Patent Document

BACKGROUND 
     1. Field of the Invention 
     The present invention is related to the field of heat sinks, and more specifically to a novel arrangement of electric power switches and heat sinks on a printed electric circuit board. 
     2. Description of the Related Art 
     Complex electric circuits, such as those of computer units, are often manufactured on generally flat printed circuit boards, which are also known as motherboards. These circuits receive electrical power, and switch it with electrical switches to the various units of the circuit. These switches, also known as power switches, generate heat commensurate with the switched electrical power. It is a common practice to deal with the generated heat by attaching a heat sink to every electrical switch. An example of this is presented below. 
     Referring to FIG. 1, an electrical switch  50  is now described. The electrical switch  50  includes an electronic component  52 , and that is typically encapsulated in electrically insulating material. The electronic component  52  is accessed by three electrical leads  54 ,  56 ,  58 , which are typically received in holes of the printed circuit board (not shown). The electronic component  52  can be a transistor, an FET, a MOSFET, etc. 
     When an electrical switch, such as electrical switch  50 , is intended for handling large amounts of electrical power, it is often provided with a heat conductive backing. The backing is typically made out of metal, for dissipating the heat generated by the electronic component  52 . 
     Typically, the heat metal backing is provided in the form of tab  62  for the switch  50 . In some methodologies, the tab  62  is soldered on the printed circuit board itself. 
     In a certain methodology, also known as TO-220 methodology, the tab  62  is intended to be arranged upright, perpendicularly to a plane of the printed circuit board, and parallel to the leads  54 ,  56 ,  58 . The tab  62  includes a hole  64 , for passing a screw (not shown). The screw is used to attach a heat sink to the switch  50 . 
     Referring now to FIG. 2, a heat sink  70  is described. The heat sink  70  includes a main panel  72 , which includes a hole  74 . The hole  74  is for receiving a screw (not shown), for attachment to the switch  50  of FIG.  1 . The heat sink  70  also includes two side panels  76 , which are also known as fin panels  76 . Optionally and preferably, the fin panels  76  include slots  78 , which are also known as cuts  78 . The heat sink  70  is typically made out of metal, and is painted black for radiating the heat better. In addition, the paint advantageously also provides electrical isolation. 
     Referring now to FIG. 3, the general attaching arrangement is illustrated. The leads  54 ,  56 ,  58  (not shown, but obscured by the electronic component  52 ) of the device  50  are inserted into holes (not shown, but obscured by the electronic component  52 ) of the printed circuit board  80 . The hole  64  of the tab  62  is aligned with the hole  74  of the main panel  72  of the heat sink  70 . 
     The attaching arrangement also illustrates the weaknesses of this methodology. More particularly, the arrangement of FIG. 3 occupies a lot of space on the printed circuit board  80 . In particular, while the switch  50  can be physically small, the heat sink  70  demands a lot of space. This forces locating other devices farther away from switch  50 . 
     The problem is made worse by the fact that typically many electrical power switches, such as switch  50 , are designed to be grouped together nearby, for sharing between them the electrical load. Each of them requires a heat sink, and therefore each requires a lot of space around it. Accordingly, the bank of electrical switches occupies a large area of the motherboard. 
     There&#39;s also another reason on why that area cannot be made smaller. Devices having heat sinks are often cooled by use of fan, which establishes an airflow. But it has proven harder to establish an air flow when the heat sinks and the switches are crowded close to each other. 
     These problems have been addressed in the past by keeping the switches close to each other, and directing their fins away from the group. Another way has been by making each of the heat sinks smaller. This means making the side panels  76  less wide. This also means making the main panel  72  less wide, which brings this side panels  76  closer to the device  50 . 
     But the rating of the heat sink  70  is determined by its dimensions. As the dimensions are getting smaller, to accommodate overcrowding on the board  80 , the heat sink  70  can dissipate less heat. This is exactly contrary to the present needs of the industry. As electrical devices increase in capability, they consume more power, which in turn requires higher heat sinking capability. In addition, making the circuit boards larger runs the risk of exceeding standard sizes and form factors, which can adversely affect the acceptance and success of the product in the market. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective diagram of a prior art electric power switch, having a tab for receiving a heat sink according to a known methodology. 
     FIG. 2 is a perspective diagram of a prior art heat sink for use with the switch of FIG.  1 . 
     FIG. 3 is a diagram of a top view of the switch of FIG. 1, having received the heat sink of FIG.  2 . 
     FIG. 4 is a diagram of a top view of an electric switch having a large heat sink that defines a large space between the fins, and further includes additional heat sink structure of another heat sink within the same space according to the present invention. 
     FIG. 5 is a diagram illustrating arranging electrical switches and heat sinks on a circuit board according to a pairing arrangement of the invention, with a first airflow scheme. 
     FIG. 6 is a diagram illustrating arranging multiple pairs of electrical switches and heat sinks on a circuit board according to the pairing arrangement of the invention, with a second airflow scheme. 
     FIG. 7 is a diagram illustrating arranging a pair of non identical electrical switches and heat sinks on a circuit board according to the pairing arrangement of the invention. 
     FIG. 8 is a diagram illustrating arranging electrical switches and heat sinks on a circuit board according to a chain arrangement of the invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention provides assemblies of electrical switches and heat sinks on printed circuit boards. The invention calls for using large heat sinks in a topology similar to the TO-220 topology, while simultaneously interleaving the fin panels of the heat sinks. In other words, the fin panel of one of the heat sinks is placed between the fin panels of an associated neighboring heat sink. Preferably replacement of the heat sinks is such that the slots of the fin panels of neighboring heat sinks are aligned, to permit streamlined airflow. 
     The invention offers the advantage that larger heat sinks can be used, which affords a higher heating sinking capability, which in turn permits the electrical switches to handle more electrical power. This is accomplished without consuming more circuit board area, which prevents having to exceed a standard motherboard size or a standard form factor. 
     Another advantage of the invention is that the topology of the invention permits efficient cooling by airflow. Indeed, the slots of the side panels become aligned with each other. This permits air to flow through all of them in series, according to an airflow scheme. 
     Referring now to FIG. 4, the heat generating electrical device  150  is provided with a heat sink  170 . The heat sink  170  includes a main panel  172  and side panels  176  (also known as fin panels) that include slots  178 . The main panel  172  is attached to the heat conductive metal backing of the device  150  (the metal backing is not shown separately). 
     The device  150  and the heat sink  170  are provided on a printed circuit board  180 . Since this is a top view, the generally flat electrical printed circuit board  180  has a plane parallel to the plane of the paper. The main panel  172  is arranged substantially perpendicularly to the plane of board  180 , such as according to the TO-220 methodology. 
     For the embodiment of FIG. 4, and for all the other descriptions of this invention, it is understood that the fin panel need not terminate in a smooth edge. If it does, the panel can have slots. Alternately, it can terminate in teeth. Whether they terminate in slots or in teeth, the fin panels  176  are said to have openings  178 . 
     In addition, it is not necessary that an edge of the fin panel  176  be attached to the main panel  172  from an edge. In other words, the fin panel  176  can extend past a main plane of the main panel  172 . In those cases the switch  150  will always be between the fin panels of its own heat sink. 
     It should be noted that the fin panels  176  are wider than the corresponding fin panels  76  of the FIG.  3 . It should be further noted that the back panel  172  is wider than panel  72  of FIG.  3 . This means that the fin panels  176  are farther away from device  150  then the corresponding ones in FIG.  3 . 
     For purposes of understanding this invention, an interstitial space  190  is defined for the heat sink  170 . The interstitial space  190  is the space between the fin panels  176 . It should be noted that, since the main panel  172  and the fin panels  176  are larger than the corresponding ones of FIG. 3, the corresponding interstitial space  190  of the arrangement of FIG. 4 is substantially larger than that of FIG.  3 . This is exactly against what the prior art teaches, for saving space on the printed circuit board  180 . 
     Further according to the present invention, the heat sink  170  is interleaved with a neighboring heat sink. This means that at least one portion  194  of a neighboring heat sink of an associated electrical device is located between the fin panels  176 . In other words, at least one portion  194  of a neighboring heat sink is located within the interstitial space  190 . 
     This interleaving can be accomplished with a number of different arrangements. Two main arrangements are described below, the pairing arrangement in FIGS. 5,  6  and  7 , and the chain arrangement in FIG.  8 . 
     Referring now to FIG. 5, a pair of switches and heat sinks is described. The pair includes two electric switches  512 ,  514  that have heat sinks  522 ,  524 , respectively attached to them. The two heat sinks  522 ,  524  are identical to each other, although that is not necessary. Each heat sink  522 ,  524  is identical to heat sink  170  of FIG. 4, although again that is not necessary. In the arrangement of FIG. 5, at least one of the fin panels of heat sink  522  is between the fin panels of heat sink  524 . In addition, the heat sinks  522 ,  524  are so close together that at least a portion of device  512  is between the fin panels of heat sink  524 . The converse is also true. 
     A benefit of the arrangement of the invention is that the fin panels of the heat sinks  522 ,  524  are close to each other, and their openings can be aligned. The benefit of the invention will be appreciated more if the system is designed such that cooling is performed with airflow. 
     According to another embodiment, the invention further includes a guide (not shown) to duct air from the top, to a point  530 . The point  530  is located between the main panel of the first heat sink, the main panel of the second heat sink, and the four fin panels. Once air is ducted to point  530  it is then pushed through the aligned openings in the four fin panels, according to the main directions  536 ,  538 . The air can be made to come from the top either by placing the fan on the top, or by placing a fan on the side, and ducting the air from the top. 
     Referring now to FIG. 6, it can be seen how the pair of FIG. 5 can be used as a building block. The pairs are arranged successively on a printed circuit board  602 . More particularly, switches  612 ,  614 ,  616 , and  618  are attached to heat sinks  622 ,  624 ,  626 , and  628 , respectively. 
     A feature of the arrangement of FIG. 6 is that the successive pairs form a duct for the airflow. Indeed, while the main panels of each heat sink  622 ,  624 ,  626 ,  628  form a duct, the openings in their fin panels permit air to flow through along the line  646 . The airflow can be drawn by a fan  652 . Alternately and equivalently, it can be forced by a fan. 
     Referring now to FIG. 7, a pair can be built differently on a printed circuit board  702 . In particular, a small switch  712  and a large switch  714  have respectively attached to them a small heat sink  722  and a large heat sink  724 . Both heat sinks  722  and  724  are arranged with their main panels substantially perpendicular to a plane of the board  702 . In this case, the fin panels of heat sink  722  are located between the fin panels of heat sink  724 . 
     The arrangement of FIG. 7 is particularly useful where a pair of switches  712 ,  714  have dissimilar power switching requirements, and therefore need to dispose of dissimilar amount of heat. The arrangement of FIG. 7 can be cooled by moving air along axis  754 , through the aligned openings of the fin panels. Air can be moved either according to the airflow scheme of FIG. 5 or of FIG.  6 . The latter will have to be chosen if the arrangement of FIG. 7 is used as a building block of linear arrangement similar to that of FIG.  6 . 
     Referring now to FIG. 8, the chain arrangement of the invention is described for a printed circuit board  802  having a main plane parallel to the drawing. Switches  812 ,  814 ,  816 , and  818  have respectively attached to them heat sinks  822 ,  824 ,  826 , and  828 . A fan  842  can be put into place to draw (or force) air along an airflow line  846 . 
     It would be appreciated that the chain arrangement of the invention consumes more space on the printed circuit board  802 . However, it renders it easier to mount the heat sinks  822 ,  824 ,  826 ,  828  on the respective devices  812 ,  814 ,  816 ,  818 . 
     It should be understood that the embodiments explained below are scalable to different sizes of switches, and also to different sizes and shapes of heat sinks. This way optimum solutions can be derived for each application, in view of the present document. 
     A person skilled in the art will be able to practice the present invention in view of the present description, where numerous details have been set forth in order to provide a more thorough understanding of the invention. In other instances, well-known features have not been described in detail in order not to obscure unnecessarily the invention. 
     While the invention has been disclosed in some of its forms, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense. Indeed, it should be readily apparent to those skilled in the art in view of the present description that the invention can be modified in numerous ways. 
     For a first example, different geometries are possible. As an option, in the embodiment of FIG. 8 the main panel of each heat sink could be made less wide, while the fin panels could be made wider. In addition, the fin panels of one device would not intrude fully within the space between the device and the fin panel of an associated neighboring heat sink device. In other words, the arrangement can be practiced with heat sinks having very wide side panels. 
     For a second example, in all of the embodiments of FIGS. 4-8, one or more of the electrical switches can be placed on the outside of its heat sink. In each case, the arrangement of the heat sinks relative to each other would be the same, while the device would be placed on the other side of the main panel of its heat sink. This may be desirable in some instances. For instance, in the embodiment of FIG. 6, the path for the airflow would be smoother if it were not constricted by the electrical devices. In addition, the path could be shaped tighter if the fin panels were less wide. In this case, the electrical switch may or may not be located within the fin panels of its own heat sink. 
     The inventor regards the subject matter of the invention to include all combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. 
     The following claims define certain combinations and subcombinations, which are regarded as novel and non-obvious. Additional claims for other combinations and subcombinations of features, functions, elements and/or properties may be presented in this or a related document.

Technology Category: 5