Patent Application
20140182644
The present invention is directed to thermoelectric devices. More particularly, the invention provides structures and methods for forming a multi-leg package (MLP) assembly. Merely by way of example, the invention has been applied to packaging a plurality of thermoelectric legs for the manufacture of a thermoelectric module. However, it would be recognized that the invention has a much broader range of applicability.
Conventional thermoelectric devices are often packaged using a plurality of thermoelectric (TE) legs arranged in multiple serial-chain configurations on a base structure. Each of the plurality of thermoelectric legs is made by either p-type or n-type thermoelectric material. The thermoelectric material, either p-type or n-type, is usually selected to be a semiconductor characterized by high electrical conductivity and high thermal resistivity. For example, as a pair, a p-type leg is coupled to an n-type leg via a conductor in the serial-chain configuration. In another example, one conductor is coupled to one end region of a leg and another conductor is coupled to another end region of the leg.
When the thermoelectric device is applied with a bias voltage across the top and bottom regions using two electrodes, a temperature difference is generated so that the thermoelectric device can be used as a refrigeration (e.g., Peltier) device. When the thermoelectric device is subjected to a thermal gradient with conductors at first end regions of the legs being attached to a cold side of the junction and conductors at second end regions of the legs being in contact with a hot side of the junction, the thermoelectric device is able to generate electrical voltage across the junction as an energy conversion (e.g., Seebeck) device.
The thermoelectric material 101 is characterized by its high electrical conductivity. For example, the thermoelectric material 101 is a semiconductor (e.g., a single-element semiconductor, a compound semiconductor, or a composite semiconductor), doped to n-type or p-type (e.g., with electrical impurities to adjust the resistivity of the semiconductor to between approximately 0.00001 Ω-m and 10 Ω-m). The thermoelectric material 101 is also characterized by its high thermal resistance. The high thermal resistance can be achieved through material selection and/or structural reconfiguration. For example, exotic compound materials such as bismuth telluride (Bi2Te3) or lead telluride (PbTe) are selected for their thermoelectric functionality by having a low lattice thermal conductivity of about 1.20 W/(m·K). Other applicable thermoelectric materials such as Mg2Si, MnSi2, or PbTe can also be used. In another example, the bulk-sized structure for the thermoelectric material 101 includes a network of nanowires without substantially aligned parallel along a length direction of the structure. The bulk-sized structure for the thermoelectric material 101 is intended for forming a leg structure that has a thermal resistance as large as possible along its length while maintaining a good electrical conduction through the structure.
As shown in
The end electrodes 111 and 113 can be formed by metallization of the end regions of the bulk-sized structure for the thermoelectric material 101 and attachment of one or more conductor materials to the metalized end regions (e.g., the metalized layers). For example, the one or more conductive materials are applied by physical deposition or plating. In another example, thermal annealing and polishing processes are also included to enhance physical coverage overlying the metalized layers and to form smoother surfaces of the end electrodes 111 and 113. One of the two end electrodes 111 and 113 is bonded to a hot-side contact when the TE leg 100 is assembled as one unit in a serial-chain configuration of a thermoelectric device while the other one of the two end electrodes 111 and 113 is bonded to a cold-side contact of the thermoelectric device. Both the hot-side contact and the cold-side contact are directly associated with the same thermal junction applied by the thermoelectric device.
The end electrodes 211 and 213 for the n-type TE leg 210 and the end electrodes 221 and 223 for the p-type TE leg 220 do not have to be formed with different materials with different processes specifically for n-type or p-type characteristics. Different bonding materials and/or different bonding processes are used to form an end electrode of a particular type of TE leg. For example, the bonding and/or brazing material is selected to make the end electrode specifically suited for accommodating different thermal stress depending on whether the end electrode is against with a cold-side contact or a hot-side contact when the TE leg is packaged into a thermoelectric device.
The energy conversion efficiency of thermoelectric devices can be measured by a so-called thermal power density or “thermoelectric figure of merit” ZT. ZT is equal to TS2 σ/k where T is the temperature, S is the Seebeck coefficient, σ is the electrical conductivity, and k is the thermal conductivity of the thermoelectric material. In order to drive up the value of ZT of thermoelectric devices utilizing the Seebeck effect, searching for high performance thermoelectric materials and developing low cost manufacturing processes are major concerns. Additionally, there are also needs for improved techniques of packaging thermoelectric devices. For example, mounting a plurality of thermoelectric legs in a serial-chain configuration needs a base structure that can handle high thermal stress induced by the ultra-high temperature gradient, especially for TE legs with relative high aspect ratio in their physical structures and/or TE legs formed by a TE material having a thermal expansion coefficient that is different from the thermal expansion coefficient of a heat sink material. In another example, reliable end-electrodes need to be developed for each TE leg, where the end-electrodes are in contact with both the thermoelectric material and the heat sink material.
Conventional thermoelectric modules and/or devices often include an alumina or similar ceramic as a substrate base plate on both sides of multiple thermoelectric legs connected in series. For example, a conventional thermoelectric device is 40-mm-long by 40-mm-wide by 3-mm-thick, and the conventional thermoelectric device includes two ceramic plates with a low coefficient of thermal expansion (CTE) (e.g., CTE being lower than 10×10−6/° C., such as CTE equal to 4×10−6/° C. at the room temperature) and also includes thermoelectric legs made of a thermoelectric material with a high coefficient of thermal expansion (e.g., CTE being higher than 10×10−6/° C., such as CTE equal to 11×10−6/° C. at the room temperature for n-type legs and CTE equal to 14×10−6/° C. at the room temperature for p-type legs), wherein the thermoelectric legs are sandwiched between the two ceramic plates and bonded to the two ceramic plates via thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature) for electrical connection of the legs. In another example, these conventional modules and/or devices are based on bismuth telluride Peltier cooling technology, and so are optimized to work with manufacturing tooling that is used to manufacture Peltier coolers. In yet another example, these conventional modules and/or devices that are based on bismuth telluride Peltier cooling technology usually include materials and structures not intended to withstand high temperatures or large temperature gradients because these Peltier coolers are designed to maintain temperature gradients smaller than 50 degrees for temperatures that are below 150° C. These conventional alumina base plates, as well as the soldering and/or brazing materials, electrical shunts, joining and interface layers, and/or associated manufacturing processes are often designed to be optimal for these Peltier products under the above stated conditions. They usually do not offer the ability to operate at temperatures above 250° C. (especially in the case of bismuth telluride devices), nor can they withstand large temperature gradients that are larger than 200 degrees without mechanical failures that can result in electrical discontinuity.
Hence, it is highly desirable to improve packaging techniques that take into consideration the thermal environment in which a thermoelectric device operates.
The present invention is directed to thermoelectric devices. More particularly, the invention provides structures and methods for forming a multi-leg package (MLP) assembly. Merely by way of example, the invention has been applied to packaging a plurality of thermoelectric legs for the manufacture of a thermoelectric module. However, it would be recognized that the invention has a much broader range of applicability.
According to one embodiment, a thermoelectric device with a multi-leg package includes a first ceramic base structure including a first surface and a second surface, and a first plurality of pads including one or more first materials thermally and electrically conductive. The first plurality of pads are attached to the first surface. Additionally, the thermoelectric device includes a second plurality of pads including the one or more first materials. The second plurality of pads are attached to the second surface and arranged in a mirror image with the first plurality of pads. Moreover, the thermoelectric device includes a plurality of thermoelectric legs attached to the first plurality of pads respectively. Each pad of the first plurality of pads is attached to at least two first thermoelectric legs of the plurality of thermoelectric legs. Also, the thermoelectric device includes a first plurality of sheet conductors attached to the plurality of thermoelectric legs respectively and including one or more second materials thermally and electrically conductive. Each sheet conductor of the first plurality of sheet conductors is attached to at least two second thermoelectric legs of the plurality of thermoelectric legs. The first plurality of pads include a first pad and a second pad configured to allow a first electrical current to flow between the first pad and the second pad only through two or more third thermoelectric legs of the plurality of thermoelectric legs, and the first plurality of sheet conductors include a first sheet conductor and a second sheet conductor configured to allow a second electrical current to flow between the first sheet conductor and the second sheet conductor only through two or more fourth thermoelectric legs of the plurality of thermoelectric legs.
According to yet another embodiment, a thermoelectric device with a multi-leg package includes a plurality of pads including one or more first materials thermally and electrically conductive. The plurality of pads are parts of a first metal lead frame without any metal tab linking the plurality of pads. Additionally, the thermoelectric device includes a plurality of thermoelectric legs attached to the plurality of pads respectively. Each pad of the plurality of pads is attached to at least two first thermoelectric legs of the plurality of thermoelectric legs. Moreover, the thermoelectric device includes a first plurality of sheet conductors attached to the plurality of thermoelectric legs respectively and including one or more second materials thermally and electrically conductive. Each sheet conductor of the first plurality of sheet conductors is attached to at least two second thermoelectric legs of the plurality of thermoelectric legs. The plurality of pads include a first pad and a second pad configured to allow a first electrical current to flow between the first pad and the second pad only through two or more third thermoelectric legs of the plurality of thermoelectric legs, and the first plurality of sheet conductors include a first sheet conductor and a second sheet conductor configured to allow a second electrical current to flow between the first sheet conductor and the second sheet conductor only through two or more fourth thermoelectric legs of the plurality of thermoelectric legs.
According to yet another embodiment, a method for making a thermoelectric device with a multi-leg package includes providing a first ceramic base structure including a first surface and a second surface. The first surface is attached to a first plurality of pads, the second surface is attached to a second plurality of pads arranged in a mirror image with the first plurality of pads, and both the first plurality of pads and the second plurality of pads include one or more first materials thermally and electrically conductive. Additionally, the method includes attaching a plurality of thermoelectric legs to the first plurality of pads respectively. Each pad of the first plurality of pads is attached to at least two first thermoelectric legs of the plurality of thermoelectric legs. Additionally, the method includes attaching a first plurality of sheet conductors to the plurality of thermoelectric legs respectively. The first plurality of sheet conductors include one or more second materials thermally and electrically conductive, and each sheet conductor of the first plurality of sheet conductors is attached to at least two second thermoelectric legs of the plurality of thermoelectric legs. The first plurality of pads include a first pad and a second pad configured to allow a first electrical current to flow between the first pad and the second pad only through two or more third thermoelectric legs of the plurality of thermoelectric legs, and the first plurality of sheet conductors include a first sheet conductor and a second sheet conductor configured to allow a second electrical current to flow between the first sheet conductor and the second sheet conductor only through two or more fourth thermoelectric legs of the plurality of thermoelectric legs.
According to yet another embodiment, a method for making a thermoelectric device with a multi-leg package includes providing a plurality of pads including one or more first materials thermally and electrically conductive. The plurality of pads are parts of a first metal lead frame without any metal tab linking the plurality of pads. Additionally, the method includes attaching a plurality of thermoelectric legs to the plurality of pads respectively. Each pad of the plurality of pads is attached to at least two first thermoelectric legs of the plurality of thermoelectric legs. Moreover, the method includes attaching a first plurality of sheet conductors to the plurality of thermoelectric legs respectively and including one or more second materials thermally and electrically conductive. Each sheet conductor of the first plurality of sheet conductors is attached to at least two second thermoelectric legs of the plurality of thermoelectric legs. The plurality of pads include a first pad and a second pad configured to allow a first electrical current to flow between the first pad and the second pad only through two or more third thermoelectric legs of the plurality of thermoelectric legs, and the first plurality of sheet conductors include a first sheet conductor and a second sheet conductor configured to allow a second electrical current to flow between the first sheet conductor and the second sheet conductor only through two or more fourth thermoelectric legs of the plurality of thermoelectric legs.
Depending upon the embodiment, one or more benefits may be achieved. These benefits and various additional objects, features, and advantages of the present invention can be fully appreciated with reference to the detailed description and accompanying drawings that follow.
The present invention is directed to thermoelectric devices. More particularly, the invention provides structures and methods for forming a multi-leg package (MLP) assembly. Merely by way of example, the invention has been applied to packaging a plurality of thermoelectric legs for the manufacture of a thermoelectric module. However, it would be recognized that the invention has a much broader range of applicability.
Since the thermoelectric power generation efficiency of a module in a temperature gradient is proportional to the temperature gradient, or the Carnot efficiency, the inability to take conventional thermoelectric materials to high temperatures often severely limits the power generation efficiency of thermoelectric products. As new thermoelectric products have been developed in recent years that can transform heat into electricity, improvements are needed in raising the power output of these products to deliver greater efficiency and lower cost. Most thermoelectric power generation products utilize some form of exhaust gas, such as from a car engine, to generate power, a two-dimensional temperature gradient is the relevant boundary condition with which to further improve thermoelectric modules. As such, structures and techniques are needed for thermoelectric modules so that these modules are able to withstand large temperature gradients, temperatures in excess of 300° C. on the hot side, and in excess of 100° C. on the cold side, according to certain embodiments.
In one embodiment, a thermoelectric leg includes a thermoelectric material. For example, an abundantly-supplied semiconductor material such as silicon is processed to form a plurality of nanostructure elements (e.g., one-dimensional wire structure, one-dimensional tube structure, two-dimensional layered structure, three-dimensional random voids and/or meshes structure) with a thermal conductivity between 0.1 W/m-K and 20 W/m-K while still provided as the bulk-sized structure for the thermoelectric material. In another example, the bulk-sized structure for the thermoelectric material includes a plurality of nanowires with high aspect ratio substantially aligned parallel along a length direction of the structure. In yet another example, the bulk-sized structure for the thermoelectric material includes a network of nanoholes, nanoparticles, and/or meshes without substantially aligned parallel along a length direction of the structure. In yet another example, the bulk-sized structure for the thermoelectric material includes a network of nanowires, nanoholes, nanoparticles, and/or meshes without a favored direction although the thermoelectric material is provided as an elongated column-like structure. In yet another example, the bulk-sized structure for the thermoelectric material includes a fill material occupying the intermediate regions between nanostructure elements (e.g., wire structure, or voids and/or meshes structure). In yet another example, the fill material is selected to bear a high thermal resistivity while keeping high electrical conductance only through the nanostructure elements (e.g., wire structure, or voids and/or meshes structure) and to also help strengthen the leg structure physically as a whole.
In another embodiment, certain structural modifications near both end regions of a TE leg are applied to at least partially relieve the thermal stress induced between the TE material and the end electrodes.
In one embodiment, each of the TE legs 310 and 320 has a long length and a small cross section in order to increase thermal resistance for maintaining a temperature difference as large as possible across a thermal junction for achieving better thermoelectric power density. But such leg structure often imposes large thermal stress near the end regions of a TE leg as the TE leg is in contact with both the hot side and the cold side of a thermal junction.
In another embodiment, each of the TE legs 310 and 320 has the bulk-sized TE material that is made from a plurality of ultra-long nanowires aligned in the length direction. For example, each nanowire has a length of 400 μm or more with an aspect ratio of 1000 to 1. In another example, the plurality of ultra-long nanowires are formed into multiple arrays, each of which has an extended bulk-sized lateral dimension with interstitial regions filled with non-conductive fill material. In yet another example, the multiple arrays of nanowires can also be stacked in the length direction to achieve a prolonged length of the bulk-sized TE material.
Although the lateral dimension of a bulk-sized TE material (e.g., the thermoelectric material 301, the thermoelectric material 302) can become much larger than its length or height dimension, the bulk-sized TE material may contain internal structural elements that have a large length-to-width aspect ratio and thus are sensitive to the lateral stress imposed by thermal expansion after the conductor material (e.g., the conductor material 330) is contacted to the hot side of a thermal junction. One or more structural modifications can help relieve the stress and reduce contact breakdown or other device failure issues according to some embodiments.
According to one embodiment, the end regions of the bulk-sized TE material (e.g., the thermoelectric material 301, the thermoelectric material 302) are to have their edges and/or corners shaped in curved tail or rounded when each TE leg (e.g., the TE leg 310, the TE leg 320) is individually fabricated. For example, when fabricating each individual TE leg out of a large wafer-sized TE material through a serial of planar and/or cutting processes, the corner regions are intentionally left with a tail structure or cut to have a truncated shape. In another example, for the TE leg 310, one or more curved tail portions 304 are left around the first end region of the TE material 301 when the TE material 301 is cut from a larger-sized material and one or more truncated edges 306 are associated with the second end region of the TE material 301.
As shown in
Also as shown in
In one embodiment, the conductive shunt material 440 is configured to be a thin plate or sheet material with a region 441 near its middle region, and the region 441 can be bended under stress and serves as an intrinsic stress relief mechanism. For example, the conductive shunt material 440 is made by highly-conductive metal or alloy (e.g., copper and/or gold) and used to associate with a cold-side contact of a thermal junction applied by the thermoelectric device that includes the TE legs 401, 402, 403, and 404. In another example, the thermal expansion of the hot-side contact induces mechanical deformation or shift of the conductor material 431 and the conductor material 432 that are bonded to the bottom end electrodes (e.g., end electrodes 321 and 311) of the two TE legs 402 and 403, and such mechanical deformation or shift in turn pulls or pushes the top end electrodes (e.g., end electrodes 323 and 313) of the two TE legs 402 and 403. In yet another example, while the top end electrodes (e.g., end electrodes 323 and 313) of the two TE legs 402 and 403 are bonded to the conductive shunt material 440, the stress imposed to the top end electrodes of the two TE legs 402 and 403 can be properly relieved by bending the region 441 and/or stretching out the bended region 441 of the shunt material 440 without affecting the bonding between the conductive shunt material 440 and the top end electrodes of the two TE legs 402 and 403.
In one embodiment, flat regions 4446 and 4449 on the conductive shunt material 440 are used for respectively bonding with two TE legs to form a thermoelectric unicouple (e.g., a thermoelectric unicouple 400), and flat regions 4447 and 4448 on the conductive shunt material 440 are used for respectively bonding with another two TE legs to form another thermoelectric unicouple (e.g., another thermoelectric unicouple 400). For example, these two thermoelectric unicouples are connected in an electrical parallel configuration. In another example, one of these two thermoelectric unicouples serves as a backup for the other thermoelectric unicouple, so that if one or two TE legs for one of the two thermoelectric unicouples fail, the electrical connection for the serial-chain configuration of the whole thermoelectric device can still work by passing the current through the backup unicouple.
In another embodiment, not only the two thermoelectric unicouples under a single piece of conductive shunt material 440 can be formed in a two-dimensional configuration, but also the serial-chain configuration of thermoelectric unicouples can be arranged in a two-dimensional package. For example, the thermal stress associated with the whole packaged thermoelectric device that includes all unicouples is also two dimensional. In another example, under stress, the middle region of the conductive shunt material 440 can be bended in each of the two directions, the first direction extending from the edge 4441 to the edge 4443 and the second direction extending from the edge 4442 to the edge 4444. In yet another example, the conductive shunt material 440 as shown in
In yet another example, the central opening 4445 also provides stress relief by taking away material from the most twisted central portion of the conductive shunt material 440. For example, the two-dimensional rectangular-shaped conductive shunt material 440 is modified to be a sheet or thin plate adaptive to the stress imposed from either one or both of two lateral directions (e.g., the first direction and/or the second direction) by allowing one-dimensional stretching and/or bending of the flexible curved regions 4441 and 4443 in only one direction and/or by allowing one-dimensional stretching and/or bending of the flexible curved regions 4442 and 4442 in only another direction.
In one embodiment, the base structure 510 is electrically insulating but thermally highly conductive. For example, the base structure 510 includes a plate made of a ceramic material. In another example, the ceramic material is silicon nitride (Si3N4). In another embodiment, a front-side surface of the base structure 510 is attached to a plurality of metal contact pads 530 (e.g., a plurality of conductor materials 431) for bonding TE legs belonging to different thermoelectric unicouples. For example, each of the plurality of metal contact pads 530 is thermally and electrically conductive. In another example, the base structure 510 is attached to one metal contact pad 530 (e.g., a conductor material 431) in order to bond the two TE legs belonging to the neighboring thermoelectric unicouples 501 and 502. In yet another example, referring to
In order to assemble a large thermoelectric device, a plurality of TE legs are included in each serial-chain configuration, and a plurality of such serial-chain configurations are aligned to form a two-dimensional array of TE legs over a large area of the base structure 510 according to certain embodiments. For example, the base structure 510 is a rectangular-shaped plate attached to N×M metal contact pads 530 and N×M metal contact pads 540, wherein N and M are integers greater than 1. In another example, each metal contact pad 530 is aligned to bond with four TE legs.
As shown in
In one embodiment, a volume of space between the hot-side plate 610 and the cold-side plate 620 is used to form a thermal junction. For example, the base structure 510 is in thermal contact with the hot-side plate 610 of the thermal junction through the plurality of metal contact pads 540 and/or the hot-side thermal interface material 611. In another example, the conductive shunt materials (e.g., the conductive shunt materials 541 and 542) are in thermal contact with the cold-side plate 620 of the thermal junction through the cold-side thermal interface material 621. In another example, the hot-side plate 610 is associated with a heat source at a high temperature (e.g., a waste-heat source with exhaust gas at 600° C. or higher), and the cold-side plate 620 is associated with a cooling source (e.g., ambient air or water at a temperature substantially less than 100° C.).
In another embodiment, when the base structure 510 is just attached to the hot-side plate 610 through the plurality of metal contact pads 540 and/or the hot-side thermal interface material 611, a large temperature difference (e.g., 600° C. or more) between the hot-side plate 610 and the just-attached base structure 510 causes mechanical deformation to the hot-side plate 610. For example, part of the hot-side plate 610 protrudes up, and part of the hot-side plate 610 bends down. In another example, such mechanical deformation further transfers the stress to push up and/or drag down the corresponding portions of the base structure 510, thereby imposing stress to the TE legs that are bonded onto the base structure 510 through the plurality of metal contact pads 530.
