Patent Publication Number: US-11664239-B2

Title: Lead frame for improving adhesive fillets on semiconductor die corners

Description:
BACKGROUND 
     Technical Field 
     The present disclosure is directed to a lead frame and methods for attaching a semiconductor die to the lead frame. 
     Description of the Related Art 
     A semiconductor package typically includes a semiconductor die and a lead frame. The lead frame supports the semiconductor die and carries electrical signals between the semiconductor die and an external source, such as a printed circuit board (PCB). Generally, a semiconductor die is attached to a die pad of a lead frame by dispensing adhesive on to the die pad, and then placing the semiconductor die on the adhesive. 
     In order for the semiconductor die to be securely attached to the die pad, it is important to have a sufficient amount of adhesive joining the outer edges of the semiconductor die and the die pad together. Portions of the adhesive at the outer edges of the semiconductor die are often referred to as adhesive fillets. There are a variety of factors that may affect the formation of proper adhesive fillets, such as the placement accuracy of the semiconductor die on to the adhesive, a dispense pattern of the adhesive, the placement accuracy of the dispense pattern, and the surface properties of the lead frame (e.g., wettability). Without proper adhesive fillets between the outer edges of the semiconductor die and the die pad, the adhesive may delaminate. Consequently, the semiconductor die may detach from the die pad and/or be damaged. 
     Proper adhesive fillets are particularly important at the corners of the semiconductor die. The corners of the semiconductor die are points of high stress and will often detach from the die pad. Unfortunately, good adhesive fillets at the corners of the semiconductor die are difficult to achieve. Often, the adhesive fillets at the corners of the semiconductor die are very small or non-existent. 
     BRIEF SUMMARY 
     The present disclosure is directed to a lead frame, and methods for attaching a semiconductor die to the lead frame. 
     The lead frame includes a die pad, and cavities in the die pad. The semiconductor die is attached to the lead frame by forming adhesive on the die pad and in the cavities, and then placing the semiconductor die on the adhesive. The semiconductor die is positioned on the die pad such that each of the corners of the semiconductor die directly overlies or is otherwise aligned with a respective cavity. 
     The cavities allow additional adhesive to be formed at the corners of the semiconductor die, and, thus, improve the formation of large adhesive fillets at the corners. As a result, the strength of the adhesion between the die pad and the semiconductor die is improved. In addition, the cavities provide a receptacle for the additional adhesive to prevent the additional adhesive from overflowing on to active areas (e.g., a sensor, electrical circuit, electrical component, etc.) of the semiconductor die, and possibly damaging the active areas. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawings, identical reference numbers identify similar features or elements. The size and relative positions of features in the drawings are not necessarily drawn to scale. 
         FIG.  1    is a plan view of a lead frame according to one embodiment disclosed herein. 
         FIG.  2    is a cross-sectional view of the lead frame shown in  FIG.  1    according to one embodiment disclosed herein. 
         FIG.  3    is a plan view of adhesive formed on the lead frame of  FIG.  1    according to one embodiment disclosed herein. 
         FIG.  4    is a cross-sectional view of the adhesive and the lead frame shown in  FIG.  3    according to one embodiment disclosed herein. 
         FIG.  5    is a plan view of a semiconductor die positioned on the adhesive and the lead frame of  FIG.  3    according to one embodiment disclosed herein. 
         FIG.  6    is a cross-sectional view of the semiconductor die, the adhesive, and the lead frame shown in  FIG.  5    according to one embodiment disclosed herein. 
         FIG.  7    is an angled, perspective view of the semiconductor die, the adhesive, and the lead frame shown in  FIG.  5    according to one embodiment disclosed herein. 
         FIG.  8    is an enlarged view of the circled area shown in  FIG.  7    according to one embodiment disclosed herein. 
         FIG.  9    is a plan view of adhesive formed on the lead frame of  FIG.  1    according to another embodiment disclosed herein. 
         FIG.  10    is a cross-sectional view of the adhesive and the lead frame shown in  FIG.  9    according to one embodiment disclosed herein. 
         FIG.  11    is a plan view of adhesive formed on the lead frame of  FIG.  1    using a stencil according to another embodiment disclosed herein. 
         FIG.  12    is a cross-sectional view of the adhesive, the lead frame, and the stencil shown in  FIG.  11    according to one embodiment disclosed herein. 
         FIG.  13    is a plan view of a lead frame according to another embodiment disclosed herein. 
         FIG.  14    is a cross-sectional view of the lead frame shown in  FIG.  13    according to one embodiment disclosed herein. 
         FIG.  15    is a plan view of a lead frame according to another embodiment disclosed herein. 
         FIG.  16    is a cross-sectional view of the lead frame shown in  FIG.  15    according to one embodiment disclosed herein. 
         FIG.  17    is a plan view of a semiconductor die positioned on adhesive and a lead frame according to another embodiment disclosed herein. 
         FIG.  18    is a cross-sectional view of the semiconductor die, the adhesive, and the lead frame shown in  FIG.  17    according to one embodiment disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various aspects of the disclosed subject matter. However, the disclosed subject matter may be practiced without these specific details. In some instances, well-known structures and methods of manufacturing electronic devices have not been described in detail to avoid obscuring the descriptions of other aspects of the present disclosure. 
     Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and variations thereof, such as “comprises” and “comprising,” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more aspects of the present disclosure. 
     Reference throughout the specification to integrated circuits is generally intended to include integrated circuit components built on semiconducting or glass substrates, whether or not the components are coupled together into a circuit or able to be interconnected. Throughout the specification, the term “layer” is used in its broadest sense to include a thin film, a cap, or the like, and one layer may be composed of multiple sub-layers. 
     It is noted that the dimensions set forth herein are provided as examples. Other dimensions are envisioned for this embodiment and all other embodiments of this application. 
     Current methods to improve the formation of adhesive fillets at the corners of the semiconductor die typically include dispensing a larger amount of adhesive on the die pad where the corners of the semiconductor die are positioned. However, such methods that simply increase the amount of adhesive are generally incompatible with semiconductor dice with exposed active areas (e.g., a sensor, electrical circuit, electrical component, etc.). When increasing the amount of adhesive at the corners of the semiconductor die, the adhesive will often overflow on to the active areas of the semiconductor die and cause the semiconductor die to malfunction. For example, the adhesive will often overflow from the die pad, along the side surfaces of the semiconductor die, and on to the active areas in an upper surface (i.e., the surface facing away from the die pad of the lead frame) of the semiconductor die. This problem is particularly common for thin semiconductor dice, as the additional adhesive may easily overflow on to the upper surface of the semiconductor die. 
     The present disclosure is directed to a lead frame and methods for attaching a semiconductor die to the lead frame. The lead frame includes a die pad with cavities that are positioned at the corners of the semiconductor die. The cavities allow for additional adhesive to be formed on the die pad at the corners of the semiconductor die, and prevent the additional adhesive from overflowing on to active areas of the semiconductor die. As a result, large adhesive fillets may be formed at the corners of the semiconductor die, and the adhesion between the semiconductor die and the lead frame is improved. 
       FIGS.  1  and  2   ,  FIGS.  2  and  3   , and  FIGS.  5  and  6    are subsequent stages of a die attach process for attaching a semiconductor die to a lead frame according to one embodiment disclosed herein. 
       FIG.  1    is a plan view of a lead frame  10  according to one embodiment disclosed herein.  FIG.  2    is a cross-sectional view of the lead frame  10  along a line  2 - 2  shown in  FIG.  1    according to one embodiment disclosed herein. It is beneficial to review  FIGS.  1  and  2    together. 
     The lead frame  10  provides a platform for a semiconductor die  11 ; and carries electrical signals between the semiconductor die  11  and an external source, such as a printed circuit board (PCB). The attachment of the semiconductor die  11  to the lead frame  10  will be discussed in further detail with respect to  FIGS.  5  and  6   . 
     The lead frame  10  includes a plurality of supports or tie bars  12 , a plurality of leads  14 , and a die pad  16 . The lead frame  10 , including the supports  12 , the leads  14 , and the die pad  16 , may be made of any type of conductive material. For example, the lead frame  10  may be made of steel, aluminum, copper, gold, or another type of conductive material. The lead frame  10  may be fabricated using standard fabrication techniques known or later developed. For example, the lead frame  10  may be formed by pattern deposition, a combination of blanket deposition and etching, or stamping a continuous conductive or metal sheet. 
     The supports  12  are coupled to and extend from corners of the die pad  16 . The supports  12  are used to mount the die pad  16  to a substrate, such as a semiconductor substrate or a PCB. In one embodiment, the supports  12  and the die pad  16  are a single, contiguous piece. 
     The leads  14  surround the die pad  16 . For example, as shown in  FIG.  1   , the leads  14  are positioned on each of the four sides of the die pad  16 . The leads  14  are used to carry electrical signals between the semiconductor die  11 , specifically an integrated circuit within the semiconductor diel  1 , and an external source, such as a PCB. In one embodiment, the leads  14  are electrically coupled to the semiconductor die  11  by bonding wires that extend between the semiconductor die  11  and the leads  14 . 
     It is noted that, although four leads are shown on each of the four sides of the die pad  16 , the lead frame  10  may include any number of leads. Further, the leads may be arranged in a variety of different patterns. For example, the lead frame  10  may include 10, 20, or 30 leads on a single side, two sides, or three sides of the die pad  16 . 
     The die pad  16  provides a platform for the semiconductor die  11 . The die pad  16  includes cavities  18  or dimples that extend in to a surface  20  of the die pad  16 . In one embodiment, the surface  20  of the die pad  16  is continuous except for the cavities  18  in the surface  20 . Stated differently, the die pad  16  is planar except for the cavities  18 . As best shown in  FIG.  2   , the cavities  18  extend partially in to the die pad  16 , and do not extend all the way through the die pad  16 . As will be discussed in further detail with respect to  FIGS.  5  and  6   , the cavities  18  ensure that there is a sufficient amount of adhesive dispensed at the corners of the semiconductor die  11 , and that the adhesive does not overflow on to active areas of the semiconductor die  11 . 
     In one embodiment, the cavities  18  are positioned to correspond with corners (i.e., where two adjacent sides of the semiconductor die  11  meet) of the semiconductor die  11 , which will be mounted on the surface  20  of the die pad  16 . For example, the dashed box  22  indicates a position of the semiconductor die  11  on the surface  20 . As the semiconductor die  11 , in this example, is rectangular in shape, each side of the semiconductor die  11  is positioned between and aligned with two of the cavities  18 , and a respective cavity of the cavities  18  is positioned to directly underlie each of the four corners  24  of the semiconductor die  11 . Stated differently, the semiconductor die  11  is positioned such that each of the corners  24  extends past an edge of the surface  20  of the die pad  16 , and overhangs above the cavities  18 . The position and attaching of the semiconductor die  11  to the die pad  16  will be discussed in further detail with respect to  FIGS.  5  and  6   . 
     In one embodiment, as shown in  FIGS.  1  and  2   , each of cavities  18  is rounded, such that the plan view of the cavities  18  shown in  FIG.  1    are circular. However, other shapes are possible. For example, each of the cavities  18  may have an oval shape or an “L” shape from a plan view. The oval shaped and “L” shaped cavities will be discussed in further detail with respect to  FIGS.  13  and  16   . 
     The semiconductor die  11  is mounted to the surface  20  of the die pad  16  by forming a layer of adhesive on the surface  20 , and placing the semiconductor die  11  on the adhesive.  FIG.  3    is a plan view of adhesive or die attach material  26  formed on the lead frame  10  according to one embodiment disclosed herein.  FIG.  4    is a cross-sectional view of the adhesive  26  and the lead frame  10  along a line  4 - 4  shown in  FIG.  3    according to one embodiment disclosed herein. It is beneficial to review  FIGS.  3  and  4    together. It is noted that the cross section shown in  FIG.  4    shows portions of the adhesive  26  that are positioned a distance from the line  4 - 4  of  FIG.  3   , such as a center  27  of the adhesive  26 . 
     The adhesive  26  is formed on the surface  20  and in the cavities  18  of the die pad  16 . The adhesive  26  may be any type of adhesive material. In one embodiment, the adhesive  26  is epoxy. 
     The adhesive  26  may formed on the surface  20  in a variety of patterns. In one embodiment, as shown in  FIG.  3   , the adhesive  26  is formed on the surface  20  in a cross or “X” shaped pattern. Namely, the adhesive  26  extends between two of the cavities  18  that are diagonal from each other. The cross or “X” shaped pattern ensures that there is sufficient adhesive between the critical areas of the semiconductor die  11  and the die pad  16 . Namely, the cross or “X” shaped pattern ensures that there is sufficient adhesive between the corners  24  and a center of the semiconductor die  11 , and the die pad  16 . Other adhesive patterns are also possible. For example, as will be discussed in further detail with respect to  FIGS.  9  and  10   , the adhesive  26  may be formed in each of the cavities  18  with a smaller cross or “X” shaped pattern that is surrounded by and spaced from the cavities  18 . 
     In one embodiment, the adhesive  26  overfills the cavities  18  such that the adhesive  26  fills cavities  18 , overflows out of the cavities  18 , and extends past (i.e., above) the surface  20 . As will be discussed in further detail with respect to  FIGS.  5  and  6   , the adhesive  26  is overfilled to ensure that a sufficient amount of adhesive is dispensed at the corners of the semiconductor die  11 , and that the adhesive  26  does not overflow on to active areas of the semiconductor die  11 . 
     In one embodiment, the cavities  18  are filled with the adhesive  26  such that the portions of the adhesive  26  that overflow out of the cavities  18  and extend past (i.e., above) the surface  20  have substantially the same thickness as portions of the adhesive  26  that are on the surface  20  (e.g., the center  27  of the adhesive  26 ). For example, as shown in  FIG.  4   , portions  25  of the adhesive  26  that directly overlie the cavities  18  and are above the surface  20  have a thickness  28 . Said differently, the adhesive at cavities  18  has a first thickness in the cavity, between the surface  20  and a bottom of the cavity, and a second thickness  28  from the surface  20  to a top or outermost surface of the adhesive. Portions of the adhesive  26  that are on the surface  20  (e.g., the center  27  of the adhesive  26 ) have a thickness  30  that is substantially equal to the thickness  28 . As will be discussed in further detail with respect to  FIGS.  5  and  6   , the substantially uniform thickness of the adhesive  26  allows the adhesive  26  to be evenly formed between the semiconductor die  11  and the surface  20  of the die pad  16 . 
     In one embodiment, the adhesive  26  is formed on the surface  20  with an adhesive dispenser  23 . The adhesive dispenser  23  scans across the surface  20  and dispenses the adhesive  26  on to the surface  20  and in to the cavities  18 . To overfill the cavities  18  as discussed above, the adhesive dispenser  23  is delayed when the adhesive dispenser  23  directly overlies the cavities  18 . Namely, when the adhesive dispenser  23  directly overlies the surface  20  (e.g., the center  27  of the adhesive  26 ), the adhesive dispenser  23  is held in the same position for a first time period before moving on, to ensure that the adhesive  26  has the thickness  30 . When the adhesive dispenser  23  directly overlies the cavities  18  as shown, for example, in  FIG.  4   , the adhesive dispenser  23  is held above the cavities  18  for a second time period, which is greater than the first time period. Delaying the adhesive dispenser  23  over the cavities  18  ensures that the adhesive  26  fills the cavities  18  and has the thickness  28  above the cavities  18 . 
     Once the adhesive  26  is formed on the surface  20  of the die pad  16 , the semiconductor die  11  is placed on the adhesive  26  to attach the semiconductor die  11  to the die pad  16 .  FIG.  5    is a plan view of the semiconductor die  11  positioned on the adhesive  26  and the lead frame  10  according to one embodiment disclosed herein.  FIG.  6    is a cross-sectional view of the semiconductor die  11 , the adhesive  26 , and the lead frame  10  along a line  6 - 6  shown in  FIG.  5    according to one embodiment disclosed herein. It is noted that, in  FIG.  6   , the portion of the adhesive  26  that is formed between the cavities  18  and on the side surface of the semiconductor die  11  is removed to show the adhesive between the semiconductor die  11  and the surface  20 .  FIG.  7    is an angled, perspective view of the semiconductor die  11 , the adhesive  26 , and the lead frame  10  according to one embodiment disclosed herein.  FIG.  8    is an enlarged view of the circled area shown in  FIG.  7    according to one embodiment disclosed herein. It is beneficial to review  FIGS.  5  to  8    together. The semiconductor die  11 , the adhesive  26 , and the lead frame  10  together may be considered to be a semiconductor package. 
     The semiconductor die  11  is attached to the die pad  16  by positioning the semiconductor die  11  on the adhesive  26 . The semiconductor die  11  may be placed on the adhesive  26  using standard die attach processing techniques known or later developed. For example, the semiconductor die  11  may be placed on the adhesive  26  using a pick-and-place tool. 
     In one embodiment, the semiconductor die  11  is positioned on the die pad  16  such that each of the corners  24  of the semiconductor die  11  directly overlies a respective cavity of the cavities  18 . Stated differently, each of the corners  24  extends past an edge of the surface  20  of the die pad  16 , and overhangs above the cavities  18 . For example, as shown in  FIGS.  5  and  6   , since the semiconductor die  11  is rectangular in shape, the four corners  24  of the semiconductor die  11  are aligned with each of the four cavities  18 . In one embodiment, each of the corners  24  of the semiconductor die  11  is positioned at or near a center of a respective cavity of the cavities  18 . 
     In one embodiment, the semiconductor die  11  includes a plurality of active areas  32 . Each of the active areas  32  may be a sensor, an electrical circuit, a processor, an electrical component, or any other type of electronic device. In one embodiment, as shown in  FIG.  5   , the active areas  32  are formed in a surface  34  of the semiconductor die  11 . 
     In one embodiment, when the semiconductor die  11  is placed on the adhesive  26  as shown in  FIG.  3   , a downward pressure (i.e., a pressure with a direction towards the surface  20  of the die pad  16 ) is applied to the semiconductor die  11  such that the adhesive  26  spreads between a surface  29  of the semiconductor die  11  and the surface  20  of the die pad  16 . As discussed with respect to  FIG.  4   , the portions of the adhesive  26  that overflow out of the cavities  18  and extend past (i.e., above) the surface  20  have substantially the same thickness as portions of the adhesive  26  that are on the surface  20  (e.g., the center  27  of the adhesive  26 ). The substantially uniform thickness of the adhesive  26  allows the adhesive  26  to be spread evenly between the surface  29  of the semiconductor die and the surface  20  of the die pad  16  when the downward pressure is applied. In one embodiment, as best shown in  FIG.  8   , the adhesive  26  also spreads along side surfaces  31  of the semiconductor die  11  to form adhesive fillets along the edges, including the corners  24 , of the semiconductor die  11 . The spreading of the adhesive  26  and the forming the adhesive fillets provide a strong adhesion between the die pad  16  and the semiconductor die  11 . It is noted the adhesive  26  may not always spread along the side surfaces  31 . In some cases, the adhesive  26  may spread to form adhesive fillets at the corners  24  without forming adhesive fillets along one or more of the side surfaces  31 . 
     As previously discussed, current methods to improve the formation of adhesive fillets at the corners of the semiconductor die typically include dispensing a larger amount of adhesive on the die pad where the corners of the semiconductor die are positioned. However, such methods are generally incompatible with semiconductor packages, particularly thin semiconductor packages, with exposed active areas, as the additional adhesive will often overflow on to active areas of the semiconductor die. The cavities  18  allow additional adhesive to be formed at the corners  24  of the semiconductor die  11 . The additional adhesive improves the formation of large adhesive fillets  36  at the corners  24 . Stated differently, as best shown in  FIG.  8   , the additional adhesive ensures that the adhesive  26  is formed at and on the corners  24 , and the adhesive  26  extends away from the semiconductor die  11 . As a result, the strength of the adhesion between the die pad  16  and the semiconductor die  11  is improved. In addition, the cavities  18  provide a receptacle for the additional adhesive to prevent the additional adhesive from overflowing on the active areas  32  of the semiconductor die  11 . Namely, the additional adhesive will flow in to the cavities  18  rather than overflow on to the surface  34  of the semiconductor die  11 . As a result, the additional adhesive is prevented from contaminating the active areas  32  and causing the active areas  32  to malfunction. 
     Once the semiconductor die  11  is attached to the die pad  16 , the semiconductor die  11  is electrically coupled to the leads  14 . In one embodiment, the semiconductor die  11  is electrically coupled to the leads  14  via a plurality of bond wires, with each of the bond wires extending from the semiconductor die  11  to a respective lead. 
     As discussed with respect to  FIG.  3   , in one embodiment, the adhesive  26  is formed on the surface  20  of the die pad  16  in a cross or “X” shaped pattern. However, other adhesive patterns are possible.  FIG.  9    is a plan view of an adhesive  42  formed on the lead frame  10  according to another embodiment disclosed herein.  FIG.  10    is a cross-sectional view of the adhesive  42  and the lead frame  10  along a line  10 - 10  shown in  FIG.  9    according to one embodiment disclosed herein. It is noted that the cross section shown in  FIG.  10    shows portions of the adhesive  42  that are positioned a distance from the line  10 - 10 , such as the center  44  of the adhesive  42 . 
     Similar to the adhesive  26 , the adhesive  42  is formed on the surface  20  and in the cavities  18  of the die pad  16 . However, in contrast to the adhesive pattern shown in  FIG.  3   , the cross or “X” shaped portion of the adhesive  42  is spaced from the cavities  18  by a distance  38 . 
     The space between the cross or “X” shaped portion of the adhesive  26  and the cavities  18  decreases the total amount of adhesive formed on the die pad  16 . As such, the adhesive pattern shown in  FIGS.  11  and  12    is suitable for adhesives with low viscosity. Generally, adhesives with low viscosity are easily spreadable compared to adhesive with high viscosity, and, thus, less adhesive may be used to adhere the semiconductor die  11  to the die pad  16 . In addition, using less adhesive decreases fabrication costs. 
     The space between the cross or “X” shaped portion of the adhesive  42  and the cavities  18  also further decreases the risk of the adhesive  42  at the corners  24  of the semiconductor die  11  (i.e., the adhesive formed in the cavities  18 ) overflowing on to the active areas  32  of the semiconductor die  11 . 
     In one embodiment, similar to the adhesive  26 , the adhesive  42  overfills the cavities  18  such that the adhesive  42  fills cavities  18 , overflows out of the cavities  18 , and extends past (i.e., above) the surface  20 . In addition, in one embodiment, the cavities  18  are filled with the adhesive  42  such that the portions of the adhesive  42  that overflow out of the cavities  18  and extend past (i.e., above) the surface  20  have substantially the same thickness as portions of the adhesive  42  that are on the surface  20  (e.g., the center  44  of the adhesive  42 ). 
       FIG.  9    illustrates an embodiment where there are cavities  18  in the lead frame with a first portion of adhesive in the cavities and a second portion of adhesive in an area defined by the cavities. Various patterns are envisioned for the second portion of the adhesive. In one embodiment, the first portion has a first thickness that is greater than a second thickness of the second portion. The first portions are spaced from the second portions by a distance. 
     As discussed with respect to  FIG.  4   , in one embodiment, adhesive is formed on the surface  20  of the die pad  16  with an adhesive dispenser  23 . In another embodiment, adhesive (e.g., the adhesive  26  and the adhesive  42 ) is formed on the surface  20  using a stencil.  FIG.  11    is a plan view of the adhesive  42  formed on the lead frame  10  using a stencil  40  according to another embodiment disclosed herein.  FIG.  12    is a cross-sectional view of the adhesive  42 , the lead frame  10 , and the stencil  40  along a line  12 - 12  shown in  FIG.  11    according to one embodiment disclosed herein. It is noted that the cross section shown in  FIG.  12    shows portions of the adhesive  42  that are positioned a distance from the line  10 - 10 , such as the center  44  of the adhesive  42 . 
     The stencil  40  includes apertures that are arranged in the same pattern as the adhesive  42 . Namely, the stencil  40  includes four circular apertures  46  that have the same diameter as the cavities  18 , and a cross or “X” shaped aperture  48  between the circular apertures  46 . 
     The stencil  40  is overlaid above the surface  20  of the die pad  16  with the four circular apertures  46  being aligned with the cavities  18 . For example, as shown in  FIG.  12   , the stencil  40  is positioned above the surface  20  such that the circular apertures  46  directly overlie the cavities  18 . 
     Once the stencil  40  is overlaid above the surface  20  of the die pad  16 , the adhesive  42  is dispensed by spreading the glue through the stencil  40 . Namely, the adhesive  42  is dispensed from a first side  50  of the stencil  40 , through the circular apertures  46  and the cross or “X” shaped aperture  48 , to a second side  52  of the stencil  40 , and on to the surface  20 , where the adhesive  42  is formed in the pattern as shown in  FIG.  9   . 
     Although the stencil  40  is discussed with respect to forming the adhesive  42 , a stencil may also be used to form the adhesive  26  shown in  FIGS.  3  and  4   . 
     As discussed with respect to  FIGS.  1  and  2   , in one embodiment, each of the cavities  18  is circular. However, larger cavities with different shapes are also possible. 
       FIG.  13    is a plan view of a lead frame  54  according to another embodiment disclosed herein.  FIG.  14    is a cross-sectional view of the lead frame  54  along a line  14 - 14  shown in  FIG.  13    according to one embodiment disclosed herein. It is beneficial to review  FIGS.  13  and  14    together. 
     Similar to the lead frame  10 , the lead frame  54  includes a plurality of supports  56 , a plurality of leads  58 , and a die pad  60 . However, the sizes of cavities  62  in the die pad  60  are larger than the cavities  18 , and the plan view of the cavities  62  shown in  FIG.  13    are oval. In one embodiment, as shown in  FIG.  13   , each of the cavities  62  extends lengthwise towards a center of the die pad  60 . 
     The cavities  62  allow an increased amount of adhesive to be formed in the cavities  62  and at the corners  24  of the semiconductor die  11 . The additional adhesive improves the formation of adhesive fillets at the corners  24  and, thus, increases the strength of the adhesion between the die pad  60  and the semiconductor die  11 . In one embodiment, each corner of the die is aligned within a wider portion of the oval, closer to a center point of the oval than a boundary of the oval. 
       FIG.  15    is a plan view of a lead frame  64  according to another embodiment disclosed herein.  FIG.  16    is a cross-sectional view of the lead frame  64  along a line  16 - 16  shown in  FIG.  15    according to one embodiment disclosed herein. It is beneficial to review  FIGS.  15  and  16    together. 
     Similar to the lead frame  10 , the lead frame  64  includes a plurality of supports  66 , a plurality of leads  68 , and a die pad  70 . However, the sizes of cavities  72  in the die pad  70  are larger than the cavities  18 , and the plan view of the cavities  72  shown in  FIG.  15    are “L” shaped. In one embodiment, as shown in  FIG.  15   , each of the cavities  72  includes a first portion that extends along a first side of the die pad  70 , and a second portion that extends along a second side, which is adjacent to the first side, of the die pad  70 . 
     Similar to the cavities  62  shown in  FIGS.  13  and  14   , the cavities  72  allow an increased amount of adhesive to be formed in the cavities  72  and at the corners  24  of the semiconductor die  11 . The additional adhesive improves the formation of large adhesive fillets at the corners  24  and, thus, increases the strength of the adhesion between the die pad  70  and the semiconductor die  11 . 
     The alternative embodiment in  FIG.  15    can be formed with a different type of etch or removal technique in that instead of curved or rounded edges, the edges may be more rectangular. While illustrated as L-shaped, these rectangular cavities may have a variety of shapes. Each cavity has a volume, and the edge of the die is aligned within each volume. Each cavity has edges or walls and the edges of the die are positioned within the edges or walls of the cavity. 
     The lead frames shown in  FIGS.  1  to  16    are shown with a downset configuration. Namely, the supports  12  and the leads  14  are multi-level (i.e., each include a first portion, and a second portion higher than the first portion) to raise the die pad. In these embodiments, the entire die pad will be encapsulated by a molding compound when packaged, and at least one surface of the leads will be left exposed. For example, referring to  FIG.  6   , both the upper surface  20  and the lower surface (i.e., the surface opposite to the surface  20 ) of the die pad  16  will be covered with a molding compound, and the leads  14  will be left exposed. However, a die pad with cavities as discussed with respect to  FIGS.  1  to  16    may be used in conjunction with other types of lead frame packages. For example, the die pad  16  with the cavities  18  shown in  FIGS.  5  and  6    may be used in leadless semiconductor packages. 
       FIG.  17    is a plan view of the semiconductor die  11  positioned on adhesive  26  and a lead frame  74  according to another embodiment disclosed herein.  FIG.  18    is a cross-sectional view of the semiconductor die  11 , the adhesive  26 , and the lead frame  74  shown in  FIG.  17    according to one embodiment disclosed herein. In contrast to the lead frame  10 , the lead frame  74  is used in, for example, a quad-flat no-leads (QFN) package. 
     Similar to the lead frame  10 , the lead frame  74  includes a plurality of leads  76  and a die pad  78 , and the die pad  78  includes cavities  80 . The die pad  78  and the cavities  80  are substantially similar to the die pad  16  and the cavities  18 . However, in contrast to the lead frame  10 , the lead frame  74  does not have a downset configuration. Namely, the lead frame  74  does not include supports or tie bars attached to the die pad  78 , and the leads  76  are not multi-level (i.e., the leads  76  are planar). In this embodiment, upper surfaces of the die pad  78  and the leads  76  will be encapsulated by a molding compound when packaged, and lower surfaces of the die pad  78  and the leads  76  will be left exposed. For example, referring to  FIG.  18   , surfaces  81  of the leads  76  and a surface  83  of the die pad  78  will be covered with a molding compound, and surfaces  84  of the leads and a surface  82  of the die pad  78  will be left exposed. 
     The various embodiments provide a lead frame including a die pad with cavities, and methods for attaching a semiconductor die to the lead frame. The cavities are positioned at the corners of the semiconductor die, and allow additional adhesive to be formed at the corners of the semiconductor die. As a result of the additional adhesive, large adhesive fillets are formed at the corners of the semiconductor die, and the adhesion between the semiconductor die and the lead frame is improved. Further, the cavities prevent the additional adhesive from overflowing on to active areas of the semiconductor die. 
     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.