Patent Publication Number: US-7902464-B2

Title: Heat sink arrangement for electrical apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a divisional application of U.S. patent application Ser. No. 11/439,412 filed May 22, 2006, now U.S. Pat. No. 7,579,554, the entirety of which is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to dissipation of heat from an electrical apparatus, e.g. a power supply apparatus, employing semiconductor devices. 
     BACKGROUND OF THE INVENTION 
     Some electrical apparatus, e.g. a power supply apparatus, uses power semiconductor devices as its components. Power semiconductor devices are connected to a driver printed circuit board on which a driver circuit for driving the power semiconductor devices is formed. The driver printed circuit board is connected to a control printed circuit board on which a control circuit for controlling the driver circuit is formed. The power semiconductor devices are mechanically coupled to a heat sink for dissipating heat from the semiconductor devices. In order to downsize the power supply apparatus, the control printed circuit board may be mounted to the heat sink on which the power semiconductor devices are mounted, with the driver printed circuit board mounted between the power semiconductor devices and the control printed circuit board, to thereby assemble them into a single block. If, however, rigid boards are used for the control and driver printed circuit boards, dimensional errors and/or assemblage errors of such printed circuit boards may place strain on the power semiconductor devices, causing the semiconductor devices to float up from the heat sink, which impedes normal heat dissipation and may break down the power semiconductor devices. In addition, the printed circuit boards themselves may be also strained. When such power supply apparatus is transported or removed to another place, vibrations caused by the moving may be applied to the power supply apparatus. Then, the vibrations are superposed on the strain on the power semiconductor devices and the printed circuit boards, which may lead to breakdown of the printed circuit boards and the power semiconductor devices. 
     JP 7-7167 U discloses use of a flexible board for connecting components mounted on a case to components mounted on a printed circuit board attached to the case. 
     Similar flexible boards would be used to connect the above-described power semiconductor devices to the driver printed circuit board and to connect the driver printed circuit board to the control printed circuit board. This arrangement, however, would require two flexible boards in addition to the driver and control printed circuit boards. In addition, a space for disposing the flexible boards must be secured, which impedes downsizing of the power supply apparatus. 
     An object of the present invention is to provide an electrical apparatus, in which electrical components are prevented from being broken down and, still, which can be small in size. 
     SUMMARY OF THE INVENTION 
     An electrical apparatus according to an embodiment of the present invention includes a first printed circuit board formed of an insulating substrate which is coated with an electrically conductive film. The first printed circuit board may be a multi-layered board or a single-layered board. An electrical component disposed external to the first printed circuit board has a rigid connector connected to the conductive film of the first printed circuit board. This connection of the connector to the conductive film may put strain to the connector, the electrical component and/or the first printed circuit board. The insulating substrate includes a flexible portion in the vicinity of the portion of the conductive film to which the electrical component is connected. 
     The flexible portion may be formed by thinning a portion, which is to become the flexible portion, of the insulating substrate relative to the remaining portion. 
     The electrical component may be a semiconductor device mounted on a heat sink. In such case, the connector is a lead of the semiconductor device. The semiconductor device may be a power semiconductor device. 
     The first printed circuit board may be disposed near the heat sink. In addition, a second printed circuit board may be mounted to the surface of the heat sink opposite to the surface on which the semiconductor device is mounted. The second printed circuit board is electrically and mechanically coupled to the first printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an electrical apparatus according to an embodiment of the present invention. 
         FIG. 2  is a front view of a heat dissipating portion of the electrical apparatus shown in  FIG. 1 . 
         FIG. 3  is a side view of the heat dissipating portion shown in  FIG. 2 . 
         FIG. 4  is a cross-sectional view along a line  4 - 4  in  FIG. 2 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION 
     An electrical apparatus according to an embodiment of the present invention is, for example, a power supply apparatus for use in welding or electroplating. The power supply apparatus includes, as shown in  FIG. 1 , an AC-to-DC converting circuit  4  for converting a three-phase commercial AC voltage, for example, applied to power supply input terminals  2   a ,  2   b  and  2   c , to a DC voltage. The AC-to-DC converting circuit  4  includes, for example, a rectifying circuit and a smoothing circuit. The DC voltage from the AC-to-DC converting circuit  4  is applied to a DC-to-AC converting circuit, e.g. an inverter  6 , which includes plural, e.g. six, power semiconductor devices, e.g. IGBTs  8 . The IGBTs  8  are connected in a full-bridge circuit configuration. The DC voltage applied to the inverter  6  is converted therein to a high-frequency voltage, which is developed between two inverter output terminals  10   a  and  10   b . The high-frequency voltage is voltage-transformed by a transformer (not shown), and the voltage-transformed high-frequency voltage is converted to a DC voltage by a high-frequency-to-DC converting circuit (not shown). The resulting DC voltage is applied across a load, for example, between a torch and workpiece in a welding machine, or between two electrodes for electroplating. 
     Control signals for controlling the respective IGBTs  8  to convert the DC voltage applied thereto to the high-frequency voltage are supplied to the respective IGBTs  8  from a driver circuit  12 . A control circuit  14  gives instructions to the driver circuit  12  regarding the manner in which the IGBTs  8  should be controlled. 
     As shown in  FIGS. 2 and 3 , each of the IGBTs  8  is arranged in a chip form and mounted on a heat sink  16 . Each IGBT  8  is the electrical component as referred to in the accompanying Claims. 
     The heat sink  16  has an IGBT mounting surface  16   a  of a rectangular shape, for example, as shown in  FIG. 3 , and also a number of fins  16   b  on the opposite surface. The fins  16   b  extend substantially perpendicularly to the mounting surface  16   a . Three IGBTs  8  are disposed in a row on the mounting surface  16   a , and their heat dissipating surfaces are in surface-contact with the mounting surface  16   a . The three IGBTs  8  are pressed against the mounting surface  16   a  by means of a retainer  18   a.    
     The retainer  18   a  has three planar portions  181   a  contacting a larger portion of the surfaces of the three IGBTs  8  opposite to the heat dissipating surfaces thereof. The three planar portions  181   a  are connected together by a connecting portion  181   b , which is bent, at a portion near a first side surface of the IGBTs  8 , toward the mounting surface  16   a  of the heat sink  16 . A lip portion  181   c  integral with the connecting portion  181   b  is in contact with the mounting surface  16   a . The lip portions  181   c  is fixed to the mounting surface  16   a  by means of two screws  20   a . The respective IGBTs  8  are screwed to the mounting surface  16   a  by three screws  22   a  extending, through the respective planar portions  181   a  of the retainer  18  and the IGBTs  8 , into the mounting surface  16   a . The remaining three IGBTs  8  are similarly mounted on the mounting surface  16   a  of the heat sink  16  by means of a retainer  18   b  and screws  20   b  and  22   b , which are similar to the retainer  18   a  and the screws  20   a  and  22   a.    
     Each IGBT  8  has three leads  24   a ,  24   b  and  24   c . The three leads  24   a - 24   c  of each IGBT  8  extend from a second side surface thereof, which is opposite to the first side surface, in the direction away from the retainers  18   a  and  18   b , and are bent in a direction away from the heat sink  16 . The leads  24   a - 24   c  are made of a material having high rigidity, e.g. metal. The leads  24   a - 24   c  are the connector referred to in the accompanying Claims. The leads  24   a - 24   c  are electrically and mechanically connected by, for example, soldering, to patterned conductors formed at predetermined locations on a printed circuit board  120 , on which the driver circuit  12  is arranged. This eliminates the need for use of wires for electrical connections between the respective IGBTs  8  and the printed circuit board  120 . The printed circuit board  120  is disposed, being spaced from and substantially in parallel with the mounting surface  16   a  of the heat sink  16 . The printed circuit board  120  slightly overlaps the mounting surface  16   a , and the remaining portion lies outside the mounting surface  16   a . The printed circuit board  120  is the first printed circuit board referred to in the accompanying Claims. 
     The printed circuit board  120  has its portion remote from the mounting surface  16   a  secured to a printed circuit board  140 , on which the control circuit  14  is arranged, by means of three screws  32 . The driver circuit on the printed circuit board  120  is electrically connected to the control circuit  14  on the printed circuit board  140 . The printed circuit board  140  is disposed, being spaced from and in parallel with the outermost fin  16   b , and is secured to the outermost fin  16   b  by means of a plurality of spacers  26  and screws  28 . Thus, the major surfaces of the printed circuit board  140  lie perpendicular to the IGBTs  8 . In this manner, the heat sink  16  with the IGBTs  8  mounted thereon and the printed circuit boards  120  and  140  form one block. The printed circuit board  140  is the second printed circuit board referred to in the accompanying Claims. 
     Generally, the printed circuit boards  120  and  140  are formed of a rigid or hard insulating materials, e.g. a glass epoxy material, with a electrically conductive film, e.g. copper foil. Electric components are soldered to the conductive films at predetermined locations. If, therefore, the dimensional precision of the printed circuit boards  120  and  140  is low, and/or the precision of assemblage of the IGBTs  8  and printed circuits boards  120  and  140  is low, strain may be put on the IGBTs  8 , which causes the IGBTs  8  to rise up from the mounting surface  16   a , resulting in insufficient heat dissipation from the IGBTs  8 . In some cases, strain is put on the leads  24   a - 24   c  of the IGBTs  8 , causing the rigid leads  24   a - 24   c  to snap or bend. 
     In order to solve this problem, according to this embodiment, a flexible portion  30  is formed in the printed circuit board  120 . As shown in  FIG. 4 , the printed circuit board  120  is a multi-layered printed circuit board formed of an epoxy glass material  120   a  within which a conductive pattern formed of plural, e.g. three, conductive films  120   b , is arranged. The flexible portion  30  is formed by removing part of the epoxy glass material  120   a  from the opposite major surfaces of the epoxy glass material  120   a , at a location slightly spaced in the direction away from the leads  24   a - 24   c . The flexible portion  30  extends in the direction along which the leads  24   a - 24   c  are arranged. 
     The flexible portion  30  can absorb strain which may be generated, as described above, when the dimensional precision of the printed circuit boards  120  and  140  and/or the precision of assembling the IGBTs  8  and the printed circuit boards  120  and  140  are low. Then, it never happens that the contact of the IGBTs  8  with the heat sink  16  becomes defective, or that the leads  24   a - 24   c  snap or bend. Since the flexible portion  30  is formed by removing part of the insulating material of the printed circuit board  120 , there is no need for preparing a separate, flexible printed circuit board for connection of the IGBTs  8  and the printed circuit board  120 , in order for strain to be absorbed. 
     The present invention has been described as being embodied in a power supply apparatus for welders or electroplating machines. However, the present invention is not limited to them, but it can be embodied in any electrical apparatuses in which electrical components need be connected to printed circuit boards. Further, the flexible portion has been described as being formed in a multi-layered printed circuit board, but, when the printed circuit board used includes a conductive film only on one surface, the flexible portion can be formed by removing part of the insulating material from the other surface of the printed circuit board. In the described embodiment, the leads of the semiconductor devices are soldered to the printed circuit board  120 , but they may be electrically and mechanically connected by screwing, caulking or the like. Furthermore, other semiconductor devices, such as bipolar transistors and FETs, than IGBTs may be used.