In yet another embodiment, under such thermal stress (e.g., the thermal stress mainly perpendicular to the backside surface of the base structure 510), the one or more line notches 515 become the weakest regions of the base structure 510. For example, a desirable manner of stress relief is to break the base structure 510 into multiple blocks along the one or more line notches 515. In another example, the multiple blocks includes a block 631 and a block 632 separated by a gap 636. In yet another example, after breaking into multiple blocks along the one or more line notches 515, each block on its backside surface still bonds to the hot-side plate 610 through one or more metal contact pads 540 and/or the hot-side thermal interface material 611, and on its front-side surface still bonds to one or more TE legs through one or more metal contact pads 530, even though the blocks may be tilted somewhat from their original positions before the breaking occurs. In yet another example, after breaking into multiple blocks along the one or more line notches 515, the stress level around the TE legs and their bonding regions with the one or more metal contact pads 530 is substantially lowered.
According to one embodiment, without any line notch 515, the thermal stress imposed onto the base structure 510 may cause bending of the base structure and further pass the thermal stress to the TE legs that are bonded to the one or more metal contact pads 530, making those TE legs, especially their bonding regions, the weakest region to break or fail. For example, with the one or more line notches 515, the base structure 510 allows the use of a large initially non-breaking area for assembling a plurality of TE legs in multiple serial-chain configurations arranged in a two-dimensional device package. In another example, breaking along the one or more line notches 515 can provides benefit to the stress relief of the whole thermoelectric device but not affect the nominal electrical and/or thermal conductions through the plurality of TE legs. In yet another example, the thermoelectric device 600 can simplify packaging technique for TE legs (e.g., silicon nanowire-based TE legs) that have high thermoelectric performance by themselves, but are relative weak in mechanical strength to handle large thermal stress. In yet another example, the thermoelectric device 600 can make the assembled thermoelectric device highly adaptive to extreme conditions under which conventional devices often are unable to generate thermoelectric power efficiently.
As shown in
Second, a bottom contact sheet 710 is placed on the base plate 701. In one embodiment, the contact sheet 710 (e.g., the base structure 510) supports a plurality of contact regions 714 (e.g., the plurality of metal contact pads 530). For example, each contact region 714 (e.g., each metal contact pad 530) serves as a bottom contact for a group of four TE legs. In another embodiment, the contact sheet 710 (e.g., the base structure 510) is made substantially of a ceramic material in order to withstanding a high temperature. For example, the ceramic material has a thermal expansion coefficient similar to that of silicon-based thermoelectric legs. In another example, silicon nitride is used as the ceramic material.
As shown in
Third, over the plurality of contact regions 714 (e.g., the plurality of metal contact pads 530), a coupling material 724 is applied. In one embodiment, over each contact region 714, the coupling material 724 is placed over four local regions. For example, the four local regions are located near four corners of a square-shaped contact region 714 respectively. In another example, each local region is configured to couple with a TE leg. In yet another example, among the four TE legs to be bonded to the four local regions, one p-type leg and one n-type leg form a thermoelectric unicouple, and the other p-type leg and the other n-type leg form a redundant unicouple as shown in
Fourth, an alignment sheet 730 is placed on top of the contact sheet 710 (e.g., through the coupling material 724). For example, the alignment is performed using one or more feature holes 735 on the alignment sheet 730 to mate with the one or more built-in alignment markers 705 of the base plate 701 respectively. In another example, the alignment sheet 730 includes multiple patterned openings 734, four in each group aligned to the corresponding four local regions (e.g., the corresponding four local regions located near four corners of a square-shaped contact region 714 respectively). In yet another example, after the placement of the alignment sheet 730, the coupling material 724 on each local region of a contact region 714 fills the corresponding patterned opening 734, ready for bonding with an individual TE leg.
Fifth, a plurality of TE legs 744 are placed onto the plurality of contact regions 714 (e.g., the plurality of metal contact pads 530) through the coupling material 724 in order to form an array of TE legs. In one embodiment, the array of the TE legs 744 includes multiple rows and columns arranged in a predetermined order that has been determined based on desired thermoelectric functionalities and electrical serial and/or parallel connections for the array. In another embodiment, each TE leg 744 (e.g., a p-type TE leg or an n-type TE leg) is aligned to engage with the coupling material 724 through a corresponding patterned opening 734. For example, a group of four TE legs are bonded to the same contact region 714 (e.g., the same metal contact pad 530) with the coupling material 724, through four patterned openings 734 aligned to the corresponding four local regions of the same contact region 714 (e.g., the corresponding four local regions located near four corners of a square-shaped contact region 714 respectively). In another example, the alignment sheet 730 is configured to facilitate placement of individual TE leg 744, each with relative small dimensions in millimeter ranges, to desired positions in order to bond with the contact region 714.
Sixth, a plurality of shunt plates 754 (e.g., a plurality of conductive shunt materials that include the conductive shunt materials 541 and 542) are placed to selectively bond with top ends of the plurality of TE legs 744. In one embodiment, each shunt plate 754 (e.g., the conductive shunt material 541 or 542) is configured to bond with four TE legs 744, two of which (e.g., on the left) come from one group of four TE legs 744 that are bonded onto one contact region 714 and the other two of which (e.g., on the right) come from another group of four TE legs 744 that are bonded onto another contact region 714. For example, the bonding of the shunt plate 754 over the four TE legs 744 forms a redundant thermoelectric unicouple for each of the two contact regions 714. In another example, the shunt plate 754 serves as an electrical current connector between the unicouples. In another embodiment, to facilitate positioning of the plurality of shunt plates 754 over the plurality of TE legs 744 previously arranged into an array, the plurality of shunt plates 754 are prefabricated into a shunt sheet 750 (e.g., a metal lead frame) by patterning. For example, the shunt sheet 750 also includes one or more alignment features 755 to be aligned with the one or more alignment markers 705 respectively when the shunt sheet 750 is placed onto the plurality of TE legs 744. In another example, the prefabrication of the plurality of shunt plates 754 within the shunt sheet 750 is performed to provide desired electrical connections from one shunt plate 754 to another shunt plate 754 that include external electrical leads for the assembled thermoelectric module 700. In yet another embodiment, the plurality of shunt plates 754 (e.g., the plurality of conductive shunt materials that include the conductive shunt materials 541 and 542) are in thermal contact with a cold-side plate (e.g., the cold-side plate 620) through a cold-side thermal interface material (e.g., the cold-side thermal interface material 621). For example, the cold-side plate (e.g., the cold-side plate 620) is placed on the plurality of shunt plates 754 (e.g., the plurality of conductive shunt materials that include the conductive shunt materials 541 and 542) through the cold-side thermal interface material (e.g., the cold-side thermal interface material 621).
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In another embodiment, each TE leg 100 has its first end placed on a metal contact pad 530 and has its second end attached to a shunt plate 440 (e.g., a sheet conductor). For example, the plurality of shunt plates 440 (e.g., the plurality of shunt plates 754) complete an electrical path throughout all of the plurality of TE legs 100 (e.g., the plurality of TE legs 744) until reaching the end terminals (e.g., the electrical leads 810 and 820). In another example, along any row direction, the electrical path is a daisy-chain connection by going from a first shunt plate 440 down to a first TE leg 100, through a metal contact pad 530 that supports the first TE leg 100, to a second TE leg that of a different type from the first TE leg 100, and then up to a second shunt plate 440 that is next to the first shunt plate 440 but have no direct mechanical connection after the mechanical connections that have existed initially in the metal lead frame are trimmed to avoid undesirable shorting from one shunt plate 440 to another shunt plate 440.
As discussed above and further emphasized here,
In yet another example, the plurality of TE legs 744 are bonded with the plurality of contact regions 714 (e.g., the plurality of metal contact pads 530) through one or more diffusion barrier materials, one or more thermionic barrier materials, and/or one or more bonding materials (e.g., one or more soldering bonding materials, one or more brazing bonding materials). In yet another example, the plurality of TE legs 744 are bonded with the plurality of shunt plates 754 (e.g., a plurality of conductive shunt materials that include the conductive shunt materials 541 and 542) through one or more diffusion barrier materials, one or more thermionic barrier materials, and/or one or more bonding materials (e.g., one or more soldering bonding materials, one or more brazing bonding materials).
In yet another example, the metal lead frame (e.g., the shunt sheet 750) is replaced by a tape-backed lead frame. In yet another example, the metal lead frame (e.g., the shunt sheet 750) is replaced by a polyimide lead frame, as shown in
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In one embodiment, after the tape-backed lead frame (e.g., the shunt sheet 750) is placed on the legs, a graphite fixture is placed on top. For example, the graphite fixture is a non-metallic structure with two predetermined through holes for placing and aligning the terminal nuts to the tape-backed lead frame. In another example, the two terminal nuts are placed in the through holes where the terminal nuts become in contact with the tape-backed lead frame to be soldered. In another embodiment, a precise weight object is placed on top of the graphite assembly jig. For example, the TE legs (e.g., the TE legs 744) in multiple rows and columns are temporarily fixed at their locations by the precise weight object. In another example, the weight object is properly aligned by placing its one or more alignment holes onto one or more alignment pins (e.g., the one or more alignment markers 705) respectively on the assembly jig. In yet another embodiment, with the weigh object, the existing structure for the multi-leg package (MLP) 700 is loaded into a group loader and are subjected to the thermal treatment together in a forming gases. For example, the two terminal nuts and the TE legs are soldered simultaneously. In yet another embodiment, one or more terminal metal nuts are attached using one or more graphite fixtures to hold the one or more nuts in place. For example, one or more preformed soldering materials are placed under the one or more nuts with one or more flux materials, and reflowed together with the tape-backed lead frame (e.g., the shunt sheet 750) being soldered to the TE legs (e.g., the TE legs 744).
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In another embodiment, the base substrate 16510 is made of a material that is an electrical insulator but a good thermal conductor. For example, the base substrate 16510 is made of a ceramic material. In yet another embodiment, the shunt plates 440 and the shunt plates 16540 are made of a material that is both thermally and electrically conductive. For example, the shunt plates 440 and the shunt plates 16540 are made of copper. In another example, the shunt plates 440 are arranged in multiple rows and columns and separated by a spacing from each other. In yet another example, the shunt plates 16540 are arranged in multiple rows and columns and separated by a spacing from each other.
In yet another embodiment, each TE leg 100 has its first end placed on a metal contact pad 530 and has its second end attached to a shunt plate 440 (e.g., a sheet conductor). For example, the plurality of shunt plates 440 (e.g., the plurality of shunt plates 754) complete an electrical path throughout all of the plurality of TE legs 100 (e.g., the plurality of TE legs 744) until reaching the end terminals (e.g., the electrical leads 810 and 820). In another example, along any row direction, the electrical path is a daisy-chain connection by going from a first shunt plate 440 down to a first TE leg 100, through a metal contact pad 530 that supports the first TE leg 100, to a second TE leg that of a different type from the first TE leg 100, and then up to a second shunt plate 440 that is next to the first shunt plate 440 but have no direct electrical connection to avoid undesirable shorting from the first shunt plate 440 to the second shunt plate 440
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In another embodiment, each TE leg 100 has its first end placed on a metal contact pad 530 and has its second end attached to a shunt plate 440 (e.g., a sheet conductor). For example, the plurality of shunt plates 440 (e.g., the plurality of shunt plates 754) complete an electrical path throughout all of the plurality of TE legs 100 (e.g., the plurality of TE legs 744) until reaching the end terminals (e.g., the electrical leads 810 and 820). In another example, along any row direction, the electrical path is a daisy-chain connection by going from a first shunt plate 440 down to a first TE leg 100, through a metal contact pad 530 that supports the first TE leg 100, to a second TE leg that of a different type from the first TE leg 100, and then up to a second shunt plate 440 that is next to the first shunt plate 440 but have no direct mechanical connection after the mechanical connections that have existed initially in the metal lead frame are trimmed to avoid undesirable shorting from one shunt plate 440 to another shunt plate 440.
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In yet another embodiment, each TE leg 100 has its first end placed on a metal contact pad 530 and has its second end attached to a shunt plate 440 (e.g., a sheet conductor). For example, the plurality of shunt plates 440 (e.g., the plurality of shunt plates 754) complete an electrical path throughout all of the plurality of TE legs 100 (e.g., the plurality of TE legs 744) until reaching the end terminals (e.g., the electrical leads 810 and 820). In another example, along any row direction, the electrical path is a daisy-chain connection by going from a first shunt plate 440 down to a first TE leg 100, through a metal contact pad 530 that supports the first TE leg 100, to a second TE leg that of a different type from the first TE leg 100, and then up to a second shunt plate 440 that is next to the first shunt plate 440 but have no direct electrical connection to avoid undesirable shorting from the first shunt plate 440 to the second shunt plate 440. In yet another embodiment, the multi-leg package (MLP) 1800 can be applied to a thermal junction with the hot-side temperature being higher than 250° C. For example, a polyimide lead frame that includes the plurality of shunt plates 440 is configured to tolerate a temperature of the base substrate 510 on the hot side even if the temperature of the base structure 510 is higher than 250° C.
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In yet another embodiment, each TE leg 100 has its first end placed on a metal contact pad 530 and has its second end attached to a shunt plate 440 (e.g., a sheet conductor). For example, the plurality of shunt plates 440 (e.g., the plurality of shunt plates 754) complete an electrical path throughout all of the plurality of TE legs 100 (e.g., the plurality of TE legs 744) until reaching the end terminals (e.g., the electrical leads 810 and 820). In another example, along any row direction, the electrical path is a daisy-chain connection by going from a first shunt plate 440 down to a first TE leg 100, through a metal contact pad 530 that supports the first TE leg 100, to a second TE leg that of a different type from the first TE leg 100, and then up to a second shunt plate 440 that is next to the first shunt plate 440 but have no direct electrical connection to avoid undesirable shorting from the first shunt plate 440 to the second shunt plate 440. In yet another embodiment, the multi-leg package (MLP) 1900 can be applied to a thermal junction with the hot-side temperature being higher than 250° C. For example, a polyimide lead frame that includes the plurality of shunt plates 440 is configured to tolerate a temperature of the metal contact pads 530 on the hot side even if the temperature of the metal contact pads 530 is higher than 250° C.
According to another embodiment, a multi-leg package thermoelectric module assembly includes a substrate including a base plate and an array of pads arranged in rows and columns and attached on both sides of the base plate in a mirror symmetry. The base plate is a thermal conductor but an electrical insulator and each pad is an electrical/thermal dual conductor spaced from each other. Additionally, the module assembly includes a plurality of thermoelectric legs being separately placed in rows and columns on the array of pads. Each pad is configured to support at least two thermoelectric legs. Furthermore, the module assembly includes a lead frame comprising a plurality of sheet conductors. Each sheet conductor is configured according to a predetermined pattern to align and form electrical coupling with four thermoelectric legs from two successive rows and two successive columns, and each of the four thermoelectric legs has its first end including bonding metals coupled with one of four separate pads via a braze alloy and its second end attached with the sheet conductor. Each row of the plurality of thermoelectric legs is arranged alternatively in N and P types semiconductor doping characteristics and two legs in a same row/column among the four thermoelectric legs attached under each sheet conductor are same/different type.
For example, the base plate is a ceramic material selected from Si3N4 and each pad is made of copper. In another example, the substrate includes multiple scribed lines cut partially into the base plate at locations between two neighbor columns/rows of the array of pads for every other few rows/columns of pads. In yet another example, the braze alloy material is printed on the array of pads for bonding with the first end of each of plurality of thermoelectric legs. In yet another example, the braze alloy material is configured to form a peritectoid compound with the pad and bonding metals on the thermoelectric legs, and the peritectoid compound is susceptible to operation temperature at least 650° C. In yet another example, the multi-leg package thermoelectric module assembly further includes a soldering alloy material being printed on the second end of each of the plurality of thermoelectric legs for bonding with the lead frame.
In yet another example, the thermoelectric leg includes a bulk-sized thermoelectric material made by one selected from Bi2Te3, Mg2Si, MnSi2, PbTe, silicon-based nanostructured materials, sintered nano-composite materials, and half heusler materials. In yet another example, the thermoelectric leg includes a thermoelectric material capable for application with a hot-side temperature over 600° C. In yet another example, the lead frame is a copper-based sheet material comprising thinned sheet members around edges of each sheet conductor to couple one or more neighboring sheet conductor. In yet another example, the lead frame includes copper foil embedded in a high-temperature polyimide film. In yet another example, the lead frame includes a patterned copper foil attached to one side of a ceramic substrate and another copper foil overlying entire area of another side of the ceramic substrate. In yet another example, each N/P type thermoelectric leg of the plurality of thermoelectric legs connects to a neighboring P/N type thermoelectric leg electrically in series. In yet another example, each N/P type thermoelectric leg of the plurality of thermoelectric legs shares with another redundant N/P type thermoelectric leg electrically in parallel. In yet another example, the lead frame includes two global leads for external electrical connection.
According to yet another embodiment, a method for assembling a multi-leg package thermoelectric module includes providing an assembly base structure. The assembly base structure includes at least two alignment pins located on two corner regions. Additionally, the method includes placing an MLP substrate in the assembly base structure. The MLP substrate includes an array of conductive pads arranged in rows and columns separated each other by a spacing. Moreover, the method includes applying a braze alloy layer on each conductive pad at least partially, disposing a plurality of thermoelectric legs to separate positions in rows and columns to align with the array of conductive pads using an alignment screen so that each pad is at least attached with two thermoelectric legs, operably fixing the plurality of thermoelectric legs in their positions via the braze alloy layer, applying a soldering alloy layer over each of the plurality of thermoelectric legs, and placing a lead frame over the plurality of thermoelectric legs. The lead frame includes a plurality of sheet conductors at least partially connected to each other. Also, the method includes operably fixing the lead frame in a predetermined position so that each sheet conductor aligns and forms an electrical coupling via the soldering alloy layer with four thermoelectric legs from two successive rows and two successive columns while being respectively attached with four separate conductive pads and optionally trimming the lead frame so that each sheet conductor is free of other mechanical contact with its neighboring sheet conductor but having a properly electrical connection only through one or two thermoelectric legs and corresponding conductive pads that support the one or two thermoelectric legs.
For example, the assembly base structure includes a recessed top region configured to load the MLP substrate so that the conductive pads have a level slightly above a surface level of the assembly base structure. In another example, each of the two alignment pins has a vertical height above the base structure and a round shape in cross-section. In yet another example, the MLP substrate comprises a ceramic material that is an electrical insulator but a good thermal conductor. In yet another example, the MLP substrate further includes another array of conductive pads formed at the other side of the ceramic material in positions mirroring the array of conductive pads.
In yet another example, the process of applying a braze alloy layer includes printing over a pre-set screen aligned with the array of conductive pads. In yet another example, the process of disposing a plurality of thermoelectric legs comprises applying a die bonder to place a plurality of the thermoelectric legs at once. In yet another example, the process of disposing a plurality of thermoelectric legs includes placing a first row of thermoelectric legs characterized by an alternative N-type and P-type order in association to a series of sheet conductors. In yet another example, the process of disposing a plurality of thermoelectric legs includes placing a redundant row of thermoelectric legs having the same an alternative N-type and P-type order in association to the first row. In yet another example, the process of disposing a plurality of thermoelectric legs includes placing at least one column of thermoelectric legs attached to a half-sized sheet conductor for connecting thermoelectric legs in different row other than the redundant row. In yet another example, the process of disposing a plurality of thermoelectric legs includes placing a redundant row of legs for each row.
In yet another example, the process of operably fixing the plurality of thermoelectric legs includes temporarily fixing each leg on a conductive pad using a pre-disposed bonding material, placing a precise weight member on the temporarily fixed leg, drying the bonding material, and performing high-vacuum braze process to allow the bonding material of each leg to react with the braze alloy layer to fix each leg on the conductive pad. The precise weight member includes a first through-hole being round in shape matching the alignment pin and a second hole being square in shape having slightly bigger size than the alignment pin. In yet another example, the process of placing a lead frame is assisted via an alignment using two holes within the lead frame matching the two alignment pins on the base structure.
According to yet another embodiment, a method for assembling a multi-leg package thermoelectric module includes providing an assembly base structure. The assembly base structure includes at least two alignment pins located on two corner regions.
Additionally, the method includes placing an MLP substrate in the assembly base structure. The MLP substrate includes an array of conductive pads arranged in rows and columns separated each other by a spacing. Moreover, the method includes applying a first braze alloy layer on each conductive pad at least partially, placing an alignment screen including layout positions for a plurality of thermoelectric legs, disposing a plurality of thermoelectric legs to the layout positions set by the alignment screen so that each pad is at least attached with two thermoelectric legs, removing the alignment screen after a drying process, providing a lead frame including a plurality of sheet conductors at least partially connected to each other, applying a second braze alloy layer over each of the plurality of sheet conductors, placing the lead frame with alignment onto the disposed plurality of thermoelectric legs, performing a brazing process to have the plurality of thermoelectric legs respectively bond to corresponding conductive pads through the first braze alloy layer and to corresponding sheet conductors through the second braze alloy layer.
According to yet another embodiment, a method for assembling a multi-leg package thermoelectric module includes providing an assembly base structure. The assembly base structure includes at least two alignment pins located on two corner regions. Additionally, the method includes placing an MLP substrate in the assembly base structure. The MLP substrate includes an array of conductive pads arranged in rows and columns separated each other by a spacing. Moreover, the method includes applying a braze alloy layer on each conductive pad at least partially, placing an alignment screen including layout positions for a plurality of thermoelectric legs, disposing a plurality of thermoelectric legs to the layout positions set by the alignment screen so that each pad is at least attached with two thermoelectric legs, and placing a precise weight member over the disposed plurality of thermoelectric legs. The precise weight member is aligned through the two alignment pins with the assembly base structure. Also, the method includes performing a brazing process to have the plurality of thermoelectric legs respectively bond to corresponding conductive pads through the braze alloy layer, removing the precise weight member and cleaning, providing a lead frame including a plurality of sheet conductors at least partially connected to each other, applying an eutectic alloy layer over each of the plurality of sheet conductors, disposing a lead frame over the plurality of thermoelectric legs with alignment through the two alignment pins, placing a precise ceramic weight member over the disposed lead frame, and applying a soldering process with a thermal profile within a forming gas to have each sheet conductor aligned to bond via the soldering alloy layer with four thermoelectric legs from two successive rows and two successive columns.
