Patent Application
20080229580
The invention relates to a method of making a brazed micro-channel cold plate assembly for cooling a heat producing electronic component.
Recirculating closed-loop liquid cooling systems are used for cooling heat generating electronic components such as computer processing units (CPU). Shown in
In reference to
U.S. patent application Ser. No. 11/221,526 discloses a cold plate assembly with engineered flow channels. The disclosed cold plate assembly includes a base plate of
U.S. patent application Ser. No. 11/221,526 discloses a cold plate 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. On the interior surface of the base plate is a series of micro-channels and micro-fins, wherein the micro-fins have coplanar surfaces. The base plate is assembled to a manifold cover, wherein the interior surface of the manifold cover has larger alternating channels with co-planer edges that cooperate with the smaller coplanar surfaces of the micro-fins. Inlet/outlet pipes are also joined to inlet/outlet ports on the manifold cover.
When the manifold cover is engaged to the base plate, the coplanar edges of the alternating channels of the manifold cover come in intimate contact with the coplanar edges of the micro-fins of the base plate forming a checkerboard pattern for fluid flow resulting in more effective and efficient heat extraction. The multiple crossing interfaces between the bottom coplanar edges of the manifold channels and the top coplanar edges of the micro-fins have to be held to very close tolerances to prevent any bypass flow of coolant, which would cause reduced heat transfer efficiency.
Providing a permanent bond and a hermetic seal at the joining surfaces of the cold plate assembly while maintaining intimate contact between the coplanar edges of the micro-fins with the coplanar edges of the alternating channels is critical. Any liquid coolant leakage from the cold plate assembly will severely damage the electronic component for which it is designed to cool, as well as any other components which the coolant may come into contact with. Also, any air introduced into the closed-loop system may risk lowering the performance of the coolant pump 22, creating unacceptable noise during the operation of the pump, and lowering heat transfer efficiency. In addition, the presence of air in the system would reduce the volume of the initial coolant charge, resulting in reduced heat transfer efficiency. Known methods of permanently bonding and hermetically sealing the base plate and inlet/outlet pipes to the manifold cover have been known to fail over prolonged use or can be too complex and expensive to be manufactured.
One known method to permanently bond and hermetically seal the base plate and inlet/outlet pipes to the manifold is by welding joining surfaces of the components. Due to the compact size of a typical cold plate required for cooling electronic components, typically in the neighborhood of 40 mm to 50 mm in diameter, the heat required to weld diminutive metal components may warp the cold plate assembly causing the coplanar edges of the micro-fins and the coplanar edges of the alternating channels to lose intimate contact and results in a non-functional unit.
Another method known is to use an elastomer seal to bond and hermetically seal the base plate and inlet/outlet pipes to the manifold. A draw back to using elastomer is the change in thickness of the elastomer as it cures or after it is exposed to the working fluid. Furthermore, the use of elastomer has proven to be unreliable where the elastomer along the joining surfaces has failed after prolonged temperature cycling.
Still another method known to permanently bond and hermetically seal the base plate and inlet/outlet pipes to the manifold cover is by resistance welding the components after assembly which is also disclosed in U.S. patent application Ser. No. 11/221,526. Resistance welding provides for a permanent bond and hermetic seal for the usable life of the cold plate; however, resistant welding may not be cost effective. Resistance welding requires the use of highly pure, oxygen free copper that is both electronically and thermally conductive. Besides the suitable material, the joining surfaces of the base plate, inlet/outlet pipes, and manifold cover have to be precision machined to exact specifications resulting in complexity and cost of manufacturing.
There exists a need for a micro-channel cold plate heat assembly wherein the joints of the base plate, manifold cover, and inlet/outlet pipes can be permanently bonded and hermetically sealed by conventional means that is predictable, easy to manufacture, and cost effective.
The invention relates to a brazed micro-channel cold plate assembly for cooling electronic components. The instant invention provides a novel combination of features and method steps that allow a micro-channel cold plate assembly to be brazed without clogging or jeopardizing the coolant flow in the micro-channels and with the assurance of a hermetic seal between joining components. A hermetic seal is critical to exclude the intrusion of air into the closed loop system and prevent the leakage of coolant onto the electronic component that the cold plate assembly is in contact with.
The primary components of a cold plate assembly are a base plate, a manifold cover, and inlet/outlet pipes; wherein the individual components are assembled and brazed into an integral unit. The joining surfaces of the components have novel features that provide for a permanent bond of the joining surfaces and a hermetic seal along the joining surfaces. The novel features also forestall excess braze alloy from contaminating the interior surfaces of the assembled cold plate and obstructing the engineered flow channels.
The base plate has an interior surface with substantially parallel micro-channels and corresponding micro-fins having coplanar edges. About the perimeter of the interior surface of the base plate is a wall with an end edge. The interior of the manifold cover has a series of substantially parallel alternating inlet/outlet channels with coplanar edges. About the perimeter of the manifold cover interior surface is a trough that is adapted to join with the wall of the base plate to form features that are conducive to brazing. Manifold cover also has inlet/outlet ports to accept inlet/outlet pipes for coolant flow into and out of the cold plate assembly.
