphere 122 with a standard reference sample 141 with a reflectivity of 1, using the same wavelength and intensity L. i(ref) The infrared light irradiates the standard reference sample 141, and the output infrared light intensity L reflected by the standard reference sample 141 is the same. r(ref) The relevant voltage signal V (ref) Under the premise that the incident infrared light intensity is the same, i.e., L i(ref) =L i(GaN) The ratio of the voltage signal of the GaN-based LED device measured by the infrared sensor 123 to that of the standard reference sample 141 is equal to the ratio of the reflected infrared light intensity of the two, i.e.

[0094] S43, Reflectivity ρ represents the intensity L of infrared light reflected from the surface of an object. r With incident intensity L i The ratio, that is Due to the different wavelengths of infrared light irradiation, the reflectance ρ of the standard reference sample... (ref) All are 1, that is The intensity L of infrared light reflected from its surface r(ref) Equal to incident intensity L i(ref) L r(ref) =L i(ref) When a GaN-based LED device is opaque, infrared light is only absorbed or reflected, and no transmission occurs; therefore, its absorptivity α is low. (GaN) and reflectivity ρ (GaN) Satisfying relation α (GaN) +ρ (GaN) =1, where the overall reflectivity of GaN-based LED devices is 1. When a GaN-based LED device is in thermal equilibrium, its infrared emissivity ε(GaN) Equal to absorption rate α (GaN) Then its infrared emissivity ε (GaN) and reflectivity ρ (GaN) Satisfying the relation ε (GaN) +ρ (GaN) =1; Substitute L r(ref) =L i(ref) and L i(ref) =L i(GaN) The overall infrared emissivity of GaN-based LED devices

[0095] S44, according to step S43 The calculation and processing steps S41 and S42 involve the voltage signal V measured by the infrared sensor 123. (GaN) and V (ref) The overall infrared emissivity of GaN-based LED devices under infrared light irradiation at a specific wavelength was obtained; the parameters of the infrared generator 121 were changed to generate an intensity of L. i(GaN) GaN-based LED devices and standard reference sample 141 were sequentially irradiated with infrared light with wavelengths of 2–20 μm to obtain the overall infrared emissivity curves of GaN-based LED devices under infrared light irradiation with wavelengths of 2–20 μm.

[0096] Figure 9 The infrared emissivity curve of the GaN-based LED device under infrared light irradiation with wavelengths of 2-20 μm is shown in the preferred embodiment of the present invention.

[0097] S45, such as Figure 9 Plot the overall infrared emissivity curves of GaN-based LED devices under infrared light irradiation with wavelengths of 2–20 μm;

[0098] Within the infrared wavelength range of 8–20 μm, as the infrared wavelength decreases, the overall infrared emission of GaN-based LED devices first decreases and then increases, reaching a minimum at a wavelength of 15 μm; according to step S24 Figure 6 Analysis showed that the sapphire substrate had 0% infrared light transmittance in this infrared wavelength range, indicating it was opaque. Even though all infrared light could pass through YAG:Ce... 3+ Phosphor adhesive is also completely blocked by the sapphire substrate and cannot reach the GaN-based LED chip; the overall infrared emissivity of 145 GaN-based LED devices in the 8-20µm range is YAG:Ce 3+ The infrared emissivity of the phosphor or sapphire substrate, not the infrared emissivity of the GaN-based LED chip;

[0099] Within the infrared wavelength range of 5–8 μm, the overall infrared emissivity of the GaN-based LED device is a constant value of 0.9; according to step S24 Figure 6Analysis showed that as the infrared wavelength decreased, the transmittance of the sapphire substrate changed significantly, increasing from 0% to 90%, and varying significantly between opaque, semi-transparent, and fully transparent states; during infrared light transmission, even if all infrared light could pass through YAG:Ce... 3+ Phosphor adhesive can also be partially blocked by the sapphire substrate, preventing it from fully reaching the GaN-based LED chip; the overall infrared emissivity of 144 GaN-based LED devices in the 5–8 μm range is YAG:Ce 3+ The combined infrared emissivity of the phosphor, sapphire substrate, and GaN-based LED chip cannot be used as the infrared emissivity of the LED chip itself, as the overall infrared emissivity of the LED device within this range is not applicable.

