U.S. patent application number 14/179549 was filed with the patent office on 2014-06-12 for thermoelectric evaluation and manufacturing methods.
This patent application is currently assigned to Jon Murray Schroeder. The applicant listed for this patent is Gerald Phillip Hirsch, Jon Murray Schroeder. Invention is credited to Gerald Phillip Hirsch, Jon Murray Schroeder.
Application Number | 20140163714 14/179549 |
Document ID | / |
Family ID | 43067517 |
Filed Date | 2014-06-12 |
United States Patent
Application |
20140163714 |
Kind Code |
A1 |
Schroeder; Jon Murray ; et
al. |
June 12, 2014 |
THERMOELECTRIC EVALUATION AND MANUFACTURING METHODS
Abstract
A means for determining the electrical resistance and
resistivity of thermoelectric material allows quality control at
all steps in the construction of a bismuth telluride and antimony
telluride thermoelectric generator. The method involves measuring
negative thermoelectric voltage with no current flowing and then a
measure of negative thermoelectric voltage while forcing known
current through the material in the same direction as shorted to
accurately determine thermoelectric resistance. A manual and
automatic method of manufacturing thermoelectric rings using
forcing current for in-process testing means.
Inventors: |
Schroeder; Jon Murray;
(Leander, TX) ; Hirsch; Gerald Phillip;
(Clarksville, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schroeder; Jon Murray
Hirsch; Gerald Phillip |
Leander
Clarksville |
TX
TN |
US
US |
|
|
Assignee: |
Schroeder; Jon Murray
Leander
TX
|
Family ID: |
43067517 |
Appl. No.: |
14/179549 |
Filed: |
February 12, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12454377 |
May 18, 2009 |
8688390 |
|
|
14179549 |
|
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Current U.S.
Class: |
700/109 ;
136/201 |
Current CPC
Class: |
H01L 35/34 20130101;
G05B 23/02 20130101; Y10T 29/49004 20150115; G01R 27/08
20130101 |
Class at
Publication: |
700/109 ;
136/201 |
International
Class: |
G05B 23/02 20060101
G05B023/02 |
Claims
1-43. (canceled)
44. An automated method for assembling and testing a ring of
coupons adapted for inclusion in a thermoelectric generator, the
method comprising steps of: A. robotically assembling an un-bonded
coupon that includes at least: i. a pair of wafers; ii. hot fin
that is juxtaposed on one side thereof with one of the wafers; and
iii. a cold fin that is juxtaposed on one side thereof with the
wafer that is juxtaposed with the hot fin; B. using a computer,
testing electrical resistance of said un-bonded coupon by: i.
robotically attaching a volt meter to said un-bonded coupon via a
probe; ii. robotically connecting an amp meter in series with said
un-bonded coupon; iii. without any external electrical current
applied to the un-bonded coupon, using the volt meter to measure a
first voltage produced by said un-bonded coupon; iv. while applying
a known forced electrical current externally through said un-bonded
coupon in a direction current would flow if the un-bonded coupon
were short circuited, using the amp meter to measure the forced
current, and using the volt meter to measure a second voltage of
said un-bonded coupon; and v. calculating electrical resistance for
said un-bond coupon using: a. the first voltage measured in step
B.iii. above while no external current flows through said un-bonded
coupon; b. the second voltage measured in step B.iv. while the
forced current flows through said un-bonded coupon; and c. the
known, externally applied forced current flowing through the
un-bonded coupon measured in step B.iv. using the amp meter; C. if
the electrical resistance calculated for said un-bonded coupon is
less than a pre-established coupon resistance threshold,
transferring the un-bonded coupon to a furnace for bonding; D.
repeating steps A. through C. until a number of un-bonded coupons
required for assembling said ring have been bonded; E. robotically
assembling the bonded coupons into said ring of coupons; F. using a
computer, testing electrical resistance of said un-bonded ring of
bonded coupons by: i. robotically attaching a volt meter output
terminals of said un-bonded ring of bonded coupons; ii. robotically
connecting an amp meter in series with output terminals of said
un-bonded ring of bonded coupons; iii. without any external
electrical current applied to the un-bonded ring of bonded coupons,
using the volt meter to measure a first voltage produced by said
un-bonded ring of bonded coupons; iv. while applying a known forced
electrical current externally through said un-bonded ring of bonded
coupons in a direction current would flow if the un-bonded ring of
bonded coupons were short circuited, using the amp meter to measure
the forced current, and using the volt meter to measure a second
voltage of said un-bonded ram of bonded coupons; and v. calculating
electrical resistance for said un-bonded ring of bonded coupons
using: a. the first voltage measured in step F.iii. above while no
external current flows through said un-bonded ring of bonded
coupons; b. the second voltage measured in step F.iv. while the
forced current flows through said un-bonded ring of bonded coupons;
and c. the known, externally applied forced current flowing through
the un-bonded ring of bonded coupons measured in step F.iv. using
the amp meter; and G. if the electrical resistance of said
un-bonded ring of bonded coupons is less than a pre-established
ring resistance threshold, transferrin the un-bonded ring of bonded
coupons to a furnace for bonding.
45. The automated method for assembling and testing of claim 44
comprising an additional step of: H. estimating electrical power
output producible by said un-bonded coupon using: i. the first
voltage measured for said un-bonded coupon in step B.iii.; and ii.
the electrical resistance of said un-bonded coupon calculated in
step B.v.
46. The automated method for assembling and testing of claim 44
comprising additional steps of while measuring the first voltage in
step B.iii, and while measuring the second voltage in step B.iv.:
H. heating hot fin of the un-bonded coupon; and I. cooling cold fin
of the un-bonded coupon.
47. The automated method for assembling and testing of claim 46
comprising an additional step of: J. estimating electrical power
output producible by said un-bonded coupon using: i. the first
voltage measured for said un-bonded coupon in step B.iii.; and ii.
the electrical resistance of said un-bonded coupon calculated in
step B.v.
48. The automated method for assembling and testing of claim 44
comprising an additional step of: H. estimating electrical power
output producible by said un-bonded ring of coupons using: i. the
first voltage measured for said un-bonded ring of coupons in step
F.iii; and ii. the electrical resistance of said un-bonded ring of
coupons calculated in step F.v.
49. The automated method for assembling and testing of claim 44
comprising additional steps of while measuring the first voltage in
step F.iii, and while measuring the second voltage in step F.iv.:
H. heating hot fins included in all of the coupons of the un-bonded
ring; and I. cooling cold fins included in all of the coupons of
the un-bonded ring.
50. The automated method for assembling and testing of claim 49
comprising an additional step of: J. estimating electrical power
output producible by said un-bonded ring of coupons using: i. the
first voltage measured for said un-bonded ring of coupons in step
F.iii.; and ii. the electrical resistance of said un-bonded ring of
coupons calculated in step F.v.
51. The automated method for assembling and testing a ring of
coupons adapted for inclusion in a thermoelectric generator of
claim 44 comprising an additional step of: H. using a computer,
testing electrical resistance of said bonded ring of coupons by: i.
robotically attaching a volt meter output terminals of said
un-bonded ring of bonded coupons; ii. robotically connecting an amp
meter in series with output terminals of said un-bonded ring of
bonded coupons; iii. without any external electrical current
applied to the un-bonded ring of bonded coupons, using the volt
meter to measure a first voltage produced by said un-bonded ring of
bonded coupons; iv. while applying a known forced electrical
current externally through said un-bonded ring of bonded coupons in
a direction current would flow if the un-bonded ring of bonded
coupons were short circuited, using the amp meter to measure the
forced current, and using the volt meter to measure a second
voltage of said un-bonded ring of bonded coupons; and v.
calculating electrical resistance for said un-bonded ring of bonded
coupons using; a. the first voltage measured in step H.iii. above
while no external current flows through said un-bonded ring of
bonded coupons; b. the second voltage measured in step H.iv. while
the forced current flows through said un-bonded ring of bonded
coupons; and c. the known, externally applied forced current
flowing through the un-bonded ring of bonded coupons measured in
step H.iv. using the amp meter.
52. The automated method for assembling and testing of claim 51
comprising an additional step of: I. estimating electrical power
output producible by said bonded ring of coupons using: i. the
first voltage measured for said bonded ring of coupons in step
H.iii.; and ii. the electrical resistance of said bonded ring of
coupons calculated in step H.v.
53. The automated method for assembling and testing of claim 51
comprising additional steps of while measuring the first voltage in
step H.iii. and while measuring the second voltage in step H.iv.:
I. heating hot fins included in all of the coupons of the bonded
ring; and J. cooling cold fins included in all of the coupons of
the bonded ring.
54. The automated method for assembling and testing of claim 53
comprising an additional step of: K. estimating electrical power
output producible by said bonded ring of coupons using: i. the
first voltage measured for said bonded ring of coupons in step
H.iii.; and ii. the electrical resistance of said bonded ring of
coupons calculated in step H.v.
Description
RELATED APPLICATIONS
[0001] Several related applications disclose details for the
manufacture of components of bismuth-telluride based thermoelectric
elements that comprise thermoelectric generators and thermoelectric
chillers. Application Ser. No. 11/517,882 is entitled
"Thermoelectric device with make-before-break high frequency
converter". United States Patent Application 20030217766 is
entitled "Torus semiconductor thermoelectric device" filed Nov. 27,
2003. Improved thermoelectric generators and thermoelectric chiller
devices are disclosed in pending patent application Ser. No.
11/259,922 entitled "Solid state thermoelectric power converter"
and Ser. No. 11/364,719 entitled "Bismuth-Tellurium and
Antimony-Tellurium-Based Thermoelectric Chiller".
TECHNICAL FIELD
[0002] This invention relates to methods of assembly and novel
testing procedures for the efficient manufacture of thermoelectric
generators and thermoelectric chillers. With regard to the testing
of components at various stages of manufacture unique methods allow
reliable data for producing finished products with few defects.
Various classical electrical evaluation methods are normally used
for determining thermoelectric properties. Improved methodology
involves thermoelectric material operated under heat flow
conditions while measuring negative, resistive performance.
BACKGROUND ART
[0003] The classical way to measure semiconductor and
thermoelectrics alike has been to apply a voltage to "force
current" through material while measuring voltage drop over a
distance through a cross section to determine bulk resistance. The
semiconductor industry was founded using V/I, 4-point probe methods
to determine material resistance. From a determination of R, it is
simple to mathematically determine bulk material resistivity based
on resistance and physical dimensions. From Ohm's law, we know that
I=V/R, R=V/I, R=resistance, V=voltage, and I=current. R=.rho.l/A,
where .rho.=resistivity, l=length, and A=area. Using the same
equation, and with careful attention to units;
[0004] .rho.=R A/l, so given the measured R and the dimensions of
the material under the probes, the resistivity .rho. (in Ohm-cm)
can be easily determined. This methodology has been the gold
standard for R and .rho. determination for germanium, silicon, and
some III-V compounds in semiconductor technology. However, this
method has been found to be in error when thermoelectric materials
are measured. Measurement values for thermoelectric material have
been found to be off by a factor of 2 and more on the high
side.
[0005] There are problems associated with thermoelectric material
measurement. Applying voltage to material under test seems to cause
the material to develop a counter voltage that inhibits current
flow in thermoelectric material thus changing the expected
measurement. Some investigators have suggested pulse methods for
determining resistivity measurements, thinking that measurements
taken with very short voltage pulses might get around the material
disturbance. Errors are found using direct current, pulse, and low
and high frequency alternating current methods of measure.
[0006] The following disclosure details a method that accurately
predicts satisfactory the performance of components as well as the
final properties of thermoelectric generators and chillers. A very
simple measuring method that predicts exactly the performance of
thermoelectric devices is based on operating the thermoelectric
material under conditions that simulate actual solid state
generator and chiller operation. With thermoelectric material tests
under high current operation, the negative resistance
characteristics of the material can be accurately determined.
Negative resistance was found to have the same V/I slope regardless
of the temperature difference, .DELTA.T, and the voltage current
ratio, V/I that was measured. Once .DELTA.T is established in
material when measuring negative resistance of thermoelectric
material connected to large mass copper heat source and sink,
changes in .DELTA.T occur very slowly, allowing time to make
accurate determination of current, and reduced negative voltage
caused by the current flow. From measurements of -V.sub.1, the
voltage when the current, I=0 and -V.sub.2, the voltage when
current is allowed to flow, and the current, I.sub.(at -V2), the
current at voltage V.sub.2 still at temperature .DELTA.T, the
negative resistance slope can be easily determined, including the
zero-voltage-crossing for material with a particular .DELTA.T. By
forcing current to flow through thermoelectric material with
.DELTA.T induced, accurate in-process material measurements can be
made. In-process material measurements are absolutely essential to
successful, low cost manufacture of solid state generators and
chillers, because completed solid state generators and chillers are
composed of many elements and ohmic connections. Any element found
faulty in assembly can be exchanged for one that performs to
specification.
[0007] Accurate measurements of thermoelectric material can be made
by using the forcing current method to determine negative
resistance for heated junctions, with or without metal contacts.
Thermoelectric device performance can be measured accurately in
ingot, wafer, coupon, and ring form, before and after contact
bonding. This method can be used during all stages of assembly and
final test, even used for non-destructive evaluation of returned
defective product. Because thermoelectric products consist of an
assembly of large numbers of elements, numbering into the hundreds
and thousands, one faulty or misplaced part can render a
sophisticated, high performance solid state generator or chiller
useless. This measuring invention has the ability to accurately
test elements of the product during assembly, as the product moves
along the assembly line, and this makes all the difference in
having all products shippable at final test, otherwise realize a
less than 10% final test yield.
[0008] This invention relates to a measuring system for determining
negative resistance in thermoelectric material under thermal
operation. Negative voltage measurements made on thermoelectric
material while large current is caused to flow along with heat, is
different than negative voltage measured with the same heat flow
but without current flow. When the current flow through the
thermoelectric material is increased until the negative voltage
produced by a certain .DELTA.T is reduced to zero volts, the
current through the material is at a maximum for the .DELTA.T of
the device under test. Zero crossing current for the material under
test can be increased by increasing .DELTA.T, but the -V/I slope
representing negative resistance of the material will stay the same
as long as current does not exceed 1,000 Ampere per square
centimeter for metal coated contacts. If current through the
material is further increased, the voltage becomes zero and then a
portion of the current flows in the positive resistance region.
With make-before-break shorted ring thermoelectric generator and
chiller devices, the thermoelectric driven ring operates in the
negative resistance region and the up-converter and primary portion
of the circuit operates in the positive resistance region, forcing
current and current drag being equal, or -V=+V. This means -V
measured across the thermoelectric ring will be driving current and
+V measured across the make-before break switch part of the
secondary is dragging with the same polarity as a resistor with
current flowing in the same direction.
[0009] Thermoelectric devices have been used for many years for
specific applications where the simplicity of design warrants their
use despite a low energy conversion efficiency.
[0010] Resistance and resistivity measurements of thermoelectric
material are difficult to make because the act of making
measurements tends to disturb the material in such a way as to
render measured results questionable. When current passes through
bulk thermoelectric material, the current also drags heat with the
current and this disturbs any voltage readings.
[0011] This invention uses heat flow defined by the measuring
system, .DELTA.T determined by the physical dimensions of the
device under test and the heat input and heat removed from the
device by heat sink. The current passing through the device under
test is limited to less than the thermoelectric device could
produce on its own if it were short circuited by a super conducting
wire. This way, the device operates with heat flow and current, the
negative drive voltage at current being less negative than open
circuit. Using only this measured data, all electrical parameters
can be determined. The measuring technique is simple and accurate,
allowing in-process use throughout the assembly, final test and
even provides a non-destructive means to analyze customer
returns.
[0012] Previous to this invention, methods of measure for
thermoelectric material included the "Harman Method", as in T. C.
Harman, J. H. Chan, and M. J. Logan, J. Appl. Phys. 30, 1351
(1957). These methods were previously considered the gold standard
for thermoelectric measurements and investigation.
[0013] A survey of measuring methods was made by J. D. Hinderman,
"Thermoelectric materials evaluation program", 3-M, Saint Paul.
04/1979, NASA/STI Keywords: Evaluation, Technology Assessment,
thermoelectric material, thermoelectricity.
[0014] Material test methods were also outlined by H. Iwasaki, M.
Koyano, Y. Yamamura, and H. Hori, School of Material Science, MIST,
Tatsunokuchi 923-1292, Ishikawa, Japan. Center for Nano Materials
and Technology, MIST, Tatsunokuchi 923-1292, Ishikawa, Japan.
[0015] It is a purpose of this invention to provide an accurate
in-process evaluation method for determining the heat to electrical
energy performance for thermoelectric material beginning with
starting materials, carrying through to assembled and bonded
devices. It is a further purpose of this invention to provide
electrical evaluation for non-bonded and bonded elements that go
into the fabrication of a thermoelectric device. It is a further
purpose of this invention to provide electrical evaluation for
non-bonded and bonded thermoelectric devices at the end points of
manufacture.
[0016] It is a further purpose of this invention to provide details
for manual and automated methods for assembling thermoelectric
generators and chillers.
[0017] It is a further purpose of this invention to disclose unique
manufacturing and assembly aspects for efficient manufacture of
thermoelectric generators and chillers.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 illustrates the first stages of a manual assembly
line method of making thermoelectric rings that provide the current
to be converted to standard AC voltages.
[0019] FIG. 2 illustrates subsequent assembly stages for completion
of a bonded ring of thermoelectric coupons and an up-converter.
[0020] FIG. 3 illustrates the classical method to determine
material resistance in wafer form, as used in the semiconductor
industry.
[0021] FIG. 4 shows how a silicon ingot can be measured using a
constant current source to determine material resistivity.
[0022] FIG. 5 shows a fixture for testing a novel forcing current
bench test method that can be used to accurately determine
thermoelectric wafer and coupon performance.
[0023] FIG. 6 shows the electronic circuit of FIG. 5 where both
p-type and n-type wafers can be evaluated simultaneously.
[0024] FIG. 7 shows how a coupon is measured with a go-no go test
fixture.
[0025] FIG. 8 shows how a raw and coated wafer can be evaluated
with a test system.
[0026] FIG. 9 shows an evaluation method similar to FIG. 8 that can
be used to evaluate green un-bonded and bonded thermoelectric
rings.
[0027] FIG. 10 shows how a completed thermoelectric generator or
chiller ring can be evaluated for output capacity, resistance and
voltage without a teardown.
[0028] FIG. 11 shows how the slope of the V/I line represents a
negative resistance of -1.04 E-5 Ohms to mean that current can flow
in this region without resistance until the negative driving
voltage -V becomes a positive voltage on the right side of zero
volts on the chart.
[0029] FIG. 12 shows what happens to thermally induced junction(s)
voltage when a fixed current is forced in the direction that
current would normally flow if the junction(s) were short-circuited
with a piece of super-conducting wire where the negative voltage
decreases becoming zero at a current of 385 Amperes.
[0030] FIG. 13 shows what happens when current is increased beyond
the zero-voltage crossing point (385.5 amps), negative voltage
becomes positive voltage to the right of zero-volts and system
resistance also becomes positive.
[0031] FIG. 14 shows what happens in the negative resistance region
when the .DELTA.T across the thermoelectric material is changed,
V/1 slope stays the same while negative voltage and current at
zero-crossing change.
[0032] FIG. 15 shows a V/I plot for a ring with 60 n-type wafers
and 60 p-type wafers arranged as a ring as the .DELTA.Ts for
thermoelectric material junctions are changed.
[0033] FIGS. 16a, b, and c shows how a thermoelectric ring can be
evaluated open-circuit voltage as in 16a, in 16b with shorted
current and in 16c as a thermoelectric ring with up-converter
attached.
[0034] FIG. 17 illustrates an exploded view of a conductive wedge,
p-type crystalline wafer, a hot fin, an n-type crystalline wafer, a
cold fin, that comprise a coupon.
[0035] FIG. 18 illustrates the final positions of the elements of
the coupon with all elements situated on an indexing substrate
carrier.
[0036] FIG. 19 illustrates an assembled coupon situated on an
indexing substrate, parts held in alignment with a clamp.
[0037] FIG. 20 illustrates how a robot picks up a coupon and
inserts it into a test fixture for on-line testing.
[0038] FIG. 21 illustrates an on-line test fixture and dynamic test
method for determining un-bonded coupon performance both before and
after thermal bonding.
[0039] FIG. 22 illustrates an automated solder paste dispenser that
facilitates the automatic coating of coupon elements and coupons by
robotic intervention.
[0040] FIG. 23 illustrates a vacuum operated parts pickup device
attached to robot jaw used for parts coating and parts
placement.
[0041] FIG. 24 illustrates a multi-color-marking device to aid in
marking parts determined faulty by on-line testing by failure
mode.
[0042] FIG. 25 illustrates a coupon-making machine capable of
assembling, on-line testing, marking, bin disposition, and brazing
passed coupons.
[0043] FIG. 26 illustrates the top view of the coupon-making
machine with part handlers, delivery chutes, robot and conveyor
bonding furnace.
[0044] FIG. 27 illustrates a means of removing coupons from bonding
furnace oriented for further processing by a second robot.
[0045] FIG. 28 illustrates a side view of coupons coming off
furnace belt to orient into an orienting chute.
[0046] FIG. 29 illustrates a top view of a second robotic work
station that assembles thermoelectric rings.
[0047] FIG. 30 illustrates a top view of a second robotic work
station that assembles and tests thermoelectric rings and places
them on a belt furnace for bonding.
[0048] FIG. 31 shows a ring entering and exiting a conveyer furnace
that presents bonded product for further generator and chiller
assembly.
[0049] FIG. 32 illustrates a system for creating a casting mold for
net-shaped thermoelectric wafers.
[0050] FIG. 33 illustrates a system for pouring a tree of
thermoelectric wafers causing each net-shaped crystal to grow
single crystal as molten metal slowly cools to solidify and then
reduced to near room temperature.
[0051] FIG. 34 illustrates a tree of net shaped thermoelectric
wafers removed from mold as single crystal caused by a seed crystal
mounted in the mold runner.
[0052] FIG. 35a shows a rectangular arrangement of linear coupons
for a thermoelectric device.
[0053] FIG. 35b illustrates a triangular arrangement of linear
coupons for a thermoelectric device.
[0054] FIG. 35c shows an octagonal arrangement of linear coupons
for a thermoelectric device.
DISCLOSURE OF THE INVENTION
[0055] To illustrate this invention the figures listed above are
drawn to show components of a few implementations of the invention.
It should be understood that these figures do not in any way limit
this invention as described in the claims.
[0056] FIG. 1 shows the top view 1 of a first phase of an operator
assisted assembly line method for making use of wafers, fins and
wedge to form ring components of a thermoelectric generator.
Operator 2 picks up an offset fin 3 from bin 4 and inserts it in a
two-sided paste dispenser 5. The offset structure is shown in
detail in FIG. 5. Operator 2 then places p-type wafer 6 from bin 7
on the offset side solder region of fin 3 forming a partially
completed p-type hot fin and places it on moving belt 8 fanning a
wafer hot fin assembly 9. Operator 10 takes a fin 3 from bin 11 and
applies paste from one-sided dispenser 12 then places an n-type
wafer 13 from bin 14 on the solder applied side of fin 3. Operator
10 then places this assembly 16 on belt 8 with the fin-offset side
upwards. Operator 15 first picks up the n-type wafer fin assembly
16 and places it in hand-held alignment template 17. Operator 15
then picks up hot fin-wafer assembly 9 and turns it over placing it
over the n-type wafer fin assembly 16 in template 17 forming a
straight hot-fin-cold-fin partially completed coupon assembly.
Operator 15 then picks up wedge 18 from bin 19 and coats it with a
one-sided paste dispenser 12 and places it solder face down over
the p-type wafer of the fin-wafer assembly 9 with the wedge taper
end facing opposite to the direction of the belt. Operator 15 takes
a clamp 20 from bin 21 and secures the completed but un-bonded
coupon formed in template 17 to form a competed clamped unbonded
coupon 22. Operator 15 places the completely assembled un-bonded
coupon 22 on bonding furnace belt 23 of furnace 24. Periodically
complete and un-bonded coupons are tested in testing unit 25 to be
described in detail below in FIGS. 5, 6 and 7.
[0057] FIG. 2 shows a top view 26 of an operator assisted assembly
line method for converting bonded coupon assemblies 27 into a ring
component for a thermoelectric generator. Bonded coupons 27 are
shown emerging from belt furnace 24 falling into holding chamber
28. Coupons are cooled by fan 29. Operator 30 removes clamps 20
from bonded coupon 27 and places clamps 20 in bin 21 for reuse.
Operator 31 places cooled bonded coupons 27 into template 32 where
operator 31 applies solder paste from supply 33 to the wedge side
of coupon 27. Template 32 is constructed to receive coupons 27 in
only one orientation with the wedge side upwards. Operator 30
serially places wedge-pasted coupons 34 into assembly fixture 35.
Ring assembly fixture 35 is comprised of internal ring support 36
that supports fins 34 in the vertical position. Fixture 35 has an
irregular bottom support that only allows each coupon 34 to be
inserted into the fixture in one direction with regard to the wedge
side. An up-converter 37 is supported in the assembly fixture 35 at
the midpoint of the coupons 34. When the prescribed number of
coupons 34 have been installed in ring assembly fixture 35 an
insulated compression ring 38 is placed and tightened around the
formed ring 39 at the wafer level. Each assembled ring 39 is tested
at station 40 prior to thermal bonding of the ring. The details of
testing at station 40 are described below in detail. After
completion and successful testing of ring 39 using station 40 the
ring assembly 39 is removed from assembly fixture 35. The assembled
ring 39 is placed on moving belt 41 for thermal bonding in oven 42
where solder-pasted bonded coupons 27 become thermally bonded as a
continuous ring when heated to a temperature of 260 degrees C. for
5 minutes.
[0058] The above detailed presentation of a preferred manual
assembly process is only one of a wide variety of methods that can
be used to assemble a completed thermoelectric ring. Other
procedures than accomplish the same final assembled product can be
developed by those skilled in the art of assembly line
processes.
[0059] Periodic testing of components in the assembly method
described above prevents components from compromising the
performance of the final product. The testing portion of this
invention, comprises a dynamic method for accurate measurement and
evaluation for thermoelectric material that can be used throughout
the thermoelectric device manufacturing process. The following
discussion will show with voltage to current ratio graphical
plotting, how a novel forcing current test method for determining
negative resistance in thermoelectric material works by describing
the significance and meaning of each plot. The discussion of the
data demonstrates a simple, quick, and valid way to actively
measure thermoelectric properties for several in-process
configurations.
[0060] FIG. 3 illustrates the classical method of determining
material resistance in wafer form, as used by the semiconductor
industry. Resistance is calculated using the voltage to current
ratio, V/I, data along with physical dimensions of the material
under the probe, i.e., the distance 47 between voltage probes.
Determination includes wafer thickness and an estimation of current
spreading in the wafer, along the test sample's width. Test
apparatus 43 uses voltmeter 44 and ammeter 45 to measure wafer 46
using a constant current source of approximately 0.1 ampere while
measuring the voltage. From wafer thickness, measured voltage from
voltmeter 44, known current from ammeter 45, and the spacing 47
between voltage probes the resistance in the vertical direction of
the wafer can be calculated. Resistivity can be determined
mathematically using Ohms law and the definition of conductivity,
.rho., in Ohm-cm. This analysis can only be made on wafers without
metal contacts. Wafers with metal contacts must be tested by other
means that require either the removal of metal contacts or taking
into consideration the conductivity of the metal contacts. The
values obtained for semiconductor material differ widely from those
obtained using the same procedure with thermoelectric material. A
novel method for determination of the electrical characteristics of
thermoelectric material is described beginning with FIG. 5.
[0061] FIG. 4 shows the classical means 48 for measuring electrical
characteristics of a silicon ingot 49 using voltmeter 44 and
ammeter 45 with a current source. Knowing the distance between
probes 50 across the voltmeter probes, the resistance of sliced
wafers from the ingot 49 can be determined in advance of
slicing.
[0062] FIG. 5 diagrams a test system 51 that more accurately
predicts thermoelectric behavior in wafers with and without metal
contacts, coupons bonded and non-bonded, and thermoelectric rings
bonded and non-bonded more accurately than semiconductor methods.
The forced current technique with heat flow produces valid,
reproducible measurements throughout thermoelectric assembly
process. Measuring system 51 is used in FIGS. 1 and 2 as in-process
test instruments 25 and 40. In FIG. 5 resistance is being measured
for a coupon 27 consisting of hot fin 52 shown with offset pins,
cold fin 53 shown with offset pins, tapered wedge 54, n-type wafer
55 and p-type wafer 56. Components of test system 51 include heater
57, clip 58, fan 59, and a constant current power supply 60
consisting of an ammeter 61, power source 62 and a means to vary
current 63, and momentary switch 64. Probe 65 and probe 66 apply
current from power supply 60 to cold fin 53 and wedge 54. Probe 67
and 68 connect voltmeter 69 across cold fin 53 and hot fin 52
respectively to measure n-type wafer 55. To analyze the p-type
wafer 56, voltmeter 70 connects across hot fin 52 and wedge 54 with
probes 68 and 71 respectively. Heater 57 heats hot fin 52. Fan 59
blows air on cold fin 53 to remove heat to ambient.
[0063] Measuring instrument 51 is used to accurately determine
thermoelectric wafer and coupon performance for various stages of
assembly. The internal resistance of the thermoelectric wafer
material, wafer contacts through heat conducting nickel coated
copper fins can be obtained. The heater 57 is used to heat the hot
fin of a thermoelectric coupon causing heat flow through p-type and
n-type wafers. Heat flows through thermoelectric wafer material
conducting through wafers to cold fin 53 and wedge 54 heat drawn
with the assist of fan 59. Voltage across the n-type wafer of the
coupon is measured with probe 67 on the cold fin and probe 68 on
hot fin 52. Voltage across the p-type wafer of the coupon is
measured with probe 68 on the hot fin and probe 71 on wedge 54. As
the heat begins to flow from hot fin 52 through the n-type
thermoelectric material of the coupon to cold fin 53, this also
heats the p-type wafer 56 with heat traveling to the wedge 54. The
voltage determines the temperature differential just as a
thermometer or thermocouple. The negative voltage with no forcing
current flowing is measured using meter 69 is recorded to measure
n-type negative voltage values at a heat flow though coupon 27.
Negative voltages are obtained first with no current flowing
through momentary switch 64 of power supply 60 in the of position.
Meter 69 is used to measure n-type negative voltage. Meter 70 is
used to measure p-type negative voltage. Momentary switch 64 in
power supply 60 is closed and negative voltage measurements are
again noted along with the current from power supply 60. Reduced
negative voltage measured with voltage meter 69 and 70 are obtained
by proper connection of the power supply leads from forcing current
supply 60. This convention allows voltage values to be less
negative when current is applied from power supply 60. The
momentary switch 64 activated and new negative voltage recorded for
each voltmeter 69 and 70 at known current, the internal resistance
of n-type, p-type and coupon can be mathematically determined from
the voltage and current measurements. The resistance data can be
used to pass or fail a wafer, coupon or even a thermoelectric ring
before thermally bonding. Testing thermoelectric elements in
process saves material and increases final test yields of
thermoelectric rings composed of 300 and more perfect elements for
proper operation.
[0064] FIG. 6 shows a test system 72, similar to test system 51
except only one volt meter 74 is used with probes 73 and 67. In
this case voltage drop toward zero when forcing current enabled
represents both n-type and p-type wafers in series, therefore the
resistance of the complete coupon in the bonded or un-bonded state
can be determined.
[0065] A typical coupon has a hot fin 52, a cold fin 53 and a wedge
54. The wedge 54 can be used as a temporary heat sink to allow
quick evaluation of thermoelectric material attached to wedge 54
while it is cold and before it soaks too much heat to operate as an
effective heat sink. This way, the material attached to the wedge
can be evaluated using the forcing current method if measurements
are performed quickly, the wedge serving as a temporary heat sink
for short duration until it becomes too heated. If tests are
performed quickly, the resistance is calculated from the
voltage-current ratios, VA. These ratios define the slopes for both
types of materials, n- and p-type. Resistance standards are set for
a coupon to pass quality assurance testing.
[0066] FIG. 7 shows production fixture 75 in box 76 providing
current probes 77 and voltage measuring contacts 78 to collect data
from n-type and n-type material in coupon 27. This method lends
itself to automation under computer control with umbilical 79.
Fixture 75 can also incorporate a temporary heat sink adjacent to
the coupon's wedge 54 to remove heat equally across both wafer
types. FIG. 7 illustrates how the test procedure of FIGS. 5 and 6
can be packaged in box 76 to conveniently evaluate non-bonded and
bonded coupons as a part of the assembly line process. Under
computer control negative voltage is measured after the coupon
achieves a pre-set temperature between wedge 54 and cold fin 53,
the -V1 recorded, current forced and -V2 measured at known current
I. A computer computation is automatically made resulting in the
illumination of either green go-lamp 80 to indicate pass or red
no-go lamp 81 to indicate the coupon resistance value exceeds
operating limit for proper thermoelectric ring operation.
[0067] FIG. 8 shows an apparatus 82 for using the forcing current
power supply 60 of FIG. 6 connecting to hot fin 83 through probe 84
and probe 85 to cold fin 86 cooled by fan 87. Raw thermoelectric
n-type and p-type wafers as well as a wafer 88 with metal coating
on wafer 88 can be evaluated this way. Individual non-bonded
thermoelectric wafer 88 is aligned so as to protrude from hot fin
83 heated by heater 89. Protruding wafer 88 is cooled on the other
side by cold fin 86. Voltage probes 90 and 91 from voltage meter 92
make contact with the bare or coated wafer 88 or metal coating on
wafer 88. The same measuring technique used in FIG. 6 allows
determination of individual wafer resistance parameters with and
without metal coating.
[0068] FIG. 9 illustrates a measuring system 93 for determining
electrical resistance in an assembled thermoelectric ring before
bonding and after bonding. System 93 with box 102 shows a constant
current source 95 connected by contacts 96 and 97 to power output
leads 98 and 99 of ring 94. Voltage meter 100 also connects to
output terminals 98 and 99 on the ring 94 side of current forcing
connections 96 and 97 so as to be independent of the contact
resistance of the current source terminals. The hot fins of the
ring are heated and negative voltage of ring 94 is measured at
temperature with voltage meter 100 and the value recorded as -V 1.
Momentary switch 101 is closed and the negative voltage, -V2, of
ring 94 is recorded as measured with meter 100 at current I
produced by constant current power supply 95. From -V1, -V2, and
the current at -V2, the internal resistance of ring 94 is
determined. The same forcing current test method can be used as a
nondestructive evaluation method for generator products returned
from the field as shown in FIG. 10. A thermal gradient is first
applied to the open circuit thermoelectric device 94. A
thermoelectric negative voltage measurement is then made with the
open circuit ring on terminals 98 and 99, with zero current
flowing. The accumulated voltage is indicative of .DELTA.T between
n-type and p-type wafers connecting the hot and cold fins for the
ring 94 as a first measurement. This measurement is actually a
negative voltage, -V.sub.1, produced by .DELTA.T that is caused by
heating the hot fins and cooling the cold fins with momentary
switch 101 in the open condition. The momentary switch 101 is
closed to force approximately 50 amps from box 102, through the
high capacity load resistor 95 properly adjusted to serve as a
constant current supply. By proper application of voltage meter 100
leads to ring 94 to output leads 98 and 99, -V1, -V2 voltage can be
measured. Current flows momentarily through the thermoelectric ring
94 under test in the same direction current would normally flow if
the thermoelectric device were shorted on itself or operating the
primary windings of an up-converter through MOSfet switch banks.
When forcing current flows through the thermoelectric device, the
open circuit negative voltage -V1 is reduced and is made more
positive, as -V2 with application of known current. The second
negative voltage -V2 is recorded, along with the magnitude of the
actual forced current I from power supply load resistor 95 flowing
through the ring device 94. From the -V1-V2 and I the resistance of
the ring can be calculated.
[0069] FIG. 10 shows apparatus 103 that represents a thermoelectric
generator ring 94 with complete electronic drive and switch
circuitry attached. Heat flow through hot fins to cold fins causes
current 104 to flow in the ring 94 when MOSfet switch banks 105 and
106 are switched "on" and conducting current through ring 94. Ring
current is maintained continuous by thermoelectric effect in only
one direction 104 by normally open make-before-break switches 105
and 106 located across power output terminals 107 and 108. Current
direction around the high frequency magnetic core 109 is switched
oppositely by electronic circuit elements driven by inverted drive
from the pulse width modulator chip 110. Forcing current tests can
be made to the heated ring 94 of a thermoelectric generator by
measuring across the thermoelectric ring output terminals 107 and
108 with MOSfet switches 105 and 106 in the inactive normally open
mode. Forcing current from power supply 95 as in FIG. 9 allows
voltage probe measurements to be made at terminals 111 and 112 with
voltage meter 100. Voltage -V1 is measured with voltmeter 100 on
ring 94 with hot fins heated and cold fins cooled and with zero
current. Voltage -V2 measured with volt meter 100 with forced
current from momentary switch 101 switched current source 95 allows
the determination of internal resistance of ring 94 from
calculation including current 104 I at voltage -V2. This
measurement of the thermoelectric ring can be made with and without
electronic drive circuitry connected with electronic drive
inactive. Initially MOSfet switch banks 105 and 106 are normally
open when pulse width modulator chip 110 is open and inactive.
Voltage probes 111 and 112 from voltmeter 100 are connected across
positions 107 and 108 but closer to the ring. The probes 111 and
112 are connected with polarity to indicate a minus voltage V1 when
the ring is heated and the MOSfet switches are open. The hot fins
of the ring are heated and voltage across the ring is measured with
the voltmeter 100 connected to result in negative voltage values.
The voltage value is noted as -V.sub.1 with no current in the ring.
Momentary switch 101 is closed to force a known amount of current,
I, about 50 amps though ring 94. This reduces negative voltage -V1
to a higher value, that is, less negative voltage as recorded from
voltmeter 100 and designated -V.sub.2. From the values -V.sub.1 and
-V.sub.2 and measured current I, the resistance of the ring is
calculated. The resistance of the ring of 60 coupons should be less
than 0.001 Ohms, both before and after solder paste bonding.
[0070] The relevance of the test method was demonstrated using the
material from a thermoelectric material library developed over a
five-year period of time when wafer contact research was conducted.
Samples from this library were re-measured over and over using the
negative voltage, forced current method, comparing these results to
classic 4-point and voltage current ratio methodology. The negative
voltage, forced current method is by far the most accurate and can
be used all along the production process for quality assurance. The
examples below provide detail data to illustrate the methods and
provide quality values for n-type wafers, p-type wafers, coupons,
thermoelectric rings and thermoelectric generator.
[0071] FIG. 11 shows the slope of the voltage to current line, V/I
line, representing a negative resistance of -1.04 E-5 Ohms when a
hot fin of a coupon is heated. A negative voltage of -4 E-3 was
measured as -V1 at 113 with no current flowing. With a forcing
current of 71 amperes, a -V2 voltage of -3.0 E-3 at 114 is
recorded. Power supply 60 in FIG. 8 causes current flow in the same
direction current would flow if coupon were shorted. A negative
voltage in this region means that current can flow in a
thermoelectric ring without resistance, up until the time the
thermoelectric driving voltage becomes positive voltage, crossing
zero from the left side of the graph to operate in the positive
side (right) of zero on the X-Y chart. The slope of the line
represents resistance (V/I) and because voltage is negative, -V/I
represents negative resistance operation. When a current of 71
amperes is forced through the coupon in FIG. 11, the negative
voltage is reduced to -3.0 E-3 shown as sloping line 115. This
data: -4.0 E-3 volts, 0 amps and -3.1 E-3 volts, 71 amps, amounts
to a resistance of -1.04 E-5 Ohms as calculated. The resistance is
negative because voltages are negative and the current is in the
positive direction that the up-converter allows current to be
driven in the ring.
[0072] FIG. 12 shows that the same resistance values are derived
when the forcing current is increase to the point that -V2 becomes
zero at a current of 385 amps at 116. Before current is applied to
the device under test with a thermal gradient present using either
a heater block or the flow of hot air across hot fins, the coupon
produces a voltage of -4 E-3, and a zero current at 117. A forcing
current of 385.5 moves V1 voltage from -4.E-3, zero current to a
-V2 at zero volts, 116. The forcing current of 385.5 is the same
current at zero crossing that would occur if the heat-induced ring
were shorted with a micro-ohm short. This performance is measured
for a single thermoelectric wafer of a 2-wafer coupon plotted as
tested in FIGS. 5 and 6 with a .DELTA.T of approximately 80 C.
Metal-coated wafers can also be accurately evaluated for electrical
performance using the test setup shown in FIG. 8 by measuring
voltage on protruding wafer sides rather than on the thermal or
current driving connections. FIG. 12 also shows negative voltage
(-V.sub.1, -V.sub.2) data plotted against currents zero and I at
V=0, on X-Y coordinates with thermoelectric junction(s) maintained
at an arbitrary .DELTA.T by heater 87 in FIG. 8.
[0073] FIG. 13 shows the thermoelectric junction of FIG. 12 when
forcing current is further increased beyond that of zero-crossing
118. The voltage becomes positive as the current increases beyond
that of zero crossing as at points 120. Current is forced beyond
that of zero crossing for thermoelectric material at a set
.DELTA.T. The forcing current is in the direction current would
normally flow if the junctions were short-circuited with a piece of
super-conducting wire. Rather than pushing the current higher each
time to achieve a zero crossing, V=0, a zero crossing can be easily
calculated using the measured data -V.sub.1, and -V.sub.2, and then
measuring I at -V.sub.1 The linear equation Y=mX+b can be used to
determine V/I which is -R, which is also the slope of the line and
the resistance of the device under test. One value at 119 shows -V
with negative current. This condition occurs when forcing current
in the ring is reversed. The linearity of the slope of voltage to
current is seen for 5 measured points, 2 of which at 120 show
positive voltage values. The resistivity (p) can be accurately
obtained by .rho.=R(A/L), which is resistance, times the area of
the wafer, divided by the wafer thickness, all in centimeters,
because the units for p are defined as being Ohm-cm in the SI
system.
[0074] FIG. 14 shows -V/I plots for various .DELTA.Ts for the same
thermoelectric junction for the wafer measured in FIG. 11. The -R
is the same for the material regardless of .DELTA.T because all V/I
slopes are parallel. For each line a different temperature was used
for which a zero voltage current applies. At each different
temperature differential the forcing current was applied until the
voltage became zero. The calculation for resistance is the same
because each slope 121, 122, and 123 are the same. This shows that
any differential temperature between hot fins and cold fins can be
used to analyze wafer, coupon, and ring resistance.
[0075] FIG. 15 plots values measured for a thermoelectric ring of
60 coupons. The hot fins are heated and the cold fins cooled to
produce -V1 shown at 124, which amounts to -3 volts when the ring
is open circuit and a self-induced current of 4,808 amperes due to
ring shorting at 125. The ring was then shorted partially by
placing an up-converter with a resistance of +6.0 E-4 Ohms, not
shown, across the ring terminals. This addition reduces -V1 to -1.5
volts shown at 126. The up-converter's resistance is mostly in the
switch bank that is composed of parallel-connected MOSfets
switches. Two make-before-break MOSfet switch banks allow 2,500
amperes to flow through the ring as shown at 127. The same current
produced in the ring circulates through ring shorted by
up-converter.
[0076] The R slopes 124, 125 in FIG. 15 are at a particular
junction temperature differential for the ring. This represents the
internal resistance for the ring. The X-Y line shifts to the right
when the load of the up-converter is connected. If junction
temperature differential is increased, the loaded -V1 becomes more
negative, increasing the current in the up-converter. Wafer
contacts are a limiting factor for the amount of current a ring may
circulate reliably. Nickel contacts on tellurium based
thermoelectric wafers have been found to operate reliably at 750
amps per square centimeter. Shorting of a thermoelectric ring on
itself can lead to high current catastrophic ring failure. To
operate properly at high power level, thermoelectric generator
material must have proper metal contacts to have high current
capacity. A load resistor must always be placed in series with a
ring when shorting to prevent over-current destruction. An
up-converter used as an output device for a thermoelectric ring can
modulate ring current at a safe and continuous controlled current
in the ring portion of the generator.
[0077] FIG. 16a through 16c illustrates three different test modes
for a heat driven thermoelectric ring 94. FIG. 16a shows heated and
cooled thermoelectric ring 94 in open circuit mode with current
being zero. Thermoelectric ring 94 is made up of 60 bonded coupons
27 that measure -3 volts open circuit with voltmeter 128.
[0078] FIG. 16b illustrates another test mode for heat induced ring
94 described in 16a. FIG. 16b shows ring 94 operating in the
ring-shorted mode with heavy-duty ammeter 129 conducting and
measuring current 130 in ring 94. Voltage across ring 94 is
measured with voltmeter 128 and found in this test to be zero.
Current 130 circulating in ring 94 in shorted mode is 4,808 amperes
as measured with ammeter 129 and plotted in FIG. 15 as 125.
[0079] FIG. 16c illustrates a test mode for heat induced ring 94
described in 16a and 16b connected to secondary winding 131 of
up-converter 132 with two ultra-low impedance make-before-break
MOSfet switch banks 133. Resistance of each of the
make-before-break MOSfet switch banks 133 is on the order of 6.0
E-4 Ohm or 0.0006 Ohm. When a current of 2,400 Amperes flows
through switch bank 133 driven by voltage from partially shorted
ring 94, voltage meter 134 measures +1.5 volts across switch banks
133. Heat induced thermoelectric ring 94 uses roughly half of the
open-circuit voltage to force current through up-converter primary
winding 131 and switch bank 133. This can be verified using
voltmeter 134 and current meter 135. High frequency, 50-kHz to
200-kHz, overlapped switching is required for efficient, switching
power supply energy transformation, ring to secondary output
windings. The on-resistance of the MOSfet switch banks can be
varied with the number of MOSfet switches used in parallel. This is
the same technique used to limit ring current through each switch
bank. A typical resistive load for a 60 coupon thermoelectric ring
connected to up-converter is 6.4 E-4 Ohms for each switch bank
which limits ring current to approximately 2,400 Amperes while the
generator is operating. Ring-generated current flows due to the
difference in temperature from one side of n-type and p-type
wafers, which creates voltage. Energy output from the ring-driven
up-converter can be adjusted by changing heat flow through ring 94,
which varies temperature differential across each thermoelectric
wafer. With heat flow adjustments voltage can be regulated, current
adjusted by the number of switches used, controlling the energy
output of ring 94.
[0080] A simple way to calculate potential output of a closed-loop
type shorted thermoelectric generator is to use the following
equation:
[0081] P.sub.o=V.sup.2/R; where P.sub.o is the potential power in
the ring over time, V is the open circuit voltage of the ring
squared, and R is the resistance or AC impedance of the
up-converter and MOSfet switch-bank.
[0082] Typical values for a 5-kW generator are: Po=(3).sup.2/1
E-3=9,000 Watts
[0083] This energy is achieved with a 9-inch diameter
thermoelectric ring 94 made up of 60 coupons 27, with an operating
.DELTA.T of approximately 200 C. Transformer losses in the
switching up-converter system is from heat dissipated in the MOSfet
switches, magnetic core losses, and primary winding losses in the
up-converter circuit. Roughly 5-kW of useful energy output is
realized from 9-kW circulating in the ring as potential energy. To
increase this output, .DELTA.T across wafers can be increased to
250 C however no test data exists at this time to support reliable
operation beyond a 250 C .DELTA.T.
[0084] Another way to increase generator output performance is to
manufacture a larger diameter ring made up of a larger number of
the same coupons 24. A 24-inch diameter ring has been modeled with
an output capacity of 333-kW, 400-hp, that uses the same wafers and
heat transfer elements as the 9-inch ring. A 13'' diameter ring,
estimated to produce 150-kW or 200-hp, would satisfy electric
automotive requirements.
[0085] The forcing current evaluation method uses three simple to
obtain measurements. The are; -V.sub.1, -V.sub.2 at I, and I (at
-V2) to determine R. The exact .DELTA.T of the measurements is
unimportant because temperature changes occur slowly due to large
copper mass of coupon fins. To determine R for a combination of
coupons, the test circuit shown in FIG. 5 is used. Heat is applied
to one side of the junction(s) while the other side(s) is cooled or
remains cooled. An automotive starter relay with a foot-switch is
used to force current through the junction(s) in the same direction
current will flow when ring elements are driving up-converter. Test
current flows through load resistor, the device under test, and
back to battery ground. Should -V become more negative across the
device under test with current application, the polarity of the
forcing current is backward, but the results will still predict the
correct R. The apparatus of FIGS. 5 through 10 is reliable for
several months of use, after which test fixture can either be
overhauled with new parts or discarded and completely replaced.
From the open circuit V.sub.1 at .DELTA.T, I.sub.0, and then
V.sub.2 at the same .DELTA.T with current flowing through the
junction(s) the R and the p of the material can be calculated using
the equation Y=m'X+b. The -R for a completed circuit or ring can
also be calculated. From these results, everything is know to
predict the performance of a thermoelectric generator operation
from the beginning as a material ingot, raw wafers, wafers with
metal contacts, assembled into coupons, and as a ring at final
assembly and for product rings returning from the field as
defective. If a coupon 34 is found during assembly that functions
below acceptance level, it can be scrapped, replaced with one that
operates in the normal performance range. The test apparatus
described in FIG. 5 through 10 was used to determine R, p, and zero
crossing current based on a library of material samples cataloged
over five years.
[0086] In a preferred embodiment the quality of wafers are tested
before being assemble in a coupon arrangement. The power output
performance Po of a completed thermoelectric coupon, or generator
is a function of the summation of the voltages squared, caused by
the temperature differential of individual wafers of the coupon or
coupons of the ring, divided by the sum of the resistances of
individual wafers, and wafer connections in the coupon that make up
the ring; Po=V.sup.2/R. Therefore, thermoelectric wafer(s) and
wafer connections within useful coupons must have resistances in
the sub-micro-Ohm range to perform well as a ring. For control of
voltage in the build cycle, incoming thermoelectric wafers are
measured using a temperature-controlled soldering iron as a
hot-point probe. The probe is placed on a wafer's topside surface
as a negative connection to a digital voltmeter. The plus
connection of the digital voltmeter is connected to a room
temperature heat sink that maintains the bottom surface of the
wafer at room temperature. A hot-point-probe measurement of 0.055
volts is typical for either p-type or n-type wafer when the
soldering iron is controlled at 250 C, and the room temperature at
25 C. The polarity of the voltage measured in this way is positive
for p-type and negative for n-type wafers. The in-process
measurement system of this patent is all about measuring and
selecting of coupons consisting of cold fin, n-type wafer, hot fin,
p-type wafer, and conductive wedge to form a coupon. Coupons that
are assembled as a ring in a thermoelectric generator then operate
with predictable electrical power output performance. This
evaluation method can determine go, no-go performance for
individual wafers, individual coupons and assembled coupons of a
ring. Being able to remove high resistance coupon components from
the build cycle allows the passing of only acceptable performance
elements for building generator rings. This is a very important
procedure because should a single coupon in the building process
have an internal resistance much higher than all others, the power
output of the completed ring is degraded.
[0087] Manual assembly methods for coupon and ring manufacture are
illustrated in FIGS. 1 and 2. These methods can be replaced with
automatic methods that test parts as they are manufactured and
remove failed parts from line. FIGS. 17 through 31 de a robotic
means of building and testing rings.
[0088] FIG. 17 exploded view 136 illustrates a cold fin 137, and an
n-type crystalline wafer 138, a hot fin 139, a p-type crystalline
wafer 140 along with a conductive wedge 141 that comprises parts of
a coupon of this invention along with substrate support piece 142.
An alignment substrate 142 is shown beneath the exploded view of
the elements of the coupon and the relative position each element
will occupy when assembled as a complete coupon. N-type wafer 138
is soldered to cold fin 137 and on the other side to hot fin 139.
P-type wafer 140 is soldered to hot fin 139 on one side and to a
conductive wedge 141 on the other side. In a preferred embodiment
solder paste bonding is 95-5 tin-silver alloy solder having 4%
additional pure silver powder added, applied in the region of
contact between the semiconductor wafer 138, 140 and the hot fin,
cold fin and wedge. It should be understood that reversing relative
positions of wafer 138 and wafer 140 creates an electronically
equivalent device with opposite electrical polarity.
[0089] FIG. 18 illustrates a cold fin 137, a hot fin 139, a p-type
crystalline wafer 140 and an n-type crystalline wafer 138 and
conductive wedge 141 that comprise a coupon 136 of this invention
shown along with alignment substrate 142.
[0090] FIG. 19 illustrates a final arrangement of the elements of
the coupons 143 mounted on alignment substrate 142. FIG. 19 uses
clamp 144 to maintain the element positions included in 143. In a
preferred embodiment sixty of these coupons complete a 5-kW, 9-inch
diameter thermoelectric ring. This number can be varied depending
on the operating voltage desired. A 333-kW generator uses 142
coupons to compose a 24-inch diameter ring. The Seebeck voltage
also effects how much voltage is produced for a given temperature
differential between the hot and cold fins. It should be understood
that the cold fins need not be directed at 180 degrees to the hot
fins. Furthermore it is possible to fashion the shape of either the
hot fin or the cold fin or both to preclude the need for the
conductive wedge component. In a preferred embodiment tin-silver
solder paste containing an additional 4% silver is applied to each
side of each coupon except where the coupon is adjacent to an
insulator component of the ring.
[0091] FIG. 20 illustrates the robotic method of the coupon making
machine placing an assembled and green solder pasted coupon 143 and
substrate into an on-line test fixture 145. Green solder paste
means solder paste applied to parts but not yet thermally melted or
in the case of one-part epoxy cured and un-cured. Placing the
coupon into the tester activates a computer-aided tester such as
LABview manufactured by National Instruments of Austin, Tex., not
shown. Current and voltage probes of 145 connect to test the coupon
under real operating conditions. The computer-controlled tester
determines whether the coupon under test passes or fails. In FIG.
20, the cold fin 137, the n-type wafer 138, the hot fin 139, the
p-type wafer 140, and the conductive wedge 141 can be seen in their
assembled position on substrate 142, held by clamp 144 being
positioned to insert into test fixture 145 by robot jaws 146.
[0092] FIG. 21 illustrates the electrical components 147 of test
fixture 145 in FIG. 20. Heating element 148 is used to heat one end
of the coupon 143, while blower 149 is used to cool the other end
of coupon 143. The test program involves heating one end of the
coupon while cooling the other with blower 149. Meters 150 and 151
are negative voltage meters that first detect -V.sub.1 at
zero-current voltage across the n-type wafer and the p-type wafers
at a temperature that is caused by heater 148 and blower 149. While
the temperature differential across wafer changes very slowly with
time caused by heater 148, computer controlled test measurements
occur very fast, much faster than temperature changes can occur.
This allows accurate measurements of -V.sub.1 and -V.sub.2 made at
150 and 151 first at zero current and then with forced current,
through coupon 143. The direction of forced current, measured at
152 is in the same direction that is caused by normal thermal heat
flow through the ring. The faster the -V.sub.1 and -V.sub.2
measurements can be made with and without forced current, the less
effect a changing temperature differential causes and affect the
measured results. The current in test fixture 147 is sourced by
battery 153. Current through coupon is regulated by variable load
resistor 154. Reliable resistance measurements can be made on
coupons clamped with green solder paste, as well as with coupons
after heat bonding. The test method of 147 was described earlier in
this patent. The test method allows on-line testing of components
through all stages of manufacture, providing reliable pass or fail
data that can be acted upon during processing. This prevents
incorrectly assembled coupons with inferior electrical performance
from entering the building cycle.
[0093] FIG. 22 illustrates a pressure operated solder paste
dispenser 155 used with a robot to coat one side of a wafer 138,
fin or wedge during robotic coupon assembly. Air pressure to the
dispenser 155 is pulsed when the robot arm nears the dispenser 155,
causing a measured amount of solder paste 156 to appear on paste
applicator 157. Lid flange and cap 158, dip tube 159 and paste
flask 160 are installed in the tabletop, mounted over dowels to
secure the applicator device 155 to a location where the robot can
be programmed to accurately home.
[0094] FIG. 23 describes a combination tool 161 that consists of a
vacuum pickup chuck 162, mounted to robot jaws 146. Vacuum supply
line 163 draws and holds articles to pickup chuck 162 for precise
holding while the robot arm positions the part in the proper place
as programmed. The vacuum supply 164 is controlled by the robot's
program to operate with arm movement, turning on-off vacuum
synchronized with arm movement for programmed parts pickup,
placement and processing.
[0095] FIG. 24 illustrates a marking fixture 165, composed of
marking pens 166 that allows robot jaws 146 to mark coupon 143 with
mark 167 using various colored pens held in holding fixture 168.
Depending on computer controlled electrical test results, the
robot, is programmed to place the coupon in contact with one of the
colored paint pens that indicated the results of the on-line
testing. The robot is then programmed to place the coupon 143 in a
fail bin, or to place it on the conveyor furnace belt for thermal
bonding.
[0096] FIG. 25 is top view of a coupon making machine 169 composed
of a one-armed robot 170 and various parts placement and test aids.
Robot 170 is mounted on a special tabletop 171 with various
fixtures positioned and attached firmly to the tabletop. Marking
fixture 165 is located near fail bin 172, which is located near
computer controlled electronic tester 145. Central to the robot's
radius of movement is a dock fixture 173 where the parts making up
a coupon 143 are assembled and aligned. Located within the robot's
radius of movement and aligned to the working radius are parts
delivery chutes 174 that deliver the various elements making up a
coupon 143. Elements making up a coupon are individually picked up
by vacuum chuck 162 attached to robot jaws 146. Paste dispenser 155
is located on tabletop 171 along the robot's operating radius to
allow solder paste application as required. Coupon assembly
involves the vacuum pickup of the alignment substrate 142 with
robot 170 and placement of substrate 142 into dock fixture 173.
After substrate 142 is placed in the dock, robot arm 175 then moves
to vacuum pickup a cold fin 137 placing this on top of the
substrate 142 already located in the dock 173. The robot arm 175
then lifts and swings to vacuum pick up an n-type wafer 138, moving
the wafer over and lightly touching the solder paste dispenser 155.
With wafer held in place over paste dispenser 155, a short pulse of
air pressure delivers paste to one side of the n-type wafer 138.
The robot-arm 175 then lifts and swings the n-type wafer over the
dock position and places the wafer 138 with solder past onto cold
fin 137. Then robot arm 175 lifts and moves vacuum chuck 162 to a
position over the chute that delivers hot fin 139. The robot arm
175 then picks up the hot fin using vacuum chuck 162 and locates
the hot fin over the paste dispenser 155 where fin 139 is one-side
coated with solder paste using dispenser 155. Robot arm 175 then
lifts hot fin 139 with green solder past applied and swings to dock
173 position lowering hot fin 139 to place in contact with n-type
138 wafer and substrate 142. Releasing vacuum, robot arm 175 lifts
and swings over p-type wafer 140. P-type wafer 140 is picked up by
robot arm 175 using vacuum and delivered over, paste dispensing
station 155, lowered, paste coated and delivered into dock 173,
placed onto hot fin 139. Robotic arm 175 then moves to vacuum
pickup wedge 141, moving 141 to solder paste dispenser 155
position, where 141 is green solder coated, moved and the one-side
coated wedge 141 is placed onto the p-type wafer 140 positioned at
the dock 173. Robot arm 175 then lifts and moves to dispensing
chute containing clamps 144, grasps and squeezes clamp 144 from the
delivery chute 174, then moves the clamp near the dock position.
Robot arm 175 squeezes clamp 144 and moves to cover the assembled
parts of coupon 143 with clamp 144 and then releases squeeze
pressure applied to clamp 144. Without moving robot arm 175 away
from dock 173, jaws 146 again grasp clamp 144 so as to hold the
coupon 143 without releasing clamping pressure on coupon 143. The
robot arm then delivers the assembled coupon over computer
controlled test fixture 145 and arm 175 rotates to insert the
clamped coupon 143 assembly into test fixture 145 to begin an
electrical test under computer control, not shown. Depending on the
results of electrical test of coupon 143, the programmable robot is
instructed to move to marking station 165 where coupon 143 is
marked with one of three colors depending on test results. A red
mark indicates fail and the robot moves to place failed coupon in
fail bin 172. A blue mark indicates pass and the coupon is moved by
robot to the furnace conveyor belt 176 placed for thermal bonding
on in-going conveyor belt.
[0097] FIG. 26 is an expanded top view 177 of FIG. 25, showing the
relationship of vibration parts feeders 178 and in-going conveyor
belt 179 and thermal bonding furnace 180. Vibration parts feeders
176, also called "Centron bowls", are used to separate, orient, and
deliver individual parts used in machine automation. Individual
bowls can hold and process enough parts to operate for 24-hours, to
place parts into individual parts delivery feed chutes 174 that are
used in the make-up of thermoelectric coupons 143 by coupon
assembly machine 169. Tested green coupons 143 are placed on the
in-going conveyor belt 179 of thermal bonding furnace 180 with
oxygen-free atmosphere. Heat bonded coupons 181 exit furnace 180 on
out-going conveyor belt 182. A controller supervises the thermal
profile and conveyor belt speed of atmosphere furnace 180.
[0098] FIG. 27 is a top view 183 of the backend of atmospheric
furnace 180 showing bonded coupons 184 exiting on out-going
conveyor belt 182 sliding one at a time down slide 185 and catch
chute 186 where bonded coupons can be picked up by robot 187.
[0099] FIG. 28 is a side view 188 of the backend of out-going
furnace conveyor belt 182 of atmospheric furnace 180 showing slide
185 and catch chute 186 with bonded, clamped coupon 184 in catch
placement position. This arrangement makes it possible for robot
187 jaws to capture and lift coupon 184 for further processing.
[0100] FIG. 29 shows a top view of thermoelectric ring making
machine 189. Bonded coupons 184 exit out-going conveyor belt 182 of
furnace 180. Coupons slide down chute 185, and become positioned
for robotic pickup 187. Chute 186 will incorporate a parts buffer
not shown to store extra coupons 184 during times when robot 187 is
busy with ring making activities. Assembly robot 187 grips coupon
184 individually to place in clamp-and-substrate-off dock 190.
Robot 187 removes clamp 144 from coupon 184 and places clamp in bin
191, substrate 142 in bin 192. Robot 187 then grips bonded coupon
184, rotates to insert into computer controlled test station 193.
Depending on computer controlled test results at 193, robot 187
marks coupon 184 at mark station 194 with red or blue paint mark.
Robot 187 then places red-marked failed coupons in fail bin 195 and
either picks up another coupon for clamp-and-substrate removal from
chute 186, or moves a blue marked coupon 184 to solder paste
dispenser station 196 for solder paste application. Once solder
paste is applied to blue mark passed, tested coupon 184, robot 187
rotates blue-marked coupon into vertical position and places coupon
184 within up-converter-strap assembly 197 for 9-inch rings and 198
for 24-inch rings located at ring assembly stations 199 and 200.
Up-converter-strap assemblies, 201, 202 are positioned by robot 187
at ring assembly stations 199, 200 to begin ring assembly.
Up-converter-strap assemblies 201, 202 are acquired from material
supply bin 203 where up-converter-straps are stored until needed to
begin the build cycle for a new ring. Up-converter-strap assemblies
are manufactured with legs to stand in proper position to receive
green-pasted coupons 184 that are used to form a ring. Testers 204
and 205 are computer controlled that perform electrical tests on
completed rings after straps 201, 202 are tightened by
strap-tightening motors 206, 207. Swing arms 208, 209 move the
completed, tested rings onto conveyor belt furnace, not shown, for
thermal bonding or pushed further onto a fail ring bin ramp
depending on test results of computer controlled testers 204, 205.
Robot 187 uses swing arms 208, 209 to effect completed ring
positioning.
[0101] FIG. 30 is an extended top view of FIG. 29 ring making
machine showing connection to ring-bonding atmospheric furnace in
211. Robot 187 is shown using swing arm 209, of set 208, 209 to
position completed ring 94 onto in-going conveyor belt 212 of
oxygen-free atmospheric furnace 211. Finished, tested,
thermoelectric rings 94 move through oxygen-free conveyor furnace
211.
[0102] FIG. 31 is an extension of top view FIG. 30 showing
out-going conveyor belt 213 discharging finished bonded
thermoelectric ring 214 onto slide chute 215 to roll slowly down
roller ramp conveyor 216 for further processing.
[0103] In a preferred embodiment finished bonded thermoelectric
rings would be cued to undergo further automatic processing. For
instance, a secondary coil with printed circuit controller board
interconnecting to up-converter, connected to computer controlled
tester will be inserted between up-converter straps on ring 94 in
FIG. 9. The switch-bank will be solder pasted and inserted between
the up-converter strap 201, 202 and a functional green-test will be
made of the complete thermoelectric system with switch-bank
installed. Upon pass of this test, the heater-equipped jaws forcing
up-converter strap 201, 202 into switch-bank, not shown, will be
activated to make connections complete. A final functional
electrical test will follow. This completes the ring making process
and passed thermoelectric systems will move by conveyor to final
assembly and test.
[0104] In a preferred embodiment the finished and passed
thermoelectric systems will be placed by robot into die-drawn
stainless case, on top of a bead of silicon, high temperature RTV
dispensed by the robot. The connecting controller board will be
positioned and snapped into place by the same robot. Top cover is
computer placed, held in place by a bead of RTV. A motor-driven
double fan with supports and hot-to-cold section baffle, is glued
and installed by computer to complete the assembly. The assembly is
loaded into a box for shipment, instruction and warranty papers
included. Box is then sealed by the computer and computer placed on
pallet for shipment.
[0105] FIG. 32 illustrates a system 217 for creating a casting mold
218 for net-shaped thermoelectric wafers. Wafer manufacture of
thermoelectric devices is a time consuming and labor intensive part
of thermoelectric manufacturing process. Shaping damage-free wafers
is problematic and shrinkage due to breakage is a major cost adder
in wafer production. The system of 217 consists of a box 218 filled
with pressed hollow ceramic beads 219 with a trace quantity of
low-dropping-point high temperature grease to hold shape. Slotted
impression mold pattern 220 with slots 221 allow pattern 222 to be
pressed into the hollow ceramic beads 219 forming wafer-shaped
cavities 223 in beads 219 along runner indentation in the otherwise
flat surface of pressed beads. The wafer cavities are connected by
trunk runner, which later receives molten thermoelectric metal.
Re-useable polycarbonate parts 222 are shown in system 217 some
shown pressed through slots 221 in pattern and one 222 carefully
removed from mold pattern 220 by wire hook 224 leaving a cavity 223
under pattern 220 in pressed beads 219. After all parts 222 are
inserted through slots 221 and carefully removed to reveal mold
cavity 223, the pattern 220 is removed to yield a ready to pour net
shape mold for casting thermoelectric material as net-shaped
wafers. Wafer cavities 223 are connected in pressed bead impression
connecting pattern 220 as a ready to pour casting mold.
[0106] FIG. 33 illustrates a system 225 for pouring a tree of
thermoelectric wafers causing each net-shaped crystal to grow
single crystal as molten metal slowly cools to solidify and then
continuing to grow single as temperature reduces to near room
temperature. Mold system 225 illustrates the casting method for
thermoelectric material resulting in a low cost, net-shaped, high
yield method for producing single crystal thermoelectric wafers. To
create single crystal net shaped wafers as poured, a single crystal
seed 226 is inserted into the pressed bead mold with half of the
seed protruding into cavity 227 that will become the runner 230
when poured. Formulated thermoelectric material 228 is melted in
crucible 229 and poured into the pressed bead imprint beginning at
the seed crystal 226 end of the mold 218. Molten thermoelectric
material 228 poured from the seed end of the mold with crucible 229
fills runner cavity 227. Thermoelectric material 228 in runner 230
micro-melts into seed crystal 226 while flowing into cavities 223
formed by the removal of the replicate polycarbonate wafers 222. As
molten runner 230 cools to a solid beginning at the seed crystal
226 end of runner imprint, runner material 230 solidification
proceeding away from the seed 226, into tilled wafer cavities 223
to become single crystal net-shaped wafers with the same
orientation as seed crystal 226. As the material in wafer cavities
223 slowly cool, they too become single crystal, with minimum
number of grain boundaries and traps for high flux electronic
carriers. Experience shows that a 5-minute cool down undisturbed in
mold fixture 218 is required to complete the single crystal wafer
growth process.
[0107] FIG. 34 illustrates a system 231 for tree growth of net
shaped thermoelectric wafers for mold growing single crystals 232
from a seed crystal 226 in the mold runner 230. System 231 shows a
single crystal tree of wafers removed from mold system 225 with
connecting net shaped wafers 232 of solidified thermoelectric
material 230 connecting runner allows material to grow single from
seed crystal to individual wafers 232 through runner 230. Wafer 233
is shown separated from runner tree 230 by scribing along a line
234 with carbide tipped pencil on wafer material then carefully
snapping wafer 233 from runner tree 230. Another method of parting
wafer 233 from tree 230 is by partly scoring along parting line 234
with a small rotary grinding tool and snapping wafer 233 from
runner tree 230. When care is taken to prevent the inadvertent
mixing of p- and n-type materials when selecting seed materials for
a type pour, the runner and seed alter wafers are removed from the
tree runner can be rough-crushed and used for subsequent pours to
reduce material waste and cost of crystal wafer manufacture.
[0108] FIG. 35a illustrates a rectangular arrangement of linear
arranged coupons 235 without individual wedges between coupons
using instead three 90 degree wedges 236 located at ends of coupon
sets 235 and one corner of the rectangle arrangement of coupons
terminating with up-converter 237 closing the circuit for current
flow in the thermoelectric device.
[0109] FIG. 35b illustrates a triangular arrangement of linear
arranged coupons 235 with special wedge 238 in two places and an
up-converter 237 closing the circuit for current flow in the
thermoelectric device.
[0110] FIG. 35c illustrates an octagonal arrangement of linear
arranged coupons 235 with special wedge 239 in seven places and an
up-converter 237 closing the circuit for current flow in a
thermoelectric device. Thermoelectric rings or loops can be
configured to work with any number of geometric shapes, even
stacked as a' coiled helix with ends terminated with an
up-converter 237 closing the circuit for current flow to output
useful electrical energy or pump heat as a chiller.
[0111] Solder paste bonding can be replaced with silver epoxy
formulated with high temperature one-part polyamide epoxy. Epoxy
Technology, 14 Fortune Drive, Biterica, Mass. 01821, single
component E3084 was evaluated. When high temperature silver epoxy
is used for bonding of thermoelectric, no metal coating of nickel
is necessary on the wafers contacting surfaces of coupons to
achieve the same electrical performance as nickel and tin-silver
solder bonding. Thermoelectric voltage evaluation results,
expressed as .alpha., measured as micro-volts/C for Sn/Ag solder
paste and then silver epoxy coupons, is charted below:
TABLE-US-00001 Hot-point probe Clamped green After bond Green ring
Ring bonded Sn/Ag paste 270 240 170 140 120 poor Silver epoxy 275
280 270 275 280 excellent
The forcing current test methodology works well for measuring
contact resistance with both tin-silver solder paste, cured and
un-cured and one-component high temperature silver epoxy from Epoxy
Technology. The above chart shows how thermoelectric voltage holds
up during process for tin-silver solder paste and silver epoxy.
[0112] Also, just like silicon electronic devices, thermoelectric
semiconductor wafers require edge passivation for long-lifetime
operation, high reliability. An edge coating of high temperature
curing varnish with dye coloring is used, red for p-type and blue
for n-type. A suitable dye for the edge-coating varnish is Rit dye
used sparingly from Phoenix Brands, Indianapolis, Ind. Wafers are
edge-only coated and cured at 150 C prior to assembly into coupons.
Edge coated wafers with polyester have 200 microvolt per degree C.
.alpha. and higher operating voltages after varnish cure. Delphon
CC-1105, one-part polyester pre-catalyzed, from John C. Dolph
Company, Monmouth Junction, N.J. is used for edge junction coating.
Unlike nickel coated wafers that tend to degrade to as low as 20
micro-volts per degree centigrade during coating, coupon bonding
and ring formation using one-part silver epoxy for wafer bonding
has significantly higher voltage and higher operating temperatures
than the nickel-plated, tin-silver, solder bonding process. This
high voltage operating performance continues through the coupon and
ring forming process, to final operating tests and on into long
term generation and chiller operation in the field as demonstrated
in the above chart.
[0113] Thus having described the method of fabricating the test
instrument, a means of measuring thermoelectric material, and a
variety of examples as to how said measuring instrument may be used
in a broad range of thermoelectric components, and having described
a manual means for manufacturing generator rings as well as an
automatic means for manufacturing generator rings,
* * * * *