Abstract:
A package device has a package substrate, a semiconductor die on the package substrate, and a molding compound on the package substrate and over the semiconductor die. The semiconductor die has a last passivation layer, an active circuit region in an internal portion of the die, an edge seal region along a periphery of the die, and a structure over the edge seal region extending above the last passivation layer, covered by the molding compound, and comprising a polymer material. The structure may extend at least five microns above the last passivation layer. The structure stops cracks in the molding compound from reaching the active circuit region. The cracks, if not stopped, can reach wire bonds in the active region and cause them to fail.

Description:
BACKGROUND  
       [0001]    1. Field 
         [0002]    This disclosure relates generally to semiconductor packages, and more specifically, to crack arrest features in semiconductor packages. 
         [0003]    2. Related Art 
         [0004]    Consumers demand smaller semiconductor devices with increased functionality. To achieve these desires, semiconductor devices can be decreased in size while adding additional circuitry. In wirebond packages, the additional circuitry requires additional wires to couple the semiconductor die to external terminals. Because the number of wires is increased and the size of the die is decreased, wires are likely to be closer together. 
         [0005]    As the spacing between wires decreases, the filler in the molding compound may be blocked resulting in the mold compound having resin-rich areas. The resin-rich areas have a higher coefficient of thermal expansion (CTE) and a decreased strength than areas with more filler. When exposed to changes in temperatures, a crack is created in the resin-rich area. The crack will propagate either in the molding compound close to the die top surface or at the interface between the molding compound and the die top surface. The crack can separate the ball bond from the semiconductor die. Hence, the increased number of wires can create cracks that damage the semiconductor device. A need exists to prevent such cracks from damaging the semiconductor device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0006]    The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. 
           [0007]      FIG. 1  illustrates a top-down view of a semiconductor die assembly while flowing the molding compound to form a semiconductor package in accordance with one embodiment; 
           [0008]      FIG. 2  illustrates a cross-section of the semiconductor package formed in  FIG. 1  in accordance with one embodiment; and 
           [0009]      FIG. 3  illustrates a cross-section of a portion of the packaged semiconductor die and a portion of the molding compound of  FIG. 2  in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION  
       [0010]    In one embodiment, a semiconductor package includes one or more molding compound crack stops  38  that are means for preventing cracks that occur in the molding compound  18  from extending into the active circuit region  28  of a semiconductor die  12 . The molding cracks stops  38  are located in an edge seal region  30 . 
         [0011]      FIG. 1  illustrates a top-down view of a semiconductor die assembly  10  while forming a molding compound  18  in accordance with one embodiment. The semiconductor die assembly  10  includes a semiconductor die  12  that is coupled to a package substrate  16  through wires  14 . In one embodiment, the number of wires per length of die edge (linear wire density) is approximately 20 wires per millimeter. In one embodiment, there are 800 wires  14  coupled to the semiconductor die  12 . The semiconductor die  12  can be any semiconductor die, such as a logic device, memory device, the like, or combinations of the above. As will be better understood after further discussion, the semiconductor die  12  includes an active circuit region  28  surrounded by an edge seal region  30 . In the embodiment illustrated, the edge seal region  30  includes a molding compound crack stop  38  that also surrounds the active circuit region  28 . The edge seal region  30  is located along a periphery of the semiconductor die  12 . The active region  28  is located in an internal portion of the semiconductor die  12 . The package substrate  16  can be any suitable package substrate, such as bismaleimide triazine (BT) resin, FR4 laminate, the like, and combinations of the above. In one embodiment, the wires  14  are gold wires. 
         [0012]    As illustrated, a molding compound  18  flows  20  from one corner of a semiconductor die assembly  10  to a diagonally opposite corner. An area near the corner where the molding compound  18  begins to flow has a nominal filler density region  22 . The nominal filler density region  22  has a filler density that is typical of the mold compound being used. For example, the nominal filler density region  22  may have silica particles that vary in size as per a normal distribution with an average diameter of approximately 30 microns. As the molding compound  18  flows  20  from one corner of the semiconductor die assembly  10  to an opposite corner, the wires  14  may block the filler in the molding compound  18  and create a low filler density region  24 . The low filler density region  24  has a filler density and concentration of filler less than that of the nominal filler density region  22 . In one embodiment, the low filler density region  24  is a resin-rich region. The filler in the molding compound  18  may be any suitable material, such as alumina, silica, boron nitride, silicon dioxide, the like, or combinations of the above. 
         [0013]      FIG. 2  illustrates a cross-section of a semiconductor package  11  which is the semiconductor die assembly  10  of  FIG. 1  after the molding compound  18  is formed over the package substrate  16 . The semiconductor package  11  includes the semiconductor die  12  formed over the package substrate  16  and coupled to the package substrate  16  through wires  14 . The semiconductor die  12  is also coupled to solder balls  26 . Due to the presence of the solder balls  26 , the semiconductor package  11  in the embodiment illustrated is a ball-grid array (BGA) package. In the embodiment illustrated, the molding compound  18  includes the low filler density region  24  under the wire  14  and adjacent the semiconductor die  12  in the corner of the semiconductor package  11  that is diagonally opposite the corner where the molding compound  18  begins to flow. In the embodiment illustrated, nominal filler density regions  22  exists over the low filler density region  24  and over the corner linearly opposite the corner where the low filler density region  24  occurs. The area under the wire  14  adjacent an edge opposite the edge where the low filler density region  24  occurs may be a nominal filler density region  22 , a low filler density region  24 , or a region that has a filler density between that of the nominal filler density region  22  and the low filler density region  24 . Hence, the filler density may vary both in the x and y directions (the directions parallel to that of the semiconductor die  12 ) and the z-direction (the direction perpendicular to the semiconductor die  12 ). 
         [0014]      FIG. 3  illustrates a cross-section of a portion of the semiconductor die  12  and a portion of the molding compound  18 . The semiconductor die  12  includes an active circuit region  28  and an edge seal region  30  located between the active circuit region  28  and the edge  32  of the semiconductor die  12 . Thus, the edge seal region  30  is adjacent to the edge  32  and is closer to the edge  32  than the active circuit region  28 . The active circuit region  28  includes the active circuitry that is used for the functionality of the device. For example, the active circuit region  28  may include circuitry used for logic or memory functions. In the embodiment illustrated, the edge seal region  30  includes a moisture barrier  34 , a dicing crack stop  36  and a molding compound crack stop  38 . 
         [0015]    The moisture barrier  34  may be formed to prevent moisture from penetrating into the active circuit region  28 . The moisture barrier  34  may include metal layers  40  formed over each other and electrically coupled to each other through vias  42 . In one embodiment, the metal layers  40  include copper and the vias  42  includes copper. In another embodiment, the metal layers  40  include aluminum and the vias  42  include tungsten. Any number of metal layers  40 , such as one or more metal layers  40  may be present. In addition, any number of vias  42  (e.g., one or more vias  42 ) may be formed between pairs of metal layers  40 . The moisture barrier  34  is formed within the semiconductor die in the edge seal region  30 . In one embodiment, the moisture barrier  34  is not formed. 
         [0016]    The dicing crack stop  36  may be formed to prevent cracks created when the semiconductor die  12  is singulated (e.g., by a saw or laser) from penetrating into the active circuit region  28 . In the embodiment illustrated, the dicing crack stop  36  includes metal layers  44  over each other and electrically coupled to each other through a via  46 . In one embodiment, the metal layers  44  include copper and the via  46  includes copper. In another embodiment, the metal layers  44  include aluminum and the via  46  includes tungsten. Any number of metal layers  44 , such as one or more metal layers  44  may be present. In addition, any number of vias  46  (e.g., one or more vias  46 ) may be formed between pairs of metal layers  44 . The metal layers  44  and the via  46  are formed within the semiconductor die in the edge seal region  30 . The dicing crack stop  36  may also include a metal end cap  48  formed over the metal layers  44  to prevent the metal layer  44  from oxidizing, if the metal layer  44  is a material that would oxidize, such as copper. The metal end cap  48  may be formed over a first passivation layer  50 . The first passivation layer  50  may be formed to protect structures, within the semiconductor die  12 , such as the moisture barrier  34 . A second passivation layer  52  may be formed over the metal end cap  48  if portions of the metal end cap  48  (not shown) are used for routing. Any number of passivation layers  50  and  52  may be present. Regardless, a last passivation layer will be present. The last passivation layer is the passivation layer that does not have another passivation layer formed over it and has a portion in contact with the molding compound  18 . Hence, in the embodiment illustrated in  FIG. 3 , the last passivation layer is the second passivation layer  52  and the first passivation layer is an underlying passivation layer. If the second passivation layer  52  was not present in the embodiment illustrated in  FIG. 3 , then the first passivation layer  50  would be the last passivation layer. 
         [0017]    In the embodiment illustrated in  FIG. 3 , the molding compound crack stop  38  is formed over the dicing crack stop  36 . The molding compound crack stop  38  has a height  54  that extends above the last passivation layer  52 . In one embodiment, the height  54  is greater than approximately 5 microns. In another embodiment, the height  54  is approximately 10 microns and yet in another embodiment, the height is approximately 18 microns. In one embodiment where the height is approximately 18 microns, the molding compound crack stop  38  includes approximately 8 microns of copper under approximately 10 microns of a polymer. In one embodiment, the molding compound crack stop  38  includes a polymer. In another embodiment, the molding compound crack stop  38  includes multiple materials, such as a polymer and a metal. The molding compound crack stop  38  is formed over the last passivation layer  52  and is in contact with the molding compound  18  and the last passivation layer  52 . (The molding compound crack stop  38  may also be in contact with other layers or features. For example, as illustrated, the molding compound crack stop  38  may be in contact with the metal end cap  48 .) The material(s) chosen for the molding compound crack stop  38  preferably have good adhesion to the molding compound  18  and the last passivation layer  52 . Since metals do not have good adhesion to the molding compound  18 , at least a portion of the molding compound crack stop  38 , which is in contact with the molding compound, includes a polymer. Hence, in one embodiment the polymer material used for at least a portion of the molding compound crack stop  38  has an interface with the molding compound. In this embodiment, the interface includes direct contact between the molding compound and the polymer material. The polymer may be polyimide, benzocyclobutene (BCB), the like or combinations of the above. The metal can be any suitable metal, such as copper, aluminum, the like, or combinations of the above. In one embodiment the metal is copper formed by electroplating. 
         [0018]    With the presence of the molding compound crack stop  38  when a crack is created near the edge  32  of the semiconductor die, the molding compound crack stop  38  will direct the crack to propagate in a substantially vertical direction and prevent the crack from entering the active circuit region  28 . If the crack does not enter the active circuit region  28 , then the wire  14  will not be disconnected from the semiconductor die  12  and functionality of the semiconductor die  12  will not be lost. 
         [0019]    Although not illustrated, a glue layer may be present between the metal end cap  48  and the molding compound crack stop  38  to improve adhesion between the metal end cap  48  and the molding compound crack stop  38 . In one embodiment, the glue layer includes titanium tungsten. In another embodiment, the glue layer includes tantalum. 
         [0020]    By now it should be appreciated that there has been provided methods and structures for preventing molding compound crack from propagating into the active circuit region  28  along the interface between the surface of the semiconductor die  12  and the molding compound  18 . 
         [0021]    Because the apparatus implementing the present invention is, for the most part, composed of electronic components and circuits known to those skilled in the art, circuit details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention. 
         [0022]    Although the invention is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. For example, the molding compound crack stop  38  can be anywhere between the edge  32  of the semiconductor die  12  and the active circuit region  28 . In other words, the molding compound crack stop  38  does not need to be over the dicing crack stop  36 . Another example is that the molding compound crack stop  38  may not surround the active circuit region  28  like a ring. Instead, the molding compound crack stop  38  can be discontinuous or in any desired shape around the active circuir region  28 . Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. Any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims. 
         [0023]    The term “coupled,” as used herein, is not intended to be limited to a direct coupling or a mechanical coupling. Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements.