Patent Publication Number: US-2005121701-A1

Title: Semiconductor device

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application is based on and incorporates herein by reference Japanese Patent Application No. 2003-405911 filed on Dec. 4, 2003.  
     FIELD OF THE INVENTION  
      The present invention relates to a semiconductor device that has a semiconductor element with a main electrode on each of its main side and its main reverse side. The semiconductor element has a first metal body on the main reverse side and second and third metal bodies on the main side, and also has a heat sensing diode for detecting temperature on the main side. The semiconductor device has a resin cover molded on it.  
     BACKGROUND OF THE INVENTION  
      In  FIG. 4A  and  FIG. 4B , a typical semiconductor device of this kind is shown schematically. The semiconductor device shown in  FIG. 4A  is proposed, for example, in US 2003/0022464 (JP-A-2003-110064).  
      In  FIG. 4A , the semiconductor element  10  is, for example, a vertical power element such as an IGBT (Insulated Gate Bipolar Transistor), and its upside is a ‘main side’ that has an element disposed on it, and its downside is a ‘main reverse side.’ 
      On the main side of the semiconductor element  10 , a heat sensing diode  11  is disposed. The heat sensing diode  11  is a typical diode element that is manufactured using a material such as polysilicon or the like by a semiconductor manufacturing method. The heat sensing diode  11  changes its voltage depending on the temperature, and is used for detecting the temperature of the semiconductor element  10 .  
      The semiconductor element  10  has a first metal body  20  as an electrode and a heatsink on its main reverse side attached electrically and thermally with a first conductive bonding material  51  such as a solder. Further, the semiconductor element  10 , on its main side, has a second metal body  40  attached electrically and thermally with a second conductive bonding material  52  such as a solder.  
      Furthermore, the second metal body  40  has, on the side opposite to a semiconductor element  10  facing side, a third metal body  30  as an electrode and a heatsink attached electrically and thermally with a third conductive bonding material  53  such as a solder.  
      Various kinds of signal terminals  60  are disposed surrounding the semiconductor element  10 , and the main side of the semiconductor element  10  and the signal terminals  60  are connected electrically by bonding wires  70 . Most part of the surface of the semiconductor device is sealed with resin molding  80  in this case.  
      Among the five signal terminals  60  shown in  FIG. 4A , two terminals on the right is for heat sensing diode  11 , that is, terminals for heat detection, and the rest of the terminals are terminals connected electrically to signal electrodes of the semiconductor element  10  and base terminals.  
      However, the semiconductor device of this kind suffers from heat generation because of the density of implementation and the like. This situation leads to a possibility of crack in the second conductive bonding material  52  between the semiconductor element  10  and the second metal body  40  in  FIG. 4A . This crack usually breaks out from the outer periphery of the second conductive bonding material  52 . That is, the second conductive bonding material  52  exfoliates at the outmost periphery of the semiconductor element  10 .  
      The above conventional semiconductor element  10  has the heat sensing diode  11  at its periphery on the main side. Therefore, the exfoliation of the second conductive bonding material  52  by a crack at the outmost periphery of the semiconductor element  10  causes a defective operation of the heat sensing diode  11 . This is because the heat sensing diode  11  is disposed at the periphery of the semiconductor element  10 , resulting in a breakage of the diode  11  from a concentrated stress of the crack.  
      Another cause of the defective operation of the heat sensing diode  11  is contributed to an interruption of a heat dissipation path caused by the crack in the second conductive bonding material  52  at the periphery of the semiconductor element  10 . The interrupted heat dissipation path causes heat accumulation around the heat sensing diode  11  resulting in a defective operation.  
     SUMMARY OF THE INVENTION  
      The present invention, in view of the above problems, devises a semiconductor device with a main electrode on each of the main side and the main reverse side of the semiconductor element having a first metal body on the main reverse side and a second/third metal body on the main side, and also having a heat sensing diode on the main side of the semiconductor element, most of the device covered by a molding material, such as a resin. The inventive structure of the semiconductor device prevents a defective operation of the heat sensing diode caused by a crack in the conductive bonding material between the main side of the semiconductor element and the second metal body.  
      In the present invention, a semiconductor device has a semiconductor element with a main electrode on each of a main side and a main reverse side. The semiconductor element has a heat sensing diode on the main side for detecting temperature. The semiconductor element has the following three parts on it, that is, a first metal body as an electrode and a heatsink attached to the main electrode on the main reverse side of the element with a first conductive bonding material, a second metal body attached to the main electrode on the main side of the semiconductor element with a second conductive bonding material, and a third metal body as an electrode and a heatsink attached to a side opposite to the semiconductor element facing side of the second metal body with a third conductive bonding material. In the semiconductor device molded for the most part by a molding material such as a resin, the heat sensing diode is disposed at the center of the main side of the semiconductor element.  
      Because of the arrangement of the heat sensing diode on the main side of the semiconductor element, a crack on the periphery of the second conductive bonding material does not affect the operation of the heat sensing diode, and thus the structure minimizes the risk of malfunction of the device.  
      The disposition location of the heat sensing diode can be described in the following ways on the main side of the semiconductor element. The location on the semiconductor element is defined as a square having the center point of the element inside, with one side being half the length of one side of the semiconductor element and the other side being half the length of the other side of the semiconductor element.  
      The location on the semiconductor element can also be defined as a area having a size of one fourth of the semiconductor element, with a base point existing on the center point of the semiconductor element.  
      The arrangement of cell blocks in a row on the semiconductor element is such that the heat sensing diode is located in between the two cell blocks at the center of the row when number of the blocks is even. The arrangement of cell blocks in a row on the semiconductor element can also be such that the heat sensing diode is located on either side of the center cell block of the row when number of the blocks is odd.  
      The first conductive bonding material, the second conductive bonding material, and the third conductive bonding material in the semiconductor device are a Sn (tin) solder. Further, the heat sensing diode and a lead of the heat sensing diode is covered by a protection cover of thickness of 2 μm or more made of polyimide on the main side of the semiconductor element in the semiconductor device.  
      The above-described structure appropriately provides a protection for the heat sensing diode and the lead of the heat sensing diode and an electrical insulation for them. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:  
       FIGS. 1A and 1B  are a schematic plan view and a schematic cross-sectional view illustrating a semiconductor device in the first embodiment of the present invention.  
       FIG. 2A  shows a schematic plan view of a semiconductor element seen from a main side, and  FIG. 2B  shows a schematic cross-sectional view along the IIB-IIB line in  FIG. 2A .  
       FIG. 3  shows a schematic plan view of a semiconductor element in the second embodiment of the present invention seen from a main side.  
       FIGS. 4A and 4B  are a schematic plan view and a schematic cross-sectional view illustrating a conventional semiconductor device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The present invention will be described in detail with respect to a semiconductor device having a crack resistance capability in terms of a semiconductor element disposed on the device.  
     First Embodiment  
      A semiconductor device S 1  in the present embodiment, as shown in  FIGS. 1A, 1B ,  2 A and  2 B, comprises a first semiconductor chip  10  as a semiconductor element, a lower heatsink  20  as a first metal body, an upper heatsink  30  as a third metal body, a heatsink block  40  as a second metal body, conductive bonding materials  51 ,  52 ,  53  placed between the semiconductor element and the metal bodies, a heat sensing diode  11  disposed on the first semiconductor chip  10 , and a resin mold  80 .  
      In the present embodiment, the first semiconductor chip  10  is sided by a second semiconductor chip  18 . In this structure, downsides of the semiconductor chips  10 ,  18  and an upside of the lower heatsink  20  are bonded by a first conductive bonding material  51 . Further, upsides of the semiconductor chips  10 ,  18  and downsides of the heatsink blocks  40  are bonded by a second conductive bonding material  52 . Furthermore, upsides of the heatsink blocks  40  and a downside of an upper heatsink  30  are bonded by a third conductive bonding material  53 .  
      As the first, second, and third conductive bonding materials  51 ,  52 ,  53 , a solder, conductive bonding materials or the like can be used. In the present embodiment, an Sn (tin) solder is used.  
      Heat dissipation is conducted through the second conductive bonding material  52 , the heatsink block  40 , the third conductive bonding material  53  and the upper heatsink  30  from the upsides of the first and second semiconductor chips  10 ,  18 . Heat dissipation from the downside of the first and second semiconductor chips  10 ,  18  is conducted through the first conductive bonding material  51  and the lower heatsink  20 .  
      As the first semiconductor chip  10 , a power semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor) or a thyristor is mainly, but not limitedly, used. As the second semiconductor chip  18 , FWD (Free Wheel Diode) or the like is used.  
      A shape of the first semiconductor chip  10  is, for example, a thin board of rectangle. In  FIG. 1B , the upside of the first semiconductor chip  10  is a main side where an element is disposed, and the downside is a main reverse side.  
      As shown in  FIG. 2A , the main side of the first semiconductor chip  10  has an odd number (e.g. seven) of cell blocks Tr arranged in a row.  
      Each cell block Tr has a main electrode for the main side (not shown in FIGS.). The main reverse side of the first semiconductor chip  10  also has a main electrode (not shown in FIGS.).  
      The main electrode of the first semiconductor chip  10  can be, for example, an emitter for the main electrode on the main side, and a collector for the main electrode on the main reverse side.  
      As shown in  FIG. 2A , the heat sensing diode  11  is disposed on the main side of the first semiconductor chip  10 .  
      The heat sensing diode  11  is a typical diode element, manufactured using a material such as polysilicon or the like by a semiconductor manufacturing method. This element has a heat sensing capability as a changing voltage, and thus it is used for detecting the temperature of the first semiconductor chip  10 .  
      As shown in  FIG. 2A , the heat sensing diode  11  has two attached leads  11   a . Each lead  11   a  is electrically connected to a pad  12  disposed at the periphery of the first semiconductor chip  10 .  
      Also as shown in  FIG. 2A , the heat sensing diode  11  is disposed at the center of the main side of the first semiconductor chip  10 .  
      That is, the heat sensing diode  11  is disposed in the rectangular area K 1  shown with a dotted line in  FIG. 2A  when the chip  10  has a rectangular board shape. In other words, the diode  11  is disposed within the area K 1  from the center point of the main side, having a longitudinal side being half the length of longitudinal side of the first semiconductor chip  10 , that is H/2, and a lateral side being half the length of lateral side of the chip  10 , that is W/2.  
      The dotted line square K 1  in  FIG. 2A , in other words, has a longitudinal side of a length of H/2 and a lateral side of a length of W/2. The heat sensing diode  11  is disposed in this square area.  
      The heat sensing diode  11  is disposed in an area that occupies one fourth size of the main side surface area around the center point of the semiconductor chip  10 , based on the relationship between each side of the square area K 1  and each side of the first semiconductor chip  10 .  
      Even when the first semiconductor chip  10  does not have a rectangular shape, the heat sensing diode  11  should be disposed in the area that occupies one fourth of the main side surface size around the center point of the semiconductor chip  10 .  
      In this case, the heat sensing diode  11  is preferably on one side of the center cell block Tr of the seven cell blocks Tr. In that way, the heat sensing diode  11  is disposed appropriately in the center of the first semiconductor chip  10 .  
      Though the heat sensing diode  11  is disposed on the left of the center cell block Tr, the diode  11  may be disposed on the right, or on both sides.  
      The heat sensing diode  11  and a lead  11   a  attached to the heat sensing diode  11  are covered with a protection cover  13  made of polyimide with thickness of 2 μm or more.  
      The main electrode on the main reverse side of the first semiconductor chip  10  is electrically connected to the lower heatsink  20  as the first metal body by the first conductive bonding material  51 . The main electrode on the main side of the first semiconductor chip  10  is electrically connected to the heatsink block  40  as the second metal body by the second conductive bonding material  52 .  
      Further, the heatsink block  40  is, on the side opposite to the semiconductor chips  10 ,  18 , electrically connected to the upper heatsink  30  as the third metal body by the third conductive bonding material  53 .  
      The lower heatsink  20 , the upper heatsink  30 , and the heatsink block  40  are made of, for example, a high heat/electrical conductivity such as a copper alloy, an aluminum alloy or the like. The heatsink block  40  may be made of a generic metal alloy.  
      The lower heatsink  20  is formed in a shape of, for example, rectangular board. A terminal  21  mounted on the lower heatsink  20  is used as an electrode for substrate mounting to be attached to the main electrode, that is a collector electrode for example, on the main reverse side of the semiconductor chip  10 .  
      The heatsink block  40  is, for example, formed in a shape of rectangular board slightly smaller than the semiconductor chip  10 .  
      The heatsink block  40  is disposed between the semiconductor chips  10 ,  18  and the upper heatsink  30  thermally and electrically connecting the chips  10 ,  18  and the heatsink  30 . The heatsink block  40  also works as a spacer between the first semiconductor chip  10  and the upper heatsink  30  so that a sufficient height for a bonding wire  70  described later can securely be reserved between the chip  10  and the heatsink  30 .  
      Further, the upper heatsink  30  is also formed in a shape of rectangular board as a whole. A terminal  31  mounted on the upper heatsink  30  is used as an electrode for substrate mounting to be attached to the main electrode, that is an emitter for example, on the main side of the semiconductor chip  10 .  
      The terminal  21  of the lower heatsink  20  and the terminal  31  of the upper heatsink  30  are, as described above, the substrate mounting electrode connected to the main electrode of the semiconductor chip  10 , that is, these terminals  21 ,  31  are disposed for a connection to a wiring outside of the semiconductor chip of the semiconductor device S 1 .  
      The lower heatsink  20  and the upper heatsink  30  are formed respectively as the first metal body and the third metal body, either of them being used as an electrode and a heatsink. That is, these metal bodies are used as electrodes of the semiconductor chip  10  in the semiconductor device S 1  as well as heatsinks for dissipating heat from the semiconductor chips  10 ,  18 .  
      A signal terminal  60  is disposed around the first semiconductor chip  10 . This signal terminal  60  is used as a terminal and a base terminal electrically connected to a signal electrode (a gate electrode, for example) on the surface of the first semiconductor chip  10 , the heat sensing diode  11  and the like.  
      Each signal terminal  60  is, for example, electrically connected by the wire  70  to a pad  12  disposed on the periphery of the first semiconductor chip  10 , as shown in  FIG. 1A . The wire  70  is formed by a wire bonding or the like, and is made of gold, aluminum or the like.  
      Each pad  12  is electrically connected to the heat sensing diode  11  or the signal electrode of the first semiconductor chip  10 .  
      The five signal terminals  60  are electrically connected to the pads  12  by the wire  70 . The lower two terminals, for example, are used as temperature detection terminals connected to the heat sensing diode  11 , and the rest are used as the terminals electrically connected to the signal electrodes on the semiconductor chip  10  and the base terminals.  
      The above components such as terminals  60 , pads  12  and bonding wires  70  are sealed and molded almost entirely by a resin  80 . That is, as shown in  FIG. 1B , a space between a pair of heatsinks  20 ,  30 , and a surrounding area of the semiconductor chips  10 ,  18  and the heatsink block  40 , are filled and sealed with the resin  80 .  
      As the material of the resin  80 , a normal mold material such as an epoxy resin and the like may be used. Molding for the heatsinks  20 ,  30  and the like is easily formed by a form block with an upper and lower molds (not shown in FIGS.) in a transfer mold method.  
      The semiconductor device S 1  is basically formed as a resin mold semiconductor device with the first semiconductor chip  10  as a vertical power element having electrically and thermally connected metal bodies  20 ,  30 ,  40  on both sides and the heat sensing diode  11  on the main side of the semiconductor chip  10 .  
      Manufacturing method of the semiconductor device S 1  is described with reference to  FIG. 1A  and  FIG. 1B . A process for soldering the upsides of the lower heatsink  20  with the semiconductor chips  10 ,  18  and the heatsink blocks  40  comes first.  
      In this case, the semiconductor chips  10 ,  18  are layered with, for example, a Sn solder foil on the upside of the lower heatsink  20 , and the heatsink blocks  40  are layer on the semiconductor chips  10 ,  18  with the same solder foil.  
      The solder foil is melted by a heating device (a reflow device) to a temperature above a melting point of the solder, and the melted solder is then hardened.  
      A process for wire-bonding the first semiconductor chip  10  and the signal terminal  60  is conducted. The semiconductor chip  10  and the signal terminal  60  are electrically connected by the wire  70 .  
      A process for soldering the upper heatsink  30  on each of the heatsink blocks  40  is conducted. In this process, the upper heatsink  30  is placed with a solder foil on the heatsink blocks  40 . The solder foil is melted by the heating device and then hardened.  
      The hardened solder foils are formed as the first, the second, and the third conductive bonding materials  51 ,  52 ,  53 .  
      These processes complete the electrical and thermal connection between the lower heatsink  20 , the semiconductor chips  10 ,  18 , heatsink blocks  40 , and the upper heatsink  30  beside physical connection by the conductive bonding materials  51 ,  52 ,  53 .  
      When a conductive adhesive is used as the first, second, and third conductive bonding material  51 ,  52 ,  53 , the processes described above are utilized to achieve a physical, an electrical and a thermal connection between the lower heatsink  20 , the semiconductor chips  10 ,  18 , the heatsink blocks  40  and the upper heatsink  30  by replacing the solder with the conductive adhesive and by replacing placement of the solder foil with application and hardening of the conductive adhesive.  
      A process for filling the resin  80  into a space between the heatsinks  20 ,  30  and other peripheral portion by using a form block (not shown in FIGS.) is then conducted. The resin  80  fills the space such as the space between the heatsink  20  and  30 , the peripheral portion and the like, in the process.  
      Manufacturing process of the semiconductor device S 1  completes when the device S 1  is taken out of the form block after the resin  80  is hardened.  
      The downside of the lower heatsink  20  and the upside of the upper heatsink  30  are exposed from the resin mold . This contributes to an increased heat dissipation capacity of the heatsinks  20 ,  30 .  
      In the present embodiment, the semiconductor device S 1  has a semiconductor element  10  with a main electrode on each of a main side and a main reverse side, having a heat sensing diode  11  on the main side for detecting temperature, the lower heatsink  20  attached to the main electrode on the main reverse side of the semiconductor element  10  with the first conductive bonding material  51 , the heatsink blocks  40  attached to the main electrode on the main side of the semiconductor element  10  with a second conductive bonding material  52 , and the upper heatsink  30  attach to a side opposite to the semiconductor element  10  facing side of the heatsink blocks  40  with a third conductive bonding material  53 , and the semiconductor device S 1  is provided with the heat sensing diode  11  disposed at the center of the main side of the semiconductor element  10 , covered almost entirely by the resin  80 .  
      According to the above embodiment, the heat sensing diode  11  disposed at the center of the main side of the first semiconductor chip  10  is not close to a position of a crack, when the crack breaks on the periphery of the second conductive bonding material  52 . Therefore, the heat sensing diode  11  will not severely be affected by the crack, that is, concentration of stress from the crack to the heat sensing diode  11 , an interruption of heat dissipation path by a exfoliation of the second conductive bonding material  52 , and the like.  
      Risk of malfunction of the heat sensing diode  11  is, thus, minimized, even when a crack breaks out in the conductive bonding material  52  that connects the main side of the first semiconductor chip  10  and the heatsink block  40  as the second metal body.  
      As a result, the semiconductor device can stably conduct a high temperature protection control by appropriately detecting the maximum temperature of the first semiconductor chip  10 .  
      The area for the heat sensing diode  11  disposition at the center of the first semiconductor chip  10  is preferably the area shown in  FIG. 2A .  
      That is, the heat sensing diode  11  on the first semiconductor chip  10  is preferably disposed from the center point of the main side within an area having half the length H/2 of longitudinal side and half the length W/2 of lateral side, when the first semiconductor chip  10  has a shape of rectangular board.  
      The heat sensing diode  11  on the first semiconductor chip  10  is preferably disposed from the center point of the main side within an area K 1  having the size of one fourth of the main side without regard to the shape of the first semiconductor chip  10 .  
      The heat sensing diode  11  on the first semiconductor chip  10  is preferably disposed on at least one side of the center cell block Tr, as shown in  FIG. 2A , when multiple cell blocks Tr are arranged in a row and the number of the cell blocks Tr is odd.  
      The heat sensing diode  11  and the lead  11   a  attached to the heat sensing diode  11  on the first semiconductor chip  10 , as shown in  FIG. 2B , are covered by the protection cover  13  having thickness of 2 μm or more made of polyimide.  
      The above-described structure is preferred, because the heat sensing diode  11  and the lead  11   a  attached to the heat sensing diode  11  is appropriately protected and insulated.  
     Second Embodiment  
      In this embodiment shown in  FIG. 3 , the multiple cell blocks Tr are arranged in a row on the main side of the first semiconductor chip  10 . The number of the cell block Tr is even (e.g. eight).  
      In this case, the heat sensing diode  11  is disposed between the two cell blocks Tr at the center in the row. According to this arrangement, the heat sensing diode  11  can appropriately be disposed at the center of the main side on the first semiconductor chip  10 .  
      Except for the difference described above, the semiconductor device in this embodiment provides the same operational effect as in the first embodiment.  
     Other Embodiments  
      The semiconductor element used for this invention is not limited to the power semiconductor element such as an IGBT, a thyristor, and the like, but a semiconductor element with a main electrode on a main side and a main reverse side.