U.S. patent application number 09/968394 was filed with the patent office on 2002-06-13 for thermoelectric device and method of manufacture.
Invention is credited to Macris, Chris.
Application Number | 20020069906 09/968394 |
Document ID | / |
Family ID | 24136397 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020069906 |
Kind Code |
A1 |
Macris, Chris |
June 13, 2002 |
Thermoelectric device and method of manufacture
Abstract
A thermoelectric device containing at least one thermoelement
formed by powder metallurgical techniques including, but not
limited to: hot pressing, hot isostatic pressing, press and sinter
and mechanical alloying.
Inventors: |
Macris, Chris; (North Bend,
WA) |
Correspondence
Address: |
Robert A. Jensen
JENSEN & PUNTIGAM, P.S.
1020 United Airlines Bldg.
2033 Sixth Avenue
Seattle
WA
98121-2584
US
|
Family ID: |
24136397 |
Appl. No.: |
09/968394 |
Filed: |
October 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09968394 |
Oct 1, 2001 |
|
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09535931 |
Mar 24, 2000 |
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Current U.S.
Class: |
136/203 ;
136/201; 136/205; 62/3.3; 62/3.5; 62/3.6 |
Current CPC
Class: |
H01L 2224/16225
20130101; H01L 35/34 20130101; H01L 2224/73253 20130101; Y10S
257/93 20130101; H01L 35/32 20130101 |
Class at
Publication: |
136/203 ;
136/205; 136/201; 62/3.3; 62/3.5; 62/3.6 |
International
Class: |
H01L 035/28; H01L
035/30; H01L 035/34; H01L 037/00; F25B 021/02 |
Claims
1. A thermoelectric device containing at least one thermoelement
formed by powder metallurgical techniques wherein each
thermoelement has a leg length range, in centimeters, equal to:
(K+0.026 centimeters) to (K+0.061 centimeters), wherein K is the
thermoelement material's thermal conductivity value, given in
watts/centimeter per degree Celsius.
2. A thermoelectric device design, providing at least one wafer
containing at least two through-hole cavities to accept
thermoelements, wherein the wafer thickness is equal to or less
than 0.125 centimeters.
3. A thermoelectric device design, as in claim 2, wherein the wafer
is composed of a metallic material.
4. A thermoelectric device design, as in claim 2, wherein the wafer
is composed of a non-ferrous metallic material.
5. A thermoelectric device design, as in claim 2, wherein the walls
of the wafer through-holes are coated with an electrically
conductive material.
6. A thermoelectric device design, as in claim 2, wherein the walls
of the wafer cavities are oxidized to mitigate the formation of an
intermetallic layer on the thermoelements.
7. A method of manufacturing a thermoelectric device, including at
least one thermoelement, one heat rejecting interconnection member,
one heat absorbing interconnection member, one wafer containing at
least two through holes, each containing dissimilar thermoelectric
material comprising the steps of: a. Simultaneously dispensing one
type of thermoelectric element materials to at least two wafer
through holes; b. Simultaneously cold compacting more than one
thermoelement with the wafer; c. Covering each wafer face with a
heat resistant material; d. Apply hot isostatic pressure to the
entire covered wafer; e. Removing the covering; f. Cleaning and
electrochemically activating the entire wafer surface including the
exposed faces of each thermoelement; g. Plating the entire wafer
surface including all exposed faces of each thermoelement; h.
Bonding a metallic sheet to each face of the wafer via the plated
layer; i. Chemically removing part of each metallic sheet and all
of the wafer material; j. Mounting the completed device to a
substrate.
8. A method of manufacture, as in claim 7, wherein the wafer is a
metallic material.
9. A method of manufacture, as in claim 7, wherein the
thermoelement material is in powder form.
10. A method of manufacture as in claim 7, wherein the
thermoelement materials is in tablet form.
11. A method of manufacture, as in claim 7, wherein step (a)
involves the use of a squeegie for the dispensation of the
thermoelement powders.
12. A method of manufacture, as in claim 7, wherein the step (c)
covering is a metallic foil.
13. A method of manufacturing, as in claim 7, wherein the
thermoelement material in step (a) is a mixture of metallic
elements which, following step (d) will become the resultant P and
N-type thermoelement compounds.
14. A method of manufacture, as in claim 7, wherein step (d)
involves the use of pressureless sintering (heat only).
15. A method of manufacture, as in claim 7, wherein step (g)
utilizes a metallic spraying process in lieu of the electroplating
and/or metallic sheet in steps (g) and (h) respectively.
16. A method of manufacture, as in claim 7, which utilizes a
conversion coated (anodized) substrate.
17. A method of manufacturing a thermoelectric device, including at
least one thermoelement, an envelope or covering, one wafer
containing at least two through holes, each containing dissimilar
thermoelectric material wherein a pressurized liquid gas is
utilized to compact the thermoelements by applying pressure against
the envelope which is in direct contact with each
thermoelement.
18. A method of manufacturing a thermoelectric device, including at
least one perforated metallic substrate with two or more through
holes (filled with dissimilar thermoelement material) in which the
completed device is bonded to a perforated metallic substrate.
19. A method of manufacture, as in claim 18, which utilizes a
conversion coated (anodized) substrate.
20. A method of manufacture, as in claim 18, in which the bonding
is accomplished through the use of an adhesive.
21. A method of manufacturing a thermoelectric device, including at
least one thermoelement, reusable magnetic mask material and at
least one wafer wherein the prepatterned magnetic mask is placed on
each face of the wafer for subsequent chemical processing.
22. A method of manufacturing a thermoelectric device, including at
least one thermoelement, one wafer containing at least two
through-holes, each containing thermoelement material and at least
one sheet of deformable material wherein the wafer and sheet of
deformable material are stacked, such that the deformable material
interfaces the exposed thermoelement faces, and subjected to heat
and pressure, thereby causing the deformable material to deform and
compress the thermoelement material into the wafer
through-holes.
23. A method of manufacturing a thermoelectric device, as in claim
22, wherein the sheet of deformable material is comprised of
aluminum.
24. A method of manufacturing a thermoelectric device, including at
least one thermoelement, one wafer containing at least two
through-holes, each containing P and N-type thermoelement material
wherein both the P and N-type thermoelement materials are hot
isostatic pressed simultaneously.
25. A method of manufacturing a thermoelectric device, as in claim
24, wherein both the P and N-type thermoelement materials are hot
pressed simultaneously.
26. A method of manufacturing a thermoelectric device, including at
least one thermoelement, in which the surface preparation of each
thermoelement for interconnection bonding comprises: a. Immersion
of the thermoelements into an alkaline solution; b. Making the
thermoelements anodic through the application of an external
positive polarity voltage to the thermoelements; c. Completing the
electrical circuit within the alkaline solution by applying the
external negative voltage polarity to a metallic member, now made
cathodic; d. Removal of thermoelements from the alkaline solution
and removal of their remaining surface layer residue
chemically.
27. A method of manufacturing, as in claim 26, wherein the alkaline
solution is a solution containing chromic acid.
28. A method of manufacturing a thermoelectric device, including at
least one thermoelement, in which the surface preparation of each
thermoelement for interconnection bonding comprises: a. Immersion
of the thermoelements into an acidic solution; b. Making the
thermoelements cathodic through the application of an external
negative polarity voltage to the thermoelements; c. Completing the
electrical circuit within the alkaline solution by applying the
external positive voltage polarity to a metallic member, now made
anodic; d. Plating a metallic layer on each surface of the
thermoelements.
29. A method of manufacturing, as in claim 28, wherein the acidic
solution is a solution containing sulfuric acid.
30. A method of manufacturing, as in claim 28, where the
thermoelement surfaces are subjected to a current density greater
than 150 amps per square foot of negatively charged surface area in
the solution.
31. A method of manufacturing, as in claim 28, wherein the
electrical potential applied to the thermoelements in steps (a)
through (d) is applied prior to immersion of the thermoelements
into each solution.
32. A method of manufacturing a thermoelectric device, including at
least one thermoelement comprising: a. Depositing a bismuth layer
on each junction face of the P and N-type thermoelements; b.
Melting and solidifying the bismuth layer; c. Depositing a metallic
layer on the bismuth layer.
33. A method of manufacturing, as in claim 32, wherein step (a)
utilizes plating to deposit the bismuth layer.
34. A method of manufacturing a thermoelectric device, including at
least one thermoelement, in which the removal of surface layers
between the hot and cold junctions of each thermoelement comprises:
a. Immersion of the thermoelements into a corrosive solution; b.
Making the thermoelements anodic through the application of an
external positive polarity voltage to the thermoelements; c.
Completing the electrical circuit within the corrosive solution by
applying the external negative voltage polarity to a metallic
member, now made cathodic; d. Removal of thermoelements from the
corrosive solution and removal of their remaining surface layer
residue chemically.
35. A method of manufacturing, as in claim 34, wherein the solution
contains chromic acid.
36. A method of manufacturing, as in claim 34, wherein step (b)
polarity is negative and the step (c) polarity is positive.
37. A method of manufacturing a thermoelectric device, including at
least one thermoelement, wherein the thermoelement materials, in
powder form, are coated with boric acid prior to thermal processing
(sintering, hot pressing, etc.) to getter surface oxides.
38. A wearable thermoelectric-based heating and cooling therapy
apparatus design, including at least one thermoelectric device and
a thermal storage medium wherein one face of the thermoelectric
device interfaces the source to be heated or cooled (wearer) and
the opposite face of the thermoelelctric device interfaces a
thermal storage medium.
39. A wearable thermoelectric-based heating and cooling therapy
apparatus design, as in claim 38, wherein the thermal storage
medium is a polymer-based material.
40. A wearable thermoelectric-based heating and cooling therapy
apparatus design, as in claim 38, wherein the thermal storage
medium is a elastomer-based material.
41. A wearable thermoelectric-based heating and cooling therapy
apparatus design, as in claim 38, wherein the thermal storage
medium is a ceramic-based material.
42. A wearable thermoelectric-based heating and cooling therapy
apparatus design, as in claim 38, wherein the thermal storage
medium comprises a phase change material.
43. A thermoelectric-based system design for conditioning the
ambient air drawn through an enclosure comprising: a. Establishing
an airflow through the enclosure; b. Conditioning the input
airstream to the enclosure with a thermoelectric device.
44. A thermoelectric-based system design for conditioning the
ambient air drawn through an enclosure, as in claim 43, wherein the
enclosure houses heat generating electronics.