[0100] Within the infrared wavelength range of 2–5 μm, the overall infrared emissivity of GaN-based LED devices remains constant at 0.9; according to step S24 Figure 6 Analysis showed that the transmittance of the sapphire substrate within this range was a constant 90%, making it almost completely transparent compared to the opaque GaN-based LED chip. Step S3, using an infrared camera, revealed the heating GaN-based LED chip, indicating that infrared light in the 2–5 μm range can completely penetrate YAG:Ce. 3+ Phosphor adhesive; the overall infrared emissivity of the GaN-based LED device in this region does not include YAG:Ce. 3+ The infrared emissivity of phosphor and sapphire substrates only includes the infrared emissivity of GaN-based LED chips; therefore, the overall infrared emissivity of GaN-based LED devices in the wavelength range of 2-5µm can be used as the infrared emissivity of GaN-based LED chips.

[0101] S46, such as Figure 8 The GaN-based LED device and the standard reference sample 141 were heated to different temperatures using heating tube 118. Steps S41 to S44 were repeated, and the overall infrared emissivity curves of the GaN-based LED device at different temperatures were tested and plotted. It was found that the curves were basically consistent with those in step S45, indicating that temperature changes do not affect the infrared emissivity of the GaN-based LED chip.

[0102] In summary, only infrared light within the wavelength range of 2–5 μm can be used to monitor YAG:Ce by infrared sensor 123. 3+ Temperature distribution of GaN-based LED chip 111 under phosphor 114 and sapphire substrate 112, and the infrared emissivity of GaN-based LED chip 111 is constant at 0.9 within this wavelength range;

[0103] S5, testing the temperature-sensitive parameter K coefficient of GaN-based LED devices;

[0104] S51, such as Figure 10A GaN-based LED device was connected to a transient thermal resistance test circuit. The positive terminal 116 and negative terminal 117 of the GaN-based LED device were connected to a VF voltage sensor 154, an IM test current 153, and an IH heating current 131, respectively. Since the actual directions of the VF voltage sensor 154, the IM test current 153, and the IH heating current 131 are the same, all three are displayed as positive (+). A T3ster device was used to apply only a 5mA IM test current 153 to the GaN-based LED device, without applying the IH heating current 131. The VF voltage sensor 154 was used to monitor the change in the PN junction voltage drop across the positive terminal 116 and the negative terminal 117 of the GaN-based LED device in real time.

[0105] S52, such as Figure 10 The entire GaN-based LED device was placed in a constant-temperature oil bath 151 and kept there for a certain period of time until the temperature of the entire GaN-based LED device became uniform, with the temperature of the GaN-based LED chip 111 equal to the temperature of the constant-temperature oil bath 152. The temperature of the constant-temperature oil bath 152 was adjusted to gradually increase the temperature of the GaN-based LED chip 111 from 25°C to 140°C at a heating rate of 5°C / minute. The PN junction voltage drop-temperature curve of the GaN-based LED chip 111 was recorded in real time to determine its temperature-sensitive parameter K coefficient. After the test, the oil on the surface of the device was cleaned.

[0106] S6, the temperature of GaN-based LED chips was tested using indium antimonide infrared transmission method and transient thermal resistance method with specific spectral wavelengths;

[0107] S61, because indium antimonide is very sensitive to infrared light with wavelengths of 2 to 5 μm, choosing an indium antimonide infrared sensor can improve the chip's temperature measurement accuracy and resolution;

[0108] S62, such as Figure 11 The GaN-based LED device is connected to the transient thermal resistance test circuit, and the indium antimonide infrared sensor 161 is positioned directly in front of the GaN-based LED device. A 2A IH heating current 131 is used to drive the device to raise the temperature of the GaN-based LED chip 111. After the chip PN junction voltage drop measured by the VF voltage sensor 154 of the T3ster device stabilizes, the chip temperature is monitored in real time using the indium antimonide infrared sensor 161 with a wavelength of 2-5μm. The chip temperature Tr1 is obtained by calibrating according to the constant infrared emissivity of 0.9 measured in the 2-5μm wavelength range in step S4.

[0109] S63, such as Figure 11The 2A IH heating current 131 is quickly switched to the 5mA IM test current 153. At the same time, the VF voltage sensor 154 is used to test the PN junction voltage drop change curve of the GaN-based LED chip 111. The transient thermal resistance method GaN-based LED chip temperature Tj1 is obtained through the K coefficient in step S5.

[0110] S7, superimpose the chip temperature curves tested by the indium antimonide infrared transmission method and the transient thermal resistance method at specific spectral wavelengths under different heating currents to verify the accuracy of the indium antimonide infrared transmission method for testing the temperature of GaN-based LED chips;

[0111] S71, using IH heating currents 131 of 4A, 6A and 8A respectively to drive GaN-based LED devices to raise the temperature of LED chip 111, repeating steps S61 to S63 to determine the indium antimonide infrared transmission chip temperature (Tr2, Tr3, Tr4) and transient thermal resistance chip temperature (Tj2, Tj3, Tj4) under the action of heating currents 131 of 4A, 6A and 8A respectively;

[0112] S72, based on Tr1, Tr2, Tr3 and Tr4 of steps S62 and S71, plot the temperature curve Tr of the indium antimonide infrared transmission method chip under different heating currents; based on Tj1, Tj2, Tj3 and Tj4 of steps S63 and S71, plot the temperature curve Tj of the transient thermal resistance method chip under different heating currents.

[0113] Figure 12 This is a superimposed graph of chip temperature curves tested by indium antimonide infrared transmission method and transient thermal resistance method with wavelengths of 2-5 μm under different heating currents, which is a preferred embodiment of the present invention.

[0114] S73, such as Figure 12 By superimposing the chip temperature curve Tr172 of the indium antimonide infrared transmission method and the chip temperature curve Tj171 of the transient thermal resistance method in step S72, it was found that the linear correlation and overlap of the two curves were high, indicating that the chip temperature tested by the indium antimonide infrared transmission method can accurately reflect the chip temperature tested by the transient thermal resistance method, and the temperature measurement result is not affected by the driving heating current.

[0115] S8, GaN-based LED devices are connected to an aging circuit, and the temperature of GaN-based LED chips is monitored in real time by indium antimonide infrared transmission method.

[0116] like Figure 13The positive terminal 116 and negative terminal 117 of the GaN-based LED device are connected to the aging circuit 181. An indium antimonide infrared sensor 161 with a wavelength of 2-5 μm is used to monitor the temperature of the GaN-based LED chip 111 in real time. The infrared emissivity of 0.9 measured in the 2-5 μm range by the integrating sphere reflectometer method in step S4 is used to calibrate the temperature of the GaN-based LED chip 111 monitored by the indium antimonide infrared sensor 161 in real time.

[0117] For using YAG:Ce 3+ For non-GaN-based LED chips that are flip-chip packaged with phosphor and sapphire substrate, the temperature of the non-GaN-based LED chip can be monitored in real time by testing the constant infrared emissivity of the LED chip in the range of 2 to 5 μm using the integrating sphere reflectometer method in step S4 and calibrating the LED chip temperature measured by the infrared detector.

[0118] For LED chips that use other types of phosphors and substrates for flip-chip packaging, as long as the range of infrared wavelengths that can penetrate the phosphors and substrates is determined through steps S2 and S3, the constant infrared emissivity of the LED chip can be tested and the infrared detector temperature calibrated within this range using the integrating sphere reflectometer method in step S4, and the LED chip temperature can also be monitored in real time.

[0119] The contents not described in detail in this specification are prior art known to those skilled in the art. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for real-time temperature monitoring of flip-chip GaN-based LED chips, characterized in that, Includes the following steps: S1. Fabrication of flip-chip packaged GaN-based LED devices; S2. Integrating sphere transmission method for testing infrared transmittance of sapphire substrate; S3, Indirect characterization of YAG:Ce by infrared camera 3+ Infrared transmission state of fluorescent adhesive; S4. Integrating sphere reflectometer method for testing the infrared emissivity of GaN-based LED chips; S5. The temperature of GaN-based LED chips was tested using the indium antimonide infrared transmission method and the transient thermal resistance method with wavelengths of 2~5μm, respectively, to verify the accuracy of the temperature measurement by the indium antimonide infrared transmission method. S6. GaN-based LED devices are connected to an aging circuit, and the temperature of the GaN-based LED chip is monitored in real time using indium antimonide infrared transmission method with a wavelength of 2~5μm. S1 includes: S11. Deposit N-type and P-type GaN on a sapphire substrate to obtain a GaN-based LED chip; S12. The GaN-based LED chip obtained in step S11 is flip-chip packaged onto the upper surface of the substrate using solder balls, and electrode leads are installed on the lower surface of the substrate. S13, in Y3Al5O 12 Medium-doped Ce 3+ Later obtained YAG:Ce 3+ Fluorescent adhesive is applied to the surface of a flip-chip sapphire substrate and cured by heating; wherein Y3Al5O 12 It is abbreviated as YAG.

2. The method for real-time temperature monitoring of a flip-chip GaN-based LED chip as described in claim 1, characterized in that, Step S2 includes: S21, Using an infrared generator to produce wavelengths of 2~20μm and intensity Infrared light is used to illuminate a sapphire substrate with uniform thickness. S22. After infrared light passes through the sapphire substrate, it undergoes multiple diffuse reflections on the inner surface of the integrating sphere, and finally converges into the infrared sensor to obtain the transmission intensity of the infrared light. ; S23. Calculate the transmission intensity I when infrared light passes through a sapphire substrate. out and incident intensity I in ratio The ratio That is, the infrared transmittance of the sapphire substrate; S24. Plot the infrared transmittance curve of the sapphire substrate under infrared light irradiation with wavelengths of 2~20μm. In the wavelength range of 5~20μm, the infrared light transmittance cannot reach 90%. When the infrared light wavelength drops to 2~5μm, most of the infrared light penetrates the sapphire substrate, the transmittance reaches 90% and remains constant, and the sapphire substrate appears completely transparent.

3. The method for real-time temperature monitoring of a flip-chip GaN-based LED chip as described in claim 2, characterized in that, Step S3 includes: S31. A heating current IH is used to drive the GaN-based LED chip, causing the chip to heat up to a certain temperature and maintain a constant temperature. S32. By setting the infrared wavelength range detected by the infrared camera to 2~5μm, the infrared camera can directly observe the heated GaN-based LED chip, indirectly indicating that YAG:Ce 3+ Fluorescent adhesive does not impede the penetration of 2~5μm infrared light, YAG:Ce 3+ The fluorescent adhesive is transparent.

4. The method for real-time temperature monitoring of a flip-chip GaN-based LED chip as described in claim 1, characterized in that, Step S4 includes: S41, Using an infrared generator to produce an intensity of When infrared light with a wavelength of 2~20um is irradiated onto the GaN-based LED device at the bottom of the integrating sphere, part of the infrared light is absorbed and part is reflected. S42. The reflected infrared light undergoes multiple diffuse reflections on the inner surface of the integrating sphere and is eventually captured by the infrared sensor, outputting the intensity of the infrared light reflected by the GaN-based LED device. Related voltage signals ; S43. Replace the GaN-based LED device with a standard reference sample with a reflectivity of 1, using the same wavelength and intensity. The standard reference sample is illuminated with infrared light, and the output is compared with the infrared light intensity reflected by the standard reference sample. Related voltage signals ; S44. Under the premise that the incident infrared light intensity is the same, that is The ratio of the voltage signal of the GaN-based LED device measured by the infrared sensor to that of the standard reference sample is equal to the ratio of the reflected infrared light intensity of the two, i.e. Since the reflectivity of the standard reference sample is 1, the intensity of infrared light reflected from its surface is... Equal to incident intensity ; S45. The formula for calculating the overall infrared emissivity of GaN-based LED devices is derived. ; Calculate the processed voltage signal according to the infrared emissivity formula. and The overall infrared emissivity of GaN-based LED devices under infrared light irradiation with wavelengths of 2~20µm was obtained. S46. Change the parameters of the infrared generator to produce an intensity of GaN-based LED devices were sequentially irradiated with infrared light of wavelengths from 2 to 20 μm to obtain the overall infrared emissivity curves of the GaN-based LED devices under 2 to 20 μm infrared light irradiation. In this curve, only the overall infrared emissivity of the GaN-based LED devices in the range of 2 to 5 μm can be used as the infrared emissivity of the GaN-based LED chip. The infrared emissivity is a constant value of 0.9 and is not affected by the ambient temperature.

5. The method for real-time temperature monitoring of a flip-chip GaN-based LED chip as described in claim 4, characterized in that, Step S5 includes: S51. Test the temperature-sensitive parameter K coefficient of GaN-based LED devices; S52. Connect the GaN-based LED device to the transient thermal resistance test circuit. Use the IH heating current to drive the device to raise the temperature of the GaN-based LED chip. After the voltage drop of the chip PN junction measured by the VF voltage sensor stabilizes, use an indium antimonide infrared sensor with a wavelength of 2~5μm to monitor the chip temperature in real time. Based on the constant infrared emissivity of 0.9, obtain the calibrated temperature of the GaN-based LED chip by indium antimonide infrared transmission method. After testing the chip temperature using the S53 indium antimonide infrared transmission method, the IH heating current is quickly switched to the IM test current. At the same time, the VF voltage sensor is used to test the PN junction voltage drop change curve of the GaN-based LED chip. The transient thermal resistance method for GaN-based LED chip temperature is obtained through the K coefficient. S54. LED devices were driven using different heating currents IH, and the chip temperature of indium antimonide was tested using infrared transmission method. Where i = 1, 2, ..., N, and N is the heating current and the transient thermal resistance chip temperature. i = 1, 2, ---, N, where N is the heating current quantity; S55. Plot the temperature curves of the indium antimonide infrared transmission chip under different heating currents. Temperature profile of the chip using transient thermal resistance method ; S56. The two curves obtained in step S55 are superimposed, and it is found that the linear correlation and overlap of the two curves are both high. This indicates that the chip temperature tested by the indium antimonide infrared transmission method can accurately reflect the chip temperature tested by the transient thermal resistance method, and the temperature measurement result is not affected by the driving heating current.

6. The method for real-time temperature monitoring of a flip-chip GaN-based LED chip as described in claim 5, characterized in that, Step S51 includes: GaN-based LED devices connected to transient thermal resistance testing circuits are placed in a constant temperature oil bath. The oil temperature is adjusted to raise the chip temperature. The PN junction voltage drop-temperature curve of the chip is recorded in real time to determine its temperature sensitivity parameter K coefficient.

7. The method for real-time temperature monitoring of a flip-chip GaN-based LED chip as described in claim 5, characterized in that, Step S6 includes: The GaN-based LED device leads were connected to an aging circuit. An indium antimonide infrared sensor with a wavelength of 2-5 μm was used to monitor the temperature of the GaN-based LED chip in real time. The infrared emissivity of 0.9 measured in the 2-5 μm range was used to calibrate the temperature of the GaN-based LED chip monitored by the indium antimonide infrared sensor in real time.

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