MOUNTING SYSTEM FOR AN ELECTRONIC DEVICE

Abstract: In a heat transfer and mounting system for electronic devices (84) which are electrically connected to a printed circuit board (30), each electronic device (84) is affixed to a respective metal plate (82) with the device (84) being positioned between the plate (82) and the board (30). Each metal plate (82) is associated with two heat transfer devices (10) each of which has a cross-bar member attached to the plate (82) and the board (30), and a leg member which passes through an opening (34) in the board (30) and which abuts against, and is attached to, a chassis (50) which acts as a heat sink. In operation, heat is conducted from each electronic device (84) to the chassis (50) via the associated metal plate (82) and the associated heat transfer devices (10).

Description: MOUNTING SYSTEM FOR AN ELECTRONIC DEVICE Technical Field This invention relates to a mounting system for an electronic device which is electrically connected to a printed circuit board, and is concerned in particular with such a system which includes means for conducting heat from the electronic device to a heat sink. Background Art In the design of certain types of electronic equipment, such as power converters, it is necessary to provide means for cooling electronic devices included in the equipment during operation of the equipment. Problems have been experienced in achieving a mounting and cooling system for electronic devices which is of simple construction and efficient as regards heat transfer. In the U.S. Patent No. 4,535,385, for example, there is disclosed a mounting system for a pair of printed circuit boards wherein a cooling plate is disposed between the two boards, a number of electronic devices being mounted on that side of each board remote from the cooling plate. Thermally conductive flow paths extend through the printed circuit boards for providing a thermal connection between the electronic devices and the cooling plate. The cooling plate is connected to the chassis of a computer or other electronic equipment, and heat is transferred in operation from the cooling plate to the chassis. The fact that the electronic devices are not directly affixed to the cooling plate detracts from the efficiency of the heat transfer between the electronic devices and the cooling plate, and gives rise to some constructional complexities. Disclosure of the Invention It is an ob ect of the invention to provide a mounting system for an electronic device electrically connected to a printed circuit board, which system is of simple construction and incorporates efficient means for transferring heat away from the electronic device. According to the invention there is provided a mounting system for an electronic device which is electrically connected, to a printed circuit board, the system including means for conducting heat from said electronic device to a chassis, characterized by a metallic plate to which said electronic device is affixed, said electronic device being positioned between said plate and said printed circuit board, and having electrical conductors which extend from said device away from said plate, said printed circuit board being provided with electrical receptacles arranged to receive and to be electrically engaged by said conductors, first and second heat transfer devices each incorporating a cross-bar member and a leg member, said cross-bar member of each heat transfer device being disposed between said plate and said board, and said leg member of each heat transfer device extending through an opening in said board and abutting against said chassis, first fastening means for attaching said board to said cross-bar member of each heat transfer device, and further fastening means for attaching said leg member of each heat transfer device to said chassis, and for attaching said cross¬ bar member of each heat transfer device to said plate, whereby heat is conducted in operation from said electronic device to said chassis via said plate and said first and second heat transfer devices. It should be appreciated that in a mounting system in accordance with the present invention more than one electronic device may be affixed to the said metallic plate. Also, it should be appreciated that more than one metallic plate, each having one or more electronic devices affixed thereto, may be included in the system, each plate being associated in a similar manner with at least two heat transfer devices which serve to conduct heat from the relevant electronic device or devices to the chassis. Brief Description of the Drawings One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in .which: Fig. 1 is a partially exploded, perspective, view of a power converter utilizing a mounting system in accordance with the present invention; Fig. 2 is a top view, partly in section, of the power converter of Fig. 1; Fig. 3 is a perspective view of a heat transfer device utilized in the power converter; and Fig. 4 is an enlarged, fragmented, view of a portion of the power converter viewed along the direction of the arrow B in Fig. 1. Best Mode for Carrying Out the Invention Referring to Figs. 1 and 2, a metal chassis 50 functions as a heat sink and as a structural base for supporting a printed circuit board 30 and a plu¬ rality of electronic modules 80. A plurality of heat transfer devices 10, each formed in the shape of a "T", are affixed to the chassis 50 for supporting the printed circuit board 30 and the electronic modules 80 and for conducting heat from the modules 80 to the chassis 50. Each electronic module 80 is comprised of a metal back plate 82 and an electronic device in the form of a block of encapsulated electronic components 84, having electrical connectors 85 projecting from the surface opposite the back plate 82, the block 84 being affixed to, and in thermal contact with, the plate 82. The width of the back plate 82, as compared to the block of encapsulated components 84, is such that a lip 87 is provided on each side of the block 84 for engaging approximately one-half the width of the upper surface of a cross-bar member 14 of an associated heat transfer device 10 (see Fig. 2 and rig. 3). Notches 86, in the back plate 82, are provided for receiving fasteners 40A and 40B. Provided in receiving and electrically engaging the printed circuit board 30 are electrical receptacles 32 for receiving and electrically engaging with the electrical connectors 85 of the electronic modules 80. A leg 12 of each "T" shaped heat transfer device 10 extends through a respective opening 34 in the printed circuit board 30 to abut against the chassis 50. The fasteners 40A affix the heat transfer devices 10, the modules 80, and the printed circuit board 30 to the chassis 50. If needed, air may be passed through a plurality of chassis openings 52 to provide additional cooling to the chassis supported electrical components. Two identical cover plates 54 (only one shown for simplicity) are affixed to the main chassis by sheet metal screws 55. The covers provide an air chamber through which cooling air passes in operation. Referring to Fig. 2, in conjunction with Fig. 3, each heat transfer device 10 is formed as a truncated T-bar with a cross-bar member 14 and a short leg member 12. Extending through the cross-bar member 14 and the leg member 12 is a hole 19 for receiving a fastener 40A, in the form of a bolt and which extends through the hole 19 and a corresponding hole 53, in the chassis 50, to engage a nut 40D. The nut 40D may be replaced with a screw type insert. for ed in opening 53, for receiving the fastener 40A. The top plate 82 of an associated module 80 fits under the fastener 40A, in the area of a slot 86. The fastener 40A when tightened, rigidly secures the module 80 to the heat transfer device 10 and the heat transfer device 10 to the chassis 50. The printed circuit board 30 is provided with openings 34 to permit the legs 12 of the heat transfer devices 10 to pass through the printed circuit board. Projections 18, on the underside of each cross-bar member 14, maintain a distance between the cross-bar member and the surface of the printed circuit board so that the printed circuit board conductors do not touch the heat transfer device 10. Two pairs of tapped holes 16, positioned on opposite surfaces of each cross-bar member 14, are counter threaded so as to receive mounting screws 40B and 40C. The mounting screws 40C extend through openings 38 in the printed circuit board 30 and fasten the printed circuit board to the undersurfaces of the cross-bar member 14. In operation, heat is conducted from the blocks 86 to the chassis 50 via the metal plates 82 and the heat transfer devices 10. Referring now to Fig. 4, the printed circuit board 30 is shown populated with IC chips 36 on its undersurface. Although not shown in complete detail, for purposes of simplicity, it is understood that conductors 37, for interconnecting the various IC chips to signal and power sources, may be positioned on either or both sides of the printed circuit board 30. In the disclosed configuration, three of the T- shaped heat transfer devices 10 can support a pair of electronic modules 80. Removal of the fasteners 40A and 40B, associated with a particular electronic module 80, will permit the module to be readily removed from the circuit board 30 simply by pulling the module away from the board. Insertion of a replacement module is accomplished by reversing the removal process. Any soldering or desoldering of a module with respect to the circuit board is thus elminated. Removal of all of the 40A fasteners will permit the removal of the printed circuit board from the chassis. While a preferred embodiment of the invention has been shown and described, various other embodi¬ ments and modifications thereof will be apparent to persons skilled in the art and thus will fall within the scope of the invention as defined in the following claims.

Claims: CLAIMS 1. A mounting system for an electronic device (84) which is electrically connected to a printed circuit board (30) , the system including means (10, 82) for conducting heat from said electronic device to a chassis (50) , characterized by a metallic plate (82) to which said electronic device (84) is afifixed, said electronic device being positioned between said plate and said printed circuit board (30) , and having electrical conductors (85) which extend from said device away from said plate, said printed circuit board (30) being provided with electrical receptacles (32) arranged to receive and to be- electrically engaged by said conductors, first and second heat transfer devices (10) each incorporating a cross-bar member (14) and a leg member (12) , said cross-bar member of each heat transfer device (10) being disposed between said plate (82) and said board (30) , and said leg member of each heat transfer device extending through an opening (34) in said board and abutting against said chassis (50) , first fastening means (40C) for attaching said board to said cross-bar member of each heat transfer device, and further fastening means (40A, 40B) for attaching said leg member of each heat transfer device to said chassis, and for attaching said cross-bar member of each heat transfer device to said plate (82) , whereby heat is conducted in operation from said electronic device to said chassis via said plate and said first and second heat transfer devices. 2. A mounting system according to claim 1, characterized in that first and second holes (19) are respectively formed in said first and second heat transfer devices (10) , each of said holes extending through said cross-bar member (14) and said leg member (12) of the respective heat transfer device, and in that a first one (40A) of said further fastening means extends through said first hole and connects said plate (82) to said chassis (50) , and a second one (40A) of said further fastening means extends through said second hole and connects said plate to said chassis. 3. A mounting system according to either claim 1 or claim 2, characterized in that each of said first and second heat transfer devices (10) is in the form of a generally "T" shaped member. 4. A mounting system according to any one of the preceding claims, characterized in that said electronic device (84) is in the form of a block of encapsulated electronic components. 5. A mounting system according to any one of the preceding claims, characterized in that said heat transfer devices (10) are made of metal. 6. A mounting system according to claim 5, characterized in that said cross-bar member (14) of each heat transfer device (10) is provided with at least one projection (18) which serves to space the cross-bar member from said printed circuit board (30) and thereby prevents conductors of said board from contacting the heat transfer device. 7. A mounting system according to any one of the preceding claims, characterized in that said first fastening means (40C) and said further fastening means (40A, 40B) are removable. 8. A mounting system according to any one of the preceding claims, characterized in that said first and second heat transfer devices (10) are respectively arranged to engage with, and extend along, opposed edges of said plate (82) . 9. A mounting system according to claim 8, characterized in that at least one of said first and second heat transfer devices (10) also engages a first edge of a further metallic plate (82) to which a further electronic device (84) is affixed, said first edge being positioned adjacent the relevant one of said opposed edges, and a second edge of said further plate, opposite said first edge, being engaged by a third heat transfer device (10) similar to said first and second heat transfer devices, said third heat transfer device being mounted in relation to said board, said chassis (50) and said further metallic plate (82) in a similar manner to that in which said first and second heat transfer devices (10) are mounted in relation to said board, said chassis and the metallic plate mutually associated therewith.

Inventors: CABANISS FRANK WAYNE, SPERAW FLOYD GIBSON, CABANISS, FRANK, WAYNE, SPERAW, FLOYD, GIBSON
Applicants: NCR CO, NCR CORPORATION
Application year: 1987
Main classification: H05K7
IPC codes: H05K7