Note: Descriptions are shown in the official language in which they were submitted.
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ADDITIVE MANUFACTURED HEAT SINK
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This PCT International Patent Application claims the benefit of
and priority
to U.S. Provisional Patent Application Serial No. 62/778,637, filed December
12, 2018,
titled "Additive Manufactured Heat Sink," the entire disclosure of which is
hereby
incorporated by reference.
FIELD
[0002] The present disclosure relates generally to a heat sink for
conveying heat
from a baseplate to a cover. More specifically, it relates to a heat sink
produced by additive
manufacturing.
BACKGROUND
[0003] Heat skinks are used to convey heat away from a heat source, such
as an
electronic device, to prevent the heat source and/or other components from
being damaged
due to excessive temperatures. One type of heat skink that is conventionally
known is a heat
pipe, which uses a refrigerant fluid that changes from a liquid to a gas at an
evaporator to
transmit heat from the heat source to a condenser, where heat exits as the
refrigerant fluid
condenses back to a liquid. Conventional heat pipes employ a wick to transfer
the
condensed refrigerant from the condenser back to the evaporator.
[0004] Additive manufacturing is used to manufacture parts in a series
of steps by
progressively adding material to the part being manufactured. One type of
conventional
additive manufacturing uses a heat source, such as a laser, to melt a source
material, such as
a metal powder. Typically, the source material is removed from areas where it
is not melted.
This allows parts to be made with a variety of complex shapes.
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SUMMARY
[0005] A heat sink including a baseplate of thermally-conductive
material defining a
lower surface for conducting heat from a heat source is provided. The heat
sink also
includes a radiator disposed upon the baseplate away from the lower surface.
The radiator
includes a skin of melted material formed by additive manufacturing and
enclosing a
chamber. An outer wick of porous material is disposed within the chamber, the
outer wick
coats an inner surface of the skin.
[0006] A method of forming a heat sink is also provided. The method of
forming a
heat sink comprises: selectively melting a source material to form a skin
defining a chamber
of a radiator; forming the source material to define an outer wick of porous
material within
the chamber coating an inner surface of the skin; and attaching a baseplate of
thermally-
conductive material to the radiator to enclose the chamber, wherein the
baseplate is
configured to be in thermal communication with a heat source.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Further details, features and advantages of designs of the
invention result
from the following description of embodiment examples in reference to the
associated
drawings.
[0008] FIG. 1 is a side cut-away view of a heat sink according to some
embodiments of the present disclosure; and
[0009] FIG. 2 is a side cut-away view of a heat sink according to some
embodiments of the present disclosure;
[0010] FIG. 3 is a side cut-away view of a heat sink according to some
embodiments of the present disclosure;
[0011] FIG. 4 is a side cut-away view of a heat sink according to some
embodiments of the present disclosure;
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[0012] FIG. 5A is a side view of a heat sink according to some
embodiments of the
present disclosure;
[0013] FIG. 5B is a cross-sectional view of the heat sink of FIG. 5A
through section
A-A;
[0014] FIG. 5C is a cross-sectional view of the heat sink of FIG. 5A
through section
B-B;
[0015] FIG. 6A is a top view of a heat sink according to some
embodiments of the
present disclosure;
[0016] FIG. 6B is a cross-sectional view of the heat sink of FIG. 6A
through section
A-A;
[0017] FIG. 6C is a cross-sectional view of the heat sink of FIG. 6A
through section
B-B;
[0018] FIG. 7 is a cut-away perspective view of a heat sink according to
some
embodiments of the present disclosure;
[0019] FIG. 8 is a perspective view of a heat sink according to some
embodiments
of the present disclosure.
[0020] Figure 9 is a flow chart listing steps in a method of forming a
heat sink; and
[0021] Figure 10 is a flow chart listing steps in a method of
dissipating heat by a
heat sink.
DETAILED DESCRIPTION
[0022] Recurring features are marked with identical reference numerals
in the
figures, in which example embodiments of a heat sink 20, 120, 220 are
disclosed. FIG. 1
shows a first example heat sink 20 that includes a baseplate 22 of thermally-
conductive
material for conducting heat from a heat source. The baseplate 22 is shaped as
a flat plate
extending between a lower surface 24 and an upper surface 25. The lower
surface 24 of the
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baseplate 22 is configured to be in thermal communication with a heat source,
such as an
integrated circuit or a power electronic device. The heat sink 20, 120, 220
also includes a
radiator 26 disposed upon the upper surface 25 of the baseplate 22, away from
the lower
surface 24 for transferring heat to atmosphere, such as air or liquid that
surrounds the
radiator 26. The radiator 26 may transfer heat to the atmosphere by any means
such as
radiation, conduction, and/or convection. The radiator 26 includes a skin 32
of melted
material formed by additive manufacturing, with the skin 32 and enclosing a
chamber 36.
For example, the skin 32 may be formed by selectively melting a source
material, such as a
loose powder, using a concentrated heat source, such as a laser.
[0023] The heat sink 20, 120, 220 also includes an outer wick 38 of
porous material
disposed within the chamber 36 and coating an inner surface 34 of the skin 32.
The outer
wick 38 is permeable to liquid, allowing liquid and/or gases to flow
therethrough with
relatively low restrictions to flow. In some embodiments, and a shown in shown
in FIGS.
1-2, the outer wick 38 comprises a permeable filling including loose granules
40 disposed
within the chamber 36. The permeable filling may completely fill the chamber
36 as shown
in FIGS. 1-2. Alternatively, the permeable filling may only partially fill the
chamber 36.
The loose granules 40 define void spaces 42 therebetween. The permeable
filling may be,
for example, a loose powder or a porous solid. In some embodiments, the
permeable filling
includes the source material in an unmelted state. For example, an outermost
area of the
source material may be melted to form the skin 32, and source material located
therein may
be left in an unmelted state or in a semi-melted state to form the permeable
filling.
[0024] In some embodiments, the permeable filling may be entirely
comprised of
the source material. In other embodiments, the permeable filling may include
the source
material with one or more other components, which may be added after the skin
32 is
formed by the additive manufacturing process. In other embodiments, the
permeable filling
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may include none of the source material. For example, the permeable filling
may be
entirely made of material that is added after the skin 32 is formed by the
additive
manufacturing process. The permeable filling is permeable to liquid flow,
allowing a liquid
or a gas to pass therethrough. The permeable filling could include other
structural
components, such as, for example, a lattice or a foam or a compacted solid of
granules with
void spaces 42 therebetween. For example, the permeable filling may comprise a
combination of loose granules and another liquid-permeable material such as a
lattice or a
foam or a compacted solid. The permeable filling preferably functions as a
porous wick,
promoting capillary action to convey liquid therethrough. In some embodiments,
the
permeable filling provides the heat sink 20, 120, 220 with structural
rigidity, which may
counteract air pressure force on the baseplate 22, the cover 30, and/or the
skin 32. This may
be especially useful in embodiments where the chamber 36 is under a vacuum.
[0025] In some embodiments, and as shown in FIGS. 1-2, the radiator 26
includes a
foundation 28 that extends between the baseplate 22 and a cover 30 that is
spaced apart
from the baseplate 22. One or both of the baseplate 22 and/or the cover 30 may
be made by
melting the source material by additive manufacturing. Alternatively or
additionally, the
baseplate 22 and/or the cover 30 may be made independently and/or by a
different process,
such as by stamping, casting, machining, etc. In some embodiments, the cover
30 is formed
as a part of the skin 32. In some embodiments, the cover 30 is generally flat
and is parallel
and spaced apart from the baseplate 22. However, the cover 30 may have
different shapes
or orientations, depending on packaging requirements and/or heat dissipation
requirements.
The foundation 28 may be hollow, defining the chamber 36 therein. In some
embodiments,
the foundation 28 may be partially or completely filled with material.
[0026] In some embodiments, and as shown in FIGS. 1-2, a refrigerant 50
is
disposed within the chamber 36. The refrigerant 50 may be free to flow through
the outer
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wick 38. The outer wick 38 may hold the refrigerant 50 near the skin 32,
thereby improving
the ability of the heat sink 20, 120, 220 to dissipate heat. The refrigerant
50 may boil, or
change between a liquid phase 52 and a vapor phase 54 to convey heat from the
baseplate
22 to the cover 30. For example, the refrigerant 50 may boil from a first
region 56
proximate to the baseplate 22 and travel in the vapor phase 54 to a second
region 58
proximate to the cover 30. At the second region 58, the refrigerant 50 may
condense back
to the liquid phase 52. The refrigerant 50 in the liquid phase 52 may be
conveyed through
the void spaces 42 within the loose granules 40 and back to the first region
56 proximate to
the baseplate 22 by capillary action.
