KR20120130568A - Real time aging test equipment for LED device - Google Patents

Abstract

PURPOSE: A real time aging test apparatus for an LED device is provided to test the electric characteristics and the optical characteristics of the LED device according to aging. CONSTITUTION: A real time aging test apparatus for LED device comprises a chamber(110), a jig plate(120), an optical measuring part(140), a thermal insulating part and a water jacket. A chamber controls the operating temperature of the LED device. A jig plate is formed in the chamber to emit the heat generated in the LED. The light measuring part measures the light emitted from the LED device. The thermal insulating surrounds the outside of the light measuring part. The water jacket is installed inside the thermal insulating part and cools the photodiode.

Description

LED real time aging test equipment {Real time aging test equipment for LED device}

The present invention relates to an LED real-time life evaluation device, and more particularly, to an LED real-time life evaluation device that can observe the changes in the electrical and optical characteristics of the LED device according to the progress of the aging by operating the LED under severe conditions .

Light emitting diodes (LEDs) are poor in electro-light conversion efficiency due to defects in the internal light emitting layer and non-emissions of various factors, so that a large part of the input power is emitted to the outside as heat. The heat generated in this way becomes a very important factor to shorten the life of the LED, and thus, the study of deriving the causal relationship between heat and life in the evaluation of the life of the LED is the key. The method of measuring the life of an LED is most accurate when the LED is emitted under the same environment in which it is actually used, and the measurement time is measured until the end of the actual life, but when the time is tens of thousands of times, it is almost impossible to measure it realistically. Do.

Most LED-related companies have difficulty securing data on warranty life due to equipment limitations, lack of technical know-how, lack of awareness of reliability, and fast delivery, and LED products that are distributed to the market without such data. Is expected to cause reliability problems such as unstable lighting and reduced brightness, which will impede the maturation of the LED industry. In addition, as the output of LED products increases, reliability evaluation and failure analysis techniques are required more and more, and it is urgent to develop a practical level of reliability equipment with a high level of function to realize this reliability technique. There is no situation. The life evaluation device currently on the market is not only limited in the actual use environment of the LED, but also a part of the characteristic evaluation is monitored in real time, and thus the accurate accelerated life test is not performed. Therefore, the complex effects of LED's primary failure factors such as temperature, light, and current are accurately verified, and the test environment (current application condition, heat dissipation condition, convection condition, etc.) is realized accordingly, and electrical, optical, and thermal characteristics are real-time. There is an urgent need for the development of monitored technologies and their implementation equipment. The reliability and lifespan of LEDs can be assessed by electrical characteristics measurement of current and voltage characteristics, optical characteristics evaluation of light output, spectrum, and color coordinates, and junction temperature measurement to evaluate LED thermal characteristics. In general, all or part of these items can be evaluated to predict the reliability and lifetime of the LED device.

The current method of measuring the life of the LED uses a correlation between the deteriorated data and the harsh condition by adding a harsher condition than the LED driving condition in the steady state to cause the LED to deteriorate quickly. However, it is difficult to apply various life assessment methods used in existing semiconductors to LEDs. Fundamentally, LED is a device that emits light when electricity is applied, unlike general semiconductors, and its life should be evaluated by measuring not only its electrical characteristics but also its intensity and junction temperature. Additional skills will be needed. That is, while applying electricity, the electrical characteristics as well as the light intensity should be measured, and accurate life prediction becomes difficult unless the junction temperature is monitored in real time.

1 is a flow chart for a conventional method for evaluating the life of the LED. Referring to FIG. 1, a method of predicting a conventional LED life is as follows. First, a plurality of LEDs are put in a high-temperature chamber and a current is applied to the LEDs while applying temperature to drive them. Subsequently, the LED is stopped after a certain time and the LED is taken out of the chamber, and then the electrical and optical characteristics of the LED are measured on a separate measuring instrument. At this time, the measurement of the LED element is sequentially performed in the measuring instrument. Subsequently, after measuring the characteristic values of the LEDs, when all the LEDs have been measured, the LEDs are put back into the chamber as needed and a current is applied to drive the LEDs to continue the reliability test. By repeating this operation, the intermittent measured data values can be used to determine the degradation characteristics of the LED, thereby predicting the lifetime of the LED.

In order to continuously measure the light output of the driven LED rather than such an intermittent method, there must be a measuring module that measures the light in the chamber. Limited. The present inventors have already disclosed in Korean Patent No. 1003189. However, in addition to the continuous electrical and optical characterization, the technology and practical level device for measuring the junction temperature, which is the most important parameter in LED reliability evaluation, in real time during aging has not been disclosed. In general, junction temperature measurement is performed on a single sample by using an expensive precision measuring instrument, a temperature controller, and an integrating sphere. When using such a device, measuring junction temperature in real time during aging of a plurality of samples is difficult. impossible. As another method of LED reliability and lifetime evaluation, a method of adding a temperature environment using a thermoelectric element (Thermo Electric Cooler, Peltier element) that can control temperature by heat conduction instead of a high temperature chamber may be used. There is a problem that the metal slug which is responsible for the heat dissipation function of the sample to be tested is necessarily limited because the temperature is controlled by the temperature control, and a detector capable of independently measuring the light output for each LED sample to be evaluated ( Photodiode). Moreover, in order to measure the spectrum and color coordinates of a sample, there is a problem in that a spectrometer equipped with a fiber is provided for each sample. In reality, this method is a limited and incomplete method of measuring only the light output of a sample of a metal slug type. Becomes

The problems with the conventional LED life assessment method is summarized as follows.

1. The LED should be taken out of the chamber after the aging test for a certain period of time because it is difficult to measure the optical characteristics of the LED when driving the LED after the LED is mounted in the chamber. The deterioration characteristics of the LEDs should be determined not only by the electrical characteristics but also by the minute changes in the light output, spectrum, and color coordinates. Therefore, if the LEDs are not measured in real time while driving the LEDs in the chamber, the progress of the LEDs cannot be clearly determined.

2. In order to measure the characteristics of the LEDs in the middle of the LED driving for life evaluation, the LEDs are taken out of the chamber and the characteristics of individual LEDs are measured one by one.

3. It is difficult to accurately predict the average life span and warranty life of the LEDs because it is difficult to measure the junction temperature and therefore the real-time measurement of thermal resistance or the measurement of multiple samples, which are important for evaluating the degradation characteristics of the LEDs.

4. The method using a thermoelectric element capable of evaluating some optical characteristics in real time may be an incomplete method because there are limitations on sample type and characteristic evaluation items as described above.

Therefore, the problem to be solved by the present invention is to determine the progress of the degradation or failure of the LED device by measuring the light output and spectrum, color coordinates and junction temperature in real time while applying a variety of complex stress to the plurality of LED devices It is to provide an LED real-time life evaluation device that can predict the life of the LED device in a short time.

In order to achieve the above object, the present invention provides a chamber for controlling an operating ambient temperature of an LED element, and a plurality of LED elements installed in the chamber and capable of dissipating heat generated from the LED element. A light measuring unit for measuring light output, spectrum, and color coordinates emitted from a jig plate, an LED element mounted inside the chamber and mounted on the jig plate, and a chamber and a light measuring unit by surrounding the outside of the light measuring unit. Provided is an LED real-time life evaluation device including a heat shield for thermally blocking, and a water jacket for cooling the photodiode installed in the heat insulating portion and included in the light measuring unit.

According to an embodiment of the present invention, the jig plate may be provided in plural in the chamber, and the operation temperature of the LED element may be changed by differently configuring the thickness, material, and shape of the jig plate.

According to another embodiment of the present invention, the LED real-time life evaluation device further comprises a junction temperature measuring unit, the junction temperature measuring unit is an aging current drive driver for applying a current required for aging of the LED element, the initial voltage of the drive of the LED element A pulse current driving driver for measuring and an electrical signal switching module for selectively transmitting a signal of the pulse current driving driver to the LED device may be included.

The LED real-time life evaluation device of the present invention has the following effects.

1. Various stresses such as temperature, current, and light, which are factors promoting LED deterioration, can be added.

2. In addition to stress, the junction temperature of the LED can be measured in real time, enabling accurate life assessment of the LED.

3. Real-time monitoring of electrical, optical, and thermal characteristics allows you to understand the progress of LED degradation or failure.

4. It can shorten the R & D time of LED products and contribute to the improvement of LED quality because it can carry out long life prediction test in a short time accurately.

1 is a flow chart for a conventional method for evaluating the life of the LED.
Figure 2 shows the LED real-time life evaluation device of the present invention.
3A and 3B illustrate arrangement states of the jig plate and the light measuring unit in the LED real-time life evaluation apparatus of the present invention.
Figure 4 shows the configuration of the light measuring unit in the LED real-time life evaluation device of the present invention.
Figure 5 shows the configuration for cooling the light measuring unit in the LED real-time life evaluation device of the present invention.
Figure 6 shows the configuration of the optical measuring unit is applied to the optical fiber in the LED real-time life evaluation apparatus of the present invention.
Figure 7 is a block diagram showing the configuration of the junction temperature measuring unit applied to the LED real-time life evaluation apparatus of the present invention.
Fig. 8 shows waveforms illustrating the measurement algorithm used for junction temperature measurement.
9A and 9B are diagrams for explaining a method of measuring junction temperature using a multipulse current and a curve fitting method.
10 is a flowchart illustrating a procedure for measuring junction temperature in accordance with the present invention.

Hereinafter, the present invention will be described in detail.

LED real-time life evaluation device of the present invention, a chamber for controlling the operating temperature of the LED element, and a jig plate which is installed inside the chamber can be equipped with a plurality of LED elements and can emit heat generated from the LED element And a light measuring unit installed inside the chamber and capable of measuring light output and spectrum and color coordinates emitted from an LED element mounted on the jig plate, and surrounding the outside of the light measuring unit to thermally open the chamber and the light measuring unit. And a heat jacket for blocking the photodiode installed inside the heat insulation unit and included in the light measuring unit.

The LED real-time life evaluation apparatus of the present invention can predict LED life more accurately and quickly by measuring the light output, spectrum, color coordinates, and junction temperature of the LED in real time while adding various stresses to the LED. In the LED real-time life evaluation apparatus of the present invention, a high temperature chamber is used to add a high temperature harsh condition to the LED. The LED element to be evaluated is mounted on a jig plate. A plurality of LED elements are first mounted on the jig plate, and then the jig plate is fixed in the chamber. In this case, a plurality of jig plates may be mounted in the chamber, and each jig plate may operate the LED element at different temperature conditions by varying thickness, shape, material, and the like. An optical measuring unit is formed at an upper portion of the jig plate, and a plurality of optical measuring units may be formed in the optical measuring unit so as to correspond to individual jig plates. The photometer can measure the light output or spectrum emitted from the LED elements mounted on the corresponding jig plate, and the number of LED elements mounted on the jig plate is such that the light generated from the individual LED elements is sufficiently received by the detector in the photometer. It may be determined to the extent possible.

Summarizing the process of the life evaluation experiment using the LED real-time life evaluation device of the present invention as follows. First, the desired temperature required for aging is set, and a constant current is applied to each LED element to emit the LED elements. The board that applies the constant current to the LED devices has a circuit that can read the source and voltage to apply the current, so that the voltage applied to each LED device during the aging can be read in real time. The photodiode of the light measuring unit is turned off while emitting the LED element for aging. Subsequently, after a certain time of aging time has elapsed, the current flowing through the LED elements is interrupted and the LED elements of each jig plate are sequentially turned on one by one, and the amount of light emitted from the photodiode in the light measuring unit installed on the LED elements is measured. Will be measured. In this case, if necessary, the spectrum and color coordinates of the sample may be measured by an optical fiber installed adjacent to the photodiode and a spectrometer connected thereto. Subsequently, when the light measurement of the LED elements is completed, all LED elements are applied with a constant current to emit light. As described above, the life of the LED element is evaluated while the lighting is turned on (start of aging), the lighting is turned off (pause of aging), and the sequential light measurement operations for the individual LED elements are repeated. Each step of this process can be pre-programmed and automatically performed, and it is desirable to perform optical measurements once every few hours per LED element in order to effectively acquire long data. This measurement time can be appropriately added or subtracted according to the number of LED elements. Progressing the light measurement of each LED element after the lighting-off is not a big problem since the light measurement time for one LED element is completed within a short time of several milliseconds (msec). In addition, in the plurality of LED elements mounted on the jig plate, as the light reaches the detector, the incident angles of the light do not matter significantly, which is the main concern of reliability and life evaluation, which is a characteristic change after a certain time compared to the initial value of each sample. Because.

Figure 2 shows the LED real-time life evaluation device of the present invention. Referring to FIG. 2, the LED real-time life evaluation apparatus includes a chamber 110, a jig plate 120, a connecting unit 130, and an optical measuring unit 140. The chamber 110 is used to operate the LED element at a high temperature to proceed aging under severe conditions. The chamber door 111 is opened to mount the LED element to the jig plate 120 and to perform the aging process. 111) to close the heat transfer to the outside. The jig plate 120 is equipped with a plurality of LED elements, the LED element mounted on the jig plate in the chamber is temperature balanced by the set test temperature, the heating of the sample and the heat dissipation capacity of the jig plate itself, and accordingly the junction The temperature is determined. Jig plate 120 is configured to mount a plurality of LED elements, a plurality of jig plate is installed in the chamber, each jig plate has a different thickness, material or shape, etc., each jig plate The LED elements mounted on the LEDs may have different electro-optical characteristics (especially junction temperature). Due to this effect, the junction temperature varies according to the heat dissipation capacity of the jig plate even under the same ambient temperature and the same input current condition, and this can be used to determine the performance reliability according to the heat dissipation capacity of the actual LED lighting module in the aging test. do. The connecting unit 130 functions to connect with an external current driving device for driving the LED element mounted on the jig plate, and is composed of a cable and a connecting slot. The connecting slot is configured with a connector so that the LED element of the jig plate can be easily connected to facilitate attachment and detachment of the LED element. When current flows from the external current driving device to the LED element, the LED element is driven to emit light. The light measuring unit 140 measures the light of the LED element to be emitted, the light measuring unit 140 is formed on the jig plate 120 inside the chamber. The optical measuring unit 140 has an optical measuring device including a fiber connected to a photodiode or a spectrometer. Depending on the purpose, one or both of these two optical analyzers can be used. The heat insulation unit is formed on the outer side of the light measurement unit 140. Since the heat insulation unit is inside the chamber, the heat measurement unit prevents heat from being transferred to the light measurement unit. This is because the photodiode included in the photometer is sensitive to the operating temperature and the measured environmental temperature must be kept constant since the measured value changes with temperature. Conventional reliability life assessment devices cannot measure the light output characteristics of the LEDs inside the chamber because the optical measuring device cannot be mounted in the chamber, but the LED real-time life evaluation device of the present invention has a thermal insulation and cooling around the optical measuring unit. The problem is solved by installing a device. Temperature control of the light measuring unit will be described in more detail with reference to FIG. 4.

3A and 3B illustrate arrangement states of the jig plate and the light measuring unit in the LED real-time life evaluation apparatus of the present invention. Referring to FIG. 3A, three jig plates 120 to which a plurality of LED elements 121 are connected are installed in the chamber. In this case, the thickness, material, and shape of the jig plate 120 may be different from each other. An insulating part 150 is formed on the jig plate 120, and the light measuring part inside the insulating part 150 includes a photodiode or an optical fiber. The heat insulator 150 may block heat from being transferred to the light measuring unit. The heat insulator 150 may be made of a material such as a low thermal conductivity ceramic or a composite of an inorganic material and a foamable resin. Although not shown in the drawings, the light measuring unit installed inside the heat insulating part 150 includes a photodiode. The number of photodiodes installed inside the heat insulating part may correspond one-to-one with the number of jig plates. However, when the number of LED elements mounted on one jig plate increases, the number of photodiodes corresponding to the jig plate is also two or more. Can be increased. The LED element 121 may be mounted by soldering directly to the jig plate 120, or may be mounted by coupling the LED element to an appropriate socket to mount the socket on the jig plate. As described above, the jig plate may have different thicknesses, shapes, materials, and the like in order to see a change in junction temperature according to heat dissipation capability even at the same ambient temperature and input current. In other words, if the jig plate is capable of dissipating the heat generated from the LED element, the operating temperature during the aging of the LED element can be lowered. For example, the thicker the jig plate, the better the heat dissipation. The LED elements mounted on the jig plate are aged at a lower operating temperature (junction temperature) than the LED elements mounted on the thin jig plate. Therefore, the LED real-time life evaluation device of the present invention can be carried out at the same time the life evaluation test for the LED element is aged at different operating temperature in one chamber.

Referring to FIG. 3B, a window 141 is installed below the heat insulating part 150. The window 141 functions to allow light generated from the LED element mounted on the jig plate 120 to be introduced into the light measuring unit. When the window 141 is formed in a double glass form, the heat of the chamber is transferred to the light measuring unit. The delivery can be minimized.

Figure 4 shows the configuration of the light measuring unit in the LED real-time life evaluation device of the present invention. Referring to FIG. 4, an optical sensor 142 and a light filter integrated optical sensor 143 are installed inside the heat insulating part 150. The optical sensor 142 is a general sensor made of a photodiode, and the optical sensor integrated light sensor 143 incorporates a luminous filter at the front of the photodiode to correct the optical characteristics of the LED according to the wavelength of the human eye. It is a sensor that includes a function. In the drawing, a total of three sets of photometers constitute a light measuring unit by using a pair of optical sensors 142 made of a photodiode and an optical sensor integrated light sensor 143.

Figure 5 shows the configuration for cooling the light measuring unit in the LED real-time life evaluation device of the present invention. Referring to FIG. 5, the heat insulator 150 has an input coolant pipe 171a, an output coolant pipe 171b, an input air pipe 173a, and an output air pipe as a means for cooling an optical measuring unit installed inside the heat insulation unit. 173b) is connected. When the temperature inside the chamber rises, the temperature of the elements installed in the chamber such as the jig plate 120 and the connecting slot 131 increases. However, the optical measuring unit may reduce an error of measurement by maintaining a constant temperature as a part of processing an electrical signal. Although the optical measuring part maintains the heat insulation state to some extent with the inside of the chamber by the heat insulating part, the temperature inside the heat insulating part is increased by the heat generated inside the chamber as the operation time becomes longer. This increase in temperature will cause a measurement error of the photodiode, so it is advantageous that a separate cooling device is installed inside the insulation. There are two methods of cooling: air cooling and water cooling. Cooling with air blows cold air into the inside of the insulator to exhaust hot heat from the inside of the insulator, while cooling with water installs a water jacket around the photodiode and adds water to the water jacket. It is a method of cooling a photodiode by circulating. If air cooling is less effective than water cooling, but the chamber temperature is not high, air cooling may be a simpler method. It may also serve to blow dry air to prevent condensation due to temperature differences in the light detector.

Figure 6 shows the configuration of the optical measuring unit is applied to the optical fiber in the LED real-time life evaluation apparatus of the present invention. Although omitted in FIG. 6, the optical fiber is connected to a spectrometer capable of measuring spectra and color coordinates. Referring to FIG. 6A, an optical fiber 144a is inserted into the heat insulation part 150. The optical fiber 144a is used to measure the spectrum and color coordinates of the LED element in real time. The optical fiber may be installed inside the heat insulation unit together with the photodiode of the optical measuring unit, or may be installed alone inside the heat insulation unit without the photodiode. Can be. 6B and 6C (the figure which shows the inside of the water jacket together in FIG. 6B), the optical fiber connection adapter 144b is formed in the inside of the heat insulation part 150. FIG. The optical fiber connection adapter 144b is a portion to which the optical fiber is connected, and the light passing through the window is connected to the spectrometer outside the chamber via the optical fiber connected to the optical fiber connection adapter 144b. Although not shown in the figure, a photodiode is provided inside the water jacket 145, and the photodiode is surrounded by the water jacket 145, so that the temperature is constantly controlled by thermal conduction. At this time, the optical fiber connection adapter 144b is not in contact with the water jacket 145, because the optical fiber does not react sensitively with temperature, so the influence of temperature is much less than that of the photodiode. It is preferable to use an optical fiber covered with a stainless steel sheath to withstand high temperatures. In this way, if the photodiode and the fiber / spectrometer are installed together, it is possible to simultaneously measure the light output and the spectrum.

The LED real-time life evaluation device of the present invention includes a function to measure the junction temperature and thermal resistance in real time, in addition to monitoring the real-time light output, spectrum, color coordinates, etc. during the long-term reliability life test of the LED device. In particular, this function is applicable not only to one LED device but also to multiple multi-channel LED devices. Junction temperature is the most accurate measurement factor for the degradation characteristics of LED devices. In the present invention, by reading the voltage across the LED element while instantaneously applying current to each LED element in a very short time during initial LED element driving, and comparing the voltage in the state where the junction temperature rises in the middle of aging The junction temperature is indirectly measured by deriving the correlation between the voltage and the junction temperature. In addition, the thermal resistance can be derived from the junction temperature by using the relationship between the thermal resistance and the junction temperature. To this end, the LED real-time life evaluation apparatus of the present invention includes a junction temperature measuring unit consisting of an aging current driving driver, a pulse current driving driver, an electrical signal switching module, the junction temperature measuring unit may be installed outside the chamber. The measurement of the junction temperature may be performed by applying a direct current to the LED device for a long time after the initial voltage measurement and aging, and measuring the junction temperature in the middle. In this way, by measuring the junction temperature of a large number of LED devices in real time during the reliability test for aging the LED devices, it provides a basis for accurately measuring the degradation process of the LED devices to enable accurate life assessment.

7 is a block diagram for explaining the configuration of the junction temperature measuring unit applied to the LED real-time life evaluation apparatus of the present invention. Referring to FIG. 7, a plurality of LED elements 205 for aging test are installed in the chamber 201, an aging current driving driver and a voltage meter 204 are connected to the LED elements 205, and pulse current driving is performed. The driver and voltage meter 202 are connected to the LED element 205 through the electrical signal switching module 203. The aging current driving driver may be configured as a multichannel driver of several tens or hundreds of channels according to the number of LED elements 205 in the chamber 201. In order to apply a precise current or measure an accurate voltage separately from the aging current driver, a pulse current driver and a voltage meter 202 having a level and precision of the instrument level are required. Since this is a very stable and accurate instrument, the number of samples of LED devices can be expensive, making the equipment expensive and not practical. The precision meter can be constructed using, for example, a pulse meter 2600 S model of Keithley, USA. In the present invention, the electric signal switching module 203 is used to measure a plurality of LED elements with one precise pulse current driving driver. That is, the pulse current driver is connected in parallel to the aging current driver and the LED element, the pulse current driver is an electrical signal switching module 203 between the LED element.

Before aging the many LED devices, it is very important to first read the voltage of the initial LED device by applying a very short current to the LED device. At this time, the amount of current and the application time require a low current and a short time such that the LED element does not generate heat due to this current. It was tested to be suitable if the current amount was 1 milliampere (mA) or less and the application time was 200 microseconds (usec) or less. If the current is larger or the pulse application time is longer than this, the temperature may fluctuate during the measurement and the measurement may be inaccurate. Before aging the LED device through the aging current driver, all LED devices are read and stored with the initial microcurrent voltage. After measuring the initial voltage, the LED device is driven by an aging current drive driver so that the aging experiment can be continued by applying a rated aging current to the LED device. In more detail, the order of measurement will be described. A pulse current is read and stored through a pulse current driving driver for the first LED element among the plurality of LED elements mounted in the chamber, and the pulse current is stored in the second LED element. In order to apply the voltage, the electrical signal of the first LED device is disconnected through the electrical signal switching module and the electrical circuit is connected to the second LED to store the voltage by flowing a microcurrent. This operation is repeated to record the voltage value of the initial microcurrent of all the LED elements installed in the chamber. After all these operations, the LED device inside the chamber is subjected to an aging current drive driver to apply the current to the LED device for aging test. In order to accurately measure the voltage during the aging test, the present invention allows the voltage to be read and accurate junction temperature measured through the following process. Figure 8 shows the time chart according to the voltage variation, junction temperature change and applied current type.

Fig. 8 shows waveforms illustrating the measurement algorithm used for junction temperature measurement. Referring to FIG. 8, when the aging current starts to flow through the LED device, as shown in FIG. 8A, the voltage V _F becomes a maximum value ① and heat is generated in the LED device thereafter. In the semiconductor device including the LED device, the voltage gradually decreases when heat is generated. In general, the pn junction temperature is correlated with the voltage so that the junction temperature can be accurately known as long as the voltage can be accurately measured. When the aging current is continuously added, the junction temperature continues to increase as shown in FIG. 8 (b), and after some time, the junction temperature T _j is stabilized (②). When the junction temperature is stabilized, switching from the aging current driver to the pulse current driver (③), and the current value maintains a direct current with the same size as the aging current. At this time, there may be a momentary change of voltage and junction temperature (③, ④), but after some time has elapsed (T _s1 in FIG. This process can be configured to be easily set up programmatically by the user on the device. After a predetermined time (T _s1 ) at which the junction temperature stabilizes, the pulse measuring source (normally available precision pulse measuring source which can flow both DC and pulse current) is changed to pulse mode momentarily (⑥ ), A monitoring current of less than about 1 milliampere (mA) flows. At this time, the pulse width is about 200 microseconds (usec). The voltage value measured under this condition should be measured as the voltage value A (V _M1 ) at the original monitoring current value, but in practice, the junction temperature has already risen under the aging current condition. The voltage value B (V _M2 ) smaller than the voltage value A is measured. The difference between these two voltage values (ΔV _F ) can be measured and the junction temperature can be derived from the relationship between junction temperature and voltage. In LED, the relationship between temperature and voltage is generally called a k-factor, and the approximate value is known as 2 mV / ℃, but this value is measured when measuring junction temperature because the characteristics of each LED element are slightly different. Needs to be accurately measured in advance. In other words, by accurately measuring such a relationship value in a separate measuring instrument and put it as a factor of the reliability life test apparatus of the present invention, it is possible to derive more precise junction temperature. The method of measuring the k-factor is a method commonly used in semiconductor devices, and thus detailed description thereof will be omitted. Dividing the measured ΔV _F value by the K-factor value gives the desired junction temperature from Equation 1 below. In addition, the thermal resistance of the sample may be derived from Equation 2 representing the relationship between the junction temperature and the thermal resistance. Once the junction temperature of one LED is obtained, the junction temperature can be calculated in the same way for another LED element under aging test.

Equation 1

(T _j : Junction temperature, T _a : Ambient temperature, ΔVf: V _M2 -V _M1 (difference between voltage value measured by monitoring current value before aging starts and voltage value measured by monitoring current value during aging process))

Equation 2

(T _j : junction temperature, T _a : ambient temperature, R: thermal resistance, Vop: measured voltage, Iop: input current)

The following is a further explanation of the measurement algorithm and measurement waveform of FIG. In the present invention, in addition to the method for obtaining the junction temperature during the aging test of the multi-channel LED, several additional functions have been devised to improve the accuracy of the junction temperature. In FIG. 8, the voltage was measured by applying a fine current through the pulse current driving driver at ⑥, but in order to measure stable voltage, several short pulse currents were applied instead of a short pulse to measure the voltage and average the voltage. You can choose how. The symbols shown in FIG. 8 are summarized as follows.

V _F : Forward Voltage

V _M1 : Monitoring Current before Aging

V _M2 : Monitoring Current after Aging

T _S1 : Settling time after changing from aging current source to pulse measuring source

T _S2 : Time from aging current to fine current before voltage saturates

Total I _F : Total forward current of aging current source and pulse measuring source

Pulse I _F : Forward current from pulse measuring source

Aging I _F : Forward current from aging current source

9A and 9B are diagrams for explaining a method of measuring junction temperature using a multipulse current and a curve fitting method. Referring to FIG. 9A, a minute current flows in a short pulse and the voltage is read and stored. Subsequently, the LED element increases in voltage as it cools down after a certain time (indicated by a blue circle). When the voltage is read at a slight time period, a curve as shown in FIG. 9B appears. At this time, the curve is obtained by the intersection of the vertical axis (marked with a blue circle) through the curve fitting method. When the junction temperature rises during aging, the reference monitoring current (Im) is applied before cooling. It can be thought of as an accurate voltage for the circuit, and thus a more accurate junction temperature can be obtained.

10 is a flowchart illustrating a method of measuring junction temperature described so far.

The above description has been made using the embodiments of the technical idea of the present invention, and those skilled in the art to which the present invention pertains various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments described in the present invention are not intended to limit the scope of the present invention but to limit the scope of the present invention. The scope of protection of the present invention should be interpreted by the claims, and all technical ideas falling within the scope of the present invention shall be included in the scope of the present invention.

100: LED real-time life evaluation device 110: chamber
111: chamber door 120: jig plate
121: LED element 130: connecting portion
131: connecting slot 140: optical measuring unit
141: window 142: light sensor
143: light sensor integrated optical sensor 144a: optical fiber
144b: optical fiber connection adapter 145: water jacket
147: photodiode 150: heat insulation
170: cooling piping 170a: input cooling piping
170b: output cooling piping 171a: input cooling water piping
171b: output coolant piping 172: water jacket
173a: input air piping 173b: output air piping
201: chamber
202: pulse current driver and voltage meter
203: electric signal switching module
204: aging current driver and voltage meter
205: LED element

Claims (3)

A chamber for controlling the operating temperature of the LED element;
A jig plate installed in the chamber and mounted with a plurality of LED elements and capable of dissipating heat generated by the LED elements;
An optical measuring unit installed inside the chamber and capable of measuring light output emitted from an LED element mounted on the jig plate;
An insulating part surrounding the outside of the optical measuring part to thermally block the chamber and the optical measuring part; And
And a water jacket installed inside the heat insulation part and cooling the photodiode included in the light measuring part. The method according to claim 1,
The jig plate is provided in plural inside the chamber, by configuring the thickness, the material and the shape of the jig plate differently, it is possible to change the operating temperature of the LED element, characterized in that the LED real-time life evaluation device. The method according to claim 1,
The LED real-time life evaluation device further comprises a junction temperature measuring unit, the junction temperature measuring unit is an aging current driving driver for applying a current required for aging of the LED element, a pulse current driving driver for measuring the driving initial voltage of the LED element and pulse LED real-time life evaluation device comprising an electrical signal switching module for selectively transmitting a signal of the current drive driver to the LED element.

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