Methods for in-situ testing of thermal conductivity of LED chip coating

Abstract

This invention discloses a method for in-situ testing of the thermal conductivity of an LED chip adhesion layer, comprising the following steps: acquiring multiple test workpieces, obtaining the cross-sectional area and the thickness of the chip adhesion layer of each test workpiece; placing the test workpieces in a constant temperature environment and energizing them, and sequentially applying multiple heating currents with different current values ​​to each test workpiece during energization, and correspondingly obtaining the electrical power P of the test workpiece when each current is applied. E Optical power P L and the temperature T of the LED functional body j The obtained data will be expressed in P E -P L As the independent variable, with T j A linear fit was performed on the dependent variable, and the slope of the fitted line was the total thermal resistance R. th The thickness d of the chip adhesion layer in the test workpiece is used as the independent variable, and the total thermal resistance R of each test workpiece is used as the independent variable. th A linear fit was performed on the dependent variable, and the slope of the resulting straight line was the thermal resistance R per unit thickness of the chip's adhesive layer. s The above-mentioned in-situ method for measuring the thermal conductivity of LED chip adhesion layers has a measurement accuracy of less than 5%, and can achieve the measurement of the thermal conductivity of chip adhesion layers.

Description

Technical Field

[0001] This invention relates to the field of LED thermal conductivity technology, and in particular to a method for testing the thermal resistance of the LED chip's adhesion layer. Background Technology

[0002] High-power LEDs generate a significant amount of heat during operation. If this heat cannot be effectively dissipated, it can lead to a decrease in luminous flux. LEDs are typically attached to a substrate surface via a chip adhesion layer, and most heat dissipation relies on the conduction of this layer. Therefore, the material of the chip adhesion layer significantly impacts the LED's performance. Materials with higher thermal conductivity generally enable LEDs to operate at higher power for longer periods, while ensuring higher luminous flux, better efficiency, color stability, and reliability. Sintered nano-silver materials are a commonly used chip adhesion layer material today.

[0003] Most of the heat dissipation in an LED relies on the conduction of the chip layer. Fluctuations in the material and even the morphology of the chip layer can affect its thermal conductivity. To control or improve the thermal conductivity of the chip layer, accurate measurement of its thermal resistance is necessary. The thermal conductivity of a chip layer using sintered nano-silver as the material is related to the size of the nano-silver particles, the solvents and resins used in the silver paste, the assembly pressure during LED fabrication, and the sintering temperature and time. Furthermore, the chip layer is typically only tens of micrometers thick and exists only between the LED functional body and the substrate; therefore, in-situ measurement of the thermal resistance of the LED chip layer is required.

[0004] In the industry, the most common in-situ assessment method for LED thermal behavior is the thermal resistance from the LED's PN junction to the environment. This test only reflects the overall thermal resistance of all layers in the LED device, failing to reflect the thermal resistance of a single layer. In particular, the thermal resistance of the sintered silver nanolayer is typically only about 0.8% of the total thermal resistance of the device, which can be considered within the range of measurement fluctuations. On the other hand, because the LED chip's attached layer is very thin and has very low thermal resistance, a relatively high layer thickness and appropriately high thermal resistance are usually required when measuring thermal conductivity; otherwise, the measurement deviation will be large. This also makes it difficult to accurately measure the thermal resistance of the chip's attached layer alone. Therefore, accurately measuring the thermal resistance of the LED chip's attached layer has become a problem that urgently needs to be solved. Summary of the Invention

[0005] Therefore, it is necessary to provide a test method that can accurately measure the thermal resistance of the LED chip's coating layer.

[0006] According to an embodiment of the present invention, a method for testing the thermal resistance of an LED chip adhesion layer is characterized by comprising the following steps:

[0007] Multiple test workpieces are obtained, each test workpiece including a substrate and a chip attachment layer and an LED functional body sequentially disposed on the substrate. The thickness of the chip attachment layer in different test workpieces is different, but the cross-sectional area perpendicular to the thickness direction is the same. The cross-sectional area and the thickness of the chip attachment layer are obtained.

[0008] Obtain the total thermal resistance R of each of the test workpieces. th Obtain the total thermal resistance R th The method includes the following steps: placing the test workpiece in an environment with a constant temperature and energizing it; sequentially applying multiple heating currents with different current values ​​to each test workpiece during energization; and obtaining the corresponding electrical power P of the test workpiece when each current is applied. E Optical power P L and the temperature T of the LED functional body j The obtained data will be expressed in P E -P L As the independent variable, with T j A linear fit is performed on the dependent variable, and the slope of the fitted line is the total thermal resistance R. th ;

[0009] Using the thickness d of the chip adhesion layer in the test workpiece as the independent variable, and the total thermal resistance R of each test workpiece as the independent variable... th A linear fit was performed on the dependent variable, and the slope of the resulting straight line was the thermal resistance R per unit thickness of the chip's adhesion layer. s ;

[0010] Calculate the thermal conductivity of the chip adhesion layer. Where A is the cross-sectional area.

[0011] In one embodiment, the temperature T of the LED functional body is obtained. j The method includes the following steps:

[0012] Immediately after the heating current is applied, a detection current is applied and the forward voltage of the LED functional body is measured at this time. The temperature of the LED functional body is then calculated using the forward voltage.

[0013] In one embodiment, the forward voltage of the LED functional body is sampled within 100 μs after the detection current is applied to obtain the forward voltage.

[0014] In one embodiment, the applied detection current has a current value of 0.005A to 0.05A.

[0015] In one embodiment, the applied heating current has a current value of 0.1A to 2A.

[0016] In one embodiment, the thickness of the chip attachment layer in each of the test workpieces is 10 μm to 160 μm.

[0017] In one embodiment, the number of test pieces is four or more.

[0018] In one embodiment, the total thermal resistance R of each of the test workpieces is obtained. th During the process, the number of current values ​​of the applied heating current is four or more.

[0019] In one embodiment, the material of the chip adhesion layer is sintered nano-silver material.

[0020] In one embodiment, the substrate is a metal substrate.

[0021] The above embodiments provide a method for in-situ measurement of the thermal conductivity of the LED chip's adhesion layer. This is achieved by utilizing the following property: First, the temperature T of the LED's functional body... j There is a linear relationship between the thermal power of the LED functional body and the coefficient is equal to the thermal power R. th And electrical power P E With optical power P L The difference is the thermal power, therefore, by measuring multiple sets of electrical power P E Optical power P L and the temperature T of the LED functional body j The total thermal resistance R of the test workpiece can then be obtained by fitting the data. th Subsequently, multiple sets of total thermal resistance R were obtained through multiple test pieces. th By performing linear fitting with the thickness d data, this calculation method cleverly avoids the problems of thin chip adhesion layers and low thermal resistance. Experiments show that the above-mentioned in-situ measurement method for the thermal conductivity of LED chip adhesion layers has a measurement accuracy within 5%, and can achieve the measurement of the thermal conductivity of chip adhesion layers. Detailed Implementation

[0022] To facilitate understanding of the present invention, a more comprehensive description is provided below. Preferred embodiments of the invention are shown herein. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items. The term “more” as used herein includes two or more items. The term “above a certain number” as used herein should be understood as a number and a range greater than a certain number.

[0024] According to one embodiment of the present invention, a method for in-situ testing of the thermal conductivity of an LED chip adhesion layer includes the following steps.

[0025] Multiple test pieces are obtained. Each test piece includes a substrate and a chip attachment layer and an LED functional body sequentially disposed on the substrate. The thickness of the chip attachment layer in different test pieces is different, but the cross-sectional area perpendicular to the thickness direction is the same. The cross-sectional area and the thickness of the chip attachment layer are obtained.

[0026] Obtain the total thermal resistance R of each test workpiece. th Obtain the total thermal resistance R th The method includes the following steps: placing the test workpiece in an environment with a constant temperature and applying electricity; sequentially applying multiple heating currents with different current values ​​to each test workpiece during the power-on process; and obtaining the corresponding electrical power P of the test workpiece when each current is applied. E Optical power P L and the temperature T of the LED functional body j The obtained data will be expressed in P E -P L As the independent variable, with T j A linear fit was performed on the dependent variable, and the slope of the fitted line was the total thermal resistance R. th ;

[0027] Using the thickness d of the chip adhesion layer in the test workpiece as the independent variable and the total thermal resistance R of each test workpiece as the independent variable... th A linear fit was performed on the dependent variable, and the slope of the resulting straight line was the thermal resistance R per unit thickness of the chip's adhesive layer. s ;

[0028] Calculate the thermal conductivity of the chip's adhesion layer Where A is the cross-sectional area.

[0029] It is understandable that, among multiple test pieces, aside from differences in the thickness of the chip adhesion layer, the materials of the substrate and the LED functional body, the specific fabrication method of the chip adhesion layer, and the cross-sectional area of ​​the chip adhesion layer should be completely identical. This is to ensure, as far as possible, that the difference in thermal conductivity between multiple test pieces is solely due to differences in thickness. Here, cross-sectional area refers to the area of ​​the cross-section perpendicular to the thickness direction of the chip adhesion layer.

[0030] The above embodiments provide a method for in-situ measurement of the thermal conductivity of the LED chip's adhesion layer. This is achieved by utilizing the following property: First, the temperature T of the LED's functional body... j There is a linear relationship between the thermal power of the LED functional body and the coefficient is equal to the thermal power R. th And electrical power P E With optical power P L The difference is the thermal power, therefore, by measuring multiple sets of electrical power P E Optical power P L and the temperature T of the LED functional body j The total thermal resistance R of the test workpiece can then be obtained by fitting the data. th This calculation method can obtain the total thermal resistance of the test workpiece as accurately as possible, avoiding inaccurate calculations due to measurement fluctuations; subsequently, multiple sets of total thermal resistance R are obtained through multiple test workpieces. th By performing linear fitting with the thickness d data, this calculation method cleverly avoids the problems associated with thin chip adhesion layers and low thermal resistance. Experiments show that the above-mentioned in-situ measurement method for the thermal conductivity of LED chip adhesion layers has a measurement accuracy within 5%, and can achieve the measurement of the thermal conductivity of a single chip adhesion layer.

[0031] To facilitate understanding and implementation of the present invention, the method for in-situ testing of the thermal conductivity of the LED chip attachment layer in the above embodiments will be further explained below through the principles on which it is based and more detailed examples.

[0032] A method for in-situ testing of the thermal conductivity of an LED chip coating layer includes steps S1 to S4.

[0033] Step S1: Obtain multiple test pieces.

[0034] Each test piece includes a substrate and a chip attachment layer and an LED functional body sequentially disposed on the substrate. The thickness of the chip attachment layer varies in different test pieces, but the cross-sectional area perpendicular to the thickness direction is the same. The LED functional body refers to a PN junction or a material that can emit light when an electric current is applied, based on a PN junction. The PN junction can be an AlGaInP structure disposed on a silicon substrate.

[0035] In this design, a chip attachment layer is stacked on a substrate, and the LED functional unit is stacked on the chip attachment layer. Heat generated by the LED functional unit is conducted to the substrate via the chip attachment layer and then dissipated through the substrate. In conventional LED devices, a dielectric layer is placed between the chip attachment layer and the substrate. This dielectric layer has high thermal resistance, meaning that a significant portion of the heat dissipation process of the LED functional unit is dominated by the thermal resistance of the dielectric layer. The inventors discovered that if a dielectric layer is placed in the test workpiece, it dominates the heat dissipation process, and the thermal resistance of the chip attachment layer accounts for a very low proportion of the total thermal resistance. For example, the thermal resistance of a sintered silver chip attachment layer accounts for only 0.8% of the total thermal resistance, which significantly reduces the measurement accuracy of the chip attachment layer. However, by directly stacking the chip attachment layer on the substrate, the proportion of the thermal resistance of the sintered silver chip attachment layer to the total thermal resistance can be increased to 8%. This significant improvement greatly enhances the measurement accuracy of the thermal resistance of the chip attachment layer. Therefore, the dielectric layer is omitted in the test piece in this embodiment. Although this type of test piece is not suitable for commercial devices, it is appropriate for the test piece used in this embodiment, and the measured thermal resistance of the chip attachment layer is also instructive for commercial devices.

[0036] In one specific example, the material of the chip adhesion layer is sintered nano-silver material.

[0037] In one specific example, the number of test pieces is four or more. Specifically, for example, the number of test pieces is four, five, six, seven, or eight. More preferably, the number of test pieces is four to seven.

[0038] In one specific example, the substrate is a metal substrate. More preferably, the substrate is selected from a silver substrate or a copper substrate. It can be understood that the higher the thermal conductivity of the substrate, the higher the proportion of the thermal resistance of the chip attachment layer in the overall test workpiece, and the more accurate the measurement of the thermal resistance of the chip attachment layer will be.

[0039] In one specific example, the cross-sectional area can be obtained through microscopic observation. Similarly, the thickness of the chip's adhesive layer can also be obtained through microscopic observation. Microscopic observation of the cross-section of the chip's adhesive layer is the most accurate method for measuring its thickness.

[0040] In another specific example, the thickness of the chip adhesion layer can also be obtained by optically measuring the chip adhesion layer on a complete test piece using a vertical microscope. Vertical microscopes have a very narrow depth of field and a calibrated focusing axis. By focusing the microscope on the surface, zeroing the z-axis, and then refocusing on the new surface, the vertical distance between the two can be measured.

[0041] In one specific example, the thickness of the chip attachment layer in multiple test pieces ranged from 10 μm to 160 μm. The thickness of the chip attachment layer in commonly used LED devices is typically 10 μm to 50 μm. Designing the chip attachment layer thickness to be distributed within the range of 10 μm to 160 μm during testing helps to reflect the thermal resistance of the chip attachment layer in actual LED devices. Furthermore, the thickness of the chip attachment layer in multiple test pieces ranged from 20 μm to 130 μm.

[0042] It is understandable that the test workpiece can be obtained through purchase or fabrication. Generally speaking, since the thermal conductivity of the chip adhesion layer is strongly correlated with factors such as the raw materials used and the specific fabrication method, the chip adhesion layer in the test workpiece should be fabricated according to the fabrication method of the chip adhesion layer in the actual LED device to ensure the comparability of the two data.

[0043] Step S2: Obtain the total thermal resistance R of each test workpiece. th .

[0044] Assuming that electricity is applied to the LED functional body, the electrical energy will be converted into heat energy and emitted light energy. The heat generated by the LED functional body will cause it to heat up briefly, at which point the temperature T of the LED functional body will be... j and the heating power P of the test workpiece H The following relationship exists.

[0045] T j =R th ·P H +T0

[0046] Among them, R th It measures the total thermal resistance of the workpiece, and its dimension is K / W. P H T0 is the heating power of the test workpiece, measured in W, and T0 is the initial temperature of the test workpiece, measured in K. When the test workpiece is placed in an environment with a constant temperature, the initial temperature of the test workpiece can be considered as the ambient temperature, which is a constant value.

[0047] Among them, the heating power P of the test workpiece H The electrical power P of the workpiece can be tested. E With optical power P L The difference is obtained. Therefore, the above relation can be transformed into the following relation.

[0048] T j =R th ·(P E -P L )+T0

[0049] Therefore, the total thermal resistance R is obtained. thThe method may include the following steps: placing the test workpiece in an environment with a constant temperature and energizing it; applying multiple heating currents with different current values ​​to each test workpiece sequentially during energization; and obtaining the corresponding electrical power P of the test workpiece when each current is applied. E Optical power P L and the temperature T of the LED functional body j The obtained multiple sets of data are arranged according to the relation T j =R th ·(P E -P L A linear fit is performed using )+c1, where c1 corresponds to a constant ambient temperature T0, and the slope of the fitted line is R. th .

[0050] Measure multiple sets of electrical power P on the same test workpiece E Optical power P L and the temperature T of the LED functional body j This can minimize random errors introduced during the measurement of total thermal resistance.

[0051] Among them, electric power P E It can be calculated from the applied voltage and current. Optical power P L The luminous flux and other parameters emitted by the LED can be measured and calculated using existing optical measurement methods. For example, the LED can be placed in an integrating sphere, and light can be collected by a CCD spectrometer through a small satellite sphere and optical fiber to measure the instrument parameters and then calculate the optical power. The specific method will not be elaborated here.

[0052] Accurately obtain the temperature T of the LED functional unit when it is powered on. j There are certain challenges involved. Since the heat of the LED functional unit dissipates through the substrate, the substrate temperature cannot be considered strictly equal to the LED functional unit temperature, which leads to some error. Therefore, accurately measuring the temperature of the LED functional unit is quite difficult. To improve measurement accuracy as much as possible, the inventors conceived of utilizing the temperature-sensitive characteristic of the LED functional unit itself to test its temperature.

[0053] Specifically, since the forward voltage of an LED diode is related to its temperature when it emits light, and the forward voltage changes with the junction temperature, the temperature of the junction in the LED functional unit can be obtained by measuring the forward voltage of the diode. Of course, to use this method to test the temperature of the LED functional unit, it is also necessary to know the relationship between the forward voltage of the LED functional unit and the junction temperature, which is usually linear. In one specific example, the temperature T of the LED functional unit is obtained. jThe method includes the following steps: immediately after applying the heating current, apply a detection current and measure the forward voltage of the LED functional body at this time, and calculate the temperature of the LED functional body from the forward voltage. It is understood that the application of the detection current and the application of the heating current cannot be performed simultaneously; therefore, the detection current must be applied immediately after the heating current application ends.

[0054] Furthermore, the inventors discovered that, unlike conventional technologies using LED devices as temperature sensors, the aforementioned test workpiece lacks a dielectric layer, resulting in very low thermal resistance. Once the heating current is switched to the test current, the temperature of the LED functional body changes rapidly, thus affecting the temperature measurement of the LED functional body. Therefore, it is necessary to measure the forward voltage of the LED functional body as quickly as possible and consider the temperature corresponding to this forward voltage as the temperature of the LED functional body during the application of the heating current. In one specific example, the forward voltage of the LED functional body is sampled within 100 μs after the application of the detection current. This requires the voltage of the LED functional body to be sampled as frequently as possible. For example, a device with a sampling frequency of 10,000 times / s can be used for monitoring.

[0055] In one specific example, the applied heating current is 0.1A to 2A. Further, the applied heating current is 0.1A to 1A. The total thermal resistance R of each test workpiece is obtained. th During the process, the number of applied heating current values ​​is four or more. For example, the applied heating current values ​​are 0.1A, 0.3A, 0.5A, and 0.7A, respectively.

[0056] In one specific example, the applied detection current is 0.005A to 0.05A. More specifically, the applied detection current is 0.005A to 0.02A. For example, the applied detection current is 0.01A. Keeping the applied detection current as low as possible minimizes the impact of heat generated by the detection current on the temperature of the LED functional unit, thereby improving the temperature measurement accuracy of the LED functional unit.

[0057] It is understandable that the total thermal resistance R of the above-mentioned test workpiece th The testing method is performed on a single test piece. Operators can use the same method to obtain the total thermal resistance R of other test pieces. th However, the total thermal resistance R th This cannot be equated to the thermal resistance of the chip attachment layer. Therefore, it is also necessary to obtain the thermal resistance of the individual chip auxiliary layer.

[0058] Step S3: Test the thermal resistance per unit thickness of the chip's adhesive layer.

[0059] Among them, the total thermal resistance R of the test workpiece can be considered as th This includes the thermal resistance of the chip attachment layer and the remaining thermal resistances of the non-chip attachment layer. The thermal resistance of the chip attachment layer should be the product of the thermal resistance per unit thickness and the thickness d of the chip attachment layer; therefore, the total thermal resistance R of the tested workpiece is... th The thickness d of the chip adhesion layer also has the following relationship: R th =R s ·d+R Rem , where R s R is the thermal resistance per unit thickness of the chip adhesion layer. Rem The remaining thermal resistance is the total thermal resistance of the workpiece excluding the chip adhesion layer, including the thermal resistance of the chip, dielectric, substrate, thermal interface material, heat sink, and boundary layer of the chip adhesion material.

[0060] The remaining thermal resistance R Rem It is difficult to measure accurately directly, but for a batch of test pieces prepared under the same conditions, the only difference should be the thickness of the chip adhesion layer. Therefore, it can be assumed that the remaining thermal resistance R of this batch of test pieces is the same. Re m is a constant value. Based on this, the total thermal resistance R of multiple test workpieces can be calculated. th The thickness d of the chip attachment layer in the corresponding test workpiece is related to the formula R. th =R s A linear fit is performed using d+c2, where c2 is a constant, and the slope R of the resulting line is measured. s This yields the thermal resistance per unit thickness of the chip's adhesive layer, also known as the proportional thermal resistance. This is a quantity that is independent of the chip's adhesive layer thickness but related to the cross-sectional area perpendicular to the thickness direction, and its unit is K / W·m.

[0061] Step S4: Calculate the thermal conductivity of the chip adhesion layer.

[0062] In step S3, the thermal resistance R per unit thickness of the chip adhesion layer has been obtained. s Thermal conductivity of the chip adhesion layer Where A is the cross-sectional area perpendicular to the thickness direction.

[0063] To verify the accuracy of the above-mentioned method for in-situ testing of the thermal conductivity of the LED chip adhesion layer, the following Example 1 was used for verification.

[0064] Example 1

[0065] Test pieces were fabricated using SAC305 solder paste as the chip adhesion layer material. The substrate was copper, and the main LED component was a PN junction, specifically AlGaInP on a silicon substrate. A total of 27 test pieces were fabricated, and the thickness of the chip adhesion layer on each piece was determined by microscopic observation. The thickness of the chip adhesion layer on the 27 test pieces ranged from a minimum of 10 μm to a maximum of 160 μm.

[0066] For each test workpiece, heating currents of 0.1A, 0.3A, 0.5A, and 0.7A were applied respectively, and the corresponding thermal power P was calculated. E Immediately after each heating current is applied, a 0.01A current is applied as a detection current. The forward voltage within the range of 30μs to 100μs after the detection current is applied is measured, and the temperature T of the LED functional body of the test workpiece is calculated according to the voltage-temperature relationship of the test workpiece. j ;

[0067] The optical power P of each test workpiece was measured using an integrating sphere when each heating current was applied. L For each test piece, the temperatures T of the four LED functional components will be obtained. j With thermal power P E Optical power P L According to the relation T j =R th ·(P E -P L Perform linear fitting on c1 and obtain the slope R of the fitted line. th This is the total thermal resistance of the workpiece being tested.

[0068] The total thermal resistance R of each test piece is... th The thickness d of the chip attachment layer in the corresponding test workpiece is related to the formula R. th =R s A linear fit is performed using d+c2, where c2 is a constant, and the slope R of the resulting line is... s Calculate the thermal resistance per unit thickness of the chip adhesion layer; and calculate the thermal conductivity of the chip adhesion layer. Where A is the cross-sectional area.

[0069] It should be noted that the thermal conductivity of solder paste SAC305 is known to be 64 W / m·K, and the thermal conductivity of the chip adhesion layer prepared by solder paste SAC305 can be considered to be approximately 64 W / m·K.

[0070] Based on the above tests, the calculated thermal conductivity k of the chip adhesion layer prepared with solder paste SAC305 is 61.5 W / m·K. The error of the thermal conductivity measured by the above test method is 3.9%. Therefore, Example 1 is sufficient to demonstrate that the above test method is relatively accurate, and the data obtained is reliable. It can be optimistically assumed that the error of the thermal conductivity measured by the above method can be controlled within 5%.

[0071] Example 2

[0072] Test pieces were fabricated using sintered silver paste as the chip adhesion layer material. The substrate was copper, and the main LED component was a PN junction, specifically AlGaInP on a silicon substrate. A total of 27 test pieces were fabricated, and the thickness of the chip adhesion layer on each piece was determined by microscopic observation. The thickness of the chip adhesion layer on the 27 test pieces ranged from a minimum of 20 μm to a maximum of 140 μm.

[0073] For each test workpiece, heating currents of 0.1A, 0.3A, 0.5A, and 0.7A were applied respectively, and the corresponding thermal power P was calculated. E Immediately after each heating current is applied, a 0.01A current is applied as a detection current. The forward voltage within the range of 30μs to 100μs after the detection current is applied is measured, and the temperature T of the LED functional body of the test workpiece is calculated according to the voltage-temperature relationship of the test workpiece. j ;

[0074] The optical power P of each test workpiece was measured using an integrating sphere when each heating current was applied. L For each test piece, the temperatures T of the four LED functional components will be obtained. j With thermal power P E Optical power P L According to the relation T j =R th ·(P E -P L Perform linear fitting on c1 and obtain the slope R of the fitted line. th This is the total thermal resistance of the workpiece being tested.

[0075] The total thermal resistance R of each test piece is... th The thickness d of the chip attachment layer in the corresponding test workpiece is related to the formula R. th =R s A linear fit is performed using d+c2, where c2 is a constant, and the slope R of the resulting line is... s Calculate the thermal resistance per unit thickness of the chip adhesion layer; and calculate the thermal conductivity of the chip adhesion layer. Where A is the cross-sectional area.

[0076] Based on the above tests, the calculated thermal conductivity k of the chip adhesion layer prepared by sintered silver paste is 206.8 W / m·K.

[0077] In contrast, bulk silver has a thermal conductivity of 429 W / m·K. The reason why the thermal conductivity of the chip adhesion layer prepared by sintered silver paste is much lower than that of bulk silver is mainly because sintered silver paste is formed by sintering a large number of nano-silver particles, which contain a large number of pores, thus making the thermal conductivity of sintered silver paste significantly lower than that of bulk silver.

[0078] Therefore, the inventors also tested the thermal conductivity of the bulk sintered silver paste, which could be tested using the commonly used method of temperature measurement to calculate thermal conductivity in the prior art. The final test result was approximately 230 W / m·K. This result is significantly closer to the thermal conductivity of the chip attachment layer measured in Example 2, but there are some differences. Besides measurement errors, this may also be due to slight differences in the internal structure caused by preparing large-sized bulk materials and thin-film chip attachment layers. However, in general, we can conclude that the in-situ measurement method of LED chip attachment layer thermal conductivity of the present invention adopts a completely different parameter acquisition approach from the prior art and achieves a more accurate measurement of the thermal conductivity of such thin films as chip attachment layers.

[0079] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0080] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for in-situ testing the thermal conductivity of an LED chip's adhesion layer, characterized in that, The steps include: Multiple test pieces are obtained, wherein the dielectric layer is omitted in the test pieces, and each test piece includes a substrate and a chip attachment layer and an LED functional body sequentially disposed on the substrate. The thickness of the chip attachment layer in different test pieces is different, but the cross-sectional area perpendicular to the thickness direction is the same. The cross-sectional area and the thickness of the chip attachment layer are obtained. Obtain the total thermal resistance R of each of the test workpieces. th Obtain the total thermal resistance R th The method includes the following steps: placing the test workpiece in an environment with a constant temperature and energizing it; sequentially applying multiple heating currents with different current values ​​to each test workpiece during energization; and obtaining the corresponding electrical power P of the test workpiece when each current is applied. E Optical power P L and the temperature T of the LED functional body j The obtained data will be expressed in P E -P L As the independent variable, with T j A linear fit is performed on the dependent variable, and the slope of the fitted line is the total thermal resistance R. th ; Using the thickness d of the chip adhesion layer in the test workpiece as the independent variable, and the total thermal resistance R of each test workpiece as the independent variable... th A linear fit was performed on the dependent variable, and the slope of the resulting straight line was the thermal resistance R per unit thickness of the chip's adhesion layer. s ; Calculate the thermal conductivity of the chip adhesion layer. Where A is the cross-sectional area; Obtain the temperature T of the LED functional body j The method includes the following steps: Immediately after applying the heating current, a detection current is applied and the forward voltage of the LED functional body is measured at this time. The temperature of the LED functional body is then calculated using the forward voltage. The forward voltage of the LED functional body is sampled within 100 μs after the detection current is applied to obtain the forward voltage.

2. The method for in-situ testing of the thermal conductivity of the LED chip adhesion layer according to claim 1, characterized in that, The applied detection current has a current value of 0.005A to 0.05A.

3. The method for in-situ testing of the thermal conductivity of the LED chip adhesion layer according to claim 1, characterized in that, The applied heating current has a current value of 0.1A to 2A.

4. The method for in-situ testing of the thermal conductivity of the LED chip adhesion layer according to claim 1, characterized in that, The thickness of the chip attachment layer in each of the test workpieces is 10μm to 160μm.

5. The method for in-situ testing the thermal conductivity of the LED chip adhesion layer according to claim 1, characterized in that, The number of test pieces is more than twenty.

6. The method for in-situ testing of the thermal conductivity of the LED chip adhesion layer according to claim 1, characterized in that, The total thermal resistance R of each of the test workpieces was obtained. th During the process, the number of current values ​​of the applied heating current is four or more.

7. The method for in-situ testing the thermal conductivity of the LED chip adhesion layer according to claim 1, characterized in that, The material of the chip adhesion layer is sintered nano-silver material.

8. The method for testing the thermal resistance of the LED chip adhesion layer according to claim 1, characterized in that, The substrate is a metal substrate.

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