A method for calculating the junction temperature of high-temperature aged LED chips using the temperature of fluorescent glue

Abstract

The embodiment of the present invention provides a method for calculating the junction temperature of a high-temperature aged LED chip using fluorescent glue temperature, including the following steps: calibrating the LED fluorescent glue temperature tested by infrared method using the LED fluorescent glue temperature tested by thermocouple to determine the calibration P coefficient; determining the temperature sensitive parameter K coefficient of the LED chip; re-measuring the fluorescent glue temperature using infrared method after calibration of thermocouple P coefficient, and testing the chip junction temperature using transient thermal resistance method; changing the constant temperature furnace temperature alone to determine its influence on the calibration infrared method fluorescent glue temperature-transient thermal resistance method chip junction temperature curve; changing the heating current alone to determine its influence on the calibration infrared method fluorescent glue temperature-transient thermal resistance method chip junction temperature curve; connecting the LED to the aging circuit, testing the fluorescent glue temperature using the calibration infrared method, and calculating the LED chip junction temperature in combination with the fluorescent glue temperature-chip junction temperature curve. The present invention does not need to test the fluorescent glue emissivity, which solves the problem that the traditional method cannot quickly and accurately measure the junction temperature of a high-temperature aged LED chip.

Description

Technical Field

[0001] The invention relates to a detection technology in the field of LED devices, and in particular to a method for rapidly and accurately calculating the junction temperature of a high-temperature aged LED chip by using the temperature of fluorescent glue. Background Art

[0002] LED devices are widely used in aerospace products due to their low power consumption, high brightness and long life. However, during the use of aerospace products, LED devices not only have to experience harsh high temperature environments, but their own high power output will also generate additional heat, causing the LED junction temperature to rise significantly. When the junction temperature is too high, the heat generated will accumulate at the solder joints and cause cracks and oxidation, which will significantly reduce the luminous efficiency and service life of the LED diode. In order to improve the reliability of LED devices in high temperature environments, it is necessary to accurately and quickly measure the junction temperature of LED devices, determine the safe operating temperature range of LED devices, and shut down the LED devices in time before the junction temperature of the LED devices reaches the maximum critical value, thereby extending the service life of the LED. At present, the thermocouple method, infrared method and thermal resistance method are mainly used to characterize the chip junction temperature of LED devices:

[0003] (1) The thermocouple method is a contact temperature test method. During the test, it is necessary to make direct contact with the test point to accurately test the temperature. It is often used to test the temperature of a specific position on the LED surface. Each thermocouple can only test the temperature of one position, and the thermocouple wiring is relatively messy. If multiple thermocouples are placed at the same time, the wiring needs to be marked and fixed separately, but the intertwined wiring will affect the electrical parameters and safety of the circuit board where the LED device to be tested is located, making it impossible to quickly measure each temperature point. In addition, if a thermocouple is used to measure the junction temperature of the LED chip, the fluorescent glue on the surface of the LED must be destroyed so that the thermocouple can be in direct contact with the LED chip before the test can be completed. This cannot meet the requirements of non-destructive testing of the junction temperature of the LED chip. Even if the fluorescent glue is destroyed, this contact temperature measurement method will damage the fragile and delicate surface of the LED chip, and even cause the LED chip to fail, such as open circuit or short circuit.

[0004] (2) The infrared method is a non-contact temperature test method. It mainly uses the infrared spectrum generated when the LED device is heated to calibrate the temperature distribution on the surface of the LED device, and the emissivity of the heating object must be considered during the test. However, since the surface of the LED chip is often covered with a thick fluorescent glue, the infrared method actually tests the temperature of the fluorescent glue on the surface of the LED. This temperature is significantly lower than the chip junction temperature inside the LED device, so the infrared method alone cannot directly obtain the LED chip junction temperature.

[0005] (3) The thermal resistance method is also a non-contact temperature test method. This method mainly calculates the chip junction temperature of the LED device indirectly by characterizing the temperature-sensitive electrical parameters of the LED device. In order to accurately test the junction temperature, the thermal resistance method requires that the device has an independent lead-out terminal, and the lead-out terminal has temperature-sensitive parameter characteristics. However, during high-temperature aging or high-temperature use, the lead-out terminal of the LED device fixed on the circuit board is connected to other devices on the circuit board. The electrical parameters of other devices will significantly affect the determination of the chip junction temperature of the LED device. In order to avoid this influence, the LED must be removed from the circuit board and connected to a complex thermal resistance test circuit and equipment to complete the chip junction temperature test. The operation process is complicated, the test process is not safe, the circuit connection reliability is not high, and the test cost is high. Even if the LED can be removed and connected to the transient test circuit, there is a significant difference between the obtained chip junction temperature and the junction temperature when it is not removed, and it is impossible to quickly test the chip junction temperature of multiple LED devices. In addition, if the LED has been fixed on the circuit board by reflow soldering, the LED cannot be removed at all, resulting in the inability to use the thermal resistance method to test the chip junction temperature.

