U.S. patent application number 10/114601 was filed with the patent office on 2003-10-02 for diamond heat sink.
Invention is credited to DeBenedictis, Matthew Michael, LeBlanc, Stephen Paul, Miller, Richard Paul, Paradis, Leo Richard.
Application Number | 20030183368 10/114601 |
Document ID | / |
Family ID | 28453813 |
Filed Date | 2003-10-02 |
United States Patent
Application |
20030183368 |
Kind Code |
A1 |
Paradis, Leo Richard ; et
al. |
October 2, 2003 |
Diamond heat sink
Abstract
A heat sink made of a natural or polycrystalline diamond
substrate with fins formed thereon. Diamond is grown to form a
substrate and a laser is used to cut channels in the substrate to
form the fins.
Inventors: |
Paradis, Leo Richard;
(Chelmsford, MA) ; DeBenedictis, Matthew Michael;
(Lynn, MA) ; LeBlanc, Stephen Paul; (Sratham,
NH) ; Miller, Richard Paul; (Franklin, MA) |
Correspondence
Address: |
Iandiorio & Teska
260 Bear Hill Road
Waltham
MA
02451-1018
US
|
Family ID: |
28453813 |
Appl. No.: |
10/114601 |
Filed: |
April 2, 2002 |
Current U.S.
Class: |
165/80.3 ;
165/185; 257/E23.098; 257/E23.111 |
Current CPC
Class: |
H01L 2924/0105 20130101;
H01L 2924/0105 20130101; H01L 2924/00 20130101; H01L 2924/01079
20130101; H01L 2924/01042 20130101; H01L 2924/01082 20130101; H01L
2924/014 20130101; H01L 2924/01005 20130101; H01L 2924/01013
20130101; H01S 5/02484 20130101; H01L 2924/12042 20130101; H01L
23/473 20130101; H01L 2924/0105 20130101; H01L 2924/19042 20130101;
H01L 2924/01082 20130101; H01L 2924/00014 20130101; H01L 2924/0132
20130101; H01L 2924/01079 20130101; H01L 23/3732 20130101; H01L
2224/8319 20130101; H01L 2224/83801 20130101; H01L 2924/01074
20130101; H01L 2224/29111 20130101; H01L 2924/01322 20130101; H01L
2924/0132 20130101; F28F 2260/02 20130101; H01L 2924/01029
20130101; H01L 2924/01079 20130101; H01L 2924/19043 20130101; H01S
5/02423 20130101; H01L 2924/157 20130101; H01L 24/83 20130101; H01L
2924/01033 20130101; H01L 2924/01078 20130101; H01L 2924/01006
20130101; H01L 2924/0132 20130101; F28D 2021/0029 20130101; F28F
3/04 20130101; F28F 21/02 20130101; H01L 2224/29111 20130101; H01L
2924/10329 20130101; H01S 5/4025 20130101; H01L 2924/12042
20130101; H01L 2924/01039 20130101; H01L 24/32 20130101; H01L
2924/1433 20130101 |
Class at
Publication: |
165/80.3 ;
165/185 |
International
Class: |
F28F 007/00 |
Claims
What is claimed is:
1. A heat sink comprising: a natural or polycrystalline diamond
substrate with fins formed thereon.
2. The heat sink of claim 1 in which the diamond is
chemical-vapor-deposited diamond or diamond-like-carbon.
3. The heat sink of claim 1 in which the fins extend continuously
along the substrate.
4. The heat sink of claim 1 in which the fins are pin fins.
5. The heat sink of claim 1 in which the substrate and the fins are
monolithic.
6. The heat sink of claim 1 in which the substrate has a plurality
of layers.
7. The heat sink of claim 6 in which the fins are cut in all of the
layers.
8. The heat sink of claim 6 in which the fins are cut in a subset
of all the layers.
9. The heat sink of claim 1 in which the fins form microchannels in
the substrate.
10. The heat sink of claim 1 in which the substrate has opposing
top and bottom planar surfaces, and the fins are formed in one said
planar surface.
11. The heat sink of claim 1 in which the fins are formed in an
edge of the substrate.
12. An integrated cooling system comprising: a heat source; a heat
sink made of a natural or synthetic diamond substrate with fins
formed thereon mounted to the heat source; a metalization layer at
the interface between the heat source and the heat sink; and a
bonding layer between the metalization layer and the heat source
for securing the heat source to the heat sink.
13. The cooling system of claim 12 further including a metalization
layer formed on the heat source and mated with the bonding
layer.
14. The cooling system of claim 12 in which the bonding layer is
solder.
15. The cooling system of claim 12 in which the bonding layer is
braze.
16. The cooling system of claim 12 in which the bonding layer is
formed by compression bonding.
17. The cooling system of claim 12 in which the diamond is
chemical-vapor-deposited diamond or diamond-like-carbon.
18. The cooling system of claim 12 in which the fins extend along
the substrate.
19. The cooling system of claim 12 in which the fins are pin
fins.
20. The cooling system of claim 12 in which the substrate and the
fins are monolithic.
21. The cooling system of claim 12 in which the substrate has a
plurality of layers.
22. The cooling system of claim 12 in which the fins are cut in all
of the layers.
23. The cooling system of claim 12 in which the fins are cut in a
subset of all the layers.
24. The cooling system of claim 12 in which the fins form
microchannels in the substrate.
25. The cooling system of claim 12 further including a diamond
support disposed between the heat sink and the heat source.
26. An optical device comprising: a reflective surface; and a heat
sink adjacent the optical surface, the heat sink including a
natural or polycrystalline diamond substrate with fins formed
thereon.
27. A window comprising: a natural or a polycrystalline diamond
substrate with upper and lower surfaces; and fins formed in at
least one edge of the substrate.
28. An integrated cooling system comprising: an integrated
electronic or optical device; and a natural or polycrystalline
diamond substrate mated on one surface with the device and
including fins formed on the substrate for cooling the device.
29. A method of manufacturing a diamond heat sink, the method
comprising: growing diamond to form a substrate; and using a laser
to cut channels in the substrate to form fins thereon.
30. The method of claim 29 further including growing multiple
diamond layers and securing the multiple diamond layers together to
form a substrate with discrete layers before the channels are
cut.
31. The method of claim 30 in which cutting includes cutting
channels in all the layers.
32. The method of claim 30 in which cutting includes cutting
channels in a subset of the layers.
33. The method of claim 29 in which growing includes
chemical-vapor-deposition of diamond.
34. The method of claim 29 in which the channels are cut to be 150
um or less in width to form microchannels.
35. The method of claim 29 in which the channels are cut to extend
in one direction to form straight fins.
36. The method of claim 29 in which the channels are cut to extend
in two different directions to form pin fins.
37. The method of claim 29 further including the addition of a
metalization layer to the substrate.
38. The method of claim 29 in which the substrate is polished
before it is cut.
39. A heat sink assembly comprising: a natural or polycrystalline
diamond substrate with fins formed thereon; and a natural or
polycrystalline diamond support attached to the substrate.
40. The heat sink of claim 1 in which the diamond is
chemical-vapor-deposited diamond or diamond-like-carbon.
41. The heat sink assembly of claim 39 in which the fins extend
continuously along the substrate.
42. The heat sink assembly of claim 39 in which the fins are pin
fins.
43. The heat sink assembly of claim 39 in which the substrate and
the fins are monolithic.
44. The heat sink assembly of claim 39 in which the substrate has a
plurality of layers.
45. The heat sink assembly of claim 44 in which the fins are cut in
all of the layers.
46. The heat sink assembly of claim 44 in which the fins are cut in
a subset of all the layers.
47. The heat sink assembly of claim 39 in which the fins form
microchannels in the substrate.
48. The heat sink assembly of claim 39 in which the substrate has
opposing top and bottom planar surfaces, and the fins are formed in
one said planar surface.
49. The heat sink assembly of claim 39 further including
metalization on the support and metalization on the substrate.
50. The heat sink assembly of claim 39 further including a heat
source mounted on the support.
51. The heat sink assembly of claim 50 further including
metalization on the heat source.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a novel heat sink made of natural
or polycrystalline diamond.
BACKGROUND OF THE INVENTION
[0002] State of the art cooling systems with integral natural or
polycrystalline diamond heat spreaders include a heat source such
as a RF power amplifier chip, a diode chip or chip array that may
be light emitting, or a power regulator chip attached to a diamond
submount, which serves as a heat spreader. The thermal purpose of
the diamond heat spreader is to reduce the intensity level of the
heat flux emanating from the heat source, thereby making it more
amenable to transfer to more conventional heat sink materials such
as copper or aluminum which possess poorer thermal transport
properties than diamond. Copper or aluminum materials are formed
into heat sinks for the purpose of further reducing the heat flux
density thereby allowing its efficient introduction into the heat
rejection medium which might be gaseous or liquid, or even a solid
thermal mass. Thus, heat dissipated in the electrical component
flows through a complex mechanical assembly encountering several
interfaces along the way.
[0003] Unfortunately, each interface resists heat flow which must
be overcome by increasing the temperature in the assembly and
ultimately, at the source. Special precautions are taken at each
interface in order to reduce the resistance to heat flow. The
bottom of the heat source and the diamond heat spreader are plated
with special materials that enhance their affinity to low
resistance interface materials including solders such as gold/tin
eutectic. However, high temperatures persist at the source leading
to premature electrical failure of the power-dissipating device and
causing system failure and downtime and increasing system-operating
expense. Alternatively, complex and bulky refrigeration systems are
required to lower device temperatures to acceptable levels.
Frequently, these systems are incapable of dramatically reducing
device temperature.
[0004] For example, one arrangement consists of an RF power
amplifier chip soldered to a diamond submount, which in turn is
soldered to chip carrier made of copper molybdenum. The carrier is
adhesively bonded to an amplifier package, which in turn is bonded
to an aluminum heat sink. A refrigerated anti-freeze solution flows
over the fin-like surfaces of the heat sink picking up the
dissipated heat and carrying it away from the heat source for
ultimate rejection to the environment.
[0005] As solid state electrical devices are made smaller and
smaller and yet at the same time designed to process more power and
thus more heat, researchers are continuously looking for ways to
lower the thermal resistance for heat transfer from the active
regions of the device to the environment.
[0006] In response, those skilled in the art have attempted to etch
microchannels in the base of silicon devices and to mount laser
diode arrays on silicon in which the microchannels have been
etched. See U.S. Pat. No. 5,548,605. Another approach uses
epitaxial lift-off (ELO) and grafting which yield epitaxial GaAs
films of thickness as thin as 200 .ANG. on diamond substrates. See
Goodson et al., "Improved Heat Sinking for Laser-Diode Arrays using
Microchannels in CVD Diamond", IEEE Transactions on Components,
Packaging, and Manufacturing Technology--Part B, vol. 20, No. 1,
February 1997, incorporated herein by this reference.
[0007] In this article, the authors theorized that microchannels
could be formed in diamond instead of silicon to lower the thermal
boundary resistance since diamond is the best heat conductor known.
The idea of forming microchannels in diamond, however, was only
notional and the authors provided only a theoretical basis for
unexplained future experimental work: "future experimental work
needs to include several technological innovations that make the
proposed cooling system ready for practical implementations." Id.
page 108 (emphasis added).
SUMMARY OF THE INVENTION
[0008] It is therefore an object of this invention to provide a
heat sink made of natural or, more typically, polycrystalline
diamond suitable for practical implementations.
[0009] It is a further object of this invention to provide such a
heat sink which greatly reduces resistance to heat transfer from a
heat source such as a power amplifier chip or a laser diode array
to the environment.
[0010] It is a further object of this invention to provide such a
heat sink which eliminates many of the interfaces between the power
dissipating device and the environment.
[0011] This invention results from the realization that the thermal
resistance to heat transfer from a heat source such as a power
amplifier chip or a semiconductor laser-diode array to the
environment can be improved and numerous interfaces between the
power dissipating chip and the heat sink eliminated by using a
laser to cut microchannels in the diamond submount previously used
as a lateral heat spreader thereby converting the diamond submount
into a heat sink with the remaining diamond material acting as heat
transfer surfaces or fins and defining microchannels between the
fins.
