Abstract:
Packaged semiconductor device having a frame, of conductive material; a body of semiconductor material, fixed to the frame through a first adhesive layer; a heat-sink element, fixed to the body through a second adhesive layer; and a packaging mass surrounding the body and, at least partially, the frame and the heat-sink element. The heat-sink element is formed by a heat-sink die facing, and coplanar to, a main face of the device and by a spacer structure, which includes a pair of pedestals projecting from the perimeter of the heat-sink die towards the body and rest on the body.

Description:
BACKGROUND 
       [0001]    1. Technical Field The present disclosure relates to an integrated electronic device having a dissipative package, in particular dual side cooling package. 
         [0002]    2. Description of the Related Art 
         [0003]    As is known, in the majority of integrated electronic devices, for example in power devices that dissipate high amounts of heat, the current flow is of a vertical type, i.e., directed from the bottom face to the top face (or vice versa) of the body or die of semiconductor material integrating the integrated electronic device. Consequently, both the faces of the die are involved in dissipation of the heat generated during operation of the integrated electronic device. 
         [0004]    To improve dissipation, dual side-cooling (DSC) packages are already available and enable extraction of the heat from both sides of the die. 
         [0005]    Known DSC packages are manufactured using various assembly processes and generally have dissipative structures arranged on or coupled to both sides of the die. For example, on one side, generally the underside to be fixed to a support, such as a printed-circuit board (PCB), the dissipative structure may be formed by a metal frame on which the die is fixed and which forms access terminals of the package. On the opposite side, DSC packages include a plate (commonly known as clip), also of good heat-conducting material, in general a metal, such as copper. 
         [0006]    An example of a device with DSC package is shown in  FIGS. 1 to 3 . In particular,  FIGS. 1 to 3  show a device  1  of a surface-mount type that includes components encapsulated in a packaging mass  2 . The packaging mass  2  is of insulating material, such as plastic, epoxy resin, or ceramic. The device  1  has two main faces  3 A,  3 B, a first face  3 A which is designed to be mounted on a structure such as a printed-circuit board (PCB) (not shown) and a second face  3 A, which is generally exposed towards the outside. 
         [0007]    The packaging mass  2  incorporates a body or die  5  ( FIG. 3 ) manufactured using semiconductor technologies and integrating an integrated component or circuit, for example a power transistor. Typically, in a way not shown, the die  5  may comprise a monolithic substrate of semiconductor material, such as silicon, covered by insulating layers surrounding conductive lines and connection structures, for example of aluminum. The die  5  is fixed, through a first adhesive layer  6 , for example a so-called “solder” layer, to a frame  7  enabling electrical connection of the component or integrated circuit with an environment outside the device. The frame  7  comprises, in a known way, a bottom plate  7 A, of a generally rectangular or square shape, and a plurality of terminals or pins  7 B. The bottom plate  7 A constitutes a substantial portion of the first face  3 A, and the terminals  7 B face the first face  3 A as well as lateral faces  3 C of the device  1 , from which they may project (as shown in the embodiment) or to which they may be aligned (in a way not shown). In a known manner, a connection wire (not shown) connects one of the terminals  7 B to a first contact pad (gate pad) formed on the body  1 , and a metal clip (not shown) connects the other terminal  7 B to another contact pad (source pad, not shown), which is also formed on the body  1 . 
         [0008]    The device  1  further comprises a heat-sink element  10 , forming a so-called “clip”. In detail, the heat-sink element  10  comprises a top plate  10 A and a support portion  10 B. The top plate  10 A is fixed to the die  5  via a second adhesive layer  11  (for example, a PbSnAg-based solder paste) and faces the second face  3 B of the device  1 , and the support portion  10 B is bent towards the terminals  7 B of the frame  7 , to which it may be bonded through one or more adhesive portions  12 , generally formed after the first adhesive layer  6 . 
         [0009]    The device  1  may be obtained by adhering the die  5  to the frame  7  through the first adhesive layer  6 ; adhering the heat-sink element  10  to the die  5  and to the terminals  7 B through the second adhesive layer  11  and the adhesive portion  12 ; inserting the assembly thus obtained in a mold, including a bottom half-mold, a top half-mold, and possibly a spacer; and filling the mold with the packaging mass (see, for example, U.S. Pat. Pub. No. 2013/0154155 filed in the name of the present applicant). 
         [0010]    Ideally, design and manufacture of the device  1  with DSC package are directed to optimize the overall thermal efficiency and the outline of the package (also referred to as “package outline assembly”—POA), wherein the exposed face (not fixed to the die  5 ) of the top plate  10 A is coplanar to the second face  3 B of the device and has a regular shape, as large as possible. To this end, some parameters are involved, among which the thickness of the second adhesive layer  11 , i.e., the distance between the die  5  and the top plate  10 A, and the inclination of the top plate  10 A, i.e., its arrangement parallel to the die  5  and to the second face  3 B of the device  1 . 
         [0011]    In fact, the thickness of the second adhesive layer  11  (also referred to as “bond-line thickness”—BLT) determines the coplanarity between the top die plate  10 A and the second face  3 B. In case of a small thickness of the second adhesive layer  11 , during molding of the packaging mass  2 , part of the material may cover the top plate  10 A at least partially, thus reducing the area of the exposed face thereof and thus the effectiveness of dissipation of the heat-sink element  10 , or in any case may cause the presence of a non-desired step. Instead, in case of excessive thickness of the second adhesive layer  11 , the top plate  10 A is arranged at a greater height than the nominal height, thus creating problems during the molding step, since the top plate  10 A may interfere with the mold and get damaged during closing. Furthermore, also in this case, the risk of lack of planarity exists. 
         [0012]    The inclination of the top plate  10 A affects the coplanarity between it and the second face  3 B. In fact, in case of non-zero inclination, a part of the top plate  10 A may project with respect to the second surface  3 B and/or a part of the top plate  10 A may be at a lower level than the second surface  3 B of the device  1 . In either case, the desired coplanarity is not achieved. Further, also here, possible parts at a lower level may be coated by the packaging mass  2 . Consequently, problems may arise of molding and/or effectiveness and in any case the device does not correspond to the desired specifications. For forming the device  1  with DSC package various solutions are known:
       Flat: the top plate  10 A is formed by a portion with rectangular area; this solution is very simple and provides a large dissipative area that responds also geometrically to the market; however, the indicated coplanarity is not provided; in fact, the second adhesive layer  11  is laid in a molten phase, very liquid, so that its thickness is not well controlled;   V-shape: this is similar to the flat solution, but the top plate  10 A has a patterned, irregular, shape, less appreciated by the market and with a reduced exposed surface, and thus with less effectiveness as to heat dissipation as compared to the previous solution; the V-shape solution further shares the limitations indicated for the flat solution;   Dimple: the top plate  10 A has a series of dimples forming portions projecting towards the die; in practice, the top plate is not planar, and the projections form a sort of spacers to preset the distance between the body and the top plate; this solution has the disadvantage that the dimples are filled with the packaging mass during molding so that the heat-sink element  10  does not have a full rectangular area, and thus there may be a reduction of effectiveness, besides having a shape that does not meet market requirements;   Coined: the top plate  10 A is coined for presenting lowered internal lines designed to rest directly on the die  5 ; this solution has the disadvantage that it has no end-of-travel control, and it is very difficult to ensure planarity;   Downset: the heat-sink element  10  has a plurality of bands with non-planar structure; this solution does not ensure planarity; furthermore the heat-sink element  10  has a very irregular shape;   Double clip: initially, a first clip or plate of an irregular shape (possibly having dimples) is formed directly on the body or at a short distance therefrom, and then a plate, intended to remain exposed, is fixed via another adhesive layer; this solution employs a complicated and costly process due to the presence of two steps for fixing two distinct elements.       