When the manifold cover is engaged with the base plate, the alternating channels coplanar edges on the manifold cover come into intimate contact with the micro-fins coplanar edges on the base plate. The perimeter trough on the manifold cover cooperates with the wall of the base plate to define an outboard radial clearance, an inboard radial clearance, and a gap in between; wherein all three spatial voids are in hydraulic communication with each other. Fitted between the base plate and manifold cover is a first braze element formed of a braze alloy.
The inlet/outlet pipe has an annular flange, a joining surface, and an annular notch on the joining surface. The joining surface of the inlet/outlet pipe is inserted into the inlet/outlet port of the manifold. Fitted between the annular flange and the manifold cover is a second braze element formed of a braze alloy.
The cold plate assembly is heated to a temperature effective to melt the first and second braze elements. Once the braze alloy enters a liquid state, the liquid alloy is drawn into the outboard radial clearance and portion of the gap by capillary forces. Air displaced by the braze alloy exits to the ambient atmosphere through the inboard radial clearance. The inboard radial clearance is essential to prevent air from being trapped in the gap. Otherwise, during the brazing process, trapped air in the gap will increase in pressure, thereby separating the manifold cover from the base plate causing the multiple crossing interfaces between the alternating channel coplanar edges and micro-fins coplanar edges to lose intimate contact.
The arrangement is then cooled at a predetermined rate, solidifying the braze alloy to bond the base plate to the manifold cover, and the inlet/outlet pipe to the manifold cover to form the cold plate assembly.
An advantage of the present invention allows the individual components of a micro-channel cold plate to be assembled, permanently bonded, and hermetically sealed by conventional means that is predictable and cost effective.
Another advantage of the present invention is that the combination of novel features on the joining surfaces of the base plate, manifold cover, and inlet/outlet pipes allows a micro-channel cold plate to be permanently bonded by brazing without braze alloy clogging or jeopardizing the coolant flow in the micro-channels.
Still another advantage of the present invention is that the combination of novel features on the individual components provides for a robust hermetic seal along the joining surfaces for the designed life of the micro-channel cold plate.
Further features and advantages of the invention will appear more clearly on a reading of the following detail 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:
Shown in
Cold plate assembly 20 is comparable in size to, and in thermal contact with a heat generating electronic component. Base plate 100 is approximately 34 mm in outer diameter with a thickness of approximately 1.0 mm. Manifold cover 200 outer-diameter is greater than outer-diameter of base plate 100 in order to overlay base plate 100. Manifold cover 200 thickness is approximately 5 mm and is largely determined by the hydraulic flow requirements for the desired cooling needs. Inlet/outlet pipes 300 are approximately 9.5 mm in outer diameter, excluding the enlarged tapered diameters for hose retention, which would be approximately 10.8 mm in outer diameter, and are approximately 25 mm in length. Preferably, base plate 100, manifold cover 200, and inlet/outlet pipes 300 are formed of copper; however, the components can be formed of any elemental metals, metal alloys, or combinations thereof that are thermal conductive and amendable to brazing.
In reference to
In reference to
In reference to
Perimeter wall 155, rim 180, and retainer shoulder 175 of perimeter wall 155 cooperate with novel features of manifold cover 200, which are described below, during the brazing process to form a permanent bond and hermetic seal along the joining surfaces, as well as to prevent excess metal braze alloy from contaminating micro-fins 140 and micro-channels 145.
Also shown in
Co-axially located with central axis 110 on manifold cover 200 is a perimeter trough 250 having a trough first face 255, a trough second face 260, and a trough bottom 265. Trough first face 255 and trough second face 260 are substantially parallel with wall outer surface 160 and wall inner surface 165 of base plate 100, respectively. Trough bottom 265 is substantially parallel with wall end edge 170 and rim 180 of perimeter wall 155.
Perimeter trough 250 is sufficient in width to accommodate wall end edge 170 and rim 180. Ultimately, perimeter wall 155 of base plate 100 is inserted into and cooperates with perimeter trough 250 of manifold cover 200 to define an inboard radial clearance 280 between trough second face 260 and wall inner surface 165, and an outboard radial clearance 275 between trough first face 255 and wall outer surface 160.
Perimeter trough 250 is also sufficient in depth to allow alternating channel coplanar edges 235 of manifold cover 200 to come into intimate contact with micro-fins coplanar edges 150 of base plate 100 without interference between trough 250 and perimeter wall 155, while also defining gap 270 between wall end edge 170 and trough bottom 265, when base plate 100 is assembled with manifold cover 200.
The spatial distance between trough first face 255 and wall outer surface 160 is effective for capillary forces to draw melted braze alloy into outboard radial clearance 275. Outboard radial clearance 275 is in hydraulic contact with gap 270, which in turn is in hydraulic contact with inboard radial clearance 280. In reference to
In reference to
Prior to assembly of the individual components, the joining surfaces of base plate 100, manifold cover 200, and inlet/outlet pipe 300 are prepared and cleaned in a manner known to those skilled in the art of brazing. After proper preparation, the components are assembled and brazed as described next.
Base plate 100 is firmly secured in a fixture. First braze element 120 is positioned onto retainer shoulder 175 of base plate 100. Base plate 100 and manifold cover 200 are then arranged so that wall end edge 170 is receivable in perimeter trough 250 of manifold cover. Perimeter wall 155 of base plate 100 is inserted into perimeter trough 250 of manifold cover 200 until alternating channels coplanar edges 235 of manifold cover 200 are in intimate contact with micro-fins coplanar edges 150 of the base plate 100 forming a checkerboard pattern. It is critical that alternating channels coplanar edges 235 are maintained in intimate contact with micro-fins coplanar edges 150 during and after the brazing process; otherwise, coolant will by pass the engineered flow pathways resulting in less efficient heat transfer.
As described herein above, perimeter trough 250 is sufficient in depth, wherein alternating channels coplanar edges 235 are in intimate contact with micro-fins coplanar edges 150 and wall end edge 170 is spaced apart from trough bottom 265 defining gap 270. Gap 270 provides a mean to capture excess melted braze alloy. Wall outer surface 160 and trough first face 255 are spaced apart defining outboard radial clearance 275. Wall inner surface 165 is spaced apart from trough second face 260 defining inboard radial clearance 280. Outboard radial clearance 275, gap 270, inboard radial clearance 280, and interior plate surface 135 are all in hydraulic communication.
Inlet/outlet pipe 300 is arranged so that first exterior pipe surface 305 is receivable in inlet/outlet port 225. Second braze element 125 is positioned on second exterior pipe surface 310 of inlet/outlet pipe 300 between the annular flange 320 and the first exterior pipe surface 305 of inlet/outlet pipe along exterior edge 325. First exterior pipe surface 305 of inlet/outlet pipe 300 is slidably inserted into inlet/outlet port 225. Second braze element 125 is held in position by annular flange 320 and manifold exterior surface 207.
The components as described are clamped onto the fixture, a sufficient force substantially parallel to central axis 110 is then applied on manifold exterior surface 207 to ensure micro-fins coplanar edges 150 of base plate 100 and alternating channel coplanar edges 235 of manifold-cover 200 remain in intimate contact. The force could be applied to the manifold exterior surface 207 by means of applying pressure on the fixture or directly onto the manifold exterior surface 207.
The multiple crossing interfaces between the alternating channel coplanar edges 235 and micro-fins coplanar edges 150 have to be maintained in intimate contact during the heating and cooling cycle of the brazing process. Were it not for the maintenance of intimate contact between the surfaces throughout the entire brazing cycle, the faying surfaces would spread apart during the cooling down period from liquiduis temperature to room temperature resulting in a spatial separation that would be highly detrimental to heat transfer efficiency.
Referring to
When manifold cover 200 is assembled with base plate 100, rim 180 of perimeter wall 155 constricts outboard radial clearance 275 and thereby retards the flow of liquid braze alloy into gap 270. Following the path of less resistance, excess braze alloy will drip off retainer shoulder 175 rather than further flowing past the constriction between rim 180 and trough first face 255. It is preferred that the volume of braze alloy in first braze element 120 is less than the sum of the volume of outboard radial clearance 275 and gap 270 to ensure that excess braze alloy does not exit inboard radial clearance 280 onto interior plate surface 135 and contaminate micro-channels 145.
When inlet/out pipe 300 is inserted into inlet/outlet port 225 on manifold cover 200, annular notch 330 together with inlet/outlet pipe clearance 315 forms an effective spatial clearance to contain excess braze alloy. It is also preferred that the volume of braze alloy in second braze element 125 is less than the sum of the volume of inlet/outlet pipe clearance 315 and annular notch 330 to ensure excess braze alloy does not enter interior plate surface 135 and contaminate micro-channels 145. Any excess braze alloy will drip off of manifold exterior surface 207 due to the path of least resistance.
The arrangement is then cooled at a predetermined rate depending upon the type of brazing process used, the section thickness of the parts being brazed, and the purity of the materials being brazed, to solidify the braze alloy to bond the base plate to the manifold cover to form the assembly.
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 actual size of cold plate 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 the specific heat transfer needs.
Furthermore, variation in the disclosed embodiment could be made. The perimeter wall 155 could be formed on the manifold cover 200 and the perimeter trough 250 could be formed on the base plate 100.
Still furthermore, the function of cold plate assembly 20 has been described as removing excess heat from a heat generating component; those skilled in the art can recognize that cold plate assembly 20 can also function as adding heat to a component by pumping preheated coolant through the cold plate assembly 20. Therefore, it will be understood that it is not intended to limit the method of the invention to just the embodiment disclosed.
