Sealed enclosure for power electronics incorporating a heat exchanger

This application claims one or more inventions which were disclosed in Provisional Application No. 61/779,469, filed Mar. 13, 2013, entitled “FUNCTIONAL HEAT EXCHANGER AND SEALED ENCLOSURE FOR POWER ELECTRONICS”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.

The invention pertains to the field of heat exchangers. More particularly, the invention pertains to a heat exchanger with a sealed enclosure for power electronics.

As the power densities in power electronic packages go up, there is an increasing demand for better thermal management solutions, both in the air and liquid cooled applications. Typical thermal solutions employ a heat sink, or a cold plate to transfer the heat from heat generating components and reject it to a cooling media, i.e. air or liquid. These heat sinks/cold plates typically have threaded holes to mount the printed circuit board assemblies and any heat generating devices. These mounting features are created by secondary machining operations. Moreover, conventional heat sink/cold plate assemblies require a metal frame built around it to provide an environmental seal where needed. Not only does this add more complexity to the design, but it also increases the cost and weight of the system.

A functional heat exchanger structure provides a hermetic seal for the power electronics. The heat exchanger includes one or more features built into the design. The features include a closed loop liquid circuit, air, or extended surfaces built-in to the design to transfer heat from the heat generating devices, spring clips snapped in built-in slots to mount heat-generating devices, preformed threaded rails to mount the printed circuit board (PCB), electrical isolation between the heat sink/cold plate and the electrical components, a sealed enclosure to provide environmental protection for the electronic components, a mounting feature to mount the sealed enclosure onto an external surface, an opening to accept a snap-in style cover, a stackable design, and an easily manifoldable configuration.

FIG. 1 shows a schematic partial cross sectional view of a heat exchanger with a U-shaped configuration in an embodiment of the present invention.

FIG. 2 shows an exploded isometric view of an enclosed heat exchanger module of FIG. 1 , with two end caps and a top cover.

FIG. 3 shows a schematic partial cross sectional view of a heat exchanger with an H-shaped configuration in an embodiment of the present invention.

FIG. 4 shows a schematic partial cross sectional view of a heat exchanger with air-cooling in an embodiment of the present invention.

FIG. 5 shows a cross sectional detail view from the area enclosed in dotted lines 5 of FIG. 1 .

FIG. 6 shows a schematic partial cross sectional view of a heat exchanger module with built-in PCB slides in an embodiment of the present invention.

FIG. 7 shows a schematic partial cross sectional view of a heat exchanger with staggered cooling channels in an embodiment of the present invention.

FIG. 8 shows a schematic partial cross sectional view of two heat exchanger modules of the embodiment of FIG. 7 , with staggered cooling channels linked by a manifold.

FIG. 9 shows a side view of two modules on a backplane and support, in the embodiment of FIG. 8 .

A functional heat exchanger structure includes one or more features built into the design and provides a hermetic seal for the power electronics. These features include:

1. Means to transfer heat from the heat generating devices to liquid, by means of closed loop liquid circuit, or to air, by means of extended surfaces built-in to the design. 2. Means to mount heat generating devices via spring clips snapped in built-in slots. 3. Means to mount the printed circuit board using preformed threaded rails. 4. Means to provide electrical isolation (creepage clearance) between the heat sink/cold plate and the electrical components. 5. Means to provide environmental protection for the electronic components by forming a sealed enclosure. 6. Means to mount the sealed enclosure onto an external surface, such as, for example, a cabinet or a frame. 7. Means to accept a snap-in style cover. 8. Stackable design. 9. Easily manifoldable configuration.

Thermal management of electronic devices plays a crucial role in the reliable operation of electronic circuits. Conventional heat exchangers are relatively flat and require another frame around them for environmental protection. Embodiments of the present invention address the shortcomings of conventional designs by having unique features embedded in the design for higher levels of productability and environmental protection.

In the figures, elements which are the same as in earlier figures will be given the same reference numbers, and may not be separately discussed with respect to later figures.

Some embodiments of the invention, as illustrated in FIG. 1 in one of its many possible configurations, are a generally U-shaped body 10 having a base 11 and two side walls 23 , where the printed circuit board 18 is mounted above the base 11 and between the side walls 23 , facing up, and the heat generating devices 9 are mated against the two side walls 23 . The heat exchanger includes bulkhead mounting feet 1 as part of the base 11 extrusion and printed circuit board (PCB) mounting extruded rails 2 . The heat exchanger has cooling channels 3 running across the length of the side walls that remove heat from electronic components. A clearance space 4 is included at the edge of the PCB 18 for voltage isolation. This built-in feature eliminates the need for extra insulation material.

The heat exchanger also includes transistor mounting clips 5 , a seal groove 6 with a seal 20 for the cover 7 to provide IP67/IP6K9K protection, and a cover 7 . Although the cover 7 is shown as a snap in cover in FIG. 1 , the cover 7 may alternatively be screwed down as shown in FIG. 4 .

The heat exchanger preferably has built-in features, i.e. slots 8 and/or grooves, to allow heat generating components 9 to be coupled to the two side walls 23 for heat transfer. A slot 8 in the heat exchanger accepts the spring clip 5 for mounting of the component. This allows any number of devices 9 to be cooled, within the physical constraints, by being clipped to the side walls 23 without requiring any modification to the heat exchanger design. This is a significant deviation from conventional methods, where extra mounting holes are drilled or machined to accommodate different number of devices.

There is an increasing demand in certain industries that the electronics should be environmentally protected from water, pollutants, dust . . . etc. Conventional designs achieve this goal by building a box around the heat exchanger and the power electronic assembly. This results in a larger number of parts to be used to create a sealed unit. Embodiments of the present invention preferably provide environmental protection for the electronics by forming three sides of the enclosure, eliminating some of the parts need be employed otherwise. As a result, only two endcaps and a top cover are needed to fully enclose the sensitive electronics and form a sealed unit, as illustrated in FIG. 2 . This approach provides a more reliable seal due to the lesser number of parts, and hence joints, forming the sealed enclosure.

An exploded isometric view of this heat exchanger configuration is shown in FIG. 2 , in which the cover 7 is unsnapped and the seal 20 is removed from grooves 6 . The printed circuit board 18 is raised above the U-shaped structure 10 .

As can be seen in FIG. 2 , the ends of the structure 10 are fitted with a first end cap 22 a and a second end cap 22 b , each end cap being sealed to the end of the structure 10 by a face gasket 21 . The first end cap 22 a is fitted with electrical connectors 26 , as might be needed to interface with the circuitry on PCB 18 . An internal bore (not shown) extending across the first end cap 22 a , connects the two cooling channels 3 , so that liquid can circulate from one to the other through end cap 22 a . The second end cap 22 b has passages aligned with the cooling channels in the side walls, passing through the end cap to fluid fittings 25 for supplying and withdrawing cooling fluid through cooling channels 3 .

In another embodiment, the heat exchanger 32 is H-shaped ( FIG. 3 ), where multiple PCB assemblies 30 and 31 can be packaged within the same structure, and the heat generating devices 39 are mated against the two side walls 38 . The heat exchanger 32 includes bulkhead mounting feet 41 as part of the extrusion and printed circuit board (PCB) mounting extruded rails 42 . The heat exchanger has cooling channels 33 running across the length of the side walls 38 that remove heat from electronic components. A clearance space 44 is included at the edge of the PCBs 30 and 31 for voltage isolation. This built-in feature eliminates the need for extra insulation material. The heat exchanger also includes transistor mounting clips 35 , a seal groove 36 with a seal 46 for the cover 37 to provide IP67/IP6K9K protection, and a cover 37 on each side. Although the covers 37 are shown as snap in covers in FIG. 3 , the covers 37 may alternatively be screwed down.

Embodiments of the present invention are not limited to liquid cooling applications. As shown in the configuration of FIG. 4 , the structure 40 can also be configured with fins 49 extending out from one or more surfaces to adapt to an air cooled application. In this embodiment, no liquid is circulated inside the channels 43 . Instead, heat is conducted through the walls 23 and gets rejected to ambient air by the fins 49 .

The electrical isolation between the electrical components and the conductive chassis is an important design consideration for safe operation of power electronics. Insufficient spacing can cause arcing and/or electrical shorts during operation and can cause catastrophic failures. In conventional designs, an insulating material is typically added to the assembly to provide required isolation.

Embodiments of the present invention preferably address the same problem by another built-in feature on the heat exchanger structure, as shown in FIG. 5 , which shows an enlarged view of the area enclosed in dotted lines 5 in FIG. 1 (cover 7 and seal 20 being omitted from FIG. 5 ).

FIG. 5 shows the spring clip 5 mounting feature and a built-in electrical isolation clearance 4 for creepage of a heat exchanger in an embodiment of the present invention. Rather than using insulation materials, embodiments of the present invention preferably have clearance 4 at strategic locations to provide sufficient clearance between the components 9 and the heat exchanger body 10 .

The heat exchanger preferably also has built-in threaded rails 2 on the bottom to allow PCBs to be mounted. This is shown in FIG. 1 .

In another version, shown in FIG. 6 , mounting slots 60 can be built-in to the side walls 23 of the heat exchanger, into which the edges 61 of a printed circuit board 18 can be slid for quick mounting.

In another embodiment, depicted in FIG. 7 through FIG. 9 , the cooling channels 73 a , 73 b on each side of the heat exchanger 72 are vertically offset to ease distributing the coolant across two or more heat exchanger modules 70 a , 70 b . The sides of the heat exchanger 72 are formed with mating side protrusions 74 a , 74 b , to facilitate registration of multiple heat exchanger modules 70 a , 70 b in a side-by-side relationship.

The cooling channels 73 a , 73 b on each manifold connect to fluid fittings 94 , 95 on the endcap 96 of each heat exchanger module 70 a , 70 b . The fluid fittings 94 , 95 plug into mating sockets 97 , 98 , which are coupled to manifolds 81 , 82 in a backplane 80 . The backplane 80 may be mounted on or incorporate a shelf 90 or other supporting means.

Each manifold 81 , 82 terminates in a fluid fitting, shown in FIG. 9 as inlet 91 and outlet 92 , which permit connection of the manifolds 81 , 82 in the backplane 80 to a source of circulating cooling fluid. Multiple backplanes 80 may, of course, be connected in series or parallel to facilitate cooling a plurality of modules 70 on a plurality of shelves 90 in a rack arrangement.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.