[0027] In some embodiments, and as shown in FIGS. 1-2, the radiator 26
includes a
plurality of fins 60 extending away from the baseplate 22. More specifically,
the cover 30
may extend in a generally flat plane, with the plurality of fins 60 extending
generally
transversely to the generally flat plane. The cover 30 could define one or
more curved
surfaces, which may or may not include the fins 60 extending therefrom. The
fins 60 may
be formed as pillars or posts. Alternatively or additionally, the fins 60 may
be formed as
ribs that extend for a substantial length along the cover 30. The fins 60 may
function to
increase the surface area of the skin 32 to promote heat transfer to a fluid,
such as a gas or a
liquid, contacting an outer surface of the skin 32 opposite the chamber 36.
[0028] In some embodiments, and as shown in FIG. 1, the fins 60 is
solid. In some
other embodiments, and as shown in FIG. 2, the outer wick 38 extends into the
fins 60. In
some embodiments, and as shown for example in FIG. 2, the fins 60 are filled
with the
permeable material, which may be in fluid communication with the permeable
material
within the foundation 28. In this way, the refrigerant 50, in the vapor phase
54, can travel
into the fins 60 to reach the second region 58, which is sufficiently cold to
cause the vapor
54 to condense back to the liquid phase 52.
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[0029] FIGS. 3-4, 5A-5C, 6A-6C, and 7 show a second example heat sink
120. The
second example heat sink 120 is similar to the first example heat sink 20,
with some
additional design features. In some embodiments, the radiator 26 is formed as
a monolithic
piece by additive manufacturing. Similarly to the first example heat sink 20,
the second
example heat sink 120 includes an outer wick 38 of porous material disposed
within the
chamber and coating an inner surface 34 of the skin 32. In some embodiments,
the outer
wick 38 comprises material melted or partially melted material by additive
manufacturing.
[0030] The second example heat sink 120 shown in FIGS. 3-7 includes a
plurality of
fins 60 extending away from the baseplate 22. In some embodiments, at least
one of the fins
60 comprises a body 62 shaped as a rod or a cone extending away from the
baseplate 22 to a
closed top 64. For example, the body 62 of one of the fins 60 may be shaped as
a cylinder
that extends for an entire length between the cover 30 and the closed top 64.
In another
example, the body 62 of one of the fins 60 may taper down from a first cross-
sectional area
at the cover 30 to a second, smaller cross-sectional area at the closed top
64.
[0031] In some embodiments, and as shown in FIGS. 3-4, the heat sink 20,
120, 220
includes an inner wick 66 of porous material disposed within the chamber 36
and coating
the upper surface 25 of the baseplate 22. In some embodiments, the inner wick
66 may be
integrally formed with the baseplate 22, for example as a monolithic piece.
Alternatively,
the inner wick 66 may be formed separately from the baseplate 22. In some
embodiments,
and as shown in FIGS. 3-4, the heat sink 20, 120, 220 includes an intermediate
wick 68 of
porous material disposed within the chamber 36 between the outer wick 38 and
the inner
wick 66 for conveying liquid therebetween. In some embodiments, and as also
shown in
FIGS. 3-4, the radiator 26 defines a cavity 70 that extends between the inner
wick 66
adjacent to the baseplate 22 into the fins 60. The cavity 70 may extend up
into the closed
top 64 of the fins 60. The vapor phase 54 of the refrigerant 50 may travel
through the cavity
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70 from the inner wick 66 and into the fins 60, where it condenses into the
liquid phase 52.
The liquid phase 52 of the refrigerant may condense within the outer wick 38
and return to
the inner wick 66 via the intermediate wick 68 by gravity and/or by capillary
action.
