Abstract:
Embodiments of the present disclosure are directed to a leadframe packages that include a leadframe having a surface that is selectively treated with chemicals that reduce the wettability of the surface and thereby reduce adhesive flow on the surface and methods of forming a packing comprising same. In one embodiment there is provided a leadframe having an upper surface that includes a first portion that is treated with an anti-epoxy bleed out chemical and a second portion that was not treated with the anti-epoxy bleed out chemical. A semiconductor die is attached to the upper surface of the leadframe at the second portion via an epoxy adhesive.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    Embodiments of the present disclosure are directed to leadframe packages and methods of making same. 
         [0003]    2. Description of the Related Art 
         [0004]    Leadframe packages are widely used in the semiconductor industry and, in general, provide low cost solutions with relatively straight forward assembly processing. However, there remains various obstacles for maintaining suitable adhesion between various materials within leadframe packages. 
         [0005]    Generally described, leadframes have a roughened upper surface in order to increase the adhesion with adhesive materials and encapsulation material that may be provided over the leadframes during assembly processing. For instance, when adhesive materials, such as epoxy glue, are used to adhere a semiconductor die to the upper surface the leadframe, the roughened surface of the leadframe increases the adhesion strength with the glue. 
         [0006]    Unfortunately, however, the roughened surface of the leadframes also increases the wettability of the surface. That is, the glue flows or bleeds on the roughened surface of the leadframe due to capillary effects caused by the roughened surface. In particular,  FIG. 1A  shows a die  12  attached to an upper surface  14  of a die pad  16  of a leadframe  18  by epoxy glue  20  that flowed outwardly due to capillary effects. The flow of the epoxy glue  20  is often referred to as epoxy bleed out (EBO). As a result of the EBO, the epoxy glue  20  has a larger footprint on the upper surface  14  of the die pad  16  than the die  12 . During subsequent packaging, encapsulation material  22  is placed over the die  12  and portions of the leadframe  18  to form a package  24  as shown in  FIG. 1B . The encapsulation material  22  typically has poor adhesion with the epoxy glue  20 . In that regard, delamination may occur between the encapsulation material  22  and the epoxy glue  20 , as shown by the jagged line  26  in  FIG. 1B . 
         [0007]      FIG. 2  illustrates another package  30  that involves a prior solution for preventing delamination between the encapsulation material  22  and the epoxy glue  20 . In particular, the package  30  includes a leadframe, including the die pad  16  and the leads  18 , that has been treated with an anti-wetting agent known to prevent EBO. Generally described, the process involves immersing an entire leadframe strip in a tank filled with the anti-wetting agent. After immersion, the treated leadframe strip is used for packaging a plurality of semiconductor devices and is then typically diced to form individual packages. 
         [0008]    Unfortunately, however, the leadframes that have been treated with the anti-wetting agent can have other delamination issues. In particular, delamination may occur between the upper surface  14  of the die pad  16  of the leadframe  32  and the epoxy glue  20  securing the die  12  to the die pad  16  as shown by the jagged line  34  in  FIG. 2 . 
       BRIEF SUMMARY 
       [0009]    Embodiments of the present disclosure are directed to packages that include a leadframe having a surface that is selectively treated with an anti-wetting agent and methods of forming a packing comprising same. In one embodiment there is provided a die pad of a leadframe having an upper surface that includes a first portion that has been treated with an anti-wetting agent and a second portion located within the first portion. The second portion has not been treated with the anti-wetting agent. A semiconductor die is attached to the upper surface of the leadframe at the second portion. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]      FIG. 1A  is a plan view of a package without encapsulation material in accordance with the prior art. 
           [0011]      FIG. 1B  is a cross-sectional view of the package of  FIG. 1A  along line A-A and with encapsulation material in accordance with the prior art. 
           [0012]      FIG. 2  is a cross-sectional view of another package in accordance with the prior art. 
           [0013]      FIG. 3A  is a plan view of a package without encapsulation material in accordance with one embodiment of the disclosure. 
           [0014]      FIG. 3B  is a cross-sectional view of the package in  FIG. 3A  along line B-B with encapsulation material. 
           [0015]      FIG. 4  is a plan view of another package without encapsulation material in accordance with another embodiment of the disclosure. 
           [0016]      FIGS. 5A and 5B  illustrate a method for selectively treating a leadframe in accordance with one embodiment of the disclosure. 
           [0017]      FIG. 6  illustrates another method for selectively treating a leadframe in accordance with another embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 3A  shows a plan view of a partial package  40  in accordance with one embodiment of the disclosure. The package  40  is partial because it does not include encapsulation material. In contrast,  FIG. 3B  shows a cross-sectional view of the package  40 , with encapsulation material  22 . 
         [0019]    The package  40  includes a semiconductor die  12  that includes an electrical device, such as a sensor, an electromechanical sensor (MEMS), an integrated circuit, or any other electrical device, located on an upper surface  14  of a die pad  16  of a leadframe  42 . The leadframe  42  also includes one or more leads  44  located proximate at least one side of the die pad  16 . In the illustrated embodiment, leads  44  surround all four sides of the die pad  16 . It is to be appreciated, however, that one or more leads  44  may be located on any number of sides of the die pad  16 , including only on one side of the die pad  16 . 
         [0020]    The leadframe  42  is a conductive material, and may be a metal material, such as copper. In some embodiments, one or more surfaces of the leadframe  42 , such as the die pad  16  and the leads  44 , are plated with a nanolayer or microlayer of metal materials, such as Ag, Ni/Pd, Ni/Pd/Ag, Ni/Pd/Au—Ag alloy, or Ni/Pd/Au/Ag, to protect the leadframe  42 , such as from corrosion and oxidation. 
         [0021]    Generally described, the leadframe  42  has a roughened upper surface to increase the adhesive properties of the material. For example, in the embodiment in which the leadframe  42  is plated with Ag, the Ag layer may be treated. In the embodiments in which the leadframe  42  is plated with one of NiPd, NiPd Au—Ag alloy and NiPdAuAg, the Ni layer may be roughened. 
         [0022]    Conductive wires  46  electrically couple the die  12  to respective leads  44 , which provides electrical connection outside of the package  40 . As discussed above and shown in  FIG. 3B , encapsulation material  22  surrounds the die  12 , portions of the die pad  16 , and portions of the leads  44  to provide protection from environmental sources of damage, such as corrosion, physical damage, moisture damage, or other causes of damage to electrical devices. 
         [0023]    The die  12  is secured to the upper surface  14  of the die pad  16  by a flowable adhesive material  48 , such as glue, paste, solder, or any other flowable adhesive. In one embodiment, the adhesive material  48  is an epoxy glue and may include resin and a filler material. 
         [0024]    The upper surface  14  of the die pad  16  is selectively treated with the anti-wetting agent to reduce adhesive bleed out described above, while at the same time maintaining properties for suitable adhesive strength with the adhesive material  48  and the encapsulation material  22 . In particular, a first portion  50  of upper surface  14  of the die pad  16  has been treated with an anti-wetting agent, while second and third portions  52   a,    52   b  of the leadframe remain untreated. In the illustrated embodiment, the first portion  50  that has been treated with the anti-wetting agent has a first side located outwardly of both the die  12  and the adhesive material  48  and a second side that is spaced apart from an outer edge of the die pad  16 . The treated first portion  50  prevents the adhesive material  48  from flowing over the upper surface  14  of the die pad  16  as described above in relation to  FIG. 1A . In that regard, the adhesive material  48  has a foot print that substantially the same size as the die  12 . 
         [0025]    Various types of anti-wetting agents for reducing adhesive bleed out are commercially available. One examples is referred to as Anti EBO T13, which is a neutral pH, sold by Atotech. 
         [0026]    As indicated above, the remaining portions that have not been treated with the anti-wetting agent include the second portion  52   a  located under the die  12  and a third portion  52   b  located at the outer perimeter of the die pad  16 . In one embodiment, the second portion  52   a  is substantially the same size and shape of the die  12  or slightly larger than the die  12 . In one embodiment, the second portion  52   a  has an area that is less than 5% larger than the area of the die  12 . The untreated second portion  52   a  of upper surface  14  of the die pad  16  provides suitable adhesion properties with the adhesive material  48 . In that regard, the untreated second portion  52   a  eliminates or reduces delamination issues between the die  12  and the die pad  16  discussed above in reference to  FIG. 2 . That is, selective treatment of upper surface  14  of the die pad  16  of the leadframe  42  eliminates or at least reduces the various delamination issues discussed above. 
         [0027]      FIG. 4  shows another plan view of a package  40   a  without encapsulation material in accordance with another embodiment of the disclosure. The package  40   a  of  FIG. 4  is substantially identical to the package  40  of  FIG. 3  except that the package  40   a  of  FIG. 4  includes leads  18  proximate two sides of the die pad  16 , rather than the four sides of the package  40  of  FIG. 3 . As indicated above, one or more leads  18  may be located proximate to any number of sides of the die pad  16  including one side. 
         [0028]      FIGS. 5A and 5B  illustrate a method  41  for selectively treating the upper surface  14  of the die pad  16  of the leadframe  42  in accordance with one embodiment of the present disclosure. In particular,  FIGS. 5A and 5B  illustrate depositing the anti-wetting agent on the first portion of the upper surface of the die pad using a stamping method. The stamping method involves a stamping device  60 , shown here in cross section, having a stamping end  62  that has a shape that corresponds to the first portion  50  of the die pad  16  of the leadframe  42  to be treated with the anti-wetting agent. The stamping end  62  is dipped in a tank  64  filled with the anti-wetting agent  66  and is then placed on the upper surface  14  of the die pad  16 , thereby treating the first portion  50  of the die pad  16 . Although  FIG. 5B  only shows a die pad  16  of a leadframe, it is to be appreciated, however, that the die pad  16  is part of a leadframe strip that includes a plurality of die pads and a plurality of leads that are connected by tie bars. 
         [0029]    In another embodiment, the anti-wetting agent  66  may also be applied by conventional printing techniques. For instance, the anti-wetting agent  66  may be applied by screen-printing, in which the anti-wetting may be applied to the die pad by pressing the anti-wetting agent through holes in a screen. 
         [0030]      FIG. 6  illustrates another method  70  for selectively treating the upper surface  14  of the die pad  16  of the leadframe  42  in accordance with another embodiment of the present disclosure. In particular,  FIG. 6  illustrates a method  70  of dispensing the anti-wetting agent  66  on the die pad  16  of the leadframe  42 , such as by using a liquid dispensing device  72 . In particular, the liquid dispensing device  72  may be configured to move relative to the upper surface  14  of the die pad  16  of the leadframe  42  (or vice-versa) and dispense the anti-wetting agent  66  at the first portion  50 , while not dispensing the anti-wetting agent  66  on the remaining second and third portions  52   a,    52   b  of the die pad  16 . 
         [0031]    Typically, the upper surface  14  of the die pad  16  of a leadframe strip will be treated with the anti-wetting agent  66  prior to die attach. After the first portion  50  of the die pad  16  has been treated, the packages may be assembled using conventional methods. For instance, the adhesive material  48  may then be deposited on the second portion  52   a  of the die pad  16 . As the die  12  is placed over the adhesive material  48 , the adhesive material  48  may flow toward the treated first portion  50  of the die pad  16 . As the adhesive material  48  flows into the treated first portion  50 , the flow of the adhesive material will substantially slow and/or stop. In that regard, the adhesive material  48  will have reduced bleed out area that surrounds the die pad  16  in comparison with the prior art as discussed in reference to  FIG. 1  B. 
         [0032]    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. 
         [0033]    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.