[0006] In summary, neither the thermocouple method nor the infrared test method can accurately test the chip junction temperature inside the LED device, and the thermal resistance method cannot quickly test the LED chip junction temperature in a high temperature environment. Therefore, a new test method is urgently needed to quickly and accurately test the LED chip junction temperature. Summary of the invention

[0007] In view of the deficiency that the prior art cannot quickly and accurately test the junction temperature of a high-temperature aged LED chip, the present invention proposes a method for quickly and accurately calculating the junction temperature of a high-temperature aged LED chip using fluorescent glue temperature: first, a constant temperature furnace is used to heat the LED device, and the LED fluorescent glue temperature is tested simultaneously by a contact thermocouple method and a non-contact infrared method, and the infrared fluorescent glue temperature is calibrated by the thermocouple method fluorescent glue temperature to determine the calibration P coefficient; then, the LED device is connected to a transient test circuit, and after determining the temperature sensitive parameter K coefficient of the chip PN junction, the fluorescent glue temperature is tested by a calibrated infrared method, and the chip junction temperature is tested by a transient thermal resistance method; the temperature of the constant temperature furnace is changed alone, and it is found that the calibrated infrared method fluorescent glue temperature and the transient thermal resistance method chip junction temperature always show a linear relationship; the heating current of the transient thermal resistance method is changed alone, and the linear relationship between the calibrated infrared method fluorescent glue temperature and the transient thermal resistance method chip junction temperature remains almost unchanged; finally, the LED device is connected to a high-temperature aging test circuit, and the fluorescent glue temperature is tested by a calibrated infrared method, and the LED chip junction temperature is accurately calculated in combination with the linear relationship between the fluorescent glue temperature and the chip junction temperature.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for quickly and accurately calculating the junction temperature of a high-temperature aged LED chip using the temperature of a fluorescent glue, characterized by comprising the following steps:

[0010] Step S10, using a constant temperature furnace to heat up the LED device, calibrating the temperature of the LED fluorescent glue tested by the infrared method with the temperature of the LED fluorescent glue tested by the thermocouple, and determining the calibration P coefficient;

[0011] Step S20, after the LED device is connected to the transient thermal resistance test circuit, the LED device is placed in the oil tank to test the temperature sensitive parameter K coefficient of the LED chip PN junction;

[0012] Step S30, the LED device is put back into the constant temperature furnace, the temperature of the fluorescent glue is re-measured by the infrared test method after the thermocouple P coefficient is calibrated, and the chip junction temperature is tested by the transient thermal resistance method;

[0013] Step S40, changing the temperature of the constant temperature furnace alone, obtaining the curves of calibrating the infrared method fluorescent glue temperature and the transient thermal resistance method chip junction temperature, and determining the influence of the constant temperature furnace temperature on the curves;

[0014] Step S50, changing the heating current of the transient thermal resistance method alone, superimposing the infrared method fluorescent glue temperature and transient thermal resistance method chip junction temperature curves calibrated under different heating currents, and determining the influence of the heating current on the curve;

[0015] Step S60, connecting the LED device to the high temperature aging test circuit, using the calibrated infrared method to test the temperature of the fluorescent glue, and combining the relationship curve between the fluorescent glue temperature and the chip junction temperature under the maximum heating current to calculate the junction temperature of the LED chip.

[0016] Further, the step S10 includes:

[0017] Step S101, using a heating current to drive the LED device to make it energized and emit light, and analyzing the radiation spectrum distribution of the LED device by a spectroradiometer, and finding that the infrared spectrum of the LED device is negligible;

[0018] Step S102, placing the entire LED device and the thermocouple in a constant temperature heating furnace containing an infrared transparent glass plate, the thermocouple is in direct contact with the fluorescent glue of the LED device, and a temperature point on the surface of the LED fluorescent glue is obtained through a thermocouple instrument panel as the fluorescent glue temperature measured by the thermocouple method;

[0019] Step S103, placing an infrared detector directly above a constant temperature heating furnace including an infrared transparent glass plate, so that the infrared detector can obtain the energy radiated by the LED fluorescent glue through the infrared transparent glass plate, and determine the surface temperature of the fluorescent glue as the uncalibrated fluorescent glue temperature measured by the infrared method;

[0020] Step S104, setting the temperature of the constant temperature heating furnace to adjust the temperature of the LED device, and keeping the temperature of the constant temperature heating furnace constant at multiple temperature points when the LED device is not powered on, and recording the fluorescent glue temperature displayed by the thermocouple instrument panel and the uncalibrated fluorescent glue temperature measured by the infrared detector;

[0021] Step S105, plotting the temperature curves of the contact thermocouple fluorescent glue and the non-contact infrared fluorescent glue, and finding that the curves present a linear relationship, and determining the calibration ratio P coefficient.

[0022] Further, the step S20 includes:

[0023] Step S201, connect the LED device to the transient thermal resistance test circuit, connect the LED positive lead end to the voltage sensor, the test current, and the positive electrode of the heating current, respectively, and connect the LED negative lead end to the voltage sensor, the test current, and the negative electrode of the heating current, respectively; use the T3ster device to load only the test current on the LED device, and use the voltage sensor to monitor the PN junction voltage drop change of the LED device in real time;

[0024] Step S202, placing the entire LED device into an oil tank, adjusting the temperature of the constant temperature oil to increase the PN junction temperature of the LED device, and recording the PN junction voltage drop-junction temperature curve of the LED device in real time to determine its temperature sensitive parameter K coefficient.