45. A thermoelectric-based system design for conditioning the
ambient air drawn through an enclosure, as in claim 43, wherein the
enclosure houses heat generating electronics.
46. A thermoelectric-based system design for conditioning the
ambient air drawn through an enclosure, as in claim 43, wherein the
enclosure's airstream exhaust, or discharge air, is directed over
one face of the thermoelectric device.
Description
TECHNICAL FIELD
[0001] This invention relates to the field of thermoelectric
devices and, more particularly, to a thermoelectric device wherein
the device consists of thermoelements and interconnects of unique
design which maximize performance while minimizing the use of
costly thermoelectric material and further results in a reduction
in the number of fabrication steps.
[0002] In one embodiment of the present invention, a metallic or
semi-metallic support, termed a "wafer", allows powdered
thermoelement material to be processed and facilitates the bonding
of these formed elements to their respective interconnection
members. Additionally, novel substrate and bonding techniques are
also disclosed.
[0003] Other embodiments of the present invention include unique
techniques relating to thermoelement surface preparation and
bonding.
[0004] Lastly, other embodiments of the present invention relate to
the application of thermoelectric devices in the medical therapy
and electronics thermal management fields.
BACKGROUND OF THE INVENTION
[0005] Conventional thermoelectric devices utilize dissimilar
conductive materials subjected to a temperature gradient across
their leg lengths to create an EMF or electromotive force. This EMF
is proportional to the intrinsic thermoelectric power of the
thermoelements employed and the temperature differential between
the hot and cold junctions. Alternatively, current may be
introduced into the circuit to move heat, absorbing it at one
junction, moving it and dissipating it at the other junction.
[0006] It is desirable that the thermoelements be of such material
that the highest EMF is developed for a given temperature
differential between the hot and cold junctions. The electrical
resistivity and thermal conductivity of the thermoelement in the
device should be as low as possible in order to reduce both
electrical and thermal losses and thus increase the efficiency.
[0007] One disadvantage of current thermoelectric devices is the
high cost of the semiconducting materials, which yield the highest
conversion efficiencies available. A reduction in a thermoelement's
cross sectional area not only reduces material volume, but
increases electrical resistance proportionately. A reduction of
element leg length reduces material volume and decreases electrical
resistance, but it becomes increasingly difficult to maintain a
temperature differential as this leg length is decreased to the
point where an impracticable heat exchange mechanism is required to
remove the heat faster than it is entering the thermoelectric
device. This is due to the thermal conduction characteristics of
the thermoelement material. Secondly, as leg lengths are further
reduced, fabrication of the thermoelements themselves becomes
increasingly difficult due to the semiconductor's fragile
nature.
[0008] U.S. Pat. No. 3,129,117, granted to Harding on Apr. 14,
1964, discloses a method of manufacturing a thermoelectric element
utilizing hot pressing in a direction perpendicular to current flow
through the thermoelement.
[0009] U.S. Pat. No. 3,182,391, granted to Charland on May 11,
1995, discloses a process for forming, in one step, a thermoelement
with a metallic electrical contact at one end, which comprises
consolidating the thermoelectric material and metallic contact
plate within a die cavity which is then hot pressed and removed
from the mold cavity.
[0010] U.S. Pat. No. 3,201,504, granted to Stevens on Aug. 17,
1965, discloses a method of molding a thermoelectric couple in
which dielectric sleeve members are inserted into a mold containing
a conductive bottom member, powdered dissimilar thermoelectric
material is added into their respective sleeves, powdered conductor
is placed on top of both thermoelements, and pressing and
subsequent sintering of the entire assembly yield a solid
thermocouple.
[0011] U.S. Pat. No. 3,248,777, granted to Stoll in August of 1966,
also discloses a thermal and electrically insulating material in
which the thermoelements are cast in cavities within this
insulator.
[0012] U.S. Pat. No. 3,264,714, granted to Baer, Jr. in May of
1966, discloses a thermoelectric device in which a block is
composed of thermally and electrically insulating material. This
block may be cut to accept inserted thermoelements or cast from a
liquid or other flowable form around the spaced thermoelements and
hardened. Additionally, the interconnecting members are created by
electroplating over perforated metal and the top faces of each
thermoelement to create the junctions.
[0013] U.S. Pat. No. 3,400,452, granted to Emley on Sep. 10, 1968,
discloses using hot isostatic pressure (even, compressive pressure
in all directions) to provide metallurgical bonding between the
thermoelemental material and the walls of a metal tube in which it
is housed.
[0014] U.S. Pat. No. 3,554,815, granted to Osborn on Jan. 12, 1971,
discloses a device consisting of a thin, flexible substrate in
which "bands" of dissimilar thermoelectric material are disposed on
opposite sides of the substrate and perforations within the
substrate contain a metallic filler to electrically connect each
thermoelement.
[0015] U.S. Pat. No. 3,601,887, granted to Mitchell on Aug. 31,
1971, also discloses the use of hot isostatic pressure to provide
bonding between the inner walls of a tube and the thermoelectric
material.
[0016] U.S. Pat. No. 4,343,960, granted to Eguchi on Aug. 10, 1982,
discloses a device consisting of a perforated dielectric substrate
in which each dissimilar thermoelement is plated, in a pattern, to
portions of both faces and to the walls of each thru-hole.
[0017] U.S. Pat. No. 4,459,428, granted to Chou on Jul. 10, 1984,
relates to the design and manufacture of a thermoelectric device
wherein the voids between each thermoelement are filled with a
ceramic compound to absorb thermal expansion. Additionally, copper
plates, which will later comprise the bus bars, are soldered
directly to each thermoelement end and then masked and etched to
form the discrete interconnects, each bridging two dissimilar
thermoelements.
[0018] U.S. Pat. No. 4,470,263, granted to Lehovee, et al on Sep.
11, 1984, relates to a peltier cooled garment in which the heat
pumped by the peltier unit is dissipated to the ambient via cooling
fins.
[0019] U.S. Pat. No. 4,905,475, granted to Tuomi on Mar. 6, 1990,
relates to a thermoelectric based personal comfort air conditioning
unit. Ambient air enters and is split to pass over both the hot and
cold faces of the thermoelectric device. Depending on the desired
air temperature by the user, a movable baffle will distribute the
correct amounts of hot and cold air to the individual.
[0020] U.S. Pat. No. 4,930,317, granted to Klein on Jun. 5, 1990,
relates to a thermoelectric based localized hot and cold therapy
apparatus which includes a heat sink and possibly a fan to
dissipate rejected heat.
[0021] U.S. Pat. No. 5,067,040, granted to Fallik on Nov. 19, 1991,
relates to the use of thermoelectric cooling to cool computer
boards within an enclosure. The thermoelectric cooling device is
mounted in an opening through a partition for transferring heat out
of the sealed enclosure.
[0022] U.S. Pat. No. 5,097,828, granted to Deutsch on Mar. 24,
1992, relates to a thermoelectric based therapy device comprising a
heat sink and fan for dissipating heat moved and generated by the
peltier devices.
[0023] U.S. Pat. No. 5,103,286, granted to Ohta on Apr. 7, 1992,
discloses a simultaneous sintering and bonding of the
thermoelements to themselves and to their respective
interconnection members in the absence of pressure. Sintering,
which is the heating of an aggregate of metal particles in order to
create agglomeration, does not involve simultaneous pressure.
[0024] U.S. Pat. No. 5,108,515, granted to Ohta on Apr. 28, 1992,
discloses a Bi, Te, Se, Sb thermoelemental material which is
pulverized to a specific particle size and then forming a green
molding which is then sintered.
[0025] U.S. Pat. No. 5,108,788 and U.S. Pat. No. 5,108,789, both
granted to Rauch, Sr. on Jan. 5, 1988 disclose a PbTe
thermoelemental material in which the compound is: melted, chill
cast into an ingot, ground to a particle size of less than 60 mesh,
cold pressed to 30-70 kpsi, and finally sintered.
[0026] U.S. Pat. No. 5,246,504, also granted to Ohta on Sep. 21,
1993, is nearly identical to what is claimed to U.S. Pat. No.
5,108,515.
[0027] U.S. Pat. No. 5,318,743, granted to Tokiai on Jun. 7, 1994,
discloses to "presinter" a Bi, Te, Se, Sb thermoelemental material,
then mold the presintered powder and sinter the resultant form also
using hot isostatic pressing technology. The actual thermoelements
are then cut from the sintered bulk.
[0028] U.S. Pat. No. 5,429,680, granted to Fuschetti in July of
1995, relates to a nickel diffusion barrier layer coated directly
onto each thermoelement end.
[0029] U.S. Pat. No. 5,434,744, granted to Fritz on Jul. 18, 1995,
discloses a substrated thermoelectric device in which
thermoelemental spacing is less than 0.010 inch and thermoelemental
thickness is less than 0.050 inch. In addition, an improved device
is claimed to have greater than 300 thermoelements and their said
thickness is "approximately" 0.020 inch.
[0030] U.S. Pat. No. 5,623,828, granted to Harrington on Apr. 29,
1997, relates to a thermoelectric air cooling device for the
passenger of a vehicle. A fan, blowing ambient air across both the
hot and cold faces of the thermoelectric device, includes a design
permitting the cold air to blow onto the passenger while the hot
air is exhausted away.
[0031] U.S. Pat. No. 5,800,490, granted to Patz, et al on Sep. 1,
1998, relates to a portable cooling or heating device incorporating
a thermoelectric assembly comprising: a peltier device, gel pack to
interface with the user along with a fan and radiator to dissipate
or absorb thermal energy from the surrounding air.
[0032] U.S. Pat. No. 5,817,188, granted to Yahatz, et al on Oct. 6,
1998, relates to a thermoelectric module comprising thermoelements
whose junctions are coated with bismuth or a bismuth alloy.
Additionally, a solder comprising bismuth and antimony is utilized
to joint the coated thermoelements to conductive interconnecting
bus bars.
[0033] U.S. Pat. No. 5,890,371, granted to Rajasubramanian, et al
on Apr. 6, 1999, relates to a passive and active air conditioning
system for an enclosure housing heat producing equipment. This
closed hybrid system cools the air existing within the heat
producing equipment enclosure housing by recirculating this air
across both a heat pipe device and also a thermoelectric device
which transfers the heat to the ambient air.
[0034] U.S. Pat. No. 5,981,863, granted to Yamashita, et al on Nov.
9, 1999, relates to manufacturing a thermoelement in which molten
thermoelement material is rapidly cooled, powdered and hot pressed
within a range of time, temperature and pressure in order to reduce
grain size, and thus increase material efficiency.
[0035] U.S. Pat. No. 5,987,890, granted to Chiu, et al on Nov. 23,
1999, relates to cooling an electronic component within a portable
computer using a heat pipe or peltier device to move heat from the
electronic component to a thermal reservoir, such as a battery.
[0036] U.S. Pat. No. 6,023,932, granted to Johnstone on Aug. 25,
1999, relates to a portable topical heat transfer device comprising
a thermoelectric unit and heat sink with a fan mounted to the warm
side of the peltier device.
[0037] U.S. Pat. No. 6,025,544, granted to Macris on Feb. 15, 2000,
relates to a block of metallic material into which cavities are
formed and filled with thermoelement material. This material is
compacted and sintered. The resultant block structure is sliced,
electroplated, etched and mounted to form a thermoelectric
device.
[0038] A disadvantage of the existing art is the bond strength
between the typically brittle thermoelements and their
interconnects. In addition, the diffusion of metallic species when
these dissimilar materials are in contact must be mitigated.
Lastly, the bonding structure, between thermoelement and its
respective interconnect, must not itself possess a significant
Seebeck Coefficient so as not to reduce the performance of the two
P and N-type thermoelements.
[0039] A disadvantage to the existing cold therapy technologies
incorporating thermoelectric devices as heat pumps is the means by
which the pumped heat is dissipated from the hot face of the
thermoelectric device. Fans and/or heat sinks are cumbersome and
reduce flexibility of the therapy unit.
[0040] A current disadvantage of the current personal computer or
electronics enclosure cooling art is the complexity and
inefficiency of the systems resulting in high costs.
SUMMARY OF THE INVENTION
[0041] Accordingly, it is the overall object of the present
invention to provide an efficient thermoelectric device, which
minimizes the device fabrication costs through the simplification
of the fabrication process and reduction of materials.
[0042] An additional object of the present invention is to provide
a thermoelectric device fabrication method in which a metallic or
semi-metallic support (termed a wafer) contains several thru-holes.
Dissimilar thermoelectric material is disposed and thermally
processed in these thruholes to yield solid thermoelements.
[0043] Again, another object of the present invention is to provide
a thermoelectric device fabrication method in which the walls of
wafer thru-holes are coated with either elements or compounds to
prevent formation of intermetallic compounds between the
thermoelements and the walls during the fabrication of a
thermoelectric device.
[0044] Yet again, an object of the present invention is to provide
a thermoelectric device fabrication method in which a reusable
magnetic mask is utilized to economically and effectively mask
regions of the wafer during chemical processing.
[0045] Still another object of the present invention is to provide
an economical thermoelectric device fabrication method which
improves the bonding between thermoelement and interconnect through
anodic cleaning/etching and cathodic surface activation in both
acid and alkaline solutions.
[0046] Another embodiment of the present invention is to provide a
thermoelectric device design wherein the completed device utilizes
novel substrates and bonding methods which facilitate economical
fabrication, yet offer high thermal performance and structural
integrity.
[0047] It is another object of the present invention to demonstrate
a formula relating the optimal range of thermoelement leg lengths
given the material's thermal conductivity value. This results in a
drastic reduction in the volume of expensive thermoelement material
required.
[0048] Still another object of the present invention is to provide
an improved thermoelectric-based heating and cooling therapy device
wherein the heat pumped from the source (user) is stored for reuse
rather than dissipated to ambient surroundings and eliminates
cumbersome heat exchangers.
[0049] Another object of the present invention is also to provide
an improvement to existing electronics enclosure air conditioning
by utilizing thermoelectric-based conditioning of an input ambient
airstream flowing through the enclosure. This allows a
thermoelectric device to operate efficiently while reducing the
internal enclosure temperature.
[0050] Lastly, the final overall object of the present invention is
to combine all these unique design aspects and individual
fabrication techniques into an overall method of thermoelectric
device manufacture, which will yield a device of superior
construction and value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] FIGS. 1a through 1m illustrate a method for the fabrication
of the present invention.
[0052] FIG. 2 is a pictorial representation illustrating the use of
a solid, reusable magnetic mask in the fabrication of the present
invention.
[0053] FIGS. 3a through 3c illustrate a method for the
metallization of the thermoelements contained within the present
invention.
[0054] FIG. 4 is a sectional view depicting intermetallic layers
deposited on each thermoelement in the present invention.
[0055] FIG. 5 is a graph of the prior art depicting a series of
optimal leg length ranges based on a relationship between a
thermoelement's Thermal Conductivity value.
[0056] FIG. 6 is a graph illustrating the empirically derived
formula between a powder metal fabricated thermoelement material
Thermal Conductivity value and its optimum thermoelement leg length
range.
[0057] FIGS. 7 and 8 illustrate one application of the present
invention wherein the apparatus is utilized for heating and cooling
therapy.
[0058] FIGS. 9 through 12 illustrate various embodiments for
conditioning an airstream through an enclosure containing
electronic components.
BEST MODE FOR CARRYING OUT THE INVENTION
[0059] To effectively absorb and dissipate heat, in addition to
providing high electrical conductivity to a thermoelectric device,
the interconnects should be of a highly electrical and thermally
conductive material such as copper, aluminum, or their respective
alloys. Optimally speaking, the thermoelement material, composed of
a bismuth-tellurium, bismuth-selenium, antimony-tellurium alloy
composition, is appropriately doped to yield both positive and
negative conductivity type thermoelements.
[0060] FIGS. 1a through 1m illustrate a process flow for the
fabrication of the present invention.
[0061] As shown in FIG. 1a, the structure, termed a "wafer" 5, is
composed of a metallic or semi-metallic material, possibly
non-ferrous based. It contains multiple thruholes formed by either
chemical milling (etching), punching or stamping which will contain
two dissimilar types of thermoelement material. The approximate
thickness (in the finished product) of this wafer will correspond
to the final thermoelement leg length. Due to the processes
involved, the wafer thickness is realistically limited to 0.125
centimeters or less.
[0062] Prior to the dispensation of the thermoelement materials,
the wafer's thru-hole walls may be coated with an oxide of the base
wafer composition or other metallics and compounds including: iron
oxide, nickel, cobalt, tungsten, molybdenum and carbon. Optimally,
the coating is electrically conductive or semi-conductive.
[0063] Depending upon the thermoelement processing temperatures,
i.e. time, temperature and pressure, coupled with the wafer and
thermoelement compositions, an intermetallic layer may form at the
thermoelement thru-hole wall interface. The intermetallic, if left
on the thermoelement, will degrade the performance of the completed
thermoelectric device, therefore, its formation must be prevented,
if formed, must be removed.
[0064] Reference is now made to FIGS. 1b and 1c wherein two similar
mechanisms 9, 16 are utilized to dispense thermoelement material
into multiple thru-holes 7 within the wafer 5. Each mechanism
corresponds to a dissimilar type of thermoelement material which is
placed in alternate rows of thru-holes.
[0065] Thermoelement material may consist of an alloyed and grown
ingot which has been pulverized to yield powdered or granular
stock, or consist of a mixture of the powdered or granular metallic
elements which are unalloyed prior to dispensation. Additionally,
tablets or pellets may be formed with either composition which can
also be dispensed into the wafer's thru-holes.
[0066] In one additional embodiment relating to the preparation of
thermoelement material, a mixture of methanol and boric acid is
applied to the thermoelement powders thereby coating the surface of
each particle. During the sintering process, any surface oxides
present on the particles are "gettered" by the boric acid,
resulting in the formation of borates. This mechanism "cleans' the
surface of each particle and thus, facilitates the bonding of each
particle to the other.
[0067] An empty wafer 5, shown in FIG. 1a, is loaded into the
dispensation mechanism 9 of FIG. 1b, mounted below a stencil-like
cover plate 10 with apertures 12 corresponding to the thru-holes
for one type of thermoelement material 13. The thermoelement
arrangement of the present invention consists of alternating P and
N-type thermoelements. The thermoelement material 13 is then poured
into the stencil reservoir 14 where it is bladed across the stencil
surface by a doctor blade or squeegie-like instrument 15. The wafer
thickness plus the stencil thickness allow for the correct volume
of powder to be dispensed into the thruholes of the wafer.
[0068] When the entire surface of the wafer has been filled and
bladed, the filled holes are then compacted with either a matrices
of metallic press pins or a flat elastomeric pad, both of which
compact the powder thru the stencil apertures and down to the wafer
surface.
[0069] Once compacted, the wafer is removed and transferred to the
second dispensation mechanism 16 in FIG. 1c, which deposits and
compacts the other dissimilar type thermoelement material 19. This
mechanism operates identically to the previous unit in FIG. 1b,
however, its stencil apertures 17 correspond to the unfilled
thru-holed 18 which remain with in the wafer.
[0070] The resultant wafer 18, filled with dissimilar type
thermoelements 20, 22, can be seen in FIG. 1d.
[0071] The wafers must now be processed thermally with powder
metallurgical techniques in order to create interparticulate
bonding, resulting in solid, dense thermoelements. The thermally
based powder metallurgical techniques include: hot pressing, hot
isostatic pressing, press and sintering, and mechanical alloying.
The first two processes involve the simultaneous application of
heat and pressure. Press and sinter technology typically applies
heat and pressure in separate steps. Lastly, mechanical alloying
can incorporate heat and pressure simultaneously or as separate,
discrete steps.
[0072] FIG. 1e discloses a method of hot pressing multiple wafers
utilizing sheets of heat resistant material 24. Compressive force
is applied to each thermoelement via their exposed surfaces. A
material, such as aluminum or other metallic sheet or foil, is
stacked alternately with the filled wafers, such that, all exposed
thermoelements 20, 22 are covered by the sheet material 24.
Pressure and heat are applied to the stack by means of a heated
press seen in FIG. 1f. The heat resistant material will deform
under this heat and pressure and transfer compressive force to each
thermoelement from both faces of the wafer.
[0073] In one embodiment of the present invention, a heat resistant
material envelops each wafer face and then is subjected to hot
isostatic pressure. This process utilizes a fluid or gas under
extreme pressure to apply compressive force to the wafer from all
directions. The force is again transferred through the heat
resistant material to each face of thermoelements resulting in a
high degree of density.
[0074] In another embodiment of the present invention, the press
and sinter technique is utilized to densify the thermoelements.
This technique, essentially a "pressureless" sinter process,
eliminates the requirement of a covering material in order to
transfer pressure to each thermoelement face.
[0075] FIG. 1g depicts the wafer 18 and heat resistant covering
material 24 following either the hot pressing or hot isostatic
operation. The heat and pressure has densified each thermoelement
20, 22 thereby reducing their respective thicknesses.
[0076] FIG. 1h depicts the wafer 18 after the removal of the
envelope or covering material 24. Prior to the bonding of
interconnection members, the thermoelement faces must be cleaned
and activated to accept a metallization layer to facilitate bonding
and mitigate diffusion between interconnect and thermoelement.
[0077] Each type of thermoelement material behaves differently to a
particular surface etchant/cleaner and activator requiring a unique
chemistry and process for each material. Both types, however, are
best etched/cleaned and activated electrochemically, in that an
electric potential is applied to the parts while in a conductive,
corrosive solution.
[0078] In one embodiment, the wafer is immersed into an alkaline
solution, preferably sodium or potatassium hydroxide-based. A
positive electric potential (voltage) is applied to the wafer (the
anode) and a negative potential is applied to a metallic member or
electrode (cathode) which is also immersed in the solution. The
wafer with its thermoelement surfaces are exposed to the electric
current via the solution, causing a surface etching of the
elements. The wafer is then rinsed and neutralized to remove the
surface residue and expose clean thermoelement surfaces.
[0079] In another embodiment, the wafer is immersed into a solution
containing chromic acid. The wafer is immersed and electrified as
in the previous embodiment.
[0080] Following the surface etching and cleaning of the
thermoelements, a metallic layer must next be deposited. The
bismuth-tellurium alloy thermoelement materials, however, easily
forms surface oxides, creating a passive condition. Therefore, it
is necessary to activate these surfaces in order to achieve an
adherent metal layer.
[0081] Cathodic activation, wherein the wafer is connected to a
negative electric potential (cathode), has been found empirically
to effectively activate the tenacious thermoelement surfaces. The
wafer is immersed into an acidic solution, preferably containing
sulfuric acid, and connected to the negative potential terminal of
a power supply. A metallic electrode, also immersed, completes the
electrical circuit through its connection with the positive
terminal of the power supply. Optimally, the wafer is subjected to
an electric current density greater than 150 amps per square foot
of total negatively charged surface area exposed in the
solution.
[0082] Immediately following the cathodic activation step, the
entire wafer is subjected to either electro less or electroplating,
as seen in FIG. 11, which deposits a continuous metallic layer 25
over the entire wafer surface the electroplating and cathodic
activation electric potential is to be applied prior to immersion
so as to not passivate, or oxidize the thermoelement surfaces.
[0083] FIG. 1j introduces a metallic sheet 30 which is soldered 31
to each face of the wafer 18 via the metallized layer 25. The
metallic sheets 30, preferably comprised of highly thermal and
electrically conductive material, will ultimately comprise the
interconnection members.
[0084] In one embodiment, a molten or semi-molten metallic spraying
process, such as plasma or flame spraying is utilized to build a
metallic deposit in lieu of the metal layers 25, 30, 31 plated
and/or soldered in FIGS. 1l and 1j.
[0085] Within FIG. 1k, it can be seen that an etch resistant mask
34 has been applied over select regions of the metallic sheet 30 in
order to protect the eventual interconnection members from chemical
attack. Typically, a screen or stencil preinked mask, or "resist",
is employed, which may later be stripped chemically.
[0086] In one embodiment of the presents invention, a reusable,
solid magnetic mask 40 (FIG. 2) is utilized on both faces of the
wafer 18 in lieu of printed resists. The masks are die or laser cut
from flexible magnetic material composed of ferrites in a polymer
binder. These masks can be utilized in both plating and chemical
etching operations.
[0087] As seen back in FIG. 11, the unmasked regions of the
metallic sheet 36 have been subjected to a selective chemical
etchant to remove regions of the metal layers and wafer in order to
create completed thermocouples 45.
[0088] Lastly, FIG. 1m contains the series thermocouples 45, minus
the etch mask 34, ready to be mounted to a structurally supporting
substrate. Bonding may be accomplished through the use of a
thermally and/or electrically conductive adhesive, such as an
epoxy. Additionally, mechanical clamping between two substrates may
also be employed.
[0089] In one embodiment, a perforated metallic substrate is
utilized in order to reduce weight and also to facilitate handling
of the fragile thermocouples following the etching step.
[0090] The metallic substrates, whether perforated or solid, may be
subjected to an anodizing or conversion coating process to create a
dielectric surface layer in order to prevent any electrical
"shorting" between the mounted thermocouples.
[0091] FIGS. 3a through 3c illustrate an alternate embodiment
wherein a bismuth layer 26 is either electrolessly (immersion) or
electroplated on each thermoelement surface.
[0092] FIG. 3a depicts a filled wafer 18 prior to
metallization.
[0093] In FIG. 3b, the bismuth layer 24 deposited onto the wafer 18
is then reflowed, or melted and solidified in order to increase the
bond strength to the thermoelements. This reflow technique creates
an alloyed bond which penetrates each thermoelement, resulting in
higher bond strength over standard metallization techniques.
[0094] Reference is now made to FIG. 3c, wherein the cathodic
activation and electroless/electroplating techniques, from the
previous embodiments, are employed to deposit an additional
adherent metal layer 28 over the reflowed bismuth layer 26. This
metal layer 28 permits the attachment of the interconnection member
layers via soldering while mitigating any diffusion between
dissimilar materials.
[0095] Next, as seen in FIG. 4, the completed series thermocouples
45 may contain an intermetallic layer 50 bonded along the leg
lengths of each thermoelement 20, 22. If left, this layer will
degrade the performance of the thermocouples by creating a partial
electrical short between the hot and cold junctions.
[0096] In one embodiment electrochemical removal is employed by
immersing the thermocouple assembly into an alkaline or acidic
solution and applying either a positive or negative potential
(voltage) to this assembly. An immersed electrode completes the
electrical circuit by accepting the voltage polarity opposite that
of the thermocouple assembly. After removal from the solution, the
assembly is chemically treated and rinsed to eliminate any
residues. One effective solution for the intermetallic removal
contains chromic acid.
[0097] With respect to FIG. 5, reference is made to U.S. Pat. No.
6,025,554, granted to Macris Feb. 15, 2000, wherein the prior art
depicts the derived relationship between any thermoelement's leg
length and its particular thermal conductivity value. When this
value is given in watts/centimeter per degress Celsius, for any
thermoelectric material, the optimum thermoelement leg length 54 is
equal to that particular thermal conductivity value with a leg
length tolerance.
[0098] As seen in FIG. 6, an optimized range of thermoelement leg
lengths 55 is disclosed, given the thermoelement material's thermal
conductivity value (K), in watts/centimeter per degree Celsius.
Through the use of thermoelements formed by powder metallurgical
techniques, such as: hot pressing and sintering, hot isostatic
pressing and mechanical alloying, an empirically derived formula
was developed. Each thermoelement has a leg length range 55, in
centimeters equal to:
[0099] (K+0.026 centimeters) to (K+0.061 centimeters).
[0100] Reference is now made to FIG. 7 wherein an application of
thermoelectric devices is depicted. A wearable heating and cooling
therapy device 65, consisting of: thermoelectric devices 60, a
thermally conductive compliant layer 61 interfacing the wearer, a
flexible thermally insulating layer 62 and a flexible thermal
storage medium 63.
[0101] When it is desirable to cool selected portions of the
wearer's body (FIG. 8), the thermoelectric devices will "pump" heat
away from the user via the compliant layer 61 to the thermal
storage medium 63. The insulating layer 62 maintains the
temperature differential, established by the thermoelectrics 60,
between the wearer and the storage medium 63. A reversal in the
polarity will cause the stored thermal energy in the storage medium
63 to be transferred to the user when heat therapy is desired.
[0102] In one embodiment, the thermal storage medium 63 may be
comprised of a phase-change material which will accommodate
additional thermal energy (per pound of medium) without
significantly raising the temperature of the thermal storage
medium. This is accomplished through the transformation from one
"phase", or form, to another when thermal energy is absorbed. For
example, a liquid phase change material (liquid at room
temperature), may absorb an order of magnitude or more thermal
energy (before its full phase transformation to a gas phase) than
an equivalent weight quantity of non-phase change material without
increasing its actual temperature.
[0103] Other embodiments include the use of polymer-based,
elastomer-based or ceramic-based materials in the construction of
the thermal storage medium 63.
[0104] Next, as seen in FIGS. 9 through 12, various embodiments are
disclosed for an additional application of thermoelectric devices
whereby the incoming airstream, through an electronics containing
enclosure, is conditioned, or cooled.
[0105] FIG. 9 displays the current construction and action of the
prior art. An enclosure 70, which may house various electronic
components and assemblies 72, 73, typically draws ambient air 71
throughout the enclosure to aid in the dissipation of heat
generated by the electronics 72, 73. A fan assembly 75, usually
located within the enclosure 70, draws this ambient air 71 past the
electronics and exhausts the heated airstream 74 back to
ambient.
[0106] Within FIG. 10, an assembly comprising a thermoelectric
device 80, a hot face heat sink 82 and cold face heat sink 81 is
mounted in front of the ambient air inlet 69 to the enclosure 70.
Ambient air 71 is actively drawn through the cold face heat sink 81
by the fan assembly 75. The thermoelectric device 80 cools this
incoming ambient airstream 71, thereby dropping the air temperature
upon entry into the enclosure. The cooled airstream 77 increases
the thermal transfer efficiency between the electronics 72, 73 and
the airstream 77. The heated air 74 is exhausted back to ambient.
The hot face heat sink 82 dissipates its pumped thermal energy
passively to ambient.
[0107] FIG. 11 illustrates an embodiment of the present invention
whereby the heated airstream 74, exhausted by the fan assembly 75,
is ducted and blown across the hot side heat sink 82, of the
thermoelectric device 80, increasing the heat dissipation of this
82 to ambient.
[0108] FIG. 12 depicts an additional embodiment wherein a fan
assembly 71 is mounted "upstream" from the thermoelectric device 80
and heat sinks 81, 82. The ambient airstream 71 is pushed through
the heat sinks 81, 82 and the enclosure 70 where the heated
airstream 74 is exhausted.
* * * * *