Direct selective adhesion promoter plating

Abstract

A method of forming an encapsulated semiconductor device, comprising: Providing a leadframe strip (100) having a plurality of unit leadframes (106), each of the unit leadframes (106) comprising a die paddle (110), a plurality of leads (112) extending away from the die paddle (110), and a peripheral ring (114) delimiting inner portions of the leads (112) from outer portions of the leads (112), the inner portions comprising wire bond pads (118); selectively plating an adhesion promoter plating material (120) within a package outline region (116) of a first unit leadframe (106), wherein the die paddle (110) and the inner portions of the leads (112) are disposed within the package outline region (116) and the outer portions of the leads (112) are disposed outside the package outline region (116), wherein the selective plating of the adhesion promoter plating material (120) onto the first unit leadframe (106) comprises a single-pass metal plating process comprising: Providing a mask (122) over the first unit leadframe (106), the mask (122) covering the outer portions of the leads (112) and including openings (124) that at least partially expose preselected regions of the first unit leadframe (106) within the package outline area (116); and Forming the adhesion promoter plating material (120) in the openings (124), wherein the wire bonding sites (118) are covered by the mask (122) such that the adhesion promoter plating material (120) is prevented from forming on the wire bonding sites (118) during the formation of the adhesion promoter plating material (120); and Processing wire bonding sites (118) in the first unit leadframe (106) such that after selectively plating the adhesion promoter plating material (120), the wire bonding sites (118) are free of the adhesion promoter plating material (120), wherein the wire bond locations (118) are arranged within the package outline area (116) and are spaced from the peripheral ring (114), and wherein processing the wire bond locations (118) comprises: after selectively plating the adhesion promoter plating material (120), applying a laser cleaning process to the wire bond sites (118) to remove any adhesion promoter plating material (120) that oozes onto the wire bond sites (118).

Description

FIELD OF THE INVENTIONThe present application relates to semiconductor packaging and, more particularly, relates to processes for enhancing adhesion between the conductive surface of a leadframe and the electrically insulating packaging material.GENERAL STATE OF THE ARTIntegrated circuit devices such as semiconductor chips are typically encapsulated using a leadframe and an encapsulation material such as a molding compound. For example, one or more semiconductor chips may be physically attached to and electrically connected to a leadframe. The encapsulation material is formed around the semiconductor chip and the electrical connections. The encapsulant protects the semiconductor chip and the electrical connections from damaging environmental conditions such as moisture, temperature, foreign objects, etc. The leads of the leadframe are all externally accessible from outside the encapsulant and in some cases protrude from the encapsulant. These outer portions of the leads provide external electrical connections that allow the packaged device to be electrically connected to a circuit board, for example.Many semiconductor processing technologies utilize leadframe strips to simultaneously encapsulate a number of semiconductor devices. A leadframe strip includes a number of unit leadframes that are continuously repeated on a planar lead, wherein openings in the planar lead define the features of the unit leadframes. Each unit leadframe provides the line construction for a single packaged device. One or more semiconductor dies may be attached to and electrically connected to each unit leadframe. Finally, the unit lead frames are singulated from each other to form individual packaged devices. The encapsulant may be formed on the lead frame before or after the unit lead frames are singulated.In semiconductor packaging, peeling is a common problem in which the packaging material separates from the lead frame due to poor adhesion between the two. This may mean an unacceptable risk of moisture and debris entering the package and may result in a number of parts being discarded after the inspection.One technique for treating the adhesion problem includes applying an adhesion promoter to the leadframe prior to forming the encapsulant on the leadframe. However, effective adhesion promoters are typically non-conductive or at least interfere with conductive compounds. Therefore, if the adhesive is not removed from certain areas of the lead frame prior to wire bonding, there is an essential possibility for wire bonding failure. Known techniques for removing adhesion promoters from certain regions of the leadframe require multiple process steps that are expensive and difficult to calibrate. DE 101 48 120 A1 relates to the electrically conductive connection of a chip island to the rear side of a semiconductor chip attached thereto by means of an electrically conductive adhesive layer. For this purpose, a coating is applied under the adhesive layer, which consists of a coplanar pattern of electrically conductive contact layer regions and insulating adhesion layer regions applied thereon. The pattern can also be applied to inner conductors, so that bonding wires can be connected to contact layer regions. DE 10 2004 048 201 A1 relates to improving the adhesion between surfaces of a semiconductor component and a plastic package compound. For this purpose, a coating of a mixture of polymeric chain molecules and carbon nanotubes is provided. The layer can be applied selectively to surfaces of a wide variety of materials by selective masking or selective detachment. For example, contact connection surfaces of an inner flat conductor are thus kept free of the coating.SUMMARY OF THE INVENTIONA method of forming an encapsulated semiconductor device according to claim 1 is disclosed. The method includes providing a leadframe strip having a plurality of unit leadframes. Each of the unit leadframes has a die paddle, a plurality of leads extending away from the die paddle, and a peripheral ring that bounds inner portions of the leads from outer portions of the leads. The method further includes selectively plating a primer plating material within a package outline region of a first unit leadframe. The die paddle and the inner portions of the leads are disposed within the package outline region and the outer portions of the leads are disposed outside the package outline region. The method further includes processing wire bonds in the first unit leadframe such that after selectively plating the adhesion promoter plating material, the wire bonds are substantially free of the adhesion promoter plating material. The wire bonds are disposed within the package outline region and are spaced from the peripheral ring.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 DRAWINGSThe 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 may be combined unless they are mutually exclusive. Embodiments are illustrated in the drawings and detailed in the description that follows. FIG. 1, including FIGS. 1A and 1B, illustrates a leadframe strip that can be selectively plated, according to an embodiment. FIG. 1A shows a top side of the leadframe strip, and FIG. 1B shows the bottom side of the leadframe strip. FIG. 2, including FIGS. 2A and 2B, illustrates a mask provided over the leadframe strip, according to an embodiment. FIG. 2A shows a top side of the leadframe strip, and FIG. 2B shows the bottom side of the leadframe strip. FIG. 3, including FIGS. 3A and 3B, illustrates the leadframe strip after adhesion promoter plating material has been selectively formed within openings of the mask, according to an embodiment. FIG. 3A shows a top side of the leadframe strip, and FIG. 3B shows the bottom side of the leadframe strip. FIG. 4 illustrates a top surface of the leadframe strip after the mask has been removed, according to an embodiment. FIG. 5 illustrates a top surface of a leadframe strip processed by a chemical treatment process, according to an embodiment. FIG. 6 illustrates a top surface of a leadframe strip processed by a laser cleaning process, according to an embodiment. FIG. 7 illustrates a top surface of a leadframe strip having a wirebondable layer formed on the wirebonds of the leadframe, according to an embodiment. FIG. 8 illustrates a top surface of a leadframe strip having a corrosion resistant coating that may be used to prevent the adhesion promoter plating material from forming at selected locations, according to an embodiment. FIG. 9 illustrates a top surface of a leadframe strip, with a pre-masking tape, that may be used to prevent the adhesion promoter plating material from forming at selected locations, according to an embodiment. FIG. 10, including FIGS. 10A and 10B, illustrates another non-inventive configuration of a leadframe strip that can be selectively plated. 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, including FIGS. 11A and 11B, illustrates the lead frame strip of FIG. 10 not in accordance with the present invention after a bond coat plating material has been selectively formed. FIG. 11A shows a top surface 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 not according to the invention, having a molded package outline formed on the lead frame strip and having a wirebondable layer formed on the lead frame strip within the molded package outline.DETAILED DESCRIPTIONEmbodiments of a method of forming an encapsulated semiconductor device are described herein. According to the method, a leadframe strip having a plurality of unit leadframes is provided. A primer plating material is selectively deposited within a package outline area of the unit lead frames. This process is a single pass direct deposition process. For example, according to an embodiment, the unit lead frames are masked, and the adhesion promoter plating material is formed only in regions exposed to the mask.The inventors have found that there are many advantages to a direct selective adhesion plating process compared 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, there is a possibility that a small amount of the adhesion promoter enters the wire bonds. The embodiments described herein address this issue by performing one or more processing steps on the wire bonds in the leadframe strip before or after (or both before and after) the selective plating of the adhesion promoter. For example, the wire bonds may be chemically treated and / or point plated with a wirebondable layer (e.g., silver). These processing steps ensure that the wire bonds prior to wire bonding are substantially free of the primer plating material. Thus, the processing steps allow the leadframe strip to be plated through a direct selective bond plating process without the bond coat plating material interfering with the formation of wire bonds.Referring to FIG. 1, a top view of a leadframe strip 100 is illustrated, according to an embodiment. The top side 102 (i.e., die attach side) of the leadframe strip 100 is shown in FIG. 1A, and the bottom side 104 of the leadframe strip 100 is shown in FIG. 1B. Leadframe strip 100 includes a plurality of unit leadframes 106, two of which are illustrated in FIG. 1. For purposes of explanation, a first unit leadframe 106 is discussed. Those of ordinary skill in the art will understand that the first unit leadframe 106 in the leadframe strip 100 may be replicated multiple times (e.g., dozens, hundreds of times, etc.), and that the configurations and processing steps discussed with reference to the first unit leadframe 106 may be universally applied to any other of the unit leadframes 106 in the leadframe strip 100.The leadframe strip 100 may be formed from a film layer of electrically conductive material (e.g., copper, aluminum, and the like). Apertures 108 are formed in the sheet metal defining the features of the unit leadframes 106. The openings 108 may be formed by, for example, stamping or etching.The first unit leadframe 106 includes a die paddle 110 and a plurality of lines 112 extending away from the die paddle 110. A peripheral ring 114 bounds inner portions of the conduits 112 from outer portions of the conduits 112. The peripheral ring 114 is an inner ring of the first unit lead frame 106 surrounding the die paddle 110. The inner portions of the leads 112 are spaced closest to the die paddle 110, and the outer portions of the leads 112 are disposed further away from the die paddle 110 on an opposite side of the peripheral ring 114 than the inner 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 completed device. In a lead trimming step, portions of the peripheral ring 114 connecting the leads 112 to each other are removed so that the leads 112 are electrically different from each other. The first unit leadframe 106 may further include retaining ridges 115 that physically support the die paddle 110 after the leads 112 have been trimmed.A package outline region 116 illustrates where a protective encapsulation material such as a molding compound is formed on the first unit leadframe 106. The package outline region 116 surrounds the die paddle 110 and the inner portions of the leads 112. The outer portions of the leads 112 are at least partially outside the package outline region 116 and thus protrude from the encapsulation material to provide electrical connections of the encapsulated device.FIG. 1A further illustrates wire bonds 118 disposed within the package outline region 116. To form an electrical bond between the semiconductor device(s) mounted on the die paddle 110 and the leads 112, wire bonds (i.e., a conductive bond wire, tapes, etc.) may be used. The wire bonds 118 represent locations where the wire bonds are connected to the leads 112 of the packaged device. The wire bonds 118 are disposed within the package outline region 116 and spaced from the peripheral ring 114. That is, the wire bonds 118 do not intersect the package outline portion 116. Rather, the wire bonds 118 are disposed only on portions of the inner portions of the leads 112 that are closest to the die paddle 110. Optionally, the leads 112 may be locally enlarged at the wire bonds 118 relative to the area of the portions of the leads 112 that extend between the wire bonds 118 and the peripheral ring 114.Referring to FIGS. 2-3, a process for selectively forming a bond coat plating material 120 within the package outline area 116 of the first unit leadframe 106 is illustrated, according to an embodiment. The top side 102 of the leadframe strip 100 is shown in FIG. 2A, and the bottom side 104 of the leadframe strip 100 is shown in FIG. 2B. This process is a single pass process whereby the adhesion promoter plating material 120 is directly applied to preselected portions of the leadframe. 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 preselected regions of the first unit leadframe 106 within the package outline region 116. The mask 122 covers preselected areas that are preferably free of (i.e., not covered by) the adhesion promoter plating material 120. The geometry of the mask 122 in FIG. 2A is merely an example, and generally any mask geometry that is technically feasible may be used to define preselected regions of the leadframe strip 100 that should contain or be free 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 leadframe strip 100 is illustrated in FIG. 3A, and the bottom side 104 of the leadframe strip 100 is illustrated in FIG. 3B. Exposed portions of the leadframe strip 100 are plated with the adhesion promoter plating material 120, and the mask 122 nominally prevents the formation of the adhesion promoter plating material 120 in any of the covered areas.The adhesion promoter plating material 120 may generally be any material that increases the bond between the electrically insulating encapsulating material (i.e., a thermosetting plastic) and an electrically conductive material disposed on a surface of the leadframe (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 leadframe strip 100 is immersed in an electric fluid and acts as an anode under an applied current. In this embodiment, the mask 122 prevents the covered area from being plated with the primer plating material 120.Referring to FIG. 4, a top surface 102 of the leadframe strip 100 after removing the mask 122 is illustrated. In the figure, transition regions 126 of the inner portions of the leads 112 have been circled. These transition regions 126 correspond to areas at or near the boundary between the adhesion promoter plating material 120 and the wire bonds 118. Without further measures, the adhesion promoter plating material 120 may warp too close to the die paddle 110 to penetrate the wire bonds 118 in the transition regions 126. That is, the transition regions 126 represent regions that should preferably be free of, but in some cases are not, the adhesion promoter plating material 120. Many variables which are difficult or impossible to control contribute to the problem. For example, the smallest opening size of the mask 122 may be such that the adhesion promoter plating material 120 extends too far into the wire bonds 118. A process variation also contributes to this effect. Additionally, even in the case of a properly sized and aligned mask 122, some adhesion promoter plating material may enter the wire bonds 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 bonds 118 if too much of the adhesion promoter plating material 120 is present in the transition regions 126.A plurality of processing steps are disclosed herein to alleviate the phenomenon described above and to remove (or cover) the adhesion promoter plating material 120 that forms in the transition regions 126. According to these embodiments, the wire bonds 118 in the first unit leadframe 106 are processed such that the wire bonds 118 are substantially free of the adhesion promoter plating material 120 after the selective plating of the adhesion promoter plating material 120. That is, the wire bonds 118 are processed to prevent the adhesion promoter plating material 120 from advancing too far to the die paddle 110 and creating an unacceptably high risk of wire bond failure. These processing steps may be performed on the leadframe strip 100 before selectively plating the adhesion promoter plating material 120, after selectively plating the adhesion promoter plating material 120, or before and after selectively plating the adhesion promoter plating material 120. In addition, any of the processing steps may be combined with each other. The term "substantially free" as used herein means that, although trace amounts of the adhesion promoter plating material 120 may be present on the wire bonds 118, the amount of adhesion promoter plating material 120 remains below a maximum threshold to ensure that conductive connection (i.e., with wire bonds) may be effected at the wire bonds 118.Referring to FIG. 5, a top surface 102 of the leadframe strip 100 is illustrated after selectively plating the adhesion promoter plating material 120, as described with reference to FIGS. 2-4. In this embodiment, the leadframe 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 transition regions 126 are substantially free of the adhesion promoter plating material 120.According to an embodiment, a chemical treatment process is applied to the first unit lead frame 106 before selectively plating the first unit lead frame 106 with the adhesion promoter plating material 120. For example, the leadframe strip 100 may be immersed in a chemically reactive solution. Exemplary chemically reactive solutions suitable for this process include a chemical anti-immersion or anti-corrosion inhibitor such as an organosulfuric acid based on, e.g., 2-thiobarbituric acid, triazole derivatives, e.g., benzotriazole and imidazoles, etc. Alternatively, a silane-based solution such as mercaptosilane, sodium metasilicate, tripolyphosphate, etc. may be used. This chemical treatment process prevents the adhesion promoter plating material 120 from forming on selected portions (e.g., the wire bonds 118) of the inner portions of the leads 112. Thus, during selective application of the primer plating material 120 described with reference to FIG. 4, the primer plating material 120 does not penetrate the wire bonds 118.In another embodiment, after the selective plating of the adhesion promoter plating material 120, portions of the adhesion promoter plating material 120 that are formed at the wire bonds 118 during the plating process are removed. This removal of the adhesion promoter plating can be effected, for example, by a chemical reaction process. For example, chemical cleaning solutions such as potassium hydroxide, ammonium acetate, potassium lactate, and acetone may be applied to the wire bonds 118. This process may be 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 remove only the adhesion promoter plating material 120 from preselected areas (e.g., the wire bonds 118 or portions of the wire bonds 118). Alternatively, in a non-selective cleaning process, the chemical cleaning solution may be exposed to the entire leadframe strip 100 for a predetermined duration to remove a portion of the adhesion promoter plating material 120.Referring to FIG. 6, a top surface 102 of the leadframe strip 100 is illustrated after selectively plating the adhesion promoter plating material 120, as described above with reference to FIGS. 2-4. In accordance with the present invention, leadframe strip 100 was subjected to selective laser cleaning in exit regions 133 surrounding wire bonds 118. This selective laser cleaning is performed after selectively plating the adhesion promoter plating material 120, as described with reference to FIGS. 2-4. Different laser parameters are possible. Laser selective laser cleaning may slightly reduce the thickness of the material under the adhesion promoter plating material 120 (e.g., silver) so that the adhesion promoter plating material 120 may be completely removed. Removal of unwanted plating may be performed, for example, by laser machine programming. Laser cleaning can be applied to various metal surfaces (Cu, Ag, Ni, pre-plating layer stack, etc.).Referring to FIG. 7, a top surface 102 of the leadframe strip 100 is illustrated after selectively plating the adhesion promoter plating material 120, as described with reference to FIGS. 2-4. In this embodiment, the leadframe strip 100 has been subjected to a plating process whereby any adhesion promoter plating material 120 present in the wire bonds 118 is covered (e.g., plated) with a wirebondable layer 128. The wirebondable layer 128 may be generally any electrically conductive material suitable for forming wire bonds thereon. According to an embodiment, the wirebondable layer 128 is a layer of silver (Ag). Alternatively, the wirebondable layer 128 may be formed of palladium (Pd), gold (Au), nickel (Ni), copper (Cu), and alloys thereof.According to an embodiment, the wirebondable layer 128 is formed by a so-called dot plating technique. According to this technique, the wirebondable material (e.g., silver) is deposited directly on the first unit leadframe 106 at preselected locations. As can be seen, the preselected locations are within the package outline area 116 and include the die paddle 110 and the wire bond portions of the leads 112. Any adhesion promoter formed on the wire bond portions of the leads 112 or near the wire bond portions of the leads 112 is covered by the wirebondable layer 128. However, the dot plating is limited within a window so that it does not arise near the package outline or peripheral ring 114. Thus, in these regions, the adhesion promoter plating material 120 remains exposed and adheres to the encapsulation material formed thereon. The wirebondable layer 128 may be formed before and after the application of the adhesion promoter plating material 120. For example, the wirebondable layer 128 may be formed first on the leadframe strip 100 prior to the process steps described with reference to FIGS. 2-3. Thereafter, a re-plating process may be applied to form another wire-sealable layer 128.Referring to FIG. 8, a top surface 102 of the leadframe strip 100 is illustrated prior to selectively plating the adhesion promoter plating material 120, as described with reference to FIGS. 2-4. According to the technique illustrated in FIG. 8, the entire leadframe strip 100 is coated with a corrosion resistance coating 129 using pore blocker chemistry techniques including bisphenol, ether-based chemistry, benzothiazole, etc. The corrosion resistance coating 129 forms a hydrophobic layer on the entire top surface 102, including the wire bonds 118, as well as the bottom surface 104 (not shown in FIG. 8). The corrosion resistant coating 129 may be used to block the formation of the adhesion promoter plating material 120 in any desired area including the wire bonds 118 and the transition regions 126. The adhesion promoter plating material 120 cannot be deposited at these locations by dipping or a small current flow. However, the adhesion promoter plating material 120 may be selectively applied to other areas where it is preferably present (e.g., the peripheral ring 114). The corrosion resistance coating 129 may be applied prior to selectively plating the adhesion promoter plating material 120, as described with reference to FIGS. 2-4, and may remain on the wire bonds 118 during wire bonding without disturbing the wire bonds due to the minimum thickness of the corrosion resistance coating 129.Referring to FIG. 9, a top surface 102 of the leadframe strip 100 is illustrated prior to selectively plating the adhesion promoter plating material 120, as described with reference to FIGS. 2-3. According to these techniques, an additional masking step is performed prior to the masking step of FIG. 2 to provide additional coverage over the wire bonds 118 and prevent the formation of the adhesion promoter plating material 120 in these regions. This additional masking step may include applying a pre-tapping process whereby a tape 131 is applied to the leadframe strip 100. The tape 131 may be any commonly used tape for line stabilization, such as a polyethylene (PE) tape or a polyester (PET) tape.Referring to Figure 10, a differently configured lead frame strip 100 not according to the invention is illustrated. The top side 102 (i.e., die attach side) of the leadframe strip 100 is illustrated in FIG. 10A. FIG. 10B shows the leadframe strip 100 along the cross-sectional line A-A' shown in FIG. 10A. In this embodiment, the leadframe strip 100 is configured to be preformed with a package outline structure prior to singulating the first unit leadframes 106.The leadframe strip 100 may include the same materials and may be formed according to the same techniques as the leadframe strip 100 described with reference to FIGS. 1-9. Leadframe strip 100 is configured differently from leadframe strip 100 of FIGS. 1-9 in at least the following manner. First, there is no die paddle 110 in the leadframe strip 100 of FIG. 10 ; instead, each of the unit leadframes 106 has a central opening 130. The unit leadframes 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 may provide access to the outside of the package so that the sensor device may measure an external environment parameter.Referring to the side profile view of FIG. 10B, it can be seen that the leadframe strip 100 may have a bent lead configuration. In particular, a raised 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 conduits 112 include a vertical bend and a raised portion 132 spaced above outer portions of the conduits 112. The raised portion 132 is closer to the central opening 130 than outer portions of the conduits 112. In addition, the leads 112 may be bent downward at inner portions of the leads 112 located at the central opening 130.Referring to FIG. 11, a bond coat plating material 120 is selectively deposited within a package outline area 116 of the first unit leadframe 106. The top side 102 (i.e., die attach side) of the leadframe strip 100 is illustrated in FIG. 11A. FIG. 11B shows the leadframe strip 100 along the cross-sectional line A-A' shown in FIG. 11A. The adhesion promoter plating material 120 may be formed on the leadframe strip of FIG. 1 in a process 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 leadframe 106 and forming (e.g., by electroplating) the adhesion promoter plating material 120 in one or more openings of the mask 122. According to an embodiment, the adhesion promoter plating material 120 is selectively formed on the first portions of the leads 112 including the raised portions 132, as shown in FIG. 11B.Referring to FIG. 12, a cavity package outline 134 has been bonded to the leadframe strip 100. Cavity package outline 134 may be a preformed structure that is adhered to leadframe strip 100 using, for example, an epoxy. Alternatively, cavity package outline 134 may be formed directly on leadframe strip 100. Cavity package outline 134 is formed on the first portions of leads 112 such that central opening 130 is enclosed by a cavity 136 formed by outer sidewalls of the encapsulation material. That is, the outer sidewalls of cavity package outline 134 enclose and surround central opening 130. The outer sidewalls of cavity package outline 134 may be formed on raised portions 132 of leads 112. The adhesion promoter plating material 120 is provided at an interface between the lead frame and the electrically insulating encapsulation material.The first unit leadframe 106 may be processed after forming the cavity package outline 134 to prevent the adhesion promoter plating material 120 from interfering with electrical connections between the first unit leadframe 106 and the components (e.g., sensor elements) mounted within the cavity 136. For example, the leadframe 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 leadframe strip 100 during processing of the leadframe strip 100, the leadframe strip 100 may be processed thereafter to eliminate potentially adverse effects of the adhesion promoter plating material 120 on the leads 112.According to an example, after the cavity package outline 134 is formed on the leadframe strip 100, the first unit leadframe 106 is plated with a wirebondable layer 128. The wirebondable layer 128 may be a layer of silver (Ag) and may be formed according to the same techniques described above with reference to FIG. 6. Therefore, any adhesion promoter plating material 120 on the leads 112 will not interfere with the electrical connections between the first unit leadframe 106 and the devices mounted within the cavity 136.FIGS. 1-9 illustrate embodiments of the first unit leadframe 106 according to the invention, and FIGS. 10-12 illustrate an exemplary first unit leadframe 106 not according to the invention. However, the configuration of the first unit leadframe 106 may vary depending on the desired configuration of the finalized package design. For example, the number and dimensions of the lines 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 the peripheral ring 114. Additionally, the conduits 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 pad processing techniques described herein may be applied to any of these constructions.The single pass process offers numerous advantages over conventional techniques that require two pass revision (e.g., a non-selective adhesion promoter step followed by selective etching of the adhesion promoter). A major advantage is a cost reduction. This cost reduction can be attributed, at least in part, to the elimination of at least one mask (i.e. the mask required for the selective etching of the adhesion promoter). Further, problems associated with conventional techniques of carrier alignment and handling are reduced due to process simplification. Thus, the yield can be improved.Another advantage of the single pass process compared to conventional techniques is that no thickness reduction of the conductive lead frame material is required. Conventional processes require overetching the adhesion promoter to remove the material underlying the adhesion promoter. This is necessary to ensure that the adhesion promoter is completely removed from the wirebondable layers. This thickness reduction of the conductive lead frame material may result in a number of adverse effects. For example, forming of shape may occur and package singulation may be more difficult due to the non-planar nature of the leadframe. Thickness reduction is not necessary using the techniques described herein because the adhesion promoter is applied only in the areas in which it is required.Another advantage of the direct selective adhesion promoter plating process described herein is an improvement in the bearing life of the direct selective adhesion promoter plating material. According to conventional techniques, the package molding process should be performed within two weeks after the adhesion promoter plating process. According to the direct selective adhesion promoter plating process described herein, the leadframe may be formed up to 12 months after application of the adhesion promoter plating material. Thus, the direct selective adhesion promoter plating process described herein provides flexibility in pre-fabrication, shipping, and delivery.Spatially relative terms such as "below," "below," "lower," "above," "upper," and the like, are used to facilitate the description to explain the positioning of an element relative to a second element. The terms are intended to include other orientations of the device in addition to different orientations than those described in the figures. Furthermore, terms such as "first", "second", and the like are also used to describe various elements, regions, sections, and so forth, and are also not intended to be limiting. Like terms refer to like elements throughout the specification.As used herein, the terms "with," "including," "comprising," and the like are open ended terms that indicate the presence of stated elements or features, but do not exclude additional elements or features. The articles "a / an," "the / s" are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.

Claims

A method of forming a packaged semiconductor device, comprising: providing a leadframe strip (100) having a plurality of unit leadframes (106), each of the unit leadframes (106) comprising a die paddle (110), a plurality of leads (112) extending away from the die paddle (110), and a peripheral ring (114) delimiting inner portions of the leads (112) from outer portions of the leads (112), the inner portions comprising wire bonds (118); selectively plating a bond coat plating material (120) within a package outline region (116) of a first unit leadframe (106), wherein the die paddle (110) and the inner portions of the leads (112) are disposed within the package outline region (116) and the outer portions of the leads (112) are disposed outside the package outline region (116), wherein selectively plating the adhesion promoter plating material (120) onto the first unit leadframe (106) comprises a single pass metal plating process comprising: providing a mask (122) over the first unit leadframe (106), wherein the mask (122) covers the outer portions of the leads (112) and comprises openings (124) at least partially exposing preselected regions of the first unit leadframe (106) within the package outline region (116); forming the adhesion promoter plating material (120) in the openings (124), wherein the wire bonds (118) are covered by the mask (122) to prevent the adhesion promoter plating material (120) from forming on the wire bonds (118) during formation of the adhesion promoter plating material (120); Processing wire bonds (118) in the first unit leadframe (106) such that after selectively plating the adhesion promoter plating material (120), the wire bonds (118) are free of the adhesion promoter plating material (120), wherein the wire bonds (118) are disposed within the package outline region (116) and are spaced apart from the peripheral ring (114), and wherein processing the wire bonds (118) comprises: after selectively plating the adhesion promoter plating material (120), applying a laser cleaning process to the wire bonds (118) to remove any adhesion promoter plating material (120) exiting the wire bonds (118).The method of claim 1, wherein processing the wire bonds (118) comprises: prior to selectively plating the adhesion promoter plating material (120), chemically treating the wire bonds (118) to prevent the adhesion promoter plating material (120) from forming during the selective application of the adhesion promoter plating material (120) to the wire bonds (118).The method of claim 2, wherein chemically treating the wire bonds (118) comprises exposing the wire bonds (118) to a chemical immersion or corrosion protection inhibitor.The method of any of claims 1 to 3, wherein processing the wire bonds (118) comprises: prior to selectively plating the bond coat plating material, applying a corrosion resistance coating to the first unit leadframe (106), the corrosion resistance preventing the bond coat plating material from forming on the wire bonds (118).The method of any of claims 1 to 4, wherein processing the wire bonds (118) comprises: prior to providing the mask (122) over the first unit leadframe (106), applying a tape over the wire bonds (118).The method of any one of claims 1 to 5, wherein the adhesion promoter plating material (120) comprises a zinc-based metal.The method of claim 6, wherein the adhesion promoter plating material (120) comprises at least one of ZnMo and ZnV.

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