System and method for measuring heat transfer characteristics of thermal interface material in vacuum environment

Abstract

The invention discloses a system for measuring heat transfer characteristics of a thermal interface material in a vacuum environment, which is characterized in that a vacuum isolation hood covers a cold trap and can form a vacuum closed space; in a closed space, a refrigeration base is placed on a cold trap, a lower thermal gradient device is arranged on the upper top face of the refrigeration base, a support is arranged beside the refrigeration base, an upper thermal gradient device is connected with a top pressing head, and a flexible heat source device is connected to the joint of the upper thermal gradient device and the top pressing head in a sleeved mode. The lower thermal gradient device and the upper thermal gradient device are coaxially arranged, the top pressure head drives the upper thermal gradient device to move towards or away from the lower thermal gradient device, and the infrared temperature sensor is arranged on one side of the lower thermal gradient device and the upper thermal gradient device; the refrigeration base is connected with a refrigeration compressor pipeline outside the closed space, and the infrared temperature sensor is connected with a processor outside the closed space. According to the method, the temperature collected by the infrared sensor and the temperature simulated by the finite element model are fused, so that the inaccuracy caused by adopting a single mode is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of thermal interface materials, and in particular to a system and method for measuring heat transfer characteristics of thermal interface materials under vacuum conditions. Background Art

[0002] Nowadays, thermal interface materials have become one of the most important factors affecting the working stability of electronic equipment. The better the heat transfer characteristics of thermal interface materials, the better the heat dissipation capacity of electronic equipment, and the more stable the equipment works. Therefore, it is of great significance to measure the heat transfer characteristics of thermal interface materials.

[0003] The previous steady-state method has the following problems: First, when measuring thermal interface materials with high thermal conductivity, it often shows great inaccuracy; for example, the temperature difference between the hot and cold ends is not large, and there is a large error in the temperature reading. When facing thermal interface materials with higher and higher thermal conductivity, the previous steady-state method can no longer meet the measurement requirements;

[0004] Second, the temperature measurement is affected by the environment. When the steady-state method is used for measurement, there is natural heat convection in the environment, which greatly affects the accuracy of the temperature measurement. In order to minimize the impact of air heat convection, it is often necessary to add insulation boards and protective plates to isolate the influence of the external environment. For example, patent CN202111606054.9, an experimental device and method for measuring thermal conductivity by a quasi-steady-state method, adds polystyrene foam boards for insulation and isolation from the external environment. Another example is patent ZL202010348174.2, a method for testing the thermal conductivity of cylindrical samples by a punching method, in which the device contains a cylindrical insulation sleeve to isolate the influence of the external environment. However, the insulation boards and protective plates used in the above scheme still have heat conduction, which will cause heat leakage. As the temperature rises and the steady-state test time increases, the heat leakage of the insulation layer will intensify, and the inaccuracy of the temperature measurement will further deteriorate;

[0005] Third, thermocouple temperature measurement affects temperature accuracy. Traditional steady-state measurements all use contact-type thermocouples for temperature measurement. For example, patent ZL202221086198.6, a quasi-steady-state method for measuring specific heat and thermal conductivity, uses a thermocouple device to measure temperature. The placement of thermocouples will affect the accuracy of temperature measurement. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a system and method for measuring the heat transfer characteristics of thermal interface materials in a vacuum environment to solve the technical problems in the prior art that high thermal conductivity thermal interface materials and heat leakage cannot be tested.

[0007] The present invention provides a system for measuring heat transfer characteristics of thermal interface materials under vacuum environment, comprising: a vacuum isolation cover, a cold trap, a refrigeration base, a bracket, a lower thermal gradient device, an upper thermal gradient device, a top pressure head, a flexible heat source device, a vacuum pump, a refrigeration compressor, an infrared temperature sensor and a processor;

[0008] The vacuum isolation cover is covered on the cold trap, and a closed space is formed between the vacuum isolation cover and the cold trap, and a vacuum closed space can be formed by a vacuum pump;

[0009] In a closed space, a refrigeration base is placed on a cold trap, a lower thermal gradient device is arranged on the upper top surface of the refrigeration base, a bracket is arranged beside the refrigeration base, an upper thermal gradient device is connected to a top pressure head, a flexible heat source device is sleeved at the connection between the upper thermal gradient device and the top pressure head, the flexible heat source device is used to heat the upper thermal gradient device, the lower thermal gradient device is coaxially arranged with the upper thermal gradient device, the top pressure head can move up and down on the bracket, the top pressure head drives the upper thermal gradient device to move toward or away from the lower thermal gradient device, an infrared temperature sensor is arranged on one side of the lower thermal gradient device and the upper thermal gradient device, and the infrared temperature sensor is used to collect the temperature and temperature gradient of the two gradient devices;

[0010] The refrigeration base is connected to the refrigeration compressor pipeline outside the enclosed space, and the infrared temperature sensor is connected to the processor outside the enclosed space; the processor measures the heat transfer characteristics of the thermal interface material through a finite element model.

[0011] Furthermore, the flexible heat source device is a hollow ring, and the electrodes are distributed on both sides of the outer circle of the ring.

[0012] Furthermore, the material of the flexible heat source device is a composite material, specifically including a polymer matrix and a conductive filler.

[0013] Furthermore, the polymer material includes: one or more of polyurethane, polyimide, polypropylene and polyurethane; the conductive filler includes: one or more of silver powder, copper powder, graphene and carbon nanotubes.

[0014] Furthermore, the mass ratio of the conductive filler to the polymer matrix is ​​1:20 to 2:1.

[0015] The present invention also provides a method for measuring the heat transfer characteristics of a thermal interface material under a vacuum environment, the method comprising the following steps:

[0016] Step 1: placing a thermal interface material on the upper surface of the lower thermal gradient device, and lowering the upper thermal gradient device until the top surface of the upper thermal gradient device contacts the upper surface of the thermal interface material;

[0017] Step 2: Use a refrigeration compressor to cool the cold trap and the refrigeration base, and when the temperature drops to the required temperature, evacuate the sealed space;

[0018] Step 3: Raise the temperature of the flexible heat source device until the desired temperature is reached;

[0019] Step 4: Obtain the temperatures of the upper and lower ends of the upper thermal gradient device and the upper and lower ends of the lower thermal gradient device through an infrared sensor;

[0020] Step 5: constructing a corresponding finite element model according to the measurement system;

[0021] Step 6: Perform steady-state thermal simulation on the constructed finite element model to obtain the temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device in the finite element model when the finite element model reaches a temperature equilibrium state;

[0022] Step 7: performing weighted average processing on the temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device obtained in Step 4 and Step 6 to obtain optimized temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device;

[0023] Step 8: Calculate the heat transfer characteristic index of the thermal interface material according to the optimized temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device.

[0024] Furthermore, in step 7, the specific formula for weighted average processing is:

[0025] K 1 =(α×K e1 +β×K s1 ) / (α+β);

[0026] K 2 =(α×K e2 +β×K s2 ) / (α+β);

[0027] K 3 =(η×K e3 +ε×K s3 ) / (η+ε);

[0028] K 4 =(η×K e4 +ε×K s4 ) / (η+ε);

[0029] In the formula, K 1 , K 2 are the temperatures of the upper and lower ends of the optimized upper thermal gradient device; K 3 , K 4are the temperatures of the upper and lower ends of the optimized lower thermal gradient device; K e1 , K e2 are the temperatures at the upper and lower ends of the upper thermal gradient device measured by the infrared temperature sensor; K e3 , K e4 are the temperatures at the upper and lower ends of the lower thermal gradient device measured by the infrared temperature sensor; K s1 , K s2 are the temperatures of the upper and lower ends of the upper thermal gradient device in the finite element model; K s3 , K s4 are the temperatures of the upper and lower ends of the lower thermal gradient device in the finite element model; α, β, η, and ε are weighting coefficients.

[0030] Furthermore, the weighting coefficient is obtained by fitting, specifically:

[0031] When the thermal conductivity of the standard sample is known, the temperature of the upper and lower ends of the upper thermal gradient device and the temperature of the upper and lower ends of the lower thermal gradient device under the standard samples of different thicknesses and different areas are measured.

[0032] Fit according to the following formula to obtain the weighting coefficient:

[0033]

[0034] Wherein, L is the thickness of the standard material; τ is the thermal conductivity of the standard material; a is the area of ​​the standard material; A is the cross-sectional area of ​​the gradient device; h is the length of the gradient device; γ is the thermal conductivity of the gradient device.

[0035] Furthermore, the specific formula for calculating the heat transfer characteristic index of the thermal interface material in step 8 is:

[0036] R=(K 2 -K 4 ) / Q int

[0037] In the formula, Q int is the heat flux, Q int =(0.5γQ 1 +0.5×Q 2 ), Q 1 is the heat flux above, Q 2 is the heat flux below, Q 1 =((K 1 -K 2 )×γ×A) / h,Q 2 =((K 3 -K 4 )×γ×A) / h,K 1 , K 2are the temperatures of the upper and lower ends of the optimized upper thermal gradient device, K 3 , K 4 They are the temperatures at the upper and lower ends of the optimized lower thermal gradient device, respectively.

[0038] Beneficial effects of the present invention:

[0039] The present invention can increase the temperature gradient of the thermal gradient device in the test by lowering the cold trap temperature, making it easier to read the temperature and effectively reducing the reading error. It can test thermal conductivity greater than 10W (m K). -1 Thermal interface materials.

[0040] The present invention adopts a vacuum environment, avoids using a heat-insulating foam board to avoid the influence of air convection, and does not have a heat conduction phenomenon between the heat-insulating foam board and the sample to be tested, further avoiding heat leakage and improving the accuracy of temperature measurement. At the same time, it can also avoid using a heat-insulating foam board, greatly simplifying the test steps of heat transfer performance and improving the test efficiency.

[0041] The present invention performs weighted calculation on the infrared sensor temperature and the temperature obtained by the finite element model to obtain the final test temperature, thereby avoiding the inaccuracy of adopting a single method. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0043] Figure 1 It is a system schematic diagram of a specific embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0045] The present invention is further illustrated below in conjunction with specific embodiments. Those skilled in the art should understand that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention, and modifications to various equivalent forms of the present invention fall within the scope defined by the appended claims of this application.

[0046] The present invention provides a system for measuring heat transfer characteristics of thermal interface materials under vacuum environment, comprising: a vacuum isolation cover 2, a cold trap 1, a refrigeration base, a bracket, a lower thermal gradient device 7, an upper thermal gradient device 8, a metal pressure head 5, a flexible heat source device 6, a vacuum pump 4, a refrigeration compressor 3, an infrared temperature sensor 11 and a processor;

[0047] A drain valve 14 is provided at the bottom of the cold trap, a vacuum isolation cover 2 is covered on the cold trap 1, a closed space is formed between the vacuum isolation cover 1 and the cold trap 2, a vacuum pump 4 is connected to the closed space through a vacuum valve 9, and a vacuum closed space can be formed by the vacuum pump 4; the refrigeration base includes a base 12 and a condensing coil 13 wound on the outer ring of the base; the bracket includes two slide rails 10 and a connecting guide rail 15;