[0032] Any or all of the wicks 38, 66, 68 may be formed by additive
manufacturing
(AM). In some embodiments, each of the wicks 38, 66, 68 may be formed together
with the
skin 32 from shared source material. For example, a first melting power and/or
speed may
be used to create the skin 32, which impermeable, and a second, lower melting
power
and/or a higher speed may be used to create any or all of the wicks 38, 66,
68, which are
permeable to liquid flow. In some embodiments, paths used in the AM process
between
adjacent layers may be rotated to form an open lattice type structure within
one or more of
the wicks 38, 66, 68.
[0033] In some embodiments, and as shown in FIG. 3, the baseplate 22 may
comprise a solid piece of material, such as metal. Alternatively, and as shown
in FIG 4, the
baseplate may comprise an insulated metal substrate (IMS) printed circuit
board, such as
ThermalClad by Henkel.
[0034] In some embodiments, the baseplate 22 may be attached to the
radiator 26
after the radiator 26 is formed. In some embodiments, unmelted source material
may be
removed from the radiator 26 prior to attaching the baseplate 22 thereto, thus
forming the
cavity 70 within the radiator 26. The baseplate 22 may be welded to the
radiator 26 to
hermetically seal the chamber 36. Alternatively or additionally, the baseplate
22 may be
attached to the radiator 26 by other means such as using an adhesive and/or
using one or
more fasteners.
[0035] FIGS. 5A-5C, FIGS. 6A-6C, and FIG. 7 show various views of the
second
example heat sink 120. In some embodiments, the baseplate 22 has a square-
shaped
footprint of 100 mm x 100 mm. The baseplate 22 may have other shapes, which
may
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depend on application requirements. The baseplate 22 may be smaller or larger
than 100
mm x 100 mm. In some embodiments, each of the fins 60 may have a circular
cross-section
with a diameter of 15 mm. However, the fins 60 may have different shapes
and/or sizes,
which may be regular or irregular. In other words, different fins 60 on one
heat sink 20,
120, 220 may have different shapes or sizes. The heat sink 20, 120, 220 may
have a total
height of 75 mm, however, the heat sink 20, 120, 220 may be smaller or larger
than 75 mm
in height. The foundation 28 may have a height of 25 mm between the lower
surface 24 of
the baseplate 22 and the cover 30. However, the foundation 28 may have a
height that is
less than or greater than 25 mm.
[0036] FIG. 8 shows a third example heat sink 220, which is similar to
the second
example heat sink 120. The third example heat sink 220 includes sixty-four
fins 60 arranged
in an 8x8 pattern. Each of the fins 60 of the third example heat sink 220 have
a conical
shape, with the body 62 tapering from a first cross-sectional area at the
foundation 28 to a
second, smaller cross-sectional area at the closed top 64.
[0037] As described in the flow chart of FIG. 9, a method 100 of forming
a heat sink
20, 120, 220 is also provided. The method 100 includes 102 selectively melting
a source
material to form a skin 32 defining a chamber 36 of a radiator 26. In some
embodiments,
the source material may be selectively melted using a laser.
[0038] The method 100 also includes 104 forming the source material to
define an
outer wick 38 of porous material within the chamber coating an inner surface
34 of the skin
32. Forming the outer wick 38 may comprise melting the source material, which
may be
performed as part of the same additive manufacturing process used to form the
skin 32. In
some embodiments, this step 104 of melting the source material to define the
outer wick 38
is performed using an energy source having an intensity that is lower than an
intensity used
to selectively melt the source material to form the skin 32.
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[0039] The method 100 also includes 106 attaching a baseplate of 22
thermally-
conductive material to the radiator 26 to enclose the chamber 36, wherein the
baseplate 22
is configured to be in thermal communication with a heat source. Attaching the
baseplate 22
may include forming a hermetic seal enclosing the chamber 36. The baseplate 22
may be
welded to the radiator 26. Alternatively or additionally, the baseplate 22 may
be attached to
the radiator 26 by other means such as using an adhesive and/or using one or
more
fasteners.
[0040] The method 100 also includes 108 removing excess source material
from the
chamber 36 to define a cavity 70. The excess source material may be, for
example, "green"
powder that was not solidified by the additive manufacturing process. In some
embodiments, the excess source material may be removed from the chamber 36
prior to
attaching the baseplate of 22. For example, the excess source material may be
removed
from a bottom surface of the radiator 26, with the baseplate of 22
subsequently covering
that bottom surface to enclose the chamber 36. In other embodiments, the
excess source
material may be removed from a hole through the skin 32 of the radiator 26.
