Method for quantitatively evaluating the heat dissipation and insulation properties of micro-arc oxidation films on aluminum substrates

Abstract

The method for quantitatively evaluating the heat dissipation and insulation of a micro-arc oxidation film on the surface of an aluminum substrate of the present invention comprises: preparing aluminum alloy substrates with different thicknesses of micro-arc oxidation films as calibration substrates; characterizing the relationship between the thickness of the micro-arc oxidation film on the surface of the aluminum alloy substrate and the insulation performance of the aluminum alloy substrate; encapsulating LED chips on each calibration substrate to obtain calibration samples; using a transient thermal resistance method to test the thermal resistance of each calibration sample; determining the independent relationship between the thickness of the micro-arc oxidation film and the thermal resistance of the micro-arc oxidation film according to a differential function curve; and determining the safe thickness range of the micro-arc oxidation film according to the relationship between the thickness of the micro-arc oxidation film, the thermal resistance of the micro-arc oxidation film and the insulation performance of the aluminum alloy substrate. The present invention solves the problem that the prior art can neither independently evaluate the influence of the thickness of the micro-arc oxidation film on the thermal resistance of the micro-arc oxidation film on the surface of the aluminum substrate, nor determine the minimum critical thickness of the micro-arc oxidation film.

Description

Technical Field

[0001] The invention relates to a detection technology in the field of electronic packaging, and in particular to a method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on the surface of an aluminum substrate. Background Art

[0002] During the use of LED devices for aerospace, a large amount of input electrical energy will be converted into heat energy and accumulated inside the LED devices, causing the junction temperature of the LED devices to increase significantly, thereby reducing the luminous efficiency, service life and luminous flux of the LED devices. Selecting a packaging substrate with excellent heat dissipation performance and stable mechanical structure can not only significantly improve the heat dissipation efficiency of LED devices, but also maintain the safety and reliability of the LED packaging structure, avoiding the safety hazards caused by installing external heat dissipation devices. At present, epoxy resin copper clad laminates, high thermal conductivity ceramic plates, metal-based copper clad laminates, etc. are mainly used as heat dissipation substrates for high-power LED devices at home and abroad. Among them, although epoxy resin copper clad laminates have the advantages of low cost and easy processing, epoxy resins with low thermal conductivity cannot meet the heat dissipation requirements of high-power LEDs. Although high thermal conductivity ceramic plates such as Al2O3 and AlN have excellent thermal conductivity, they have high processing requirements and cannot manufacture substrates with complex structures, limiting their application range. Metal-based copper clad laminates are the most widely used heat dissipation substrates in LED devices, but polymer insulating materials need to be inserted between the metal substrate and the surface copper clad layer of such substrates to prevent short circuits between the metal substrate and the copper clad layer circuit. However, most polymer insulating materials have low thermal conductivity, which significantly increases the overall thermal resistance of metal-based copper-clad laminates and limits their development. Micro-arc oxidation technology can grow a ceramic oxide film with excellent insulating properties on the surface of the metal substrate. The thermal conductivity of this micro-arc oxidation film is significantly better than that of traditional polymer insulating materials. Therefore, metal substrates with micro-arc oxidation films are expected to replace traditional metal-based copper-clad laminates as heat dissipation substrates for LED devices.

[0003] The traditional thermal resistance test method has analyzed the effect of aluminum alloy substrates with micro-arc oxidation films on the overall heat dissipation efficiency of LED devices: when the thickness of the micro-arc oxidation film on the surface of the aluminum alloy substrate continues to decrease, the overall junction-to-shell thermal resistance of the LED device packaged with this type of substrate continues to decrease, and the overall heat dissipation efficiency of the device continues to improve. However, the traditional thermal resistance test method can only evaluate the effect of the change in the thickness of the micro-arc oxidation film on the overall junction-to-shell thermal resistance of the LED device. It is difficult to eliminate the effect of the inconsistency of the thickness of the LED chip, solder, and aluminum alloy substrate on the overall junction-to-shell thermal resistance of the LED device, and it is impossible to independently evaluate the effect of the thickness of the micro-arc oxidation film on the thermal resistance of the micro-arc oxidation film. On the other hand, during the process of reducing the thickness of the micro-arc oxidation film, the insulation performance of the aluminum alloy substrate will continue to decrease, causing the LED device to have the risk of short-circuit failure. Traditional technology does not consider the impact of the micro-arc oxidation film thickness on the safety of LED devices when it is too small, and does not determine the minimum critical thickness of the micro-arc oxidation film. Only by comprehensively evaluating the correspondence between the thickness of the micro-arc oxidation film, the thermal resistance of the micro-arc oxidation film and the insulation performance of the aluminum substrate, and determining the minimum critical thickness of the micro-arc oxidation film on the surface of the aluminum substrate, can the aluminum alloy substrate with a micro-arc oxidation film be used safely and effectively in the LED device packaging process. Summary of the invention

[0004] The purpose of the present invention is to provide a method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate surface, so as to solve the problem that the prior art can neither independently evaluate the influence of the thickness of the micro-arc oxidation film on the thermal resistance of the micro-arc oxidation film on the aluminum substrate surface, nor determine the minimum critical thickness of the micro-arc oxidation film.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on the surface of an aluminum substrate, comprising: preparing aluminum alloy substrates with different micro-arc oxidation film thicknesses as calibration substrates; characterizing the relationship between the thickness of the micro-arc oxidation film on the surface of the aluminum alloy substrate and the insulation performance of the aluminum alloy substrate; packaging LED chips on each calibration substrate to obtain calibration samples; using a transient thermal resistance method to test the thermal resistance of each calibration sample; determining the independent relationship between the thickness of the micro-arc oxidation film and the thermal resistance of the micro-arc oxidation film according to a differential function curve; and determining the safe thickness range of the micro-arc oxidation film according to the relationship between the thickness of the micro-arc oxidation film, the thermal resistance of the micro-arc oxidation film and the insulation performance of the aluminum alloy substrate.

[0006] The above-mentioned method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of an aluminum substrate, wherein the calibration substrate comprises an aluminum alloy substrate, and a micro-arc oxidation film is provided on one surface of the aluminum alloy substrate; the thickness of the micro-arc oxidation film of each calibration substrate is different, and the thickness of the aluminum alloy substrate of each calibration substrate is the same.

[0007] The above-mentioned method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of the aluminum substrate, wherein the characterization of the relationship between the thickness of the micro-arc oxidation film on the surface of the aluminum alloy substrate and the insulation performance of the aluminum alloy substrate includes: calibrating the thickness of the micro-arc oxidation film of each calibrated substrate; detecting the breakdown voltage of each calibrated substrate, and determining the relationship between the thickness of the micro-arc oxidation film and the insulation performance of the aluminum alloy substrate.

[0008] The above-mentioned method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of the aluminum substrate, wherein as the thickness of the micro-arc oxidation film increases, the breakdown voltage of the aluminum alloy substrate increases, and the insulation resistance of the aluminum alloy substrate continues to increase; however, as the thickness of the micro-arc oxidation film continues to increase, the increase in the breakdown voltage continues to slow down; the insulation resistance enhancement effect of the aluminum alloy substrate is most obvious in the thickness range of 10μm to 20μm.

[0009] The above-mentioned method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of the aluminum substrate, wherein the transient thermal resistance method is used to test the thermal resistance of each calibration sample, including: testing the temperature sensitive parameter K coefficient of each calibration sample: monitoring the PN junction voltage drop of the calibration sample, obtaining the differential function curve of the calibration sample through mathematical transformation, and extracting the thermal resistance parameters.

[0010] The above-mentioned method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of the aluminum substrate, wherein, in the calibration sample, the LED chip is soldered on the micro-arc oxidation film of the calibration substrate using tin-lead solder; after the bottom of the aluminum alloy substrate of the calibration sample is coated with thermal conductive silicone grease, the calibration sample is fixed to a constant temperature heat dissipation Cu block cold plate, and a transient thermal resistance test circuit is used to monitor the PN junction voltage drop of the calibration sample to obtain the PN junction voltage drop curve of the calibration sample; the PN junction voltage drop curve is converted into a transient cooling curve using the K coefficient; the transient cooling curve is converted into a differential function curve through mathematical transformation; the micro The differential function curve has the thermal resistance value on the abscissa and the heat capacity value on the ordinate. The thermal resistance value on the abscissa corresponding to the origin to the first main peak represents the thermal resistance of the LED chip. The thermal resistance value on the abscissa corresponding to the first main peak to the second main peak represents the thermal resistance of the tin-lead solder. The thermal resistance value on the abscissa corresponding to the second main peak to the third main peak represents the thermal resistance of the micro-arc oxidation film. The thermal resistance value on the abscissa corresponding to the third main peak to the rightmost end of the differential function curve represents the sum of the thermal resistances of the aluminum alloy substrate, thermal grease and constant temperature heat dissipation Cu block cold plate. The thermal resistance value on the abscissa corresponding to the origin to the rightmost end of the differential function curve represents the total thermal resistance of the calibration sample.

[0011] The above-mentioned method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of the aluminum substrate, wherein the independent relationship between the thickness of the micro-arc oxidation film and the thermal resistance of the micro-arc oxidation film determined according to the differential function curve includes: superimposing the differential function curves of each calibration sample, the thermal resistance of the LED chip corresponding to the calibration samples with different micro-arc oxidation film thicknesses is the same; the corresponding tin-lead solder thermal resistance is the same; the corresponding micro-arc oxidation film thermal resistance is different, as the thickness of the micro-arc oxidation film increases, the thermal resistance of the micro-arc oxidation film increases, and the growth rate of the thermal resistance of the micro-arc oxidation film in the range of 50μm to 100μm is greater than the growth rate of the thermal resistance of the micro-arc oxidation film in the range of 10μm to 50μm; the sum of the thermal resistances of the corresponding aluminum alloy substrate, thermal conductive silicone grease and heat dissipation Cu block cold plate is the same; the corresponding total thermal resistance of the calibration samples is different, as the thickness of the micro-arc oxidation film increases, the total thermal resistance of the calibration samples increases; for any two calibration samples with different micro-arc oxidation film thicknesses, the difference in the total thermal resistance of the calibration samples is equal to the difference in the thermal resistance of the micro-arc oxidation film.

[0012] The above method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of the aluminum substrate, wherein the thermal resistance proportional coefficient of the micro-arc oxidation film of each calibration sample relative to its total thermal resistance is calculated. If the thermal resistance proportional coefficient u≥30%, the change in the thickness of the micro-arc oxidation film has a greater impact on the total thermal resistance; if the thermal resistance proportional coefficient u≤30%, the change in the thickness of the micro-arc oxidation film has a smaller impact on the total thermal resistance.

[0013] The above-mentioned method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of the aluminum substrate, wherein the determination of the safe thickness range of the micro-arc oxidation film according to the relationship between the thickness of the micro-arc oxidation film, the thermal resistance of the micro-arc oxidation film and the insulation performance of the aluminum alloy substrate comprises: superimposing the aluminum alloy substrate breakdown voltage-micro-arc oxidation film thickness curve and the micro-arc oxidation film thermal resistance-micro-arc oxidation film thickness curve; when the thickness of the micro-arc oxidation film increases, the corresponding breakdown voltage of the aluminum alloy substrate increases successively, and the insulation resistance enhancement effect of the aluminum alloy substrate in the thickness range of 10μm to 20μm is most obvious; the corresponding thermal resistance of the micro-arc oxidation film increases successively, and the growth range of the thermal resistance of the micro-arc oxidation film in the thickness range of 50μm to 100μm is greater than the growth range of the thermal resistance of the micro-arc oxidation film in the thickness range of 10μm to 50μm, and the heat dissipation performance of the aluminum alloy substrate continues to deteriorate; in the thickness range of 10μm to 20μm, according to the minimum value j of the breakdown voltage of the aluminum alloy substrate min , combined with the corresponding relationship between breakdown voltage and micro-arc oxidation film thickness, the minimum micro-arc oxidation film thickness T is calculated. min ; In the thickness range of 10μm to 50μm, according to the maximum thermal resistance y of the micro-arc oxidation film max , combined with the corresponding relationship between the thermal resistance of the micro-arc oxidation film and the thickness of the micro-arc oxidation film, the maximum micro-arc oxidation film thickness T is calculated. max ; According to the minimum micro-arc oxidation film thickness T min and the maximum micro-arc oxidation film thickness T max, determine the safe thickness range of micro-arc oxidation film.

