The present invention relates to a method for producing a thermoelectric generator, and to a corresponding thermoelectric generator.
The “Internet of Things” (IoT) is identified as one of the most important future developments in information technology. The IoT is understood to mean that, not only people have access to the Internet and are networked via the latter, but that devices are also networked to each other via the Internet. One area of the “Internet of Things” has its base in the area of production automation and home automation. For example, temperature sensors on the heating system, gyroscopes, acceleration sensors, pressure sensors and microphones may be used for this.
The electrical energy required for this can be obtained from the environment by means of so-called “energy harvesters”. The classic harvesters are PV cells for obtaining energy from sunlight, and the thermoelectric generators (TEG), described here, for obtaining energy from a temperature difference, for example on a heating system.
Against this background, the approach presented here presents a thermoelectric generator (TEG), a method for producing a thermoelectric generator, furthermore a device that uses this method, and finally a corresponding computer program, according to the main claims. Advantageous designs are disclosed by the respective dependent claims and the following description.
A TEG converts a temperature difference on a thermoelectric material into a voltage. The thermoelectric material is usually electrically connected in series and thermally connected in parallel between two substrates. In order to increase the converted voltage to a useful range, a plurality of leads (n-doped and p-doped) on the substrates are electrically connected in series. As a result of the series connection of the many leads, the TEG may lose its functionality completely as a result of one connection being damaged. The maximum stability may be exceeded as a result of thermal and/or mechanical stresses, as a result of which the electrically conductive connection may be impaired and/or broken. In order to increase the load capability of the entire generator, an electrically insulating material may at least partly support the thermal and/or mechanical stresses. As a result, the generator can more easily be machined mechanically and/or integrated into an overall system.
Presented is a thermoelectric generator that has a first substrate, a thermoelectric generator material, electrical connections (track conductors, pads, etc.), and a second substrate, wherein a first side of the generator material is connected in a thermally conductive manner to the first substrate, and a second side of the generator material that is opposite the first side is connected in a thermally conductive manner to the second substrate, wherein there is a support material disposed between the first substrate and the second substrate in order to support the first substrate and the second substrate against each other and/or mechanically connect them to each other.
Additionally presented is a method for producing a thermoelectric generator, wherein the method has the following steps:
providing a first substrate, a thermoelectric generator material and a second substrate;
connecting the generator material to the first substrate and to the second substrate, wherein a first side of the generator material is connected to the first substrate in an electrically and thermally conductive manner, and a second side of the generator material that is opposite the first side is connected to the second substrate in an electrically and thermally conductive manner; and inserting a support material between the first substrate and the second substrate, in order to support the first substrate and the second substrate against each other and/or mechanically connect them to each other.
A substrate may be understood to be a plate-type material. Between the two substrates is the thermoelectric generator material that, in the case of a temperature difference, generates a first voltage, owing to the Seebeck effect. In order to obtain a technically useful voltage, a multiplicity of leads of thermoelectric material may be connected in series. A doping (n- and p-doping) is normally used in the thermoelectric material, in order to adjust the Seebeck coefficient. The support material may be electrically insulating, in order to avoid an electrical short circuit. The support material may be mechanically connected to the first substrate and to the second substrate.
The support material may be inserted between the first substrate and the second substrate, after the first substrate, the generator material and the second substrate have been connected. For example, the support material may be injected between the first substrate and the second substrate.
The support material may be inserted before the second substrate is connected to the generator material. For example, the support material may be applied as a preshaped film to the first substrate. The support material may have recesses for the generator material. The support material may likewise be inserted before the first substrate is connected to the already connected second substrate and generator material.
The support material may be applied to the first substrate. The generator material may be connected to the first substrate in recesses of the support material. As a result of the support material being applied to the first substrate, the support material can be inserted particularly easily. The support material may likewise be applied to the second substrate before the generator material is connected to the second substrate.
The support material may be inserted into an edge region of the first substrate and/or of the second substrate. A lesser material consumption and thermal influencing can be achieved as a result.
The method may have a step of removing the support material. In this case, the support material may be removed, in particular, after the support material has supported shear forces during machining and/or processing of the generator. The removal makes it possible to achieve an increase in the thermal resistance, and consequently an increase in the temperature gradient on the thermoelectric generator material can be achieved.
The method may have a step of coupling the generator. In this case, the first substrate may be thermally coupled to a first carrier substrate, in particular a first printed circuit board. Alternatively or additionally, the second substrate may be thermally coupled to a second carrier substrate, in particular a second printed circuit board. In particular, the first and the second carrier substrate may be at least mechanically connected to each other. Owing to the carrier substrate, or printed circuit board, the generator can be a constituent part of a system and be used for supplying energy to the system. The printed circuit board/the carrier substrate may have heat-conducting elements, in order to couple the temperature difference into and out of the generator.
Additionally advantageous is an embodiment of the approach presented here having a step of coupling the generator, wherein, before the substrates are coupled to the carrier substrates, thermally conductive regions are made in the carrier substrates and are contacted to the substrate in a thermally conductive manner. Such an embodiment of the approach presented here offers the advantage that it is possible to effect electrical rewiring and a possible functional enclosure of the TEG by the carrier substrate, with good thermal coupling and, at the same time, increased mechanical stability. Besides the enclosure, the carrier substrates may also have other electronic components and functionality. The support material may be inserted into a gap between the first substrate and the second substrate. The support material may surround the generator material, in order to support the generator material laterally. The support material may be mechanically connected to the generator material. The generator, with the support material, can thereby withstand even greater loads.
The method may have a step of enclosing the generator in which one of the two substrates is coupled to a carrier substrate, and a housing, in particular a cover, projects over at least a sub-region of the generator. A housing of plastic or metal can protect the generator against environmental influences.
According to a further embodiment of the approach presented here, the method may have a step of enclosing the generator, wherein the enclosure is effected by a plastic, in particular a thermosetting plastic, by injection molding, transfer molding or casting. Such an embodiment of the approach presented here offers the advantage of mechanically stabilizing the TEG and protecting the leads against media such as, for example, moisture. At the same time, the enclosure by means of thermosetting plastic is an established standard process in electronics, and can thus be realized at low cost.
Also favorable is an embodiment of the approach presented here having a step of removing the support material, wherein the support material is removed, in particular, after the step of enclosing has been effected. Such an embodiment of the approach presented here offers the advantage that the support material provides the required additional mechanical stability during enclosure, but at the same time, as the result of being removed after the process, influence caused by the thermal conductivity of the material is no longer relevant.
In addition, according to a further embodiment, the method may have a step of enclosing the generator, wherein, before or in the step of enclosure by a plastic, a tolerance compensating material, in particular a thermally conductive pad, is applied on the surface of the substrate oriented toward the enclosure, and is omitted on the side facing away from the substrate. Such an embodiment of the approach presented here offers the advantage that the tolerance compensation can be decomposed together with the support material or, if a thermal pad is used, this can be directly processed concomitantly in the packaging process.
Particularly advantageous is an embodiment of the approach presented here having a step of enclosing the generator wherein, before the step of enclosure by a plastic, a damming material, in particular a plastic, is applied at least to a sub-region of the vertical faces of the generator, such that it leaves the region between the substrates free of the plastic of the enclosure. Such an embodiment of the approach presented here offers the advantage that, owing to the damming material, it is possible to prevent the region between the substrates from being filled in an undefined manner by the thermosetting housing material. In addition, the material may be realized such that it can be removed again after the packaging process.
The approach presented here additionally creates an apparatus that is designed to perform, control or implement the steps of a variant of a method presented here, in corresponding items of equipment. This embodiment variant of the invention, in the form of a control device, also enables the object on which the invention is based to be achieved in a rapid and efficient manner.
An apparatus in this case may be understood to mean an electrical device that processes sensor signals and that, in dependence thereon, outputs control signals and/or data signals. The apparatus may have an interface, which may be realized as hardware and/or software. If realized as hardware, the interfaces may be, for example, part of a so-called system ASIC, which includes a great variety of functions of the apparatus. It is also possible, however, for the interfaces to be separate integrated circuits or to be composed, at least partly, of discrete components. If realized as software, the interfaces may be software modules that, for example, are present on a microcontroller in addition to other software modules.
Also advantageous is a computer program product or computer program, having program code, which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory, and which is used to perform, implement and/or control the steps of the method according to one of the embodiments described above, in particular when the program product or program is executed on a computer or an apparatus.
The approach presented here is explained exemplarily in greater detail in the following on the basis of the appended drawings. There are shown:
In the following description of favorable exemplary embodiments of the present invention, elements, represented in the various figures, that are similar in their effect are denoted by the same or similar references, and description of these elements is not repeated.
It is also conceivable for the generator material 104 to be on the one substrate, and the generator material 105 to be on the second substrate, and these then to be thus joined together.
A thermoelectric generator (TEG) 100 normally consists of an upper substrate 106 and a lower substrate 102 that are connected to each other via leads 104 and 105 of thermoelectric material 104, 105. The leads 104 and 105 are connected thermally in parallel and electrically in series. Within the TEG 100, in the presence of a temperature gradient, a voltage is generated as a result of the Seebeck effect.
In the case of current assembly concepts for “packaging” TEGs 100 in electronic housings, the TEG 100 is rigidly connected, on the upper side 106 and lower side 102, to the cold side and hot side of the housing by means of thermally conductive materials. Thermomechanical strains are thereby transferred directly to the leads 104 and 105 of the TEG 100. These strains can result in damage to the leads 104, 105, and consequently to the entire module 100. Already in the assembly process, the TEG 100 is subjected to high thermomechanical and mechanical loads.
In the case of the approach presented here, an assembly material 108 is used to protect a thermoelectric generator 100 in a mechanically robust manner against influences in the process chain and in production.
In order to impart robustness to the thermoelectric generator 100, a filler material 108 is inserted into the clearances or spaces of a thermoelectric generator 100. The clearances or spaces extend laterally between the thermoelectrically active leads 104 and vertically between the at least two substrates 102, 106 of the thermoelectric generator 100.
The filler material 108 in this case may be inserted temporarily, and removed after the assembly process chain, or may remain permanently in the TEG 100.
The thermal conductivity of the permanent filler material 108 in this case is in the range of ≦1.5 W/mK, in particular in the range of ≦0.5 W/mK, in particular in the range of ≦0.3 W/mK.
In general, the permanent or temporary filler material 108 may be, in particular, materials from the group of polymers, which are inserted by dispensing, jetting, injection molding, diffusing, transfer molding at wafer level or chip level, or by deposition in the TEG production process. The temporary material 108 may be removed by chemical, wet-chemical or dry-chemical means, in particular thermally, at a temperature of ≦500° C., in particular ≦280° C., in particular ≦200° C.
The approach presented here makes it possible to achieve a reduction in the mechanical loading caused, inter alia, by thermomechanical stress, on the thermoelectric leads 104, 105 of the TEG 100 during the packaging and production process.
Furthermore, it is possible to achieve a reduction in the mechanical influences on the TEG 100 that are caused by stresses during production. For example, these loads occur when the sensor modules, fitted with the TEG 100, are being singled out of a larger panel by sawing. Mechanical loads such as impacts, free fall or moisture during transport, during storage or handling by the end user may also occur.
The use of a temporary material 108, for example a thermally decomposable polymer 108 or a water-soluble adhesive 108, enables the region between the leads 104 and 105 of the TEG 100 to be freed of the material 108 again after loading, in order to ensure the original thermal performance.
The temporary material 108 additionally offers protection against moisture in differing process steps.
The structure presented here includes at least one thermoelectric generator 100, which is composed of two substrates 102, 106. These substrates 102, 106 are connected to each other by thermoelectric material 104, 105 in the form of “leads”.
A thermoelectric generator 100 having a filler material 108, for example underfill, is represented in
In an exemplary embodiment, the thermoelectric generator 100 is represented with a temporary stabilization 108. The two substrates 102, 106 may be referred to as TEG upper side 106 and TEG lower side 102. In addition to the substrates 102, 106, the thermoelectric leads 104, 105 and the temporary stabilization 108 are represented. During operation, the temperature T1 is present on the upper side 106, and the temperature T2 is present on the lower side. The difference of these two temperatures is approximately the usable temperature gradient.
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In other words, the thermoelectric generator 100, having the temporary stabilization 108, is adhesive-bonded to a substrate 400 or to a printed circuit board 400, and coated with mold compound 500.
In an exemplary embodiment, the support material has been removed by thermal decomposition. In other words, the support material is vaporized.
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In an exemplary embodiment, the generator 100 is disposed in the recess 1206, and is connected to the second printed circuit board 1200 before the second printed circuit board 1200 and the generator 100 are connected to the first printed circuit board 400. The two printed circuit boards 1200 and 400 are connected to each other via a contact material 403. This contact material may be an adhesive, a soldered connection or a bonded connection. In an ideal case, this material is of poor thermal conductivity, in order to avoid a thermal short circuit between the two printed circuit boards, past the TEG.
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The exemplary embodiments described and shown in the figures have been selected merely as examples. Differing exemplary embodiments may be combined with each other in their entirety or in respect of individual features. Also, one exemplary embodiment may be complemented by features of another exemplary embodiment.
Further, the method steps presented here may be repeated, and executed in a sequence other than that described.
If an exemplary embodiment includes an “and/or” link between a first feature and a second feature, this is to be construed such that the exemplary embodiment according to one embodiment has both the first feature and the second feature, and according to a further embodiment has either only the first feature or only the second feature.
Number | Date | Country | Kind |
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10 2015 207 941.4 | Apr 2015 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/055284 | 3/11/2016 | WO | 00 |