Patent Publication Number: US-11024565-B2

Title: Direct selective adhesion promotor plating

Description:
PRIORITY CLAIM 
     This application is continuation of U.S. application Ser. No. 15/605,093 filed on 25 May 2017, which in turn is a continuation of U.S. application Ser. No. 14/866,050 filed on 25 Sep. 2015, patented as U.S. Pat. No. 9,704,786, the content of each application incorporated herein by reference their entirety. 
    
    
     TECHNICAL FIELD 
     The instant application relates to semiconductor packaging, and particularly relates to processes for enhancing adhesion between the conductive surface of a lead frame and the electrically insulating packaging material. 
     BACKGROUND 
     Integrated circuit devices, such as semiconductor chips, are commonly packaged using a lead frame and encapsulant material, such as a molding compound. For example, one or more semiconductor chips may be physically attached and electrically connected to a lead frame. The encapsulant material is formed around the semiconductor chip and electrical connections. The encapsulant protects the semiconductor chip and electrical connections from damaging environmental conditions, such as moisture, temperature, foreign particles, etc. The leads of the lead frame are externally accessible from outside of the encapsulant, and in some cases protrude away from the encapsulant. These outer portions of the leads provide external electrical terminals that allow the packaged device to be electrically connected to a printed circuit board, for example. 
     Many semiconductor processing technologies utilize lead frame strips to simultaneously package a number of semiconductor devices. A lead frame strip includes a number of unit lead frames continuously repeated on a sheet conductor, with openings in the sheet conductor defining the features of the unit lead frames. Each unit lead frame provides the lead construction for a single packaged device. One or more semiconductor dies can be affixed to and electrically connected with each unit lead frame. Eventually, the unit lead frames are singulated from one another to form individual packaged devices. The encapsulant may be molded on the lead frame before or after the unit lead frames are singulated. 
     In semiconductor packaging, delamination is a common problem in which the packaging material separates from the lead frame due to poor adhesion between the two. This may present an unacceptable risk that moisture and foreign particles will penetrate the package, and may result in a number of parts being discarded after inspection. 
     One technique for addressing the adhesion problem involves the application of an adhesion promoter to the lead frame prior to forming the encapsulant on the lead frame. However, effective adhesion promoters are typically non-conducting or at least interfere with conductive connections. Therefore, if the adhesion promoter is not removed from certain regions of the lead frame prior to wire bonding, there is a substantial possibility of wire bond failure. Known techniques for removing adhesion promotors from certain regions of the lead frame require multiple process steps that are costly and difficult to calibrate. 
     SUMMARY 
     A method of forming a packaged semiconductor device is disclosed. According to an embodiment, the method includes providing a lead frame strip having a plurality of unit lead frames. Each of the unit lead frames have a die paddle, a plurality of leads extending away from the die paddle, and a peripheral ring delineating interior portions of the leads from exterior portions of the leads. The method further includes selectively plating an adhesion promoter plating material within a package outline area of a first unit lead frame. The die paddle and the interior portions of the leads are disposed within the package outline area and the exterior portions of the leads are disposed outside of the package outline area. The method further includes processing wire bond sites in the first unit lead frame such that, after selectively plating the adhesion promoter plating material, the wire bond sites are substantially devoid of the adhesion promoter plating material. The wire bond sites are disposed within the package outline area and are spaced apart from the peripheral ring. 
     According to another embodiment, the method includes providing a lead frame strip having a plurality of unit lead frames. Each of the unit lead frames have a central opening and a plurality of leads extending away from the central opening. The method further includes selectively plating an adhesion promoter plating material on a first unit lead frame within a package outline area of on first portions of the leads. The method further includes molding an electrically insulating encapsulant material on the first portions of the leads such that the central opening is enclosed by a cavity formed by outer sidewalls of the encapsulant material. 
     According to another embodiment, the method includes providing a lead frame strip having a plurality of unit lead frames. Each of the unit lead frames have a die paddle and a plurality of leads extending away from the die paddle. A first one of the unit lead frames is plated with an adhesion promoter plating material within a package outline area of the first unit lead frame. The package outline area includes one of the die paddles and interior portions of the leads. Wire bond sites are processed in the first unit lead frame before or after the plating of the first lead frame such that, after the plating of the first lead frame. The wire bond sites are substantially devoid of the adhesion promoter plating material. The wire bond sites are disposed within the package outline area at an end of the interior portions of the leads that is closest to the die paddle. 
     According to another embodiment, the method includes providing a lead frame strip having a plurality of unit lead frames. Each of the unit lead frames have a central opening and a plurality of leads extending away from the central opening. An adhesion promoter plating material is selectively plated on a first unit lead frame within a package outline area of on first portions of the leads. An electrically insulating encapsulant material is formed on the first portions of the leads such that the central opening is enclosed by a cavity formed by outer sidewalls of the encapsulant material. Selectively plating the adhesion promoter plating material includes a single pass plating process. The single pass plating process includes providing a mask over the first unit lead frame, the mask covering the exterior portions of the leads and comprising openings that expose the elevated portions of the leads, and forming the adhesion promoter plating material in the openings. 
     A packaged semiconductor device is disclosed. According to an embodiment, the packaged semiconductor device includes a lead frame having a central opening and a plurality of leads extending away from the central opening. At least one of the leads has an elevated portion that is closer to the central opening than outer portions of the leads. The packaged semiconductor device further includes an electrically insulating encapsulant material formed on a package outline area of the lead frame such that the central opening is enclosed by a cavity formed by outer sidewalls of the encapsulant material. The packaged semiconductor device further includes an adhesion promoter plating material formed on the lead frame at an interface between the lead frame and the electrically insulating encapsulant material. 
     A packaged semiconductor device is disclosed. According to an embodiment, the packaged semiconductor device includes a lead frame having a central opening and a plurality of leads extending away from the central opening. At least one of the leads includes an elevated portion. The elevated portion is closer to the central opening than outer portions of the leads. An electrically insulating encapsulant material is formed on a package outline area of the lead frame such that the central opening is enclosed by a cavity formed by outer sidewalls of the encapsulant material. An adhesion promoter plating material is formed on the lead frame at an interface between the lead frame and the electrically insulating encapsulant material. 
     A semiconductor device is disclosed. According to an embodiment, the semiconductor device includes a die paddle, a plurality of electrically conductive leads extending away from the die paddle, and an adhesion promoter plating material selectively formed on the electrically conductive leads such that outer portions of the leads are covered by the adhesion promoter plating material, and interior portions of the leads that are disposed between the die paddle and the respective outer portions of each lead are substantially devoid of the adhesion promoter plating material. 
     According to another embodiment, the semiconductor device includes a plurality of leads extending away from a central opening such that interior ends of each lead face the opening, an adhesion promoter plating material formed on each one of the leads, and wire bondable material selectively formed on the electrically conductive leads such that the adhesion promoter plating material is covered by the wire bondable material on interior portions of the leads and such that the adhesion promoter plating material is exposed from the wire bondable material on outer portions of the leads. The interior portions of the leads that are disposed between the outer portions and the interior ends. 
     Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. The features of the various illustrated embodiments can be combined unless they exclude each other. Embodiments are depicted in the drawings and are detailed in the description which follows. 
         FIG. 1 , which includes  FIGS. 1A and 1B , illustrates a lead frame strip that may be selectively plated, according to an embodiment.  FIG. 1A  shows a top side of the lead frame strip and  FIG. 1B  shows the bottom side of the lead frame strip. 
         FIG. 2 , which includes  FIGS. 2A and 2B , illustrates a mask being provided over the lead frame strip, according to an embodiment.  FIG. 2A  shows a top side of the lead frame strip and  FIG. 2B  shows the bottom side of the lead frame strip. 
         FIG. 3 , which includes  FIGS. 3A and 3B , illustrates the lead frame strip after adhesion promoter plating material is selectively formed within openings of the mask, according to an embodiment.  FIG. 3A  shows a top side of the lead frame strip and  FIG. 3B  shows the bottom side of the lead frame strip. 
         FIG. 4  illustrates a top side of the lead frame strip after the mask has been removed, according to an embodiment. 
         FIG. 5  illustrates a top side of a lead frame strip that has been processed by a chemical treatment process, according to an embodiment. 
         FIG. 6  illustrates a top side of a lead frame strip that has been processed by a laser cleaning process, according to an embodiment. 
         FIG. 7  illustrates a top side of a lead frame strip with a wire bondable layer being formed on the wire bond sites of the lead frame, according to an embodiment. 
         FIG. 8  illustrates a top side of a lead frame strip with a corrosion resistance coating that can be used to prevent the adhesion promoter plating material from forming in select locations, according to an embodiment. 
         FIG. 9  illustrates a top side of a lead frame strip with a pre-mask tape that can be used to prevent the adhesion promoter plating material from forming in select locations, according to an embodiment. 
         FIG. 10 , which includes  FIGS. 10A and 10B , illustrates another configuration of a lead frame strip that may be selectively plated, according to an embodiment.  FIG. 10A  shows a top side of the lead frame strip and  FIG. 10B  shows a cross-sectional view of the lead frame strip. 
         FIG. 11 , which includes  FIGS. 11A and 11B , illustrates the lead frame strip of  FIG. 10  after an after adhesion promoter plating material is selectively formed.  FIG. 11A  shows a top side of the lead frame strip and  FIG. 11B  shows a cross-sectional view of the lead frame strip. 
         FIG. 12  illustrates a top side of a lead frame strip with a molded package outline formed on the lead frame strip and with a wire bondable layer being formed on the lead frame strip within the molded package outline, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of a method of forming a packaged semiconductor device are described herein. According to the method, a lead frame strip having a plurality of unit lead frames is provided. An adhesion promoter plating material is selectively applied within a package outline area of the unit lead frames. This process is a single pass, direct application process. For example, according to an embodiment, the unit lead frames are masked, and the adhesion promoter plating material is only formed in regions that are exposed from the mask. 
     The inventors have found that there are many advantages to a direct selective adhesion plating process in comparison to conventional techniques, which may include non-selective plating of an adhesion promoter followed by an etching process, for example. However, in a direct selective adhesion plating process, the possibility exists that a small amount of the adhesion promoter will encroach into the wire bond sites. The embodiments described herein address this issue by performing one or more processing steps to the wire bond sites in the lead frame strip before or after (or both before and after) the selective plating of the adhesion promoter. For example, the wire bond sites may be chemically treated and/or may be spot plated with a wire bondable layer (e.g., Silver). These processing steps ensure that the wire bond sites are substantially devoid of the adhesion promoter plating material before wire bonding. Thus, the processing steps allow for the lead frame strip to be plated by a direct selective adhesion plating process without the adhesion promoter plating material interfering with the formation of wire bonds. 
     Referring to  FIG. 1 , a plan view of a lead frame strip  100  is depicted, according to an embodiment. The top side  102  (i.e., the die attachment side) of the lead frame strip  100  is depicted in  FIG. 1A  and the bottom side  104  of the lead frame strip  100  is depicted in  FIG. 1B . The lead frame strip  100  includes a plurality of unit lead frames  106 , two of which are depicted in  FIG. 1 . For the purposes of explanation, a first unit lead frame  106  will be discussed. It will be appreciated by those of ordinary skill that the first unit lead frame  106  may be replicated a number of times (e.g., tens, hundreds, etc.) in the lead frame strip  100 , and that the configurations and processing steps discussed with reference to the first unit lead frame  106  are universally applicable to every other one of the unit lead frames  106  in the lead frame strip  100 . 
     The lead frame strip  100  may be formed from a sheet layer of electrically conductive material (e.g., copper, aluminum and the like). Openings  108  are formed in the sheet metal that define the features of the unit lead frames  106 . The openings  108  may be formed by stamping or etching, for example. 
     The first unit lead frame  106  includes a die paddle  110  and a plurality of leads  112  extending away from the die paddle  110 . A peripheral ring  114  delineates interior portions of the leads  112  from exterior portions of the leads  112 . The peripheral ring  114  is an interior ring of the first unit lead frame  106  that surrounds the die paddle  110 . The interior portions of the leads  112  are spaced closest to the die paddle  110  and the exterior portions of the leads  112  are arranged further away from the die paddle  110 , on an opposite side of the peripheral ring  114  as the interior portions of the leads  112 . The die paddle  110  may be connected to one of the leads  112  to connect the die paddle  110  to allow the die paddle to be connected to a reference potential in the finalized device. In a lead trimming step, portions of the peripheral ring  114  that connect the leads  112  together are removed so that the leads  112  are electrically distinct from one another. The first unit lead frame  106  may further include tie bars  115  that physically support the die paddle  110  after the leads  112  are trimmed. 
     A package outline area  116  represents where a protective encapsulate material, such as a molding compound, is formed on the first unit lead frame  106 . The package outline area  116  encompasses the die paddle  110  and the interior portions of the leads  112 . The exterior portions of the leads  112  are at least partially outside of the package outline area  116  and thus protrude out of the encapsulant material to provide electrical terminals of the packaged device. 
       FIG. 1A  further depicts wire bond sites  118  that are disposed within the package outline area  116 . In order to form an electrical connection between the semiconductor device(s) mounted to the die paddle  110  and the leads  112 , wire bonds (e.g., conductive bond wire, ribbon, etc.) can be used. The wire bond sites  118  represent locations at which the wire bonds are connected to the leads  112  of the packaged device. The wire bond sites  118  are disposed within the package outline area  116  and are spaced apart from the peripheral ring  114 . That is, the wire bond sites  118  do not intersect with the package outline area  116 . Rather, the wire bond sites  118  are only disposed on portions of the interior portions of the leads  112  that are closest to the die paddle  110 . Optionally, the leads  112  may be locally enlarged at the wire bond sites  118  relative to the area of the portions of the leads  112  extending between the wire bond sites  118  and the peripheral ring  114 . 
     Referring to  FIGS. 2-3 , a process for selectively forming an adhesion promoter plating material  120  within the package outline area  116  of the first unit lead frame  106  is depicted, according to an embodiment. The top side  102  of the lead frame strip  100  is depicted in  FIG. 2A  and the bottom side  104  of the lead frame strip  100  is depicted in  FIG. 2B . This process is a single pass process whereby the adhesion promoter plating material  120  is directly applied to pre-selected portions of the lead frame. According to the method, a mask  122  is provided over the first unit lead frame  106 . The mask  122  includes one or more openings  124  that at least partially expose pre-selected regions of the first unit lead frame  106  within the package outline area  116 . The mask  122  covers pre-selected areas that are preferably devoid of (i.e., not covered with) the adhesion promoter plating material  120 . The geometry of the mask  122  in  FIG. 2A  represents just one example, and in general any mask geometry that is technically feasible may be used to define pre-selected regions of the lead frame strip  100  that should contain or be devoid of the adhesion promoter plating material  120 . 
     Referring to  FIG. 3 , the adhesion promoter plating material  120  has been selectively formed on the lead frame strip  100 . The top side  102  of the lead frame strip  100  is depicted in  FIG. 3A  and the bottom side  104  of the lead frame strip  100  is depicted in  FIG. 3B . Exposed portions of the lead frame strip  100  are plated with the adhesion promoter plating material  120  and the mask  122  nominally prevents the adhesion promoter plating material  120  from forming in any of the covered areas. 
     The adhesion promoter plating material  120  may generally be any material that enhances the bond between electrically insulating packaging material (e.g., a thermoset plastic) and an electrically conductive material that is disposed on a surface of the lead frame (e.g., copper, aluminum, silver, etc.). According to an embodiment, the adhesion promoter plating material  120  is a Zinc based compound. For example, the adhesion promoter plating material  120  may be an alloy of Zinc and Chromium (e.g., ZnCr). Other suitable Zinc based alloys for the adhesion promoter plating material  120  include ZnMo or ZnV. According to an embodiment, the adhesion promoter plating material  120  is formed by an electrolytic plating process in which the lead frame strip  100  is immersed in an electrolytic fluid and acts as an anode under an applied current. In this embodiment, the mask  122  prevents the covered region from being plated with the adhesion promoter plating material  120 . 
     Referring to  FIG. 4 , a top side  102  of the lead frame strip  100  is depicted after removal of the mask  122 . In the figure, transitional regions  126  of the interior portions of the leads  112  have been encircled. These transitional regions  126  correspond to areas at or near the boundary between the adhesion promoter plating material  120  and the wire bond sites  118 . Without further measures, the adhesion promoter plating material  120  may skew too close to the die paddle  110  so as to encroach upon the wire bond sites  118  in the transitional regions  126 . That is, the transitional regions  126  represent regions that should preferably be devoid of the adhesion promoter plating material  120 , but in some cases are not. Many variables that are difficult or impossible to control contribute to the problem. For example, the minimum opening size of the mask  122  may be such that the adhesion promoter plating material  120  extends too far into the wire bond sites  118 . Process variation also contributes to this effect. Further, even in the case of a properly sized and aligned mask  122 , some adhesion promotor plating material may leak into the wire bond sites  118  after the plating process. Because the adhesion promoter plating material  120  is non-conductive, it may be difficult or impossible to form wire bonds at the wire bond sites  118  if there is too much of the adhesion promoter plating material  120  present in the transitional regions  126 . 
     A variety of processing steps are disclosed herein to mitigate the above described phenomenon and remove (or cover) the adhesion promoter plating material  120  that forms in the transitional regions  126 . According to these embodiments, the wire bond sites  118  in the first unit lead frame  106  are processed such that, after selectively plating the adhesion promoter plating material  120 , the wire bond sites  118  are substantially devoid of the adhesion promoter plating material  120 . That is, the wire bond sites  118  are processed to prevent the adhesion promoter plating material  120  from encroaching too far toward the die paddle  110  and create an unacceptably high risk of wire bond failure. These processing steps may be performed on the lead frame strip  100  before the selective plating of the adhesion promoter plating material  120 , after the selective plating of the adhesion promoter plating material  120 , or before and after the selective plating the adhesion promoter plating material  120 . Furthermore, any of the processing steps may be combined with one another. The term “substantially devoid” as used herein means that, while trace amounts of the adhesion promoter plating material  120  may be present on the wire bond sites  118 , the amount of adhesion promoter plating material  120  remains below a maximum threshold so as to ensure that a conductive connection (e.g., with wire bonds) can be effectuated at the wire bond sites  118 . 
     Referring to  FIG. 5 , a top side  102  of the lead frame strip  100  is depicted after the selective plating of the adhesion promoter plating material  120  as described with reference to  FIGS. 2-4 . In this embodiment, the lead frame strip  100  has been subjected to a chemical treatment process, either before or after the selective plating of the adhesion promoter plating material  120  as described with reference to  FIGS. 2-3 . As a result, the transitional regions  126  are substantially devoid of the adhesion promoter plating material  120 . 
     According to one embodiment, a chemical treatment process is applied to the first unit lead frame  106  prior to selectively plating the first unit lead frame  106  with the adhesion promoter plating material  120 . For example, the lead frame strip  100  may be submerged in a chemically reactive solution. Exemplary chemically reactive solutions that are suitable for this process include an anti-immersion or anti-tarnish chemical inhibitor such as an Organosulphur acid based e.g., 2-thiobarbituric acid, triazole derivatives e.g., Benzatriazole, and imidazoles, etc. Alternatively, a Silane based solution such as Mercapto silane, Sodium metasilicate, tripolyphosphate, etc. may be used. This chemical treatment process prevents the adhesion promoter plating material  120  from forming on select portions (e.g., the wire bond sites  118 ) of the interior portions of the leads  112 . Thus, the adhesion promoter plating material  120  does not encroach upon the wire bond sites  118  during the selective application of the adhesion promoter plating material  120  described with reference to  FIG. 4 . 
     According to another embodiment, after selectively plating the adhesion promoter plating material  120 , portions of the adhesion promoter plating material  120  that form on the wire bond sites  118  during the plating process are removed. This removal of the adhesion promoter plating may be done, e.g., by a chemical reaction process. For example, a chemical cleaning solution such as Potassium hydroxide, Ammonium acetate, Potassium lactate, and Acetone may be applied to the wire bond sites  118 . This process may be a selective or non-selective and may be an electrolytic or non-electrolytic process. For example, in a selective cleaning process, a mask may be used to only remove the adhesion promoter plating material  120  from preselected areas (e.g., the wire bond sites  118  or portions of the wire bond sites  118 ). Alternatively, in a non-selective cleaning process, the chemical cleaning solution may be exposed to the entire lead frame strip  100  for a predetermined duration to remove some of the adhesion promoter plating material  120 . 
     Referring to  FIG. 6 , a top side  102  of the lead frame strip  100  is depicted after the selective plating of the adhesion promoter plating material  120  as described with reference to  FIGS. 2-4 . In this embodiment, the lead frame strip  100  has been subjected to a selective laser cleaning leakage regions  127  that encompass the wire bond sites  118 . This selective laser cleaning is performed after the selective plating of the adhesion promoter plating material  120  as described with reference to  FIGS. 2-4 . Various laser parameters are possible. The laser selective laser cleaning may slightly reduce the thickness of the material beneath the adhesion promoter plating material  120  (e.g., silver) so that the adhesion promoter plating material  120  can be removed completely. Removal of unwanted plating can be performed by laser machine programming, for example. Laser cleaning can be applied on different metal surfaces (Cu, Ag, Ni, pre-plating layer stacks etc.). 
     Referring to  FIG. 7 , a top side  102  of the lead frame strip  100  is depicted after the selective plating of the adhesion promoter plating material  120  as described with reference to  FIGS. 2-4 . In this embodiment, the lead frame strip  100  has been subjected to a plating process whereby any adhesion promoter plating material  120  that is present in the wire bond sites  118  is covered (e.g., plated) with a wire bondable layer  128 . The wire bondable layer  128  may generally be any electrically conductive material that is suitable for the formation of wire bonds thereon. According to an embodiment, the wire bondable layer  128  is a layer of Silver (Ag). Alternatively, the wire bondable layer  128  may be formed from Palladium (Pd), Gold (Au), Nickel (Ni), Copper (Cu), and alloys thereof. 
     According to an embodiment, the wire bondable layer  128  is formed by a so-called spot plating technique. According to this technique, the wire bondable material (e.g., silver) is directly applied to the first unit lead frame  106  in pre-selected locations. As can be seen, the pre-selected locations are within the package outline area  116  and encompass the die paddle  110  and the wire bonding portions of the leads  112 . Any adhesion promotor that forms on the wire bonding portions of the leads  112  or near the wire bonding portions of the leads  112  is covered by the wire bondable layer  128 . However, the spot plating is constrained within a window such that it does not form near the package outline or the peripheral ring  114 . Thus, in these regions, the adhesion promoter plating material  120  remains exposed and will adhere to the packaging material that is formed thereon. The wire bondable layer  128  may be formed before and after application of the adhesion promoter plating material  120 . For example, the wire bondable layer  128  may first be formed on the lead frame strip  100  prior to the process steps described with reference to  FIGS. 2-3 . Afterwards, a re-plating process may be applied so as to form another wire bondable layer  128 . 
     Referring to  FIG. 8 , a top side  102  of the lead frame strip  100  is depicted before the selective plating of the adhesion promoter plating material  120  as described with reference to  FIGS. 2-4 . According to the technique depicted in  FIG. 8 , the entire lead frame strip  100  is coated with a corrosion resistance coating  129  using pore blocker chemistry techniques, including include bisphenol, ether based chemistry, Benzothiazole, etc. The corrosion resistance coating  129  forms a hydrophobic layer on the entire top side  102 , including the wire bond sites  118 , as well as bottom side  104  (not shown in  FIG. 8 ). The corrosion resistance coating  129  can be used to inhibit the formation of the adhesion promoter plating material  120  in any desired area, including the wire bond sites  118  and the transitional regions  126 . The adhesion promoter plating material  120  cannot be deposited at these locations by immersion or low current flow. However, the adhesion promoter plating material  120  can be selectively applied to other areas in which it is preferably present (e.g., the peripheral ring  114 ). The corrosion resistance coating  129  can be applied prior to the selective plating of the adhesion promoter plating material  120  as described with reference to  FIGS. 2-4 , and can remain on the wire bond sites  118  during wire bonding without interfering with the wire bonds, due to the minimal thickness of the corrosion resistance coating  129 . 
     Referring to  FIG. 9 , a top side  102  of the lead frame strip  100  is depicted before the selective plating of the adhesion promoter plating material  120  as described with reference to  FIGS. 2-3 . According to this technique, an additional masking step is performed prior to the masking step of  FIG. 2  to provide additional coverage over the wire bond sites  118  and prevent the adhesion promoter plating material  120  from forming in these regions. This additional masking step may include applying a pre-taping method, whereby a tape  131  is applied to the lead frame strip  100 . The tape  131  may be any commonly used tape for lead stabilization, such as polyethelene (PE) or polyester (PET) tape. 
     Referring to  FIG. 10 , a differently configured lead frame strip  100  is depicted. The top side  102  (i.e., the die attachment side) of the lead frame strip  100  is depicted in  FIG. 10A .  FIG. 10B  depicts the lead frame strip  100  along the cross sectional line A-A′ depicted in  FIG. 10A . In this embodiment, the lead frame strip  100  is configured to be pre-molded with a package outline structure prior to singulation of the first unit lead frames  106 . 
     The lead frame strip  100  may include the same materials and may be formed according to the same techniques as the lead frame strip  100  described with reference to  FIGS. 1-9 . The lead frame strip  100  is configured differently from the lead frame strip  100  of  FIGS. 1-9  at least in the following way. First of all, there is no die paddle  110  in the lead frame strip  100  of  FIG. 10 . Instead, the each of the unit lead frames  106  has a central opening  130 . The unit lead frames  106  additionally include a plurality of leads  112  extending away from the central opening  130 . This configuration may be used for a sensor package structure in which the sensor device is placed over the central opening  130 . The central opening  130  can provide access to outside of the package so that the sensor device can measure and exterior environmental parameter. 
     Referring to the side profile view of  FIG. 10B , it can be seen that the lead frame strip  100  may have a bent lead configuration. More particularly, an elevated portion  132  is provided in first portions of the leads  112 . That is, the leads  112  do not extend along a single plane. Rather, the leads  112  include a vertical bend and an elevated portion  132  that is spaced above outer portions of the leads  112 . The elevated portion  132  is closer to the central opening  130  than outer portions of the leads  112 . Furthermore, the leads  112  may bend downward at inner portions of the leads  112  that are adjacent the central opening  130 . 
     Referring to  FIG. 11 , an adhesion promoter plating material  120  is selectively applied within a package outline area  116  of the first unit lead frame  106 . The top side  102  (i.e., the die attachment side) of the lead frame strip  100  is depicted in  FIG. 11A .  FIG. 11B  depicts the lead frame strip  100  along the cross sectional line A-A′ depicted in  FIG. 11A . The adhesion promoter plating material  120  may be formed on the lead frame strip of  FIG. 1  in a process that is substantially similar or identical to the selective plating process described with reference to  FIGS. 2-4 . For example, the adhesion promoter plating material  120  may be selectively plated by providing a mask  122  over the first unit lead frame  106  and forming the adhesion promoter plating material  120  in opening(s) of the mask  122  (e.g., by electroplating). According to an embodiment, the adhesion promoter plating material  120  is selectively formed on the first portions of the leads  112 , which include the elevated portions  132 , as is depicted in  FIG. 11B . 
     Referring to  FIG. 12 , a cavity package outline  134  has been adhered to the lead frame strip  100 . The cavity package outline  134  may be a pre-molded structure that is adhered to the lead frame strip  100  using an epoxy, for example. Alternatively, the cavity package outline  134  can be molded directly on the lead frame strip  100 . The cavity package outline  134  is formed on the first portions of the leads  112  such that the central opening  130  is enclosed by a cavity  136  formed by outer sidewalls of the encapsulant material. That is, the outer sidewalls of the cavity package outline  134  enclose and surround the central opening  130 . The outer sidewalls of the cavity package outline  134  may be formed on the elevated portions  132  of the leads  112 . The adhesion promoter plating material  120  is provided at an interface between the lead frame and the electrically insulating encapsulant material. 
     The first unit lead frame  106  may be processed after molding the cavity package outline  134  so as to prevent the adhesion promoter plating material  120  from interfering with electrical connections between the first unit lead frame  106  and the devices (e.g., sensor elements) assembled within the cavity  136 . For example, the lead frame strip  100  may be chemically treated before or after the selective plating process in a similar manner as described with reference to  FIG. 5 . However, these steps may be omitted. Because the electrically insulating encapsulant is formed on the lead frame strip  100  during the processing of the lead frame strip  100 , the lead frame strip  100  can processed afterwards to eliminate the potentially detrimental impacts of the adhesion promoter plating material  120  on the leads  112 . 
     According to an embodiment, after the cavity package outline  134  has been molded on the lead frame strip  100 , the first unit lead frame  106  is plated with a wire bondable layer  128 . The wire bondable layer  128  may be a layer of Silver (Ag), and may be formed according to the same techniques previously described with reference to  FIG. 6 . Therefore, any of the adhesion promoter plating material  120  on the leads  112  will not interfere with the electrical connections between the first unit lead frame  106  and the devices assembled within the cavity  136 . 
       FIGS. 1-12  illustrate two possible embodiments of the first unit lead frame  106 . However, the configuration of the first unit lead frame  106  may vary depending upon the desired configuration of the finalized package design. For example, the number and dimensions of the leads  112  and the size of the die paddle  110  may vary. The first unit lead frame  106  may be formed along a single plane or may be formed along more than one plane. For example, the first unit lead frame  106  may be vertically offset from peripheral ring  114 . Furthermore, the leads  112  may have one or more bends or otherwise include a non-planar geometry. In any case, the selective plating of the adhesion promoter plating material process and the wire bond site processing techniques described herein are applicable to any of these constructions. 
     The single pass process offers numerous advantages over conventional techniques that require two pass processing (e.g., a non-selective adhesion promoter step followed by a selective etching of the adhesion promoter). One major advantage is a reduction in cost. This cost reduction is at least partially attributable to the elimination of at least one mask (i.e., the mask required for the selective etching of the adhesion promoter). Furthermore, frame alignment and handling issues associated with the conventional techniques are mitigated, due to the simplification of the process. Thus, yield can be improved. 
     Another advantage of the single pass process in comparison to conventional techniques is that a thickness reduction of the conductive lead frame material is not required. Conventional processes require the adhesion promoter to be over etched to remove the material that is beneath the adhesion promoter. This is required to ensure that the adhesion promoter is completely removed from the wire bondable layers. This thickness reduction of the conductive lead frame material may lead to a number of detrimental effects. For example, mold flashing may occur, and package singulation may be more difficult, due to the non-planar nature of the lead frame. The thickness reduction is not necessary using the techniques described herein because the adhesion promoter is only applied in the regions in which it is required. 
     Another advantage of the direct selective adhesion promoter plating process described herein is an improvement to the shelf life of the direct selective adhesion promoter plating material. According to conventional techniques, the package molding process should be carried out within two weeks of the adhesion promoter plating process. According to the direct selective adhesion promoter plating process described herein, the lead frame can be molded as long as 12 months after the application of the adhesion promoter plating material. Thus, the direct selective adhesion promoter plating process described herein offers flexibility wire regard to pre-fabrication, shipment and delivery. 
     Spatially relative terms such as “under,” “below,” “lower,” “over,” “upper” and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first,” “second,” and the like, are also used to describe various elements, regions, sections, etc. and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
     As used herein, the terms “having,” “containing,” “including,” “comprising” and the like are open-ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a,” “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
     With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.