[0025] Further, the step S30 includes:

[0026] Step S301, placing the LED device connected to the transient thermal resistance test circuit back into a constant temperature heating furnace containing an infrared transparent glass plate, so that the furnace temperature remains constant;

[0027] Step S302, using a 0.5A heating current to drive the LED device to increase the junction temperature, after the PN junction voltage drop measured by the T3ster device voltage sensor is stable, using an infrared detector to test the temperature of the fluorescent glue through the infrared transparent glass plate, and through the P coefficient calibration of step S10, obtain the LED fluorescent glue temperature y1 measured by the calibrated infrared method;

[0028] Step S303, the T3ster heating current is quickly switched to the test current, and a voltage sensor is used to monitor the PN junction voltage drop curve of the LED device in real time, and the junction temperature j1 of the LED chip under the action of the 0.5A heating current is obtained through the K coefficient of step S20.

[0029] Further, the step S40 includes:

[0030] Step S401, keep the furnace temperature at 40, 80 and 100°C respectively, and still use 0.5A heating current to drive the LED device to change the junction temperature of the LED chip; at each temperature point, repeat step S30, use the infrared method calibrated by the thermocouple method to measure the temperature of the LED fluorescent glue (y2, y3, y4), and use the transient thermal resistance method to test the junction temperature of the LED chip (j2, j3, j4);

[0031] In step S402, the calibrated infrared fluorescent glue temperature (y1, y2, y3, y4) under the action of 0.5A heating current and the transient thermal resistance method chip junction temperature (j1, j2, j3, j4) are plotted into curve w1, and it is found that the calibrated infrared fluorescent glue temperature Ty and the transient thermal resistance method chip junction temperature Tj in curve w1 show a linear relationship; through linear fitting, the relationship Ty=k1*Tj+b1 is obtained, indicating that the linear relationship is not affected by the furnace temperature.

[0032] Further, the step S50 includes:

[0033] Step S501, using heating currents of 1A, 2A and 4A to drive the LED device respectively to increase the junction temperature of the LED chip, repeating steps S30 and S40, respectively determining the relationship curves w2, w3 and w4 between the calibration infrared method fluorescent glue temperature and the transient thermal resistance method chip junction temperature under the action of heating currents of 1A, 2A and 4A; it is found that the calibration infrared method fluorescent glue temperature Ty and the transient thermal resistance method chip junction temperature Tj in the curves w2, w3 and w4 also present a linear relationship, and the relationship formulas Ty=k2*Tj+b2, Ty=k3*Tj+b3 and Ty=k4*Tj+b4 can be obtained through linear fitting;

[0034] Step S502, superimpose the relationship curves (w1, w2, w3, w4) between the calibrated infrared fluorescent glue temperature and the transient thermal resistance chip junction temperature obtained under different driving currents (0.5A, 1A, 2A and 4A) to obtain a superposition diagram of the calibrated infrared fluorescent glue temperature and the transient thermal resistance chip junction temperature curves driven by different heating currents; the linear correlation and overlap of w1, w2, w3, and w4 are both high, and the slope correlation and intercept correlation of each curve are calculated, and it is found that they are all less than or equal to 5%, indicating that the relationship curve is not affected by the driving heating current.

[0035] Further, the step S60 includes:

[0036] Step S60, connect the LED device to the high-temperature aging test circuit, use the calibrated infrared method to test the LED fluorescent glue temperature during the high-temperature aging process, and use the P coefficient of step S10 to obtain the calibrated fluorescent glue temperature Ty; combine the relationship curve fitting formula Ty=k4*Tj+b4 under the maximum heating current to quickly and accurately calculate the LED chip junction temperature Tj.

[0037] Compared with the prior art, the beneficial effects of the present invention include:

[0038] 1. Aiming at the error existing in the traditional infrared method for testing the temperature of LED fluorescent glue, the present invention first analyzes the emission spectrum distribution of LED through a spectroradiometer, proving that the energy generated by the infrared spectrum of LED will not affect the temperature of LED fluorescent glue, thus ensuring the feasibility of infrared method for testing the temperature of LED fluorescent glue. Then, the fluorescent glue temperature measured by infrared method is calibrated by the fluorescent glue temperature measured by thermocouple, which not only eliminates the influence of environmental factors on infrared temperature measurement, but also avoids the trouble of testing the emissivity of fluorescent glue, thus ensuring that the calibration infrared method result can truly reflect the temperature of fluorescent glue.

[0039] 2. In order to solve the problem that there is a large difference between the fluorescent glue temperature and the chip junction temperature, the present invention obtains the fluorescent glue temperature by calibrating the infrared method and obtains the LED chip temperature by the thermal resistance method, thereby determining the linear correspondence between the two. Using this relationship, the LED chip junction temperature is inferred from the fluorescent glue temperature, thus realizing the quantitative calculation of the LED chip junction temperature during the aging process. Since this relationship is not affected by the heating current and the ambient temperature, and is only related to the LED packaging structure and materials, the present invention can be used for the rapid detection of the junction temperature of the same type of LED chips.

[0040] 3. The traditional thermal resistance test method can only test one LED device at a time, and requires complex circuit connections for the LED device. The method of indirectly calculating the chip junction temperature by calibrating the infrared LED fluorescent glue temperature can not only avoid repeated disassembly of multiple LED devices during the high-temperature aging process of LED devices, but also avoid complex circuit connections for LED devices, and can quickly calculate the chip junction temperature of multiple LED devices, significantly improving the test efficiency of the LED chip junction temperature, and solving the problem that the traditional method cannot quickly and accurately determine the LED chip junction temperature.