[0014] Compared with the prior art, the beneficial effects of the present invention include:

[0015] 1) The present invention adopts a transient thermal resistance test method to separate the thermal resistance of the micro-arc oxidation film from the overall junction thermal resistance of the LED device, thereby eliminating the influence of the inconsistency of the thickness of the LED chip, solder, and aluminum alloy substrate in the preparation process on the thermal resistance test of the micro-arc oxidation film, more accurately characterizing the one-to-one correspondence between the thickness of the micro-arc oxidation film and the thermal resistance of the micro-arc oxidation film, and determining the maximum micro-arc oxidation film thickness corresponding to the maximum micro-arc oxidation film thermal resistance, thereby solving the deficiency that the traditional thermal resistance test method cannot independently evaluate the influence of the thickness of the micro-arc oxidation film on the thermal resistance of the micro-arc oxidation film on the aluminum substrate surface;

[0016] 2) The present invention uses the insulation performance of the micro-arc oxidation aluminum substrate to approximately represent the insulation performance of the micro-arc oxidation film. By characterizing the relationship between the thickness of the micro-arc oxidation film on the top surface of the aluminum alloy substrate and the breakdown voltage of the aluminum alloy substrate, the minimum thickness of the micro-arc oxidation film under the minimum breakdown voltage of the substrate is determined, which solves the problem that the traditional method does not give the minimum thickness of the micro-arc oxidation film. In addition, according to the contradictory relationship between the thermal resistance of the micro-arc oxidation film and the breakdown voltage of the micro-arc oxidation aluminum substrate, the present invention determines the safe thickness range of the micro-arc oxidation film on the surface of the aluminum substrate, which can help LED devices select suitable micro-arc oxidation aluminum alloys as packaging substrates within the safe thickness range.

[0017] 3) The present invention characterizes the thermal resistance ratio coefficient of the micro-arc oxidation film relative to the overall thermal resistance of the LED device, and considers the influence of the micro-arc oxidation film thermal resistance on the overall thermal resistance of the LED device when the thickness of the micro-arc oxidation film changes. By comprehensively considering the thermal resistance ratio coefficient and the safe thickness range of the micro-arc oxidation film, the optimal micro-arc oxidation film thickness can be given for LED devices with specific packaging structures, guiding the production and manufacturing of micro-arc oxidation aluminum substrates for LEDs.

[0018] 4) The present invention adopts a wire cutting method, which, on the one hand, ensures that each substrate has almost the same aluminum alloy substrate thickness, and at the same time calculates the thickness ratio coefficient of the top surface micro-arc oxidation film thickness relative to the aluminum alloy substrate thickness, thereby eliminating the influence of the aluminum alloy substrate thickness difference on the thermal resistance of the micro-arc oxidation film; on the other hand, only the micro-arc oxidation film on the top surface of the aluminum alloy substrate is retained, and the micro-arc oxidation film on the four side surfaces and the bottom surface of the substrate is removed, thereby effectively eliminating the influence of the micro-arc oxidation film on the side and bottom surfaces on the differential function curve, thereby improving the accuracy of extracting the thermal resistance of the top surface single-layer micro-arc oxidation film, and improving the test process of the thermal resistance of the micro-arc oxidation film. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The method of quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of an aluminum substrate of the present invention is given by the following examples and drawings.

[0020] Figure 1 A schematic flow chart of a method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate surface according to a preferred embodiment of the present invention;

[0021] Figure 2 Schematic diagram of the micro-arc oxidation process for an aluminum alloy substrate in a preferred embodiment of the present invention;

[0022] Figure 3 A schematic diagram of cutting to retain the micro-arc oxidation film on the top surface of the aluminum alloy substrate in a preferred embodiment of the present invention;

[0023] Figure 4 Schematic diagram of micro-arc oxidation of aluminum alloy substrate before and after wire cutting in a preferred embodiment of the present invention;

[0024] Figure 5 It is a cross-sectional schematic diagram of calibrating the thickness of a micro-arc oxidation film on a substrate in a preferred embodiment of the present invention;

[0025] Figure 6 A schematic diagram of detecting and calibrating the breakdown voltage of a substrate in a preferred embodiment of the present invention;

[0026] Figure 7 It is a superposition diagram of the loading voltage-loading time curves corresponding to each calibration substrate in a preferred embodiment of the present invention;

[0027] Figure 8 It is a schematic diagram of fixing the LED chip and installing the electrode on the surface of the micro-arc oxidation film on the top layer of the calibration substrate in a preferred embodiment of the present invention;

[0028] Fig. 9 A schematic diagram of bonding electrodes and LED chips in a preferred embodiment of the present invention;

[0029] Fig.10 This is a schematic diagram of LED glue filling and capping in a preferred embodiment of the present invention;

[0030] Fig.11 This is a circuit diagram for calibrating a sample transient thermal resistance test in a preferred embodiment of the present invention;

[0031] Fig.12 A cross-sectional diagram of a one-dimensional heat dissipation path of a calibration sample during a transient thermal resistance test in a preferred embodiment of the present invention;

[0032] Fig.13 is a differential function curve w10 corresponding to a calibration sample with a micro-arc oxidation film thickness of 10 μm in a preferred embodiment of the present invention;

[0033] Fig.14 It is a superposition diagram of differential function curves corresponding to calibration samples with micro-arc oxidation film thicknesses of 10 μm, 20 μm, 50 μm and 100 μm respectively in a preferred embodiment of the present invention;

[0034] Fig.15 Schematic diagram of the safe thickness range of the micro-arc oxidation film on the top surface of the aluminum alloy substrate in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined Figure 1 to Figure 15 The method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of the aluminum substrate of the present invention is further described in detail.

