Patent Document

BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention is generally related to a system for clamping a heat sink. More specifically, the invention relates to a system for clamping a heat sink that prevents excessive clamping force. 
     2. Related Art 
     When performing various functions, integrated circuits tend to generate heat. The integrated circuit may be cooled by dissipating heat into the surrounding environment. Particularly in the audio electronics industry, the market has required manufacturers to provide smaller electronic packages along with improved audio performance and power. To improve heat dissipation, heat sinks or blocks of metal may be connected with semiconductor devices to conduct heat away from the semiconductor device and provide a larger surface area from which to dissipate the heat. The heat sink often include fins to increase the surface area for heat dissipation and may even include a channel that provides fluid cooling. This may be particularly important with regard to power amplifiers and audio circuits, as they can generate a significant amount of heat and may require cooling to maintain audio performance of the electronic component. 
     When attaching a heat sink to the semiconductor device, it may be important to have a tight mechanical coupling of the surface of the heat sink with the surface of the semiconductor device to minimize thermal resistance when transferring heat from the semiconductor device to the heat sink. Often, the components must be securely attached in a manner that will withstand harsh vibration and shock. For example, harsh shock and vibration are often encountered in an automotive audio environment. However, clamping the semiconductor device with excessive force can cause damage to the semiconductor device. Accordingly, there is a need to control the force used in securely clamping a heat sink to a semiconductor device. 
     SUMMARY 
     This invention provides a system for clamping a heat sink that prevents excessive clamping force. The system may include a heat sink, a semiconductor device, a printed circuit board, and a cover. The semiconductor device may be mounted onto the circuit board and attached to the cover. The heat sink may be designed to interface with the semiconductor device to transfer heat away from the semiconductor device and dissipate the heat into the environment. Accordingly, the heat sink may be clamped into a tight mechanical connection to minimize thermal resistance between the semiconductor device and the heat sink. 
     The clamping may be accomplished using bolts that are inserted through openings in the cover and threaded into the heat sink. Tightening the bolts may apply a clamping force that presses the heat sink against the semiconductor device. To prevent excessive clamping force from damaging the semiconductor device, loading columns may extend between the cover and the heat sink. The loading columns serve as a stop or structural support that act against the clamping force when the bolts are torqued. In addition, a button may be formed in the cover beneath the semiconductor device to act as a support for the semiconductor device. Further, a teardrop shaped support may be formed in the cover to support the printed circuit board. The teardrop shaped support may include a head portion with bolt openings and a tail portion that extends toward the semiconductor device to support the printed circuit board. 
     Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a sectional front view of a system for clamping a heat sink. 
         FIG. 2  is a sectional side view of a system for clamping a heat sink. 
         FIG. 3  is a perspective view of a cover for an electronic assembly. 
         FIG. 4  is a top plan view of a cover for an electronic assembly. 
         FIG. 5  is a sectional front view of the cover in  FIG. 4 . 
         FIG. 6  is a flowchart illustrating a method for clamping a heat sink. 
         FIG. 7  is a sectional front view of another embodiment of a system for clamping a heat sink. 
         FIG. 8  is another sectional front view of yet another embodiment of a system for clamping a heat sink. 
         FIG. 9  is another sectional front view of yet another embodiment of a system for clamping a heat sink. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , an example of an electronic assembly  10  is provided. The electronic assembly  10  may include a semiconductor device  12 , a circuit board  14 , a heat sink  18  and a cover  16 . The semiconductor device  12  may be in the form of a power amplifier or other semiconductor device that generates heat during usage. These devices often include a ceramic casing and metal pins or pads for facilitating electrical connection. One such device may be the TDA8594J amplifier from PHILIPS electronics. Accordingly, the heat sink  18  may be provided to receive heat from the semiconductor device  12 . The heat sink  18  transfers heat away from the semiconductor device  12  and provides an increased surface area allowing improved dissipation of the heat into the environment of the electronic assembly  10 . 
     The electronic assembly  10  may also include a circuit board  14  such as a printed circuit board to which the semiconductor device  12  may be mounted. The circuit board  14  may be made of a plastic and may include metal traces that may be coupled to the semiconductor device  12 . The traces may provide electrical power as well as data signals, such as audio data signals, and/or control signals to the semiconductor device  12  for processing. In addition, the circuit board  14  may include additional traces for communicating output signals, such as audio signals, to other components or a speaker system after processing. A cover  16  extends around and protects the circuit board  14  and semiconductor device  12 . The cover  16  may be formed from a metal sheet, for example, through a series of forming or stamping events. The cover may be made of from any rigid material such as a steel or other metal, although the cover may also be made from other deformable materials such as plastic or a fibrous material. The cover may include a corrosion resistant plating. For example, the cover can be made of a steel sheet with a thickness of 1.0 mm and including a zinc coating. The cover  16  includes loading columns  24  that extend from an outer surface of the cover through a hole in the circuit board  14  toward the heat sink  18 . The loading columns  24  prevent the application of excessive clamping force on the heat sink  18 . As such, the loading columns  24  provide structural support to the heat sink  18  and prevent damage to the semiconductor device  12 . 
     The heat sink  18  may be clamped to the semiconductor device  12  using a fastener  20 . In  FIGS. 1 and 2 , the fastener  20  is shown as a bolt that may be threaded into a bore  22  formed in the heat sink  18 . Accordingly, the fastener  20  extends through an opening in the cover  16 , continues through an opening in the circuit board  14 , and engages the heat sink  18 . As mentioned, the fastener  20  may engage the heat sink  18  through a threaded engagement. Screws, rivets, clamps or any other fasteners may also be readily used. In the bolt arrangement shown, providing increased torque on the fastener  20  generates additional clamping forces by compressing the semiconductor device  12  between the heat sink  18  and the cover  16 . As shown in  FIG. 1 , the loading columns  24  and fastener arrangement may be provided at multiple locations around the semiconductor device  12 , for example on the opposite sides of the semiconductor device  12  to securely balance compression of the heat sink  18  against the semiconductor device  12 . The columns  24  may extend slightly above the semiconductor device  12  requiring compression of the columns  24 . Alternatively, the columns  24  may extend flush with or below the semiconductor device  12 . Similarly, the columns  24  may all be the same length or may be different lengths thereby providing additional support as the compression increases. In addition, a button  28  may be formed in the cover  16  to act as a spring between the cover  16  and the semiconductor device  12  to absorb forces that may otherwise over compress the semiconductor device  12 . Further, the button  28  may have a rounded or generally dome shape causing the bend of the sheet metal to act as a deformable spring. Further, the button  28  may include a flat top surface that reacts with the semiconductor device  12  through the printed circuit board  14 . As such, the cover  16  forms a planar surface and a button  28  extends from the planar surface and forms a second planar surface parallel to the first planar surface that reacts with the semiconductor device  12 . Further, the loading columns  24  also extend from the planar surface and may be formed substantially perpendicular to a planar surface. It is also understood that other deformable springs for example, leaf springs or coil springs may be used in place of the button  28  to absorb forces. However, the button  28  may be integrally formed in the cover  16 . As may further be seen in  FIG. 2 , the heat sink  18  may include fins  32  extending away from the semiconductor device  12  providing additional surface area to improve heat dissipation through convection cooling. In addition, the fastener  20  may be located in a channel  30  formed in the cover  16 . 
     In  FIGS. 3 ,  4  and  5 , additional views of the cover  16  from  FIG. 2  are provided. The cover  16  may extend along and around the printed circuit board  14  and may include cooling holes  50  allowing for the flow of air for convection cooling of the heat sink  18 , semiconductor device  12 , and the circuit board  14 . The cover  16  may interface with another housing portion that forms part of the heat sink  18  (seen in  FIG. 2 ). The cover  16  may surround and protect the components of the electronic assembly including the circuit board  14  and the semiconductor device  12 . The cover  16  may be formed of a metal sheet through various stamping and forming processes. The trench  30  may be formed across the cover and may be used for housing multiple semiconductor devices, for example a pair of power amplifiers. The button  28  may be stamped into the cover forming a rounded domed configuration including a flattened top surface providing a more stable mechanical interface. The button  28 , as described previously, may act as a spring against semiconductor device  12  to absorb the clamping force. In a similar manner, the loading columns  24  may be stamped into cover  16  and bent perpendicular to a top surface of the trench  30  to absorb additional clamping force and prevent over clamping of the heat sink  18  and damage to the semiconductor device  12 . In addition, a recess  42  may be formed in the cover  16  for supporting the circuit board  14  and distributing the force from the fastener  20  across the circuit board  14 . The recess  42  may extend from the planar surface of the cover  16  toward the circuit board  14 . The recess  42  may include a flat surface parallel to the planar surface that is elongated and extends towards the middle of the semiconductor device  12  to provide additional support for the semiconductor device  12 . As such, the recess  42  may have a generally teardrop shape with the head of the teardrop surrounding the fastener opening  44  and the tail of the teardrop extending towards the middle of the semiconductor device  12 . This configuration may be mirrored on the opposite side of the cover  16  as denoted by recess  46  and fastener opening  48 , symmetrically forming a generally teardrop shape with the tail extending towards the semiconductor device  12 . Other shapes for the recess may also be used, such as ovals or polygons, however the teardrop shape may provide improved support due to support by the head of the screw on one end and the converging tail lines on the opposite end. Although the cover  12 , as shown in  FIGS. 3-5 , is configured to accommodate two semiconductor devices, it is readily understood that multiple additional semiconductor devices could be accommodated by duplicating this arrangement in various additional locations along the cover  16 . Alternatively, a single semiconductor device may be accommodated in a single location on the cover  16 . 
     In  FIG. 6 , an example method  100  is provided for clamping a heat sink  18  to a semiconductor device  12 . The method starts in block  101 . The cover  16  may be formed from a sheet of metal through various stamping operations. In block  102 , one or more columns  24  may be formed in a surface of the cover  16 . At this stage, the column(s)  24  may resemble a strip parallel with the surface extending into an opening formed in the surface of the sheet. In block  104 , a button  28  may be formed in the surface of the sheet at a semiconductor device location. Further, if two columns are used, the columns  24  may be juxtaposed and the button  28  may be formed in between the two columns  24 . The button  28  may be formed by stamping a portion of the surface into a dome shape. Alternatively, slits may be stamped in the surface and a portion of the surface between the slits may be bent and/or stretched outwardly into a curved shape. Further, the top of the button may be formed into a flat surface that is configured to interface with a surface of the circuit board  14  or semiconductor device  12 . In block  106 , teardrop shape supports  42  may be formed in the surface of the cover. Openings  44  may be formed in the cover  16  to be aligned with the teardrop shape supports  42  as denoted by block  108 . In block  110 , a trench  30  may be formed in the surface of the cover  16  such that the columns  24 , the button  28 , and the supports  42  are located in the trench and generally protected by other extended surfaces of the cover  16 . In block  112 , the columns may be bent such that columns  24  extend away from the surface of the cover  16 . For example, the columns  24  may extend at approximately a 90° angle with respect to the surface of the cover  16  allowing the columns  24  to extend between the surface of the cover  16  and the heat sink  18  during later assembly steps. The semiconductor device  12  may be attached to a circuit board  14  as denoted in block  114 . In block  116 , a circuit board  14  may be attached to the cover  16  such that the columns  24  extend through the circuit board  14  upwardly around the semiconductor device  12 . The heat sink  18  may be attached to the semiconductor device  12  such that the columns  24  extend between the cover  16  and the heat sink  18  as denoted by block  118 . The heat sink  18  may be attached to the semiconductor device  12  utilizing fasteners  20  such as bolts that extend through openings  42  in the cover  16  and thread into the heat sink  18 . When the bolts  20  are tightened, the columns  24  provide a structural support acting to relieve the clamping force against the semiconductor device  12 . In this configuration, the button  28  and the teardrop shape supports  42  serve to support the circuit board  14  and semiconductor device  12  thereby reducing flex or stress imposed upon the assembly. The end of the method is denoted by block  120 . 
     In  FIG. 7 , another example of an electronic assembly  210  is provided. The electronic assembly  210  may include a semiconductor device  212 , a circuit board  214 , a heat sink  218 , and a cover  216 . The heat sink  218  may be provided to receive heat from the semiconductor device  212 . The electronic assembly  210  may also include a circuit board  214  such as a printed circuit board to which the semiconductor device  212  may be mounted. Traces on the circuit board  214  may provide electrical power as well as data signals and/or control signals to the semiconductor device  212 . A cover  216  extends about and protects a circuit board  214  and the semiconductor device  212 . The cover  216  may be formed from a sheet metal for example, through a series of forming or stamping events. The cover may be made from any rigid material, for example metal, plastic, or other similar material. The heat sink  218  may be clamped to the semiconductor device  212  using a fastener  220 . The fastener  220  is shown as a bolt. Although the fastener  220  may be threaded into the heat sink  218  as depicted in  FIG. 1 , alternatively, in any of the embodiments discussed, the fastener  220  may pass through a bore  222  in the heat sink  218  and be threaded into the cover  216 . Alternatively, the fastener  220  may extend through the cover  216  and be threaded into a nut on an opposite side of the cover  216  from the heat sink  218 . 
     The heat sink  218  may include columns  224  that extend around the semiconductor device  212  to absorb force from over clamping of the heat sink  218  by the fasteners  220 . In other alternative embodiments, the columns may be independent spacers extending between the cover and the heat sink. The columns  224  may extend through openings  226  in the circuit board  214  to contact the cover  216 . In particular, the columns  224  may contact buttons  270  formed in the cover  216  that also act to absorb over clamping of the heat sink  218 . Buttons  270  may include a first segment  252  of the cover  216  that extends angularly towards the heat sink  218  with respect to a planar region  250  of the cover that is generally parallel to the heat sink  218 . The button  270  forms a top surface  254  that is substantially parallel to the planar region  250  and aligned to interact with the column  224  of the heat sink  218 . Similar to the first segment  252 , button includes a second segment  256  that is angularly formed with respect to the planar region  250  and that extends between the top surface  254  and the planar region  250  thereby forming the button  270 . 
     The cover  216  may also include a button  228  aligned with the center of the semiconductor device  212 . The button  228  may be surrounded by a planar region  250  of the cover  216 . The button  228  may include a first segment  230  that extends angularly away from the integrated circuit  212  and that is connected to a planar portion  232  that is substantially parallel to the planar portion  250  of the cover  216 . The planar portion  232  may be connected to a second segment  336  that extends angularly toward the semiconductor device  212 , between the planar portion  232  and a planar surface  238 . The planar surface  238  may be substantially parallel to the planar region  250  of the cover  216 , as well as, the circuit board  214  and the semiconductor device  212 . Accordingly, the surface  238  is configured to interact with the circuit board  214  or the semiconductor device  212  through the circuit board  214 . In addition, it can be readily understood that the surface  238  may directly support the semiconductor device  212  as described in other embodiments provided below. The first segment  230  and the second segment  236  may cause a gap  234  to be formed between the cover  216  and the circuit board  214 . Similarly, a third segment  240  may extend angularly between the planar surface  238  and a planar segment  244  that is substantially parallel to the planar region  250 , similar to segment  232 . A fourth segment  246  extends between the planar segment  242  and the planar region  250  forming a gap  244  between the cover  216  and the circuit board  214 , similar to gap  234 . The segments of the button  228  act together as a deformable spring to absorb any over clamping force and prevent damage to the semiconductor device  212 . 
     In  FIG. 8 , another example of an electronic assembly  310  is provided. The electronic assembly  310  may include a semiconductor device  312 , a heat sink  318 , and a cover  316 . The heat sink  318  may be provided to receive heat from the semiconductor device  312 . A cover  316  may extend about and protect the semiconductor device  312 . The cover  316  may be formed from a metal sheet, for example, through a series of forming or stamping events. The cover  316  may be made from any rigid material, for example metal, plastic, or other similar material. The heat sink  318  may be clamped to the semiconductor device  312  using a fastener  320 . The fastener  320  is shown as a bolt that may be threaded into a bore  322  formed in the heat sink  318 . Accordingly, the fastener  320  extends through an opening in the cover  316  and engages the heat sink  318 . As mentioned, the fastener  320  may engage the heat sink  318  through a threaded engagement. Screws, rivets, clamps or any other fasteners may readily be used. In the bolt arrangement shown, providing increased torque on the fastener  320  generates additional clamping forces by compressing the semiconductor device  312  between the heat sink  318  and the cover  316 . 
     Loading columns  324  may extend from the cover  316  toward the heat sink  318  to absorb compression force if the semiconductor device  312  is cover compressed. The loading columns  324  and fastener arrangement may be provided at multiple locations around the semiconductor device  312 , for example on the opposite sides of the semiconductor device  312  to securely balance compression of the heat sink  318  against the semiconductor device  312 . In addition, a button  328  may be formed in the cover  316  to act as a spring between the cover  316  and the semiconductor device  312  to absorb forces that may otherwise over compress the semiconductor device  312 . Further, the button  328  may have a rounded or generally dome shape causing the bend of the sheet metal to act as a deformable spring. Further, the button  328  may include a flat top surface that contacts the semiconductor device  312 . As such, the cover  316  forms a planar surface and a button  328  extends from the planar surface and forms a second planar surface parallel to the first planar surface that reacts with the semiconductor device  312 . Further, the loading columns  324  also extend from the planar surface and may be formed substantially perpendicular to a planar surface. It is also understood that other deformable springs for example, leaf springs or coil springs may be used in place of the button  328  to absorb forces. However, the button  328  may be integrally formed in the cover  316 . The button  328  may act as a deformable spring to absorb any over clamping force and prevent damage to the semiconductor device  312 . 
     In  FIG. 9 , another example of an electronic assembly  410  is provided. The electronic assembly  410  may include a semiconductor device  412 , a first heat sink  418 , a second heat sink  414 , and a cover  416 . The first and second heat sink  418  and  414  may be provided to receive heat from the semiconductor device  412 . A cover  416  may extend about and protect the semiconductor device  412 . The cover  416  may be formed from a metal sheet, for example, through a series of forming or stamping events. The cover  416  may be made from any rigid material, for example metal, plastic, or other similar material. The first and second heat sink  418 ,  414  may be clamped to the semiconductor device  412  using a fastener  420 . The fastener  420  is shown as a bolt that may extend through the first heat sink  418  and be threaded into a bore  422  formed in the second heat sink  414 . Accordingly, the fastener  420  extends through an opening in the cover  416  and engages the second heat sink  414 . In the bolt arrangement shown, providing increased torque on the fastener  420  generates additional clamping forces by compressing the semiconductor device  412  between the first and second heat sink  418 ,  414 . 
     Loading columns  424  may extend from the cover  416  toward the heat sink  418  to absorb compression force if the semiconductor device  412  is cover compressed. The loading columns  424  and fastener arrangement may be provided at multiple locations around the semiconductor device  412 , for example on the opposite sides of the semiconductor device  412  to securely balance compression of the heat sink  418  against the semiconductor device  412 . In addition, a button  428  may be formed in the cover  416  to act as a spring between the cover  416  and the semiconductor device  412  to absorb forces that may otherwise over compress the semiconductor device  412 . Further, the button  428  may have a rounded or generally dome shape causing the bend of the sheet metal to act as a deformable spring. Further, the button  428  may include a flat top surface that reacts with the semiconductor device  412  through the printed circuit board  414 . As such, the cover  416  forms a planar surface and a button  428  extends from the planar surface and forms a second planar surface parallel to the first planar surface that reacts with the semiconductor device  412 . Further, the loading columns  424  also extend from the planar surface and may be formed substantially perpendicular to a planar surface. It is also understood that other deformable springs for example, leaf springs or coil springs may be used in place of the button  428  to absorb forces. However, the button  428  may be integrally formed in the cover  416 . The button  428  may act as a deformable spring to absorb any over clamping force and prevent damage to the semiconductor device  412 . 
     While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.

Technology Category: 5