 
       BRIEF SUMMARY 
       [0019]    One or more embodiments of the present disclosure may overcome one or more of the drawbacks discussed above. According to one embodiment of the present disclosure, a packaged device includes a frame of conductive material and first and second adhesive layers. The device further includes a die of semiconductor material coupled to the frame by the first adhesive layer. The device further including a heat-sink coupled to the die. The heat-sink includes a main portion and a spacer structure extending from the main portion. The main portion is coupled to the die by a second adhesive layer and the spacer structure is coupled to the die by a third adhesive layer. The third adhesive layer is thinner than the first adhesive layer. The device further includes a packaging mass surrounding the die and at least a portion of the frame and the heat-sink. The packaging mass has a surface that is coplanar with a surface of the main portion of the heat-sink. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0020]    For a better understanding of the present disclosure preferred embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein: 
           [0021]      FIG. 1  is a perspective top view of a device with DSC package; 
           [0022]      FIG. 2  is a perspective bottom view of the device of  FIG. 1 ; 
           [0023]      FIG. 3  is a cross-section of the device of  FIGS. 1 and 2 ; 
           [0024]      FIG. 4  is a cross-section of an embodiment of the present device with DSC package; 
           [0025]      FIG. 5  is a see-through top plan view of a portion of the device of  FIG. 4 ; 
           [0026]      FIG. 6  is a perspective view of a detail of the device of  FIG. 4 ; 
           [0027]      FIGS. 7 to 9  are see-through top plan views of different embodiments of the present device; 
           [0028]      FIG. 10  is a perspective view of an embodiment of a detail of the present device; 
           [0029]      FIG. 11  is a see-through top plan view of another embodiment of the present device; and 
           [0030]      FIG. 12  is a perspective view of a detail of the device of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIGS. 4-6  show an embodiment of a device  20  with DSC packaging having a heat-sink element shaped to optimize the thermal efficiency and the outline of the package. 
         [0032]    The device  20  has a general structure similar to that of the device  1  of  FIG. 1 , and comprises, in particular, a die  21  formed using semiconductor technology and coupled, through a first adhesive layer  22 , to a frame  23 , such as a leadframe, and, through a second adhesive layer  24 , to a heat-sink element  25 . 
         [0033]    A packaging mass  26  surrounds the die  21 . The device  20  thus has a generally parallelepipedal shape defining a first main face  20 A, a second main face  20 B, and lateral faces  20 C. The die  21 , the leadframe material, and packaging mass  26  are the same material as discussed in reference to device  1 . 
         [0034]    The main faces  20 A,  20 B define (in a Cartesian reference system) two axes here identified by X and Y, and the lateral faces  20 C further define a third axis, here designated by Z. 
         [0035]    The frame  23  comprises a plate  23 A and terminals  23 B, which are aligned and have an outer surface coplanar to the first main face  20 A of the device  20 . 
         [0036]    The heat-sink element  25  is also here formed by a top plate  25 A and by a support portion  25 B, similar to the corresponding parts of the heat-sink element  10  of  FIG. 1 . In particular, the top plate  25 A has a generally parallelepipedal shape with an outer face (not fixed to the die  21 ) of a rectangular shape lying in a plane parallel to the plane XY and coplanar to the top surface  20 B of the device  20 . The support portion  25 B extends in a transverse direction from one of the sides of the rectangular shape, and more in particular in the direction of axis Z, as far as the terminals  23 B, to which it is fixed through one or more adhesive portions  28 . 
         [0037]    As discussed above, in a known manner, a connection wire (not shown) connects one of the terminals  23 B to a first contact pad (gate pad) formed on the body  20 , and a metal clip (not shown) connects the other terminal  23 B to another contact pad (source pad, not shown), which is also formed on the body  20 . 
         [0038]    The heat-sink element  25  further has a pair of lowered spacer elements or pedestals  25 C, which extend and project from the perimeter of the top plate  25 A. In  FIGS. 4 and 5 , the pedestals  25 C extend from the side of the top plate  25 A opposite to the support portion  25 B. 
         [0039]      FIG. 5  is a top plan view of the device  20  without the packaging mass  26 , while  FIG. 6  is a partial isometric view of the heat sink element  25 . The pedestals  25 C project, with respect to the top plate  25 A, both laterally in direction XY, as may be seen in particular from the top plan view of  FIG. 5  and in the perspective view of  FIG. 6 , and in direction Z, as may be seen in the cross-section of  FIG. 4  and in the perspective view of  FIG. 6 . In particular, the pedestals  25 C rest directly on the die  21  and ensure, together with the support portion  25 B, positioning of the top plate  25 A at the height set during design, such as to ensure the desired thickness of the second adhesive layer (i.e., of the preset BLT). 
         [0040]    The pedestals  25 C are made in a single piece, and are thus monolithic, with the heat-sink element  25  using a technique that enables correct sizing thereof, for example via coining. 
         [0041]    It is to be noted that the pedestals are in contact with the die  21  with interposition of a third adhesive layer  27  of a smaller thickness as compared to the second adhesive layer  24 . The third adhesive layer  27  may be of the same material as the second adhesive layer  24  (a solder paste or preform), but has a negligible thickness for ensuring exact vertical positioning and exact inclination of the top plate  25 A with respect to the die  21 . For example, the second adhesive layer  24  may have a thickness of approximately 25 μm, and the third adhesive layer  27  may have a thickness of 5 μm. 
         [0042]    In this way, the position of the heat-sink element  25  with respect to the die  21  is predetermined and practically independent of the more or less fluid state of the second adhesive layer  24  during assembly. 
         [0043]    Due to the not coplanar, namely lowered position of the pedestals  25 C with respect to the outer face of the top plate  25 A (that is the second main face  20 B of the device  20 ), they are covered by the packaging mass  26  in the final molding step, such as the molding step described in reference to  FIGS. 1-3 , so that the finished device  20  has a thermal dispersion region of a rectangular shape corresponding to the area of the top plate  25 A. 
         [0044]    It follows that the device  20  has the DSC according to design, with a large exposed area, equal to the entire area of the top plate  25 A. Assembly is optimized, since deposition of the second adhesive layer  24  is not critical, and no further steps are envisaged, as in the double-clip solution. Furthermore, the shape of the exposed area of the top plate  25 A may be designed at will; in particular, it may be rectangular or square. 
         [0045]    Further, the position of the pedestals  25 C may be chosen as desired, on the basis of the dimensions and layout of the die  21 , as shown, for example, in  FIGS. 7-12 . 
         [0046]      FIG. 7  shows an embodiment of the device  20  where the pedestals  25 C are arranged on the sides adjacent to that of the support portion  25 B. Further four pedestals  25 C are provided, two for each side. 
         [0047]      FIG. 8  shows an embodiment of the device  20  where two pedestals  25 C are arranged on the sides adjacent to that of the support portion  25 B, and the top portion  25 A extends, in direction X, so as not to project beyond the die  21 . 
         [0048]      FIG. 9  shows an embodiment of the device  20  where the die  21  has a markedly rectangular shape, with its short sides parallel to the axis X, and the top portion  25 A of the heat-sink element  25  projects beyond the die  21  in the direction X. 
         [0049]      FIG. 10  shows a different embodiment of the heat-sink element  25 , wherein the heat-sink element  25  has lateral pedestals  25 C, projecting from the long sides of the top plate  25 A, parallel to axis X, and a support portion  25 B divided into two parts. 
         [0050]      FIGS. 11 and 12  show an embodiment of the device  20  where the pedestals  25 C are formed within the perimeter of the top plate  25 A of the heat-sink element  25 . 
         [0051]    With this solution, the packaging mass  26 , after molding, covers the pedestals  25 C and the perimeter of the exposed face of the top plate  25 A, after molding of the packaging mass  26 , is no longer rectangular. This solution makes it, however, possible to have a regular and uniform exposed area. 
         [0052]    Finally, it is clear that modifications and variations may be made to the device described and illustrated herein, without thereby departing from the scope of the present disclosure. 
         [0053]    For example, the individual characteristics described with reference to each specific embodiment are in general interchangeable with other characteristics described with reference to different embodiments. 
         [0054]    The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.