DEVICE AND METHOD FOR MEASURING THE THERMAL CONDUCTIVITY OF A TEST SUBJECT

Description

[0001] The invention relates to a device for measuring the thermal conductivity of a test specimen, wherein the device comprises a first test specimen, a second test specimen, a heat source, at least one first temperature sensor for measuring a first temperature of the first test specimen, and at least one second temperature sensor for measuring a second temperature of the second test specimen. The invention also relates to a method for measuring the thermal conductivity of a test specimen using a device according to the invention.

[0002] To dissipate heat, for example from an electronic circuit on a printed circuit board (PCB), it is known to connect heat sinks to the PCB using a film, paste, or other material. This material may also serve to electrically insulate the heat sink from the PCB. A suitable material, known as a "thermal interface material," fills air pockets between two surfaces, which inevitably arise due to surface roughness. This improves heat transfer between the surfaces because the thermal conductivity of the filled air pockets is significantly increased. Furthermore, thermal interface materials are used to compensate for tolerances while maintaining sufficient thermal conductivity.

[0003] To measure the thermal conductivity or thermal resistance of a test specimen made of a thermal interface material, the stationary cylinder method according to ASTM D5470 is frequently used. In this method, the specimen is clamped between two parallel cylinders and subjected to a heat flow, which allows conclusions to be drawn about the thermal conductivity or thermal resistance of the specimen. The specimen can be tested with a constant contact pressure and variable thickness or with a variable contact pressure and constant thickness.

[0004] From DE 11 2016 004 973 B4, a device and a method for measuring the thermal conductivity of a test object are known. The test object is clamped between two holding elements. A heating element is located against one holding element, and a cooling element is located against the other holding element.

[0005] From DE 101 44 873 A1 a micromechanical thermal conductivity sensor is known which comprises a thermally insulated membrane formed by a recess in a poorly thermally conductive base plate.

[0006] Sensors for measuring thermal conductivity are also known from the document WU ET AL: "Fabrication and characterization of thermal conductivity detectors (TCDs) of different flow channel and heater designs", SENSORS AND ACTUATORS A, Vol. 100, No. 1, August 15, 2002 (2002-08-15), pages 37-45, XP0043737 59, ISSN: 0924-4247, DOI: 10.1016 / S0924-4247(02)00144-9.

[0007] From WO 2019 / 145549 A1, a device and a method for measuring the thermal conductivity of a sample are known. The device comprises a temperature sensor arrangement with several temperature sensors for determining temperature measurements at multiple locations.

[0008] The cylinders are typically made of aluminum alloys with relatively high thermal conductivity, such as EN AW 6060 or EN AW 6063. To determine the heat flow through the test specimen as accurately as possible, a temperature measurement is performed inside the cylinders. This also requires precise knowledge of the cylinders' thermal conductivity.

[0009] The resulting problem is that aluminum alloys do not always have the same composition. Manufacturing tolerances in the composition mean that each batch exhibits variations in material properties. Consequently, different cylinders typically have different thermal conductivities. Therefore, measurements taken with different cylinders usually yield different results for the thermal conductivity of the test specimen.

[0010] The invention is based on the objective of further developing a device and a method for measuring the thermal conductivity of a test specimen.

[0011] The object of the invention is achieved by a device for measuring the thermal conductivity of a test specimen having the features specified in claim 1. Advantageous embodiments and further developments are the subject of the dependent claims. The object of the invention is also achieved by a method for measuring the thermal conductivity of a test specimen having the features specified in claim 12.

[0012] An inventive device for measuring the thermal conductivity of a test specimen comprises a first test body having a first base and an opposing first end face, a second test body having a second base and an opposing second end face, a heat source arranged on the first base of the first test body, at least one first temperature sensor for measuring a first temperature of the first test body, and at least one second temperature sensor for measuring a second temperature of the second test body. The test bodies are arranged such that the test specimen can be positioned between the end faces of the test bodies. The first and second test bodies are made of silicon.

[0013] Silicon exhibits a relatively high thermal conductivity and is therefore suitable for thermal conductivity measurements. Industrially, silicon wafers are manufactured for the production of electronic components. Wafers are discs cut from monocrystalline silicon into cylindrical shapes. Since such processes are used in mass production, blanks for wafer production can be acquired cost-effectively and used as test specimens. Due to the high purity of silicon, the thermal conductivity of the test specimens is constant; there are only very minor deviations in the material properties, especially the thermal conductivity. Thus, the problem of deviations in the thermal material properties of the test specimens when using aluminum alloys in the test setup can be eliminated.

[0014] According to an advantageous embodiment of the invention, the device further comprises a heat sink which is arranged on the second base surface of the second test body. The heat sink allows for a more precise measurement of the heat flow passing through the first test body, the specimen under test, and the second test body when measuring the thermal conductivity of the specimen under test.

[0015] According to an advantageous embodiment of the invention, the heat sink is designed as a Peltier element. A hot side of the Peltier element faces away from the end faces of the test specimens, and a cold side of the Peltier element faces the end faces of the test specimens. When an electric current flows through the Peltier element, the cold side of the Peltier element is cooled.

[0016] According to an advantageous embodiment of the invention, the first test specimen and the second test specimen are each cylindrical, in particular circular cylindrical, and the base surfaces of the test specimens extend parallel to the end faces of the test specimens. Test specimens designed in this way are relatively readily available as blanks, in particular as monocrystalline blanks, for the production of wafers.

[0017] According to a preferred embodiment of the invention, the first test specimen and the second test specimen are each made of monocrystalline silicon. This results in a particularly constant thermal conductivity of the test specimens, and deviations in the material properties, especially thermal conductivity, are further reduced.

[0018] According to an advantageous embodiment of the invention, at least one first temperature sensor is arranged on the first end face of the first test specimen. According to an advantageous embodiment of the invention, at least one second temperature sensor is arranged on the second end face of the second test specimen. Thus, the temperature sensors are in direct contact with the surfaces of the test specimen.

[0019] According to an advantageous embodiment of the invention, at least one first temperature sensor is arranged within the first test body, spaced apart from the first end face and from the first base. According to an advantageous embodiment of the invention, at least one second temperature sensor is arranged within the second test body, spaced apart from the second end face and from the second base.

[0020] According to an advantageous embodiment of the invention, the at least one first temperature sensor is designed as a discrete component. According to an advantageous embodiment of the invention, the at least one second temperature sensor is designed as a discrete component. Such temperature sensors are known, for example, as measuring resistors, such as PT100 resistors, whose ohmic resistance is temperature-dependent. The relationship between the ohmic resistance and the temperature is preferably linear.

[0021] According to an advantageous embodiment of the invention, the at least one first temperature sensor is configured as a dopant on the first test specimen. According to an advantageous embodiment of the invention, the at least one second temperature sensor is configured as a dopant on the second test specimen. The use of silicon as the material for the test specimens allows the integration of additional functions, such as temperature measurement, by selectively introducing dopants. The temperature sensors are thus integrated into the test specimens. Depending on the type of dopant, the relationship between the ohmic resistance of the dopant and the temperature is linear or non-linear.

[0022] According to an advantageous embodiment of the invention, the heat source is designed as a dopant in the first test specimen. The use of silicon as the material for the test specimens allows the integration of additional functions, such as heat generation, through the targeted introduction of dopants. The heat source is thus integrated into the first test specimen. A current flowing through the dopant creates a voltage drop within the dopant, thereby generating heat within the dopant.

[0023] According to another advantageous embodiment of the invention, the heat source is designed as a Peltier element. In this configuration, a hot side of the Peltier element faces the end faces of the test specimens, and a cold side of the Peltier element faces away from the end faces of the test specimens. When an electric current flows through the Peltier element, the hot side of the Peltier element is heated.

[0024] In carrying out a method according to the invention for measuring the thermal conductivity of a test specimen using a device according to the invention, the test specimen is first positioned between the end faces of the test bodies. Heat energy is introduced into the device via the first base surface of the first test body by means of the heat source. At least one temperature sensor measures at least one temperature of the first test body. At least one temperature sensor measures at least one temperature of the second test body. The thermal conductivity of the test specimen is then calculated from the introduced heat energy, the at least one temperature, and the at least one second temperature.

[0025] The test specimen is, in particular, a film, paste, or other form of material that constitutes a "thermal interface material." Such a material is relatively soft and compressible. During the measurement of the thermal conductivity of the test specimen, a contact pressure is applied to the specimen, causing it to deform. This clamps the test specimen between the first and second test specimens, in particular by frictional engagement. The method according to the invention allows for a relatively accurate and reproducible measurement of the thermal conductivity of the test specimen.

[0026] In particular, the measurement result is only marginally dependent on the test specimens used. Using an identical device with different silicon test specimens yields the same results.

[0027] The invention will now be explained in more detail with reference to the illustrations. The invention is not limited to the embodiments shown in the illustrations. The illustrations only depict the subject matter of the invention schematically. They show: Figure 1: a schematic representation of a device for measuring the thermal conductivity of a test specimen.

[0028] Figure 1 Figure 1 shows a schematic representation of a device for measuring the thermal conductivity of a test specimen 40. The device comprises a first test specimen 10 and a second test specimen 20. The first test specimen 10 and the second test specimen 20 are each made of silicon. In particular, the first test specimen 10 and the second test specimen 20 are each made of monocrystalline silicon.

[0029] The first test specimen 10 is cylindrical, in particular circular-cylindrical, and has a first base surface 12 and a first end face 14 opposite the first base surface 12. The first base surface 12 of the first test specimen 10 extends parallel to the first end face 14 of the first test specimen 10.

[0030] The second test specimen 20 is cylindrical, in particular circular-cylindrical, and has a second base surface 22 as well as a second end face 24 opposite the second base surface 22. The second base surface 22 of the second test specimen 20 extends parallel to the second end face 24 of the second test specimen 20.

[0031] The test specimen 40 is positioned between the first test specimen 10 and the second test specimen 20. The test specimen 40 is a film, paste, or other form of material that functions as a "thermal interface material." In the illustration shown here, the test specimen 40 extends slightly laterally beyond the test specimens 10 and 20. The diameter of the test specimen 40 should not significantly exceed that of the test specimens 10 and 20, as this would otherwise increase undesirable heat loss to the outside.

[0032] The test specimens 10 and 20 are arranged such that the first end face 14 of the first test specimen 10 faces the second end face 24 of the second test specimen 20. The first end face 14 extends parallel to the second end face 24. The test specimen 40 is positioned between the first end face 14 and the second end face 24. The test specimen 40 is thus in direct contact with both the first end face 14 and the second end face 24.

[0033] The device comprises a heat source 31. The heat source 31 is arranged on the first base surface 12 of the first test body 10. The heat source 31 is, for example, designed in the form of an insulated heating coil which rests against the first base surface 12 or is mechanically connected to the first base surface 12, in particular by bonding. Alternatively, the heat source 31 is designed as a dopant of the first test body 10. Thus, the heat source 31 is integrated into the first test body 10 in the form of a dopant.

[0034] The device comprises a heat sink 33. The heat sink 33 is arranged on the second base surface 22 of the second test body 20. The heat sink 33 is, for example, designed in the form of a cooling element which rests against the second base surface 22 or is mechanically connected to the second base surface 22, in particular by bonding. The heat sink 33 is advantageously liquid-cooled.

[0035] The device comprises two first temperature sensors 16. The first temperature sensors 16 each serve to measure a first temperature of the first test body 10. Each of the first temperature sensors 16 measures the first temperature at a different location on the first test body 10.

[0036] In this case, one of the first temperature sensors 16 is arranged on the first end face 14 of the first test specimen 10. This first temperature sensor 16 is thus in direct contact with a surface of the test specimen 40. It is also conceivable to insert several PT100 temperature sensors radially through bores as close as possible to the first end face 14.

[0037] In the present case, one of the first temperature sensors 16 is also arranged within the first test body 10. This first temperature sensor 16 is thus arranged at a distance from the first end face 14 and at a distance from the first base face 12.

[0038] In the present case, one of the first temperature sensors 16 is designed as a discrete component. For example, this first temperature sensor 16 is designed in the form of a measuring resistor whose ohmic resistance is temperature-dependent.

[0039] In the present case, one of the first temperature sensors 16 is also designed as a dopant in the first test body 10. Thus, this first temperature sensor 16 is integrated into the first test body 10 in the form of a dopant.

[0040] The device comprises two second temperature sensors 26. The second temperature sensors 26 each serve to measure a second temperature of the second test body 20. Each of the second temperature sensors 26 measures the second temperature at a different location on the second test body 20.

[0041] In this case, one of the second temperature sensors 26 is arranged on the second end face 24 of the second test specimen 20. This second temperature sensor 26 is thus in direct contact with a surface of the test specimen 40.

[0042] In this case, one of the second temperature sensors 26 is also arranged within the second test body 20. This second temperature sensor 26 is thus arranged at a distance from the second end face 24 and at a distance from the second base face 22.

[0043] In the present case, one of the second temperature sensors 26 is designed as a discrete component. For example, this second temperature sensor 16 is designed in the form of a measuring resistor whose ohmic resistance is temperature-dependent.

[0044] In the present case, one of the second temperature sensors 26 is also designed as a dopant of the second test body 20. Thus, this second temperature sensor 26 is integrated into the second test body 20 in the form of a dopant.

[0045] To measure the thermal conductivity of the test specimen 40 using the device, the test specimen 40 is first positioned between the end faces 14, 24 of the test bodies 10, 20, as shown in the illustration.

[0046] Then, a force is exerted on the heat source 31 or directly on the first base 12 of the first test specimen 10 in the direction of the test specimen 40. Likewise, a force is exerted on the heat sink 33 or directly on the second base 22 of the second test specimen 20 in the direction of the test specimen 40. These forces each cause a contact pressure P acting on the test specimen 40. The test specimen 40 is thus clamped between the first test specimen 10 and the second test specimen 20, in particular held by frictional contact.

[0047] It is conceivable to apply a constant contact pressure P to the test specimen 40. In this case, the test specimen 40 will be deformed differently depending on the magnitude of the contact pressure P, and thus will have a thickness that depends on the contact pressure P. The thickness of the test specimen 40 corresponds to the distance between the first end face 14 and the second end face 24.

[0048] It is also conceivable to keep the thickness of the test specimen 40 constant by specifying the distance between the first end face 14 and the second end face 24. In this case, the magnitude of the contact pressure P is variable and depends on the specified thickness of the test specimen 40.

[0049] Heat energy is introduced into the device via the first base surface 12 of the first test body 10 by means of the heat source 31. The introduced heat energy causes a heat flow W, which flows through the first test body 10, the test specimen 40 and the second test body 20 to the heat sink 33 at the second base surface 22 of the second test body 20.

[0050] Using the first temperature sensors 16, initial temperatures of the first test specimen 10 are measured at several points on the first test specimen 10. Using the second temperature sensors 26, secondary temperatures of the second test specimen 20 are measured at several points on the second test specimen 20.

[0051] The thermal conductivity of the test specimen 40 is then calculated from the applied heat energy, the measured first temperatures and the measured second temperatures.

[0052] The aforementioned calculation of the thermal conductivity of the test specimen 40 also incorporates other parameters, in particular the arrangement of the temperature sensors 16, 26 in the test bodies 10, 20, as well as the thermal conductivity of the test bodies 10, 20. However, these are all constant parameters that are known before the start of the measurement. Reference symbol list

[0053] 10. First test body 12. First base surface 14. First end surface 16. First temperature sensor 20. Second test body 22. Second base surface 24. Second end surface 26. Second temperature sensor 31. Heat source 33. Heat sink 40. Test specimen Heat flow Contact pressure

Claims

1. A device for measuring the thermal conductivity of a test object (40), comprising a first test body (10), which has a first base (12) and also a first end face (14) lying opposite, a second test body (20), which has a second base (22) and also a second end face (24) lying opposite, a heat source (31), which is arranged on the first base (12) of the first test body (10), and at least one first temperature sensor (16) for measuring a first temperature of the first test body (10), and at least one second temperature sensor (26) for measuring a second temperature of the second test body (20), wherein the test bodies (10, 20) are arranged in such a way that the test object (40) can be positioned between the end faces (14, 24) of the test bodies (10, 20), characterised in that the first test body (10) and the second test body (20) are manufactured from silicon.

2. A device according to claim 1, characterised in that a heat sink (33) is arranged on the second base (22) of the second test body (20).

3. A device according to claim 2, characterised in that the heat sink (33) is formed as a Peltier element, with a hot side of the Peltier element facing away from the end faces (14, 24) of the test bodies (10, 20), and in that a cold side of the Peltier element faces the end faces (14, 24) of the test bodies (10, 20) [of the].

4. A device according to one of the preceding claims, characterised in that the first test body (10) and the second test body (20) are each cylindrical in form, and in that the bases (12, 22) of the test bodies (10, 20) extend parallel to the end faces (14, 24) of the test bodies (10, 20).

5. A device according to one of the preceding claims, characterised in that the first test body (10) and the second test body (20) are each manufactured from monocrystalline silicon.

6. A device according to one of the preceding claims, characterised in that at least one first temperature sensor (16) is arranged on the first end face (14) of the first test body (10), and / or in that at least one second temperature sensor (26) is arranged on the second end face (24) of the second test body (20).

7. A device according to one of the preceding claims, characterised in that at least one first temperature sensor (16) is arranged within the first test body (10), spaced apart from the first end face (14) and spaced apart from the first base (12), and / or in that at least one second temperature sensor (26) is arranged within the second test body (20), spaced apart from the second end face (24) and spaced apart from the second base (22).

8. A device according to one of the preceding claims, characterised in that the at least one first temperature sensor (16) is formed as a discrete component, and / or in that the at least one second temperature sensor (26) is formed as a discrete component.

9. A device according to one of the preceding claims, characterised in that the at least one first temperature sensor (16) is formed as a doping means of the first test body (10), and / or in that the at least one second temperature sensor (26) is formed as a doping means of the second test body (20).

10. A device according to one of the preceding claims, characterised in that the heat source (31) is formed as a doping means of the first test body (10).

11. A device according to one of claims 1 to 9, characterised in that the heat source (31) is formed as a Peltier element, with a hot side of the Peltier element facing the end faces (14, 24) of the test bodies (10, 20), and in that a cold side of the Peltier element faces away from the end faces (14, 24) of the test bodies (10, 20).

12. A method for measuring the thermal conductivity of a test object (40), by means of a device according to one of the preceding claims, wherein the test object (40) is positioned between the end faces (14, 24) of the test bodies (10, 20); by means of the heat source (31) thermal energy is introduced into the device by way of the first base (12) of the first test body (10); by means of the at least one first temperature sensor (16) at least one first temperature of the first test body (10) is measured, and by means of the at least one second temperature sensor (26) at least one second temperature of the second test body (20) is measured; the thermal conductivity of the test object (40) is calculated from the thermal energy introduced, the at least one first temperature and the at least one second temperature.