U.S. patent application number 10/669736 was filed with the patent office on 2004-09-23 for heat exchange system chip temperature sensor.
This patent application is currently assigned to Micro Control Company. Invention is credited to Tremmel, Tom A..
Application Number | 20040182564 10/669736 |
Document ID | / |
Family ID | 46300024 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040182564 |
Kind Code |
A1 |
Tremmel, Tom A. |
September 23, 2004 |
Heat exchange system chip temperature sensor
Abstract
A chip temperature sensor includes a support member, a
resistance temperature detector (RTD), and signal leads. The
support member is slidably mountable within a heat sink bore of a
burn-in oven heat exchange system and includes first and second
ends, a socket formed in the first end, a bore extending from the
socket through the second end, and a flange positioned between the
first and second ends. The RTD is seated in the socket and includes
a chip contact surface that is raised relative to the first end.
The RTD is configured to produce a temperature signal that is
indicative of a temperature at the chip contact surface. The signal
leads are attached to the RTD and extend through the bore of the
support member and out the second end of the support member. A heat
exchange system that includes the above-described chip temperature
sensor.
Inventors: |
Tremmel, Tom A.; (New
Brighton, MN) |
Correspondence
Address: |
Brian D. Kaul
Westman, Champlin & Kelly
Suite 1600
900 Second Avenue South
Minneapolis
MN
55402-3319
US
|
Assignee: |
Micro Control Company
Coon Rapis
MN
|
Family ID: |
46300024 |
Appl. No.: |
10/669736 |
Filed: |
September 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10669736 |
Sep 24, 2003 |
|
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10322001 |
Dec 17, 2002 |
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Current U.S.
Class: |
165/247 ;
165/11.1 |
Current CPC
Class: |
G01R 31/2862 20130101;
G01R 31/2874 20130101 |
Class at
Publication: |
165/247 ;
165/011.1 |
International
Class: |
F24F 011/04 |
Claims
What is claimed is:
1. A temperature sensor configured for slidable mounting within a
heat sink bore of a heat sink of a burn-in of a heat exchange
system, the temperature sensor comprising: a support member
slidably mountable within the heat sink bore and having first and
second ends, a socket formed in the first end, a bore extending
from the socket through the second end, and a flange positioned
between the first and second ends; a resistance temperature
detector (RTD) seated in the socket and having a chip contact
surface that is raised relative to the first end, the RTD
configured to produce a temperature signal that is indicative of a
temperature at the chip contact surface; and signal leads attached
to the RTD and extending through the bore of the support member and
out the second end of the support member.
2. The temperature sensor of claim 1, wherein the socket is
rectangular.
3. The temperature sensor of claim 1, wherein the signal leads
extend from a bottom of the RTD, which opposes the chip contact
surface.
4. A heat exchange system for controlling a temperature of an
integrated circuit chip mounted in a burn-in oven, the system
comprising: a heat sink having a chip engaging surface that is
positionable to engage a surface of a chip, a heat sink bore
extending through the chip engaging surface, and a shoulder formed
within the heat sink bore; a temperature sensor including: a
support member slidably mounted in the heat sink bore and having
first and second ends, a socket formed in the first end, a bore
extending from the socket through the second end, and a flange
positioned between the first and second ends, wherein movement of
the support member within the heat sink bore is limited by
engagement of the shoulder by the flange; a resistance temperature
detector (RTD) seated in the socket and having a chip contact
surface that is raised relative to the first end, the RTD
configured to produce a temperature signal that is indicative of a
temperature at the chip contact surface; and signal leads attached
to the RTD and extending through the bore of the support member and
out the second end of the support member; and a resilient member
configured to urge the first end of the temperature sensor through
the chip-engaging surface of the heat sink.
5. The system of claim 4, wherein the socket is rectangular.
6. The system of claim 4, wherein the signal leads extend from a
bottom of the RTD, which opposes the chip contact surface.
7. The system of claim 4, wherein the resilient member is a spring
that engages the flange on a side that is opposite the RTD.
8. The system of claim 4 including: a liquid source; an inlet port
fluidically coupled to the liquid source and in fluid communication
with a heat exchange gap between the surface of the chip and the
chip engaging surface of the heat sink; and a liquid flow
travelling from the liquid source through the inlet port, and into
the heat exchange gap to thereby form a liquid layer.
9. The system of claim 8, wherein the heat exchange gap is defined
by non-contacting portions of the chip engaging surface of the heat
sink and the surface of the chip.
10. The system of claim 8, wherein the heat sink includes a
plurality of passageways in fluid communication with a source of
heat exchanging fluid.
11. The system of claim 8, including a cup member for supporting
the heat sink, the cup member having a wall portion encircling the
heat sink and providing an opening through which a boss of the heat
sink extends.
12. The system of claim 11, including at least one resilient member
for urging the chip engaging surface of the heat sink against the
surface of the chip.
13. The system of claim 8, wherein the liquid flow has a flow rate
that is controlled in response to the temperature signal.
14. The system of claim 8, including: a heat sink temperature
sensor having a heat sink temperature output signal that is
indicative of a temperature of the heat sink; and a liquid
controller for controlling the liquid flow in response to the heat
sink temperate output signal from the heat sink temperature sensor
and the temperature signal from the RTD.
15. The system of claim 14, wherein the liquid controller controls
the liquid flow in response to a thermal resistance between the
chip engaging surface of the heat sink and the surface of the chip
using the heat sink temperature output signal and the temperature
signal from the RTD.
16. The system of claim 8, wherein the liquid source contains
distilled water.
17. The system of claim 8, wherein the heat sink includes a moat
surrounding the chip-engaging surface.
18. A heat exchange system for controlling a temperature of an
integrated circuit chip during burn-in temperature stressing of the
chip, the system comprising: a chip mount for supporting a chip; a
liquid source; a heat sink having a chip engaging surface facing
the chip mount, and having a plurality of inlet ports each
fluidically couple to the liquid source, a heat sink bore extending
through the chip engaging surface, and a shoulder formed within the
heat sink bore; and a temperature sensor including: a support
member slidably mounted in the heat sink bore and having first and
second ends, a socket formed in the first end, a bore extending
from the socket through the second end, and a flange positioned
between the first and second ends, wherein movement of the support
member within the heat sink bore is limited by engagement of the
shoulder by the flange; a resistance temperature detector (RTD)
seated in the socket and having a chip contact surface that is
raised relative to the first end, the RTD configured to produce a
temperature signal that is indicative of a temperature at the chip
contact surface; and signal leads attached to the RTD and extending
through the bore of the support member and out the second end of
the support member; a resilient member configured to urge the first
end of the temperature sensor through the chip engaging surface of
the heat sink; and a liquid flow controller for controlling a
liquid flow travelling from the liquid source through the inlet
ports.
19. The system of claim 18, wherein the socket is rectangular.
20. The system of claim 18, wherein the signal leads extend from a
bottom of the RTD, which opposes the chip contact surface.
21. The system of claim 18, wherein the liquid flow is controlled
by the liquid flow controller based upon the temperature signal
from the RTD.
22. The system of claim 18 including a heat sink temperature sensor
having a heat sink temperature output signal that is indicative of
a temperature of the heat sink.
23. The system of claim 22, wherein the liquid flow controller
controls the liquid flow in response to the heat sink temperature
output signal from the heat sink temperature sensor and the
temperature signal from the RTD.
24. The system of claim 22, wherein the liquid flow controller
controls the liquid flow in response to a thermal resistance
between the chip engaging surface and a surface of a chip being
temperature stressed, wherein the thermal resistance is calculated
using the heat sink temperature output signal and the temperature
signal from the RTD.
25. The system of claim 18 including a cup member for supporting
the heat sink, the cup member having a wall portion encircling the
heat sink and providing an opening through which a boss of the heat
sink extends.
26. The system of claim 18, including at least one resilient member
for urging the chip-engaging surface of the heat sink toward the
chip mount.
27. The system of claim 18, wherein the liquid source comprises
distilled water.
28. The system of claim 18, wherein the heat sink includes a moat
surrounding the chip-engaging surface.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation-in-part of U.S.
patent application Ser. No. 10/322,001, filed Dec. 17, 2002, the
content of which is hereby incorporated by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to devices for
controlling or conditioning the temperature of electronic
components which are being temperature stressed in "burn-in" ovens,
or the like, to determine characteristics of the electronic
components. More particularly, the present invention relates to a
chip temperature sensor for use in a heat exchange system.
BACKGROUND OF THE INVENTION
[0003] Electronic components, such as silicon integrated circuit
chips or other semiconductor devices, are subject to early failure
during their life cycle. Thus, producers of these electronic
components have found it cost-effective to rigorously temperature
stress electronic components prior to their inclusion in electronic
products. By conducting such temperature stressing, and by the
elimination of under-performing electronic components that fail
during the temperature stressing, the reliability of the electronic
components that make it to market by passing the temperature
stressing is greatly enhanced.
[0004] During such "burn-in" temperature stressing, burn-in boards
are used to support a number of electronic components inside a
burn-in oven. Burn-in ovens are typically large enough to hold
several racks of burn-in boards with each burn-in board holding
several integrated circuit chips. The chips are powered and exposed
to heat stress over an extended period of time. During burn-in
temperature stressing of the chips, heat exchange systems are
employed to maintain the chips within a desired temperature range
to prevent overheating of the chips, which can damage properly
functioning chips.
[0005] Heat exchange systems, such as that described in U.S. Pat.
No. 6,288,371 (Hamilton et al.), which is assigned to the Assignee
of the present invention, utilize a heat sink that contacts the
chip being temperature stressed. A helium layer is provided between
the heat sink and the chip to decrease thermal resistance and
increase thermal conductivity there between. Thus, the heat
exchange system of Hamilton et al. is more effective at maintaining
the desired chip temperature than would be possible without the
helium layer since the heat generated by the chip can be exchanged
with the heat exchange system at a higher rate.
[0006] Heat exchange systems can also include a chip temperature
sensor for detecting the temperature of the chip being stressed.
Such temperature sensors typically utilize a thermocouple due to
its compact size. Unfortunately, thermocouples produce voltage
signals that must be converted into a form that indicates the
temperature of the chip being sensed. This is generally
accomplished using a cold junction compensator and an amplifier.
Additionally, highly efficient couplings, such as gold pins and
other special connectors, must be used when relaying the voltage
signals from the thermocouple to prevent signal losses.
[0007] There is a continuing need for improvements to heat exchange
systems, including improvements to the temperature sensors used by
such systems and the thermal conductance between the heat sink and
the chip being stressed.
SUMMARY OF THE INVENTION
[0008] The present invention is generally directed to a heat
exchange chip temperature sensor and a heat exchange system that
includes the chip temperature sensor. The chip temperature sensor
generally includes a support member, a resistance temperature
detector (RTD), and signal leads. The support member is slidably
mountable within a heat sink bore of a burn-in oven heat exchange
system and includes first and second ends, a socket formed in the
first end, a bore extending from the socket through the second end,
and a flange positioned between the first and second ends. The RTD
is seated in the socket and includes a chip contact surface that is
raised relative to the first end. The RTD is configured to produce
a temperature signal that is indicative of a temperature at the
chip contact surface. The signal leads are attached to the RTD and
extend through the bore of the support member and out the second
end of the support member.
[0009] The heat exchange system includes the chip temperature
sensor and the heat sink described above. The heat sink includes a
chip engaging surface that is adapted to engage a surface of the
chip being stressed. A liquid layer fills a heat exchange gap
between the surface of the chip and the chip engaging surface of
the heat sink. The liquid layer provides a low thermal resistance
path between the chip engaging surface of the heat sink and the
surface of the chip, which allows for greater heat transfer there
between for greater control of the chip temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic perspective view of a burn-in oven
having a rack supporting heat exchange systems made in accordance
with the present invention above burn-in boards.
[0011] FIG. 2 is a fragmentary schematic front view of a rack
supporting a thermal board having heat exchange systems made in
accordance with the present invention installed thereon, shown
underlying a burn-in board supporting integrated circuit chips that
are associated with the heat exchange systems with an inset
perspective view of a cam drive used for moving thermal boards into
contact with an associated burn-in board.
[0012] FIG. 3 is a top plan view of a typical thermal board having
heat exchange systems and mounting made according to the present
invention.
[0013] FIG. 4 is a bottom perspective view of a heat exchange
system and support cup in accordance with the present
invention.
[0014] FIG. 5 is a top plan view of the heat exchange system and
cup of FIG. 4.
[0015] FIG. 6 is an end view of the heat exchange system and cup of
FIG. 5.
[0016] FIG. 7 is a sectional view taken on line 7-7 in FIG. 6.
[0017] FIG. 8 is a sectional view taken on line 8-8 in FIG. 6.
[0018] FIG. 9 is a side view of the heat exchange system and cup
from a side opposite from that shown in FIG. 4.
[0019] FIG. 10 is a sectional view taken on line 10-10 of FIG.
5.
[0020] FIG. 11 is a simplified sectional view of a chip engaging
surface of a heat sink and a chip temperature sensor of the heat
exchange system of the present invention in contact with a surface
of an integrated circuit chip.
[0021] FIG. 12 is a magnified sectional view illustrating a heat
exchange gap between a chip engaging surface of a heat sink of the
heat exchange system of the present invention and a surface of an
integrated circuit chip.
[0022] FIG. 13 is a sectional view taken on line 13-13 of FIG.
6.
[0023] FIG. 14 is a schematic diagram of a control system of a
burn-in oven for controlling a heat exchange system that provides a
liquid flow to the heat exchange gap illustrated in partial
cross-section, in accordance with embodiments of the invention.
[0024] FIG. 15 is a partial top perspective view of a heat sink in
accordance with an embodiment of the invention.