For example, a
hole may be drilled through the skin 32 for draining the excess source
material from the
chamber 36 of the radiator 26. Such a hole may be plugged or filled after the
excess
material is removed. The source material from the additive manufacturing
process may be
removed from the chamber 36, for example by suction or by shaking it out of
one or more
holes in the baseplate 22 and/or the skin 32. Additional material may be added
into the
chamber 36 to comprise the permeable filling. The amount and/or the
composition of the
permeable filling within the chamber 36 may be selected to optimize wicking of
the
refrigerant 50. Alternatively or additionally, the amount and/or the
composition of the
permeable filling within the chamber 36 may be selected to provide structural
rigidity to the
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heat sink 20, 120, 220, and particularly to counteract air pressure where the
chamber 36
contains a vacuum.
[0041] In some embodiments, the method 100 of forming the heat sink 20,
120, 220
may further include 110 evacuating air from the chamber 36. This step may be
unnecessary
if, for example, the chamber 36 is formed in a vacuum, so that it contains
little to no air in
the first place.
[0042] In some embodiments, the method 100 of forming the heat sink 20,
120, 220
may further include 112 adding a refrigerant 50 into the chamber 36; and 114
sealing the
chamber 36 after adding the refrigerant 50 into the chamber 36. Sealing the
chamber 36
may be performed by attaching the baseplate 22 to the radiator 26 and/or by
fixing a cap or
a plug to cover a passage into the chamber 36, where the passage is used at an
earlier stage
for adding the refrigerant 50 into the chamber 36, and/or for evacuating air
from the
chamber 36. Such a passage may be formed as part of the additive manufacturing
process.
Alternatively, the passage may be formed, for example by drilling or
puncturing, after the
chamber 36 is formed. Alternatively, the passage may be integrally formed in
the baseplate
22 before the skin 32 is formed.
[0043] In some embodiments, the method 100 of forming the heat sink 20
may
further include 116 forming an inner wick 66 of porous material coating an
upper surface 25
of the baseplate 22. In some embodiments, the method 100 of forming the heat
sink 20 may
further include 118 forming an intermediate wick 68 of porous material
disposed within the
chamber 36 between the outer wick 38 and the inner wick 66 for conveying
liquid
therebetween.
[0044] As described in the flow chart of FIG. 10, a method 200 of
dissipating heat
by a heat sink 20, 120, 220 is also provided. The method 200 of dissipating
heat by the heat
sink 20 includes 202 evaporating a refrigerant 50 from a first region 56
proximate to a
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baseplate 22 to a gaseous state, also called a vapor phase 54. The method 200
of dissipating
heat by the heat sink 20, 120, 220 also includes 204 condensing the
refrigerant 50 from the
gaseous state to a liquid state, also called a liquid phase 52, at a second
region 58 proximate
to a skin 32 of a radiator 26.
[0045] The method 200 of dissipating heat by the heat sink 20, 120, 220
proceeds
with 206 conveying the refrigerant 50 in the liquid phase 52 from the second
region 58 to
the first region 56. In some embodiments, the step of 206 conveying the
refrigerant 50 in the
liquid phase 52 is performed, at least in part, by capillary action through
one or more wicks
38, 66, 68. Alternatively or additionally, the step of 206 conveying the
refrigerant 50 in the
liquid phase 52 may be performed, at least in part, by gravity. In this case,
the heat sink 20,
120, 220 may have a preferred orientation in which it is most effective to
remove heat from
the baseplate 22.
[0046] The foregoing description of the embodiments has been provided
for
purposes of illustration and description. It is not intended to be exhaustive
or to limit the
disclosure. Individual elements or features of a particular embodiment are
generally not
limited to that particular embodiment, but, where applicable, are
interchangeable and can be
used in a selected embodiment, even if not specifically shown or described.
The same may
also be varied in many ways. Such variations are not to be regarded as a
departure from the
disclosure, and all such modifications are intended to be included within the
scope of the
disclosure.
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