Abstract:
An electronic device/heat sink assembly having at least first and second heat generating electronic devices, a heat sink member, a resilient integral spring clip, the clip including a base member and first and second oppositely facing resilient leg members extending from opposite ends of the base member, the heat sink member having oppositely facing first and second surfaces, a separate one of the electronic devices positioned on each of the first and second sink surfaces, the clip dimensioned and positioned such that the leg members sandwich the devices and heat sink therebetween.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/036,888 that was filed on Mar. 6, 1998 having the same tile and which is now abandoned. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to semiconductor heat dissipation and more particularly to a spring clip for securing heat sinks to electronic devices (e.g. TO-218, TO-247, TO-264, TO-3P, TO-3PL, etc.) and a unique inverter/converter power device configuration. 
     Semiconductor switching devices generate heat which must be dissipated to maintain device integrity. One way to dissipate device heat is to provide heat sinks. A sink typically includes a thermally conductive material attached to a device. To increase dissipation efficiency, most sinks include a plurality of dissipation fins or apertures which increase the amount of sink surface area exposed to the ambient (i.e. increase radiation area). In addition, most devices include a primary heat dissipating surface (i.e. a baseplate) which is securable to the sink to facilitate efficient heat flow. 
     Some mechanisms for securing a semiconductor switching device to a sink include a simple screw (see U.S. Pat. No. 5,592,021, FIG. 1, Prior Art), a clamp and screw (see U.S. Pat. No. 4,259,685), or a clamp integrally attached to a sink (see U.S. Pat. No. 5,068,764). Unfortunately, while these mechanisms, when properly employed, can prevent device overheating, they have a number of shortcomings. 
     For example, some of these mechanisms provide uneven pressure on the semiconductor devices causing the primary heat dissipating surface to buckle whereby a portion of the dissipating surface is raised away from the sink. This separation results in a significant reduction in reliability and increases heat transfer resistance, thereby reducing dissipation effectiveness. 
     In addition, these mechanisms can cause what is referred to as “voltage creep”. Because sinks have to be thermally conductive, most sinks are metallic. When a device is connected directly to a metallic sink, in addition to making thermal contact, the sink and device make electrical contact. When any connected metallic components are at different potentials, the potential “creeps” along the metallic surfaces and can cause unintended and undesirable voltage stresses or electrical shorting in the sink and switching devices, hence the phrase “voltage creep”. 
     Moreover, device/sink configurations often require a large amount of space. This is particularly true in applications which require a large number of switching devices. One such application is a converter/inverter for changing AC to DC voltage and DC to AC voltage. As well known in the art, at a minimum, six separate switching devices are required to efficiently convert DC to AC voltage and another six devices are required to rectify AC voltage and provide DC voltage (assuming a standard three phase system). Space is often saved by providing the rectifying devices in a single integrated in-line package (SIP). Nevertheless, the SIP, like the DC to AC devices, generates an appreciable amount of heat which must be dissipated. Because dissipation effectiveness typically increases with exposed sink surface area, large and/or separate sinks are often provided for each power device and another for the SIP, resulting in a configuration which requires a substantial amount of space. 
     One other problem with conventional securing mechanisms, is that a relatively large number of components are required to secure devices to sinks. As evidenced by the art cited above, typical securing mechanisms may include a plurality of mechanical components (e.g. clamps, screws, etc.) for connecting each device to an associated sink. Extra components increase hardware costs and assembly time. 
     The industry has recognized and attempted to address at least some of the problems identified above. For example, to eliminate or reduce voltage creep, a thermally conductive, electrically insulative and mechanically separating layer of material is often positioned between the primary heat dissipating surface of a semiconductor device and a heat sink. In this manner, heat is dissipated but voltage is blocked. 
     One solution which addresses many of the problems described above is disclosed in U.S. Pat. No. 5,450,284 which issued on Sep. 12, 1995. The assembly described therein uses a single clamping device bolted to a single heat sink to secure a plurality (i.e.  4 ) of semiconductor devices to the sink. The devices are separated from the sink by two separate thermally conductive and electrically insulating insulators which eliminate voltage creep. 
     While this solution reduces the overall mechanical parts count, eliminates voltage creep, provides even pressure on each device thereby eliminating device buckling and reduces overall device/sink space, this solution still has several shortcomings. First, this solution still requires several securing components and most of the components are relatively complex. For example, the clamp requires a separate retaining finger for each device secured to the sink and all components require a number of precisely located apertures. Second, this solution is difficult to assemble (e.g. has many different apertures and elements which must be precisely aligned). Third, this solution requires an elongated, relatively large space to accommodate a plurality of separate switching devices. For example, in order to configure an inverter/converter with this solution, all six required switching devices and the SIP would have to be placed next to each other in a single row on a single sink. While such a configuration might be possible, the sink length required to accommodate so many devices in a single row would render the assembly to large for many applications. In the alternative, two or more separate assemblies including a separate sink for each assembly could be configured according to this solution and the separate assemblies could be positioned in parallel to provide inverter/converter power devices. This, however, would increase the parts count and also the space required to house the power components. 
     Therefore, it would be advantageous to have an apparatus for inexpensively and easily securing a heat sink to a semiconductor switching device and, in addition, it would be particularly advantageous to have such an apparatus for securing together inverter/converter power components so as to efficiently dissipate heat, eliminate voltage creep and require minimal space. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention includes a resilient spring clip for coupling a semiconductor switching device to a heat sink. The clip is formed of stainless steel and includes a base member and two essentially oppositely facing leg members extending from opposite ends of the base member. The leg members can be forced apart such that the device and sink can be placed therebetween in a predetermined configuration. When the legs resume their original position, the legs press against the sink and device sandwiched therebetween with sufficient force to maintain the sink and device in the predetermined configuration. Thus, a single piece clip can be used to secure a device and a sink together. Preferably the clip is formed of stainless steel. 
     The invention also includes a “power structure” assembly consisting of an inventive clip, heat sinks and the power devices required to configure an inverter/converter for rectifying AC voltage and converting DC to AC voltage. To this end, the brick includes a clip securing together six semiconductor switching devices, a SIP configured to rectify AC voltage, at least one heat sink and at least one thermally conductive and electrically insulating insulator. Preferably the sink includes first and second sinks, the insulator includes first, second and third insulators and the brick further includes a spacer. 
     In this case, the first insulator can be sandwiched between a first device pair and a first sink first surface, the second insulator can be sandwiched between a second device pair and a first sink second surface opposite the first sink first surface, the SIP can be placed against a second sink second surface, the third insulator can be sandwiched between a third device pair and a second sink first surface opposite the second sink second surface and the spacer can be sandwiched between the second and third device pairs. The first leg member contacts the second surfaces of the first device pair while the second leg member contacts a SIP second surface opposite the SIP first surface, with sufficient force to maintain all of the components therebetween in the predetermined configuration. 
     Thus, a primary object of the invention is to provide a simple, inexpensive and easy to assemble mechanism for attaching a semiconductor device to a heat sink. To these ends, the inventive clip includes only three resilient and integrally connected members which can be forced from a rest configuration into a configuration wherein a device and heat sink can be sandwiched therebetween. No screws or bolts are required. No apertures need be formed in the device or sink. 
     Another object of the invention is to provide a single clip of the above kind which can be used to secure more than one semiconductor device to one or more heat sinks. To this end the inventive clip can be used to sandwich several devices and one or more sinks between the leg members. 
     Yet another object of the invention is to provide all of the power components required to configure an inverter/converter in a single compact module referred to herein as a “power structure”. To this end, all of the power components and required heat sinks and insulators can be positioned such that the boundaries between adjacent components are perpendicular to pressure provided via the leg members. In this manner, all of the components can be sandwiched between the leg members and held in desired positions. 
     In one aspect the base member includes anterior and posterior edges, the first leg member includes at least first anterior and first posterior leg members extending from the first end adjacent the anterior and posterior edges, respectively, and the second leg member includes at least second anterior and second posterior leg members extending from the second end adjacent the anterior and posterior edges, respectively. 
     One other object of the invention is to provide pressure on all of the semiconductor devices in the power structure despite the fact that some of the devices might be positioned next to each other. To this end, the anterior and posterior legs cooperate to independently provide pressure across the power structure. When a section of the power structure components aligned with the anterior legs defines a distance smaller than a section aligned with the posterior legs, the anterior legs contract more than the posterior legs and both sets of legs are functional to maintain brick components therebetween. 
     In another aspect the leg members extend from a first side of the base member and the base member is pre-bowed such that, prior to positioning the semiconductor and sink components between the leg members, the base member is concave toward the first side. In addition, prior to positioning components between the leg members, the base member is concave to a first degree and, after the components are positioned between the leg members, the base member is concave to a second relatively reduced degree such that the base member is essentially flat. 
     One other object of the invention is to provide a clip of the above kind wherein, after components are secured together via the clip, the clip itself requires minimal space. To this end, the inventive clip is pre-bowed so that, when stretched to accommodate components therebetween, the base member becomes essentially flat requiring very little additional space. 
     These and other objects, advantages and aspects of the invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made therefor, to the claims herein for interpreting the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a perspective view of an inventive spring clip securing together the power components of an inverter/converter; 
     FIG. 2 is a is an exploded view of the of FIG. 1; 
     FIG. 3 is a side elevational view of the clip of FIG. 1; 
     FIG. 4 is a side elevational view of the assembly of FIG. 1; 
     FIG. 5 is and end elevational view of the clip of FIG. 1; and 
     FIG. 6 is a top elevational view of the clip of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A. Hardware 
     Referring now to the drawings, wherein like reference characters represent corresponding elements throughout the several views, and more specifically referring to FIG. 1, an inventive spring clip  10  is shown which holds various semiconductor switching devices and a single inline integrated circuit package (SIP) in thermal contact with heat radiating sinks. In the description which follows, the switching devices and the SIP constitute the power section of an inverter/converter and, in order to simplify this explanation, the entire assembly illustrated in FIG. 1 will be referred to as a “power structure”  12 . 
     Referring also to FIG. 2, power structure  12  includes first, second, third, fourth, fifth and sixth semiconductor switching devices  14 ,  15 ,  16 ,  17 ,  18  and  19 , respectively, first, second and third thermally conductive and electrically insulative insulators,  21 ,  22  and  23 , respectively, first and second heat sinks  25  and  26 , respectively, a single spacer member  28 , SIP  30  and clip  10 . 
     Referring to FIGS. 2 and 4, switching devices  14 ,  15 ,  16 ,  17 ,  18  and  19  are preferably high power transistors (e.g. IGBT&#39;s). These types of transistors are well known in the art and therefore will not be explained here in detail. In addition, to the extent that devices  14  through  19  will be explained, all of the devices are identical and therefore, only device  14  will be described. Device  14  includes a body section  34  including a clip housed in a resin housing and three electrical leads (i.e. a gate, a collector and an emitter) collectively referred to by numeral  32  which extend downwardly from section  34 . Section  34  is a flat member and includes first and second essentially parallel and oppositely facing surfaces  36 ,  38 , respectively, and has a width dimension W 3  in a direction parallel to leads  32  and a length dimension L 3  perpendicular to dimension W 3 . Surface  36  is metallic and forms a primary heat dissipating surface. 
     Electrical leads extending from devices  15 ,  16 ,  17 ,  18  and  19  are also collectively referred by numeral  32  while the first or primary heat dissipating surfaces are collectively referred to by numeral  36 . As will become apparent below, first surfaces  36  of devices  14 ,  15 ,  18  and  19  face in a first direction indicated by a first arrow  40  while first surfaces  36  of devices  16  and  17  face the opposite direction indicated by arrow  42 . In addition, for the purposes of this explanation, devices  14  and  15  will be referred to as a first devices pair  41 , devices  16  and  17  will be referred to as a second device pair  43  and devices  18  and  19  will be referred to as a third device pair  45 . In addition, devices  14 ,  16  and  18  will be referred to as anterior devices while devices  15 ,  17  and  19  are referred to as posterior devices. 
     Insulators  21 ,  22  and  23  are essentially identical and therefore, only insulator  21  will be explained here in detail. Insulator  21  has width W 1  and length L 1  dimensions which are equal to or slightly larger than similar dimensions W 2  and L 2  of an adjacent heat sink  25  surface  44 . Insulator  21  is formed of a material that is electrically insulating, heat-conducting and mechanically isolating and can be a silicon-based or epoxy-based composition. Preferred materials for insulator  21  include the material commercially available and sold under the registered trademark KAPTON (from by E. I. DuPont de Nemours, Wilmington, Del.) and the material commercially available under the trademark SILPAD (from Bergquist Company). 
     First and second heat sinks  25  and  26  are essentially identical and therefore, only sink  25  will be explained here in detail. Sink  25  includes a block of extruded thermally conductive material (e.g. aluminum, copper) having first and second essentially parallel and oppositely facing surfaces  44  and  46 , respectively. The dimensions of each surface  44  and  46  are identical being width W 2  and length L 2 . A third sink dimension is depth D 2  between surfaces  44  and  46 . Sink  25  forms a plurality of elongated slots collectively referred to by numeral  48  which extend along entire length L 2 . Slots  48  increase the sink surface area which is exposed to the ambient air or forced air and thereby increase heat dissipation. Width W 2  should be approximately one and one-half times the width dimension W 3  of first surface  36 . Length L 2  should be approximately three times the length dimension L 3  of first surface  36 . These dimensions allow sufficient spacing between switch pairs  14  and  15  and sufficient heat dissipation when power structure  12  is assembled (see FIG.  1 ). 
     Spacer  28  has essentially the same width and length dimensions (not illustrated) as insulator  21  (i.e. the width and length dimensions are W 1  and L 1 , respectively) but is slightly thicker than insulator  21 . Spacer  28  is preferably formed of a polycarbonate material. 
     SIP  30  includes a body section  48 , three input leads collectively referred to by numeral  49  and two output leads collectively referred to by numeral  54 , leads  49  and  54  extending from body  48  in a single line. As well known in the controls art, body  48  includes a six diode bridge for rectifying three-phase AC input voltage provided to leads  49 , providing DC output voltage on output leads  54  (i.e. leads  54  constitute positive and negative DC buses). Body  48  is essentially a flat member including first and second essentially parallel and oppositely facing surfaces  50  and  52 . First surface  50  is a primary heat dissipating surface. 
     Referring now to FIGS. 2 through 6, clip  10  generally includes a base member  58  and first and second leg members  60  and  62 . Base member  58  includes first and second essentially flat lateral members  64 ,  66 , respectively which are connected by an elbow section  68 . Member  58  has first and second ends  70 ,  72 , respectively, and anterior and posterior edges  71 ,  73 , respectively. Prior to assembling brick  12 , section  68  forms an arc a such that member  58  is concave in the direction that leg members  60  and  62  extend (see FIG.  3 ). 
     Members  60  and  62  are resilient, extend from first and second ends  70 ,  72 , are oppositely facing and each terminates at a distal end  78 ,  80 , respectively. Adjacent distal ends  78  and  80 , each member  60 ,  62  includes a bowed section  82 ,  83 , respectively which curves inwardly toward the other leg member forming facing contact surfaces  74 ,  76 , respectively. 
     Referring to FIGS. 2,  5  and  6 , each leg member  60 ,  62  is bifurcated such that each member forms separate anterior and posterior legs. The anterior legs are identified by numerals  60   a  and  62   a  and are adjacent anterior edge  71  while the posterior legs are identified by numerals  60   b  and  62   b  and are adjacent posterior edge  73 . Leg slits  85  and  86  define adjacent edges of anterior and posterior legs. 
     Clip  10  is preferably formed of resilient non-corrosive material such as stainless steel. 