[0025] FIG. 16 is a perspective view of a support member of a chip
temperature sensor in accordance with an embodiment of the
invention.
[0026] FIG. 17 is a simplified cross-sectional view of a chip
temperature sensor in accordance with an embodiment of the
invention.
[0027] FIG. 18 is a front end view of a chip temperature sensor in
accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] A burn-in oven that is shown only fragmentarily in FIG. 1 at
10 is used to perform burn-in temperature stressing of integrated
circuit chips 12 on burn-in boards 14. A rack 15 supports the
boards 14 in the oven on tracks 15A. The burn-in boards 14
generally, in the form shown, mount several (typically four or
more) chips 12 having circuits, and each of these chips 12 is
mounted in a chip mount 13 along the plane of the burn-in board 14.
The circuits on the chips 12 are connected with suitable connectors
to external control circuitry 12A (FIG. 2) for operating the
circuits and carrying out conventional burn-in temperature
stressing of the chips 12. The chips 12 have upper plane surfaces
16 that are to be contacted with a heat exchange system of the
present invention for removing excess heat generated in response to
the power consumption of the circuits to maintain the chips 12
within a desired temperature range during burn-in temperature
stressing.
[0029] A thermal board assembly shown at 20 in FIGS. 1, 2 and 3, is
mounted on movable frames 21 on each side of the rack 15 that slide
vertically, and include uprights 21A that are slideably mounted
relative to fixed frame uprights 15B on which burn-in board tracks
15A are supported. As shown in FIG. 1, the rack 15 includes eight
burn-in boards 14 and eight thermal boards 20, however the rack 15
can be configured to handle more or fewer burn-in and thermal
boards. The slidable frames 21 are provided on each side of the
rack 15. Thermal board support tracks 21C are mounted on the
vertically movable uprights 21A and have grooves 21D to receive
flanges 20E on the thermal boards (see FIG. 2). The frames 21 are
vertically slidable to move thermal board assemblies 20 toward and
away from the chips 12 on the overlying burn-in board 14. The side
flanges 20A on the thermal boards 20 slide into the grooves 21D on
the tracks 21C. The thermal board assemblies are supported parallel
to the respective burn-in board 14. The movement of the thermal
board assemblies 20 can be accomplished in any desired manner, so
the structure for supporting and moving it is shown only
schematically.
[0030] The movable frames 21, in addition to the tracks 15A, that
are bolted to and hold the vertical uprights 21A together and lower
and upper cross plates 22 and 22A also join the uprights 21A (see
FIGS. 1 and 2). The lower cross plate 22 on each movable frame 21
has a cam follower pin 22B mounted thereon and protruding out to
the side. The cam follower pin serves as a drive for vertically
reciprocating the frame 21. A cam and drive assembly 25B is mounted
onto a fixed cross plate 25A mounted to the uprights 15B of the
rack supporting the burn-in boards and thermal boards. The cam and
drive assembly 25B includes a gear box 25C that is driven from a
motor 25D (see also FIG. 2) that includes an output shaft 25E that
extends through the fixed plate 25A and has a spiral cam member 25F
mounted on the shaft. Motors 25D are stepper motors, which are
synchronized and operated by a controller 25H shown schematically
in FIG. 2. The spiral cam member will rotate when the motor is
running, and has a spiral groove 25G that receives the cam follower
pin 22B so that when the cam motor 25D is driven and the gear box
25C drives the spiral cam 25C, the pin 22B, which is in the groove
25G, will be moved relative to the central axis of the shaft 25E.
The movement of the pin 22B will reciprocate the frames 21 so that
the movement of the thermal board assemblies 20 is accomplished to
move the thermal boards toward or away from the burn-in boards, as
shown in FIG. 2. There are guide pins 23D on the thermal board
assembles that mate with guide tubes 14E on the burn-in boards for
alignment. Also, extractor handles 15H are shown. These are used
for extracting the burn-in boards.
[0031] The thermal board assemblies 20 include metal heat
conductive plates 23, on which heat exchange systems 26 of the
present invention are mounted, as shown in FIGS. 2 and 3. Each chip
12 has a corresponding heat exchange system 26, with which it is
aligned. Each heat exchange system 26 includes a central heat sink
block 29 that has an end boss 27 having a chip engaging surface 28
that will contact a surface 16 of one of the chips 21 that is being
temperature stressed on the burn-in board 14.