[0041] 4. In view of the problem of the numerous test steps of the traditional thermal resistance method, the present invention only needs to use the thermal resistance method to test the chip junction temperature when determining the relationship between the fluorescent glue temperature and the chip junction temperature, and no thermal resistance test is required during the LED aging process, which greatly simplifies the chip junction temperature test process. In addition, the present invention does not need to install contact thermocouples on LED devices during the aging process, avoiding the influence of thermocouples on the aging circuit and improving the test safety.

[0042] 5. For LED devices that have been welded and fixed on a stand-alone circuit board and cannot be disassembled, the present invention can calculate the chip junction temperature of the LED device during the aging process by simply determining the corresponding relationship between the fluorescent glue temperature and the chip junction temperature before welding and fixing. The chip junction temperature obtained by this indirect calculation method is not affected by the circuit and electrical structure of the stand-alone circuit board, and the test error is smaller. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0044] Figure 1 It is a schematic diagram of the process of the method of the present invention;

[0045] Figure 2 It is a schematic diagram of the radiation spectrum test of LED devices;

[0046] Figure 3 Schematic diagram of calibrating the temperature of non-contact infrared fluorescent glue by contact thermocouple method after heating LED in constant temperature furnace;

[0047] Figure 4 It is the temperature curve of the fluorescent glue using the contact thermocouple method and the temperature curve of the fluorescent glue using the non-contact infrared method;

[0048] Figure 5 This is a schematic diagram of measuring the temperature sensitive parameter K coefficient of LED using the transient thermal resistance method;

[0049] Figure 6 Schematic diagram for calibrating the infrared method to test the temperature of the fluorescent glue and the transient thermal resistance method to test the junction temperature of the chip;

[0050] Figure 7 The calibrated infrared fluorescent glue temperature and transient thermal resistance chip junction temperature curve w1 measured under 0.5A heating current;

[0051] Figure 8 It is an overlay diagram of the calibrated infrared fluorescent glue temperature and transient thermal resistance chip junction temperature curve driven by different heating currents;

[0052] Fig. 9 This is a schematic diagram of inferring the chip junction temperature based on the temperature of the fluorescent glue during the LED aging process. DETAILED DESCRIPTION

[0053] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the scheme of the present invention is described below in conjunction with the accompanying drawings and specific implementation methods.

[0054] The present invention solves the problem that the prior art cannot quickly and accurately test the junction temperature of a high-temperature aging LED chip: first, a constant temperature furnace is used to heat the LED device, and the LED fluorescent glue temperature is tested simultaneously by a contact thermocouple method and a non-contact infrared method, and the infrared fluorescent glue temperature is calibrated using the thermocouple method fluorescent glue temperature to determine the calibration P coefficient; then, the LED device is connected to a transient test circuit, and the fluorescent glue temperature is tested by a calibrated infrared method, and after the temperature sensitive parameter K coefficient of the chip PN junction is determined, the chip junction temperature is tested by a transient thermal resistance method; the temperature of the constant temperature furnace is changed alone, and it is found that the calibrated infrared method fluorescent glue temperature and the transient thermal resistance method chip junction temperature always present a linear relationship; the heating current of the transient thermal resistance method is changed alone, and the linear relationship between the calibrated infrared method fluorescent glue temperature and the transient thermal resistance method chip junction temperature remains almost unchanged; finally, the LED device is connected to a high-temperature aging test circuit, and the fluorescent glue temperature is tested by a calibrated infrared method, and the LED chip junction temperature is accurately calculated in combination with the linear relationship between the fluorescent glue temperature and the chip junction temperature.

[0055] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0056] Figure 1 The flowchart of the method of the present invention is as follows. The method of the present invention for quickly and accurately calculating the junction temperature of a high-temperature aged LED chip using the temperature of the fluorescent glue comprises the following steps:

[0057] Step S10, using a constant temperature furnace to heat up the LED device, calibrating the temperature of the LED fluorescent glue tested by the infrared method with the temperature of the LED fluorescent glue tested by the thermocouple, and determining the calibration P coefficient;

[0058] Step S20, after the LED device is connected to the transient thermal resistance test circuit, the LED device is placed in the oil tank to test the temperature sensitive parameter K coefficient of the LED chip PN junction;

[0059] Step S30, the LED device is put back into the constant temperature furnace, the temperature of the fluorescent glue is re-measured by the infrared test method after the thermocouple P coefficient is calibrated, and the chip junction temperature is tested by the transient thermal resistance method;

[0060] Step S40, changing the temperature of the constant temperature furnace alone, obtaining the curves of calibrating the infrared method fluorescent glue temperature and the transient thermal resistance method chip junction temperature, and determining the influence of the constant temperature furnace temperature on the curves;

[0061] Step S50, changing the heating current of the transient thermal resistance method alone, superimposing the infrared method fluorescent glue temperature and transient thermal resistance method chip junction temperature curves calibrated under different heating currents, and determining the influence of the heating current on the curve;

[0062] Step S60, connecting the LED device to the high temperature aging test circuit, using the calibrated infrared method to test the temperature of the fluorescent glue, and combining the relationship curve between the fluorescent glue temperature and the chip junction temperature under the maximum heating current to calculate the junction temperature of the LED chip.