[0048] In a confined space, a base 12 is placed on the cold trap 1, a lower thermal gradient device 7 is arranged on the top surface of the base 12, two slide rails 10 are vertically arranged beside the base 12, a connecting guide rail 15 is erected between the two slide rails 10, and moves up and down on the two slide rails 10, an upper thermal gradient device 8 is connected to a metal pressure head 5, a flexible heat source device 6 is sleeved at the connection between the upper thermal gradient device 8 and the metal pressure head 5, the flexible heat source device 6 is used to heat the upper thermal gradient device 8, the lower thermal gradient device 7 is coaxially arranged with the upper thermal gradient device 8 and the material is consistent, the connecting guide rail 15 is connected to the metal pressure head 5, the metal pressure head 5 can move up and down on the two slide rails 10 with the connecting guide rail 15, the metal pressure head 5 drives the upper thermal gradient device 8 to move toward or away from the lower thermal gradient device 7, an infrared temperature sensor 11 is arranged on one side of the lower thermal gradient device 7 and the upper thermal gradient device 8, and the infrared temperature sensor 11 is used to collect the temperature and temperature gradient of the two gradient devices;

[0049] The condensing coil 13 is connected to the refrigeration compressor 3 pipeline outside the enclosed space, and the infrared temperature sensor 11 is connected to the processor outside the enclosed space; the processor measures the heat transfer characteristics of the thermal interface material through a finite element model.

[0050] The flexible heat source device is a hollow ring with electrodes distributed on both sides of the outer ring. The material of the flexible heat source device is a composite material, specifically including a polymer matrix and a conductive filler, and the mass ratio of the conductive filler to the polymer matrix is ​​1:20 to 2:1. The polymer material includes one or more of polyurethane, polyimide, polypropylene and polyurethane; the conductive filler includes one or more of silver powder, copper powder, graphene and carbon nanotubes. The resistivity of the flexible heat source device is greater than 0.18Ω·cm, the heating rate is 10℃-68℃ / min, and the power density is 500-2100W / m 2 , can provide 40-200℃ temperature change, and the time to reach steady-state temperature is 10-15 minutes. Table 1 below shows the relevant characteristic parameters of two sets of flexible heat source devices:

[0051] Conductive filler Polymer matrix Filler mass ratio Resistivity Heating power Carbon Nanotubes Polyurethane 13％ 8.41Ω·cm <![CDATA[780W / m 2 ]]> Graphite Nanosheets Polyimide 23％ 0.23Ω·cm <![CDATA[1300W / m 2 ]]>

[0052] Table 1

[0053] A specific embodiment of the present invention further provides a method for measuring the heat transfer characteristics of a thermal interface material under a vacuum environment, the method comprising the following steps:

[0054] Step 1: placing a thermal interface material on the upper surface of the lower thermal gradient device, and lowering the upper thermal gradient device until the top surface of the upper thermal gradient device contacts the upper surface of the thermal interface material;

[0055] Step 2: Use a refrigeration compressor to cool the cold trap and the refrigeration base, and when the temperature drops to the required temperature, evacuate the sealed space;

[0056] Step 3: Raise the temperature of the flexible heat source device until the desired temperature is reached;

[0057] Step 4: Obtain the temperatures of the upper and lower ends of the upper thermal gradient device and the upper and lower ends of the lower thermal gradient device through an infrared sensor;

[0058] Step 5: constructing a corresponding finite element model according to the measurement system;

[0059] Step 6: Perform steady-state thermal simulation on the constructed finite element model to obtain the temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device in the finite element model when the finite element model reaches a temperature equilibrium state;

[0060] Step 7: Perform weighted average processing on the temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device obtained in step 4 and step 6 to obtain optimized temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device. The specific formula for weighted average processing is:

[0061] K 1 =(α×K e1 +β×K s1 ) / (α+β);

[0062] K 2 =(α×K e2 +β×K s2 ) / (α+β);

[0063] K 3 =(η×K e3 +ε×K s3 ) / (η+ε);

[0064] K 4 =(η×K e4 +ε×Ks4 ) / (η+ε);

[0065] In the formula, K 1 , K 2 are the temperatures of the upper and lower ends of the optimized upper thermal gradient device; K 3 , K 4 are the temperatures at the upper and lower ends of the optimized lower thermal gradient device; K e1 , K e2 are the temperatures at the upper and lower ends of the upper thermal gradient device measured by the infrared temperature sensor; K e3 , K e4 are the temperatures at the upper and lower ends of the lower thermal gradient device measured by the infrared temperature sensor; K s1 , K s2 are the temperatures of the upper and lower ends of the upper thermal gradient device in the finite element model; K s3 , K s4 are the temperatures of the upper and lower ends of the lower thermal gradient device in the finite element model; α, β, η, ε are weighting coefficients;

[0066] Among them, the weighting coefficient is obtained by fitting, specifically:

[0067] When the thermal conductivity of the standard sample is known, the temperature of the upper and lower ends of the upper thermal gradient device and the temperature of the upper and lower ends of the lower thermal gradient device under the standard samples of different thicknesses and different areas are measured.

[0068] Fit according to the following formula to obtain the weighting coefficient:

[0069]

[0070] Wherein, L is the thickness of the thermal interface standard material; τ is the thermal conductivity of the oriented graphite thermal interface material standard; a is the area of ​​the oriented graphite thermal interface material standard;

[0071] Step 8: Calculate the heat transfer characteristic index of the thermal interface material according to the optimized temperatures at the upper and lower ends of the upper thermal gradient device and the temperatures at the upper and lower ends of the lower thermal gradient device. The specific formula is:

[0072] R=(K 2 -K 4 ) / Q int

[0073] In the formula, Q int is the heat flux, Q int =(0.5×Q 1 +0.5×Q 2 ), Q 1 is the heat flux above, Q 2 is the heat flux below, Q1 =((K 1 -K 2 )×γ×A) / h,Q 2 =((K 3 -K 4 )×γ×A) / h,K 1 , K 2 are the temperatures of the upper and lower ends of the optimized upper thermal gradient device, K 3 , K 4 They are the temperatures at the upper and lower ends of the optimized lower thermal gradient device, respectively.

[0074] The following is an example to illustrate the method:

[0075] Step 1: Measure the thickness of the thermal interface material to be 3 mm, and the length and width to be 2 cm respectively; select the material of the lower thermal gradient device to be copper, the length of the lower thermal gradient device to be 65 cm, and the thermal conductivity to be 398 W (m K) -1 ; Place a thermal interface material on the top surface of the lower thermal gradient device so that the lower surface of the thermal interface material contacts the lower thermal gradient device; Select the conductive filler of the flexible heat source device as carbon nanotubes, the polymer matrix as polyurethane, the resistivity is 0.4Ω·cm, and the heating power is 780W / m 2 ; The material of the upper thermal gradient device is selected as copper, with a thermal conductivity of 398W (m K) -1 ;

[0076] lowering the upper thermal gradient device until the top surface of the upper thermal gradient device contacts the upper surface of the thermal interface material;

[0077] Step 2: Use the refrigeration compressor to cool down the cold trap and the refrigeration base. After cooling for 30 minutes, the temperature of the cold trap is -45°C. Evacuate the sealed space for 30 minutes and maintain the vacuum degree at 1Pa.

[0078] Step 3: Raise the temperature of the flexible heat source device, and wait for 10 minutes until the temperature of the flexible heat source device reaches a steady state;

[0079] Step 4: Obtain the temperature K at the upper and lower ends of the upper thermal gradient device through the infrared sensor e1 , K e2 And the temperature K at the upper and lower ends of the thermal gradient device below e3 , K e4 , K e1 At 41°C, K e2 At 2℃, K e3 -12.3℃, K e4 is -39.7℃;

[0080] Step 5: Construct the corresponding finite element model according to the measurement system; divide each part of the system into finite element meshes and assign corresponding material properties, and set boundary conditions such as thermal convection and thermal radiation;

[0081] Step 6: Perform steady-state thermal simulation on the constructed finite element model to obtain the temperature K at the upper and lower ends of the upper thermal gradient device in the finite element model when the finite element model reaches the temperature equilibrium state. s1 , K s2 And the temperature K at the upper and lower ends of the thermal gradient device below s3 , K s4 , K s1 47.6℃, K s2 9.1℃, K s3 -8.6℃, K s4 -45℃;

[0082] Step 7: Perform weighted average processing on the temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device obtained in Step 4 and Step 6 to obtain optimized temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device.

[0083] The specific formula for weighted average processing is:

[0084] K 1 =(α×K e1 +β×K s1 ) / (α+β);

[0085] K 2 =(α×K e2 +β×K s2 ) / (α+β);

[0086] K 3 =(η×K e3 +ε×K s3 ) / (η+ε);

[0087] K 4 =(η×K e4 +ε×K s4 ) / (η+ε);

[0088] Using oriented growth graphite blocks as standard samples, the fitting weight coefficients α are 4.1, β is 6.7, η is 5.3, and ε is 4.9;

[0089] K 1 is 45.09℃, K 2 6.40℃, K 3 -10.52℃, K 4 is -42.25℃;

[0090] Step 8: Calculate the heat flux Q above 1 With the heat flux Q below 2 , Q 1 =9.47W, Q 2 =7.85W;

[0091] Calculate the heat flux Q int , Q int =8.66W;

[0092] The thermal resistance R of the thermal interface material is calculated, where R = 5.62°C / W.

[0093] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A system for measuring heat transfer characteristics of thermal interface materials under vacuum environment, characterized in that: include: Vacuum isolation cover, cold trap, refrigeration base, bracket, lower thermal gradient device, upper thermal gradient device, top pressure head, flexible heat source device, vacuum pump, refrigeration compressor, infrared temperature sensor and processor; The vacuum isolation cover is covered on the cold trap, and a closed space is formed between the vacuum isolation cover and the cold trap, and a vacuum closed space can be formed by a vacuum pump; In a closed space, a refrigeration base is placed on a cold trap, a lower thermal gradient device is arranged on the upper top surface of the refrigeration base, a bracket is arranged beside the refrigeration base, an upper thermal gradient device is connected to a top pressure head, a flexible heat source device is sleeved at the connection between the upper thermal gradient device and the top pressure head, the flexible heat source device is used to heat the upper thermal gradient device, the lower thermal gradient device is coaxially arranged with the upper thermal gradient device, the top pressure head can move up and down on the bracket, the top pressure head drives the upper thermal gradient device to move toward or away from the lower thermal gradient device, an infrared temperature sensor is arranged on one side of the lower thermal gradient device and the upper thermal gradient device, and the infrared temperature sensor is used to collect the temperature and temperature gradient of the two gradient devices; The refrigeration base is connected to the refrigeration compressor pipeline outside the enclosed space, and the infrared temperature sensor is connected to the processor outside the enclosed space; the processor measures the heat transfer characteristics of the thermal interface material through a finite element model.

2. The thermal interface material heat transfer characteristics measurement system under vacuum environment as claimed in claim 1, characterized in that: The flexible heat source device is a hollow ring, and the electrodes are distributed on both sides of the outer ring.

3. The thermal interface material heat transfer characteristics measurement system under vacuum environment as claimed in claim 1, characterized in that: The material of the flexible heat source device is a composite material, specifically including a polymer matrix and a conductive filler.

4. The thermal interface material heat transfer characteristic measurement system under vacuum environment as claimed in claim 3, characterized in that: The polymer material includes: one or more of polyurethane, polyimide, polypropylene and polyurethane; the conductive filler includes: one or more of silver powder, copper powder, graphene and carbon nanotubes.

5. The thermal interface material heat transfer characteristic measurement system under vacuum environment as claimed in claim 3 or 4, characterized in that: The mass ratio of the conductive filler to the polymer matrix is ​​1:20 to 2:

1.

6. A method for measuring the heat transfer characteristics of a thermal interface material under a vacuum environment, applicable to the system for measuring the heat transfer characteristics of a thermal interface material under a vacuum environment as claimed in any one of claims 1 to 5, characterized in that: The method comprises the following steps: Step 1: placing a thermal interface material on the upper surface of the lower thermal gradient device, and lowering the upper thermal gradient device until the top surface of the upper thermal gradient device contacts the upper surface of the thermal interface material; Step 2: Use a refrigeration compressor to cool the cold trap and the refrigeration base, and when the temperature drops to the required temperature, evacuate the sealed space; Step 3: Raise the temperature of the flexible heat source device until the desired temperature is reached; Step 4: Obtain the temperatures of the upper and lower ends of the upper thermal gradient device and the upper and lower ends of the lower thermal gradient device through an infrared sensor; Step 5: constructing a corresponding finite element model according to the measurement system; Step 6: Perform steady-state thermal simulation on the constructed finite element model to obtain the temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device in the finite element model when the finite element model reaches a temperature equilibrium state; Step 7: performing weighted average processing on the temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device obtained in Step 4 and Step 6 to obtain optimized temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device; Step 8: Calculate the heat transfer characteristic index of the thermal interface material according to the optimized temperatures of the upper and lower ends of the upper thermal gradient device and the temperatures of the upper and lower ends of the lower thermal gradient device.

7. The method for measuring the heat transfer characteristics of thermal interface materials under vacuum environment according to claim 6, characterized in that: In step 7, the specific formula for weighted average processing is: K1=(α×K e1 +β×K s1 ) / (α+β); K2=(α×K e2 +β×K s2 ) / (α+β); K3=(η×K e3 +ε×K s3 ) / (η+ε); K4=(η×K e4 +ε×K s4 ) / (η+ε); Where K1 and K2 are the temperatures of the upper and lower ends of the optimized upper thermal gradient device, respectively; K3 and K4 are the temperatures of the upper and lower ends of the optimized lower thermal gradient device, respectively; K e1 , K e2 are the temperatures at the upper and lower ends of the upper thermal gradient device measured by the infrared temperature sensor; K e3 , K e4 are the temperatures at the upper and lower ends of the lower thermal gradient device measured by the infrared temperature sensor; K s1 , K s2 are the temperatures of the upper and lower ends of the upper thermal gradient device in the finite element model; K s3 , K s4 are the temperatures of the upper and lower ends of the lower thermal gradient device in the finite element model; α, β, η, and ε are weighting coefficients.

8. The method for measuring the heat transfer characteristics of thermal interface materials under vacuum environment according to claim 7, characterized in that: The weighting coefficient is obtained by fitting, specifically: When the thermal conductivity of the standard sample is known, the temperature of the upper and lower ends of the upper thermal gradient device and the temperature of the upper and lower ends of the lower thermal gradient device under the standard samples of different thicknesses and different areas are measured. Fit according to the following formula to obtain the weighting coefficient: Wherein, L is the thickness of the standard material; τ is the thermal conductivity of the standard material; a is the area of ​​the standard material; A is the cross-sectional area of ​​the gradient device; h is the length of the gradient device; γ is the thermal conductivity of the gradient device.

9. The method for measuring the heat transfer characteristics of thermal interface materials under vacuum environment according to claim 7 or 8, characterized in that: The specific formula for calculating the heat transfer characteristic index of the thermal interface material in step 8 is: R=(K2-K4) / Q int In the formula, Q int is the heat flux, Q int =(0.5×Q1+0.5×Q2), Q1 is the heat flux density at the top, Q2 is the heat flux density at the bottom, Q1=((K1-K2)×γ×A) / h, Q2=((K3-K4)×γ×A) / h, K1 and K2 are the temperatures of the upper and lower ends of the optimized upper thermal gradient device, respectively, and K3 and K4 are the temperatures of the upper and lower ends of the optimized lower thermal gradient device, respectively.

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