According to yet another embodiment, a method for assembling a multi-leg package thermoelectric module includes providing an assembly base structure. The assembly base structure includes at least two alignment pins located on two corner regions. Additionally, the method includes placing an MLP polyimide film in the assembly base structure. The MLP polyimide film includes an array of conductive pads arranged in rows and columns separated each other by a spacing. Moreover, the method includes applying a first eutectic solder layer on each conductive pad at least partially, placing an alignment screen including layout positions for a plurality of thermoelectric legs, disposing a plurality of thermoelectric legs to the layout positions set by the alignment screen so that each pad is at least attached with two thermoelectric legs, and placing a precise weight member over the disposed plurality of thermoelectric legs. The precise weight member is aligned through the two alignment pins with the assembly base structure. Also, the method includes performing a drying process, applying a first soldering process with a thermal profile within a forming gas to have each thermoelectric leg aligned to bond via the first eutectic alloy layer with a corresponding conductive pad, providing a lead frame including a plurality of sheet conductors at least partially connected to each other, and printing a second eutectic solder layer over a plurality of sheet conductors configured to match the positions of the plurality of thermoelectric legs. Additionally, the method includes placing the lead frame with alignment to have the second eutectic alloy layer on each sheet conductors in contact with four thermoelectric legs, placing a precise ceramic weight member over the lead frame, and applying a second soldering process containing a forming gas with a thermal profile to have each sheet conductor aligned to bond with the four thermoelectric legs.
According to yet another embodiment, a thermoelectric device with a multi-leg package includes a first ceramic base structure including a first surface and a second surface, and a first plurality of pads including one or more first materials thermally and electrically conductive. The first plurality of pads are attached to the first surface. Additionally, the thermoelectric device includes a second plurality of pads including the one or more first materials. The second plurality of pads are attached to the second surface and arranged in a mirror image with the first plurality of pads. Moreover, the thermoelectric device includes a plurality of thermoelectric legs attached to the first plurality of pads respectively. Each pad of the first plurality of pads is attached to at least two first thermoelectric legs of the plurality of thermoelectric legs. Also, the thermoelectric device includes a first plurality of sheet conductors attached to the plurality of thermoelectric legs respectively and including one or more second materials thermally and electrically conductive. Each sheet conductor of the first plurality of sheet conductors is attached to at least two second thermoelectric legs of the plurality of thermoelectric legs. The first plurality of pads include a first pad and a second pad configured to allow a first electrical current to flow between the first pad and the second pad only through two or more third thermoelectric legs of the plurality of thermoelectric legs, and the first plurality of sheet conductors include a first sheet conductor and a second sheet conductor configured to allow a second electrical current to flow between the first sheet conductor and the second sheet conductor only through two or more fourth thermoelectric legs of the plurality of thermoelectric legs. For example, the thermoelectric device is implemented according to at least
In another example, the first plurality of sheet conductors are parts of a metal lead frame without any metal tab linking the first plurality of sheet conductors (e.g., implemented according to at least
According to yet another embodiment, a thermoelectric device with a multi-leg package includes a plurality of pads including one or more first materials thermally and electrically conductive. The plurality of pads are parts of a first metal lead frame without any metal tab linking the plurality of pads. Additionally, the thermoelectric device includes a plurality of thermoelectric legs attached to the plurality of pads respectively. Each pad of the plurality of pads is attached to at least two first thermoelectric legs of the plurality of thermoelectric legs. Moreover, thermoelectric device includes a first plurality of sheet conductors attached to the plurality of thermoelectric legs respectively and including one or more second materials thermally and electrically conductive. Each sheet conductor of the first plurality of sheet conductors is attached to at least two second thermoelectric legs of the plurality of thermoelectric legs. The plurality of pads include a first pad and a second pad configured to allow a first electrical current to flow between the first pad and the second pad only through two or more third thermoelectric legs of the plurality of thermoelectric legs, and the first plurality of sheet conductors include a first sheet conductor and a second sheet conductor configured to allow a second electrical current to flow between the first sheet conductor and the second sheet conductor only through two or more fourth thermoelectric legs of the plurality of thermoelectric legs. For example, the thermoelectric device is implemented according to at least
In another example, the first plurality of sheet conductors are parts of a second metal lead frame without any metal tab linking the first plurality of sheet conductors (e.g., implemented according to at least
According to yet another embodiment, a method for making a thermoelectric device with a multi-leg package includes providing a first ceramic base structure including a first surface and a second surface. The first surface is attached to a first plurality of pads, the second surface is attached to a second plurality of pads arranged in a mirror image with the first plurality of pads, and both the first plurality of pads and the second plurality of pads include one or more first materials thermally and electrically conductive. Additionally, the method includes attaching a plurality of thermoelectric legs to the first plurality of pads respectively. Each pad of the first plurality of pads is attached to at least two first thermoelectric legs of the plurality of thermoelectric legs. Additionally, the method includes attaching a first plurality of sheet conductors to the plurality of thermoelectric legs respectively. The first plurality of sheet conductors include one or more second materials thermally and electrically conductive, and each sheet conductor of the first plurality of sheet conductors is attached to at least two second thermoelectric legs of the plurality of thermoelectric legs. The first plurality of pads include a first pad and a second pad configured to allow a first electrical current to flow between the first pad and the second pad only through two or more third thermoelectric legs of the plurality of thermoelectric legs, and the first plurality of sheet conductors include a first sheet conductor and a second sheet conductor configured to allow a second electrical current to flow between the first sheet conductor and the second sheet conductor only through two or more fourth thermoelectric legs of the plurality of thermoelectric legs.
For example, the method further includes providing the first plurality of sheet conductors as parts of a metal lead frame without any metal tab linking the first plurality of sheet conductors. In another example, the method further includes providing the first plurality of sheet conductors as parts of a polyimide lead frame including a plurality of polyimide tabs linking the first plurality of sheet conductors. In yet another example, the method further includes providing a second ceramic base structure including a third surface and a fourth surface. The third surface is attached to the first plurality of sheet conductors, the fourth surface is attached to a second plurality of sheet conductors arranged in a mirror image with the first plurality of sheet conductors, and both the first plurality of sheet conductors and the second plurality of sheet conductors include one or more second materials thermally and electrically conductive.
According to yet another embodiment, a method for making a thermoelectric device with a multi-leg package includes providing a plurality of pads including one or more first materials thermally and electrically conductive. The plurality of pads are parts of a first metal lead frame without any metal tab linking the plurality of pads. Additionally, the method includes attaching a plurality of thermoelectric legs to the plurality of pads respectively. Each pad of the plurality of pads is attached to at least two first thermoelectric legs of the plurality of thermoelectric legs. Moreover, the method includes attaching a first plurality of sheet conductors to the plurality of thermoelectric legs respectively and including one or more second materials thermally and electrically conductive. Each sheet conductor of the first plurality of sheet conductors is attached to at least two second thermoelectric legs of the plurality of thermoelectric legs. The plurality of pads include a first pad and a second pad configured to allow a first electrical current to flow between the first pad and the second pad only through two or more third thermoelectric legs of the plurality of thermoelectric legs, and the first plurality of sheet conductors include a first sheet conductor and a second sheet conductor configured to allow a second electrical current to flow between the first sheet conductor and the second sheet conductor only through two or more fourth thermoelectric legs of the plurality of thermoelectric legs.
For example, the method further includes providing the first plurality of sheet conductors as parts of a second metal lead frame without any metal tab linking the first plurality of sheet conductors. In another example, the method further includes providing the first plurality of sheet conductors as parts of a polyimide lead frame including a plurality of polyimide tabs linking the first plurality of sheet conductors.
According to certain embodiments, a thermoelectric device needs to withstand large temperature gradients across its thickness in order to operate at high efficiencies and generate high power densities. For example, the thermoelectric device also needs to remain flat because the out-of-plane deflection can result in loss of thermal contact with the heat source and/or the heat sink and thus result in a loss of power production. In another example, a mismatch in thermal expansion created by the large temperature gradient can also cause high stress and potentially failure of the device parts.
According to some embodiments, finite element stress analysis (FEA) has been conducted to quantify the reduction in thermally-induced stresses and to also quantify the reduction in thermally-induced deflections for certain device structures. In each of the six examples presented below, the device modeled is 40-mm-long by 40-mm-wide by 3-mm-thick, operating in a 500° C.-to-150° C. thermal gradient, and the simulations have used particular properties of selected thermoelectric and substrate materials. Also, for each of these six examples presented below, the simulations have been conducted using the COSMOS software, with results shown in
A conventional thermoelectric device includes two ceramic plates with a low coefficient of thermal expansion (CTE) (e.g., CTE being lower than 10×10−6/° C., such as CTE equal to 4×10−6/° C. at the room temperature). Additionally, the conventional thermoelectric device further includes thermoelectric legs made of a thermoelectric material with a high coefficient of thermal expansion (e.g., CTE being higher than 10×10−6/° C., such as CTE equal to 11×10−6/° C. at the room temperature for n-type legs and CTE equal to 14×10−6/° C. at the room temperature for p-type legs), wherein the thermoelectric legs are sandwiched between the two ceramic plates and bonded to the two ceramic plates via thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature) for electrical connection of the legs.
For each of Examples 1-6, Table 1 presents peak Von Mises stresses in each of certain components and in each joint between some of these components according to certain embodiments. As shown in Table 1, for Example 1, the peak stresses in all components are very high, particularly in the thermoelectric legs, which often are the weakest component, thus likely to cause mechanical failure of the thermoelectric device.
According to one embodiment of the present invention, one side of a thermoelectric device is made flexible in order to reduce stresses and deflections, so a thermoelectric device includes only one, not two, ceramic plate with a low coefficient of thermal expansion (CTE) (e.g., CTE being lower than 10×10−6/° C., such as CTE equal to 4×10−6/° C. at the room temperature). Additionally, the thermoelectric device further includes thermoelectric legs made of a thermoelectric material with a high coefficient of thermal expansion (e.g., CTE being higher than 10×10−6/° C., such as CTE equal to 11×10−6/° C. at the room temperature for n-type legs and CTE equal to 14×10−6/° C. at the room temperature for p-type legs), wherein the thermoelectric legs are, on one side, in contact with some thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature), and on the other side, bonded to the ceramic plate via other thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature). For example, on the side without the ceramic plate, movement between the thin metal shunts is not constrained.
According to another embodiment of the present invention, one side of a thermoelectric device is made flexible in order to reduce stresses and deflections, so a thermoelectric device includes one ceramic plate with a low coefficient of thermal expansion (CTE) (e.g., CTE being lower than 10×10−6/° C., such as CTE equal to 4×10−6/° C. at the room temperature) and one flexible plate (e.g., a polyimide plate with CTE equal to 20×10−6/° C.), instead of two ceramic plates. Additionally, thermoelectric device further includes thermoelectric legs made of a thermoelectric material with a high coefficient of thermal expansion (e.g., CTE being higher than 10×10−6/° C., such as CTE equal to 11×10−6/° C. at the room temperature for n-type legs and CTE equal to 14×10−6/° C. at the room temperature for p-type legs), wherein the thermoelectric legs are, on one side, bonded to the ceramic plate via some thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature), and on the other side, bonded to the flexible plate via other thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature). In another example, the polyimide plate is made of Kapton.
According to one embodiment of the present invention, one side of a thermoelectric device, even though remaining rigid, is made of a material with a high coefficient of thermal expansion (CTE), in order to reduce stresses and deflections, so a thermoelectric device includes one ceramic plate with a low coefficient of thermal expansion (CTE) (e.g., CTE being lower than 10×10−6/° C., such as CTE equal to 4×10−6/° C. at the room temperature), and one ceramic plate with a high coefficient of thermal expansion (CTE) (e.g., CTE being higher than 10×10−6/° C., such as CTE equal to 11×10−6/° C. at the room temperature). Additionally, the thermoelectric device further includes thermoelectric legs made of a thermoelectric material with a high coefficient of thermal expansion (e.g., CTE being higher than 10×10−6/° C., such as CTE equal to 11×10−6/° C. at the room temperature for n-type legs and CTE equal to 14×10−6/° C. at the room temperature for p-type legs), wherein the thermoelectric legs are, on one side, bonded to the low-CTE ceramic plate via some thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature), and on the other side, bonded to the high-CTE ceramic plate via other thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature). For example, the low-CTE ceramic plate is placed on the hot side and the high-CTE ceramic plate is placed on the cold side, so that the difference in thermal expansion between the hot side and the cold side due to the thermal gradient is reduced.
According to one embodiment of the present invention, both sides of a thermoelectric device are made flexible in order to reduce stresses and deflections, so a thermoelectric device does not include any ceramic plate, but does include thermoelectric legs made of a thermoelectric material with a high coefficient of thermal expansion (e.g., CTE being higher than 10×10−6/° C., such as CTE equal to 11×10−6/° C. at the room temperature for n-type legs and CTE equal to 14×10−6/° C. at the room temperature for p-type legs), wherein the thermoelectric legs are in contact with some thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature) on one side, and in contact with other thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature) on the other side. For example, on either side, movement between the thin metal shunts is not constrained
According to another embodiments of the present invention, both sides of a thermoelectric device are made flexible in order to reduce stresses and deflections, so a thermoelectric device does not include any rigid ceramic plate, but does include one flexible plate (e.g., a polyimide plate with CTE equal to 20×10−6/° C.). Additionally, the thermoelectric device further includes thermoelectric legs made of a thermoelectric material with a high coefficient of thermal expansion (e.g., CTE being higher than 10×10−6/° C., such as CTE equal to 11×10−6/° C. at the room temperature for n-type legs and CTE equal to 14×10−6/° C. at the room temperature for p-type legs), wherein the thermoelectric legs are, on one side, in contact with some thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature), and on the other side, bonded to the flexible plate via other thin metal shunts (e.g., CTE of the thin metal shunts being equal to 16×10−6/° C. at the room temperature). In another example, the polyimide plate is made of Kapton.
Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. For example, various embodiments and/or examples of the present invention can be combined. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.
This application claims priority to U.S. Provisional Application No. 61/713,767, filed Oct. 15, 2012, and U.S. Provisional Application No. 61/802,097, filed Mar. 15, 2013, commonly assigned and incorporated by reference herein for all purposes. Additionally, this application is related to U.S. patent application Ser. Nos. 13/299,179, 13/308,945, 13/331,768, and 13/364,176, which are incorporated by reference herein for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61713767 | Oct 2012 | US | |
| 61802097 | Mar 2013 | US |