     B. Assembly of Hardware 
     To assembly power structure  12 , referring to FIG. 2, first insulator  21  is placed on first sink first surface  44  and first device pair  41  is placed with first surfaces  36  against insulator  21  (i.e. insulator  21  is between surfaces  44  and  36 ) with leads  32  aligned in a single plane and extending downwardly below a lower edge of sink  25  (see FIG.  4 ). Next, second device pair  43  and second insulator  22  are similarly arranged on first sink second surface  46 . To this end, second insulator  22  is positioned between the first surfaces  36  of devices  16  and  17  and surface  46  with devices  16  and  17  arranged next to each other and spaced apart and leads  32  aligned in a single plane and extending downwardly below a lower edge of sink  25 . 
     Referring still to FIG. 2, SIP  30  is placed in direct contact with a second side  46  of second sink  26  with leads  49  and  54  aligned and extending downwardly therefrom below sink  26 . Third insulator  23  is arranged between switching devices  18  and  19  and second sink  26  first surface  44 , with devices  18  and  19  next to each other and spaced apart and leads  32  therefrom arranged in a single plane (see FIG.  4 ). Spacer  28  is arranged between device pairs  43  and  45 . At this point, the power structure  12  components appear as illustrated in FIG. 4 except that clip  10  is not secured therearound. 
     Referring still to FIG. 4, importantly, when brick components are configured, insulators  21 ,  22  and  23  should each extend down below the body sections  34  of adjacent devices  14  thorough  19  to minimize voltage creep. In addition, insulators  21 ,  22  and  23  should extend laterally of adjacent devices for the same purpose (see FIG.  1 ). Moreover, all devices and SIP electrical leads  54 ,  32  (and  49 , not illustrated in FIG. 4) should extend below sinks  25 ,  26 , spacer  28  and insulators  21 ,  22  and  23  so that connection to a circuit board is unimpeded. 
     To secure brick components together, a machine is used to grasp and force distal ends  78 ,  80  apart in the directions indicated by arrows  90  and  91 . When sufficiently apart, elbow section  68  deforms substantially and, as can be seen in FIG. 4, becomes essentially flat (i.e. lateral sections  64  and  66  become essentially co-planar). 
     With ends  78  and  80  forced outwardly, brick components are placed between contact surfaces  74  and  76  and ends  78  and  80  are allowed to move back toward their original positions. Contact surface  74  contacts second surfaces  38  of first device pair  41  while contact surface  76  contacts SIP second surface  52 . The force generated by clip  10  is sufficient to grasp and hold together all components of the power structure  12  in the configuration illustrated. When power structure  12  is completely assembled, as best seen by comparing FIGS. 3 and 4, pre-bowed arc α is essentially 180° thereby insuring a reduced overall height of power structure  12 . In other words, prior to forcing ends  78  and  80  apart, arc α is of a first degree and after clip  10  is forced around brick components, while there may be some bow left at elbow section  68 , the bow will be extremely small and certainly of a degree less than the unstressed arc α. 
     It should be understood that the methods and apparatuses described above are only exemplary and do not limit the scope of the invention, and that various modifications could be made by those skilled in the art that would fall under the scope of the invention. For example, while the preferred clip is formed of stainless steel, clearly, other materials (e.g. resilient plastic or other metallic materials) could be used to form the clip. In addition, while the clip is illustrated as having both anterior and posterior legs, clearly, the clip could be provided with a single leg extending from each of the first and second ends of the base member. Moreover, more than two legs could be provided extending from each of the first and second ends of the base member. Furthermore, while the clip is illustrated in the context of securing all of the power components required to configure an inverter/converter, clearly the clip could be used to secure fewer or greater numbers of semiconductor devices to heat sinks. For example, a reduced sized clip could be used to secure a single semiconductor switching device to a suitable heat sink. 
     In addition, the order of power structure components or the components themselves could be altered. For example SIP  30  and switching devices  18  and  19  could be switched or all of devices  14  through  19  and SIP could be sandwiched to a single, albeit larger, sink. Moreover, sinks  25  and  26  can be formed in any manner well known in the art. 
     To apprise the public of the scope of this invention, we make the following claims: