RU2704568C1 - Installation method of thermoelectric modules - Google Patents

Abstract

FIELD: instrument making.SUBSTANCE: invention relates to instrument making and can be used for development of devices, including laser, especially at their serial production and operated in conditions of impact and vibration loads. Technical effect is achieved due to that in addition to tightening screws assembly is equipped with thrust screws, screwed in radiator, height of protrusion of which relative to radiator surface is adjusted during assembly erection using calibrated gaskets, thickness, determined by total allowance for flatness of connected parts and providing process clearances between planes of thermally stabilized element, radiator and surfaces of ceramic plates of TEM with possibility of their filling with heat conducting paste.EFFECT: technical effect consists in excluding the effect of dynamic loads on structural elements of thermoelectric modules (TEM) occurring during operation during vibrations and impacts from elements in mechanical contact with TEM.1 cl, 6 dwg

Description

The invention relates to instrumentation, and can be used in the development of various devices, including laser, with temperature stabilization systems based on thermoelectric modules (TEM), especially in their mass production.

The task to which the claimed invention is directed is to develop a method for installing a TEM, which eliminates the influence of dynamic loads on structural elements of the TEM that occur during operation during vibration and shock from elements that are in mechanical contact with the TEM.

Currently, semiconductor TEMs are widely used in various devices - in the cooling systems of active elements of solid-state lasers, computer processors, in medical equipment, household and industrial refrigerators, etc.

The TEM is based on the Peltier effect (B. M. Yavorsky, A. A. Detlaf, Handbook of Physics. For engineers and university students. Ed. 2nd, M., Science. 1964). A single TEM element (Fig. 1) is a thermocouple consisting of one n-type conductor (branch) and one p-type conductor (positions 1 and 2., respectively, in Fig. 1). When several such thermocouples are connected in series, the heat (Qc) absorbed at the np type contact is released at the pn (Qh) type contact. A thermoelectric module is a combination of such thermocouples, usually interconnected in series in current and in parallel in heat flow. Thermocouples are placed between two ceramic plates (position 4, FIG. 1). The branches are soldered onto copper conductive pads (item 3, Fig. 1), which are attached to special heat-conducting ceramics, for example, from aluminum oxide (AlO ₃ ) or aluminum nitride (AlN). The number of thermocouples can vary widely - from several units to several hundred, which allows you to create a TEM with a cooling capacity from tenths of a watt to hundreds of watts. The highest thermoelectric figure of merit among industrial materials used for the manufacture of TEM is bismuth telluride, in which special additives, for example, selenium and antimony, are added to obtain the required type and conductivity parameters. In FIG. 1 shows a TEM device, where the positions show:

1 - n-type semiconductor;

2 - p-type semiconductor;

3 - conductive sites;

4 - ceramic plates.

Various companies in different countries of the world mass-produce thermoelectric modules of approximately the same parameters and sizes. The leading place in the world in the quality of produced modules is occupied by such Russian companies as Krioterm, Nord, Osterm and others.

It should be noted that the TEM-based assembly cannot work without heat removal from the hot side, therefore it always consists of three parts (Handbook of Thermoelectric - London. N.Y .: CRC Press, 1995):

- thermoelectric module or modules;

- a radiator on the hot side of the module;

- a cooled (thermostabilized) object on the cold side.

In FIG. Figure 2 shows a photograph of a standard commercially available single-stage TEM (item 5) with power wires (item 5a), taken from the Kriotherm product catalog (www.kriotherm.ru). According to the TEM installation instructions (www. Kriotherm.ru), there are two of the most common ways to install a module in an assembly with a heat-stabilized element and a radiator: using a screw connection and using soldering. The second method requires a technological operation to metallize the outer surfaces of ceramic plates. In this case, the TEM installation in the assembly is carried out by soldering with flux-free solder. With this installation method, the necessary rigidity of the assembly and ideal thermal contact of the metallized surfaces of the TEM with the surfaces of the connected parts are ensured. Disadvantages inherent in the installation method considered:

- the method is difficult to implement with materials not suitable for soldering;

- the method is incompatible with assembly parts, which heating is contraindicated;

- limited maintainability of the assembly after installation;

- the cost of metallized TEM is much higher than the usual standard;

- the method does not exclude the influence of dynamic loads on the structural elements of the TEM in harsh operating conditions.

The closest analogue of the claimed invention for the problem to be solved and the number of similar features is a method of installing a thermoelectric module using a screw connection (Kriotherm catalog, TEM installation instructions (www.kriotherm.ru)). In this case, to ensure good thermal contact of the thermostabilized element with the cold, and the radiator with the hot sides of the TEM, a special heat-conducting paste (for example, KPT-8) is usually used. To reduce thermal resistance, the thermal paste layer should be as small as possible. The tightening torque of the screws providing the clamp of the thermostabilized element and the radiator to the TEM can be determined by the following formula (www.kriotherm.ru):

T = Pm × Sm × Nm × K × d / N,

Where:

T - torque values on each screw;

Pm is the developed pressure of the clamp;

Sm is the surface area of thermoelectric modules in the assembly;

Nm is the number of thermoelectric modules in the assembly;

N is the number of screws used for mounting the assembly;

K is the reduced coefficient of friction (for example, K = 0.2 for steel, K = 0.15 for nylon);

d is the nominal diameter of the screw.

For standard single-stage non-metalized TEMs, the recommended clamping pressure during installation is Pm = 5-12 kg / cm ² and is governed by the mechanical strength of the most fragile ceramic plate element.

So that the screws do not greatly affect the heat flux from the hot side of the TEM to the cold side, their diameter is chosen to be minimal and, preferably, they should be made of a material with low thermal conductivity. In addition, when mounting the radiator assembly. TEM and the cooled element to prevent direct contact of the fixing screws with the cooled element, heat-insulating sleeves are used. The recommended material for heat-insulating sleeves is polycaproamide (caprolon).

In FIG. 3 shows a drawing of a mounted assembly of a thermostabilized element. TEM and radiator according to the standard TEM installation method using tightening screws. In FIG. 3 positions show:

5 - TEM;

6 - a radiator;

7 - thermostabilized element;

8 - tightening screw;

9 - heat-insulating sleeve.

Thus, the closest analogue allows us to solve the problem of installing a TEM in an assembly with a heat-stabilizing element and a radiator using tightening (fixing) screws and heat-insulating sleeves, providing the necessary clamping pressure and thermal insulation of the cooled element from the radiator, minimizing thermal resistance over the contact area of contacting parts due to the use of heat transferring paste. However, the standard method of installing TEM has limitations on the use of assemblies with TEM in the conditions of operation of the product with unregulated loads. The main disadvantage of the standard TEM fastening method is that the power load distribution circuit is a circuit that is closed to the TEM. The weak link in the design of TEM, in terms of mechanical strength, are ceramic plates. In conditions of tough operation of a device equipped with a TEM, in addition to constant clamping pressure from the fixing screws, under the influence of vibration and shock, the TEM is additionally loaded with unregulated inertial forces arising from elements in contact with the TEM. If the level of mechanical loads is higher than permissible, destruction of the TEM elements and loss of its performance is possible.

The technical result of the claimed invention is a method of installing a TEM in an assembly with a thermostabilized element and a radiator, is a guaranteed increase in the rigidity of the assembly to ensure the possibility of its operation in conditions of shock and vibration loads.

The claimed technical result is achieved by the fact that in the method of installing a TEM based on tightening screws that provide mechanical contact with a certain clamping pressure of the surfaces of the thermally stabilized element and radiator to the ceramic plates of the thermoelectric module (TEM) through a layer of heat-conducting paste, the assembly is new, in addition to the tightening screws, the assembly equipped with stop screws screwed into the radiator, the protrusion height of which relative to the surface of the radiator is adjusted when the assembly installation using calibrated gaskets, the thickness determined by the total tolerance on the flatness of the parts to be joined and providing technological gaps between the planes of the thermostabilized element and the radiator and the surfaces of the TEM ceramic plates with the possibility of filling them with heat-conducting paste.

Compared with the prototype (see drawbacks) in the proposed solution, thrust screws screwed into the radiator allow changing the load distribution circuit when installing the TEM in an assembly with a thermostabilizing block and transferring the action of constant clamping pressure from the fixing screws and inertial loads to the external circuit formed thrust screws together with the radiator and the surface of the thermostabilized element, which leads to power unloading of the TEM and protecting it from destruction. The selection of the height of the protrusion of the thrust screws by pre-mounting the assembly using calibrated gaskets of a certain declared thickness makes it possible to reliably distribute the main load on the thrust screws, minimize the size of the technological clearances and. accordingly, the value of thermal resistance when filling gaps with heat-conducting paste.

Thus, the implementation of the specified installation method TEM allows you to:

- provide a guaranteed increase in rigidity of the assembly;

- exclude control of the tightening torque of the fixing screws during assembly;

- provide the same amount of thermal resistance during installation of identical assemblies;

Here is a general list of used figures and graphic images.

In FIG. 1 schematically shows a TEM, where 1 and 2 are thermocouple forming, n-type and p-type semiconductors, respectively; 3 - conductive pad of copper; 4 - two ceramic plates.

In FIG. 2 shows a photograph of a standard commercially available single-stage TEM - 5 with power wires - 5a.

In FIG. 3 shows a drawing of a mounted assembly of a thermostabilized element, a TEM and a radiator according to the standard TEM installation method using tightening screws. In FIG. 3 positions show: 5 - TEM; 6 - a radiator; 7 - thermostabilized element; 8 - tightening screw; 9 - heat-insulating sleeve.

In FIG. 4 is a drawing of an assembly of a thermostabilized element, a TEM and a radiator, made according to the claimed method of installing a TEM using additional thrust screws, where the positions denote: 5 - TEM; 6 - a radiator; 7 - thermostabilized element: 8 - tightening screw: 9 - heat-insulating sleeve; 10 - persistent screws; 10a - the height of the protruding thrust screws relative to the surface of the radiator equal to the sum of the height of the TEM and the thickness of the calibrated gasket.

In FIG. 5 shows a photograph of the constituent parts — a thermostabilized element (a nonlinear optical crystal attachment assembly (NOC) assembly) and a radiator made to install a TEM according to the claimed method. In FIG. 6 shows a photograph of the assembly after installation. In figures 5, 6, the positions indicate the following details: 5 - TEM; 6 - a radiator; 7 - thermostabilized element (mounting unit NOC 12); 8 - tightening screw; 9 - heat insulating sleeve; 10 - persistent screws; 11 - metal washer; 12 - optical element (NOC) Let us consider a practical example of the installation of TEM according to the claimed method in an assembly with a thermostabilized element - an NOC mount.

The thermostabilized element 7 (Fig. 4, Fig. 5, Fig. 6) is a collapsible NOC mount, made of heat-conducting copper material. Radiator 6 is made of aluminum alloy D16. The tightening 8 and thrust screws 10 are made of titanium alloy VT3-1 with a diameter of 3 mm and 2.5 mm to minimize thermal conductivity. respectively. The assembly used the standard commercially available single-stage TEM (5, Fig. 4) - TV-83-1.0-1.5 with dimensions A × B × H = 22 × 19 × 3.8 mm, where A is the length, B- width and H-height of the module. Thermal insulation of the tightening screws from the thermostabilized element was provided by caprolon 9 bushes. For uniform distribution of the load from the tightening screws 8 to the bushings 9, metal washers 11 were used (Fig. 5, Fig. 6) with an external diameter larger than the maximum diameter of the heat-insulating bushes. The height of the protruding thrust screws relative to the surface of the radiator was set during preliminary assembly of the assembly using a calibrated metal gasket (foil) installed between the plane of the NOC 7 mount and the TEM 5 ceramic plate. The minimum thickness of the gasket for a particular assembly was 0.02 mm and was selected based on total tolerance on the flatness of the connected parts. After the installation of the gasket, the tightening screws were evenly and freely screwed into the radiator 6 until the plane of the attachment point NOC 7 touched the foil plane (until the resistance increased sharply). Then, the stop screws 10 were screwed until the contact (a sharp increase in resistance) of the plane of the NOC mount 7. To fix the height of the protrusion of the stop screws, they were locked with paint. After preliminary installation, the assembly was disassembled, the gasket was removed, the TEM ceramic plates were covered with a thin layer of KPT8 heat-conducting paste. At the final assembly, tightening screws were uniformly tightened to a sharp increase in resistance, indicating the distribution of the main load on the thrust screws. The initial technological gap with a thickness of 0.02 mm during compression of the TEM is converted into two gaps with a thickness of ~ 0.01 mm filled with paste, while ensuring low thermal resistance.

This technical solution was successfully tested in the manufacture and testing of individual samples of solid-state lasers in which thermostable units based on TEM are used.

Based on the foregoing, it can be argued that the inventive method provides an increase in the rigidity of the assembly due to the redistribution of the load from the TEM to the thrust screws.

At the same time, there are additional advantages consisting in the low thermal resistance of the assemblies and the identity of the assemblies in terms of thermal resistance and structural rigidity, which simplifies the process of assembling an assembly with a TEM and eliminates the need to control the thermal resistance and the tightening torque of the fixing screws, which is especially important in mass production.

Thus, the inventive method of installing a heat-stabilizing unit based on TEM can be applied in the design and manufacture of various devices, including laser, especially in their mass production, which use heat-stabilized nodes based on TEM. The introduction of this method of installing TEM allows you to increase the rigidity of the assembly of the thermal stabilization system and ensure the operation of the device under shock and vibration loads.

Claims (1)

A method of installing a thermoelectric module based on tightening screws, which provides mechanical contact with a certain clamping pressure of the surface of the thermally stabilized element and the radiator to the ceramic plates of the thermoelectric module through a layer of heat-conducting paste, characterized in that the assembly is additionally equipped with stop screws screwed into the radiator, with an adjustable protrusion height above the surface of the radiator, determined during the preliminary installation of the assembly using calibrated gaskets, with a thickness determined by the total tolerance on the flatness of the parts to be joined and providing technological gaps between the planes of the thermostabilized element, the radiator and the surfaces of the ceramic plates of the thermoelectric module to fill them with heat-conducting paste.

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