Abstract:
A package and a package assembly for a power device having a high operation voltage and impulse voltage are provided. The package assembly for a power device comprises an assembly wherein the power device is encapsulated and electrically connected to a lead protruding outside the package, and an isolation spacer filling a clearance distance between the package and a heat sink attached to the package.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2006-0020413, filed on Mar. 3, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a package and a package assembly, and more particularly, to a package and a package assembly for a power device. 
     2. Description of the Related Art 
     A power semiconductor device such as a silicon-controlled rectifier (SCR), a power transistor, an insulated-gate bipolar transistor (IGBT), a MOS transistor, a power rectifier, a power regulator, an inverter, a converter, or a combination thereof, is designed to operate at a voltage of 30V-1000V or greater. Since a power device operates at a high voltage, unlike a logic or memory device, its package must have excellent heat dissipation and high voltage insulation properties. 
       FIG. 1  is a sectional view of a conventional package  50  for a power device with a heat sink  60 . 
     Referring to  FIG. 1 , a substrate  10  on which a power device  5  is formed is connected to a heat conductive electrical isolator  20  which, in turn, is connected to a metallic heat conductive plate  30  for heat release. The power device  5 , the substrate  10 , the isolator  20 , and the conductive plate  30  are encapsulated by epoxy mold compound (EMC) or ceramic molding members. The encapsulated power device  5  is electrically connected to a lead  40  protruding outside the package  50 . 
     In general, the metallic heat conductive plate  30  is exposed at the surface of the package  50 . The heat sink (or a cooling block)  60  is connected to the exposed metallic heat conductive plate  30  to absorb and dissipate heat from the heat conductive plate  30 . The heat sink  60  is generally formed of a metal having high heat conductivity. When the power device  5  operates at a high voltage, an electrical short may occur between the lead  40  of the package  50  and the heat sink  60 . To prevent this, isolation distances such as a creepage distance L 1  and a clearance distance L 2  are determined considering the intended voltages such as the operation voltage and the impulse voltage when the package  50  and the heat sink  60  are designed. As the operation voltage and the impulse voltage of the power device increase, the creepage distance L 1  and clearance distance L 2  must also increase. 
     To increase heat dissipation capacity, it may be necessary to increase the area of the heat sink  60 . For example, as illustrated in  FIG. 1 , the width of the heat sink  60  may increase from A 1  to A 2 . To reduce the manufacturing cost of the heat sink  60  or for various other design considerations, the area of the heat sink  60  may also be increased. For example, one heat sink  60  may be used in the package for two power devices, to reduce the cost. Also, the contact area between the heat sink  60  and the package  50  may need to be increased to enhance heat transfer. 
     However, the width of the heat sink  60  may need to be restricted to maintain the clearance distance L 2 , and the contact area between the heat sink  60  and the package  50  may need to be restricted to maintain the creepage distance L 1  in order to ensure isolation when the power device operates at a high voltage. 
     SUMMARY OF THE INVENTION 
     The present invention provides a package for a power device, which can be used with heat sinks of various sizes and contact areas according to the amount of heat to be dissipated, manufacturing cost or various other design conditions, without the prior art level of restraint on creepage distance. 
     The present invention also provides an assembly for a power device, which can be used with heat sinks of various sizes and contact areas according to the amount of heat to be dissipated, manufacturing cost or various other design conditions, without the prior art levels of restraint on clearance distance and creepage distance. 
     According to an aspect of the present invention, there is provided a package for a power device, in which the power device is encapsulated and electrically connected to a lead protruding outside the package, the package comprising: an irregular portion formed on the package between the lead and a heat sink attached to the package, wherein the maximum height of the irregular portion is less than the height of a portion contacting the heat sink. 
     The irregular portion is formed on an edge of the package where the lead is positioned. The irregular portion may have a linear shape parallel to the edge of the package where the lead is positioned. Further, the irregular portion may be formed integrally along the edge on the package where the lead is positioned, without interruption. 
     According to another aspect of the present invention, there is provided a package assembly for a power device, comprising: a package in which a power device is encapsulated and is electrically connected to a lead protruding outside the package; and an isolation spacer filling a clearance distance between the package and a heat sink attached to the package. 
     The isolation spacer may be formed of inorganic oxide, rubber or polymer (resin) materials. The isolation spacer may include an edge portion protruding horizontally past the edge of the heat sink. The isolation spacer may also include an edge portion covering part of the lead. 
     The package may include an irregular portion formed between the heat sink and the lead. In this case, the isolation spacer includes another irregular portion shaped to fit into the irregular portion of the package. 
     The isolation spacer may be formed in one piece so as to fill the clearance distance between the package and the heat sink. The isolation spacer may include a support portion fixed to a printed circuit board on which the package is mounted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a sectional view of a conventional package and attached heat sink for a power device, 
         FIGS. 2A and 2B  are sectional views of packages for a power device and attached heat sinks for power devices according to two embodiments of the present invention; 
         FIGS. 3A and 3B  are plan views of the packages of  FIGS. 2A and 2B ; 
         FIGS. 4A and 4B  are sectional views of package assemblies for power devices and attached heat sinks according to two additional embodiments of the present invention; 
         FIGS. 5A through 5D  are sectional views of package assemblies for a power device and attached heat sinks according to four more embodiments of the present invention; 
         FIG. 6  is a plan view of the package assembly of  FIG. 5A ; and 
         FIG. 7  is a sectional view of a package assembly for a power device and an attached heat sink according to still another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms, and should not be construed as being limited to the embodiments set forth herein. In drawings, the relative thickness and size of some components may be exaggerated for clarity. Like numbers refer to like elements throughout the specification. 
       FIGS. 2A and 2B  are sectional views of packages  100  and  110 , respectively, each with heat sinks  250  for power devices according to two embodiments of the present invention. 
     Referring to  FIGS. 2A and 2B , a substrate  102  on which a power device  101  is formed is attached to a metallic heat conductive plate  104  and encapsulated to transfer heat generated by the power device  101  outside the package  100 . For electrical isolation between the power device  101  and the metallic heat conductive plate  104 , an electrical isolator  103  may be positioned between the substrate  102  and the metallic heat conductive plate  104 . The metallic heat conductive plate  104 , which is exposed outside the packages  100  and  110 , contacts a heat sink  250  attached to the packages  100  and  110 . 
     The package  100  includes an irregular portion  200  thereon between the heat sink  250  and a lead  105 . The irregular portion  200  may have one raised part as shown in  FIG. 2A . Alternatively, an irregular portion  210  may have a shape in which raised parts and recessed parts are arranged alternately as shown in  FIG. 2B . 
     The maximum height h 1  of the irregular portions  200  and  210  is less than the height h 2  of a portion of the package  100  contacting the heat sink  250 , so that the irregular portions  200  and  210  do not contact the heat sink  250  when the heat sink  250  is installed. 
     If the irregular portion  200  and  210  were to contact the heat sink  250 , the creepage distance L 1  would be shortened. Thus, for the irregular portions  200  and  210  to increase the creepage distance L 1  it is preferable that its maximum height is less than the height of the portion of which the packages  100  and  110  contacts the heat sink  250 . 
     The packages  100  and  110  with the irregular portions  200  and  210  increase the creepage distance L 1  by increasing the surface path from the lead  105  to the heat sink  250 , which is an electric conductor. As a result, the present invention provides a package having a sufficient creepage distance L 1  when used for a power device with an operation voltage or impulse voltage in the range of 600V-2000V. 
       FIGS. 3A and 3B  are plan views of the packages for power devices shown in  FIGS. 2A and 2B .  FIG. 2A  is a sectional view taken along line A-A of  FIG. 3A , and  FIG. 2B  is a sectional view taken along line B-B of  FIG. 3B . 
     Referring to  FIGS. 3A and 3B , the irregular portions  200  and  210  are formed on an edge of the packages  100  and  110  where the lead  105  is positioned. The irregular portions  200  and  210  may have a linear shape parallel to the edge of the packages  100  and  110  where the leads  105  are positioned, and be formed integrally along the edge of the packages  100  and  110 , without interruption. Coupling holes  106  may be formed in the packages  100  and  110  to couple the heat sink  250  of  FIGS. 2A and 2B  to the packages  100  and  110 . 
       FIGS. 4A and 4B  are sectional views of package assemblies  120  and  130  and attached heat sinks  250  for power devices according to two additional embodiments of the present invention. 
     Referring to  FIGS. 4A and 4B , the package assemblies  130  and  140  include isolation spacers  300  and  310 , respectively, filling a clearance distance L 2  between the leads  105  and the heat sink  150  attached to the package  50 . The isolation spacers  300  and  310  may be made of ordinary isolating materials known in this field, e.g. inorganic oxide, rubber, silicone rubber, or polymer (resin) material. 