[0012] This invention features a heat sink comprising a natural or
polycrystalline diamond substrate with fins formed preferably via
laser cutting operations thereon. In the preferred embodiment, the
diamond is chemical-vapor deposited diamond but it may also be
diamond-like-carbon. The fins typically extend continuously along
the substrate but may instead be pin fins. In some embodiments, the
substrate and the fins are monolithic. In other embodiments,
substrate has a plurality of layers and the fins are cut in all of
the layers or instead only a subset of all the layers.
[0013] In the preferred embodiment, the fins form microchannels in
the substrate. Typically, the substrate has opposing top and bottom
planar surfaces and the fins are formed in one said planar surface.
In other embodiments, however, the fins are formed in an edge of
the substrate.
[0014] An integrated cooling system in accordance with the subject
invention includes a heat source, a heat sink made of a natural or
synthetic diamond substrate with fins formed thereon mounted to the
heat source, a metalization layer at the interface between the heat
source and the heat sink, and a bonding layer between the
metalization layer and the heat source for securing the heat source
to the heat sink. In the preferred embodiment, the metalization
layer is a gold layer formed on the heat sink substrate and there
is also a metalization layer formed on the heat source and mated
with the bonding layer. The bonding layer is typically solder, but
may also be braze, or formed by compression bonding.
[0015] An optical device in accordance with the subject invention
includes a reflective surface and a heat sink adjacent the optical
surface, the heat sink including a natural or polycrystalline
diamond substrate with fins formed thereon.
[0016] A window in accordance with this invention includes a
natural or a polycrystalline diamond substrate with upper and lower
surfaces and fins formed in at least one edge of the substrate.
[0017] A method of manufacturing a diamond heat sink according to
this invention includes growing diamond to form a substrate and
using a laser to cut channels in the substrate to form fins
thereon. In some embodiments, multiple diamond plates are grown and
secured together to form a substrate with discrete layers before
the channels are cut. The channels may be cut in all the layers or
only in a subset of the layers.
[0018] Chemical-vapor-deposition of diamond is the preferred
technique for growing the diamond and the channels are preferably
cut to be 150 um or less in width to form microchannels.
[0019] The channels may be cut to extend in one direction to form
straight fins or instead cut to extend in two different directions
to form pin fins. A metalization layer may be added to the
substrate and substrate polished before it is cut by the laser.
[0020] In another embodiment, the heat source is mounted to a
diamond support or strong back which is attached to the diamond
heat sink.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Other objects, features and advantages will occur to those
skilled in the art from the following description of a preferred
embodiment and the accompanying drawings, in which:
[0022] FIG. 1 is a schematic cross-sectional view of a prior
state-of-the-art integrated cooling system using microchannel flow
passages in an aluminum heat sink;
[0023] FIG. 2 is a schematic cross-sectional view of an integrated
cooling system incorporating a diamond heat sink in accordance with
the subject invention;
[0024] FIG. 3 is a schematic view of a rectangular cross-section
pin fin embodiment of the diamond heat sink of the subject
invention;
[0025] FIG. 4 is a top view of a parallelogram cross-section pin
fin embodiment of the diamond heat sink of the subject
invention;
[0026] FIG. 5 is a photograph of a diamond heat sink with deepcut
microchannels manufactured in accordance with the subject
invention;
[0027] FIG. 6 is a photograph of a diamond heat sink with shallow
cut microchannels manufactured in accordance with the subject
invention;
[0028] FIG. 7 is a schematic cross sectional view of a diamond
structural strongback embodiment of the subject invention;
[0029] FIG. 8 is a schematic cross sectional view of a laminated
diamond structural strongback embodiment of the subject
invention;
[0030] FIG. 9 is a photograph of an integrated assembly
manufactured in accordance with the subject invention;
[0031] FIG. 10 is a schematic view of an edge cooled
electromagnetic or light window embodiment of the diamond heat sink
of the subject invention;
[0032] FIG. 11 is a schematic top view of a diamond optical or
electromagnetic energy reflector with integral cooling channels in
accordance with the subject invention;
[0033] FIG. 12 is a bottom view of the reflective device shown in
FIG. 11; and
[0034] FIG. 13 is a schematic view of a RF power amplifier mounted
in a radar embodiment of the diamond heat sink in accordance with
the subject invention.
DISCLOSURE OF THE PREFERRED EMBODIMENT
[0035] As delineated in the Background of the Invention section
above, a prior state of the art in integrated cooling systems is
shown in FIG. 1. Heat source 10 is an electrical device which may
be a power amplifier chip or a laser diode array with a gold
adherence promoting metalization layer 12 plated on the bottom side
thereof as shown. A heat spreader in the form of diamond submount
18 is metalized on both sides with adherent 16 and 20. AuSn solder
layer 14 secures heat source 10 to diamond submount 18. Another
AuSn solder layer 22 secures this subassembly to copper molybdenum
carrier 24. Solder layer 26 is used to secure carrier 24 to
aluminum silicon carbide (AlSiC) package 28. Package 28 is adhesive
bonded as shown by layer 30 to aluminum microchannel heat sink 36.
Antifreeze coolant flows between fins 32 in channels 34 to remove
heat emanating at source 10.
[0036] In one embodiment, heat source 10 is a power amplifier chip
6.6 mm by 4.9 mm in area including a GaN layer 2 um thick and a SiC
layer 100 um thick. Gold adherent layers 12 and 16 are 5 um thick
and AuSn solder layer 14 is 5 um thick. Diamond submount 18 is 380
um thick. Gold adherent layer 20 is 5 um thick and AuSn solder
layer 22 is 5 um thick. CuMo carrier 24 is 1 mm thick and
approximately 25 mm by 25 mm in area. Solder layer 26 is 50 um
thick. AlSiC package 28 is 1 mm thick. Adhesive layer 30 is 250 um
thick. Heat sink 36 comprises a 1 mm face plate with a fin pitch of
.32 mm, and 150 um thick aluminum fin stock 2 mm high. Fins 32
interface with a coolant such as an ethylene glycol/water
composition at a 20.degree. C. inlet temperature. When the coolant
which flows through the microchannels 34 (e.g., 150 um or less in
width) between fins 32 is at this temperature, the temperature of
the active regions of the power amplifier chip 10 (determined by
computer modeling) can be maintained at 233.degree. C.
[0037] Still, as devices are made smaller and smaller and yet at
the same time process more power and thus generate more heat,
researchers have searched for ways to lower the resistance to heat
transfer from the active regions of device 10 to the environment as
represented by the coolant flowing between the microchannels 34 of
heat sink 36.
[0038] This invention results in part from the realization that if
diamond submount 18 is made thicker and is cut with a laser to form
microchannels, it will then perform two functions: lateral
spreading of heat from the active regions of chip 10 and the heat
transfer function previously supplied by aluminum heat sink 36.
Thus, aluminum heat sink 36 can be eliminated and at the same time
many undesirable interfaces which impede heat transfer are also
eliminated (e.g., solder layer 22, carrier 24, solder layer 26, and
adhesive layer 30). In addition, manufacturing process steps are
eliminated including two soldering steps, one adhesive bonding
operation and two gold plating steps.
[0039] Accordingly, the subject invention features diamond heat
sink 40, FIG. 2. Heat sink 40 is made by cutting channels 50 in
diamond submount 52 to form fins 54. Submount 52 is typically
polycrystalline chemical-vapor-deposition (CVD) diamond but could
also be diamond-like-carbon or even natural diamond. Fins 54
typically extend continuously along one surface (typically the
bottom) of the diamond submount but if channels 50 are cut in two
directions, pin fins 53, FIG. 3 may be formed. In FIG. 4, pin fins
53' have a parallelogram cross-section.
[0040] As shown in FIG. 2, the top surface of heat sink 40
typically includes gold adherent plated layer 16 which is attached
via AuSn solder layer 14 to gold adherent layer 12 of heat source
10. Other types of solder or brazing materials or even compression
bonding techniques may be used to secure heat sink 40 to heat
source 10.
[0041] A comparison of FIGS. 1 and 2 reveals the advantages of the
diamond heat sink of the subject invention: in FIG. 2, the
following components of FIG. 1 are eliminated: adherent 20, solder
22, carrier 24, adhesive 26, AlSic package 28, SnPb solder layer
30, and aluminum heat sink 36. In addition, heat sink 40, FIG. 2
performs the function of diamond submount 18, FIG. 1 (lateral heat
spreading) and yet also acts as the cooling interface by virtue of
fins 54, FIG. 2 and channels 50. Furthermore, in FIG. 1, when the
coolant was at 20.degree. C., the maximum temperature of heat
source 10 was 233.degree. C. In contrast, in accordance with the
design of FIG. 2, when the coolant was at 20.degree. C., the
maximum temperature of heat source 10 (determined by computer
modeling) was much lower--162.degree. C. As such, novel diamond
heat sink 40 can result in the elimination of the refrigeration
subsystems of the prior art for a given device temperature, while
reducing the temperature of the heat source thus improving
electrical performance and increasing the useful life of the heat
source. The elimination of the refrigeration system reduces system
weight, space, power consumption and maintenance requirements.
[0042] The microchannels cut in the diamond submount may be forced
to intersect one another if the laser cutter is so programmed. FIG.
3 shows a rectangular cross-section `pin-fins` 53 that results from
channels cut along orthogonal axes. The microchannels may also be
formed to have a parallelogram cross-section by cutting along
non-orthogonal axes, as shown in FIG. 4. These channels forming
approaches may be beneficial to reduce coolant hydrodynamic
boundary layer build-up along the coolant flow through the
microchannels, and thus enhance heat transfer, or reduce coolant
pressure drop. In either case, the basic stack-up of FIG. 2 is
maintained, with the power dissipating device 10 attached via gold
adherent 12 to solder 14 and another gold adherent layer 16 on the
heat sink 40.
[0043] As shown in FIGS. 5 and 6, microchannels 50 cut by a laser
in a CVD submount 52 maybe 150 um in width or less, maybe 0.5 mm
(FIG. 6) to 0.8 mm (FIG. 5) in depth or greater, and may have walls
contoured to correspond to the reduced fin cross sectional area
required to conduct heat at fin tips. The latter may reduce coolant
pressure drop and subsequent pumping power requirements.
[0044] FIG. 7 is a schematic representation of diamond microchannel
heat sink 63, which has been attached to a diamond structural
support or strongback 66. In this embodiment, the power dissipating
device 10 is plated with gold adherent 12 and attached to diamond
strongback 66 via AuSn solder 14. Strongback 66 has been plated top
and bottom with gold adherent 16, thereby allowing the heat sink 63
to be soldered to strongback 66. Strongback 66 provides mechanical
support for heat sink 63 and the electrical devices as well as
providing an electrical ground plane for those devices. In
addition, the strongback serves as a carrier for the electrical
devices as well as providing a mounting frame for bonding into
higher assemblies. Another feature of strongback 66 is that it can
emulate the heat spreader function of the current diamond and, as
such, can be made of higher quality diamond than heat sink 63,
which can reduce overall assembly costs.
[0045] FIG. 8 is a schematic representation of a laminated diamond
microchannel heat sink, which has been attached to a strongback
similar to that shown in FIG. 7. Heat sink 63' is fabricated from a
lamination of thinner diamond submounts 64 and 60 that are plated
with gold adherent 101 and 103 and attached to each other using
AuSn solder 102. After being joined, microchannels 104 are cut
using the laser in accordance with the subject invention. The
lamination approach allows thinner and thus lower cost diamond
material to be fabricated into thicker heat sinks. It also permits
the use of poorer quality diamond material with lower thermal
conductivities at distances further removed from the heat source
where heat flux is reduced. Laminations consisting of three plies
have been successfully fabricated in the laboratory. In some
embodiments, channels 104 may not extend through all the plies as
shown at 104'.
[0046] FIG. 9 is a view of a diamond microchannel heat sink 40,
which has been attached, via gold adherent and AuSn solder to a
diamond strongback 66. Four power dissipating resistors have been
gold adherent plated and soldered to the strongback, and the
diamond microchannel shown in FIG. 6 has been soldered to the
bottom of the strongback in accordance with the subject
invention.
[0047] Thus far, the fins have been shown to be formed in the top
or bottom planar surface of the diamond plate. This, however, is
not a necessary limitation of the subject invention as shown in
FIG. 10 where diamond plate 70 has channels 72 cut in edge surface
74 so as not to interfere with top and bottom planar surfaces 76
and 78 thus rendering diamond plate 70 suitable for use as a
window--i.e., a window between the environment and an infrared
radiation detection subsystem in a missile.
[0048] In FIGS. 11-12, top surface 80 of diamond substrate 82 is
rendered optically reflective by a gold coating, for example, and
channels 84 are cut in bottom surface 88 to form an optical device
with integral cooling channels.
[0049] In FIG. 2, no system packaging is shown. In contrast, in
FIG. 13, there are two diamond heat sinks 40 each with heat source
10 mounted thereto and this subassembly is mounted in package 90
which includes a vacuum brazed aluminum manifold 92 which drives
coolant 94 in the microchannels of each heat sink.
[0050] Heat sink 40, FIGS. 5 and 6 was manufactured as follows. A
CVD diamond blank approximately 1 mm thick and 125 mm diameter was
grown using a microwave assisted CVD diamond reactor at Raytheon
Company's Advanced Materials Laboratory, Lexington, Mass., the
assignee of the subject application, and delivered to the
Mechanical and Materials Engineering Laboratory diamond cutting and
polishing facility to be cut by a laser into the desired
rectangular shape and then ground to a near-optical quality finish.
The blanks were then cut into pieces measuring 18 mm by 8 mm and
placed in the laser cutting facility where a YAG laser was
programmed to transverse the diamond material is an X-Y plane with
various material feed rates along the X-direction to provide the
channel cuts at the approximate desired depth. At the completion of
each X-direction pass, the material was indexed approximately 50 um
inches in the Y-direction and the pass repeated in the opposite
direction. Upon completing each channel cut, which required 3
passes, the material was indexed 150 um in the Y-direction, and the
channel cutting resumed. Channel depth, spacing and contours are
controlled by virtue of the programming loaded into the piece drive
controls, the laser pulse duty cycle, and the number of passes.
This process resulted in producing channels 50 with a depth of 800
um and a width of 150 um.
[0051] Accordingly, in accordance with the subject invention, the
resistance to heat transfer from a heat source such as power
amplifier chip or semi-conductor laser-diode array to the
environment is greatly improved and numerous interfaces between the
power dissipating chip and the heat sink eliminated by using a
laser to cut microchannels in the diamond submount previously used
as a lateral heat spreader to turn the diamond submount into a heat
sink with fins and microchannels.
[0052] The diamond microchannel heat sink in accordance with the
subject invention exhibits the capability to accommodate high heat
flux levels (3,200 W/cm.sup.2)--an order of magnitude above current
technology. As stated above, the diamond heat sink of the subject
invention performs two functions: heat spreading and heat
dissipation. The life expectancy of GaAs type chips is expected to
increase by at least a factor of 2 per Mil-HDBK-217F for a
25.degree. C. reduction.
[0053] In full production runs, a diamond wafer up to 125 mm in
diameter is grown, cut to a convenient size and polished. Many heat
sinks may be manufactured at once by laser cutting the
microchannels and then laser cutting the plurality of heat sinks
from the wafer. Such heat sinks can be used in conjunction with
many different types of heat sources such as power amplifiers,
laser diode chips, integrated electronic devices (ASICs), optical
devices, and the like.
[0054] Therefore, although specific features of the invention are
shown in some drawings and not in others, this is for convenience
only as each feature may be combined with any or all of the other
features in accordance with the invention. The words "including",
"comprising", "having", and "with" as used herein are to be
interpreted broadly and comprehensively and are not limited to any
physical interconnection. Moreover, any embodiments disclosed in
the subject application are not to be taken as the only possible
embodiments.
[0055] Other embodiments will occur to those skilled in the art and
are within the following claims:
* * * * *