[0036] The present invention aims to solve the problem that the prior art can neither independently evaluate the influence of the thickness of the micro-arc oxidation film on the surface of the aluminum substrate on the thermal resistance of the micro-arc oxidation film, nor determine the minimum critical thickness of the micro-arc oxidation film.

[0037] The method for quantitatively evaluating the heat dissipation and insulation of a micro-arc oxidation film on the surface of an aluminum substrate of the present invention comprises: preparing aluminum alloy substrates with different thicknesses of micro-arc oxidation films as calibration substrates; characterizing the relationship between the thickness of the micro-arc oxidation film on the surface of the aluminum alloy substrate and the insulation performance of the aluminum alloy substrate; packaging LED chips on each calibration substrate to obtain calibration samples; using a transient thermal resistance method to test the thermal resistance of each calibration sample; determining the independent relationship between the thickness of the micro-arc oxidation film and the thermal resistance of the micro-arc oxidation film according to a differential function curve; and determining a safe thickness range of the micro-arc oxidation film according to the relationship between the thickness of the micro-arc oxidation film, the thermal resistance of the micro-arc oxidation film and the insulation performance of the aluminum alloy substrate.

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0039] Figure 1 Schematic diagram of the process of quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate according to a preferred embodiment of the present invention.

[0040] See also Figure 1 The method for quantitatively evaluating the heat dissipation and insulation properties of the micro-arc oxidation film on the surface of the aluminum substrate according to the embodiment of the present invention comprises the following steps:

[0041] S10, preparing aluminum alloy substrates with the same base material thickness and different top surface micro-arc oxidation film thicknesses as calibration substrates;

[0042] S11, such as Figure 2First, phosphate, silicate and tungstate are mixed to form a micro-arc oxidation electrolyte 114; then the aluminum alloy substrate 112 is connected to the positive electrode of the AC pulse power supply 115 as an anode, and the stainless steel plate 113 is connected to the negative electrode of the AC pulse power supply 115 as a cathode; then the aluminum alloy substrate 112 and the stainless steel plate 113 are simultaneously immersed in the micro-arc oxidation electrolyte 114 and fixed; the electrolyte circulation device 111 is turned on to circulate the electrolyte 114; the AC pulse power supply 115 is turned on, the AC voltage is adjusted within the range of 500V to 750V, and the micro-arc oxidation time is adjusted within the range of 10min to 120min; by changing the working voltage (500V to 750V) and the micro-arc oxidation time (10min to 120min) of the micro-arc oxidation, aluminum alloy substrates with the same thickness of the aluminum substrate, the micro-arc oxidation film fully covering the surface of the aluminum substrate, and the micro-arc oxidation film with different thicknesses are obtained;

[0043] S12, such as Figure 3 , the aluminum alloy substrate 116 with the surface fully covered with micro-arc oxidation film is cut five times by wire cutting method, namely: two cuts 117 (L1 and L2) are made parallel to the XZ plane of the aluminum alloy substrate 116, two cuts 118 (M1 and M2) are made parallel to the YZ plane of the aluminum alloy substrate 116, and one cut 119 (H1) is made parallel to the XY plane of the aluminum alloy substrate 116, so as to remove the four side micro-arc oxidation films 121 and one bottom micro-arc oxidation film 122 of the aluminum alloy substrate 116; after wire cutting, only the top micro-arc oxidation film 120 is retained on the aluminum alloy substrate 124, as shown in FIG. Figure 4 Then the five cut surfaces (L1, L2, M1, M2 and H1) were ground and polished to obtain an aluminum alloy substrate with only a single-layer micro-arc oxidation film on the top surface as a calibration substrate;

[0044] The micro-arc oxidation aluminum alloy substrate is subjected to five wire cuttings, which mainly plays three roles: first, the thickness and shape size of the aluminum alloy substrate of each calibration substrate are made uniform; second, it is ensured that in the process of loading the DC voltage on the micro-arc oxidation aluminum alloy substrate in step S30, the DC high voltage only needs to penetrate one layer of micro-arc oxidation film, instead of two layers of micro-arc oxidation film, so as to improve the sensitivity of testing the DC breakdown voltage of the micro-arc oxidation aluminum alloy substrate; third, it is ensured that in the transient test process, the heat generated by the LED chip is conducted to the thermal conductive silicone grease through the micro-arc oxidation aluminum alloy substrate through only one layer of micro-arc oxidation film, instead of two layers of micro-arc oxidation film, which can reduce the number of main peaks and curve complexity of the differential function in step S60 and step S70, and improve the accuracy of extracting the thermal resistance of a single-layer micro-arc oxidation film; the aluminum alloy substrates with different thickness of the micro-arc oxidation film are all cut five times, and the aluminum alloy substrates with the same thickness of the aluminum alloy substrate and different thickness of the top surface micro-arc oxidation film are obtained as calibration substrates for the thickness calibration, insulation performance detection and thermal resistance performance detection of the micro-arc oxidation film;

[0045] S20, calibrating the thickness of the micro-arc oxidation film on the top surface of each calibration substrate;

[0046] like Figure 5 , prepare a sample for microscopic inspection of the calibration substrate, observe the cross-sectional morphology of the calibration substrate using a scanning electron microscope, calibrate the thickness (Q) of the micro-arc oxidation film 120 on the top surface of the calibration substrate and the thickness (S) of the aluminum alloy substrate 124 of the calibration substrate, and calculate the thickness ratio coefficient R (R=Q / S) of the micro-arc oxidation film thickness relative to the aluminum alloy substrate thickness. If the thickness ratio coefficient R≤5%, it indicates that the change in the thickness of the micro-arc oxidation film has a negligible effect on the insulation and thermal conductivity of the aluminum alloy substrate.