     The isolation spacers  300  may include edge portions  300   a  protruding horizontally past the edges of the heat sinks  250 . Alternatively, the isolation spacers  310  may include edge portions  310   a  covering part of the leads  105 , as shown in  FIG. 4B . 
     In the package assemblies  120  and  130  the clearance distance L 2  between the leads  105  and the heat sinks  250  is filled by the isolation spacers  300  and  310 , thereby increasing the area of the heat sink  250  for improving heat transfer, without restricting the clearance distance L 2 . 
     FIGS. SA through  5 D are sectional views of package assemblies  140  through  170 , respectively, for power devices with heat sinks  250  attached according to four more embodiments of the present invention. 
     In  FIGS. 5A and 5C  package assemblies  140  and  160  include packages  100  with the irregular portions  200  that include one or more raised parts formed between the heat sinks  250  and the leads  105  as shown in  FIG. 2A . In  FIGS. 5B and 5D  package assemblies  150  and  170  include packages  110  with the irregular portion  210  that include raised parts and one or more recessed parts formed alternately between the heat sinks  250  and the leads  105  as shown in  FIG. 2B . 
     The irregular portions  200  and  210  are formed on the edges of the packages  100  and  110  where the leads  105  are positioned, as shown in  FIGS. 3A and 3B . The irregular portions  200  and  210  may have a linear shape parallel to the edge of the packages  100  and  110  where the leads  105  are positioned, and may be formed integrally along the edges of the packages  100  and  110  without interruption. 
     In  FIGS. 5A and 5B  package assemblies  140 ,  150  include isolation spacers  320 ,  330  which have an irregular portion  320   a  shaped to fit into the irregular parts  200  and  210 , respectively, of the packages  100  and  110 , respectively. Also, the isolation spacer  320 ,  330  may include an edge portion  320   b,    330   b  protruding horizontally past the edge of the heat sinks  250   
     IN  FIGS. 5C and 5D  package assemblies  160 ,  170  include isolation spacers  340 ,  350  which have irregular portions  340   a,    350   a  shaped to fit into the irregular portions  200  and  210 , respectively, of the packages  100  and  110 , respectively. Also, the isolation spacer  340 ,  350  may include an edge portion  340   b,    350   b  covering part of the leads  105 . 
       FIG. 6  is a plan view of the package assembly  140  for a power device of  FIG. 5A .  FIG. 6  can also illustrate the package assemblies  120 ,  130 ,  150 - 170  shown in  FIGS. 4A ,  4 B,  5 B,  5 C and SD, except the difference in the shape of the irregular portion  320   a  of the isolation spacer  320  fitted into the irregular portion  200  of the package  100 . 
     Referring to  FIGS. 6 , the isolation spacers  300 - 350  are fabricated in one piece so as to fill the clearance distance between the heat sinks  250  and the packages  100  and  110 . On the edges of the packages  100  and  110  where the leads  105  is formed, the isolation spacers  300 - 350  are inserted to fill the clearance distance between the heat sinks  250  and the edges of the packages  100  and  110 . On the edges of the packages  100  and  110  where no leads are formed, the isolation spacers  300 - 350  surround the outside of the packages  100  and  110 . As a result, the isolation spacers  300 - 350  may be firmly supported between the heat sinks  250  and the packages  100  and  110  without any adhesive or joining member. 
       FIG. 7  is a sectional view of an isolation spacer  360  of a package assembly  180  for a power device with a heat sink  250  attached according to another embodiment of the present invention. 
     Referring to  FIG. 7 , the isolation spacer  360  may further include support portions  360   a  and  360   b  which are fixed to a printed circuit board  160  on which the package  100  is mounted. The support portions  360   a  and  360   b  mechanically support the isolation spacer  360  by passing through and/or holding the printed circuit board  160 , respectively. 
     As described above, the package for a power device includes the irregular portion on the package between the heat sink attached to the package and the lead, thereby increasing the surface path from the lead to the heat sink for increasing the creepage distance L 1 . Thus, heat sinks of various sizes and contact areas can be used for the package for a power device, without the prior art level of restraint on creepage distance. 
     Further, the package assembly for a power device includes the isolation spacer which fills the clearance distance between the package and the heat sink to stabilize the clearance distance between the lead and the heat sink, so that heat sinks of various sizes and contact areas can be used for the package assembly for a power device without the restraint of the clearance distance. In addition, the package of the package assembly for a power device includes the irregular portion thereon between the heat sink and the lead, and thus the package assembly can be used with heat sinks of various sizes and contact areas, without the prior art levels of restraint on clearance distance and creepage distance. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.