Apparatus and method for measuring thermal conductivity of specimen

Abstract

The invention relates to a device for measuring the thermal conductivity of a specimen (40), comprising: a first test block (10) having a first base surface (12) and an opposite first end surface (14); a second test block (20) having a second base surface (22) and an opposite second end surface (24); a heat source (31) arranged on the first base surface (12) of the first test block (10); at least one first temperature sensor (16) for measuring a first temperature of the first test block (10); and at least one second temperature sensor (26) for measuring a second temperature of the second test block (20), the test blocks (10, 20) being arranged such that the specimen (40) can be positioned between the end faces (14, 24) of the test blocks (10, 20), the first test block (10) and the second test block (20) being made of silicon.

Description

Technical Field

[0001] The invention relates to a device for measuring the thermal conductivity of a test piece / specimen, wherein the device comprises: a first test block / test body; a second test block; a heat source; at least one first temperature sensor for measuring a first temperature of the first test block and at least one second temperature sensor for measuring a second temperature of the second test block. The invention also relates to a method for measuring the thermal conductivity of a test piece by means of the device according to the invention. Background Art

[0002] In order to dissipate heat, for example from electronic circuits on a printed circuit board, it is known to connect a cooling body to the printed circuit board by means of a foil, paste or other type of material. This material may also, if necessary, take on the task of electrically insulating the cooling body from the printed circuit board. A suitable material, called a "thermal interface material", fills the air gap between two surfaces, which is necessarily formed by roughness of the surfaces. This improves the heat transfer between the surfaces, since the thermal conductivity of the filled air gap is significantly increased. In addition, the thermal interface material serves to compensate for tolerances with sufficient thermal conductivity.

[0003] To measure the thermal conductivity or thermal resistance of test pieces made of thermal interface materials, the fixed cylinder method according to ASTM D5470 is usually used. Here, the test piece is clamped between two plane-parallel cylinders and a heat flow is applied, which can be used to infer the thermal conductivity or thermal resistance of the test piece. The test piece can be tested with a constant contact force and a variable thickness or with a variable contact force and a constant thickness.

[0004] DE 11 2016 004 973 B4 discloses a device and a method for measuring the thermal conductivity of a measurement object. Here, the measurement object is clamped between two holding elements. A heating element rests on one of the holding elements, and a cooling element rests on the other of the holding elements.

[0005] WO 2019 / 145549 A1 discloses a device and a method for measuring the thermal conductivity of a sample. The device comprises a temperature sensor assembly having a plurality of temperature sensors for determining temperature measurement values ​​at a plurality of locations.

[0006] The cylinder is usually made of an aluminum alloy with a relatively high thermal conductivity, such as EN AW 6060 or EN AW 6063. In order to determine the heat flow through the test piece as accurately as possible, temperature measurements are performed in the cylinder. Here, too, precise knowledge of the thermal conductivity of the cylinder is required.

[0007] The problem that arises from this is that aluminum alloys do not always have the same composition. Manufacturing is subject to errors in the individual components, which lead to deviations in the material properties for each batch. As a result, different cylinders usually have thermal conductivities that differ from one another. Measurements using different cylinders therefore usually provide different results for the thermal conductivity of the test piece. Summary of the invention

[0008] The object of the present invention is to improve a device and a method for measuring the thermal conductivity of a test piece.

[0009] According to the invention, this object is achieved by a device for measuring the thermal conductivity of a test piece having the features specified in claim 1. Advantageous embodiments and improvements are the subject matter of the dependent claims. This object is also achieved by a method for measuring the thermal conductivity of a test piece having the features specified in claim 12.

[0010] The device for measuring the thermal conductivity of a test piece according to the present invention comprises: a first test block having a first base surface and an opposite first end surface; a second test block having a second base surface and an opposite second end surface; a heat source arranged on the first base surface of the first test block; at least one first temperature sensor for measuring a first temperature of the first test block; and at least one second temperature sensor for measuring a second temperature of the second test block. Here, the test blocks are arranged so that the test piece can be positioned between the end surfaces of the test blocks. Here, the first test block and the second test block are made of silicon.

[0011] Silicon has a relatively high thermal conductivity and is therefore suitable for carrying out thermal conductivity measurements. In industry, wafers made of silicon are used to produce electronic components. Wafers are disks cut from cylindrical single crystal silicon. Since this method is used for mass production, blanks for producing wafers can be obtained at low cost and used as test blocks. Due to the high purity of silicon, the thermal conductivity of the test blocks is constant, with only very small deviations in the material data, in particular the thermal conductivity. Therefore, when using aluminum alloys in the test structure, the problem of deviations in the thermal material properties of the test blocks can be eliminated.

[0012] According to an advantageous improvement of the present invention, the device further comprises a heat sink / heat sink The heat well is arranged on the second base surface of the second test block. When measuring the thermal conductivity of the test piece, the heat well allows more accurate detection of the heat flow through the first test block, the test piece and the second test block.

[0013] According to an advantageous design of the present invention, the heat sink is designed as a Peltier element. Here, the hot side of the Peltier element faces away from the end face of the test block, while the cold side of the Peltier element faces the end face of the test block. When current flows through the Peltier element, the cold side of the Peltier element is cooled.

[0014] According to an advantageous design of the present invention, the first test block and the second test block are respectively configured as a column, in particular a cylindrical shape, and the base surface of the test block extends parallel to the end surface of the test block. The test block configured in this way is relatively easy to use as a blank, in particular a single crystal blank, for manufacturing a wafer.

[0015] According to a preferred design of the present invention, the first test block and the second test block are respectively made of single crystal silicon, so that the thermal conductivity of the test blocks is particularly constant, and the deviation of material data, especially thermal conductivity, is further reduced.

[0016] According to an advantageous design of the present invention, at least one first temperature sensor is arranged on a first end face of the first test block. According to an advantageous design of the present invention, at least one second temperature sensor is arranged on a second end face of the second test block. Therefore, the temperature sensor is in direct contact with the surface of the test piece.

[0017] According to an advantageous design of the present invention, at least one first temperature sensor is arranged in the first test block, spaced apart from the first end face and spaced apart from the first base face. According to an advantageous design of the present invention, at least one second temperature sensor is arranged in the second test block, spaced apart from the second end face and spaced apart from the second base face.

[0018] According to an advantageous embodiment of the invention, at least one first temperature sensor is designed as a decentralized / discrete component. According to an advantageous embodiment of the invention, at least one second temperature sensor is designed as a decentralized component. Such temperature sensors are known, for example, as measuring resistors, for example as PT100 resistors, whose ohmic resistance is temperature-dependent. The ohmic resistance is preferably linearly dependent on the temperature.

[0019] According to an advantageous embodiment of the invention, at least one first temperature sensor is designed as a doped part of the first test block. According to an advantageous embodiment of the invention, at least one second temperature sensor is designed as a doped part of the second test block. Using silicon as the material of the test block allows the integration of additional functions, such as temperature measurement, by targeted application of the doped part. The temperature sensor is thus integrated in the test block. Depending on the type of doped part, the ohmic resistance of the doped part is linearly or nonlinearly correlated with the temperature.

[0020] According to an advantageous development of the invention, the heat source is designed as a doped part of the first test block. Using silicon as the material of the test block allows the integration of additional functions, such as heat generation, by the targeted application of the doped part. The heat source is thus integrated in the first test block. The current flowing through the doped part generates a voltage drop in the doped part, thereby generating heat in the doped part.

[0021] According to another advantageous improvement of the present invention, the heat source is designed as a Peltier element. Here, the hot side of the Peltier element faces the end face of the test block, while the cold side of the Peltier element faces away from the end face of the test block. When current flows through the Peltier element, the hot side of the Peltier element is heated.

[0022] When carrying out the method according to the invention for measuring the thermal conductivity of a test piece by means of the device according to the invention, the test piece is first positioned between the end faces of the test blocks. Thermal energy is input into the device via a first base surface of a first test block by means of a heat source. At least one first temperature of the first test block is measured by means of at least one first temperature sensor. At least one second temperature of the second test block is measured by means of at least one second temperature sensor. The thermal conductivity of the test piece is calculated from the input thermal energy, the at least one first temperature and the at least one second temperature.

[0023] The test piece is in particular a foil, paste or other form of material which forms a "thermal interface material". Such a material is relatively soft and compressible. When measuring the thermal conductivity of the test piece, a pressing force acts on the test piece, as a result of which the test piece is deformed. As a result, the test piece is clamped between the first test block and the second test block, in particular held in a force-locking manner. The method according to the invention allows a relatively precise and reproducible measurement of the thermal conductivity of the test piece. In particular, the result of the measurement is not dependent on the test block used. Using a structurally identical device with other test blocks made of silicon provides the same results.

[0024] The present invention is not limited to the feature combinations of the claims. For a person skilled in the art, in particular from the purpose proposed and / or by comparison with the prior art, other reasonable combinations of the claims and / or individual claim features and / or description features and / or drawing features may be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will now be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments shown in the accompanying drawings. The accompanying drawings only schematically illustrate the subject matter of the present invention. The drawings show:

[0026] Figure 1 Schematic diagram showing a device for measuring the thermal conductivity of a test piece. DETAILED DESCRIPTION

[0027] Figure 1 A schematic diagram of a device for measuring the thermal conductivity of a test piece 40 is shown. The device includes a first test block 10 and a second test block 20. The first test block 10 and the second test block 20 are respectively made of silicon. In particular, the first test block 10 and the second test block 20 are respectively made of single crystal silicon.

[0028] First test block 10 is cylindrical, in particular circular cylindrical, and has a first base surface 12 and a first end surface 14 opposite first base surface 12. First base surface 12 of first test block 10 extends parallel to first end surface 14 of first test block 10.

[0029] Second test block 20 is cylindrical, in particular circular cylindrical, and has a second base surface 22 and a second end surface 24 opposite second base surface 22. Second base surface 22 of second test block 20 extends parallel to second end surface 24 of second test block 20.

[0030] A coupon 40 is placed between the first test block 10 and the second test block 20. The coupon 40 is a foil, paste or other form of material that functions as a "thermal interface material". In the view shown here, the coupon 40 slightly protrudes laterally beyond the test blocks 10, 20. The diameter of the coupon 40 should not significantly exceed the diameter of the test blocks 10, 20, otherwise undesirable heat losses to the outside will be increased.

[0031] The test blocks 10 and 20 are arranged such that the first end face 14 of the first test block 10 is opposite to the second end face 24 of the second test block 20. Here, the first end face 14 is parallel to the second end face 24. Here, the test piece 40 is positioned between the first end face 14 and the second end face 24. Therefore, the test piece 40 directly abuts against the first end face 14 and the second end face 24.

[0032] The device comprises a heat source 31. The heat source 31 is arranged on the first base surface 12 of the first test block 10. The heat source 31 is configured, for example, in the form of an insulating heating ring, which is in contact with the first base surface 12 or mechanically connected, in particular bonded, to the first base surface 12. Alternatively, the heat source 31 is designed as a doped part of the first test block 10. Therefore, the heat source 31 is integrated in the first test block 10 in the form of a doped part.

[0033] The device comprises a heat sink 33. The heat sink 33 is arranged on the second base surface 22 of the second test block 20. The heat sink 33 is configured, for example, in the form of a cooling body, which rests on the second base surface 22 or is mechanically connected, in particular adhesively bonded, to the second base surface 22. The heat sink 33 is advantageously cooled by a liquid.

[0034] The device comprises two first temperature sensors 16. The first temperature sensors 16 are respectively used to measure the first temperature of the first test block 10. In this case, each of the first temperature sensors 16 measures the first temperature at a different location of the first test block 10.

[0035] Here, one of the first temperature sensors 16 is arranged on the first end face 14 of the first test block 10. Therefore, the first temperature sensor 16 is in direct contact with the surface of the test piece 40. It is also conceivable to extend a plurality of PT100 temperature sensors radially into holes as close to the first end face 14 as possible.

[0036] Here, one of the first temperature sensors 16 is also arranged in the first test block 10 . The first temperature sensor 16 is therefore arranged at a distance from the first end face 14 and at a distance from the first base face 12 .

[0037] In this case, one of the first temperature sensors 16 is designed as a decentralized component. For example, the first temperature sensor 16 is designed in the form of a measuring resistor, the ohmic resistance of which is temperature-dependent.

[0038] Here, one of the first temperature sensors 16 is also designed as a doped part of the first test block 10. Therefore, the first temperature sensor 16 is integrated in the first test block 10 in the form of a doped part.

[0039] The device comprises two second temperature sensors 26. The second temperature sensors 26 are respectively used to measure the second temperature of the second test block 20. Each of the second temperature sensors 26 measures the second temperature at a different location of the second test block 20.

[0040] Here, one of the second temperature sensors 26 is arranged on the second end face 24 of the second test block 20. Therefore, the second temperature sensor 26 is in direct contact with the surface of the test piece 40.

[0041] Here, one of the second temperature sensors 26 is also arranged in the second test block 20 . Therefore, the second temperature sensor 26 is arranged at a distance from the second end face 24 and at a distance from the second base face 22 .

[0042] In this case, one of the second temperature sensors 26 is designed as a decentralized component. For example, the second temperature sensor 16 is designed in the form of a measuring resistor, the ohmic resistance of which is temperature-dependent.

[0043] Here, one of the second temperature sensors 26 is also designed as a doped part of the second test block 20. Therefore, the second temperature sensor 26 is integrated in the second test block 20 in the form of a doped part.

[0044] In order to measure the thermal conductivity of a test piece 40 by means of the device, the test piece 40 is first positioned between the end faces 14 , 24 of the test blocks 10 , 20 , as shown in the drawing.

[0045] Then, a force is applied to the heat source 31 or directly to the first base surface 12 of the first test block 10 in the direction of the test piece 40. Similarly, a force is applied to the heat sink 33 or directly to the second base surface 22 of the second test block 20 in the direction of the test piece 40. These forces respectively cause a pressing force P acting on the test piece 40. As a result, the test piece 40 is clamped between the first test block 10 and the second test block 20, and in particular is held therebetween in a force-locking manner.

[0046] It is conceivable to apply a constant pressing force P to the test piece 40. In this case, the test piece 40 deforms differently depending on the magnitude of the pressing force P, that is, has a thickness related to the pressing force P. The thickness of the test piece 40 corresponds to the distance between the first end face 14 and the second end face 24.

[0047] It is also conceivable to keep the thickness of the test piece 40 constant by predefining the distance between the first end face 14 and the second end face 24 . In this case, the magnitude of the contact force P is variable and depends on the predefined thickness of the test piece 40 .

[0048] Thermal energy is input into the device via the first base surface 12 of the first test block 10 by means of a heat source 31. The input thermal energy causes a heat flow W which flows through the first test block 10, the test piece 40 and the second test block 20 to a heat sink 33 on the second base surface 22 of the second test block 20.

[0049] The first temperature sensor 16 measures a first temperature of the first test block 10 at a plurality of locations on the first test block 10 . The second temperature sensor 26 measures a second temperature of the second test block 20 at a plurality of locations on the second test block 20 .

[0050] Then, the thermal conductivity of the test piece 40 is calculated from the input thermal energy, the measured first temperature, and the measured second temperature.

[0051] Further parameters are also included in the calculation of the thermal conductivity of the test piece 40, in particular the arrangement of the temperature sensors 16, 26 in the test blocks 10, 20 and the thermal conductivity of the test blocks 10, 20. However, these further parameters are each constant parameters that are already known before the start of the measurement.

[0052] List of reference numerals:

[0053] 10 First test block

[0054] 12 First base

[0055] 14 First end face

[0056] 16 First temperature sensor

[0057] 20 Second test block

[0058] 22 Second base

[0059] 24 Second end face

[0060] 26 Second temperature sensor

[0061] 31 Heat Source

[0062] 33 Heat Trap

[0063] 40 Specimens

[0064] W Heat flow

[0065] P Clamping force

Claims

1. A device for measuring the thermal conductivity of a test piece (40), the device comprising: A first test block (10) having a first base surface (12) and an opposite first end surface (14); A second test block (20) having a second base surface (22) and an opposite second end surface (24); A heat source (31) disposed on a first base surface (12) of a first test block (10); at least one first temperature sensor (16) for measuring a first temperature of the first test block (10); and at least one second temperature sensor (26) for measuring a second temperature of the second test block (20), The test blocks (10, 20) are arranged so that the test piece (40) can be positioned between the end faces (14, 24) of the test blocks (10, 20). It is characterized in that The first test block (10) and the second test block (20) are made of silicon.

2. The device according to claim 1, characterized in that The heat well (33) is arranged on the second base surface (22) of the second test block (20).

3. The device according to claim 2, characterized in that The heat sink (33) is designed as a Peltier element, wherein: The hot side of the Peltier element faces away from the end face (14, 24) of the test block (10, 20), The cold side of the Peltier element faces the end surface (14, 24) of the test block (10, 20).

4. A device according to any one of the preceding claims, characterised in that The first test block (10) and the second test block (20) are each cylindrically configured. The base surface (12, 22) of the test block (10, 20) extends parallel to the end surface (14, 24) of the test block (10, 20).

5. A device according to any one of the preceding claims, characterised in that The first test block (10) and the second test block (20) are respectively made of single crystal silicon.

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

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

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

9. A device according to any one of the preceding claims, characterised in that The at least one first temperature sensor (16) is designed as a doped part of the first test block (10), and / or The at least one second temperature sensor (26) is designed as a doped part of the second test block (20).

10. The device according to any one of the preceding claims, characterized in that The heat source (31) is designed as a doped portion of the first test block (10).

11. The device according to any one of claims 1 to 9, characterized in that The heat source (31) is designed as a Peltier element, wherein: The hot side of the Peltier element faces the end surface (14, 24) of the test block (10, 20), The cold side of the Peltier element faces away from the end face (14, 24) of the test block (10, 20).

12. A method for measuring the thermal conductivity of a test piece (40) by means of a device according to any one of the preceding claims, wherein: Positioning a test piece (40) between end faces (14, 24) of the test blocks (10, 20); Using a heat source (31), heat energy is input into the device through a first base surface (12) of a first test block (10); measuring at least one first temperature of the first test block (10) by means of at least one first temperature sensor (16); measuring at least one second temperature of the second test block (20) by means of at least one second temperature sensor (26); The thermal conductivity of the test piece (40) is calculated from the input thermal energy, the at least one first temperature and the at least one second temperature.

Images