[0047] In this embodiment, the thickness Q of the micro-arc oxidation film on the top surface of each calibration substrate is measured to be 10 μm, 20 μm, 50 μm and 100 μm respectively, the thickness S of the aluminum alloy substrate is 2 mm (2000 μm), and the thickness ratio coefficient R of the thickness of the micro-arc oxidation film on each calibration substrate relative to the thickness of the aluminum alloy substrate is less than or equal to 5%, indicating that the change in the thickness of the micro-arc oxidation film has a negligible effect on the insulation and thermal conductivity of the aluminum alloy substrate.

[0048] S30, detecting the breakdown voltage of each calibration substrate;

[0049] S31, such as Figure 6 , connect the calibration substrate with the micro-arc oxidation film 120 on the top surface, the adjustable DC high-voltage power supply 126, and the voltage collection device 127 to the circuit in sequence, wherein the positive and negative electrodes of the adjustable DC high-voltage power supply 126 are respectively connected to the micro-arc oxidation film 120 on the top surface of the calibration substrate and the bottom surface of the aluminum alloy substrate 124 in a surface contact manner, and the two ports of the voltage collection device 127 are also connected to the micro-arc oxidation film 120 on the top surface of the calibration substrate and the bottom surface of the aluminum alloy substrate 124 in a surface contact manner, and the voltage collection device 127 will record the loaded voltages at both ends of the top surface micro-arc oxidation film 120 and the bottom surface of the aluminum alloy substrate 124 in real time, and save them to a PC;

[0050] S32, continuously increasing the loading voltage applied to both ends of the top micro-arc oxidation film 120 and the bottom surface of the aluminum alloy substrate 124, and drawing a loading voltage-loading time curve through the voltage acquisition device 127; when the loading voltage at both ends of the top micro-arc oxidation film 120 and the bottom surface of the aluminum alloy substrate 124 drops suddenly, it indicates that the micro-arc oxidation film is broken down by the high voltage, and the peak voltage of the loading voltage-loading time curve is the breakdown voltage of the calibration substrate;

[0051] Record the loading voltage-loading time curve for each calibration substrate and superimpose the curves, such as Figure 7As shown in the figure, the loading voltage-loading time curves corresponding to the calibration substrates with micro-arc oxidation film thickness of 10μm, 20μm, 50μm and 100μm are n10, n20, n50 and n100 respectively. When the thickness of the micro-arc oxidation film increases from 10μm, 20μm, 50μm to 100μm, the corresponding breakdown voltage increases from j10, j20, j50 to j100 in sequence, and the insulation resistance of the calibration substrate is continuously enhanced; however, as the thickness of the micro-arc oxidation film continues to increase, the breakdown voltage increases. The amplitude gradually slowed down, and the increase from j10 to j20 was the largest, indicating that the insulation performance of the micro-arc oxidation aluminum alloy substrate was most significantly improved when the thickness of the micro-arc oxidation film was in the range of 10μm to 20μm, while the insulation performance of the micro-arc oxidation aluminum alloy substrate was not significantly improved in the range of 20μm to 100μm; since the insulation performance of the micro-arc oxidation aluminum alloy substrate was mainly determined by the micro-arc oxidation film, not by the conductive aluminum alloy substrate, the insulation performance of the micro-arc oxidation aluminum alloy substrate can approximately represent the insulation performance of the micro-arc oxidation film;

[0052] S40, encapsulating the LED chips on different calibration substrates to obtain LED devices with different micro-arc oxidation film thicknesses as calibration samples;

[0053] S41, such as Figure 8 , using tin-lead solder 128 to fix the LED chip 129 on the upper surface of the micro-arc oxidation film 120 on the top surface of the calibration substrate;

[0054] S42, such as Figure 8 , installing a fixed electrode 130 on the upper surface of the micro-arc oxidation film 120 on the top surface of the calibration substrate;

[0055] S43, such as Fig. 9 , using bonding wire 131 to connect electrode 130 and LED chip 129;

[0056] S44, after heating and mixing the phosphor and silica gel, pour them into a glue dispenser, and evenly coat them on the surface of the micro-arc oxide film 120, the LED chip 129 and the bonding wire 131 through the glue dispenser, while ensuring that the phosphor glue partially covers the electrode 130; bake and cure the phosphor glue to obtain the phosphor glue 132 after capping, and then obtain a single packaged LED device as a calibration sample, such as Fig.10 ;

[0057] Repeat steps S41 to S44 for each calibration substrate to obtain calibration samples with different thicknesses of micro-arc oxidation films;

[0058] S50, test the temperature sensitive parameter K coefficient of each calibration sample:

[0059] S51, according to Fig.11The calibration sample 138 is connected to the circuit; since the VF voltage sensor 135, the IM test current 136 and the IH heating current 137 have the same actual direction, all three are displayed as positive values ​​(+); the T3ster device is used to load only the 5mA IM test current 136 on the calibration sample 138, and the IH heating current 137 is not loaded, and the VF voltage sensor 135 is used to monitor the PN junction voltage drop change of the calibration sample 138 in real time;

[0060] S52, placing the calibration sample 138 in an oil tank, the temperature of the oil tank being equal to the PN junction temperature of the sample; adjusting the temperature of the constant temperature oil tank so that the PN junction temperature of the calibration sample 138 gradually increases from 25°C to 140°C, with a heating rate of 5°C / min; recording the PN junction voltage drop-junction temperature curve of the calibration sample 138 in real time, and obtaining the K coefficient of the calibration sample 138;

[0061] Execute steps S51 to S52 for each calibration sample to obtain the K factor of each calibration sample;

[0062] S60, monitoring the PN junction voltage drop of the calibration sample, obtaining the differential function curve of the calibration sample through mathematical transformation, and extracting the thermal resistance parameter;

[0063] S61, such as Fig.12 After coating the thermal conductive silicone grease 133 on the bottom of the calibration sample aluminum alloy substrate 124, it is fixed to the upper surface of the constant temperature heat dissipation Cu block cold plate 134, and the temperature of the Cu block cold plate 134 is maintained at 25°C; during the transient thermal resistance test, the calibration sample meets the one-dimensional heat dissipation path, and the heat generated by the LED chip 129 is mainly conducted outward through the heat dissipation path of tin-lead solder 128-micro-arc oxidation film 120-aluminum alloy substrate 124-thermal conductive silicone grease 133-constant temperature heat dissipation Cu block cold plate 134;

[0064] S62, using the T3ster device to load the calibration sample 138 with an IH heating current 137 of 5A, and after the junction temperature of the calibration sample 138 reaches a thermal steady state, the IH heating current 137 is quickly switched to the IM test current 136, and the VF voltage sensor 135 is used to monitor the PN junction voltage drop curve of the calibration sample 138, until the PN junction voltage drop of the calibration sample 138 reaches a stable value;

[0065] S63, converting the PN junction voltage drop curve into a transient temperature drop curve using a K coefficient;

[0066] S64, converting the transient cooling curve into a differential function curve through mathematical transformation;

[0067] Steps S61 to S64 are performed on each calibration sample to obtain a differential function curve of each calibration sample; the differential function curves corresponding to the calibration samples with micro-arc oxidation film thicknesses of 10 μm, 20 μm, 50 μm and 100 μm are assumed to be w10, w20, w50 and w100 respectively;

[0068] Fig.13 FIG. 1 is a differential function curve w10 corresponding to a calibration sample with a micro-arc oxidation film thickness of 10 μm in a preferred embodiment of the present invention; Fig.13 , in the differential function curve w10, the abscissa is the thermal resistance value, and the ordinate is the heat capacity value; the abscissa thermal resistance value corresponding to the origin to the first main wave peak represents the thermal resistance x10 of the calibration sample LED chip; the abscissa thermal resistance value corresponding to the first main wave peak to the second main wave peak represents the thermal resistance h10 of the tin-lead solder; the abscissa thermal resistance value corresponding to the second main wave peak to the third main wave peak represents the thermal resistance y10 of the micro-arc oxidation film of the calibration sample; the abscissa thermal resistance value corresponding to the third main wave peak to the rightmost end of the differential function curve represents the sum of the thermal resistances m10 of the aluminum alloy substrate, thermal grease and constant temperature heat dissipation Cu block cold plate of the calibration sample; the abscissa thermal resistance value corresponding to the origin to the rightmost end of the differential function curve represents the total thermal resistance z10 of the calibration sample (z10=x10+h10+y10+m10);

[0069] Assume that the thermal resistance of the calibration sample LED chip with the thickness of micro-arc oxidation film is x20, x50 and x100 respectively; the thermal resistance of tin-lead solder is h20, h50 and h100 respectively; the thermal resistance of micro-arc oxidation film is y20, y50 and y100 respectively; the sum of the thermal resistance of aluminum alloy substrate, thermal conductive silicone grease and constant temperature heat dissipation Cu block cold plate is m20, m50 and m100 respectively; the total thermal resistance of the calibration sample is z20, z50 and z100 respectively;

[0070] S70, superimposing the differential function curves of each calibration sample, determining the thermal resistance and total thermal resistance of the micro-arc oxidation film of each calibration sample, and obtaining the relationship between the thickness of the micro-arc oxidation film and the thermal resistance of the micro-arc oxidation film;

[0071] Fig.14 It is an overlay diagram of differential function curves corresponding to calibration samples with micro-arc oxidation film thicknesses of 10 μm, 20 μm, 50 μm and 100 μm, respectively, in a preferred embodiment of the present invention;

[0072] like Fig.14In the superimposed differential function curve, the thermal resistance of the LED chip corresponding to the calibration samples with different micro-arc oxidation film thickness is the same, that is, x10=x20=x50=x100, and the differential function curve segments from the origin to the first main wave peak overlap each other; the corresponding tin-lead solder thermal resistance is also the same, that is, h10=h20=h50=h100, and the differential function curve segments from the first main wave peak to the second main wave peak also overlap each other; the differential function curve segments corresponding to the LED chip and tin-lead solder show that the LED chip and tin-lead solder of different calibration samples will not affect the total thermal resistance;

[0073] like Fig.14 , the thermal resistance of the micro-arc oxidation film corresponding to different calibration samples is different. As the thickness of the micro-arc oxidation film increases from 10μm, 20μm, 50μm to 100μm, the thermal resistance of the micro-arc oxidation film increases from y10, y20, y50 to y100, and the differential function curve segment from the second main peak to the third main peak shifts to the right. The offset is related to the thickness of the micro-arc oxidation film. The larger the thickness, the greater the rightward offset; as the thickness of the micro-arc oxidation film increases, the increase in the thermal resistance of the micro-arc oxidation film also increases; the growth rate of the thermal resistance of the micro-arc oxidation film in the range of 50μm to 100μm is significantly greater than the growth rate of the thermal resistance of the micro-arc oxidation film in the range of 10μm to 50μm;

[0074] like Fig.14 , the sum of the thermal resistances of the aluminum alloy substrate, thermal grease and constant temperature heat dissipation Cu block cold plate corresponding to different calibration samples is the same, that is, m10=m20=m50=m100. Although the corresponding differential function curve segments do not overlap with each other, the basic trends are consistent. This curve segment shows that the aluminum alloy substrate, thermal grease and constant temperature heat dissipation Cu block cold plate of different calibration samples will not affect the total thermal resistance;

[0075] like Fig.14 , the total thermal resistance corresponding to different calibration samples is different. As the thickness of the micro-arc oxidation film increases from 10μm, 20μm, 50μm to 100μm, the total thermal resistance of the LED calibration sample from the origin to the rightmost end of the differential function curve increases from z10, z20, z50 to z100; for any two calibration samples with different micro-arc oxidation film thicknesses, the difference in the total thermal resistance of the calibration samples is equal to the difference in the corresponding micro-arc oxidation film thermal resistance, that is, z100-z10=y100-y10, z50-z10=y50-y10, z20-z10=y20-y10, indicating that the difference in the total thermal resistance of the calibration samples is mainly caused by the difference in the thickness of the micro-arc oxidation film, excluding the influence of other packaging structures on the total thermal resistance of the calibration samples;

[0076] like Fig.14, calculate the thermal resistance proportional coefficient u of the micro-arc oxidation film thermal resistance relative to the total thermal resistance of each calibration sample, u10=y10 / z10, u20=y20 / z20, u50=y50 / z50, u100=y100 / z100; if the thermal resistance proportional coefficient u≥30%, it indicates that the thickness change of the micro-arc oxidation film has a greater impact on the total thermal resistance of the LED device, and special attention should be paid to the thickness change of the micro-arc oxidation film; if the thermal resistance proportional coefficient u≤30%, it indicates that the thickness change of the micro-arc oxidation film has a smaller impact on the total thermal resistance of the LED device;

[0077] S80, determine the safe thickness range of the micro-arc oxidation film according to the thickness, breakdown voltage and thermal resistance of the micro-arc oxidation film of different calibration samples;

[0078] Fig.15 141 is a schematic diagram of the safe thickness range of the micro-arc oxidation film on the top surface of the aluminum alloy substrate in a preferred embodiment of the present invention; 141 is the safe thickness range of the micro-arc oxidation film;

[0079] like Fig.15 After excluding the influence of other packaging structures on the total thermal resistance, the insulation performance of the micro-arc oxidation aluminum alloy substrate is used to approximately represent the insulation performance of the micro-arc oxidation film, and the breakdown voltage-micro-arc oxidation film thickness dotted line 139 and the micro-arc oxidation film thermal resistance-micro-arc oxidation film thickness solid line 140 are superimposed; it can be seen from the breakdown voltage-micro-arc oxidation film thickness dotted line 139 that when the thickness of the micro-arc oxidation film increases from 10μm, 20μm, 50μm to 100μm, the corresponding breakdown voltage increases from j10, j20, j50 to j100 in sequence, and the insulation resistance of the micro-arc oxidation aluminum alloy substrate increases within the thickness range of 10μm to 20μm. The effect of the strong micro-arc oxidation film is the most obvious; it can be seen from the solid line 140 of the micro-arc oxidation film thermal resistance-micro-arc oxidation film thickness that when the micro-arc oxidation film thickness increases from 10μm, 20μm, 50μm to 100μm, the corresponding micro-arc oxidation film thermal resistance increases from y10, y20, y50 to y100 in sequence, and the growth rate of the micro-arc oxidation film thermal resistance in the thickness range of 50μm to 100μm is significantly greater than the growth rate of the micro-arc oxidation film thermal resistance in the thickness range of 10μm to 50μm, and the heat dissipation performance of the substrate continues to deteriorate; therefore, it is necessary to determine the safe thickness range of the micro-arc oxidation film to balance the insulation performance and heat dissipation performance of the micro-arc oxidation film;

[0080] like Fig.15 , in the thickness range of 10μm to 20μm, according to the minimum breakdown voltage j min , combined with the corresponding relationship between breakdown voltage and micro-arc oxidation film thickness (breakdown voltage-micro-arc oxidation film thickness dashed line 139), the minimum micro-arc oxidation film thickness T is calculated. min ;

[0081] like Fig.15, in the thickness range of 10μm to 50μm, according to the maximum thermal resistance y of the micro-arc oxidation film max , combined with the corresponding relationship between the thermal resistance of the micro-arc oxidation film and the thickness of the micro-arc oxidation film (the thermal resistance of the micro-arc oxidation film-the solid line of the micro-arc oxidation film thickness is 140), the maximum micro-arc oxidation film thickness T is calculated. max ;

[0082] like Fig.15 , according to the minimum micro-arc oxidation film thickness T min and the maximum micro-arc oxidation film thickness T max , determine the safe thickness range of micro-arc oxidation film141.

[0083] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate, characterized in that: include: Aluminum alloy substrates with different thickness of micro-arc oxidation films were prepared as calibration substrates; Characterize the relationship between the thickness of micro-arc oxidation film on the surface of aluminum alloy substrate and the insulation performance of aluminum alloy substrate; The calibration samples are prepared by packaging LED chips on each calibration substrate; The transient thermal resistance method is used to test the thermal resistance of each calibration sample; the independent relationship between the thickness of the micro-arc oxidation film and the thermal resistance of the micro-arc oxidation film is determined based on the differential function curve; According to the relationship between the thickness of micro-arc oxidation film, the thermal resistance of micro-arc oxidation film and the insulation performance of aluminum alloy substrate, the safe thickness range of micro-arc oxidation film is determined; The method for characterizing the relationship between the thickness of the micro-arc oxidation film on the surface of the aluminum alloy substrate and the insulation performance of the aluminum alloy substrate comprises: calibrating the thickness of the micro-arc oxidation film on each calibrated substrate; detecting the breakdown voltage of each calibrated substrate to determine the relationship between the thickness of the micro-arc oxidation film and the insulation performance of the aluminum alloy substrate; The independent relationship between the thickness of the micro-arc oxidation film and the thermal resistance of the micro-arc oxidation film determined according to the differential function curve includes: The differential function curves of the calibration samples are superimposed. The thermal resistance of the LED chips corresponding to the calibration samples with different micro-arc oxidation film thicknesses is the same; the corresponding thermal resistance of the tin-lead solder is the same; the corresponding thermal resistance of the micro-arc oxidation film is different, and as the thickness of the micro-arc oxidation film increases, the thermal resistance of the micro-arc oxidation film increases, and the growth rate of the thermal resistance of the micro-arc oxidation film in the range of 50μm to 100μm is greater than the growth rate of the thermal resistance of the micro-arc oxidation film in the range of 10μm to 50μm; the sum of the thermal resistances of the corresponding aluminum alloy substrate, thermal conductive silicone grease and heat dissipation Cu block cold plate is the same; the corresponding total thermal resistance of the calibration samples is different, and as the thickness of the micro-arc oxidation film increases, the total thermal resistance of the calibration samples increases; for any two calibration samples with different micro-arc oxidation film thicknesses, the difference in the total thermal resistance of the calibration samples is equal to the difference in the thermal resistance of the micro-arc oxidation film.

2. The method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate according to claim 1, wherein: The calibration substrate comprises an aluminum alloy substrate, and a micro-arc oxidation film is provided on one surface of the aluminum alloy substrate; the thickness of the micro-arc oxidation film of each calibration substrate is different, and the thickness of the aluminum alloy substrate of each calibration substrate is the same.

3. The method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate according to claim 1, wherein: As the thickness of the micro-arc oxidation film increases, the breakdown voltage of the aluminum alloy substrate increases, and the insulation resistance of the aluminum alloy substrate continues to increase; however, as the thickness of the micro-arc oxidation film continues to increase, the increase in the breakdown voltage continues to slow down; the insulation resistance enhancement effect of the aluminum alloy substrate is most obvious in the thickness range of 10μm to 20μm.

4. The method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate according to claim 1, wherein: The method of testing the thermal resistance of each calibration sample by using the transient thermal resistance method includes: Test the temperature sensitive parameter K factor of each calibration sample; Monitor the PN junction voltage drop of the calibration sample, obtain the differential function curve of the calibration sample through mathematical transformation, and extract the thermal resistance parameters.

5. The method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate according to claim 4, characterized in that: In the calibration sample, the LED chip is soldered on the micro-arc oxidation film of the calibration substrate using tin-lead solder; after the bottom of the aluminum alloy substrate of the calibration sample is coated with thermal conductive silicone grease, the calibration sample is fixed to the constant temperature heat dissipation Cu block cold plate, and the PN junction voltage drop of the calibration sample is monitored by a transient thermal resistance test circuit to obtain the PN junction voltage drop curve of the calibration sample; the PN junction voltage drop curve is converted into a transient cooling curve using the K coefficient; the transient cooling curve is converted into a differential function curve through mathematical transformation; The differential function curve of the calibration sample, the horizontal axis is the thermal resistance value, and the vertical axis is the heat capacity value; the horizontal axis thermal resistance value corresponding to the origin to the first main peak represents the thermal resistance of the LED chip; The thermal resistance value on the abscissa corresponding to the first main wave peak to the second main wave peak represents the thermal resistance of tin-lead solder; The thermal resistance value on the abscissa corresponding to the second main wave peak to the third main wave peak represents the thermal resistance of the micro-arc oxidation film; The thermal resistance value on the horizontal axis corresponding to the third main peak to the rightmost end of the differential function curve represents the sum of the thermal resistances of the aluminum alloy substrate, thermal grease, and constant temperature heat dissipation Cu block cold plate; the thermal resistance value on the horizontal axis corresponding to the origin to the rightmost end of the differential function curve represents the total thermal resistance of the calibration sample.

6. The method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate according to claim 1, wherein: Calculate the thermal resistance proportional coefficient of the micro-arc oxidation film of each calibration sample relative to its total thermal resistance. If the thermal resistance proportional coefficient u≥30%, the change in the thickness of the micro-arc oxidation film has a greater impact on the total thermal resistance; if the thermal resistance proportional coefficient u≤30%, the change in the thickness of the micro-arc oxidation film has a smaller impact on the total thermal resistance.

7. The method for quantitatively evaluating the heat dissipation and insulation properties of a micro-arc oxidation film on an aluminum substrate according to claim 1, wherein: According to the relationship between the thickness of the micro-arc oxidation film, the thermal resistance of the micro-arc oxidation film and the insulation performance of the aluminum alloy substrate, the safe thickness range of the micro-arc oxidation film is determined to include: The aluminum alloy substrate breakdown voltage-micro-arc oxidation film thickness curve and the micro-arc oxidation film thermal resistance-micro-arc oxidation film thickness curve are superimposed; when the thickness of the micro-arc oxidation film increases, the corresponding aluminum alloy substrate breakdown voltage increases successively, and the insulation resistance enhancement effect of the aluminum alloy substrate in the thickness range of 10μm to 20μm is the most obvious; the corresponding micro-arc oxidation film thermal resistance increases successively, and the growth range of the micro-arc oxidation film thermal resistance in the thickness range of 50μm to 100μm is greater than the growth range of the micro-arc oxidation film thermal resistance in the thickness range of 10μm to 50μm, and the heat dissipation performance of the aluminum alloy substrate continues to deteriorate; in the thickness range of 10μm to 20μm, according to the minimum value j of the breakdown voltage of the aluminum alloy substrate min , combined with the corresponding relationship between breakdown voltage and micro-arc oxidation film thickness, the minimum micro-arc oxidation film thickness T is calculated. min ; In the thickness range of 10μm to 50μm, according to the maximum thermal resistance y of the micro-arc oxidation film max , combined with the corresponding relationship between the thermal resistance of the micro-arc oxidation film and the thickness of the micro-arc oxidation film, the maximum micro-arc oxidation film thickness T is calculated. max ; According to the minimum micro-arc oxidation film thickness T min and the maximum micro-arc oxidation film thickness T max , determine the safe thickness range of micro-arc oxidation film.

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