This invention relates to a method of manufacturing an all-metal cold plate heat exchanger assembly.
Forced air-cooling is typically used to remove excess heat generated by computing processing units (CPUs); however, forced air-cooling alone is no longer sufficient to meet the cooling needs of increasingly faster and hotter CPUs. An alternate to forced air-cooling is a recirculating closed-loop liquid cooling system. Recirculating closed-loop liquid cooling systems are known for their higher efficiency and capacity for excess heat removal.
A schematic of a typical recirculating closed-loop liquid cooling system for cooling a heat generating electronic component is shown in
The coolant pump 22 transfers a liquid coolant from the reservoir tank 15 to the cold plate heat exchanger assembly 25. Within the cold plate heat exchanger assembly 25 are engineered flow channels, which provide a tortuous path for flow of liquid coolant in order to optimize heat transfer from the heat generating electronic component 30 to the coolant. After exiting the cold plate heat exchanger assembly 25, the heated coolant continues to the radiator 35 where the heat is released to the ambient air by convection with the aid of a fan 40 blowing a stream of cooler air across the radiator 35. The cooled coolant then returns to the reservoir tank 15 to repeat the heat transfer process.
U.S. patent application Ser. No. 11/221,526 discloses an all-metal cold plate heat exchanger assembly with engineered flow channels. The disclosed cold plate assembly includes a base plate of copper having a flat exterior surface that is adapted to thermally bond to a heat generating electronic component. Located on the interior surface of the copper base plate are a series of micro-channels and associated micro-fins with coplanar edges. The base plate is assembled to a manifold cover and the interior surface of the manifold cover has manifold channels with corresponding co-planer surfaces that cooperate with the smaller coplanar edges of the micro-fins to define a path for coolant flow.
When the manifold cover is engaged to the base plate, the coplanar surfaces of the manifold channel are in intimate contact with the coplanar edges of the micro-fins of the base plate forming a checkerboard pattern for fluid flow, providing more effective and efficient heat extraction. The contact between the coplanar surfaces of the manifold channels and the coplanar edges of the micro-fins must be sufficiently tight, to prevent flow from bypassing the manifold channels, which would impair the regularity of the flow pattern and result in reduced heat transfer efficiency.
One known method of manufacturing a cold plate assembly having good sealing characteristics between the contact surfaces of the manifold channels and the micro-fins is to utilize materials such as solder, braze cladding, or adhesives to provide a gasket material between the coplanar surfaces of the manifold channels and the coplanar edges of the micro-fins. A drawback for such materials is the tendency during the assembly process for such materials to seep into and clog the micro-channels.
Another known method of manufacturing a cold plate assembly having good sealing characteristics between the contact surfaces of the manifold channels and the coplanar edges of the micro-fins is resistance welding, which is disclosed in U.S. patent application Ser. No. 11/221,526. The drawbacks to resistance welding are the cost of materials and complexity of the manufacturing operation. Resistance welding requires the use of highly pure, oxygen free copper that is both electronically and thermally conductive. In addition to the material requirements, the joining surfaces of the cold plate assembly require precision machining to exact specifications.
There exists a need for an economical method of manufacturing an all-metal micro-channel cold plate heat exchanger assembly that assures a tight interface seal between the contact surfaces of the manifold channels and the micro-fins without clogging the micro-channels.
The subject invention provides a method of manufacturing an all-metal cold plate heat exchanger assembly for removing excess heat from a heat generating electronic component. The method assures a tight interface seal between the contact surfaces of the alternating channels of the manifold plate and the coplanar edges of the micro-fins which prevents coolant by-pass flow, but does not clog or jeopardize the coolant flow through the micro-channels, and is economical to manufacture and assemble. This method utilizes recast metallic particulates, a natural by-product of laser machining, as a compliant gasket material between the coplanar surfaces of the alternating channels and the coplanar edges of the micro-fins.
The method includes providing a base plate formed of a material suitable for laser machining, preferably copper. A beam of laser energy is provided to machine alternating substantially parallel micro-channels and associated micro-fins into the interior surface of the copper base plate. During the laser machining process, the laser-machined surface of the copper base plate is vaporized into microscopic aerosol particulates, which are then cooled and condensed onto the coplanar edges of the micro-fin to form a layer of recast metal. The recast layer is microscopic and cannot be seen without magnification.
A manifold cover and a manifold plate, which may be integrated with the interior surface of the manifold cover, are provided. The manifold plate has alternating inlet-outlet channels with at least one face having coplanar edges. The manifold cover is arranged onto the base plate with the manifold plate in between, such that one face of inlet-outlet channel coplanar edges is disposed adjacent to the micro-fin edges with the recast layer in between. The manifold cover is then pressed toward the base plate to compress the recast layer to form a compliant gasket between the contact surfaces of the alternating inlet-outlet channels and micro-fins. The exterior joining surfaces of the base plate and manifold cover are hermetically sealed.
One advantage of the present invention is that it utilizes the vapor-deposited copper particulate that is a natural by-product of the laser machining process used in the formation of the micro-channels to form a compliant gasket that facilitates the intimate contact between the micro-channels and the manifold channels, thus preventing flow by-pass and increasing thermal performance.
Another advantage of the present invention is the elimination of the need to remove the recast layer prior to assembly; this, simplifies the manufacturing process and reduces cost.
Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.
This invention will be further described with reference to the accompanying drawings in which:
In accordance with a preferred embodiment of this invention, referring to
In reference to
Base plate 100 is substantially circular in shape and is approximately 34 mm in outer diameter with a thickness of approximately 1.0 mm. Base plate 100 has a perimeter wall 110 that is approximately 3.0 mm in height demarcating an inner surface 120 from outer surface 130 of base plate 100. Inner surface 120 and outer surface 130 are machined to a high degree of flatness. Outer surface 130 is adapted to be thermally bonded to a heat producing electronic component. Inner surface 120 is laser machined to form a fin-channel pattern 135 that includes a dense pattern of extremely thin structures, alternating micro-channels 140 and micro-fins 150. These are shown in greater detail in
Manifold cover 200 is also substantially circular in shape having an outer diameter of approximately 42 mm and is approximately 2 mm thick. Manifold cover 200 is adapted to engage perimeter wall 110 of base plate 100 and form a hermetically sealed structure. Located between the inner surface 120 of base plate 100 and interior face 210 of manifold cover 200 is a manifold plate 300, which may be formed as an integral part of interior face 210 of manifold cover 200 as shown in
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As discussed herein above, inner surface 120 of base plate 100 is machined to a high degree of flatness. The inner surface 120 is then laser machined to form a fin-channel pattern 135 that includes a dense pattern of extremely thin structures that include micro-channels 140 and micro-fins 150, which have corresponding coplanar edges 160 that are substantially planer to inner surface 120. In reference to
The process of laser machining micro-channels onto a flat metallic surface is generally known in the art. As a high-powered laser is focused on a targeted material, the mass of the material is removed by vaporization caused by the intense heat generated by the laser beam at the point of contact. The amount of material removed is determined by the pulse duration, energy, and wavelength of the laser, as well as by the number of passes by the laser beam. These variables can be controlled according to the need of the material targeted to be removed. The desired setting of the laser should be adequate to remove the material by vaporization and not so high as to cause liquid ejection or phase explosion of the targeted material.
In reference to
The blanket of inert gas cools plume 530 as it expands outward. The aerosol particulate matter 540 collides with each other and coalesces into larger particulates in the range of nanometers. The larger particulate matter condenses and settles onto the coplanar edges 160 of the micro-fins 150 forming a layer of recast metal. Contrary to the teachings of the prior art to use an acid solution to remove the recast layer, the recast layer is allowed to remain on top of the coplanar edges 160 of micro-fins 150. Recast layer 500 consists of the same metallic material as base plate 100 and is at a consistency that is malleable enough to form a compliant gasket 510 between coplanar edges 160 of micro-fins and coplanar surfaces 330 of manifold plate 300.
As discussed herein above, it is critically important to insure intimate contact between the coplanar edges 160 of micro-fins 150 and coplanar surfaces 330 of manifold plate 300 to prevent fluid bypass. The recast layer 500 aids in the critical seal by deforming on a microscopic level to average out any inconsistencies in the micro-channel peak-to-peak dimensions and facilitates the required intimate contact.
The height and percentage coverage of the recast layer can be controlled by varying the intensity of the laser, temperature of the inert cover gas, and duration of cut. It is preferable that the temperature is below the dew point of the vaporized metallic particulates.
The height of the recast layer 500 is defined by the distance between the coplanar edges 160 of micro-fins 150, which is substantially planar with inner surface 120 of base plate 100, and plateau 550 of recast layer 500 shown as distance ‘X’ in
Once recast layer 500 has been formed on coplanar edges 160 of micro-fins 150, a manifold cover 200 having a manifold interior face 210 and manifold plate 300 is arranged over base plate 100, with the channels 320 of manifold plate 300 substantially perpendicular to micro-channels 140 of base plate 100. Manifold cover 200 is then positioned onto base plate 100 such that the coplanar surfaces 330 of manifold plate 300 are disposed adjacent to the micro-fin coplanar edges 160 with recast layer 500 in between. Manifold cover 200 is pressed toward base plate 100 to compress recast layer 500 to form a compliant gasket 510 in between.
The exterior joining surfaces of the base plate 100 and manifold cover 200 are hermetically sealed by any of the known methods in the art; however, brazing is preferable. At temperatures favorable to brazing, recast layer 500 becomes more ductile and lends itself readily to act as a conformable layer to reduce fluid bypass.
While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow. Dimensions are only presented to illustrate the diminutive size of cold plate heat exchanger assembly 20 and are not intended to be limiting. Those skilled in the art can adjust the dimensions of cold plate assembly 20 to accommodate specific heat transfer requirements.
Furthermore, the function of cold plate assembly 20 has been described as removing excess heat from a heat generating electronic component; those skilled in the art can recognize that cold plate assembly 20 can also function by adding heat to a component by pumping preheated coolant through the cold plate assembly 20.
Still furthermore, cold plate assembly has been described as being all-metal. Those skilled in the art can substitute alternative materials other than metal for components that are not crucial to the making or using of the present invention. Therefore, it will be understood that it is not intended to limit the method of the invention to just the embodiment disclosed.