Rotatable portable computer remote heat exchanger with heat pipe

A portable computer includes a base having a heat producing electronic component mounted therein. A heat sink, also referred to as a remote heat exchanger, is positioned in the base adjacent to the heat producing component. A heat pipe has a first end permanently bonded to the heat sink and extends to a second end thermally engaged with the heat producing component. The heat sink and heat pipe assembly is rotatable about an axis of the heat sink so as to move the second end of the heat pipe into and out of thermal engagement with the heat producing component.

CROSS REFERENCE TO CO-PENDING APPLICATIONS
 This application relates to co-pending U.S. patent application Ser. No.
 09/170,510, filed on Oct. 13, 1998, entitled "Heat Sink Assembly with
 Rotating Heat Pipe", naming Hood, III et al. as inventors. The co-pending
 application is incorporated herein by reference in its entirety, and is
 assigned to the assignee of this invention.
 This application relates to co-pending U.S. patent application Ser. No.
 09/129,930, filed on Aug. 6, 1998, entitled "Smart Bi-Metallic Heat
 Spreader", naming Moore et al. as inventors. The co-pending application is
 incorporated herein by reference in its entirety, and is assigned to the
 assignee of this invention.
 This application relates to co-pending U.S. patent application Ser. No.
 09/174/201, filed on Oct. 16, 1998, entitled "Heat Transfer from Base to
 Display Portion of a Portable Computer", naming Philip Gold as the
 inventor. The co-pending application is incorporated herein by reference
 in its entirety, and is assigned to the assignee of this invention.
 This application relates to co-pending U.S. patent application Ser. No.
 09/228,939, filed on Jan. 12, 1999, entitled "Hybrid Cooling Heat
 Exchanger Fin Geometry and Orientation", naming Podwany et al. as
 inventors. The co-pending application is incorporated herein by reference
 in its entirety, and is assigned to the assignee of this invention.
 BACKGROUND
 The disclosures herein relate generally to heat dissipation and more
 specifically to heat dissipation within a portable computer.
 A portable computer is a self-contained personal computer which can be
 easily moved to and operated at various locations. Portable computers are
 often referred to as laptop or notebook computers. To be portable, these
 computers must be small, compact, and lightweight. The conventional
 portable computer includes a base portion and a lid portion that pivotally
 opens from the base portion when the portable computer is in use. The lid
 portion contains a flat panel display such as a liquid crystal display
 (LCD) or other suitable display.
 Portable computers are being required to accommodate increasingly higher
 thermal loads. Central Processing Unit (CPU) power requirements are
 increasing along with other higher-power motherboard components. In order
 to cool the computer properly, larger cooling solutions are being
 implemented, which include heat spreaders, heat sinks, fans, and heat
 pipes.
 One known type of heat spreader used for distributing heat away from a
 processor in a portable computer is a piece of metal thermally coupled to
 the processor. Such a heat spreader is typically made of relatively pure
 aluminum. Aluminum exhibits good thermal conductivity and has reduced
 weight over other types of metal. However, aluminum is subject to
 oxidation, whereby aluminum oxide coatings typically form on the outside
 surfaces of exposed aluminum. In the case of an aluminum heat spreader,
 aluminum oxide reduces the ability of the aluminum heat spreader to
 provide for a low impedance thermal connection.
 In addition to heat spreaders, the combination of fans and heat sinks have
 been used to provide cost effective mechanisms for thermally managing the
 cooling requirements of many types of computer systems. However, fans
 require power and heat sinks require space. While power and space are
 generally in abundant supply in rack and desktop-type computers, portable
 computers have only a limited supply of both power and space. An operable
 fan may unduly draw upon the batteries of a portable computer, thus making
 the fan and heat sink cooling solution unattractive for long periods of
 battery-powered portable computer operation.
 Heat pipes offer another option for a cooling solution. Heat pipes are self
 contained, phase transformation, heat carrying devices, i.e. each is a
 superconductor of heat. A typical heat pipe may comprise a closed copper
 tube having a partial vacuum internally. Pre-existing liquid, such as
 water, CCFC, or other suitable liquid, in a hot portion of the tube boils
 at a lower than usual temperature in the partial vacuum. The boiling
 liquid forms steam, which seeks a cooler spot. The steam moves to carry
 heat to the cooler spot where the steam condenses to cooler liquid. The
 cooler liquid then returns to the hot spot. The cycle is ongoing, which
 provides a self-contained circulating cooling system.
 The following U.S. patent addresses the issue of heat dissipation within a
 computer. U.S. Pat. No. 5,598,320 discloses a rotatable and slidable heat
 pipe apparatus for transferring heat away from a microprocessor chip more
 rapidly than by heat sink surface area dissipation to the surrounding air
 alone. The apparatus includes a heat sink with an integral cylindrical
 passageway adapted to receive a first end of a heat pipe shaped like a
 crankshaft and a heat spreader formed from a metal plate with a first end
 rolled up to define a cylindrical opening adapted to receive a second end
 of the heat pipe. The heat spreader is attached to an underside of a
 keyboard. Since the heat pipe is able to rotate within the cylindrical
 passageway and the cylindrical opening, the keyboard can be raised to an
 open position and lowered to a closed position quickly and simply without
 the risk of breaking or bending the heat pipe, and manufacturing position
 tolerances between the heat pipe apparatus components are increased
 resulting in a simplified manufacturing process. The heat pipe can also be
 slid in and out of the cylindrical passageway or the cylindrical opening,
 thereby enabling computer manufacturers to incorporate the heat pipe into
 portable battery powered notebook-type computer systems designed to allow
 a user to remove, replace, or swap internal components by simply flipping
 open or removing the keyboard, and further enabling a user to perform
 maintenance work or repairs on the computer system without concern for
 damage to the heat pipe.
 Co-pending U.S. patent application Ser. No. 09/170,510 is another example
 that addresses the issue of heat dissipation within a computer system. In
 the embodiment of FIG. 1, a first end of a heat pipe 2 is connected to a
 heat sink 4 by a rotatable thermal connection 6. Heat sink 4 is mounted on
 and fastened to a bottom member 16. Rotatable thermal connection 6 enables
 heat pipe 2 to retract from a first position to a second position,
 indicated in FIG. 1, to allow a CPU 8 to be installed directly on top of a
 motherboard 10. Once CPU 8 is installed, heat pipe 2 is rotated back to
 its first position, represented in FIG. 2, in order for a thermal block
 12, which is connected to a second end of heat pipe 2, to be thermally
 coupled to CPU 8. A set of mounting screws 14, or other suitable
 fasteners, are then used to secure thermal block 12 to CPU 8.
 In a build-to-order computer system manufacturing process, custom
 configured computer systems are assembled with hardware and software based
 upon a customer order. With respect to portable computers, in order to
 fulfill build-to-order manufacturing requirements, the CPU is preferably
 installed at final assembly. For the vast majority of portable computer
 layouts, the CPU is directly on top of the motherboard and the CPU cooling
 solution installed on top of the CPU. While cooling solutions can be
 installed after installation of the CPU, some layouts cause the cooling
 solution to be trapped under a palmrest and LCD. Therefore, in order to
 install the CPU during the build-to-order manufacturing process, either
 the palmrest and/or LCD assembly must be installed after the cooling
 solution is installed. Unfortunately, this method is undesirable since it
 requires additional disassembly/assembly procedures in the build-to-order
 manufacturing process. Further, a greater inventory of component parts is
 required to be maintained.
 Accordingly, an improved cooling solution that can be installed in a
 portable computer prior to the installation of the CPU during the
 manufacturing process is desired.
 SUMMARY
 One embodiment provides a rotatable heat transfer assembly, consisting of a
 heat pipe permanently bonded to a heat sink, which is also referred to as
 a remote heat exchanger. The heat transfer assembly is rotatable about a
 prescribed axis to permit subsequent installation of a CPU during the
 manufacturing process by rotating the heat transfer assembly from a first
 position to a second position.
 A principal advantage of this embodiment is that the build-to-order
 manufacturing process is improved and the requirements for maintaining
 additional inventory for extra parts is dramatically reduced. The CPU can
 now be easily installed after installation of the cooling solution.
 Furthermore, the present embodiments provide a rotatable heat transfer
 assembly held in position by a bottom contoured surface and a top
 contoured surface for minimizing the formation of a hot spot typically
 found on the bottom skin of portable computers. The hot spot is reduced
 since the heat sink is no longer directly mounted to a bottom member of a
 computer base. The present embodiments also provide for greater heat
 transfer between the CPU and ambient air by permanently bonding the heat
 pipe to the heat sink, accordingly reducing the thermal resistance at that
 junction.

DETAILED DESCRIPTION
 In one embodiment, depicted in FIG. 3, computer system 30 includes a
 microprocessor 32, which is connected to a bus 34. Bus 34 serves as a
 connection between microprocessor 32 and other components of computer
 system 30. An input device 36 is coupled to microprocessor 32 to provide
 input to microprocessor 32. Examples of an input device can include one or
 more of the following: keyboard, touchscreen, and a pointing device such
 as a mouse, trackball, and a trackpad. Programs and data are stored on a
 mass storage device 38, which is coupled to microprocessor 32. Mass
 storage device 38 can include at least one of the following devices, such
 as a hard disk, optical disk, magneto-optical drive, floppy drive and the
 like. Computer system 30 further includes a display 40, which is coupled
 to microprocessor 32 by a video controller 42. A system memory 44 is
 coupled to microprocessor 32 to provide the microprocessor with fast
 storage to facilitate execution of computer programs by microprocessor 32.
 It should be understood that other busses and intermediate circuits can be
 deployed between the components described above and microprocessor 32 to
 facilitate interconnection between the components and the microprocessor.
 Referring to FIG. 4, depicted is a portable, notebook size computer
 designated 50 comprising a self-contained system, such as that illustrated
 as 30 in FIG. 3. Computer 50 also includes a hinged top or lid 52
 rotatable about a hinge or hinges 54 from a nested position "N", with a
 horizontal base 56, to substantially vertical or open position "V."
 Opening of the notebook style portable computer by manipulation of a latch
 58, reveals a plurality of keys 60 on base 56, and a monitor screen 62
 mounted in lid or top 52. Base 56 includes a bottom or first member 56a
 and a top or second member 56b.
 Next, in FIG. 5, computer 50 is illustrated in a partially disassembled
 state showing the first member 56a of base 56 with the second or keyboard
 member 56b removed. With keyboard member 56b removed, some of the
 components mounted in base 56 are exposed. Some of the exposed components
 include a heat transfer assembly 64a, an audio subsection 66, a CD floppy
 module section 68, a battery bay section 70, a hard-disk drive section 72
 and a motherboard 74. In FIG. 5, top 52 is illustrated in the open
 position V, with monitor screen 62 removed. Heat transfer assembly 64a
 includes a heat spreader cap 76 thermally coupled to CPU 78. Also included
 in heat transfer assembly 64a is a heat sink 80 commonly referred to as a
 remote heat exchanger, a fan housing 82 that includes a fan 84 mounted in
 a fan duct 86 in base 56. A heat pipe 88 is provided to thermally
 interconnect a thermal block 90, heat spreader cap 76, and heat sink 80.
 A heat transfer assembly 64b, which is an alternative embodiment of
 assembly 64a, is represented in FIG. 6. Here, a first end 88a of heat pipe
 88 is permanently bonded to a cylindrical heat sink 80 to create a minimum
 amount of thermal resistance at that junction. A rigid connection is
 formed at that junction as a by product of the permanently bonded
 junction. Accordingly, an improved heat transfer is achieved. Thermal
 block 90 is connected to a second end 88b of heat pipe 88. In the absence
 of a rotatable connection between heat pipe 88 and heat sink 80, the
 entire heat transfer assembly 64b is made to be rotatable, thus enabling
 heat pipe 88 to be rotated by simply rotating heat transfer assembly 64b
 about a central axis of heat sink. 80. To facilitate rotation of heat
 transfer assembly 64b, bottom member 56a includes a contoured surface 56c
 that extends upward and top member 56b includes a contoured surface 56d
 that extends downward. Contoured surfaces 56c and 56d engage heat sink 80
 to hold heat sink 80 in place while still allowing the heat sink to
 rotate, as needed. Heat pipe 88 is rotated from a first position to a
 second position via rotation of assembly 64b, illustrated in FIG. 6, to
 allow for installation of CPU 78. Note that the dimensions of CPU 78 vary
 according to its specifications. Once CPU 78 is installed on top of
 motherboard 74, heat pipe 88 is rotated from the second position back to
 the first position via rotation of assembly 64b, as illustrated in FIG. 7.
 A set of mounting screws 94, or other suitable fasteners, are then used to
 secure and thermally couple thermal block 90 to CPU 78. An exploded
 perspective view of heat assembly 64b is represented in FIG. 8. FIG. 8
 also clearly shows a plurality of fins 96, a plurality of ribs 98, and a
 central axis 100 of heat sink 80 about which assembly 64b rotates.
 In operation, the embodiments disclosed herein utilize a rotatable heat
 transfer assembly to allow the CPU to be accessed during the manufacturing
 of a notebook computer with minimal disassembly of the system. The heat
 transfer assembly is thus able to be positioned within the computer base
 in advance of a final assembly without unduly impeding installation of the
 CPU at final assembly.
 As a result, one embodiment provides a heat transfer assembly that includes
 a heat pipe permanently bonded to a heat sink.
 Another embodiment provides a portable computer having a heat producing
 component mounted therein. A heat sink is positioned in a computer base. A
 heat pipe has a first end permanently bonded to the heat sink and a second
 end in thermal engagement with the heat producing component, wherein the
 heat sink and heat pipe assembly is rotatable about a central axis of the
 heat sink to move or disengage the second end of the heat pipe away from
 the heat producing component.
 Meanwhile, another embodiment provides a computer system including a
 microprocessor, an input coupled to provide input to the microprocessor, a
 mass storage coupled to the microprocessor, a display coupled to the
 microprocessor by a video controller, and a memory coupled to provide
 storage to facilitate execution of computer programs by the
 microprocessor. A heat sink is positioned in a computer base. A heat pipe
 has a first end permanently bonded to a heat sink and a second end in
 thermal engagement with the microprocessor, wherein the heat sink and heat
 pipe assembly is rotatable about a central axis of the heat sink to move
 or disengage the second end of the heat pipe from the microprocessor.
 A further embodiment provides a method of mounting a heat transfer assembly
 in a computer base. The method includes mounting a heat producing
 component in the computer base, positioning a heat sink in the computer
 base, and permanently bonding a heat pipe to the heat sink so that the
 heat sink and heat pipe assembly is capable of a prescribed rotational
 movement into and out of thermal engagement with the heat producing
 component.
 A principal advantage of these embodiments is that the CPU can be easily
 installed during the manufacturing process after installation of the
 cooling solution. The entire cooling solution can be tested at the board
 assembly level prior to a final assembly, thus reducing opportunities for
 defects in the cooling solution during the manufacturing process. With the
 present embodiments, fewer parts need to be handled at final assembly.
 Furthermore, connection of the heat pipe to the CPU during the
 manufacturing process is self-fixtured at final assembly. As a result,
 installation of the CPU and the manufacturing process are less prone to
 defects.
 With the present embodiments, a fixed thermal connection between the heat
 pipe and heat sink provides an improved cooling solution having a lower
 thermal resistance, advantageously enabling the portable computer to
 accommodate increasing thermal demands. Furthermore, the rotatable heat
 transfer assembly that is held in position by a bottom contoured surface
 and a top contoured surface minimizes the hot spot typically found on the
 bottom skin of portable computers. The hot spot is reduced since the heat
 sink is no longer directly mounted on and fastened to a bottom member of a
 computer base. The present embodiments also provide for greater heat
 transfer between the heat sink and ambient air due to the improved
 reduction in thermal resistance at the junction of the heat pipe and heat
 sink.
 Although illustrative embodiments have been shown and described, a wide
 range of modifications, change and substitution is contemplated in the
 foregoing disclosure and in some instances, some features of the
 embodiments may be employed without a corresponding use of other features.
 Accordingly, it is appropriate that the appended claims be construed
 broadly and in a manner consistent with the scope of the embodiments
 disclosed herein.