CA1199425A - Thermoelectric device and method of making same - Google Patents
Thermoelectric device and method of making sameInfo
- Publication number
- CA1199425A CA1199425A CA000426918A CA426918A CA1199425A CA 1199425 A CA1199425 A CA 1199425A CA 000426918 A CA000426918 A CA 000426918A CA 426918 A CA426918 A CA 426918A CA 1199425 A CA1199425 A CA 1199425A
- Authority
- CA
- Canada
- Prior art keywords
- thermoelectric
- elements
- conducting
- copper
- thermoelectric elements
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/10—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects
- H10N10/17—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects characterised by the structure or configuration of the cell or thermocouple forming the device
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/80—Constructional details
- H10N10/81—Structural details of the junction
- H10N10/817—Structural details of the junction the junction being non-separable, e.g. being cemented, sintered or soldered
Abstract
ABSTRACT
A thermoelectric device includes first and second sets of spaced apart copper plate seg-ments. Thermoelectric elements which generate electricity are disposed between the sets of cop-per plate segments. The elements are electrically and thermally fastened thereto by a solder paste screen printed on the inner surfaces of the sets of copper plate segments. A ceramic potting com-pound which absorbs thermal expansion of the de-vice fills the voids between the thermoelectric elements and the copper plate segments and a thick film ceramic insulator coats the outer surfaces of the sets of copper plate segments.
Also disclosed is a method for manufacturing the device of the present invention.
A thermoelectric device includes first and second sets of spaced apart copper plate seg-ments. Thermoelectric elements which generate electricity are disposed between the sets of cop-per plate segments. The elements are electrically and thermally fastened thereto by a solder paste screen printed on the inner surfaces of the sets of copper plate segments. A ceramic potting com-pound which absorbs thermal expansion of the de-vice fills the voids between the thermoelectric elements and the copper plate segments and a thick film ceramic insulator coats the outer surfaces of the sets of copper plate segments.
Also disclosed is a method for manufacturing the device of the present invention.
Description
The present invention relates to a new and improved thermoelectric device for the generation of electricity and a method for manufacturing the same.
It has been recognized that the world supply of fossil fuels for the production of energy is being exhausted at ever increasing rates. This realization has resulted in an energy crisis which impacts not only the world's economy, but threat-ens the peace and stability of the world. The solution to the energy crisis lies in the develop-ment of new fuels and more efficient techniques to utilize them. To that end, the present invention deals with energy conservation, power generation, pollution, and the generation of new business op-portunities by the development of new thermoelec-tric devices which provide more electricity.
An important part of the solution with re-spect to the development of permanent, economical ~0 energy conversion lies in the field of thermoelec-trics wherein electrical power is generated by heat. It has been estimated that more than two-thirds of all our energy, for example, from auto-mobile exhausts or power plants, is wasted and given off to the environment. Up until now, there has been no serious climatic effect from this thermal pollution. ~lowever, it has been predicted that as the world's energy consumption increases, the effects of thermal pollution will ultimately lead to a partial melting of the polar ice caps with an attendant increase in sea level.
The efficiency of a thermoelectric device can be expressed in terms of a figure of merit (Z) for the material forming the device, wherein Z is de-fined as:
Z = s2 ~here: Z is expressed in units x 103 S is the Seebeck coefficient in V/C
K is the thermal conductivity in mW/cm-C
a is the electrical conductivity in (Q -cm)-l From the above, one can see that in order for a material to be suitable for thermoelectric power conversion, it must have a large value for the thermoelectric power Seebeck coefficient (S~, a high electrical conductivity t ~), and a low ther-mal conductivity (K). Further~ there are two com-ponents to the thermal conductivity (K): Kl, the lattice component; and Ke~ the electrical compo-nent. In non-metals, Kl dominates and it is this component which mainly determines the value o~ K.
Stated in another way, in order for a materi-al to be efficient for thermoelectric power con-version, it is important to allow carriers to dif-fuse easily from the hot junction to the cold junction while maintaining the temperature gradi-ent. Hence, high electrical conductivity is re-quired along with low thermal conductivity.
Thermoelectric power conversion has not found wide usage in the past. The major reason for this is that prior art thermoelectric materials which are at all suitable for commercial applications have been crystalline in structure. Crystalline solids cannot attain large values of electrical conductivity while maintaining low thermal conduc-tivity. Most importantlyl because of crystallinesymmetry, thermal conductivity cannot be con-trolled by modification~
In the case o the conventional polycrystal-line approach, the problems of single crystalline materials still dominate. However, new problems are al50 encountered by virtue of the polycrystal-line grain boundaries which cause these materials to have relatively low electrical conductivities.
In addition, the fabrication of these materials is also difficult to control as a result of their more complex crystalline structure. The chemical modification or dopin~ of these materials, because of the above problems are especially difficult.
Among the best known currently existing poly-crystalline thermoelectric materials are (Bi,Sb)2Te3, PbTe, and Si-Ge. The (Bi,Sb)2Te3 ma-terials are best suited for applications in the -10C + 150C range with its best Z appearing at around 30C. (Bi,~b)2Te3 represents a continuous solid solution system in which the relative amount of Bi and Sb are from 0 to 100%. The Si-Ge mate-rial is best suited for high temperature applica-tions in the 600C to 1000C range with a satis-factory Z appearing at above 700C. The PbTe polycrystalline material e~hibits its best figure of merit in the 300C to 500C range. None of these materials is well suited for applications in the 100C to 300C range. This is indeed unfortu-nate, because it is in this temperature range where a wide variety of waste heat applications are found. Among such applications are geothermal waste heat and waste heat from internal combustion engines in, for example, trucks, buses, and auto-mobiles. Applications of this kind are important because the heat is truly waste heat. Heat in the higher temperature ranges must be intentionally gerlerated with other Euels and therefore is not truly waste heat.
New and improved thermoelectric alloy materials kave been discovered for use in the aforesaid temperature ranges. These materials are disclosed and clalmed in copending Canadian application Serial No. 419,580, filed January 17, 1983 in the names of Tumkur S. Jayadev and On Van Nguyen for NEW MULTIPHASE THERMOELECTRIC ALLOYS AND
METHOD OF MAKING SAME, which application is assigned to the assignee of the present invention.
The thermoelec-tric materials there disclosed can be utilized in the device herein. These materials are not single phase crystalline materials, but instead, are disordered materials. Further, these materials are mul~iphase materials kaving both amorphous and multiple crystalline phases. Materials of this type are good thermal insulators. Tkey include grain boundaries of various transitional phases varying in composition from the composition of matrix crystallites to the composition of the various phases in the grain boundary regions. The grain boun~aries are kighly disordered with the transitional phases including cr~J~
1~'3~
phases of high thermal resistivity to provide high resistance to thermal conduction. Contrary to conventional materials, the material is designed such that the grain boundaries define regions in-cluding conductive phases therein providing numer-ous electrical conduction paths through the bulk material for increasing electrical conductivity without s~bstantially effecting the thermal con-ductivity. In essence, these materials have all of the advantages of polycrystalline materials in desirably low thermal conductivities and crystal-line bul~ Seebec~ properties. ~owever, unlike the conventional polycrystalline materials, these dis-ordered multiphase materials also have desirably high electrical conductivities. ~ence, as dis-closed in the aforesaid referenced application, the S2a product for the figure of merit of these materials can be independently maximized with de-sirably low thermal conductivities for thermoelec-tric power generation~
Amorphous materials, representing the highest degree of disorder, have been made for thermoelec-tric applications. The materials and methods for making the same are fully disclosed and claimed, 25 for example, in U.S. Patents 4,177,~73, 4,177,474, and 4,178,415 which issued in the name of Stanford R. Ovshinsky. The materials disclosed in these patents are formed in a solid amorphous host matrix having structural configurations which have local rather than longrange order and electronic configurations which have an energy gap and an electrical activation energy. Added to the amor-phous host matrix is a modifier material having orbitals which interact with the amorphous host matrix as well as themselves to form electronic states in the energy gap. ~his interaction sub-stantially modifies the electronic configurations of the amorphous host matrix to substantially re-duce the activation energy and hence, increase substantially the electrical conductivity of the material. The resulting electrical conductivity can be controlled by the amount of modifier mate-rial added to the host matrix. I'he amorphous host matrix is normally of intrinsic-like conduction and the modified material changes the same to ex-trinsic-like conduction.
As also disclosed therein, the amorphous host matrix can have lone-pairs having orbitals wherein the orbitals of the modifier material interact therewith to form the new electronic states in the energy gap. In another form, the host matrix can have primarily tetrahedral bonding wherein the modifier material is added primarily in a non-substitutional manner with its orbitals interact-ing with the host matrix. soth d and f band mate-rials as well as boron and carbon, which add multiorbital possibilities can be used as modi-fiers to form the new electronic states in the energy gap.
As a result of the foregoing, these amorphous thermoelectric materials have substantially in-creased electrical conductivity. However, because they remain amorphous after modification, they re-tain their low thermal conductivities making them well suited for thermoelectric applications, espe-cially in high temperature ranges above 400C.
These materials are modified on an atomic or microscopic level with the atomic configurations thereof substantially changed to provide the here-tofore mentioned independently increased electri-cal conductivities. In contrast, the materials disclosed in the aforesaid referenced application are not atomically modified. Rather, they are fabricated in a manner whieh introduces disorder into the material on a maeroscopic level. ~his disorder allows various phases including conduc-tive phases to be introduced into the material much in the same manner as modification atomically in pure amorpho~s phase materials to provide con-trolled high electrical conductivity while thedisorder in the other phases provides low thermal conductivity. These materials therefore are in-termediate in terms of their thermal conductivity between amorphous and regular polycrystalline ma-l~ terials.
A thermoelectric device generates electricityby the establishment of a temperature differential across the materials contained therein. The thermoelectric devices generally include elements of both p-type and n-type material. In the p-type material the temperature differential drives posi-tively charged carriers from the hot side to the cold side of the elements, while in the n-type material the temperature differential drives nega-
It has been recognized that the world supply of fossil fuels for the production of energy is being exhausted at ever increasing rates. This realization has resulted in an energy crisis which impacts not only the world's economy, but threat-ens the peace and stability of the world. The solution to the energy crisis lies in the develop-ment of new fuels and more efficient techniques to utilize them. To that end, the present invention deals with energy conservation, power generation, pollution, and the generation of new business op-portunities by the development of new thermoelec-tric devices which provide more electricity.
An important part of the solution with re-spect to the development of permanent, economical ~0 energy conversion lies in the field of thermoelec-trics wherein electrical power is generated by heat. It has been estimated that more than two-thirds of all our energy, for example, from auto-mobile exhausts or power plants, is wasted and given off to the environment. Up until now, there has been no serious climatic effect from this thermal pollution. ~lowever, it has been predicted that as the world's energy consumption increases, the effects of thermal pollution will ultimately lead to a partial melting of the polar ice caps with an attendant increase in sea level.
The efficiency of a thermoelectric device can be expressed in terms of a figure of merit (Z) for the material forming the device, wherein Z is de-fined as:
Z = s2 ~here: Z is expressed in units x 103 S is the Seebeck coefficient in V/C
K is the thermal conductivity in mW/cm-C
a is the electrical conductivity in (Q -cm)-l From the above, one can see that in order for a material to be suitable for thermoelectric power conversion, it must have a large value for the thermoelectric power Seebeck coefficient (S~, a high electrical conductivity t ~), and a low ther-mal conductivity (K). Further~ there are two com-ponents to the thermal conductivity (K): Kl, the lattice component; and Ke~ the electrical compo-nent. In non-metals, Kl dominates and it is this component which mainly determines the value o~ K.
Stated in another way, in order for a materi-al to be efficient for thermoelectric power con-version, it is important to allow carriers to dif-fuse easily from the hot junction to the cold junction while maintaining the temperature gradi-ent. Hence, high electrical conductivity is re-quired along with low thermal conductivity.
Thermoelectric power conversion has not found wide usage in the past. The major reason for this is that prior art thermoelectric materials which are at all suitable for commercial applications have been crystalline in structure. Crystalline solids cannot attain large values of electrical conductivity while maintaining low thermal conduc-tivity. Most importantlyl because of crystallinesymmetry, thermal conductivity cannot be con-trolled by modification~
In the case o the conventional polycrystal-line approach, the problems of single crystalline materials still dominate. However, new problems are al50 encountered by virtue of the polycrystal-line grain boundaries which cause these materials to have relatively low electrical conductivities.
In addition, the fabrication of these materials is also difficult to control as a result of their more complex crystalline structure. The chemical modification or dopin~ of these materials, because of the above problems are especially difficult.
Among the best known currently existing poly-crystalline thermoelectric materials are (Bi,Sb)2Te3, PbTe, and Si-Ge. The (Bi,Sb)2Te3 ma-terials are best suited for applications in the -10C + 150C range with its best Z appearing at around 30C. (Bi,~b)2Te3 represents a continuous solid solution system in which the relative amount of Bi and Sb are from 0 to 100%. The Si-Ge mate-rial is best suited for high temperature applica-tions in the 600C to 1000C range with a satis-factory Z appearing at above 700C. The PbTe polycrystalline material e~hibits its best figure of merit in the 300C to 500C range. None of these materials is well suited for applications in the 100C to 300C range. This is indeed unfortu-nate, because it is in this temperature range where a wide variety of waste heat applications are found. Among such applications are geothermal waste heat and waste heat from internal combustion engines in, for example, trucks, buses, and auto-mobiles. Applications of this kind are important because the heat is truly waste heat. Heat in the higher temperature ranges must be intentionally gerlerated with other Euels and therefore is not truly waste heat.
New and improved thermoelectric alloy materials kave been discovered for use in the aforesaid temperature ranges. These materials are disclosed and clalmed in copending Canadian application Serial No. 419,580, filed January 17, 1983 in the names of Tumkur S. Jayadev and On Van Nguyen for NEW MULTIPHASE THERMOELECTRIC ALLOYS AND
METHOD OF MAKING SAME, which application is assigned to the assignee of the present invention.
The thermoelec-tric materials there disclosed can be utilized in the device herein. These materials are not single phase crystalline materials, but instead, are disordered materials. Further, these materials are mul~iphase materials kaving both amorphous and multiple crystalline phases. Materials of this type are good thermal insulators. Tkey include grain boundaries of various transitional phases varying in composition from the composition of matrix crystallites to the composition of the various phases in the grain boundary regions. The grain boun~aries are kighly disordered with the transitional phases including cr~J~
1~'3~
phases of high thermal resistivity to provide high resistance to thermal conduction. Contrary to conventional materials, the material is designed such that the grain boundaries define regions in-cluding conductive phases therein providing numer-ous electrical conduction paths through the bulk material for increasing electrical conductivity without s~bstantially effecting the thermal con-ductivity. In essence, these materials have all of the advantages of polycrystalline materials in desirably low thermal conductivities and crystal-line bul~ Seebec~ properties. ~owever, unlike the conventional polycrystalline materials, these dis-ordered multiphase materials also have desirably high electrical conductivities. ~ence, as dis-closed in the aforesaid referenced application, the S2a product for the figure of merit of these materials can be independently maximized with de-sirably low thermal conductivities for thermoelec-tric power generation~
Amorphous materials, representing the highest degree of disorder, have been made for thermoelec-tric applications. The materials and methods for making the same are fully disclosed and claimed, 25 for example, in U.S. Patents 4,177,~73, 4,177,474, and 4,178,415 which issued in the name of Stanford R. Ovshinsky. The materials disclosed in these patents are formed in a solid amorphous host matrix having structural configurations which have local rather than longrange order and electronic configurations which have an energy gap and an electrical activation energy. Added to the amor-phous host matrix is a modifier material having orbitals which interact with the amorphous host matrix as well as themselves to form electronic states in the energy gap. ~his interaction sub-stantially modifies the electronic configurations of the amorphous host matrix to substantially re-duce the activation energy and hence, increase substantially the electrical conductivity of the material. The resulting electrical conductivity can be controlled by the amount of modifier mate-rial added to the host matrix. I'he amorphous host matrix is normally of intrinsic-like conduction and the modified material changes the same to ex-trinsic-like conduction.
As also disclosed therein, the amorphous host matrix can have lone-pairs having orbitals wherein the orbitals of the modifier material interact therewith to form the new electronic states in the energy gap. In another form, the host matrix can have primarily tetrahedral bonding wherein the modifier material is added primarily in a non-substitutional manner with its orbitals interact-ing with the host matrix. soth d and f band mate-rials as well as boron and carbon, which add multiorbital possibilities can be used as modi-fiers to form the new electronic states in the energy gap.
As a result of the foregoing, these amorphous thermoelectric materials have substantially in-creased electrical conductivity. However, because they remain amorphous after modification, they re-tain their low thermal conductivities making them well suited for thermoelectric applications, espe-cially in high temperature ranges above 400C.
These materials are modified on an atomic or microscopic level with the atomic configurations thereof substantially changed to provide the here-tofore mentioned independently increased electri-cal conductivities. In contrast, the materials disclosed in the aforesaid referenced application are not atomically modified. Rather, they are fabricated in a manner whieh introduces disorder into the material on a maeroscopic level. ~his disorder allows various phases including conduc-tive phases to be introduced into the material much in the same manner as modification atomically in pure amorpho~s phase materials to provide con-trolled high electrical conductivity while thedisorder in the other phases provides low thermal conductivity. These materials therefore are in-termediate in terms of their thermal conductivity between amorphous and regular polycrystalline ma-l~ terials.
A thermoelectric device generates electricityby the establishment of a temperature differential across the materials contained therein. The thermoelectric devices generally include elements of both p-type and n-type material. In the p-type material the temperature differential drives posi-tively charged carriers from the hot side to the cold side of the elements, while in the n-type material the temperature differential drives nega-
2~ tively charged carriers from the hot side to thecold side of the elements.
Thermoelectric power conversion has not found wide usage in the past not only because of materi-al limitations but also because of device limita-tions. Among the device limitations are bowing or ~'3~
warping of device substrates, loss of broad sur-face contact between the device and a heat ex-changer when utilized in a thermoelectric system and temperature losses across the substrate~s.
Thermoelectric devices of the prior art use copper lead patterns placed upon a ceramic sub-strate for the attachment of thermoelectric ele-ments thereto. In the manufacture of these de-vices, a second ceramic substrate having another copper lead pattern is sweated onto the thermo-electric elements. Due to the difference in the coefficient of thermal expansion between the ce-ramic substrates and the copper lead patterns, there occurs a bowing or warping of the substrates during the sweating operation which causes a num-ber of related probelms.
First, because of the warping of the sub-strates, it is difficult if not impossible to ohtain a good thermal connection between the ele-ments and the copper lead patterns of the sub-strates. Additionally, because the ceramic sub-strates are brittle, the bowing or warping, if severe enough, can cause cracking of the sub-strates and other physical degradation of the 11~9~
devices. Furthermore, to be employed in a thermo-electric system, the outer surfaces of the sub-strates ~ust make intimate broad surface contact with a heat exchanger. The warping or bowing of the substrates also makes proper connection be-tween the devices and a heat exchanger difficult.
To overcome these problems, the forces im-parted to the substrates caused by the difference in the coefficients ofthermal expansion between the copper lead patterns and the ceramic sub-strates are equalized by applying copper in sub-stantially identical patterns to the other side of the substrates. Unfortunately, the additional copper increases the material cost of the devices and adds extra processing steps to their manufac-ture.
During the operation of tilermoelectric de-vices a temperature differential is applied across the device to generate electricity. Due to the difference in the coefficient of thermal expansion between the substrates and the thermoelectric ele-ments, loss of broad surface contact occurs be-tween the device and the heat exchanger when uti-lized in a thermoelectric system. This loss of broad surface contact results in less heat tran-sfer which tran~slates to a lower temperature dif-ferential across the device, and lower efficiency of the device.
It has also been Eound that a substantial temperature drop occurs across the ceramic sub-strates. The voltage output and the current of a thermoelectric element is proportional to the tem-perature differential across the element. There-fore, the power is proportional to the square of the temperature differential. Therefore any change in temperature differential across the ele~
ments has a substantial effect on the power output of the device. As a result, the temperature drop across the substrates reduces the temperature dlf-ferential otherwise available to the elements for power generation. Further, the additional copper used to overcome the warping problems adds addi-tional temperature losses across the substrates.
These losses undesirably decrease the temperature differential across the thermoelectric elements from the temperature differential available across the devices thereby adversely decreasing the power output of the devices.
The present invention therefore provides a device that solves all of the above noted prob-lems. The device overcomes the problems of warp-ing due to the elimination of dissimilar substrate S materials having different coefficients of thermal expansion. Also, when utilized in a thermoelec-tric system it maintains broad surface contact with the heat exchanger. The device also allows a greater temperature differential to exist across the thermoelectric elements for a given tempera-ture differential across the device due to the elimination of the ceramic substrates, The greater temperature differential across the ele-ments of the device of the present invention af-ford an increase in electrical power output of atleast 70% over the electrical power output obtain-able from prior art devices for a given total tem-perature differential. The device uses less cop-per, has fewer processing steps, is lighter, thin-ner and costs less to manufacture than prior artdevices.
We have found that the above disadvantages may be overcome by employing the method of manu-facturing and the thermoelectric device so manu-factured of the present invention. The device includes a plurality of thermoelectric elements, copper plate segment electrical connections and means for absorbing thermal expansion of the de-vice during use to maintain broad surface contact with the heat exchanger when used in a thermoelec-tric system. The absorbing means may be, for example, a ceramic potting compound having high thermal and electrical resistivity with which the voids between the thermoelectric elements and the copper plate segments are filled. Thus, the pot-ting compound serves also to insulate and protect the thermoelectric elements.
The device of the present invention also eliminates the relatively thick ceramic substrates of the prior art. Therefore, the substrateless device of the present invention is lighter in weight and thinner than such prior art devices.
Also, excessive temperature losses across the device are eliminated which allows a greater tem-2~ perature differential to be applied across thethermoelectric elements which generate the elec-tricity. Therefore, a substantial increase in electrical power output is realized.
The elimination of the substrate also sub-stantially simplifies the manufacturing process by eliminating the previously experienced bowing or warping of the substrates ancl simultaneously avoids the need for extra material to correct the bowing and warping.
The present invention provides a new ar.d im-proved thermoelectric device for the generation of electricity and a method of manufacturing the same. The new thermoelectric device includes ab-sorbing means for absorbing thermal expansion of the device during use to maintain broad surface contact with a heat exchanger when used in a thermoelectric system. The new thermoelectric de-vice also has fewer component parts and is less costly to manufacture than thermoelectric devices of the prior art. Also, the device is thinner, lighter and able to utilize more of the tempera-ture differential across the device for the gener-ation of electricity.
The thermoelectric device of the present in-vention includes first and second sets of copper plate segments with a solder paste screen printed onto the inner surfaces thereof. The first and second sets of copper plate segments are spaced apart with the thermoelectric elements, which gen-erate the electricity, being disposed between and o~
soldered to the copper plate segment inner sur-faces. The copper segments define a lead pattern which connect the thermoelectric elements electri-cally in series and thermally in parallel. A
ceramic potting compound having high electrical and thermal resistivity fills the voids between the thermoelectric elements and the copper plate segments to thus insulate and protect the ele-ments. The copper plate segments also include a layer of thick film insulator on the outer sur-faces thereof opposite the solder paste. These insulating thick films serve as a mask for fabri-cating the copper plate segments during an etching operation in the manufacture of the device and also serve to electrically insulate the copper segments and thermoelectric elements from a heat exchanger when incorporated into a thermoelectric system.
The above described thermoelectric device is manufactured in accordance with the present inven-tion by first providing first and second relative-ly thin and substantially planar copper plates. A
thick film of ceramic paste insulating material is applied onto one surface of each copper plate in a pattern which duplicates the size, shape, and J~
orientation of the copper plate segments of the finished device. Next, a solder paste is then screen printed onto the other side of each plate.
The solder paste is applied in a pattern which re-sembles the thick film pattern of the respectiveplates. The solder paste printed onto the first plate preferaby has a higher melting temperature than the solder paste printed onto the second cop-per plate. The thermoelectric elements are then soldered to the first plate by a reflow solderin~
process in an inert atmosphere of nitrogen, for example. Thereafter, the second plate is applied to the other side of the elements and soldered thereto by a similaK reflow soldering process in an inert atmosphere.
The device is now ready for final process-ing. All of the sides but one side of the par-tially completed device are bordered by a suitably configured jig to form a cavity with the copper plates. A ceramic potting compound having high thermal and electrical resistivity is then flowed into the cavity to fill the open spaces about the elements. After the potting compound is dried, the outer surfaces of the copper plates having the thick film ceramic paste thereon are subjected to a copper etchant. During this etching operation the etchant attacks and etches away the exposed copper defined by the ceramic thick film pattern.
The etching operation continues until the exposed copper portions are fully etched leaving the heretofore mentioned copper plate segments which now connect the elements electrically in series and thermally in parallel. The completed device is now ready for final rinsing and drying.
The thermoelectric device and method of man-ufacture hereinabove described provides a more ef-ficient device for the generation of electricity responsive to a temper~ture differential there-across without the associated disadvantages of devices incorporating substrates.
By eliminating the relatively thick ceramic substrates of the prior art, the substrateless de-vice of the present invention is lighter in weight and thinner than such prior art devices. Also, excessive temperature losses across the device are eliminated with the elimination of the sub-strates previously employed. This allows a greater temperature differential to be applied across the thermoelectric elements which generate the electricity. Because the power output of such devices is directly proportional to the square of the temperature differential across the thermo-electric elements, a substantial increase in elec-trical power output is obtained for a given total temperature differential.
The elimination of the substrate also aids in the manufacture of such devices by eliminating the previously experienced bowing or warping of the substrates while simultaneously avoiding the need for extra material to correct it. The ceramic potting compound absorbs any thermal expansion of the device in use, tc maintain broad surface con-tact between the device and heat exchanger when used in a thermoelectric system. Further, the copper plate segments experience a locali~ed ther-mal expansion rather than a total or entire ther-mal expansion of prior art substrates to distri-bute the expansion and to lessen any deleterious effects caused thereby. All of the foregoing re-duces the cost of materials and the number of re-quired process steps.
Fig. 1 is a bottom plan view of a planar cop-per plate having solder paste screen printed thereon in accordance with the present invention;
i3.'3'~
Fig. 2 is a top plan view of another planar copper plate having solder paste screen printed thereon in accordance with the present invention;
Fig. 3 is a side view of a partially complet-ed thermoelectric device embodying the ~resent in-vention at one stage of its manufacture;
Fiy. 4 is a cross sectional view taken along lines 4-4 of Fig. 3;
Fig. 5 is a side view of the partially com-1~ pleted thermoelectric device of Fig. 3 embodyingthe present invention at a further stage of its manu f acture;
Fig. 6 is a side view of the partially con-pleted thermoelectric device of Fig~ 3 embodying the present invention at a still further stage of its manufacture; an Fig. 7 is a side view of the completed thermoelectric device embodying the present inven-tion.
In accordance with the present invention the new and improved thermoelectrc device and method for manufacturing the same, shall now be described with reference to ~he drawings.
Fig, 7 discloses a substrateless thermoelec-tric device embodying the present invention at re-ference numeral 10. The device 10 generates elec-tricity by the establishment of a temperature dif-ferential thereacross. The temperature differen-tial drives flux through p-type and n-ty~e thermo-electric elements 12 and 14. In the n-type ele-ment 14 the temperature differential drives nega-tive carriers from the hot side to the cold side.
In the p-type element 12 the temperature differen-tial drives positive carriers from the hot side to the cold side. It is the movement of the positive and negative carriers which generates electricity.
The p-type and n-type thermoelectric elements 12 and 14 are equal in number and alternate throughout as best shown in Fig. 4. ~ig. 4 il-lustrates thirty-two p-type elements 12 and thirty-two n-type elements 14 by way of example, but any equal number of p-type and n-type elements ~ill suffice. A representive composition utilized for the p-type elements 12 comprises from about ten to twenty percent bismuth, about twenty to thirty percent antimony, about sixty percent tel-lurium, and less than one percent silver. This material and others usable as p-type elements are disclosed and clairned in the aforementioned copending Canadian Application 419,580, f:iled January 17, 1983, for New Multiphase Thermoelectric Alloys and Method for Making Same, which application is assiyned to the assignee of the pxesent invention. The n-type el~ments mdy comprlse about forty percent bismuth, about fifty-four percent tellurium, and about six percent selenium.
Referring again to Fig. 7, the p-type and n-type elements 12 and 14 of the substrateless thermoelectric device 10 are thermally affixed to interior surfaces of spaced apart first and second sets of copper plate segments 22 and 18 respectively. The interior surfaces of the copper plate segments 18 and 22 have a solder paste 16 and 24 screen printed thereon for thermally and electrically connecting the elements 12 and 14 to the copper plate segments 18 and 22 respectively. The copper plate segments 18 and 22 define a lead pattern for connecting the elements 12 and 14 electrically in series and thermally in parallel.
A ceramic potting compound 30 such as Aremco 554 or the like for example, fills the voids between the elements 12 and 14 and the copper plate * Trademark cr/~-"
segments 18 and 22. The ceramic potting compound 30 has qualities of h;gh electrical and thermal resistivity to insulate the elements and to pro-tect the elements from contamination. The ceramic potting compound 30 also acts to absorb thermal expansion of the device during its use. The cop-per plate segments 18 and 22 also include a layer of a thick film ceramic 20 such as ESL M4906 man-ufactured by Electro-Science Laboratories, Inc.
for example or the like, on the outer surfaces of the segments 18 and 22 opposite the solder paste 16 and 24. The thick film ceramic 20 has hi~h electrical resistivity to electrically insulate the copper plate segments 18 and 22 when employed in conjunction with a heat exchanger and has a high thermal conductivity to maximize the tempera-ture differential across the elements 12 and 14 for a given temperature differential across the device 10. The thick film ceramic 20 has a dual function of serving as a mask Eor fabricating the copper plate segments 18 and 22 which will be dis-cussed in greater detail subse~uently and electri-cally insulating the thermoelectric device 10 from a heat exchanger when utilized in a thermoelectric system to generate electricity.
* Trademark The substrateless thermoelectric device 10 is manufactured in accordance ~ith the present inven-tion by providing a pair of relatively thin and substantially planar copper plates 19 and 23. The copper plates 19 and 23 are about .020 inches in thickness.
A thick film ceramic paste 20 is screen printed on the opposite side of the copper plate 19 shown in Fig. 1, in a pattern which resembles the patterns there shown. The thick film ceramic paste 20 has the characteristics of being a good electrical insulator and a good thermal conductor and may be ESL r~4906 or the like for example. The thick film ceramic is dried at 125C for 15 min-15 utes and then fired for 30 minutes at 900C.
After the thick film has been fired, a solder paste 16 is screen printed upon copper plate 19 in a pattern as shown in Fig. 1 which duplicates the size, shape and orientation of the copper plate segments 18 of the finished device 10. The copperplate 19 with the solder paste 16 thereon is then dried at about 120C for 15 minutes.
The thick film ceramic paste 20 screen print-ed on the opposite side of the copper plate 22, shown in Fig. 2, in a pattern which resembles the s pattern there shown. The copper plate 23 is then screen printed with a solder paste 24 in a pattern as shown in Fig. 2. The copper plate 23 is then prepared in an analogous fashion to the copper plate 19.
Referring now to Fig. 3, the p-type and n-type elements 12 and 14 are connectecl to the cop-per plate 23 in eq~al number and alternating throughout, by reflowing the solder paste 24 in the presence of an inert atmosphere~ such as ni-trogen for example, at about 350C. The copper plate 19 is then placed upon the p-type and n-type elements 12 and 14 with the solder paste 16 con-tacting the elements. The solder paste 16 is then lS reflowed in an inert atmosphere at a temperature of about 300C or lower to connect the elements 12 and 14 to the copper plate 19 to form the partial-ly completed device 26 of Fig. 3 in accordance with the present invention.
The solder paste 16 is chosen to melt at a lower temperature than that of the solder paste 24. This facilitates the assembly of the copper plates 19 and 23 to the thermoelectric elements 12 and 14 without melting the previously reflowed solder 24.
As shown in Fig. 5 the partially completed device 26 of Fig. 3 is placed in a jig 23 which encloses all of the sides of the device 26 but one side to form with the copper plates 19 and 23 a cavity 31. This facilitates the injection of the ceramic potting compound into the cavity 31 to fill the area betweer, the copper plates 19 and 23 and the elements 12 and 14. The ceramic potting compound exhibits the qualities of high thermal resistivity and electrical resistivity and may be Aremco 554 or the like for example. The compound acts to absorb thermal expansion of the device while in use to maintain broad surface contact be-tween the elements and the segments. Further, the compound 30 protects the elements 12 and 14 from the environment and possible contamination there-from.
As shown in Fig. 6, once the ceramic potting compound 30 has filled all the voids between the plates 19 and 23, the partially completed device is dried for 24 hours at 90C. After drying, the assembly 32, of Fig. 6 is formed. The asse~bly 32 is now ready for final processing. The outer sur-faces of the copper plates 19 and 23 having the thick film ceramic 20 ~hereon are then exposed to a copper etchant such as Ultra Etch S0 by McDer~ott, Inc. for example. The etchant is ap-plied to ~ttack and etch away the exposed copper surfaces of the copper plates 19 and 23 def ined by the pattern of the thick film ceramic 20. The etching process continues until the exposed copper surfaces are fully etched leaving the copper plate segments 18 and 22 which now connect the elements 12 and 14 electrically in series and thermally in parallel. The co~pleted device is then rinsed and dried.
The substrateless thermoelectric device 10 providés a thin, lightwei~ht construction by the elimination of the ceramic substrate utili~ed in prior art devices. The ceramic pottinq co~pouna 30 serves as a support for the device, as ~n ab-sorber of thermal expansion for the device in use as well as protecting the thermoelectric elements 12 and 14 from the environment. The potting com-pound 30 also is a ~ood electrical and ther~al in-sulator for the elements 12 and 14. The thic~
film ceramic 20 electrically insulates the copper segments 18 and 22 of the device 10 when connected to a heat exchanger and used to generate elec-tricity in a thermoelectric system. The copper * Trademark
Thermoelectric power conversion has not found wide usage in the past not only because of materi-al limitations but also because of device limita-tions. Among the device limitations are bowing or ~'3~
warping of device substrates, loss of broad sur-face contact between the device and a heat ex-changer when utilized in a thermoelectric system and temperature losses across the substrate~s.
Thermoelectric devices of the prior art use copper lead patterns placed upon a ceramic sub-strate for the attachment of thermoelectric ele-ments thereto. In the manufacture of these de-vices, a second ceramic substrate having another copper lead pattern is sweated onto the thermo-electric elements. Due to the difference in the coefficient of thermal expansion between the ce-ramic substrates and the copper lead patterns, there occurs a bowing or warping of the substrates during the sweating operation which causes a num-ber of related probelms.
First, because of the warping of the sub-strates, it is difficult if not impossible to ohtain a good thermal connection between the ele-ments and the copper lead patterns of the sub-strates. Additionally, because the ceramic sub-strates are brittle, the bowing or warping, if severe enough, can cause cracking of the sub-strates and other physical degradation of the 11~9~
devices. Furthermore, to be employed in a thermo-electric system, the outer surfaces of the sub-strates ~ust make intimate broad surface contact with a heat exchanger. The warping or bowing of the substrates also makes proper connection be-tween the devices and a heat exchanger difficult.
To overcome these problems, the forces im-parted to the substrates caused by the difference in the coefficients ofthermal expansion between the copper lead patterns and the ceramic sub-strates are equalized by applying copper in sub-stantially identical patterns to the other side of the substrates. Unfortunately, the additional copper increases the material cost of the devices and adds extra processing steps to their manufac-ture.
During the operation of tilermoelectric de-vices a temperature differential is applied across the device to generate electricity. Due to the difference in the coefficient of thermal expansion between the substrates and the thermoelectric ele-ments, loss of broad surface contact occurs be-tween the device and the heat exchanger when uti-lized in a thermoelectric system. This loss of broad surface contact results in less heat tran-sfer which tran~slates to a lower temperature dif-ferential across the device, and lower efficiency of the device.
It has also been Eound that a substantial temperature drop occurs across the ceramic sub-strates. The voltage output and the current of a thermoelectric element is proportional to the tem-perature differential across the element. There-fore, the power is proportional to the square of the temperature differential. Therefore any change in temperature differential across the ele~
ments has a substantial effect on the power output of the device. As a result, the temperature drop across the substrates reduces the temperature dlf-ferential otherwise available to the elements for power generation. Further, the additional copper used to overcome the warping problems adds addi-tional temperature losses across the substrates.
These losses undesirably decrease the temperature differential across the thermoelectric elements from the temperature differential available across the devices thereby adversely decreasing the power output of the devices.
The present invention therefore provides a device that solves all of the above noted prob-lems. The device overcomes the problems of warp-ing due to the elimination of dissimilar substrate S materials having different coefficients of thermal expansion. Also, when utilized in a thermoelec-tric system it maintains broad surface contact with the heat exchanger. The device also allows a greater temperature differential to exist across the thermoelectric elements for a given tempera-ture differential across the device due to the elimination of the ceramic substrates, The greater temperature differential across the ele-ments of the device of the present invention af-ford an increase in electrical power output of atleast 70% over the electrical power output obtain-able from prior art devices for a given total tem-perature differential. The device uses less cop-per, has fewer processing steps, is lighter, thin-ner and costs less to manufacture than prior artdevices.
We have found that the above disadvantages may be overcome by employing the method of manu-facturing and the thermoelectric device so manu-factured of the present invention. The device includes a plurality of thermoelectric elements, copper plate segment electrical connections and means for absorbing thermal expansion of the de-vice during use to maintain broad surface contact with the heat exchanger when used in a thermoelec-tric system. The absorbing means may be, for example, a ceramic potting compound having high thermal and electrical resistivity with which the voids between the thermoelectric elements and the copper plate segments are filled. Thus, the pot-ting compound serves also to insulate and protect the thermoelectric elements.
The device of the present invention also eliminates the relatively thick ceramic substrates of the prior art. Therefore, the substrateless device of the present invention is lighter in weight and thinner than such prior art devices.
Also, excessive temperature losses across the device are eliminated which allows a greater tem-2~ perature differential to be applied across thethermoelectric elements which generate the elec-tricity. Therefore, a substantial increase in electrical power output is realized.
The elimination of the substrate also sub-stantially simplifies the manufacturing process by eliminating the previously experienced bowing or warping of the substrates ancl simultaneously avoids the need for extra material to correct the bowing and warping.
The present invention provides a new ar.d im-proved thermoelectric device for the generation of electricity and a method of manufacturing the same. The new thermoelectric device includes ab-sorbing means for absorbing thermal expansion of the device during use to maintain broad surface contact with a heat exchanger when used in a thermoelectric system. The new thermoelectric de-vice also has fewer component parts and is less costly to manufacture than thermoelectric devices of the prior art. Also, the device is thinner, lighter and able to utilize more of the tempera-ture differential across the device for the gener-ation of electricity.
The thermoelectric device of the present in-vention includes first and second sets of copper plate segments with a solder paste screen printed onto the inner surfaces thereof. The first and second sets of copper plate segments are spaced apart with the thermoelectric elements, which gen-erate the electricity, being disposed between and o~
soldered to the copper plate segment inner sur-faces. The copper segments define a lead pattern which connect the thermoelectric elements electri-cally in series and thermally in parallel. A
ceramic potting compound having high electrical and thermal resistivity fills the voids between the thermoelectric elements and the copper plate segments to thus insulate and protect the ele-ments. The copper plate segments also include a layer of thick film insulator on the outer sur-faces thereof opposite the solder paste. These insulating thick films serve as a mask for fabri-cating the copper plate segments during an etching operation in the manufacture of the device and also serve to electrically insulate the copper segments and thermoelectric elements from a heat exchanger when incorporated into a thermoelectric system.
The above described thermoelectric device is manufactured in accordance with the present inven-tion by first providing first and second relative-ly thin and substantially planar copper plates. A
thick film of ceramic paste insulating material is applied onto one surface of each copper plate in a pattern which duplicates the size, shape, and J~
orientation of the copper plate segments of the finished device. Next, a solder paste is then screen printed onto the other side of each plate.
The solder paste is applied in a pattern which re-sembles the thick film pattern of the respectiveplates. The solder paste printed onto the first plate preferaby has a higher melting temperature than the solder paste printed onto the second cop-per plate. The thermoelectric elements are then soldered to the first plate by a reflow solderin~
process in an inert atmosphere of nitrogen, for example. Thereafter, the second plate is applied to the other side of the elements and soldered thereto by a similaK reflow soldering process in an inert atmosphere.
The device is now ready for final process-ing. All of the sides but one side of the par-tially completed device are bordered by a suitably configured jig to form a cavity with the copper plates. A ceramic potting compound having high thermal and electrical resistivity is then flowed into the cavity to fill the open spaces about the elements. After the potting compound is dried, the outer surfaces of the copper plates having the thick film ceramic paste thereon are subjected to a copper etchant. During this etching operation the etchant attacks and etches away the exposed copper defined by the ceramic thick film pattern.
The etching operation continues until the exposed copper portions are fully etched leaving the heretofore mentioned copper plate segments which now connect the elements electrically in series and thermally in parallel. The completed device is now ready for final rinsing and drying.
The thermoelectric device and method of man-ufacture hereinabove described provides a more ef-ficient device for the generation of electricity responsive to a temper~ture differential there-across without the associated disadvantages of devices incorporating substrates.
By eliminating the relatively thick ceramic substrates of the prior art, the substrateless de-vice of the present invention is lighter in weight and thinner than such prior art devices. Also, excessive temperature losses across the device are eliminated with the elimination of the sub-strates previously employed. This allows a greater temperature differential to be applied across the thermoelectric elements which generate the electricity. Because the power output of such devices is directly proportional to the square of the temperature differential across the thermo-electric elements, a substantial increase in elec-trical power output is obtained for a given total temperature differential.
The elimination of the substrate also aids in the manufacture of such devices by eliminating the previously experienced bowing or warping of the substrates while simultaneously avoiding the need for extra material to correct it. The ceramic potting compound absorbs any thermal expansion of the device in use, tc maintain broad surface con-tact between the device and heat exchanger when used in a thermoelectric system. Further, the copper plate segments experience a locali~ed ther-mal expansion rather than a total or entire ther-mal expansion of prior art substrates to distri-bute the expansion and to lessen any deleterious effects caused thereby. All of the foregoing re-duces the cost of materials and the number of re-quired process steps.
Fig. 1 is a bottom plan view of a planar cop-per plate having solder paste screen printed thereon in accordance with the present invention;
i3.'3'~
Fig. 2 is a top plan view of another planar copper plate having solder paste screen printed thereon in accordance with the present invention;
Fig. 3 is a side view of a partially complet-ed thermoelectric device embodying the ~resent in-vention at one stage of its manufacture;
Fiy. 4 is a cross sectional view taken along lines 4-4 of Fig. 3;
Fig. 5 is a side view of the partially com-1~ pleted thermoelectric device of Fig. 3 embodyingthe present invention at a further stage of its manu f acture;
Fig. 6 is a side view of the partially con-pleted thermoelectric device of Fig~ 3 embodying the present invention at a still further stage of its manufacture; an Fig. 7 is a side view of the completed thermoelectric device embodying the present inven-tion.
In accordance with the present invention the new and improved thermoelectrc device and method for manufacturing the same, shall now be described with reference to ~he drawings.
Fig, 7 discloses a substrateless thermoelec-tric device embodying the present invention at re-ference numeral 10. The device 10 generates elec-tricity by the establishment of a temperature dif-ferential thereacross. The temperature differen-tial drives flux through p-type and n-ty~e thermo-electric elements 12 and 14. In the n-type ele-ment 14 the temperature differential drives nega-tive carriers from the hot side to the cold side.
In the p-type element 12 the temperature differen-tial drives positive carriers from the hot side to the cold side. It is the movement of the positive and negative carriers which generates electricity.
The p-type and n-type thermoelectric elements 12 and 14 are equal in number and alternate throughout as best shown in Fig. 4. ~ig. 4 il-lustrates thirty-two p-type elements 12 and thirty-two n-type elements 14 by way of example, but any equal number of p-type and n-type elements ~ill suffice. A representive composition utilized for the p-type elements 12 comprises from about ten to twenty percent bismuth, about twenty to thirty percent antimony, about sixty percent tel-lurium, and less than one percent silver. This material and others usable as p-type elements are disclosed and clairned in the aforementioned copending Canadian Application 419,580, f:iled January 17, 1983, for New Multiphase Thermoelectric Alloys and Method for Making Same, which application is assiyned to the assignee of the pxesent invention. The n-type el~ments mdy comprlse about forty percent bismuth, about fifty-four percent tellurium, and about six percent selenium.
Referring again to Fig. 7, the p-type and n-type elements 12 and 14 of the substrateless thermoelectric device 10 are thermally affixed to interior surfaces of spaced apart first and second sets of copper plate segments 22 and 18 respectively. The interior surfaces of the copper plate segments 18 and 22 have a solder paste 16 and 24 screen printed thereon for thermally and electrically connecting the elements 12 and 14 to the copper plate segments 18 and 22 respectively. The copper plate segments 18 and 22 define a lead pattern for connecting the elements 12 and 14 electrically in series and thermally in parallel.
A ceramic potting compound 30 such as Aremco 554 or the like for example, fills the voids between the elements 12 and 14 and the copper plate * Trademark cr/~-"
segments 18 and 22. The ceramic potting compound 30 has qualities of h;gh electrical and thermal resistivity to insulate the elements and to pro-tect the elements from contamination. The ceramic potting compound 30 also acts to absorb thermal expansion of the device during its use. The cop-per plate segments 18 and 22 also include a layer of a thick film ceramic 20 such as ESL M4906 man-ufactured by Electro-Science Laboratories, Inc.
for example or the like, on the outer surfaces of the segments 18 and 22 opposite the solder paste 16 and 24. The thick film ceramic 20 has hi~h electrical resistivity to electrically insulate the copper plate segments 18 and 22 when employed in conjunction with a heat exchanger and has a high thermal conductivity to maximize the tempera-ture differential across the elements 12 and 14 for a given temperature differential across the device 10. The thick film ceramic 20 has a dual function of serving as a mask Eor fabricating the copper plate segments 18 and 22 which will be dis-cussed in greater detail subse~uently and electri-cally insulating the thermoelectric device 10 from a heat exchanger when utilized in a thermoelectric system to generate electricity.
* Trademark The substrateless thermoelectric device 10 is manufactured in accordance ~ith the present inven-tion by providing a pair of relatively thin and substantially planar copper plates 19 and 23. The copper plates 19 and 23 are about .020 inches in thickness.
A thick film ceramic paste 20 is screen printed on the opposite side of the copper plate 19 shown in Fig. 1, in a pattern which resembles the patterns there shown. The thick film ceramic paste 20 has the characteristics of being a good electrical insulator and a good thermal conductor and may be ESL r~4906 or the like for example. The thick film ceramic is dried at 125C for 15 min-15 utes and then fired for 30 minutes at 900C.
After the thick film has been fired, a solder paste 16 is screen printed upon copper plate 19 in a pattern as shown in Fig. 1 which duplicates the size, shape and orientation of the copper plate segments 18 of the finished device 10. The copperplate 19 with the solder paste 16 thereon is then dried at about 120C for 15 minutes.
The thick film ceramic paste 20 screen print-ed on the opposite side of the copper plate 22, shown in Fig. 2, in a pattern which resembles the s pattern there shown. The copper plate 23 is then screen printed with a solder paste 24 in a pattern as shown in Fig. 2. The copper plate 23 is then prepared in an analogous fashion to the copper plate 19.
Referring now to Fig. 3, the p-type and n-type elements 12 and 14 are connectecl to the cop-per plate 23 in eq~al number and alternating throughout, by reflowing the solder paste 24 in the presence of an inert atmosphere~ such as ni-trogen for example, at about 350C. The copper plate 19 is then placed upon the p-type and n-type elements 12 and 14 with the solder paste 16 con-tacting the elements. The solder paste 16 is then lS reflowed in an inert atmosphere at a temperature of about 300C or lower to connect the elements 12 and 14 to the copper plate 19 to form the partial-ly completed device 26 of Fig. 3 in accordance with the present invention.
The solder paste 16 is chosen to melt at a lower temperature than that of the solder paste 24. This facilitates the assembly of the copper plates 19 and 23 to the thermoelectric elements 12 and 14 without melting the previously reflowed solder 24.
As shown in Fig. 5 the partially completed device 26 of Fig. 3 is placed in a jig 23 which encloses all of the sides of the device 26 but one side to form with the copper plates 19 and 23 a cavity 31. This facilitates the injection of the ceramic potting compound into the cavity 31 to fill the area betweer, the copper plates 19 and 23 and the elements 12 and 14. The ceramic potting compound exhibits the qualities of high thermal resistivity and electrical resistivity and may be Aremco 554 or the like for example. The compound acts to absorb thermal expansion of the device while in use to maintain broad surface contact be-tween the elements and the segments. Further, the compound 30 protects the elements 12 and 14 from the environment and possible contamination there-from.
As shown in Fig. 6, once the ceramic potting compound 30 has filled all the voids between the plates 19 and 23, the partially completed device is dried for 24 hours at 90C. After drying, the assembly 32, of Fig. 6 is formed. The asse~bly 32 is now ready for final processing. The outer sur-faces of the copper plates 19 and 23 having the thick film ceramic 20 ~hereon are then exposed to a copper etchant such as Ultra Etch S0 by McDer~ott, Inc. for example. The etchant is ap-plied to ~ttack and etch away the exposed copper surfaces of the copper plates 19 and 23 def ined by the pattern of the thick film ceramic 20. The etching process continues until the exposed copper surfaces are fully etched leaving the copper plate segments 18 and 22 which now connect the elements 12 and 14 electrically in series and thermally in parallel. The co~pleted device is then rinsed and dried.
The substrateless thermoelectric device 10 providés a thin, lightwei~ht construction by the elimination of the ceramic substrate utili~ed in prior art devices. The ceramic pottinq co~pouna 30 serves as a support for the device, as ~n ab-sorber of thermal expansion for the device in use as well as protecting the thermoelectric elements 12 and 14 from the environment. The potting com-pound 30 also is a ~ood electrical and ther~al in-sulator for the elements 12 and 14. The thic~
film ceramic 20 electrically insulates the copper segments 18 and 22 of the device 10 when connected to a heat exchanger and used to generate elec-tricity in a thermoelectric system. The copper * Trademark
3~ 5 segments 18 and 22 experience a more localized thermal expansion versus a total or long range expansion experienced by substrates of the prior art and is thus at,le to distribute the expansion equally without harming the device. This new con-cept decreases material and production costs.
It is well known that electrical power output is proportional to the square of the temperature differential because the voltage and the current of a ther~oelectric device are proportional to the temperature differential across the elements of the deviceO Therefore the electrical power output of a thermoelectric device is proportional to the square of the temperature differential across the elements. For a given temperature differential across a thermoelectric device any temperature losses which decrease the temperature differential across the thermoelectric elements markedly reduce the electrical power output of the deviceO
The substrateless thermoelectric device of the present invention, by eliminating the thick ceramic substrates exhibits lower temperature losses and therefore higher temperature differen-tials across the thermoelectric elements. For e~-ample, in a given application wherein there was available a 280C temperature differential, a prior art device of the type previously described exhibited a substantial temperature loss of 80C
across the ceramic substrates to reduce the tem-perature differential available across the thermo-electric elements to 200C. In a device struc-tured in accordance with the present invention, for the same 280C temperature differential, there was a total temperature differential loss of only 20C to provide a 260C temperature differential across the thermoelectric elements. ~s a result, there was a seventy percent increase in electrical power output provided by the thermoelectric device of the present invention over that provided by the thermoelectric device of the prior art.
Modifications and variations of the present invention are possible in light of the above teachings. It is therefore, to be understood that within the scope of the appended claims the inven-tion may be practiced otherwise than as specifi-cally described.
It is well known that electrical power output is proportional to the square of the temperature differential because the voltage and the current of a ther~oelectric device are proportional to the temperature differential across the elements of the deviceO Therefore the electrical power output of a thermoelectric device is proportional to the square of the temperature differential across the elements. For a given temperature differential across a thermoelectric device any temperature losses which decrease the temperature differential across the thermoelectric elements markedly reduce the electrical power output of the deviceO
The substrateless thermoelectric device of the present invention, by eliminating the thick ceramic substrates exhibits lower temperature losses and therefore higher temperature differen-tials across the thermoelectric elements. For e~-ample, in a given application wherein there was available a 280C temperature differential, a prior art device of the type previously described exhibited a substantial temperature loss of 80C
across the ceramic substrates to reduce the tem-perature differential available across the thermo-electric elements to 200C. In a device struc-tured in accordance with the present invention, for the same 280C temperature differential, there was a total temperature differential loss of only 20C to provide a 260C temperature differential across the thermoelectric elements. ~s a result, there was a seventy percent increase in electrical power output provided by the thermoelectric device of the present invention over that provided by the thermoelectric device of the prior art.
Modifications and variations of the present invention are possible in light of the above teachings. It is therefore, to be understood that within the scope of the appended claims the inven-tion may be practiced otherwise than as specifi-cally described.
Claims (40)
1. A thermoelectric device comprising:
at least two thermoelectric elements;
coupling means for coupling said elements electrically in series and thermally in parallel;
and absorbing means for absorbing the thermal ex-pansion of said thermoelectric elements and said coupling means when a temperature differential is applied across said device.
at least two thermoelectric elements;
coupling means for coupling said elements electrically in series and thermally in parallel;
and absorbing means for absorbing the thermal ex-pansion of said thermoelectric elements and said coupling means when a temperature differential is applied across said device.
2. The thermoelectric device as defined in claim 1, wherein said coupling means include a first set of conducting plate segments each seg-ment having an inner surface and a second set of conducting plate segments each segment having an inner surface spaced from said first set of con-ducting plate segment inner surfaces.
3. The thermoelectric device as defined in claim 2, wherein said at least two thermoelectric elements are disposed between said first and sec-ond conducting plate segments and are fastened to said inner surface.
4. The thermoelectric device as defined in claim 3, wherein two thermoelectric elements of said elements are fastened to one conducting plate segment of one set of conducting plate segments and each element of said two thermoelectric ele-ments is fastened to a conducting plate segment of the other set of said conducting plate segments.
5. The thermoelectric device as defined in claim 4, wherein said absorbing means is an insu-lating material surrounding said at least two thermoelectric elements between said coupling means.
6. The thermoelectric device as defined in claim 5, wherein said insulating material is a potting ceramic.
7. A thermoelectric device comprising:
first conducting plate segment means having an inner surface;
second conducting plate segment means having an inner surface spaced from said first conducting plate segment means inner surface;
at least two thermoelectric elements disposed between said first and second conducting plate segment means and being fastened to the inner sur-faces of said first and second conducting plate segment means;
a first insulating material surrounding said elements between the conducting plate segment means; and said first and second conducting plate seg-ment means being fastened to said at least two thermoelectric elements to couple said elements electrically in series and thermally in parallel.
first conducting plate segment means having an inner surface;
second conducting plate segment means having an inner surface spaced from said first conducting plate segment means inner surface;
at least two thermoelectric elements disposed between said first and second conducting plate segment means and being fastened to the inner sur-faces of said first and second conducting plate segment means;
a first insulating material surrounding said elements between the conducting plate segment means; and said first and second conducting plate seg-ment means being fastened to said at least two thermoelectric elements to couple said elements electrically in series and thermally in parallel.
8. The thermoelectric device as defined in claim 7, wherein the outer surfaces of said first and second conducting plate segment means are coated with a second insulating material.
9. The thermoelectric device as defined in claim 8, wherein said second insulating material serves for fabricating said first and second con-ducting plate segment means.
10. The thermoelectric device as defined in claim 9, wherein said second insulating material has high thermal conductivity and low electrical conductivity.
11. The thermoelectric device as defined in claim 10, wherein said second insulating material is a thick film ceramic.
12. The thermoelectric device as defined in claim 7, wherein said insulating material is a potting ceramic.
13. The thermoelectric device as defined in claim 7 or 8 wherein said first and second con-ducting plate segment means are copper.
14. The thermoelectric device as defined in claim 7 wherein said thermoelectric elements are fastened to said first and second conducting plate segment means by solder.
15. The thermoelectric device as defined in claim 14 wherein the solder fastening said thermo-electric elements to said first conducting plate segment means has a higher melting temperature than the solder fastening said thermoelectric ele-ments to said second conducting plate segment means.
16. The thermoelectric device as defined in claim 7 wherein said at least two thermoelectric elements comprise at least one p-type element and at least one n-type element.
17. The thermoelectric device as defined in claim 16 further comprising a plurality of said n-type and p-type elements in equal number.
18. A thermoelectric device comprising:
a first set of copper plate segments having an inner surface;
a second set of copper plate segments having an inner surface spaced from said first set of copper plate segments;
a plurality of thermoelectric elements elec-trically and thermally connected to the inner sur-faces of said first and second sets of copper plate segments;
said first and second sets of copper plate segments defining a lead pattern which connects said thermoelectric elements electrically in series and thermally in parallel; and a ceramic potting compound for absorbing the thermal expansion of said thermoelectric elements and said copper plate segments when a temperature differential is applied across the device, having high electrical and thermal resistivity filling the voids between said thermoelectric elements and said first and second sets of copper plate seg-ments.
a first set of copper plate segments having an inner surface;
a second set of copper plate segments having an inner surface spaced from said first set of copper plate segments;
a plurality of thermoelectric elements elec-trically and thermally connected to the inner sur-faces of said first and second sets of copper plate segments;
said first and second sets of copper plate segments defining a lead pattern which connects said thermoelectric elements electrically in series and thermally in parallel; and a ceramic potting compound for absorbing the thermal expansion of said thermoelectric elements and said copper plate segments when a temperature differential is applied across the device, having high electrical and thermal resistivity filling the voids between said thermoelectric elements and said first and second sets of copper plate seg-ments.
19. The thermoelectric device as defined in claim 18, wherein said thermoelectric elements are fastened to said first and second sets of copper plate segments by solder paste.
20. The thermoelectric device as defined in claim 19, wherein said solder paste fastening said thermoelectric elements to said first set of cop-per plate segments has a higher melting point than said solder paste fastening said thermoelectric elements to said second set of copper plate seg-ments.
21. The thermoelectric device as defined in claim 18 to 20 wherein the outer surfaces of said first and second sets of copper plate segments are coated with a thick film insulator.
22. A method of manufacturing a thermoelec-tric device comprising the steps of:
fastening at least two thermoelectric ele-ments to the inner surface of a substantially planar first conducting layer;
fastening the inner surface of a substantial-ly planar second conducting layer to said at least two thermoelectric elements on the side thereof opposite said first conducting layer;
injecting an insulating material between said elements and said layers; and etching said first and second conducting lay-ers in a pattern to form first and second conduct-ing plate segment means whereby said at least two thermoelectric elements are connected electrically ing series and thermally in parallel by said first and second conducting plate segment means.
fastening at least two thermoelectric ele-ments to the inner surface of a substantially planar first conducting layer;
fastening the inner surface of a substantial-ly planar second conducting layer to said at least two thermoelectric elements on the side thereof opposite said first conducting layer;
injecting an insulating material between said elements and said layers; and etching said first and second conducting lay-ers in a pattern to form first and second conduct-ing plate segment means whereby said at least two thermoelectric elements are connected electrically ing series and thermally in parallel by said first and second conducting plate segment means.
23. The method as defined in claim 22 in-cluding the initial step of coating the outer sur-faces of said first and second conducting layers with a second insulating material.
24. The method as defined in claim 23 in-cluding the further step of coating said second insulating material onto said outer surfaces of said first and second conducting layer to form an etching pattern for the formation of said first and second conducting plate segment means.
25. The method as defined in claim 24 where-in said second insulating material has a high thermal conductivity and a low electrical conduc-tivity.
26. The method as defined in claim 25 where-in said second insulating material is a thick film ceramic.
27. The method as defined in claim 22 where-in said insulating material is a potting ceramic.
28. The method as defined in claim 22 where-in said first and second conducting layers are copper.
29. The method as defined in claim 23 in-cluding the additional step of screen printing the inner surfaces of said conducting layers with a solder paste in a pattern which resembles the pat-tern etched in said first and second conducting layers to form said first and second conducting plate segment means.
30. The method as defined in claim 29 in-cluding the additional step of drying said solder paste.
31. The method as defined in claim 22 where-in said at least two thermoelectric elements are fastened to said conducting layers by reflowing said solder.
32. The method as defined in claim 31 where-in the solder used to fasten said at least two thermoelectric elements to said first conducting layer has a higher melting point than the solder used to fasten said thermoelectric elements to said second conducting layer.
33. The method as defined in claim 32 com-prising the additional step of reflowing said sol-der in a reducing atmosphere.
34. The method as defined in claim 24 where-in said at least two thermoelectric elements com-prise one p-type and one n-type element.
35. The method as defined in claim 34 where-in there are soldered to the conducting layers a plurality of n-type and p-type elements in equal number.
36. The method as defined in claims 22, 23 or 30 including the additional step of rinsing said device after etching.
37. A method of manufacturing a thermoelec-tric device comprising the steps of:
electrically and thermally fastening a plu-rality of thermoelectric elements to the inner surface of a thin, substantially planar first cop-per plate;
electrically and thermally fastening the in-ner surface of a thin substantially planar second copper plate to said plurality of thermoelectric elements on the side thereof opposite said first copper plate;
flowing a ceramic potting compound having a high electrical and thermal resistivity between said thermoelectric elements and said first and second copper plates; and etching said first and second copper plates to form copper plate segments which define a lead pattern coupling said thermoelectric elements electrically in series and thermally in parallel.
electrically and thermally fastening a plu-rality of thermoelectric elements to the inner surface of a thin, substantially planar first cop-per plate;
electrically and thermally fastening the in-ner surface of a thin substantially planar second copper plate to said plurality of thermoelectric elements on the side thereof opposite said first copper plate;
flowing a ceramic potting compound having a high electrical and thermal resistivity between said thermoelectric elements and said first and second copper plates; and etching said first and second copper plates to form copper plate segments which define a lead pattern coupling said thermoelectric elements electrically in series and thermally in parallel.
38. The method as defined in claim 37 where-in a solder paste is screen printed onto said first and second copper plates in a pattern which duplicates the size, shape and orientation of said copper plate segments.
39. The method as defined in claim 38, wherein the solder paste screen printed on said first copper plate has a higher melting point than the solder paste screen printed on said second copper plate.
40. The method as defined in claim 37 or 38 including the initial step of coating the outer surfaces of said first and second copper plates with a thick film ceramic insulating material in a pattern which duplicates the size, shape and orientation of said copper plate segments.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/372,688 US4459428A (en) | 1982-04-28 | 1982-04-28 | Thermoelectric device and method of making same |
| US372,688 | 1982-04-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1199425A true CA1199425A (en) | 1986-01-14 |
Family
ID=23469223
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000426918A Expired CA1199425A (en) | 1982-04-28 | 1983-04-28 | Thermoelectric device and method of making same |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US4459428A (en) |
| JP (1) | JPS58212377A (en) |
| AU (1) | AU551394B2 (en) |
| BE (1) | BE896531A (en) |
| CA (1) | CA1199425A (en) |
| DE (1) | DE3314198A1 (en) |
| FR (1) | FR2526228A1 (en) |
| GB (1) | GB2119170A (en) |
| IL (1) | IL68388A0 (en) |
| IN (1) | IN159006B (en) |
| IT (1) | IT1171668B (en) |
| NL (1) | NL8301432A (en) |
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- 1982-04-28 US US06/372,688 patent/US4459428A/en not_active Expired - Lifetime
-
1983
- 1983-04-14 IL IL68388A patent/IL68388A0/en unknown
- 1983-04-19 DE DE19833314198 patent/DE3314198A1/en not_active Withdrawn
- 1983-04-20 AU AU13689/83A patent/AU551394B2/en not_active Expired - Fee Related
- 1983-04-21 IT IT20728/83A patent/IT1171668B/en active
- 1983-04-21 BE BE0/210606A patent/BE896531A/en not_active IP Right Cessation
- 1983-04-21 FR FR8306538A patent/FR2526228A1/en not_active Withdrawn
- 1983-04-22 IN IN477/CAL/83A patent/IN159006B/en unknown
- 1983-04-22 NL NL8301432A patent/NL8301432A/en not_active Application Discontinuation
- 1983-04-22 JP JP58071316A patent/JPS58212377A/en active Pending
- 1983-04-25 GB GB08311180A patent/GB2119170A/en not_active Withdrawn
- 1983-04-28 CA CA000426918A patent/CA1199425A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NL8301432A (en) | 1983-11-16 |
| BE896531A (en) | 1983-08-16 |
| AU1368983A (en) | 1983-11-03 |
| DE3314198A1 (en) | 1983-11-03 |
| FR2526228A1 (en) | 1983-11-04 |
| GB8311180D0 (en) | 1983-06-02 |
| IL68388A0 (en) | 1983-07-31 |
| IT1171668B (en) | 1987-06-10 |
| IN159006B (en) | 1987-03-07 |
| GB2119170A (en) | 1983-11-09 |
| AU551394B2 (en) | 1986-04-24 |
| IT8320728A0 (en) | 1983-04-21 |
| JPS58212377A (en) | 1983-12-10 |
| US4459428A (en) | 1984-07-10 |
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