Abstract:
A dual base plate heatsink for use in dissipating heat for electronic devices with thermal contact between fins and the base plates and manufactured without welding. Separately extruded fins are connected to both base plates by placing the fins side by side in channels in both base plates. In order to couple the base plates and finds, the base plates are maintained at a constant relative distance and a swaging tool is passed adjacent the fins and between the base plates in a direction parallel to the surface of the base plates. The swaging tool applies pressure to the base plates to thereby swage the base plates against the ends of the fins.

Description:
This application is a divisional of U.S. application Ser. No. 11/106,440 filed Apr. 25, 2005. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to the manufacture of heatsinks, and more specifically to a method for coupling fins in a high fin-density heatsink to dual heat-dissipating base plates. 
     BACKGROUND OF THE INVENTION 
     Heatsinks are known in the art for receiving and then dissipating heat generated by electronic circuits in modern devices. Such well known heatsinks typically comprise one base unit to which the heat generating electronic devices are mounted, and a plurality of fins projecting from the base unit for dissipating the generated heat. It is a challenge to maximize the surface area of the fins in order to provide optimum heat transfer from the heat sink to the surrounding atmosphere while ensuring good thermal contact between the base unit and the fins. 
     Heatsinks fabricated by metal extrusion have been proposed, wherein the fins and the base units are of integral construction and thereby have the optimum thermal contact. However, as discussed in the disclosure of U.S. Pat. No. 5,406,698 (Lipinksi), it has been shown that there are limits to the size and shape of fins that may be made by way of extrusion manufacturing. There has thus been proposed various methods of manufacturing whereby the fins are extruded separately from the base unit, and subsequently coupled using various methods. 
     U.S. Pat. No. 5,771,966 (Jacoby) discloses a folded heat conducting member or fin with at least one annealed metal insert having a predetermined thickness corresponding to a distance between the first and second heat conductive portions of the fin and a predetermined thickness corresponding to a depth of the groove in the base plate so that the annealed metal insert conforms to the shape of the groove when deformed to secure the base portion engaging region of the folded heat conducting member into the groove. The Jacoby patent proposes an impacting die to perform a deforming or swaging function to deform the fin while in the groove so that it is not removable. 
     U.S. Pat. No. 6,263,956 to Tang et al. sets forth a heat dissipating structure and method of manufacture where each slot in the base has a width slightly less than a thickness of an inserting portion of the associated heat dissipating fin, so that it will allow the heat dissipating fin to tightly insert therein. A fixing frame is then moulded into place for securing the fins. The fixing frame is formed by introducing a melt fixing material inside of fixing recesses and thereafter cooling. As the material forms a solid, it forms the fixing frame that secures the heat dissipating fins onto the base. 
     Published U.S. Pat. Application No. 2002/0007936 (Woerner et al.) discloses one or more folded-fin assemblies “tacked” to the base at selected points by laser welds. In a subsequent operation, the full surface of the lower web portions of the folded-fin assemblies are bonded to the base, typically by brazing. According to the Woerner disclosure, some suitable mechanical means is used to urge the lower web portions against the base prior to the laser welding, to optimize the contact between the lower web portions and the base when the subsequent brazing takes place. Also, a finger tool is used to maintain the desired spacing between adjacent fins prior to laser welding, to optimize that spacing and avoid the possibility of adjacent fins being positioned unevenly or in contact with each other. The heatsink assembly is said to be unloaded from the laser welding apparatus and taken for brazing, soldering or other suitable bonding to the base. As an example, the heatsink assembly may receive a spray application of flux which is then oven-dried and may be passed to a brazing furnace for heating to a temperature range of 1100-1120° F. to carry out the brazing. 
     Published U.S. Patent Application No. 2002/0043359 (Mizutani) sets forth a method of manufacturing a heatsink wherein fins are pressed by means of a mould so that protrusions provided on the back side of the metal plate are pressed into “bottom-expanded recesses” to fix the heat dissipation fins and the base plate together. Mizutani teaches an impact-die mold for pressing protrusions in the base plate against the fins to keep them secure to the base plate. 
     Mentioned above, U.S. Pat. No. 5,406,698 (Lipinksi), proposes a heat sink manufactured by providing a baseplate with several parallel grooves in its surface. Individual fins are manufactured having a dovetail or bell-bottom at their end, the ends then being inserted into respective grooves. The base plate is subsequently deformed in the areas between the parallel channels by rolling a plurality of coaxial rollers through the areas in order to crimp or swage the fins into the grooves. The Lipinski apparatus is an excellent design that requires little pressure to be transmitted though the fins themselves, so that their tendency to undesirably buckle under downward pressure is minimised. However, in the process of deforming the base unit in the areas between the parallel channels, the entire base unit tends to warp. To this end, U.S. Pat. No. 5,638,715 (Lipinski) sets forth an apparatus for subsequently reversing the warp effect. 
     With increased consumer demand for more complex electronic systems, the need has arisen for the more efficient use of space when manufacturing these systems. To help meet this demand, dual base plate heatsinks have been proposed that are mounted to more than one electronic device but that dissipate heat through a common set of fins. With these proposals have come a corresponding set of challenges for manufacturing the heatsinks to specifications that promote excellent heat transfer and good contact between the base plates and the fins. For example, the Lipinksi apparatus would not be sufficient for the manufacture of dual baseplate heatsinks because the proposed roller assembly would not be permitted to pass through the spaces between the fins once the second base plate was in place. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a high fin-density dual base plate heatsink is manufactured by placing fins side by side in channels formed in each of two opposing base plates. In order to couple the base plates and the fins, the relative distance between the base plates is held constant and a swaging tool is passed both adjacent the fins and between the base plates in a direction parallel to the base plates. The pressure exerted by the swaging tool against the base plates adjacent the fins as the base plates are held at a constant relative distance swages the base plate adjacent each fin against the fin. Pressure is thus applied to the end of each fin inserted in each channel thereby securing the fin to the base plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of the preferred embodiment is set forth in detail below, with reference to the following drawings, in which: 
         FIG. 1  is a perspective view of a completed heatsink made according to the preferred method of the present invention; 
         FIG. 2  is a perspective view of fins being mounted into a single base plate, prior to the swaging operation according to the preferred method of the present invention; 
         FIG. 3  is a partial front view of a heatsink with a swaging tool being passed adjacent its fins and against the base plates according to the preferred method of the present invention; 
         FIG. 4  is a partial front view of a heatsink with the swaging tool having passed further adjacent the fins thereby having caused swaging of the base plates against each of the fins according to the preferred method of the present invention; 
         FIG. 5  is a cutaway partial side view of a shorter end of a tine of the swaying tool being passed adjacent a fin prior to swaging the base plates, according to the preferred method of the present invention; 
         FIG. 6  is a cutaway partial side view of a taller end of a tine of the swaging tool being passed adjacent a fin and against the base plates to swage the base plates against the fin, according to the preferred method of the present invention; and 
         FIG. 7  is a cutaway perspective view of the apparatus for manufacturing high-density heatsinks in accordance with the preferred method of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     According to the present invention in its most general aspect, a dual base plate heatsink is manufactured by providing two opposing base plates, each with an inward facing surface and a number of elongate landing areas separated by elongate channels. Fins are placed into the channels of the opposing base plates and, while the base plates are being maintained at a constant relative distance, a swaging tool is passed in a direction parallel to the surface adjacent the fins and between the base plates. As the tool is passed it increasingly applies pressure to the landing areas of the base plate adjacent the fins to swage the base plate material against the fins. The swaging of the base plate causes pressure to be applied to the fins to force them to remain coupled to the base plates. 
     With reference to  FIG. 1 , there is shown a dual base plate heatsink  10  made according to the preferred method of the present invention. The heatsink  10  comprises two opposing base plates  12 , each base plate having an inward-facing surface  14 . Landing areas  11  of base plate  12  are separated by channels  16  and comprise an elongate jaw pair  18 , having jaws  20 . Fins  22  have flared ends  24  that fit in between adjacent jaw pairs  18  of respective base plates  12 . The channels  16  in the surface  14  between the jaw pairs  18  receive the flared ends  24  of the fins  22 . As can be seen from the diagram, the fins  22  are held in place by jaws  20  which have been swaged towards the fins  22  to apply pressure to the flared ends  24  of the fins  22 . The advantage of the flared ends  24  of the fins  22  is that when the jaws  20  have been swaged, a more uniform and secure fit is achieved for increased heat transfer. 
     With reference to  FIG. 2 , there is shown a heatsink  10  being made according to the method of the present invention, wherein a fin  22  is being lowered into one of the channels  16  between landing areas  11  of a base plate  12 . Once all of the fins  22  have been placed into corresponding channels  16  between said jaw pairs  18 , the second base plate  12  is fit onto the flared ends  24  of the fins  22 . 
     With reference to  FIG. 3 , there is shown a front view of the heatsink  10  being made according to the principles of the present invention. In this diagram, the fins  22  have been placed into corresponding channels  16  between landing areas  11  of the base plates  12 , and a swaging tool  40  (fully illustrated in  FIG. 7 ) has been placed through the fins  22  and into the space between jaws  20  in each jaw pair  18 . This diagram shows clearly the flared ends  24  of the fins  22  in between jaw pairs  18 . 
     Furthermore, the shape of each jaw  20  is shown clearly. The jaws  20  progressively widen in cross section from the end distal to the surface  14  of the base plate  12  towards the surface  14 , and then narrow again. The base plates are maintained at a constant relative distance, as discussed in greater detail below with reference to  FIG. 7 . The widening of the jaws  20  co-operates with the wedge shape of the swaging tool  40  to progressively force the jaws  20  apart when the tines  42  of the swaging tool  40  are being passed between the respective jaws  20  in the jaw pairs  18 . Furthermore, the narrowing ensures that swaging the jaws  20  causes minimal warping of the base plates  12  because of a lower bending moment. 
     In  FIG. 4 , the tines  42  of the swaging tool  40  are caused to slide in a direction parallel to the surfaces  14  of base plates  12  and between the jaws  20 . Because the tines  42  of the swaging tool  40 , shown more clearly in  FIGS. 5-7 , are increased in height towards its second end, they push against the jaws  20  of the landing area  11  to swage them apart and against the flared ends  24  of the fins  22 . Because the base plates  12  are being maintained at a constant relative distance, the jaws  20  are forced apart due to the increase in pressure from the tines  42  as the swaging tool  40  is pulled through the fins  22 . The flared ends  24  of the fins  22  are pressed into channels  16  of each base plate  12  and, because the jaws  20  of base plates  12  have been deformed, are retained therein. 
       FIGS. 5 and 6  show a side cutaway view of a single tine  42  of the swaging tool  40  being passed between the base plates  12 . As can be seen, the widened second end of the tine  42  pushes against both jaw pairs  18  of the landing areas  11  on both base plates  12  to progressively force open the jaws  20  and push them against the flared ends  24  of the fin  22 . 
       FIG. 7  shows an exemplary view of the apparatus used to form the heatsink  10  according to the present invention. The uncoupled heatsink  10  is placed in a retaining structure having expansion-preventing walls  50  to maintain the base plates  12  at a constant relative distance. The swaging tool  40  is shown having multiple tines  42  that are each pulled past the fins  22  of the heatsink  10  to force open the jaws  20  in each jaw pair  18  of the landing area  11  so that the jaws  20  push against the flared ends  24  of the fins  22  to hold them in place in the channel  16  of the base plate  12 . 
     In the embodiment of  FIG. 7 , the tines  42  are pulled by a shaft  54  passing through a hole in each tine. The shaft is, in turn, pulled by a hydraulic motor or other motive apparatus. An alternate shaft attachment hole  56  is shown in each of the tines  42 . 
     Also shown in  FIG. 7  are slide-preventing walls  52  which act to prevent the fins  22  from sliding relative to the base plates  12  when the tines  42  of said swaging tool  40  are pulled from left to right. The slide-preventing walls avoid the requirement set forth in U.S. Pat. No. 5,406,698 to, after coupling of the fins  22  to the base plates  12 , remove the parts of the fins  22  that have slid relative to the base plates  12  during application of swaging pressure. 
     A person understanding the present invention may conceive of alternatives and variations thereof. For instance, rather than employing slide-preventing walls for preventing the fins from sliding relative to the base plates, a pressure force can be applied to both base plates to increase the friction force between the fins and the base plates thereby reducing or prevent any relative movement. Furthermore, whereas the flared fin ends of the preferred embodiment provide a more uniform fit for better heat transfer with the jaw pairs when swaged, uniform thickness fins can also be used. 
     An alternative to the smooth-sided fin shape, whether flared or not, is to provide serrations on the end of the fin to improve bonding when the base plate material is deformed against the fin. 
     All such embodiments and variations are believed to be within the purpose, sphere and scope of the invention as defined by the claims appended hereto.