Method for obtaining highest temperature of LED fluorescent adhesive by structural difference method

Abstract

The application provides a method for obtaining the highest temperature of LED fluorescent glue by structural difference method, and has the characteristics that the method comprises the following steps: S1, preparing three kinds of LED devices with different packaging structures, the chip of LED device I is exposed, the chip surface of LED device II is covered with silicone, and the chip surface of LED device III is covered with fluorescent glue; S2, three models with different optical and thermal structures are respectively established corresponding to the three devices; S3, the light radiation power of LED device II and LED device III is respectively tested by an integrating sphere, and the chip heating power and the fluorescent glue heating power of LED device III are respectively obtained; S4, the chip junction temperature and the chip PN junction-environment overall thermal resistance of the three devices are tested by using a transient thermal resistance method; and S5, the highest temperature of the fluorescent glue of LED device III is obtained according to the structural difference method. The highest temperature of the fluorescent glue of LED device III is obtained, the deficiency that the highest temperature of the fluorescent glue on the surface of the LED chip cannot be tested by a traditional method is solved, and the influence of the excessively high temperature of the fluorescent glue on the LED light-emitting efficiency and the packaging reliability is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the detection technology in the field of LED semiconductor, and in particular to a method for obtaining the highest temperature of LED fluorescent glue by structural difference method. BACKGROUND

[0002] LED light-emitting diode is widely used in the field of lighting signals of aerospace products due to its high reliability, high luminous efficiency and low power consumption. The traditional LED can only produce monochromatic light and cannot directly obtain white light. In order to obtain white LED, yellow fluorescent glue needs to be coated on the blue LED chip to convert the blue light emitted by the chip into yellow light, and then the converted yellow light and the transmitted blue light of the chip are mixed to finally produce mixed white light.

[0003] In the thermal characterization of traditional LED devices, only the chip junction temperature is often concerned, and the test of the temperature of the fluorescent glue is less. However, in the process of converting the light emitted by the chip by the fluorescent glue, due to factors such as non-radiative recombination and absorption of light energy by the fluorescent glue, the emitted light will be lost and converted into heat, resulting in local heating of the fluorescent glue and making it another heat source inside the LED device.

[0004] Although the heat generated by the fluorescent glue is usually less than that generated by the chip PN junction, compared with the high-efficiency one-dimensional heat dissipation path of the chip PN junction-solder-substrate, the thermal conductivity of the fluorescent glue is poor, which will cause the heat generated by the fluorescent glue to quickly accumulate inside it. The accumulated heat will reduce the LED luminous efficiency and aggravate the loss of emitted light, and ultimately lead to local high temperature of the fluorescent glue. Therefore, the highest temperature inside the fluorescent glue may be higher than the temperature of the chip PN junction.

[0005] During the long-term aging and service of the LED, the local high temperature of the fluorescent glue not only reduces the quantum conversion efficiency of the fluorescent glue, affects the service life and overall luminous efficiency of the LED device, but also causes internal stress between the fluorescent glue and the chip, resulting in delamination and fracture of the LED and other failure phenomena. In summary, in addition to the chip junction temperature, the temperature of the fluorescent glue is also one of the important parameters for characterizing the heat dissipation performance of the LED device. However, the fluorescent glue is mainly composed of fluorescent powder and silicone glue mixed together, and the fluorescent powder particles are dispersed in the silicone glue matrix, so it is difficult to directly and accurately test the temperature of the fluorescent glue by traditional methods.

[0006] The thermocouple method mainly characterizes the surface temperature of the fluorescent glue by contacting the fluorescent glue, but even if the fluorescent glue covering the LED chip is destroyed and a micro thermocouple is used to test the temperature inside the fluorescent glue, the temperature field inside the fluorescent glue will be destroyed, and there will be a significant difference between the tested temperature and the internal temperature of the undamaged fluorescent glue.

[0007] The infrared testing method can obtain the surface temperature of the fluorescent glue by a non-contact method, but the emissivity of the fluorescent glue will significantly affect the infrared temperature measurement result, and the infrared light generated by the high temperature point in the fluorescent glue will also be lost when it transmits through the fluorescent glue, so there is also a difference between the temperature measured by the infrared method and the internal temperature of the fluorescent glue.

[0008] The traditional thermal resistance method can only test the chip junction temperature and cannot obtain the internal temperature of the fluorescent glue.

[0009] In summary, the current temperature measurement method cannot accurately obtain the maximum temperature of the fluorescent glue, and cannot evaluate the relationship between the temperature of the fluorescent glue and the chip junction temperature, so it is of great significance to develop a new method to characterize the maximum temperature of the fluorescent glue. SUMMARY

[0010] The purpose of the present application is to provide a method for obtaining the maximum temperature of the LED fluorescent glue by structural difference, which solves the problem that the prior art cannot test the maximum temperature of the fluorescent glue on the surface of the LED chip.

[0011] In order to achieve the above purpose, the present application provides a method for obtaining the maximum temperature of the LED fluorescent glue by structural difference, characterized in that it comprises the following steps: S1, preparing three kinds of LED devices with different packaging structures, the LED device I is bare, the LED device II is covered with silicone on the surface of the chip, and the LED device III is covered with fluorescent glue on the surface of the chip; S2, three models with different optical and thermal structures are respectively established corresponding to the three devices, wherein the thermal resistance R yg of the fluorescent glue of the LED device III is equal to the thermal resistance R gj of the silicone of the LED device II, and the chip PN junction-substrate-environmental thermal resistance R jsa 3 of the LED device III is the same as the chip PN junction-substrate-environmental thermal resistance R jsa 1 of the LED device I; S3, the optical radiation power of the LED device II and the LED device III is tested by the integrating sphere, and the chip heat power P chip and the fluorescent glue heat power P yg-j of the LED device III are respectively obtained by using the structural difference of the two devices; S4, the chip junction temperature and the chip PN junction-environmental overall thermal resistance of the three devices are tested by using the transient thermal resistance method; S5, according to the structural difference method, the data obtained from steps S3 and S4 are substituted into the model established in step S2 to obtain the maximum temperature T yg of the fluorescent glue of the LED device III.

[0012] Further, step S1 comprises: firstly mounting the LED chip on the surface of the substrate, then bonding the LED chip and the electrode lead-out end, mounting the reflector to make the light generated by the chip upwardly emit, obtaining the LED device I with the chip surface not coated with silicone and fluorescent glue; coating the chip surface of the LED device I with silicone and heating to solidify, obtaining the LED device II; coating the chip surface of the LED device I with fluorescent glue and heating to solidify, obtaining the LED device III.

[0013] Further, step S2 comprises:

[0014] Modeling the LED device I: the chip of the LED device I generates heat power P chip conducted to the substrate and the external environment in turn through one-dimensional heat dissipation path, so formula (1) is obtained: wherein, T a is the ambient temperature, which remains unchanged in the LED device I, the LED device II and the LED device III, R ja 1 is the overall thermal resistance of the chip PN junction-environment of the LED device I, R jsa 1 is the corresponding thermal resistance, which is the thermal resistance of the chip PN junction-substrate-environment, T j1 is the junction temperature of the chip of the LED device I.

[0015] Modeling the LED device II: the chip of the LED device II generates heat power P chip , a part of which is conducted to the substrate and the external environment P chip 1 , so formula (3) is obtained: wherein, R ja 2 is the overall thermal resistance of the chip PN junction-environment of the LED device II, R jsa 2 is the corresponding thermal resistance, which is the thermal resistance of the chip PN junction-substrate-environment, T j2 is the junction temperature of the chip of the LED device II; another part is conducted to the silicone and the external environment P chip 2 , so formula (4) is obtained: wherein, R gj is the thermal resistance of the chip PN junction-silicone-environment; further derivation obtains formula (7):

[0016] Modeling the LED device III: the highest point of the fluorescent glue generates heat power P yg , a part of which is conducted to the external environment P yg-a , and a part of which is conducted to the chip PN junction P yg-j , so formula (8) is obtained: P yg = P yg-a + P yg-j ; the chip generates heat power P chip , and the fluorescent glue generates heat power P yg-jAll of them are gathered at the chip PN junction, so the total heat power P of the chip PN junction-substrate-environment of LED device III is ja There is formula (9): P ja =P chip +P yg-j ; Due to the thermal resistance R of LED device III fluorescent glue yg Equal to the thermal resistance R of LED device II silicone rubber gj , LED device III chip PN junction-substrate-ambient thermal resistance R jsa 3 The chip PN junction-substrate-environment thermal resistance R of LED device I jsa 1 The same, then by deduction we can get formula (15): R ja 3 is the chip PN junction-ambient overall thermal resistance of LED device III, formula (25): where R yg-a is the thermal resistance from the highest temperature point of the fluorescent glue of LED device III to the environment, and formula (26): the highest temperature of the fluorescent glue T yg =T a +R yg-a *P yg-a .

[0017] Furthermore, step S3 includes: fixing a standard LED with known light radiation power at the bottom of the integrating sphere, driving the standard LED with IH heating current, testing the voltage value of the standard LED with a VF voltage sensor and obtaining its input power P in , Formula (27): P in =IH*VF. The light generated by the standard LED chip is diffusely reflected by the integrating sphere and then received by the detector. The light radiation power tested by the detector is compared with the known light radiation power to calibrate the integrating sphere detector parameters. The standard LED is replaced by LED device II and LED device III in turn. The IH heating current is used to drive LED device II and LED device III in turn. The input power P of the two devices is determined by combining the voltage value measured by the VF voltage sensor. in , Formula (27): P in =IH*VF, and the optical radiation power P of the two devices is measured by the calibrated detector. fg 2 and P fg 3 .

[0018] Furthermore, step S3 includes: the input power P of the LED device II in For chip heating power P chip and optical radiation power P fg 2 , formula (28): P in =P chip +P fg 2Input power P of LED device III in Respectively for the chip heating power P chip , light radiation power P fg 3 and fluorescent glue heating power P yg , formula (29): P in = P chip + P fg 3 + P yg ; by derivation, the chip heating power P chip of LED device III under different IH heating currents can be obtained, formula (30): P chip = P in - P fg 2 and the fluorescent glue heating power P yg , formula (31): P yg = P fg 2 - P fg 3 .

[0019] Further, step S4 includes: testing the temperature sensitive parameter K coefficient of LED device I, LED device II and LED device III; driving the three devices respectively with different heating currents to raise the chip junction temperature, monitoring the change of chip PN junction voltage drop through the voltage sensor, combining the K coefficient, obtaining the chip junction temperature curve, and determining the highest chip junction temperature T j1 , T j2 and T j3 under different currents; performing mathematical transformation on the chip junction temperature curve to obtain the transient thermal resistance curve, and determining the chip PN junction-environment overall thermal resistance R ja 1 , R ja 2 and R ja 3 under different currents.

[0020] Further, the testing of the temperature sensitive parameter K coefficient of LED device I, LED device II and LED device III includes: placing LED device III connected to the transient thermal resistance test circuit into a constant temperature oil tank, adjusting the oil temperature to raise the chip PN junction temperature of the device, recording the chip PN junction voltage drop-junction temperature curve in real time, and determining the temperature sensitive parameter K coefficient; the circuit structures of the three devices are the same, so the K coefficients are the same.

[0021] Further, step S5 includes: according to the structural difference method, first obtaining the heating power P yg-j of the highest temperature point of the fluorescent glue of LED device III to the chip PN junction and the heating power P yg-a to the environment; then obtaining the thermal resistance R yg-a of the highest temperature point of the fluorescent glue of LED device III to the environment; and finally obtaining the highest temperature T yg of the fluorescent glue of LED device III.

[0022] Furthermore, step S5 includes: obtaining the silicone thermal resistance R of the LED device II gj , formula (7): And the total heat generation power P of LED device III chip PN junction-substrate-environment ja , formula (15): Among them, R ja 1 、R ja 2 and R ja 3 The chip PN junction-environment overall thermal resistance of the three LED devices is obtained respectively; then, the heating power P from the highest temperature point of the fluorescent glue of LED device III to the chip PN junction is obtained. yg-j According to formula (9), we can know that: P yg-j =P ja -P chip ; Then, the heating power P from the highest temperature point of LED device III fluorescent glue to the environment is obtained yg-a According to formula (8), we can know that: P yg-a =P yg -P yg-j ; Thus, we get P yg-j and P yg-a .

[0023] Furthermore, step S5 further includes: obtaining the thermal resistance R from the highest temperature point of the fluorescent glue of the LED device III to the environment yg-a , formula (25): Then, the maximum temperature T of the fluorescent glue of LED device III is obtained. yg , formula (26): T yg =T a +R yg-a *P yg-a .

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] Based on the similarities and differences in the structures of LED devices I, LED devices II and LED devices III, the present invention combines the light radiation power, chip junction temperature and the chip PN junction-environment overall thermal resistance to effectively obtain the maximum temperature of the fluorescent glue of LED device III, thereby solving the problem that traditional methods cannot test the maximum temperature of the fluorescent glue on the surface of the LED chip, and avoiding the influence of excessive fluorescent glue temperature on the LED luminous efficiency and packaging reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The method of obtaining the maximum temperature of LED fluorescent glue by the structural difference method of the present invention is given in the following examples and drawings.

[0027] Figure 1The flow chart of the method for obtaining the highest temperature of LED fluorescent glue by structural difference method for the preferred embodiment of the present application;

[0028] Figure 2 The cross-sectional schematic diagram of LED device I in the preferred embodiment of the present application;

[0029] Figure 3 The cross-sectional schematic diagram of LED device II in the preferred embodiment of the present application;

[0030] Figure 4 The cross-sectional schematic diagram of LED device III in the preferred embodiment of the present application;

[0031] Figure 5 The heat transfer path of the chip in LED device I in the preferred embodiment of the present application;

[0032] Figure 6 The heat transfer path of the silicone and the chip in LED device II in the preferred embodiment of the present application;

[0033] Figure 7 The heat transfer path of the fluorescent glue and the chip in LED device III in the preferred embodiment of the present application;

[0034] Figure 8 The simplified model of the heat transfer path of LED device I, LED device II and LED device III in the preferred embodiment of the present application;

[0035] Figure 9 The schematic diagram of testing the optical radiation power of LED device II and LED device III by integrating sphere in the preferred embodiment of the present application;

[0036] Figure 10 The transient circuit connection diagram of LED device III in the preferred embodiment of the present application;

[0037] Figure 11 The transient thermal resistance curve of LED device I, LED device II and LED device III under the action of 0.2A heating current in the preferred embodiment of the present application;

[0038] Figure 12 The LED device III chip junction temperature curve T j3(cal) obtained by structural difference method in the preferred embodiment of the present application; j3(test) And the LED device III chip junction temperature curve T yg(test) tested by transient thermal resistance method in the preferred embodiment of the present application;

[0039] Figure 13 The schematic diagram of testing the surface temperature T yg(test) of the fluorescent glue of LED device III by thermocouple in the preferred embodiment of the present application;

[0040] Figure 14The highest temperature curve T of the phosphor glue of the LED device III is obtained by the structural difference method in the preferred embodiment of the present application yg(cal) The surface temperature curve T of the phosphor glue of the LED device III is tested by the thermocouple yg(test) The superimposed graph. DETAILED DESCRIPTION

[0041] The present application will be described in detail below Figures 1-14 The method for obtaining the highest temperature of the phosphor glue of the LED by the structural difference method of the present application will be described in detail.

[0042] The present application solves the problem that the highest temperature of the phosphor glue on the surface of the LED chip cannot be tested in the prior art. Figure 1 The flowchart of the method for obtaining the highest temperature of the phosphor glue of the LED by the structural difference method of the preferred embodiment of the present application is shown in FIG. 1. Figure 1 The method for obtaining the highest temperature of the phosphor glue of the LED by the structural difference method of the embodiment of the present application includes the following steps: S1, preparing three kinds of LED devices with different packaging structures, the LED device I has exposed chip, the LED device II has the chip surface covered with silicone, and the LED device III has the chip surface covered with phosphor glue; S2, establishing three models with different optical and thermal structures respectively corresponding to the three devices; S3, testing the optical radiation power of the LED device II and the LED device III respectively by the integrating sphere, and obtaining the chip heat power P chip and the phosphor glue heat power P yg-j of the LED device III respectively by the structural difference; S4, testing the chip junction temperature and the overall thermal resistance from the chip PN junction to the environment of the three devices by the transient thermal resistance method; S5, obtaining the highest temperature T yg of the phosphor glue of the LED device III according to the model established in step S2 and the data obtained in steps S3 and S4 according to the structural difference method.

[0043] The present application will be described in detail below.

[0044] S1, preparing three kinds of LED devices with different packaging structures, the LED device I has exposed chip, the LED device II has the chip surface covered with silicone, and the LED device III has the chip surface covered with phosphor glue.

[0045] Figure 2 The cross-sectional schematic diagram of the LED device I in the preferred embodiment of the present application is shown in FIG. 2. Figure 2 First, the tin-lead solder 112 is used to mount and fix the LED chip 111 on the surface of the substrate 113, then the bonding wire 114 is used to bond and connect the LED chip 111 with the positive electrode lead-out end 115 and the negative electrode lead-out end 116 respectively, the reflector 117 is installed to make the light generated by the LED chip 111 emit upward, and the LED device I with the surface of the LED chip 111 not coated with silicone and phosphor glue is obtained.

[0046] Figure 3 is a cross-sectional schematic view of LED device II in the preferred embodiment of the present application. As Figure 3 , after obtaining LED device I according to the above, silicon glue 118 is coated on the chip surface of the obtained LED device I and is heated and cured to obtain LED device II.

[0047] Figure 4 is a cross-sectional schematic view of LED device III in the preferred embodiment of the present application. As Figure 4 , after obtaining LED device I according to the above, fluorescent glue 119 is coated on the chip surface of the obtained LED device I and is heated and cured to obtain LED device III.

[0048] S2, three models with different optical and thermal structures are respectively established corresponding to the three devices.

[0049] Figure 5 is a heat transfer path of the chip in LED device I in the preferred embodiment of the present application; Figure 8 is a simplified model of the heat transfer path of LED device I, LED device II and LED device III in the preferred embodiment of the present application. According to Figure 5 the heat transfer path of LED chip 111 in LED device I, a simplified model of LED device I is established in Figure 8 . The overall thermal resistance of the chip PN junction-environment of LED device I is recorded as R ja 1 . The heat generation power P chip of the chip of LED device I is mainly conducted to the substrate and the external environment through a one-dimensional heat dissipation path in turn, and the corresponding thermal resistance is the chip PN junction-substrate-environment thermal resistance R jsa 1 , so formula (1) is obtained: wherein, T j1 is the junction temperature of the chip of LED device I. T a is the ambient temperature, which remains unchanged in LED device I, LED device II and LED device III.

[0050] Figure 6 is a heat transfer path of the silicon glue and the chip in LED device II in the preferred embodiment of the present application; Figure 8 is a simplified model of the heat transfer path of LED device I, LED device II and LED device III in the preferred embodiment of the present application. According to Figure 6 the heat transfer path of silicon glue 118 and LED chip 111 in LED device II, a simplified model of LED device II is established in Figure 8 . The heat generation power P chip of the chip is conducted to the external environment through two paths respectively, which is divided into two parts P chip 1 and P chip 2 , one part is conducted to the substrate and the external environment Pchip 1 , a part of which is conducted upward to the silica gel and the external environment P chip 2 , where formula (2) is P chip = P chip 1 + P chip 2 The first path of the LED device II is the same as that of the LED device I, which is conducted downward from the chip PN junction to the substrate and the external environment in turn, and the corresponding chip PN junction-substrate-environment thermal resistance R jsa 2 is the same as the chip PN junction-substrate-environment thermal resistance R jsa 1 of the LED device I, that is, formula (3) is , where T j2 is the chip junction temperature of the LED device II. T a is the ambient temperature, which remains unchanged in the LED device I, the LED device II and the LED device III.

[0051] The second path of the LED device II is conducted upward from the chip PN junction to the silica gel and the external environment in turn, and the corresponding chip PN junction-silica gel-environment thermal resistance R gj is formula (4): , where T j2 is the chip junction temperature of the LED device II. T a is the ambient temperature, which remains unchanged in the LED device I, the LED device II and the LED device III.

[0052] The chip PN junction-environment overall thermal resistance of the LED device II is denoted as R ja 2 . According to the definition of the chip PN junction-environment overall thermal resistance R ja 2 of the LED device II, formula (5) is According to the above formula (2) P chip = P chip 1 + P chip 2 and the definitions of formula (1) R ja 1 , formula (4) R gj , formula (5) R ja 2 , formula (6) can be derived as Then formula (7) is obtained: , where R ja 2 and R ja 1 are obtained through the following step S4.

[0053] Figure 7 is the heat transfer path of the fluorescent glue and the chip in the LED device III in the preferred embodiment of the present application; Figure 8 is a simplified model of the heat transfer path of the LED device I, the LED device II and the LED device III in the preferred embodiment of the present application. According to Figure 7the heat transfer path of the phosphor glue 119 and the LED chip 111 in the LED device III is established Figure 8 A simplified model of the LED device III. The heat generation power P yg comprising a first heat generation power P yg-a conducted upward to the external environment and a second heat generation power P yg-j conducted downward to the chip PN junction, then there is equation (8): P yg = P yg-a + P yg-j The heat generation power P chip generated by the chip of the LED device III and the second heat generation power P yg-j as a part of the heat generation power generated by the phosphor glue are all gathered at the chip PN junction, then the total heat generation power P ja of the chip PN junction-substrate-ambient of the LED device III has equation (9): P ja = P chip + P yg-j The thermal resistance R yg of the phosphor glue is composed of two parts, respectively, the first thermal resistance R yg-a of the phosphor glue temperature highest point conducted upward to the external environment and the second thermal resistance R yg-j conducted downward to the chip PN junction. Since the difference of the thermal conductivity coefficients of the silicone glue and the phosphor glue is small, the thermal resistance R gj of the silicone glue of the aforementioned LED device II is equivalent to the thermal resistance R yg of the phosphor glue of the LED device III, that is, equation (10): R gj = R yg = R yg-j + R yg-a The total heat generation power P ja of the chip PN junction-substrate-ambient of the LED device III can be conducted downward to the substrate and the external environment in turn from the chip PN junction, and the corresponding chip PN junction-substrate-ambient thermal resistance R jsa 3 is the same as the chip PN junction-substrate-ambient thermal resistance R jsa 1 of the LED device I, that is, equation (11): R jsa 3 = R jsa 1 = R ja 1 .

[0054] According to the definition of the chip PN junction-substrate-ambient thermal resistance R jsa 3 of the LED device III, there is equation (12): In addition, according to the definition of the chip PN junction-ambient overall thermal resistance R ja 3 of the LED device III, considering that the overall heat generation power of the device comprises the heat generation power P chip of the chip and the heat generation power Pyg Then, formula (13) is obtained: Where T j3 is the chip junction temperature of LED device III. T a is the ambient temperature, which remains unchanged in LED device I, LED device II and LED device III.

[0055] Through derivation, formula (14) is obtained: T j3 -T a = R ja3 *(P chip + P yg ) = R ja1 * P ja , then the total heat generation power P ja of LED device III chip PN junction-substrate-ambient is: Combined with the aforementioned formula (9): P ja = P chip + P yg-j , formula (16) is obtained: Combined with the aforementioned formula (8): P yg = P yg-a + P yg-j , formula (17) is obtained:

[0056] According to the definition of the first thermal resistance R yg-a from the highest temperature point of the phosphor glue of LED device III to the ambient, formula (18) is obtained: Where T yg is the highest temperature of the phosphor glue. T a is the ambient temperature, which remains unchanged in LED device I, LED device II and LED device III. According to the definition of the second thermal resistance R yg-j from the highest temperature point of the phosphor glue of LED device III to the chip PN junction, formula (19) is obtained: Through derivation, formula (20) is obtained: T yg = T a + R yg-a * P yg-a = T j3 + R yg-j * P yg-j , then formula (21) is obtained: T j3 -T a = R yg-a * P yg-a -R yg-j * P yg-j .

[0057] According to the aforementioned formula (13): Then, formula (22) is obtained: T j3 -T a = R ja 3 *P chip + P yg . Combined with formula (21) above: T j3 -T a = R yg-a *P yg-a -R yg-j *P yg-j , formula (23) is obtained: R ja 3 *P chip + P yg = R yg-a *P yg-a -R yg-j *P yg-j . Substituting formula (10) above: R gj = R yg-j + R yg-a , formula (24) is obtained: R ja 3 *P chip + P yg = R yg-a *P yg-a -(R gj -R yg-a )P yg-j = R yg-a *P yg-a + P yg-j -R gj *P yg-j . Substituting formula (8) above: P yg = P yg-a + P yg-j , formula (25) is obtained: According to formula (18) above: formula (26) is obtained: the highest temperature T yg = T a + R yg-a *P yg-a .

[0058] S3, the light radiation power of LED device II and LED device III is tested by the integrating sphere, and the chip heat power P chip and the heat power P yg-j of the fluorescent glue of LED device III are obtained by using the structural difference of the two devices.

[0059] Figure 9 Fig. 1 is a schematic diagram of testing the light radiation power of LED device II and LED device III by the integrating sphere in the preferred embodiment of the present application; as Figure 9A standard LED 133 with known optical radiation power is fixed at the bottom inside the integrating sphere 136, and the electrode leads of the standard LED 133 are connected to the IH heating current 131 and the VF voltage sensor 132 of the T3ster device, respectively. The standard LED 133 is driven by different IH heating currents (0.2, 0.4, 0.6 and 0.8 A), and the voltage value across the standard LED 133 is tested by the VF voltage sensor 132, respectively, to obtain the input power P in = IH * VF of the standard LED 133. The light generated by the standard LED 133 is diffusely reflected multiple times on the inner wall of the integrating sphere 136, and the light intensity on the entire inner wall is uniformly distributed, and finally all received by the detector 135. The baffle 134 is to avoid the light generated by the standard LED chip directly irradiating the detector 135, to prevent affecting the test accuracy. The optical radiation power received by the detector 135 is compared with the known optical radiation power of the standard LED 133, to calibrate the parameters of the integrating sphere detector.

[0060] LED device II and LED device III are sequentially replaced by the standard LED 133 at the bottom inside the integrating sphere, and the IH heating current of 0.2 A is used to drive LED device II and LED device III, respectively, and the voltage value measured by the VF voltage sensor 132 is used to determine the input power P in of the two devices, respectively. Formula (27): P in = IH * VF. The optical radiation power P fg 2 and P fg 3 of LED device II and LED device III are tested by the calibrated detector 135, respectively. Since the circuit structures of the two devices are the same, the input power P in and the chip heating power P chip of LED device II and LED device III are the same. In LED device II, the light generated by the LED chip is almost not absorbed by the silica gel, and the input power P in is partly used for the chip heating power P chip and partly used for the optical radiation power P fg 2 received by the detector 135 in the integrating sphere 136, so formula (28) is P in = P chip + P fg 2 . In LED device III, the light generated by the LED chip is absorbed by the fluorescent gel to increase the temperature of the fluorescent gel, and the input power P in is not only used for the chip heating power P chip and the optical radiation power P fg 3 received by the detector 135 in the integrating sphere 136, but also used for the heating power P yg of the fluorescent gel itself, so formula (29) is P in = Pchip +P fg 3 +P yg By deduction, we can obtain the chip heating power P of LED device III under the action of 0.2A current. chip Formula (30): P chip =P in -P fg 2 , and the heating power of fluorescent glue P yg Formula (31): P yg =P fg 2 -P fg 3 .

[0061] The LED device II and LED device III are driven by IH heating currents 131 of 0.4, 0.6, and 0.8 A, respectively. The above test steps are repeated to obtain the chip heating power P of LED device III under different currents. chip And the heating power of fluorescent glue P yg .

[0062] S4: Use the transient thermal resistance method to test the chip junction temperature and chip PN junction-ambient overall thermal resistance of the three devices

[0063] Figure 10 FIG. 1 is a transient circuit connection diagram of LED device III in a preferred embodiment of the present invention. Figure 10 LED device III was connected to a transient thermal resistance test circuit. The positive electrode lead 115 and the negative electrode lead 116 of the LED were connected to the VF voltage sensor 132, the IM test current 142, and the IH heating current 131, respectively. Since the VF voltage sensor 132, the IM test current 142, and the IH heating current 131 all have the same direction, they all display a positive value (+). Using the T3ster device, only the 5mA IM test current 142 was applied to LED device III, without the IH heating current 131. The VF voltage sensor 132 was used to monitor the PN junction voltage drop across the LED device III in real time.

[0064] Place LED device III, connected to the transient thermal resistance test circuit, in a constant-temperature oil bath. After a certain period of time, the constant-temperature oil temperature is maintained equal to the PN junction temperature of LED device III. The constant-temperature oil temperature is adjusted to gradually increase the PN junction temperature of LED device III from 25°C to 140°C at a rate of 5°C / minute. Record the PN junction voltage drop-to-junction temperature curve of LED device III in real time to determine its temperature-sensitive parameter, the K coefficient. Since LED devices I, II, and III share the same circuit structure, their temperature-sensitive parameter, the K coefficient, is the same, and the transient thermal resistance test circuit connection method is also the same. After the test, clean the oil from the surface of LED device III.

[0065] As Figure 10 , the LED device I, the LED device II and the LED device III are connected to the transient thermal resistance test circuit respectively, 0.2A IH heating current 131 is used to drive the LED device I, the LED device II and the LED device III respectively to make the chip junction temperature rise, after the chip PN junction voltage drop measured by the T3ster equipment VF voltage sensor 132 is stable, the IH heating current 131 of the T3ster is rapidly switched to the IM test current 142, at the same time, the VF voltage sensor 132 is used to monitor the chip PN junction voltage drop change curve of the LED device I, the LED device II and the LED device III in real time, the chip junction temperature curve under the action of 0.2A IH heating current 131 is obtained through the above K coefficient, and the highest chip junction temperature T j1 (LED device I), T j2 (LED device II) and T j3 (LED device III) in the initial stage are determined respectively.

[0066] Figure 11 The transient thermal resistance curves of the LED device I, the LED device II and the LED device III under the action of 0.2A heating current in the preferred embodiment of the present application are shown in the following figure: Figure 11 , the transient thermal resistance curves of the LED device I 147, the LED device II 148 and the LED device III 149 are obtained through mathematical transformation of the above chip junction temperature curve, and the chip PN junction-environment overall thermal resistance R ja 1 (LED device I), R ja 2 (LED device II) and R ja 3 (LED device III) under the action of 0.2A heating current are determined.

[0067] 0.4A, 0.6A and 0.8A IH heating current is used to drive the three devices respectively to make the chip junction temperature rise, the above test steps are repeated, the highest chip junction temperature T j1 (LED device I), T j2 (LED device II) and T j3 (LED device III) under the action of 0.4A, 0.6A and 0.8A current are determined respectively. Through mathematical transformation, the chip PN junction-environment overall thermal resistance R ja 1 (LED device I), R ja 2 (LED device II) and R ja 3 (LED device III) under the action of 0.4A, 0.6A and 0.8A current are determined respectively.

[0068] In order to verify the method of the present application, the following experiments are carried out:

[0069] Experiment 1

[0070] LED device III chip junction temperature curve T obtained by the structural difference method of the present application j3(cal) LED device III chip junction temperature curve T obtained by the transient thermal resistance method j3(test) , to verify the accuracy of the structural difference method.

[0071] According to formula (13) of step S2: T of step S2 combined with step S2 a , formula (30) of step S3 combined with step S3: chip and formula (31): P yg , combined with the definition of R ja 3 in step S4, the chip junction temperature of LED device III under different currents is obtained respectively, formula (32): T j3 = T a + R ja 3 *(P chip + P yg ). Draw the LED device III chip junction temperature-heating current curve T j3(cal) obtained by the structural difference method under different heating currents (0.2, 0.4, 0.6 and 0.8 A).

[0072] According to the highest chip junction temperature T j3 of LED device III in step S4, draw the LED device III chip junction temperature-heating current curve T j3(test) tested by the transient thermal resistance method under different heating currents (0.2, 0.4, 0.6 and 0.8 A).

[0073] Figure 12 The LED device III chip junction temperature curve T j3(cal) obtained by the structural difference method and the LED device III chip junction temperature curve T j3(test) tested by the transient thermal resistance method in the preferred embodiment of the present application are superimposed. As Figure 12 , the LED device III chip junction temperature-heating current curve T j3(cal) 152 obtained by the above-mentioned structural difference method and the LED device III chip junction temperature-heating current curve T j3(test) 151 tested by the transient thermal resistance method are superimposed, and it is found that the two curves overlap to a high degree, indicating that the structural difference method of the present application can accurately obtain the chip junction temperature of LED device III.

[0074] S5, according to the structural difference method, the highest temperature of the fluorescent glue of LED device III is obtained according to the data obtained by substituting the model established in step S2 into steps S3 and S4.

[0075] First, the heating power P yg-j of the highest temperature point of the fluorescent glue of LED device III to the chip PN junction and the heating power Pyg-a .

[0076] According to R ja 1 and R ja 2 , the thermal resistance of the silicone gel of the LED device II R gj is obtained, formula (7):

[0077] According to R ja 1 and R ja 3 , P chip and P yg of step S3, the total heat generation power P ja of the LED device III chip PN junction-substrate-environment is obtained, formula (15):

[0078] According to P chip of step S3 and the above P ja , the heat generation power P yg-j of the LED device III fluorescent gel maximum temperature point to the chip PN junction is obtained, according to formula (9): P yg-j =P ja -P chip .

[0079] According to P yg of step S3 and the above P yg-j , the heat generation power P yg-a of the LED device III fluorescent gel maximum temperature point to the environment is obtained, according to formula (8): P yg-a =P yg -P yg-j .

[0080] Then, the thermal resistance R yg-a of the LED device III fluorescent gel maximum temperature point to the environment and the fluorescent gel maximum temperature T yg are obtained, and the LED device III fluorescent gel maximum temperature curve T yg(cal) obtained by the structure difference method is drawn.

[0081] According to P chip and P yg of step S3, R ja3 of step S4, the above R gj , P yg-j , the thermal resistance R yg-a of the LED device III fluorescent gel maximum temperature point to the environment is obtained, formula (25):

[0082] According to T a of step S2, the above P yg-a , R yg-a, obtain the maximum temperature T of LED device III fluorescent glue yg , formula (26): T yg =T a +R yg-a *P yg-a .

[0083] Changing the heating driving current (0.2, 0.4, 0.6 and 0.8A), the maximum temperature curve T of the LED device III fluorescent glue obtained by the structural difference method under different currents was plotted. yg(cal) .

[0084] In order to verify the method of the present invention, the following experiments were also carried out:

[0085] Experiment 2

[0086] Comparative structural difference method to obtain the maximum temperature curve T of LED device III fluorescent glue yg(cal) LED device III fluorescent glue surface temperature curve T tested by thermocouple yg(test) , verifying the accuracy of the structural difference method.

[0087] Figure 13 The surface temperature T of the fluorescent glue of LED device III is measured by thermocouple in the preferred embodiment of the present invention. yg(test) Schematic diagram of . Figure 13 , connect the heating current IH 131 to the positive electrode 115 and the negative electrode 116 of the LED device III, and directly contact the thermocouple 182 with the surface of the fluorescent glue 119 of the LED device III. Drive the LED device III with different heating currents IH 131, use the thermocouple instrument panel 183 to measure the surface temperature of the fluorescent glue 119 of the LED device III, and draw the surface temperature curve T of the fluorescent glue of the LED device III under different currents tested by the thermocouple. yg(test) .

[0088] Figure 14 The maximum temperature curve T of the fluorescent glue of LED device III obtained by the structural difference method in the preferred embodiment of the present invention is yg(cal) And thermocouple test LED device III fluorescent glue surface temperature curve T yg(test) Overlay graph. Figure 14 , the maximum temperature curve T of the LED device III fluorescent glue obtained by the above structural difference method yg(cal) Surface temperature curve T of LED device III fluorescent glue tested by 185 and thermocouple yg(test) 186 superposition. Figure 14 In the initial stage, the maximum temperature curve T of the LED device III fluorescent glue obtained by the structural difference method yg(cal) Surface temperature curve T of LED device III fluorescent glue tested by 185 and thermocoupleyg(test) 186 Good overlap. When raised to a certain critical temperature, the two curves begin to separate, and the LED device III phosphor glue highest temperature curve T yg(cal) 185 Slightly higher than the LED device III phosphor glue surface temperature curve T yg(test) 186 With the temperature rising, the LED device III phosphor glue highest temperature curve T yg(cal) 185 significantly higher than the LED device III phosphor glue surface temperature curve T yg(test) 186. Since the thermocouple tests the surface temperature of the phosphor glue in direct contact with the external environment, the test temperature point is not the highest temperature point of the phosphor glue. When the heating current is low, the chip light radiation power is not large, and the phosphor glue absorbs less light, and the heat is not obvious, and the temperature difference between the highest temperature of the phosphor glue and the surface temperature is not large. When the heating current is significantly increased, the light generated by the chip is absorbed by the phosphor glue and gathered in the phosphor glue, so that the temperature difference between the highest temperature of the phosphor glue and the surface temperature is significantly increased. Figure 14 The results effectively show that when the LED device III works in a large current state, the traditional thermocouple method cannot accurately test the highest temperature of the LED device III phosphor glue, and the structural difference method of the present application can accurately obtain the highest temperature of the LED device III phosphor glue, avoiding the significant failure of the phosphor glue due to high temperature. For example Figure 14 , according to the limit working temperature T yg-max 187 of the highest temperature of the phosphor glue, in combination with the LED device III phosphor glue highest temperature curve T yg(cal) 185 obtained by the structural difference method, the critical maximum working current I max 188 of the LED device III is determined.

[0089] The advantages of the present application include:

[0090] First, the present application effectively obtains the highest temperature of the phosphor glue coated on the surface of the chip of the LED device III according to the same and different points of the structures of the LED device I, the LED device II and the LED device III, in combination with the light radiation power, the chip junction temperature and the overall thermal resistance of the chip PN junction-environment, solves the deficiency that the traditional method cannot test the highest temperature of the phosphor glue on the surface of the LED chip, and avoids the influence of the too high temperature of the phosphor glue on the LED light-emitting efficiency and the packaging reliability.

[0091] Secondly, the application compares the LED device III chip junction temperature obtained by the structure difference method under different currents with the LED device III chip junction temperature tested by the transient thermal resistance method, verifies the accuracy and repeatability of the structure difference method, and compares the LED device III phosphor gel maximum temperature obtained by the structure difference method under different currents with the LED device III phosphor gel surface temperature tested by the thermocouple, verifies the fact that the internal temperature of the phosphor gel is significantly higher than the surface temperature of the phosphor gel under a large current, and the test method of the application can more accurately reflect the internal temperature of the phosphor gel.

[0092] Thirdly, for the LED to-be-tested device with different packaging structures and packaging materials, as long as the to-be-tested device meets the model of the LED device III and can test the light radiation power, chip junction temperature and transient thermal resistance curve, the phosphor gel maximum temperature of the to-be-tested device can be obtained by designing the model of the LED device I and the LED device II. For the LED to-be-tested device with the same packaging structure and packaging material, as long as the light radiation power, chip junction temperature and transient thermal resistance curve are tested, the phosphor gel maximum temperature can be quickly obtained according to the structure difference method of the application.

[0093] Fourthly, the LED phosphor gel maximum temperature obtained by the structure difference method of the application can be compared with the chip junction temperature tested by the transient thermal resistance method, the phosphor gel surface temperature tested by the thermocouple method and the environmental temperature, which is beneficial to the comprehensive analysis of the temperature distribution of the LED device structure, the determination of the heat dissipation weak point of the LED, the provision of reference for improving the LED packaging structure and packaging material, and the provision of data support for the LED thermal simulation.

[0094] The above specific embodiments can be adjusted in different ways by those skilled in the art without departing from the principles and purposes of the application, the protection scope of the application is subject to the claims and is not limited by the above specific embodiments, and each implementation scheme within the scope is subject to the constraints of the application.

Claims

1. A method for obtaining the maximum temperature of LED fluorescent glue using a structural difference method, characterized in that: The method comprises the following steps: S1, preparing three LED devices with package structures, wherein the LED device I chip is exposed, the LED device II chip surface is covered with silicone, and the LED device III chip surface is covered with fluorescent glue; S2, establishing three models with different optical and thermal structures corresponding to the three devices, wherein the thermal resistance R yg Equal to the thermal resistance R of LED device II silicone rubber gj , LED device III chip PN junction-substrate-ambient thermal resistance R jsa3 The chip PN junction-substrate-environment thermal resistance R of LED device I jsa1 Same; S3, the integrating sphere tests the light radiation power of LED device II and LED device III respectively, and uses the structural difference of the two devices to obtain the chip heating power P of LED device III respectively. chip And the heating power of fluorescent glue P yg-j ; S4: Use the transient thermal resistance method to test the chip junction temperature and chip PN junction-environment overall thermal resistance of the three devices; S5, according to the structural difference method, substitute the data obtained in steps S3 and S4 into the model established in step S2 to obtain the maximum temperature T of the fluorescent glue of LED device III yg .

2. The method for obtaining the maximum temperature of LED fluorescent glue by the structural difference method according to claim 1, characterized in that: Step S1 includes: first, fixing the LED chip on the surface of the substrate, then bonding the LED chip to the electrode lead end, installing a reflector to emit the light generated by the chip upward, and obtaining an LED device I whose chip surface is not coated with silicone and fluorescent glue; coating the chip surface of LED device I with silicone and heating and curing it to obtain LED device II; coating the chip surface of LED device I with fluorescent glue and heating and curing it to obtain LED device III.

3. The method for obtaining the maximum temperature of LED fluorescent glue by the structural difference method according to claim 1, characterized in that: Step S2 includes: Establish the model of LED device I: the chip heating power P of LED device I chip Through the one-dimensional heat dissipation path, it is conducted downward to the substrate and the external environment in turn, and then there is formula (1): Among them, T a is the ambient temperature, which remains unchanged in LED device I, LED device II and LED device III, R ja1 is the chip PN junction-environment overall thermal resistance of LED device I, R jsa1 The corresponding thermal resistance is the chip PN junction-substrate-environment thermal resistance, T j1 is the chip junction temperature of LED device 1; Establish the model of LED device II: the chip heating power P of LED device II chip Part of it is conducted downward to the substrate and the external environment P chip1 , then we have formula (3): Among them, R ja2 is the chip PN junction-environment overall thermal resistance of LED device II, R jsa2 The corresponding thermal resistance is the chip PN junction-substrate-environment thermal resistance, T j2 The chip junction temperature of LED device II; the other part is conducted upward to the silicone and the external environment P chip2 , then we have formula (4): Among them, R gj is the chip PN junction-silicone-environment thermal resistance; further deduction yields formula (7): Establish the model of LED device III: the heating power P at the highest point of the fluorescent glue temperature yg , part of it is conducted upward to the external environment P yg-a , part of it is conducted downward to the chip PN junction P yg-j , that is, formula (8): P yg =P yg-a +P yg-j ; Chip heating power P chip And the heating power of fluorescent glue P yg-j All of them are gathered at the chip PN junction, so the total heat power P of the chip PN junction-substrate-environment of LED device III is ja There is formula (9): P ja =P chip +P yg-j ; Due to the thermal resistance R of LED device III fluorescent glue yg Equal to the thermal resistance R of LED device II silicone rubber gj , LED device III chip PN junction-substrate-ambient thermal resistance R jsa3 The chip PN junction-substrate-environment thermal resistance R of LED device I jsa1 The same, then by deduction we can get formula (15): R ja3 is the chip PN junction-ambient overall thermal resistance of LED device III, formula (25): where R yg-a is the thermal resistance from the highest temperature point of the fluorescent glue of LED device III to the environment, and formula (26): the highest temperature of the fluorescent glue T yg =T a +R yg-a *P yg-a .

4. The method for obtaining the maximum temperature of LED fluorescent glue by the structural difference method according to claim 1, characterized in that: Step S3 includes: fixing a standard LED with known light radiation power at the bottom of the integrating sphere, driving the standard LED with IH heating current, testing the voltage value of the standard LED with a VF voltage sensor and obtaining its input power P in , Formula (27): P in =IH*VF. The light generated by the standard LED chip is diffusely reflected by the integrating sphere and then received by the detector. The light radiation power tested by the detector is compared with the known light radiation power to calibrate the integrating sphere detector parameters. The standard LED is replaced by LED device II and LED device III in turn. The IH heating current is used to drive LED device II and LED device III in turn. The input power P of the two devices is determined by combining the voltage value measured by the VF voltage sensor. in , Formula (27): P in =IH*VF, and the optical radiation power P of the two devices is measured by the calibrated detector. fg2 and P fg3 .

5. The method for obtaining the maximum temperature of LED fluorescent glue by the structural difference method according to claim 4, characterized in that: Step S3 includes: the input power P of LED device II in For chip heating power P chip and optical radiation power P fg2 , formula (28): P in =P chip +P fg2 ; Input power P of LED device III in For chip heating power P chip , optical radiation power P fg3 And the heating power of fluorescent glue P yg , formula (29): P in =P chip +P fg3 +P yg By deduction, the heating power P of LED device III chip under different IH heating current can be obtained. chip , formula (30): P chip =P in -P fg2 And the heating power of fluorescent glue P yg , formula (31): P yg =P fg2 -P fg3 .

6. The method for obtaining the maximum temperature of LED fluorescent glue using the structural difference method according to claim 1, characterized in that: Step S4 includes: testing the temperature sensitive parameter K coefficient of LED device I, LED device II and LED device III; using different heating currents to drive the three devices respectively to increase the chip junction temperature, monitoring the chip PN junction voltage drop change through the voltage sensor, combining the K coefficient to obtain the chip junction temperature curve, and determining the maximum chip junction temperature T under different currents. j1 、T j2 and T j3 Perform mathematical transformation on the chip junction temperature curve to obtain the transient thermal resistance curve and determine the chip PN junction-environment overall thermal resistance R under different currents. ja1 、R ja2 and R ja3 .

7. The method for obtaining the maximum temperature of LED fluorescent glue using the structural difference method according to claim 6, characterized in that: The method for testing the temperature-sensitive parameter K coefficient of LED devices I, II, and III includes placing LED device III, connected to a transient thermal resistance test circuit, in a constant-temperature oil bath, adjusting the oil temperature to increase the PN junction temperature of the device chip, and recording the chip PN junction voltage drop-junction temperature curve in real time to determine the temperature-sensitive parameter K coefficient. The three devices have the same circuit structure and therefore the same K coefficient.

8. The method for obtaining the maximum temperature of LED fluorescent glue by using the structural difference method as claimed in claim 1, characterized in that: Step S5 includes: firstly obtaining the heating power P from the highest temperature point of the fluorescent glue of the LED device III to the chip PN junction according to the structural difference method. yg-j and the heat output to the environment P yg-a ; Then obtain the thermal resistance R from the highest temperature point of LED device III fluorescent glue to the environment yg-a ; Finally, the maximum temperature T of LED device III fluorescent glue is obtained yg .

9. The method for obtaining the maximum temperature of LED fluorescent glue using the structural difference method according to claim 8, characterized in that: Step S5 includes: obtaining the silicone thermal resistance R of the LED device II gj , formula (7): And the total heat generation power P of LED device III chip PN junction-substrate-environment ja , formula (15): Among them, R ja1 、R ja2 and R ja3 The chip PN junction-environment overall thermal resistance of the three LED devices is obtained respectively; then, the heating power P from the highest temperature point of the fluorescent glue of LED device III to the chip PN junction is obtained. yg-j According to formula (9), we can know that: P yg-j =P ja -P chip ; Then, the heating power P from the highest temperature point of LED device III fluorescent glue to the environment is obtained yg-a According to formula (8), we can know that: P yg-a =P yg -P yg-j ; Thus, we get P yg-j and P yg-a .

10. The method for obtaining the maximum temperature of LED fluorescent glue by using the structural difference method according to claim 9, characterized in that: Step S5 further includes: obtaining the thermal resistance R from the highest temperature point of the fluorescent glue of the LED device III to the environment yg-a , formula (25): Then, the maximum temperature T of the fluorescent glue of LED device III is obtained. yg , formula (26): T yg =T a +R yg-a *P yg-a .

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