[0063] (1) Step S10 includes:

[0064] Figure 2 The schematic diagram of the radiation spectrum test of the LED device is shown, wherein 101 is a spectrum radiator, 102 is an LED device, and 103 is a heating current.

[0065] In step S101, a heating current 103 is used to drive the LED device 102 to emit light. The radiation spectrum distribution of the LED device 102 is analyzed by the spectroradiometer 101, and it is found that the infrared spectrum of the LED device 102 is negligible, indicating that the infrared method is not affected by the emission spectrum of the LED device 102 when testing the temperature of the LED fluorescent glue.

[0066] Figure 3 The schematic diagram shows the contact thermocouple method for calibrating the temperature of the non-contact infrared fluorescent glue after the constant temperature furnace heats the LED. Among them, 102 is the entire LED device, 111 is the LED chip, 112 is the tin-lead solder, 113 is the metal copper-clad board, 114 is the LED device fluorescent glue, 115 is the LED positive lead terminal, 116 is the LED negative lead terminal, 117 is the contact thermocouple, 118 is the thermocouple instrument panel, 119 is the infrared transparent glass plate sealed on the top of the constant temperature heating furnace, 120 is the infrared detector, and 121 is the constant temperature heating furnace containing the infrared transparent glass plate.

[0067] In step S102, if Figure 3 As shown, the entire LED device 102 and the thermocouple 117 are placed in a constant temperature heating furnace 121 containing an infrared transparent glass plate 119. The thermocouple 117 is in direct contact with the fluorescent glue 114 of the LED device 102, and a temperature point on the surface of the LED fluorescent glue 114 is obtained through the thermocouple instrument panel 118 as the fluorescent glue temperature measured by the thermocouple method. The infrared transparent glass plate 119 in the closed state is sealed with the constant temperature heating furnace 121, so that during the process of the thermocouple 117 testing the temperature of the LED fluorescent glue 114, the air convection effect on the surface of the fluorescent glue 114 is significantly weakened, which helps to improve the accuracy of the thermocouple 117 testing the temperature of the fluorescent glue 114.

[0068] In step S103, Figure 3As shown, the infrared detector 120 is placed directly above the constant temperature heating furnace 121 including the infrared transparent glass plate 119, so that the infrared detector 120 can obtain the energy radiated by the LED fluorescent glue 114 through the infrared transparent glass plate 119 and determine the surface temperature of the fluorescent glue 114. Since the fluorescent glue 114 is not infrared transparent, the infrared detector 120 measures the surface temperature distribution map of the fluorescent glue 114, not the surface temperature distribution map of the LED chip 111 located below the fluorescent glue 114. According to the surface temperature distribution map of the fluorescent glue 114, multiple temperature points are selected at the horizontal position of the surface of the fluorescent glue 114, and their average value is calculated as the uncalibrated fluorescent glue temperature measured by the infrared method.

[0069] In step S104, Figure 3 As shown, the temperature of the constant temperature heating furnace 121 is set to adjust the temperature of the LED device 102. When the LED device 102 is not powered on, the temperature of the constant temperature heating furnace 121 is kept constant at 20, 40, 80, and 100°C, respectively, and the fluorescent glue temperature (a1, a2, a3, and a4) displayed by the thermocouple instrument panel 118 and the uncalibrated fluorescent glue temperature (b1, b2, b3, and b4) measured by the infrared detector 120 are recorded respectively.

[0070] Figure 4 The temperature curves of the fluorescent glue using the contact thermocouple method and the fluorescent glue using the non-contact infrared method are shown.

[0071] In step S105, Figure 4 As shown, the contact thermocouple method fluorescent glue temperature and the non-contact infrared method fluorescent glue temperature curves are plotted, and it is found that the curves show a linear relationship, and their calibration ratio P coefficients are determined. In the present invention, the surface temperature of the fluorescent glue tested by the infrared detector does not take into account the emissivity of the fluorescent glue, and is an uncalibrated fluorescent glue temperature; while the fluorescent glue temperature tested by the thermocouple is not affected by the emissivity of the fluorescent glue, and is closer to the actual value of the fluorescent glue temperature. Therefore, the fluorescent glue temperature tested by the infrared method can be calibrated with the P coefficient through the fluorescent glue temperature tested by the thermocouple, so that the calibrated infrared method fluorescent glue temperature is closer to the actual value.

[0072] (2) Step S20 includes:

[0073] Figure 5 Schematic diagram of measuring the temperature sensitive parameter K coefficient of LED by transient thermal resistance method. 102 is the whole LED device, 115 is the positive lead terminal of LED, 116 is the negative lead terminal of LED, 122 is the oil tank, 123 is the constant temperature heating oil, 130 is the VF voltage sensor of T3ster device, 131 is the IM test current of T3ster device, and 132 is the IH heating current of T3ster device.

[0074] In step S201, Figure 5 As shown, the LED device 102 is connected to the transient thermal resistance test circuit, the LED positive lead 115 is respectively connected to the positive poles of the VF voltage sensor 130, the IM test current 131, and the IH heating current 132, and the LED negative lead 116 is respectively connected to the negative poles of the VF voltage sensor 130, the IM test current 131, and the IH heating current 132. Since the VF voltage sensor 130, the IM test current 131, and the IH heating current 132 have the same actual direction, all three are displayed as positive values ​​(+). The T3ster device is used to load only the 5mA IM test current 131 on the LED device 102, and the IH heating current 132 is not loaded, and the VF voltage sensor 130 is used to monitor the PN junction voltage drop change of the LED device 102 in real time.

[0075] In step S202, if Figure 5 As shown, the entire LED device 102 is placed in the oil tank 122, and the temperature of the oil 123 is equal to the PN junction temperature of the LED device 102. The temperature of the constant temperature oil 123 is adjusted to gradually increase the PN junction temperature of the LED device 102 from 20°C to 150°C, and the heating rate is 5°C / minute. The PN junction voltage drop-junction temperature curve of the LED device 102 is recorded in real time to determine its temperature sensitive parameter K coefficient. After the test, clean the oil on the surface of the LED device 102.

[0076] (3) Step S30 includes:

[0077] Figure 6 The schematic diagram of calibrating the infrared method to test the temperature of the fluorescent glue and the transient thermal resistance method to test the junction temperature of the chip is shown. Among them, 102 is the entire LED device, 111 is the LED chip, 114 is the LED device fluorescent glue, 119 is the infrared transparent glass plate sealed on the top of the constant temperature heating furnace, 120 is the infrared detector, 121 is the constant temperature heating furnace containing the infrared transparent glass plate, 130 is the VF voltage sensor of the T3ster device, 131 is the IM test current of the T3ster device, and 132 is the IH heating current of the T3ster device.

[0078] In step S301, the LED device 102 connected to the transient thermal resistance test circuit is placed back in the constant temperature heating furnace 121 containing the infrared transparent glass plate 119, and the furnace temperature is maintained at 20°C.

[0079] In step S302, a 0.5A IH heating current 132 is used to drive the LED device 102 to increase the junction temperature. After the PN junction voltage drop measured by the VF voltage sensor 130 of the T3ster device is stabilized, the infrared detector 120 is used to test the temperature of the fluorescent glue 114 through the infrared transparent glass plate 119, and the P coefficient is calibrated through step S10 to obtain the LED fluorescent glue temperature y1 measured by the calibrated infrared method.

[0080] In step S303, after the calibration infrared test is completed, the IH heating current 132 of T3ster is quickly switched to the IM test current 131, and the VF voltage sensor 130 is used to monitor the PN junction voltage drop change curve of the LED device 102 in real time. The junction temperature j1 of the LED chip 111 under the action of the IH heating current 132 of 0.5A is obtained through the K coefficient of step S20.

[0081] (4) The step S40 comprises:

[0082] In step S401, the furnace temperature is maintained at 40, 80 and 100°C respectively, and the IH heating current 132 of 0.5A is still used to drive the LED device 102 to change the junction temperature of the LED chip 111. At each temperature point, step S30 is repeated, and the infrared method calibrated by the thermocouple method is used to measure the temperature (y2, y3, y4) of the LED fluorescent glue 114, and the transient thermal resistance method is used to test the junction temperature (j2, j3, j4) of the LED chip 111.

[0083] Figure 7 The calibrated infrared fluorescent glue temperature and transient thermal resistance chip junction temperature curve w1 measured under 0.5A heating current.

[0084] In step S402, the temperature (y1, y2, y3, y4) of the calibrated infrared fluorescent glue 114 under the action of the IH heating current 132 of 0.5A and the junction temperature (j1, j2, j3, j4) of the transient thermal resistance chip 111 are plotted into a curve w1. Figure 7 As shown, it is found that the calibrated infrared method fluorescent glue temperature Ty and the transient thermal resistance method chip junction temperature Tj in curve w1 show a linear relationship. Through linear fitting, the relationship Ty = k1*Tj+b1 can be obtained, indicating that the calibrated infrared method fluorescent glue temperature and the chip junction temperature under the same heating current and different ambient temperatures have a very high correlation, and the linear relationship is not affected by the ambient temperature (furnace temperature); because the heat generated by the LED chip 111 is transferred to the surface of the fluorescent glue 114, it will be affected by the thermal resistance of the fluorescent glue 114, and there is a certain degree of air convection on the surface of the fluorescent glue, so the surface temperature of the LED fluorescent glue 114 is significantly lower than the temperature of the LED chip 111.

[0085] (5) The step S50 includes:

[0086] In step S501, the LED device 102 is driven by the IH heating current 132 of 1A, 2A and 4A respectively to increase the junction temperature of the LED chip 111, and steps S30 and S40 are repeated to determine the calibration infrared method fluorescent glue temperature and transient thermal resistance method chip junction temperature curves w2, w3 and w4 under the action of the heating current of 1A, 2A and 4A respectively. It is found that the calibration infrared method fluorescent glue temperature Ty and the transient thermal resistance method chip junction temperature Tj in the curves w2, w3 and w4 also show a linear relationship, and the relationship Ty=k2*Tj+b2, Ty=k3*Tj+b3 and Ty=k4*Tj+b4 can be obtained through linear fitting.

[0087] Figure 8 The graph shows the overlay of the calibrated infrared fluorescent glue temperature and transient thermal resistance chip junction temperature curves driven by different heating currents.

[0088] In step S502, the calibrated infrared fluorescent glue temperature and transient thermal resistance chip junction temperature curves (w1, w2, w3, w4) obtained under different driving currents (0.5A, 1A, 2A and 4A) are superimposed to obtain a superposition diagram of the calibrated infrared fluorescent glue temperature and transient thermal resistance chip junction temperature curves driven by different heating currents, as shown in FIG. Figure 8 As shown; the linear correlation and overlap of w1, w2, w3, and w4 are all high. The slope correlation (m1, m2, m3, and m4) and intercept correlation (n1, n2, n3, and n4) of each curve are calculated, where m1 = (k1-k2) / k2, m2 = (k1-k3) / k3, m3 = (k1-k4) / k4; n1 = (b1-b2) / b2, n2 = (b1-b3) / b3, n3 = (b1-b4) / b4. It is found that the slope correlation (m1, m2, m3) and intercept correlation (n1, n2, n3) are all less than or equal to 5%, indicating that the fluorescent glue temperature tested by the calibration infrared method under different driving heating currents and the same ambient temperature (furnace temperature) and the chip junction temperature tested by the transient thermal resistance method also have a very high correlation, and the relationship curve is not affected by the driving heating current.

[0089] (6) Step S60 includes:

[0090] Fig. 9 It is a schematic diagram of inferring the chip junction temperature according to the temperature of the fluorescent glue during the LED aging process, wherein 102 is the LED device, 111 is the LED chip, 114 is the LED fluorescent glue, 120 is the infrared detector, and 133 is the aging circuit.

[0091] In step S60, if Fig. 9As shown, for the LED device 102 with the same packaging structure and material, it is connected to the high-temperature aging test circuit 133. During the high-temperature aging process, the temperature of the LED fluorescent glue 114 is tested by the calibrated infrared method, and the calibrated fluorescent glue temperature Ty is obtained by using the P coefficient of step S10. Combined with the relationship curve fitting formula Ty=k4*Tj+b4 under the maximum heating current IH, the junction temperature Tj of the LED chip 111 is calculated quickly and accurately. Since the larger the heating current IH, the higher the junction temperature of the LED chip 111, the more accurate the fitting curve formula obtained, and thus the measured LED chip junction temperature is more accurate. In addition, the maximum fluorescent glue temperature Tymax can be reversely determined by the maximum chip junction temperature Tjmax provided in the LED product manual, and the temperature of the fluorescent glue 114 can be monitored in real time by the calibrated infrared method to prevent the LED chip 111 from being burned due to excessive temperature.

[0092] Obviously, those skilled in the art can make various changes and modifications to the invention without departing from the spirit and scope of the invention. Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of a fluorescent glue, characterized in that: Includes steps: Step S10, using a constant temperature furnace to heat up the LED device, calibrating the temperature of the LED fluorescent glue tested by the infrared method with the temperature of the LED fluorescent glue tested by the thermocouple, and determining the calibration P coefficient; Step S20, after the LED device is connected to the transient thermal resistance test circuit, the LED device is placed in the oil tank to test the temperature sensitive parameter K coefficient of the LED chip PN junction; Step S30, the LED device is put back into the constant temperature furnace, the temperature of the fluorescent glue is re-measured by the infrared test method after the thermocouple P coefficient is calibrated, and the chip junction temperature is tested by the transient thermal resistance method; Step S40, changing the temperature of the constant temperature furnace alone, obtaining the curves of calibrating the infrared method fluorescent glue temperature and the transient thermal resistance method chip junction temperature, and determining the influence of the constant temperature furnace temperature on the curves; Step S50, changing the heating current of the transient thermal resistance method alone, superimposing the infrared method fluorescent glue temperature and transient thermal resistance method chip junction temperature curves calibrated under different heating currents, and determining the influence of the heating current on the curve; Step S60, connecting the LED device to the high temperature aging test circuit, using the calibrated infrared method to test the temperature of the fluorescent glue, and combining the relationship curve between the fluorescent glue temperature and the chip junction temperature under the maximum heating current to calculate the junction temperature of the LED chip.

2. The method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of the fluorescent glue as claimed in claim 1, characterized in that: The step S10 comprises: Step S101, using a heating current to drive the LED device to make it energized and emit light, and analyzing the radiation spectrum distribution of the LED device by a spectroradiometer, and finding that the infrared spectrum of the LED device is negligible; Step S102, placing the entire LED device and the thermocouple in a constant temperature heating furnace containing an infrared transparent glass plate, the thermocouple is in direct contact with the fluorescent glue of the LED device, and a temperature point on the surface of the LED fluorescent glue is obtained through a thermocouple instrument panel as the fluorescent glue temperature measured by the thermocouple method; Step S103, placing an infrared detector directly above a constant temperature heating furnace including an infrared transparent glass plate, so that the infrared detector can obtain the energy radiated by the LED fluorescent glue through the infrared transparent glass plate, and determine the surface temperature of the fluorescent glue as the uncalibrated fluorescent glue temperature measured by the infrared method; Step S104, setting the temperature of the constant temperature heating furnace to adjust the temperature of the LED device, and keeping the temperature of the constant temperature heating furnace constant at multiple temperature points when the LED device is not powered on, and recording the fluorescent glue temperature displayed by the thermocouple instrument panel and the uncalibrated fluorescent glue temperature measured by the infrared detector; Step S105, plotting the temperature curves of the contact thermocouple fluorescent glue and the non-contact infrared fluorescent glue, and finding that the curves present a linear relationship, and determining the calibration ratio P coefficient.

3. The method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of fluorescent glue as claimed in claim 2, characterized in that: The step S20 comprises: Step S201, connect the LED device to the transient thermal resistance test circuit, the LED positive lead end is connected to the positive pole of the voltage sensor, test current, and heating current respectively, and the LED negative lead end is connected to the negative pole of the voltage sensor, test current, and heating current respectively; use the T3ster device to only load the test current on the LED device, and use the voltage sensor to monitor the PN junction voltage drop change of the LED device in real time.

4. The method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of fluorescent glue as claimed in claim 3, characterized in that: The step S201 includes: Step S202, placing the entire LED device into an oil tank, adjusting the temperature of the constant temperature oil to increase the PN junction temperature of the LED device, and recording the PN junction voltage drop-junction temperature curve of the LED device in real time to determine its temperature sensitive parameter K coefficient.

5. The method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of fluorescent glue as claimed in claim 4, characterized in that: The step S30 comprises: Step S301, placing the LED device connected to the transient thermal resistance test circuit back into a constant temperature heating furnace containing an infrared transparent glass plate, so that the furnace temperature remains constant; Step S302, using a 0.5A heating current to drive the LED device to increase the junction temperature, after the PN junction voltage drop measured by the T3ster device voltage sensor is stable, using an infrared detector to test the temperature of the fluorescent glue through the infrared transparent glass plate, and through the P coefficient calibration of step S10, obtain the LED fluorescent glue temperature y1 measured by the calibrated infrared method; Step S303, the T3ster heating current is quickly switched to the test current, and a voltage sensor is used to monitor the PN junction voltage drop curve of the LED device in real time, and the junction temperature j1 of the LED chip under the action of the 0.5A heating current is obtained through the K coefficient of step S20.

6. The method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of the fluorescent glue as claimed in claim 5, characterized in that: The step S40 comprises: In step S401, the furnace temperature is maintained at 40, 80 and 100°C respectively, and a heating current of 0.5A is still used to drive the LED device to change the junction temperature of the LED chip; at each temperature point, step S30 is repeated, and the infrared method calibrated by the thermocouple method is used to measure the LED fluorescent glue temperatures y2, y3, y4, and the transient thermal resistance method is used to test the LED chip junction temperatures j2, j3, j4.

7. The method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of fluorescent glue as claimed in claim 6, characterized in that: The step S401 includes: In step S402, the calibrated infrared fluorescent glue temperatures y1, y2, y3, y4 and the transient thermal resistance chip junction temperatures j1, j2, j3, j4 under the action of a heating current of 0.5A are plotted into a curve w1. It is found that the calibrated infrared fluorescent glue temperature Ty and the transient thermal resistance chip junction temperature Tj in the curve w1 present a linear relationship. The relationship Ty=k1*Tj+b1 is obtained through linear fitting, indicating that the linear relationship is not affected by the furnace temperature.

8. The method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of fluorescent glue as claimed in claim 7, characterized in that: The step S50 comprises: In step S501, the LED devices are driven by heating currents of 1A, 2A and 4A respectively to increase the junction temperature of the LED chip. Steps S30 and S40 are repeated to respectively determine the relationship curves w2, w3 and w4 between the calibrated infrared method fluorescent glue temperature and the transient thermal resistance method chip junction temperature under the action of heating currents of 1A, 2A and 4A. It is found that the calibrated infrared method fluorescent glue temperature Ty and the transient thermal resistance method chip junction temperature Tj in the curves w2, w3 and w4 also show a linear relationship. Through linear fitting, the relationship formulas Ty=k2*Tj+b2, Ty=k3*Tj+b3 and Ty=k4*Tj+b4 can be obtained.

9. The method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of fluorescent glue as claimed in claim 8, characterized in that: The step S501 includes: Step S502, superimpose the relationship curves w1, w2, w3, and w4 between the calibrated infrared fluorescent glue temperature and the transient thermal resistance chip junction temperature obtained under different driving currents of 0.5A, 1A, 2A, and 4A to obtain a superposition diagram of the calibrated infrared fluorescent glue temperature and the transient thermal resistance chip junction temperature curves driven by different heating currents; the linear correlation and overlap of w1, w2, w3, and w4 are both high, and the slope correlation and intercept correlation of each curve are calculated, and it is found that they are all less than or equal to 5%, indicating that the relationship curve is not affected by the driving heating current.

10. The method for calculating the junction temperature of a high-temperature aged LED chip using the temperature of fluorescent glue as claimed in claim 9, characterized in that: The step S60 includes: connecting the LED device to a high-temperature aging test circuit, using a calibrated infrared method to test the temperature of the LED fluorescent glue during the high-temperature aging process, and using the P coefficient of step S10 to obtain the calibrated fluorescent glue temperature Ty; combining the relationship curve fitting formula Ty=k4*Tj+b4 under the maximum heating current to quickly and accurately calculate the LED chip junction temperature Tj.

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