[0032] FIG. 10 and other cross-sectional views of heat exchange
system 26 show the central block or heat sink 29. As shown, the
block 29 has a plurality of longitudinal passageways 30 bored
therethrough, with end cross passages that connect the passageways
so that water from a water input connector and line 32, shown in
FIGS. 3-7, will enter a first passageway 34A, and the water then
will be circulated through additional passageways 34B, 34C, 34D,
34E, 34F, 34G and 34H in sequence. The waste water or water that
has been used for cooling, comes through the last passageway 34H
and is discharged through a connector and line 36 and sent to a
drain. FIG. 7 shows a connecting passageway 35A that connects
passageways 34D and 34E and FIG. 10 shows a passageway 35B connects
passageways 34F and a passageway 35C that connects passageway 34G
and 34H. The connecting passageways are made in the ends of the
block. End caps are made in a conventional manner and are soldered
or otherwise sealed on the ends of block 29 to enclose the
passageways cut therein. The end caps are soldered in place so the
central block becomes unitary as is generally shown in the
cross-sectional views of FIGS. 7, 8 and 10.
[0033] The heat sink block 29 has a central passageway 40 that is
bored into the block 29 at the boss 27. A shoulder 31 surrounds an
opening 43 in boss 27. The passageway 40 has an axis that is at
right angles to the plane of the block and plate 23 and at right
angles to the axes of passageways 30. The through passageway 40
extends upwardly, and a cap 42 has a threaded neck that threads
into the end of passageway 40 and seals it. The cap 42 also has a
flange 42A that bears upon a cover plate 42B that covers a layer of
insulation 42C that, in turn, overlies a heater 44 sandwiched
between the insulation layer 42B and an upper surface 46 of the
central block 29. The neck of cap 42 has a passageway 42D that
aligns with passageway 40 and is of smaller diameter. The threads
on the neck of the cap seal the passageway 40 along its edge and
the heater 44 and insulation layer 42C form a gas and liquid tight
seal.
[0034] There are two stacked gaskets 50 and 52 on top of the
flanges 42A. A clamp plate 54 is used for holding the cover plate
in position on top of the cap 42. The gaskets 50 and 52 have
central holes aligning with passageway 42D and clamp plate 54
closes off the holes the passageway 42D. The clamp plate 54 is held
with screws 55 threaded into flange 42A.
[0035] A chip temperature sensor 60 is slidably mounted in the end
of the heat sink bore 40, as shown in FIG. 7. Sensor 60 generally
includes a support member 61, a resistance temperature detector
(RTD) 62, and signal leads 63. One embodiment of sensor 60 is
illustrated schematically in FIGS. 16-17. Support member 61 is
preferably a cylindrical member that includes first and second ends
64 and 65, a socket 66 formed in first end 64, and a bore 67
extending from socket 66 through second end 65, as shown in the
perspective view of FIG. 16. Support member 61 also includes an
annular flange 68 that is positioned between first and second ends
64 and 65. Heat sink bore 40 includes a shoulder 41 at the lower
end, which engages flange 68 to retain sensor 60 within the bore
40. The flange 68 slides in the larger part of the bore 40. There
is a small space or clearance between the periphery of the bore 40
and the flange 68 and also between cylindrical portion 69 and the
surface defining opening 43, which allow chip temperature sensor 60
to slide within bore 40 and extend first end 64 through heat sink
bore opening 43.
[0036] RTD 62 is received by socket 66 of support member 61. Socket
66 is preferably shaped to conform to the RTD 62, which can be
secured therein using an adhesive, by swaging the preferably
plastic support member 61 against RTD 62, or using other methods.
In accordance with one embodiment of the invention, socket 66 is
rectangular to receive a rectangular RTD 62. However, socket 66 can
take on other conforming shapes including those that pre-set the
orientation of RTD 62 relative to support member 61.
[0037] RTD 62 includes a chip contact surface 70, at which RTD 62
is configured to detect a temperature of the surface 16 of the chip
12 when in contact therewith. Chip contact surface 70 is preferably
raised relative to the first end 64 to ensure good contact with
chip surface 16 of chip 12. A current is conducted through signal
leads 63, shown in FIG. 17, and through RTD 62. The chip
temperature signal produced by RTD 62 is in the form of a voltage
drop across RTD 62 that is measured at signal leads 63 by a voltage
detector, which can be a component of the control electronics for
the heat exchange system or burn-in oven. Although support member
61 insulates RTD 62 from the cool heat sink 29, the chip
temperature indicated by RTD 62 is preferably compensated to
account for the cool surroundings.
[0038] In accordance with one embodiment of RTD 62, signal leads 63
extend from bottom 73 that opposes the chip contact surface 70,
through the bore 67, and out the second end 65 to communicate the
chip temperature signal to appropriate control circuitry (not
shown) of the heat exchange system 26 or burn-in oven 10. This
configuration reduces the size of the RTD 62 as compared to typical
RTD's having signal leads extending from the side. As a result,
first end 64 of support member can be made smaller than would
otherwise be possible. Additionally, the bottom extending signal
leads 63 of RTD 62 are protected from potentially damaging wear
that could occur if they extended from a side of the RTD as a
result of sliding engagement with bore 40.
[0039] RTD 62 provides advantages over other temperature detectors,
such as thermocouples. For example, the temperature detected by the
RTD can be directly determined through measurement of a voltage
drop across the RTD 62 at signal leads 63. Thermocouples, on the
other hand, produce a voltage signal that must be transformed into
something that represents the temperature sensed by the
thermocouple using a cold junction compensator and an amplifier.
Additionally, highly efficient couplings, such as gold pins and
other special connectors, must be used when relaying the voltage
signal of a thermocouple to prevent signal losses, something which
is unnecessary for RTD's.
[0040] A low force coil spring 75 is mounted in bore 40 and bears
against the flange 68 and is held in the bore 40 by cap 42. When
unrestrained, the spring 75 directs the support member 61 along
with RTD 62 outwardly such that flange 68 contacts shoulder 41 and
end 64 extends through opening 43 of bore 40. The cross-sectional
view of FIG. 7, shows the support member 61 retracted slightly from
heat sink 29. It can be seen in FIG. 11 that the low force spring
75 will hold RTD 62 in engagement with the chip surface 16 under
spring load, but the spring 75 will yield to permit the chip and
RTD 62 at end 64 of support member 61 to be in intimate contact
when the chip engaging surface 28 of heat sink 29 contacts the
surface 16 of the chip 12.
[0041] Even though good contact is established between chip
engaging surface 28 and surface 16 of chip 12, the thermal
resistance between heat sink 29 and chip 12 limits the rate of heat
transfer between heat sink 29 and chip 12, which, in turn, limits
the amount of power that can be applied to the chip during burn-in
temperature stressing. The primary reason for the high thermal
resistance is due to incongruities between the chip engaging
surface 28 of heat sink 29 and the surface 16 of chip 12, that
results in the formation of a heat exchange gap 78 between
non-contacting portions of the surfaces 16 and 28, as shown in FIG.
12. When the heat exchange gap 78 is filled with air, the thermal
resistance between chip engaging surface 28 and chip surface 16 is
increased due to the low thermal conductivity of air.
[0042] In accordance with one aspect of the present invention,
thermal resistance between heat sink 29 and the chip 12 is
decreased through an introduction of a liquid layer 71 there
between, as shown in FIG. 12. Liquid layer 71 is preferably formed
of distilled water, but other suitable liquids can be used. Liquid
layer 71 has a high thermal conductivity relative to air, or even
helium, resulting in a significant reduction to the thermal
resistance between heat sink 29 and chip 12. Estimates indicate
that the thermal resistance between a heat sink 29 with an eighteen
by eighteen millimeter chip engaging surface 28 and a chip 12, can
drop from approximately 0.3.degree. C./Watt when helium fills the
heat exchange gap 78, to approximately 0.06.degree. C./Watt when
the liquid layer 71 formed by distilled water is used to fill the
heat exchange gap 78. This configuration allows for the temperature
stressing of high performance chips through application of high
power (e.g., 625 watts) while maintaining the temperature of the
chips within the desired stressing range (e.g., typically
120-140.degree. C.).
[0043] Liquid layer 71 can be formed of a small volume of liquid,
(such as 0.05 cubic centimeters) in order to fill the heat exchange
gap 78 that is formed between the non-contacting surfaces of heat
sink 29 and the chip 12 being temperature stressed. Liquid layer 71
can be formed as a fixed volume of liquid, or can be formed by a
liquid flow that is injected into heat exchange gap 78. Liquid
layer 71 can be formed of a cooled liquid to provide further
cooling of an integrated circuit chip 12 under stress. The flow
rate of the liquid flow can be adjusted to provide additional heat
transfer from the chip 12 being temperature stressed.
[0044] In accordance with one embodiment of the invention, heat
exchange system 26 includes a liquid source 74 that is fluidically
coupled to the heat exchange gap 78 to provide the liquid layer 71,
as shown in FIGS. 6 and 7. In accordance with one embodiment, the
liquid source 74 is coupled to at least one inlet port 120, which
is in fluid communication with the heat exchange gap. In accordance
with one embodiment, the inlet ports 120 are formed in heat sink 29
and open to the heat exchange gap 78 through chip engaging surface
28, as illustrated in FIGS. 4, 12 and 13. As shown in FIG. 7, it
can be seen that an input line and connector 122 is connected to a
hose barb 72 that in turn is connected to liquid source 74 through
a valve 76. Valve 76 is preferably a solenoid valve that can be
manually operated, operated by a controller, or operated in some
other desired manner. Input line 122 is connected to a connecting
passageway 124 that in turn is connected to a horizontal
passageways 126 and 128 that are fluidically coupled to inlets 120
through vertical passageways 130, as shown in FIGS. 7, 10 and 13.
Additional inlets 120 can be provided as desired.
[0045] During burn-in temperature stressing, the liquid layer may
runoff, evaporate, or be converted into steam. The liquid layer in
the heat exchange gap can be replenished by the liquid flow from
liquid source 74. In accordance with one embodiment of the
invention, burn-in oven 10 can purge the moist air in the burn-in
chamber 132, in which the thermal and burn-in boards are mounted,
with air purging system 134, shown in FIG. 1. Air purging system
134 includes a source of compressed gas 136, that is fluidically
coupled to the burn-in chamber 132 by an air duct 138. A valve 140
is positioned in line with the air duct 138 and is configured to
control an airflow (indicated by arrow 142) from the source of
compressed gas 136 into the burn-in chamber 132. Source of
compressed gas 136 includes compressed dry air, nitrogen, or other
gas, which replaces the moist air within chamber 132 as airflow 142
is introduced therein. In addition to exhausting the moist air in
the burn-in chamber 132, the air purging system 134 can provide
additional cooling of the burn-in boards. A dehumidifier can also
be included in the system to remove moisture from the air.
[0046] Liquid runoff from heat exchange gap 78 can be accommodated
by the formation of a moat 160 surrounding chip engaging surface 28
of heat sink 29, as illustrated in FIG. 15. The moat 160 is defined
by channel sections 162, 164, 166, and 168 that are formed in heat
sink 29 and surround chip engaging surface 28. The moat 160 is
sized to contain liquid overflow from the heat exchange gap 78 to
prevent liquid from accumulating on the thermal board 20 to which
heat sink 29 is mounted or contacting other components there below.
One or more drains 169 are formed at the base of one of the channel
sections. Drain 169 is preferably fluidically coupled to a vacuum
system that sucks the liquid overflow from moat 160 into drain 169.
The drained liquid overflow can then be delivered to waste or
recovered for reuse.
[0047] The heat exchanger 26 is mounted in an outer cage or housing
called a "cup" 77 that has a flange 79 around the periphery thereof
that bolts or fastens in a suitable manner with fasteners to the
metal thermal plate 23. The cup 77 has an opening 80 at the top and
side walls 82 on two spaced sides with inwardly turning flanges 84
at the lower ends. The sides of the cup at right angles to walls 82
form openings 88 and 90, but there are internal flanges 84A, which,
together with edges 84, surround a central opening 86 through which
the end portion 29A of the thermal block extends with some
clearance. The heat sink block 29 has a larger upper portion that
forms a shoulder 29B that rests on the flange 84 when the portion
29A extends through the opening 86, as shown in FIGS. 7, 8 and 10.
The openings 88 and 90 are at right angles to the main depending
walls 82, to permit connections for water, and for the electrical
connections to extend to the heat sink block. The portion 29A is
encircled by the flanges 84 and 84A and the shoulder 29B is
contained and rests thereon.
[0048] A resilient member 90, depicted as a compression coil
spring, is mounted in a cavity 92 formed in the clamp plate 54. The
resilient member 90 bears against the underside of the thermal
plate 23, as shown in the cross-sectional views to provide a spring
load urging the shoulder 29B down against the flanges or bottom
edge walls 84 and 84A.
[0049] It should also be noted that the heat sink block 29 is
spaced from the side walls 82, and the partial side walls forming
the end openings 88 and 90, so that the block 29 can move up to
displace the shoulders 29B from the wall flanges 84 and 84A under
pressures applied when the thermal plate assembly 20 is moved down
against an aligned burn-in board 14. The block 29 can cock slightly
because the opening 86 is made slightly larger than the end portion
29A that extends through it. This permits the block 29 to generally
align with the surface of the chip that it is moved against, so
that the chip engaging surface 28 of the boss 27 of the heat sink
will come into as close to continuous contact as possible as shown
in FIG. 11. Additionally, the chip temperature sensor 60 will
retract, as permitted by the spring 75.
[0050] The spring 90 will also retract and yield so that the heat
sink 29 can move upwardly and self-aligning because the cup 77 will
positively capture the heat sink and yet permit it to retract and
move for self-alignment.
[0051] Thus, the chip temperature sensor 60 is spring loaded with a
light spring, and the entire heat sink block is spring loaded with
at least a second spring 90 of different strength. The structure
permits the signal leads indicated 63 to pass upwardly through the
bore 40, and through the bore 42D, and through the center opening
in the gasket 50, and then laterally out sandwiches between the
gaskets 50 and 52, as shown in FIGS. 7 and 10. This eliminates the
need for providing a groove or opening for the sensor wires and yet
keeps the passageway 40 sealed.
[0052] The heater 44 also has wires or leads 98 that pass out along
the top plate 42B, and are supported thereby.
[0053] The temperature of the heat sink block 29 also is sensed and
controlled with a suitable heat sink temperature sensor 100 that is
installed in a bore in the block portion 29A as shown in FIG. 7.
Suitable leads 101 can be used for sensor 100, which could be a
thermocouple or other suitable temperature sensor.
[0054] As shown in FIG. 3, manifolds indicated at 102 are provided
for the water connections, and are shown schematically, and
solenoid valves shown schematically at 104 can be used for
providing water to each of the individual heat sinks. A controller
106 shown schematically receives the signals from chip temperature
sensor 60 and will provide signals to the individual solenoid
valves 104 in a suitable manner to open them if cooling is needed
and close them if the chip temperature is in the desired range.
Controller 106 also can receive a signal from the heat sink
temperature sensor 100 for overall temperature control and will
provide output signals to the leads 98 for the heater, when that is
needed. Control of the sensors 60 and 100 can be through suitable
connectors and circuitry shown schematically on a circuit board 108
in FIG. 3. Other suitable connectors can be used for carrying the
power to the solenoids 104, and the overall arrangement can be made
so that the controller 106 is not on the thermal board, but is kept
separate. By regulating the flow of water using individual solenoid
valves for each of the heat sinks that are used with a burn-in
board assembly (four in the situation shown) the temperature of the
chips can be maintained in a desired stressing range, and again,
the introduction of the liquid layer 71 to the heat exchange gap 78
provides good thermal coupling between the heat sink blocks and the
associated chip on the burn-in board to accommodate irregularities
in the surfaces that mate.
[0055] FIG. 14 is a schematic diagram of the control system of the
heat exchange system 26 that is used to control the liquid flow
between liquid source 74 and the heat exchange gap 78. As
illustrated, controller 106 can receive a chip temperature output
signal (depicted as arrow 150) from chip temperature sensor 60, and
a heat sink temperature output signal (depicted as arrow 152) from
heat sink temperature sensor 100. The chip temperature output
signal 150 is indicative of a temperature of the chip 12 being
stressed. The heat sink temperature output signal 152 is indicative
of a temperature of the heat sink 29. Controller 106 can control
the liquid flow (depicted as arrow 154) traveling to the heat
exchange gap 78 in response to the temperature output signals.
[0056] In general, the liquid flow 154 can be triggered when the
temperature of the chip 12 exceeds a threshold value. Accordingly,
burn-in temperature stressing of chip 12 can be conducted without
the formation of liquid layer 71 in the heat exchange gap 78 until
the temperature of the chip 12, as indicated by chip temperature
output signal 150, exceeds the threshold value, at which time
controller 106 can open valve 76 to introduce the liquid layer 71
in the heat exchange gap 78 and thereby decrease the thermal
resistance between heat sink 29 and chip 12 and increase the
thermal transfer therebetween to cool chip 12 below the threshold
value.
[0057] In accordance with another embodiment of the invention,
controller 106 is adapted to calculate a thermal resistance between
heat sink 29 and chip 12 using the chip temperature output signal
150 and the heat sink temperature output signal 152 from sensors 60
and 100, respectively. The thermal resistance can be calculated in
accordance with the following equation:
Q=[T.sub.chip-T.sub.heat sink]/power
[0058] where Q is the thermal resistance, T.sub.chip is the
temperature of the chip being temperature stressed, and T.sub.heat
sink is the temperature of heat sink 29. In accordance with this
embodiment, controller 106 introduces the liquid layer 71 in the
heat exchange gap 78 when the thermal resistance (Q) rises above a
threshold value. In the event that the thermal resistance (Q)
exceeds the threshold value, the introduction of the liquid layer
71 to the heat exchange gap 78 by controller 106 will decrease the
thermal resistance between heat sink 29 and the chip 12 being
stressed to prevent the overheating of the chip. The threshold
value of the thermal resistance (Q) can be selected to provide a
sufficient safety factor that ensures that the system will not
overheat.
[0059] The heater 44 can be used where the chip being stressed has
circuits that do not consume much power, and the temperature has to
be maintained at a particular level requiring the addition of heat.
Of course, during that time, the water cooling would not be used,
but heat would be added through the thermal block, and the heat
conducting layer of liquid can also be provided at that time for
conducting heat to a chip.
[0060] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *