Abstract:
Embodiments of the present disclosure are directed to leadframes having the cantilevered extension that includes an integral support on the end of the lead nearest the die pad. A support integral to the leadframe allows the support to be built to the proper height to support the cantilevered lead in each package and reduces or eliminates the upward, downward, and side to side deflections caused or allowed by supports built-in to the tooling of the manufacturing equipment. Also, by building the support into the leadframe, the leadframes may be pretaped prior to the die attach and wire bonding steps of the manufacturing process.

Description:
BACKGROUND 
     Technical Field 
     Embodiments of the present disclosure are directed to leadframe packages and methods of manufacturing and assembling leadless packages. 
     Description of the Related Art 
     Leadless, or no lead packages are often utilized in applications in which small sized packages are desired. In general, flat leadless packages provide a chip scale or near chip-scale encapsulated package that includes a planar leadframe. Lands located on a bottom surface of the package provide electrical connection to a substrate, such as a printed circuit board (PCB). The leadless packages can be mounted directly on the surface of the PCB using surface mount technology (SMT). 
     The die in leadframe packages, and in particular quad-flat no lead packages are wire bonded to the ends of the leads in the package. The wire bonding process includes using a force and heat to apply the solder and attach a conductive wire to the lead and a semiconductor die. The leads in the quad flat no lead packages may be cantilevered and the conductive wire is bonded to the free end of the cantilevered lead. The force applied to the free end of the lead during the wire bonding process causes bending and deformation of the lead. Such bending and deformation can cause defects in the connection between the conductive wire and the lead and may lead to premature failure of leadframe packages. 
     The tooling used to manufacture leadframe packages may include an extension that supports the free end of the cantilevered lead during the wire bonding process, but due to variations in manufacturing, the extension may not properly support the cantilevered end of the lead. For example, if the support is too high, the lead may be biased upward during the wire bonding step, whereas if the support is too low, the lead may be biased downward during the wire bonding step. The extensions on the tooling also do not provide resistance to side to side forces, allowing the cantilevered leads to deform side to side, potentially causing misalignment of the lead and the conductive wire and additional defects. 
     Leadframe strips, which are composed of an array of units connected with tie bars, may be pre-taped during the manufacturing and assembly process for ease of handling and to aid in preventing encapsulant bleed out. When taped, the bottom surfaces of the leadframe strip are adhered to a tape, but, when the tooling includes extensions that support the cantilevered leads on a leadframe, the leadframe strip cannot be pre-taped because the tape interferes with the extension&#39;s ability to support the leads. Thus, when the extension is built into the tooling the leadframe strip is handled without tape until after the wire bonding step. 
     BRIEF SUMMARY 
     Embodiments of the present disclosure are directed to leadframes having cantilevered leads with that include an integral support on the end of the lead nearest a die pad. A support integral to the leadframe allows the support to be built to the correct height to support the cantilevered lead in each package and reduces or eliminates the upward, downward, and side to side deflections caused or allowed by supports built-in to the tooling of the manufacturing equipment. Also, by building the support into the leadframe, the leadframes may be pretaped prior to the die attach and wire bonding steps of the manufacturing process. 
     After the wire bonding and encapsulation steps in a leadframe package manufacturing process, the support structure may be etched away to create a cavity beneath the cantilevered end of the lead. This cavity may remain open or, in some embodiments, the cavity may be refilled or sealed. By etching away or otherwise removing the support, the lead is supported during manufacture of the package, but excess conductive material, which may cause shorting and other problems in the final device, is removed, thereby reducing or eliminating the potential for shorting electrical connections in the final package. 
     In one embodiment disclosed herein a semiconductor package includes a die pad having a die attach surface and a semiconductor die coupled to the die attach surface of the die pad. The semiconductor package may also include a plurality of leads spaced apart from at least one side of the die pad. Each of the plurality of leads has a first end and second end with lands at the second end of each of the plurality of leads. The first ends are nearer the die pad than the second ends. The leads include a cantilevered beam extending from the lands and forming the first end of the leads and has a first surface and a second surface opposite the first surface. The semiconductor package also includes encapsulation material located over the semiconductor die and a portion of the leads and a cavity formed in the encapsulation material that exposes a portion of the second surface of the leads. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a cross-sectional view of a semiconductor package in accordance with one embodiment. 
         FIG. 2  is a schematic illustration of a cross-sectional view of a semiconductor package in accordance with one embodiment. 
         FIG. 3  is a schematic illustration of a cross-sectional view of a semiconductor package in accordance with one embodiment. 
         FIG. 4A  is a schematic illustration of a cross-sectional view of a leadframe in accordance with one embodiment. 
         FIG. 4B  is an isometric view of a leads of a leadframe in accordance with one embodiment. 
         FIGS. 5A-5G  are cross-sectional views illustrating the packages of  FIGS. 1-3  being assembled at various stages of manufacture in accordance with one embodiment. 
         FIG. 6A  is a schematic illustration of a bottom view of a package being formed at the stage shown in  FIG. 5D . 
         FIG. 6B  is a schematic illustration of an isometric bottom view of the package of  FIG. 6B  with conductive bumps. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a cross-sectional view of a leadframe package  100   a  made in accordance with one embodiment of the disclosure. The leadframe package  100   a  shows a die pad  102  and two leads  107  located on opposing sides of the die pad  102 . The die pad  102  has an upper surface  103  and an opposite lower surface  105  and the leads  107  have upper surface  112  and a lower surface  108 . The lower surfaces  108  of the leads  107  may also be referred to as the lands of the package  100   a . The die pad  102  and the leads  107  are made of a conductive material, such as copper or a copper alloy. 
     The package includes a plurality of leads  107  on each side of the die pad  102 . It is to be appreciated that any number of leads may be included in the package including one lead on just one side of the die pad  102 . In some embodiments, the leads are provided on two sides or four sides of the die pad. For example, the leads may be on two parallel sides of the package or on four sides of a square or rectangular package. 
     The package  100   a  further includes a semiconductor die  104  coupled to the upper surface  103  of the die pad  102  by an adhesive material  106 . The semiconductor die  104  is any semiconductor die configured to send and/or receive electrical signals. For instance, the semiconductor die may be an integrated circuit, micro-electromechanical sensor (MEMS), and any other electronic chip. The adhesive material  106  may be any material configured to hold the semiconductor die  104  in place during the assembly process. The adhesive material  106  may be double sided tape, epoxy, glue, or any suitable material for adhering the die  104  to the upper surface  103  of the die pad  102 . 
     The semiconductor die  104  includes conductive pads  116  that are electrically connected to one or more electrical circuits formed in the semiconductor die  102 , as is well known in the art. Conductive wires  114  electrically couple the semiconductor die  104  to the leads  107 . For instance, a first end of the conductive wire  114  is coupled to a conductive pad  116  of the die  104  and a second end of the conductive wire  114  is coupled to a conductive pad  116  on the upper surface  112  of the first end of the lead  107 . 
     Encapsulation material  118  is located over the die  104 , die pad  102 , and the leads  107 , enclosing the die  104  and the conductive wires  114 . The encapsulation material  118  is also located beneath the leads  107  and the die pad  102  and forms a portion of bottom surface  111  of the package  100   a . The encapsulation material  118  may be any material configured to provide protection from environmental sources of damage, such as corrosion, physical damage, moisture damage, or other causes of damage to electrical devices. The encapsulation material  118  may be a molding compound that includes one or more of polymer, polyurethane, acrylic, epoxy resin, silicone, or any other suitable material. 
     In some embodiments, the package  100   a  includes a cavity  120  formed in the encapsulation material  118  below the end of the cantilevered portion of the lead  107 . The cavity  120  may be formed via an etching process or other material removal process in which a support  113  that extends from the lead  107  is etched away. The support is shown in more detail in  FIGS. 4A and 4B . In some embodiments, the support  113  is completely etched away such that the bottom surface  109  of a cantilevered portion  110  of the lead  107  is in a single plane. In some embodiments, the cavity  120  is formed by etching only a portion of the support  113  away such that the support  113  extends from the plane of the lower surface  109  of the cantilevered portion  110  of the lead  107 , but the support  113  does not extend to the bottom surface  111  of the package  100   a.    
       FIG. 2  shows a cross-sectional view of a leadframe package  100   b  made in accordance with one embodiment of the disclosure. The leadframe package  100   b  is similar to the leadframe package  100   a  and shows a die pad  102  and two leads  107  located on opposing sides of the die pad  102 . The die pad  102  has an upper surface  103  and an opposite lower surface  105  and the leads  107  have upper surface  112  and a lower surface  108 . 
     The package includes a plurality of leads  107  on each side of the die pad  102 . It is to be appreciated that, similar to the leadframe package  100   a , any number of leads may be included in the package including one lead  107  on just one side of the die pad  102  and that in some embodiments, the leads  107  are provided on two sides of the die pad, four sides of the die pad, or any number of sides of the die pad  102 . 
     The package  100   b  further includes a semiconductor die  104  coupled to the upper surface  103  of the die pad  102  by an adhesive material  106 . The semiconductor die  104  includes conductive pads  116  that are electrically connected to one or more electrical circuits formed in the semiconductor die  102 , as is well known in the art. Conductive wires  114  electrically couple the semiconductor die  104  to the leads  107 . 
     Encapsulation material  118  is located over the die  104 , die pad  102  and the leads  107  enclosing the die  104  and the conductive wires  114 . The encapsulation material  118  is also located between the leads  107  and the die pad  102  and forms a bottom surface  111  of the package  100   b.    
     The package  100   b  includes a cavity  120  formed in the encapsulation material  118  below the end of the cantilevered portion of the lead  107 . The cavity  120  may be formed via an etching process or other material removal process in which a support  113  that extends from the lead  107  is etched away. In some embodiments, the support  113  is completely etched away such that the bottom surface of the cantilevered portion  110  of the lead  107  is in a single plane. In some embodiments, the cavity  120  is formed by etching only a portion of the support  113  away such that the support  113  extends from the plane of the lower surface of the cantilevered portion  110  of the lead  107 , but the support  113  does not extend to the bottom surface  111  of the package  100   b.    
     In contrast to the embodiment shown in  FIG. 1 , in the embodiment shown in  FIG. 2 , the cavity  120  is backfilled to create a sealing member  122   a . The material used to fill the cavity  120  and create the sealing member  122   a  may be the same as the encapsulation material  118  and may include a molding compound that includes one or more of polymer, polyurethane, acrylic, epoxy resin, silicone, or any other suitable material. 
     Leaving the cavity  120  unfilled, for example, as shown in  FIG. 1 , is suitable for many applications, in particular, applications in which foreign object debris, corrosion and other detrimental environmental effects are minimized. In some applications, particularly those in which debris, corrosion, and other environmental effects may compromise an exposed surface of the lead, sealing the cavity, which may include backfilling, may be desirable. For example, by filling the cavity  120  with a sealing member  122   a , the formerly exposed portion of the lead  107  is sealed, thereby aiding in reducing corrosion and in preventing short-circuits that may be caused by debris or other contaminants that would otherwise enter an unsealed cavity  120 . 
     In some embodiments, for example, as shown in  FIG. 2 , the bottom surface  123  of the sealing member  122   a  may be flush with the bottom surface  111  of the package  100   b . The bottom surface  123  of the sealing member  122   a  may also be flush with the bottom surface of the lands, the bottom surface  108  of the leads. In this way, the bottom surface  111  of the package, the bottom surface  123  of the sealing member  122   a , and the bottom surface  108  of the lead  107  may form a single planar surface. 
       FIG. 3  shows a cross-sectional view of a leadframe package  100   c  made in accordance with one embodiment of the disclosure. The leadframe package  100   c  is similar to the leadframe package  100   a  and the leadframe package  100   b  and shows a die pad  102  and two leads  107  located on opposing sides of the die pad  102 . The die pad  102  has an upper surface  103  and an opposite lower surface  105  and the leads  107  have upper surface  112  and a lower surface  108 . 
     The leadframe package  100   c  includes a plurality of leads  107  on each side of the die pad  102 . It is to be appreciated that, similar to the leadframe package  100   a , any number of leads may be included in the package including one lead on just one side of the die pad  102 , and that in some embodiments, the leads are provided on two sides of the die pad, four sides of the die pad, or any number of sides of the die pad. 
     The package  100   c  further includes a semiconductor die  104  coupled to the upper surface  103  of the die pad  102  by an adhesive material  106 . The semiconductor die  104  includes conductive pads  116  that are electrically connected to one or more electrical circuits formed in the semiconductor die  102 , as is well known in the art. Conductive wires  114  electrically couple the semiconductor die  104  to the leads  107 . 
     Encapsulation material  118  is located over the die  104 , die pad  102  and the leads  107  enclosing the die  104  and the conductive wires  114 . The encapsulation material  118  is also located between the leads  107  and the die pad  102  and forms a bottom surface  111  of the package  100   c.    
     The package  100   c  includes a cavity  120  formed in the encapsulation material  118  below the end of the cantilevered portion of the lead  107 . The cavity  120  may be formed via an etching process or other material removal process in which a support  113  that extends from the lead  107  is etched away. In some embodiments, the support  113  is completely etched away such that the bottom surface of the cantilevered portion  110  of the lead  107  is in a single plane. In some embodiments, the cavity  120  is formed by etching only a portion of the support  113  away such that the support  113  extends from the plane of the lower surface of the cantilevered portion  110  of the lead  107 , but the support  113  does not extend to the bottom surface  111  of the package  100   c.    
     In contrast to the embodiment shown in  FIGS. 1 and 2 , in the embodiment shown in  FIG. 3 , the cavity  120  is backfilled to create a sealing member  122   b  with an extension  124  that extends beyond the plane of the bottom surface  111  of the package  100   c . The extension  124  of the sealing member  122   b  extends beyond the plane of the bottom surface  111 , a distance D. 
     The extension  124  aides in separating the bottom surface  111  of the package  100   c  from a surface of a substrate, such as a printed circuit board, to which the package  100   c  may be attached, for example, when the package  100   c  is integrated into an electronic device. 
     The bondline thickness of an electronic device is the thickness of the filler material, such as solder, that bonds a conductive element, such as a land, of the package with a conductive element, such as a bond pad, of the substrate to which the package is attached. The bondline thickness affects the quality and cost of the joint between the package and the substrate. If the bond line thickness of the solder or other filler material is too thick, then filler material is wasted and manufacturing costs increase, but if the bondline thickness is too thin, then the joint may be weak and susceptible to failure. For example, the joint may fail due to fatigue caused by varying magnitudes of thermal expansion between the package and the substrate due to different coefficients of thermal expansion between the two parts. Therefore, the extensions  124  set the bondline thickness D at a predictable and repeatable height that provides for adequate reliability and fatigue resistance. The extensions  124  also reduce variability in the bondline thickness from part to part and also aid in creating a reliable joint. An example of such a joint formed between the package  100   c  and a substrate  50  is shown in  FIG. 5G . 
     With reference to  FIGS. 4A and 4B , an embodiment of bare leadframe  101  will now be described.  FIG. 4A  shows a cross-section of the bare leadframe  101  and  FIG. 4B  shows an isometric view of the leads  110  of the leadframe  101 . 
       FIG. 4A  shows a cross-sectional view of a leadframe  101  made in accordance with one embodiment of the disclosure. The leadframe  101  includes a die pad  102  and two leads  107  located on opposing sides of the die pad  102 . The die pad  102  has an upper surface  103  and an opposite lower surface  105  and the leads  107  have upper surface  112  and a lower surface  108 . 
     The leads  107  include a cantilevered portion  110  that extends from the end of the lead furthest from the die pad  102  and is supported by a support structure  113  at the end nearest the die pad  102 . The cantilevered portion  110  also includes a lower surface  109  that is in a plane different from the plane of the lower surface  108  that comprises the land. 
       FIG. 4B  shows a detailed isometric view of a plurality of leads  107  that may be spaced apart from the die pad  102 . In the embodiment shown in  FIG. 4B , the support structure  113  is a continuous bar that extends along the length the leadframe  101 . The support structure  113  extends from and connects the ends of the cantilevered portions  110  of each of the plurality of leads  107 . 
     By connecting the ends of multiple leads  107  together, the support structure  113  aids in preventing deflection of the cantilevered portion  110  of the lead  107  in both up and down directions, up and down in  FIG. 4A , and in side to side directions, which is in a direction into and out of the page in  FIG. 4A . 
     In some embodiments, the leadframe  101  may have a plurality of support structures  113 . Each of the plurality of support structures  113 , may extend from and be connected to multiple leads  107 . 
     In some embodiments, a single support structure  113  may extend from a single, respective, cantilevered portion  110  of a lead  107 , such that each support structure  113  is independent from each other support structure  113 . Independent support structures do not resist side to side movement of the cantilevered portion  110  of a lead  107  in the same way that connected support structures  113  would, but such support structures may require less material etching than connected support structures  113  during the removal process described below with respect to  FIG. 5D . 
       FIGS. 5A through 5G  illustrate various stages of manufacturing of the packages  100   a ,  100   b ,  100   c  of  FIGS. 1 through 3 , in accordance with one or more embodiments disclosed herein. 
       FIG. 5A  shows the leadframe  101  and a portion of an embodiment of a method of producing a leadframe package. The leadframe  101  is a conductive material, such as metal, and in some embodiments is made of copper or a copper alloy. The leadframe  101  is formed to have a die pad  102  and leads  107 . As shown in  FIG. 5A , tape  130  is applied to the bottom surfaces  103 ,  115 ,  108  of the leadframe  101 . In some embodiments the leadframe  101  may be one of many leadframes connected together in a strip to which the tape  130  is applied. 
       FIG. 5B  another portion of an embodiment of method of producing a leadframe package. As shown in  FIG. 5B , an adhesive material  106  is applied to the top surface  103  of the die pad  102 . After application of the adhesive material  106 , a die  104  is attached to the die pad  102  of the leadframe  101 . 
     After installation of the die  104 , conductive wire  114  is attached between the die and the leads  107 . A first end of the conductive wire  114  is attached to conductive pad  116  on the die  104  and a second end of the conductive wire  114  is attached to the conductive pad  116  at the end of an adjacent lead  107 . During this process, the support structure  113  supports the cantilevered portion  110  of the lead  107  and aids in reducing or preventing deflection of the cantilevered portion  110  of the lead  107 . 
     As shown in  FIG. 5C , after installation of the conductive wire  114 , encapsulation material  118  is formed over the leadframe  101  such that the encapsulation material  118  surrounds the die  102 , the conductive wires  114 , and the upper surfaces  112  and the lower surface  109  of the leads  107 . The encapsulation material  118  may be formed on the leadframe  101  by conventional techniques, for example by a molding process, and in some embodiments is hardened during a curing step. 
     As shown in  FIG. 5D , after the encapsulation material  118  is formed over the leadframe  101 , the tape  130  may be removed from the bottom surfaces of the leadframe  101 . Also, shown in  FIG. 5D  is the removal of the support structure  113  and formation of the cavity  120 . The cavity  120  is formed using standard semiconductor processing techniques, including patterning with light sensitive materials and etching techniques. In some embodiments, for example, wherein the support structure  113  extends from and connects the cantilevered portions  110  of a plurality of leads  107 , the cavity may be an elongated trench. See for example  FIGS. 6A and 6B  illustrating a single, continuous cavity  121  in the encapsulation material  18  that exposes the first ends of the plurality the leads  107  at the second surfaces of the cantilevered beams and exposes surfaces  19  of the encapsulation material  18  to an environment outside the semiconductor package.  FIG. 6B  shows the package with conductive bumps  54 . In an embodiment wherein each lead  107  has an independent support structure  113 , multiple independent cavities  120  may be formed, each one of the multiple independent cavities being beneath a lead  107 . In some embodiments, the leadframe package  100   a  may be complete after formation of the cavities  120  and may be subsequently coupled to a substrate, such as a printed circuit board. 
     In  FIG. 5E , the cavities  120  are sealed with a sealing member  122   a  that has a bottom surface in the same plane as the bottom surface  111  of the leadframe package  100   b  and also in the same plane as the bottom surface  108 , the land, of the lead  107 . In some embodiments, the leadframe package  100   b  may be complete after formation of the cavities  120  and may be subsequently coupled to a substrate, such as a printed circuit board. 
     In  FIG. 5F , the cavities  120  are sealed with a sealing member  122   b  that includes an extension  124  that extends a distance beyond the plane of the bottom surface  111  of the leadframe package  100   c , and also a distance beyond the plane of the bottom surface  108 , the land, of the lead  107 . In some embodiments, the leadframe package  100   c  may be complete after formation of the cavities  120  and may be subsequently coupled to a substrate, such as a printed circuit board, for example, as shown in  FIG. 5G . 
     In  FIG. 5G  the leadframe package  100   c  is coupled to the substrate  50  via filler material  54 , which may be solder. The lands  108  of the leadframe package  100   c  may be coupled to the conductive pads  52  of the substrate  50  via the solder. In this way, electronic signals from the die  104  may pass through the conductive wires  114 , then through the leads  107 , the filler material  54 , and into the substrate  50 . 
     The bondline thickness of the filler material  54  may be approximately equal to the distance D, which represents the distance. The extension  124  extends beyond the plane of the bottom surface  111  of the leadframe package  100   c.    
     The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet 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.